What is Like to Be a Rat

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Applied Animal Behaviour Science (2008) Volume 112: 1-32 doi: 10.1016/j.applanim.2008.02.007 Final Revision – NOT EDITED by the journal

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What is it like to be a rat? Rat sensory perception and its implications for experimental design and rat welfare
Charlotte C. Burn Department of Clinical Veterinary Science, University of Bristol, Bristol BS40 5DU, UK Running title: Rat sensory perception and its implications

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Correspondence address: Department of Clinical Veterinary Science, University of Bristol, Bristol BS40 5DU, UK

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Abstract
This review of rat sensory perception spans eight decades of work conducted across diverse research fields. It covers rat vision, audition, olfaction, gustation, and somatosensation, and describes how rat perception differs from and coincides with ours. As Nagel’s seminal work (1974) implies, we cannot truly know what it is like to be a rat, but we can identify and acknowledge their perceptual biases. These primarily nocturnal rodents are extremely sensitive to light, with artificial lighting frequently causing retinal degeneration, and their vision extends into the ultraviolet. Their olfactory sensitivity and ultrasonic hearing means they are influenced by environmental factors and conspecific signals that we cannot perceive. Rat and human gustation are similar, being opportunistic omnivores, yet this sense becomes largely redundant in the laboratory, where rodents typically consume a single homogenous diet. Rat somatosensation differs from ours in their thigmotactic tendencies and highly sensitive, specialised vibrissae. Knowledge of species-specific perceptual abilities can enhance experimental designs, target resources, and improve animal welfare. Furthermore, the sensory environment has influences from neurone to behaviour, so it can not only affect the senses directly, but also behaviour, health, physiology, and neurophysiology. Research shows that environmental enrichment is necessary for normal visual, auditory, and somatosensory development. Laboratory rats are not quite the simple, convenient models they are sometimes taken for; although very adaptable, they are complex mammals existing in an environment they are not evolutionarily adapted for. Here, many important implications of rat perception are highlighted, and suggestions are made for refining experiments and housing.

Keywords: Animal Welfare; Communication; Olfaction; Perception; Rats; Refinement; Vision

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Introduction

The stimuli that an animal can perceive depend on the available sensory apparatus, while the way stimuli are evaluated in terms of their biological relevance depends on the animal’s innate biases, cognitive abilities and experiences. Perception is therefore a subjective distortion of reality, differing between species and even between individuals within a species. Since rats and mice, which have similar perceptual abilities to each other, constitute over 80% of all research animals in the European Union (Commission of the European Communities, 2003), and they have been bred for research since the late 1800s (Krinke, 2000; Whishaw & Kolb, 2005), much is known about their perceptual biases. However, the information is scattered through time and across different research fields, so it is not easily available to researchers, rat caretakers, and other rat specialists. The resulting lack of awareness can have serious implications, sometimes leading to poorly designed experiments and harming rat welfare. This review brings current information together, to help inform and refine rodent experiments and housing. The review concentrates on the laboratory rat, Rattus norvegicus, since summaries of mouse sensory perception are included within several other review papers (Sherwin, 2002; Olsson et al., 2003; Latham & Mason, 2004). Much of the information will also be true for mice and other rodents, but care should still be taken if extrapolating between species. The species’ natural ecology – such as whether they are diurnal or nocturnal, social or solitary, arboreal, burrowing or terrestrial – will profoundly affect their sensory perception. These ethological considerations are highly relevant in laboratory rats despite their domestication; adult laboratory rats retain so many of their wild instincts that, when released into a naturalistic habitat,

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their resulting community and behaviour rapidly resembles that of their wild relatives (Berdoy, 2002). This review is organised around the classic ‘five senses’: vision, audition, olfaction, gustation and somatosensation. It should be remembered that these are actually not the only senses; indeed rats may even possess a magnetic compass, like mice (Muheim et al., 2006) and hamsters (Deutschlander et al., 2003), but most published information currently covers the aforementioned five senses. For each sense, the rat’s sensory biases relative to humans are first described, then some practical implications of its perception with respect to welfare and experimental design are discussed. This is an applied review, focussing on the known or suspected implications of each sense, and aiming to provide enough information to allow readers to extrapolate to their own situations. The review cannot be completely comprehensive, and it will become clear that in many cases, rat sensory perception is still poorly understood.

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Vision
An obvious difference between human and rat vision is that rats’ eyes are

located on the sides of their heads, rather than the front. They therefore have a wider field of view, but less binocular overlap than us: wild rats have a binocular overlap of 35o, domestic rats 76o, and humans 105o (Heffner & Heffner, 1992a). Wild rats usually inhabit burrows or other enclosed environments, and tend to be nocturnal or crepuscular, so most of their activities occur under low light conditions (e.g. Calhoun, 1963). Consequently, rats rely relatively little on vision, but they are dramatically more sensitive to dim light than we are, able to discriminate tiny increments in intensity, indiscernible to us, including discriminating ‘total darkness’ from 0.107 lux (Campbell & Messing, 1969).

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Rats, especially albinos, have much poorer visual acuity (Lashley, 1938; Creel et al., 1970; Prusky et al., 2002) and narrower depth perception than humans (O'Sullivan & Spear, 1964; Routtenberg & Glickman, 1964). For example, human acuity can be around 30 c/d (‘cycles per degree’ – a measure of spatial resolution accounting for stimulus size and distance), while pigmented rats’ acuities are only 1– 1.5 c/d and albino strains have even lower acuities of 0.5 c/d (Prusky et al., 2002). This presumably gives an extremely blurred image by human standards (Figure 1, reprinted from Prusky and colleagues, 2002). Poor acuity in rats is probably partly due to their eyes’ relatively small size, and partly because their eyes appear to have very limited abilities to focus light from different distances or angles compared with human eyes (Artal et al., 1998). Rats often bob their heads which may help them gain motion cues about the distance of objects (Legg & Lambert, 1990). Experiments in the 1930s suggested that, contrary to popular belief, rats possess colour vision (e.g. Munn & Collins, 1936; Walton & Bornemeier, 1938), which has recently been confirmed through electroretinograms and quantitative behavioural tests (Jacobs et al., 2001). Rod cells comprise 99% of rat photoreceptors, but rats also have two cone cell types (Szel & Rohlich, 1992). Around 93% of the cones respond maximally to blue–green light (around 510 nm), while the remaining 7% respond to ultraviolet (UV) (around 360 nm) (Jacobs et al., 2001; Akula et al., 2003). Cone responses are normally distributed, so rats actually perceive hues ranging from ultraviolet (400 nm) to orange-red (around 635 nm) (Jacobs et al., 2001), but they are most responsive to colours near their peak sensitivities (Jacobs et al., 2001; Akula et al., 2003). Flicker fusion thresholds (when emitted light flickers rapidly enough to appear constant) for rats are not yet known, but are relevant for their perception of video images and artificial lighting (D'Eath, 1998). Flicker fusion thresholds decrease with high light intensity, and increase with fatigue. Animals with high proportions of rod
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cells, like rats, generally have high flicker fusion thresholds, so rats might perceive videos, computer monitors, and some fluorescent lighting as flickering (Jarvis et al., 2003). Discussion of the implications of rat vision is separated according to sensitivity to light generally, colour vision, periodicity, and acuity. 2.1 Sensitivity to light

The sensitivity of rats to light (Campbell & Messing, 1969) means that light levels comfortable for humans can rapidly cause retinal atrophy (reviewed in Schlingmann et al., 1993a; Schlingmann et al., 1993b) and cataract formation in rats (Rao, 1991). Albinos are particularly susceptible because they lack protective melanin in the iris and retinal epithelium, and the entire eyeball is slightly transparent (Schlingmann et al., 1993b). Consequently, even when the iris contracts in bright light, most of the light still enters the eye (Williams et al., 1985). In fact, albino rats may be the most susceptible of all laboratory animals to light-induced retinal degeneration (Bellhorn, 1980). To illustrate the relevant range of light intensities, the UK code of practice for the care and use of laboratory animals suggests that “350–400 lux at bench level is adequate for routine experimental and laboratory activities” (Home Office, 1989). Light intensities within cages are commonly between about 150 and 550 lux (Schlingmann et al., 1993c), but are higher in laboratory rooms, with upper limits approaching 10,000 lux due to current technological limitations (e.g. Light Therapy ProductsTM, 2006; Outside In Ltd., 2006). Humans can tolerate still higher intensities – outdoors on sunny days light often exceeds 50,000 lux, and only at this order of magnitude are discomfort and potential retinal damage likely in humans. Light intensities of only 65 lux can cause retinal degeneration in albino rats, even on a 12 h light-dark cycle (Semple-Rowland & Dawson, 1987). Half the photoreceptors were permanently damaged after just 3 days at 133 lux in albinos, but
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pigmented rats were less susceptible, with equivalent damage occurring at 950 lux (Williams et al., 1985). Rod cells are particularly vulnerable to light destruction, but cones often survive even after all rods have been destroyed (Cicerone, 1976; La Vail, 1976). Long-term cyclical light intensities of about 500 lux within an animal room can also cause cataracts in albino rats (Rao, 1991). These problems are worst in rats housed closest to the light source, usually those highest in the rack (Rao, 1991; Perez & Perentes, 1994). Surprisingly, some vision can remain after constant long-term light exposure, even when no intact photoreceptor cells can be observed (e.g. Lemmon & Anderson, 1979). This might be conferred by a few remaining cones that may be so sparse that they were undetectable by the quantitative techniques used (Cicerone, 1976; La Vail, 1976). Even so, under ‘ordinary’ laboratory conditions, visual impairments can confound some tests. For example, in the Morris water maze – a test of cognitive function – rats with incidental light-induced retinal damage perform as poorly as rats with cognitive deficits, both groups displaying difficulties locating the platform (Osteen et al., 1995; Lindner et al., 1997). Also, in commonly used ‘anxiety’ tests, such as open field tests and light-dark boxes, visually impaired individuals might venture into the exposed/light areas more than fully sighted ones, through their lesser ability to discriminate light from dark, but this requires experimental confirmation. Therefore, light-induced retinopathy should be controlled for in such tests, or nonvisual tests used alongside the established visual ones. Welfare problems might arise at even lower light levels than those causing retinal damage, because of motivation to hide, as well as to avoid ocular discomfort (Schlingmann et al., 1993c). Rats, especially albinos, reliably choose the lowest light intensities available, even when all the choices are very dim, appearing indistinguishable to humans (Campbell & Messing, 1969; Woodhouse & Greenfeld, 1985; Blom et al., 1995). Rats’ aversion to light was clearly demonstrated in a study showing that sleeping pigmented and albino rats awoke and moved to areas of lower
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illumination at thresholds of only 60 and 25 lux, respectively (Schlingmann et al., 1993c). Consistent with such behaviour, chromodacryorrhoea, an aversion-related secretion from the Harderian gland (e.g. Mason et al., 2004), increases with brighter light (Hugo et al., 1987). There is clearly a conflict between human workers needing adequate light to inspect rats, for example for signs of illness, and rats needing to avoid damaging or aversive light levels. Schlingmann (1993a) therefore stresses the importance of providing shelters within cages, allowing rats some control over their light exposure. As described below, coloured shelters exist that allow humans to see rodents, while it supposedly appears dark to the rodents inside the shelter, although their efficacy requires confirmation. Light levels affect commonly used psychological tests, such as elevated plusmazes in which exploration of the exposed arms is taken to indicate reduced anxiety; rats explore the exposed arms more in dim than bright light (Cardenas et al., 2001; Garcia et al., 2005). Moreover, some effects are only found under certain light conditions. For example, the anxiolytic effects of gentling only emerge in brightly lit open fields (Hirsjarvi & Valiaho, 1995), and some drug effects are influenced by plus maze illumination (Clenet et al., 2006). Therefore, some control and careful description of lighting conditions during these tests is necessary to account for its influence on psychological measures. Surgery presents a difficult situation because good lighting is essential for delicate operations, but the anaesthetised, unblinking rat is unable to protect its eyes from that light. Care should therefore be taken, not only to keep the eyes hydrated, but also to protect them from prolonged bright light. Interestingly, the anaesthetic agent, halothane, prevents retinal degeneration (Keller et al., 2001); other anaesthetics have not yet been investigated. This protection is afforded under white, but not blue, light.

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Despite the above evidence that bright light is harmful to rats, this aspect of their biology is not always considered in some fields of research. An example is the use of rats as models for seasonal affective disorder in humans, exploring whether bright light therapy (up to 11,500 lux for 2 weeks) can cure depression in rats (e.g. Dilsaver & Majchrzak, 1988; Giroux et al., 1991; Humpel et al., 1992; Overstreet et al., 1995). Unsurprisingly, the depression was not cured, and the one study that considered the effects of light on rat vision discovered massive destruction of the albinos’ photoreceptors (Humpel et al., 1992). These examples illustrate how crucial knowledge of species-specific perception is for generating reasonable hypotheses and preventing animal suffering. 2.2 Colour vision

Rats are not colour-blind (Muenzinger & Reynolds, 1936; Munn & Collins, 1936; Walton & Bornemeier, 1938; Lemmon & Anderson, 1979; Jacobs et al., 2001). However, relative to humans, they perform poorly when discriminating between colours of similar wavelengths (Walton, 1933), and they take longer to learn colour discriminations than light intensity ones (Jacobs et al., 2001). To discuss the implications of rats’ colour sensitivity, the implications for emitted light and that reflected by objects in the environment will be dealt with separately, as their effects are quite distinct. 2.2.1 Emitted light

Standard artificial lighting rarely emits UV wavelengths (e.g. Bellhorn, 1980; Latham & Mason, 2004), since human cones are insensitive to it. To date, no studies have apparently investigated the effects of UV-deficient light on rats. In some birds, UV light is important for their welfare (Moinard & Sherwin, 1999; Maddocks et al., 2001) and normal behaviour (Bennett & Cuthill, 1994), but laboratory mice appear to have, if anything, a slight aversion to it (C. M. Sherwin, personal communication). Also, high levels of UV can cause cataracts in mice (in Bellhorn, 1980), and can affect
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reproductive and circadian rhythms in rats (reviewed in Brainard et al., 1994). In fact, the colour composition of artificial light can have large effects. In rats, blue light (around 490 nm) causes most retinal degeneration (reviewed in Schlingmann et al., 1993b), and also more disruption to fertility (Tong & Goh, 2000) than any other wavelengths tested; UV light was not included in these studies, but is of a shorter wavelength than blue light so may be more harmful. At the opposite end of the spectrum, dim red light is sometimes used to observe nocturnal behaviour in rats, because it is on the upper edge of the wavelengths visible as colour to them (Jacobs et al., 2001). However, rats’ rod cells are stimulated by similar wavelengths to human rod cells, including red light (Akula et al., 2003). This means that, provided some rod cells remain intact, rats can see red light, even if only as light and dark contrast. This may not be a problem in experiments if rats are habituated to it, since moonlight would provide illumination in the wild. As an alternative to red light, sodium lamps, which emit very narrow peaks of yellow– orange (589 and 589.6 nm) light, can be used (McLennan & Taylor-Jeffs, 2004). Not only is it more visible to humans than red light, but there were no long-term differences between the activity levels of mice when illuminated by this lamp or in darkness. However, in studies unequivocally requiring rats to behave as if in pitch darkness, infra-red light and the necessary viewing equipment should be used. It is also worth noting that most video equipment and computer monitors, which create images using emitted light, include no UV emissions and the colour balance is optimised for human vision (D'Eath, 1998). Even in black-and-white images and light from white artificial light bulbs, ‘white’ is composed of red, green and blue light adjusted for humans, and so would not appear as white to rats. Therefore, any such images presented to species with different colour sensitivities, particularly UVsensitive animals, could lack important information.

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2.2.2

Colour in the environment

Caution is required when presenting images to rats in discrimination tests, even if the cues reflect rather than emit light. Different inks have different spectral properties that may be invisible to the human eye, and some might even reflect UV. Moreover, different pigments might differ in their olfactory qualities, which could be more salient to rats than their visual qualities. Even if this does not harm the experimental purpose, it can make standardisation between experiments difficult. Outside experimental situations, there are also some relevant implications of rodent colour vision within the homecage. In recent years, manufacturers of rodent environmental enrichments have produced transparent shelters in various colours (e.g. Robbins, 2004; Datesand Ltd, 2005). The idea behind them is that, while rodents supposedly blind to the shelter’s colour - perceive themselves as being sheltered in a dark environment, human carers can inspect them without disturbing them. However, these shelters seem not to have been independently evaluated for their efficacy. Red transparent material might make a suitable shelter, being the least visible colour to rats (Jacobs et al., 2001), but as explained earlier, it would still stimulate rod cells and possibly some cones. The colour of the homecage itself might also affect rats. Sherwin and Glen (2003) housed mice in different coloured cages and found that they had significantly different preferences for cage-colours. Moreover, the colour affected their food-tobody mass conversion rates and their elevated plus-maze anxiety. Assuming these effects were due to the colours directly (rather than the scents, tastes, or textures of the dyes used), this study shows that environmental colour can have surprisingly strong effects on mouse behaviour and physiology, and so possibly that of rats too. 2.3 Periodicity

Rats tend to be most active at dusk and dawn, although their circadian rhythms are relatively flexible (e.g. Calhoun, 1963). Because we are diurnal, many rodent
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experiments are carried out in the light, so much of our knowledge of this species comes from individuals awakened during their resting period, and tested under much brighter conditions than they would voluntarily experience. The implications of this can be profound, but time-shifted experiments are still rare in some fields. The brain state changes radically between sleep and activity, with whole populations of neurons shifting between activity and inactivity (Hobson, 2005; Saper et al., 2005). The time of testing can strongly influence the variables of interest in experiments. For example, during the light phase, rats’ cardiovascular responses to various stressors are more pronounced (Schnecko et al., 1998), and they show less exploratory behaviour in an elevated plus-maze than in the dark phase (Andrade et al., 2003). For most experiments, rats will be in a wakeful state provided they have sufficient time to awaken, but little published information is available on how long rodents require to fully awaken (i.e. be in the same state as during the active phase). Any conclusions drawn from light phase studies of rats as human models could suffer from interpretive problems, because it is unclear whether the observed state would reflect a similar state in our light (active) phase or our (dark) resting phase. Time shifted experiments and husbandry can be made possible by using red or sodium illumination as described above, and also by feeding rats only during the phase when we wish them to be active (cited in Saper et al., 2005); a situation that sometimes occurs in the wild (Calhoun, 1963). 2.4 Acuity

As described above, rats have very poor acuity (Figure 1). Their image resolution is at least 20 times poorer than ours (Artal et al., 1998). Note though that the studies investigating rat visual acuity (Lashley, 1938; Creel et al., 1970; Artal et al., 1998; Robinson et al., 2001; Prusky et al., 2002) have used laboratory rats, whose acuity might have been further reduced by their artificially lit environments.

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Apart from the damaging effects of light itself, several other factors can affect rat vision, including the early environment. Complete lack of light impairs rats’ visual development (Fagiolini et al., 1994), but providing environmental enrichment to these dark-reared animals can eliminate this effect (Bartoletti et al., 2004). In mice, enriched environments during rearing accelerate visual development and improve adult acuity (Prusky et al., 2000; Cancedda et al., 2004). Also, diet has a large influence on vision (Berson, 2000). For example, caloric restriction can prevent cataracts (e.g. Wolf et al., 2000), and antioxidant intake and consumption of certain vitamins can prevent retinal damage (Li et al., 1985; Berson, 2000). Dietary composition is discussed in more detail in the Gustation section of this paper. The research implications of rats’ poor visual acuity depends on the experiment in question, but if visual cues are used they should be relatively large and high contrast, but not too bright as to be aversive. Also, visual cues may not be as salient to rats as cues in other modalities. Few experiments have tested this directly, but rats do remember auditory associations for longer than equivalent visual ones (Wallace et al., 1980), and can more rapidly learn discriminations using multimodal stimuli (floor surfaces differing in appearance, smell, and texture Dymond, 1995; Dymond et al., 1996) or olfactory or tactile cues (Birrell & Brown, 2000). However, vision is often the most appropriate sense for guiding rats in water mazes (Prusky & Douglas, 2005), for comparison with past studies, and for certain models of human activities.

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Audition

Sound can be described in terms including its frequency, intensity, timbre (frequency spectrum) and envelope (shape of sound pressure through time). While young humans hear frequencies from about 0.02 kHz to 20 kHz (Moore, 2003), hearing in rats is shifted upwards to include the ultrasonic range (Kelly & Masterton, 1977). The

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lowest frequency rats have been reported to hear is 0.25 kHz and the highest is 80 kHz (Kelly & Masterton, 1977; Heffner & Heffner, 1992b; Heffner et al., 1994). They can also detect lower sound frequencies (Petounis et al., 1977), probably through contact with vibrating surfaces, and can even perceive low frequency sounds using their vibrissae (Neimark et al., 2003) (see the section on Somatosensation). Auditory sensitivity decreases near the extremes of the detectable frequencies, so sounds at the lower and higher extremes must be louder before rats can detect them. The rat’s peak sensitivity is estimated to lie between about 8 and 50 kHz (Kelly & Masterton, 1977; Heffner & Heffner, 1992b), although estimates vary, probably due to factors including strain, age, and background noise. Even whether the homecages of rats are barren or environmentally enriched can greatly affect hearing sensitivity; auditory neurone performance is vastly improved by environmental enrichment (Engineer et al., 2004). The implications of rat auditory perception include what sound characteristics are harmful, vocal communication between rats, perception of the human voice, and experimental use of sound cues. There has also been debate about whether rats can echolocate. 3.1 Audiogenic damage in the laboratory

Interactions between sound intensity and frequency (Fleshler, 1965; Voipio et al., 1998; Björk et al., 2000) make it difficult to determine detection- and safetythresholds for sound intensities. The decibel (dB) scale is logarithmic, so even small numerical increases represent large increases in the actual intensity. European Union legislation (2003) states that advice and hearing-protection must be provided for human workers frequently exposed to sounds of 80 dB or more. Above about 150 dB, auditory damage is inevitable with most perceivable sounds (Gamble, 1982). Equivalent thresholds are unknown for rats, but young rats are more sensitive to

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sounds than older ones, and permanent audiogenic damage is most likely in pups between about 12 and 22 days of age (Voipio, 1997). In the laboratory, audible sounds as loud as 80–90 dB have been recorded; and 50–75 dB for ultrasound (Milligan et al., 1993), so conceivably, audiogenic damage could occur in both humans and rats. Husbandry procedures cause the loudest sounds, especially if metallic equipment is involved (Gamble & Clough, 1976; Milligan et al., 1993; Sales et al., 1999). Filling metal food hoppers made 80 dB of (mostly ultrasonic) sound, which would occur about once a week for the rats’ lifetimes (Sales et al., 1999). This was measured from a distance of 50 cm, approximately the furthest that a caged rat could get from the sound. Many apparently silent activities or devices actually produce high levels of ultrasound (Sales et al., 1988; Sales et al., 1999). Examples include computer monitors, making 68–84 dB of broadband ultrasound (Sales et al., 1988), and some fluorescent lighting (G. J. Mason personal communication, and personal observation). Cage washers, hoses, running taps, squeaky chairs, and rotating glass stoppers (Sales et al., 1988) produce both ultrasound and audible sound, as do some air-flow hoods worn to prevent allergy in human workers (Picciotto et al., 1999). Similarly, standard fire alarms produce loud high and low frequency sounds, which laboratory animals cannot escape, so laboratories can be fitted with fire alarms that only emit sound audible to humans but not rodents (Home Office, 1989); although note that even frequencies below rats’ audible range can affect them (Petounis et al., 1977). Whether common laboratory sounds affect rodent welfare has not been investigated directly, but loud noises generally can trigger seizures, reduce fertility, and cause diverse metabolic changes (Sales et al., 1988; Milligan et al., 1993). Repeated short bursts of 2 kHz sound at 120 dB caused ‘behavioural despair’ in rats (Bulduk & Canbeyli, 2004). Longer-lasting sounds can also affect animals, although that has apparently not been tested in rats. In pigs, 90 dB prolonged or intermittent

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broadband noise increased cortisol, ACTH, noradrenaline:adrenaline ratios and time lying down, and decreased growth and social interactions (Otten et al., 2004). Conceivably then, a fluorescent light emitting loud ultrasound could cause significant stress in rats housed near it. The envelopes and timbres of sounds also determine how aversive or damaging they are. Noise-type sounds, e.g. white noise or the sound of tearing paper, cause stronger fear reactions in rats than equivalent harmonic or pure tones, or audible rat vocalisations (Voipio, 1997). Sudden sounds are probably also more startling than those with gradual onsets. It should be noted that avoidance of sound occurs at still lower thresholds than those causing startle reactions (in Fleshler, 1965), or physical damage. Ultrasound detectors (e.g. bat detectors), which represent ultrasounds in a form that humans can hear or visualise, would be useful as standard pieces of laboratory equipment to regularly check whether ultrasound of certain frequencies is being emitted in the animal rooms and to test experimental set-ups. Few experimenters would choose to carry out experiments during loud building work, for example, because of potential effects on the animals’ performances, and the same meticulousness should apply to ultrasound. Indeed, background noise levels during behavioural experiments do affect the apparent learning abilities of rats, with louder white noise leading to faster completion of a maze task (Prior, 2006). Moreover, even loud infrasound affects rat behaviour, reducing their activity and triggering sleep (Petounis et al., 1977). 3.2 Vocalisations and communication

As well as audible ‘squeaks’, rats produce at least three types of ultrasonic vocalisations. Firstly, juvenile rats produce a 40–50 kHz vocalisation (Noirot, 1968), which together with olfactory cues, causes pup-retrieval by the mother (e.g. Allin & Banks, 1972; Farrell & Alberts, 2002).
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The second ultrasonic vocalisation is the ‘22 kHz long-call’, which occurs mainly in aversive situations and might therefore indicate negative affect (Knutson et al., 2002). Examples of such situations include social defeat (Van der Poel & Miczek, 1991), exposure to cat odour (Blanchard et al., 1991), administration of naloxone or lithium chloride (Burgdorf et al., 2001), arthritic pain without analgesia (Calvino et al., 1996), acute pain (Jourdan et al., 1995), acoustic startle (Kaltwasser, 1990) and electric shocks (Kaltwasser, 1991). However, male rats make a similar vocalisation after ejaculation (Van der Poel & Miczek, 1991), so this call might occur in two subtly different forms, or might not reliably indicate negative affect. The third ultrasonic vocalisation is the ‘50 kHz chirp’, which is apparently associated with positive events (Knutson et al., 2002), and has even been suggested as a form of laughter (Panksepp & Burgdorf, 2000). It occurs in anticipation of positive social contact (Knutson et al., 1998; Brudzynski & Pniak, 2002), rewarding ‘tickling’ by humans (Panksepp & Burgdorf, 2000; Burgdorf & Panksepp, 2001; Panksepp, 2006), amphetamine or morphine administration (Knutson et al., 1999), and feeding or rewarding electrical stimulation of the brain (Burgdorf et al., 2000), and also during play (Knutson et al., 1998; Brudzynski & Pniak, 2002; Burn, 2006). However, again, this vocalisation does not reliably indicate positive affect because it occurs in some aversive situations, e.g. during morphine withdrawal (Vivian & Miczek, 1991), aggression (Sales, 1972), and in certain painful situations (Hawkins et al., 2005). Surprisingly little work has investigated the audible squeak. There may in fact be several different types of squeak, because subjectively there is variation in the quality of sounds produced (O. H. P. Burman, personal communication; personal observation). Pups and their mothers make audible squeaks in the nest (e.g. Voipio, 1997), but this may be different from squeaking in other contexts. Squeaks occur during nociception as they persist even when central nervous system analgesics are given, which might suggest that they are detached from the emotional experience of pain (Jourdan et al., 1995). They also occur during playing and fighting (Voipio,
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1997; Burn et al., 2006a), and sometimes during handling, especially alongside struggling behaviour (van Driel et al., 2004; Burn, 2006). They generally seem to indicate negative affect, but do not necessarily occur alongside the 22 kHz long-call, so there must be some qualitative or quantitative difference between the motivations behind the two call types. All of these vocalisations could have practical implications. Procedures or environments that cause rats to vocalise could affect the behaviour and physiology of all neighbouring rats within audible range. For example, playbacks of 22 kHz longcalls caused freezing and decreased activity (Sales, 1991; Brudzynski & Chiu, 1995) and increased latencies to emerge into an arena (Burman et al., 2007). Playbacks of audible squeaks also caused conspecifics to orientate towards the speaker and occasionally to squeak themselves (Voipio, 1997). 3.3 Perception of the human voice

An awareness that rats can hear our voices is important, because of affects on experimental results and rat welfare. Rats can hear and discriminate many elements of the human voice (e.g. Pons, 2006), and pet rats can learn to respond to verbal commands (e.g. Fox, 1997). In fact, rats can distinguish between some languages (Toro et al., 2003), so the pitches, rhythms and accents of different human workers could be at least partly responsible for rats being able to distinguish between individual humans (McCall et al., 1969; Morlock et al., 1971; Davis et al., 1997; van Driel & Talling, 2005). Shouting causes stress responses in farm animals (Hemsworth, 2003), so this may also be true for laboratory rats, especially because when humans speak with more emotional content, the higher-pitched and ultrasonic content of our speech increases (Mason, 1969). 3.4 Sound recordings and playbacks

By default, most standard recording devices and speakers include no ultrasound, so specialised equipment is necessary, such as ‘tweeter’ speakers and ultrasonic
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microphones (Björk et al., 2000). White noise, although aversive to rats (Voipio, 1997), is commonly used to standardise background noise in experiments, but different speakers differ in their ultrasonic output, so comparisons across studies might sometimes be invalid. Even a study that specifically investigated how background noise affected rat behaviour in a maze, neither mentioned their ultrasonic hearing abilities, nor used specialist equipment to produce the experimental white noise (Prior, 2006), indicating that awareness of these auditory issues may be lacking in some fields. 3.5 Echolocation There has been some debate about whether rats can echolocate (e.g. Rosenzweig et al., 1955; Riley & Rosenzweig, 1957; Kaltwasser & Schnitzler, 1981; Forsman & Malmquist, 1988). Blind rats can use self-generated sounds, reflected off solid objects, to guide them in mazes (Rosenzweig et al., 1955; Riley & Rosenzweig, 1957). Also, sighted rats in darkness can discriminate between shelves close enough to jump to and those too far away, but not if they are deafened (Chase, 1980). Some studies described quiet ultrasonic ‘clicks’ (Chase, 1980; Graver et al., 2004), which were produced more in darkness than in light, more before rats jumped to the platform than after, and the decision to jump was faster in rats that clicked more (Graver et al., 2004). However, rats seem not to have anything like the specialised echolocation abilities of mammals such as bats or cetaceans. Indeed, some blind and blindfolded humans can ‘echolocate’ using reflected sound, similar to rats (in Riley & Rosenzweig, 1957), but there is no evidence that either species can use sound to build up a detailed picture of their environment, as bats or cetaceans can.

4

Olfaction

Rats rely heavily on olfaction (e.g. Doty, 1986). They can quickly associate olfactory cues with food rewards (Le Magnen, 1999a; Birrell & Brown, 2000), with this ability even making them a suitable alternative to ‘sniffer’ dogs for locating contraband
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substances (Otto et al., 2002). Rats can locate the direction of odorants, without moving their heads, three orders of magnitude more quickly than we can (Rajan et al., 2006). It is sometimes stated that albinism dampens olfaction, because albinos show weaker avoidance of garlic than pigmented rats do (Keeler, 1942), but of course they might simply be less averse to the scent. Humans are unusual mammals because a much smaller proportion of our genome is devoted to olfaction, than other species (Gilad et al., 2003; Emes et al., 2004; Rat Genome Sequencing Project Consortium, 2004; Quignon et al., 2005), and our vomeronasal organ is vestigial or non-existent (e.g. Brennan & Keverne, 2004). In contrast, rats not only possess main olfactory epithelia, but also well-developed vomeronasal organs. Although the two systems overlap (reviewed in Shepherd, 2006), the vomeronasal organ seems specialised for instinctive recognition of pheromones and evolutionarily relevant compounds (Dulac, 1997; Holy et al., 2000; Brennan & Keverne, 2004), while the olfactory epithelium is specialised for learned associations between volatile scents and their implications (Dulac, 1997). The vomeronasal system detects relatively non-volatile compounds, requiring the rat to lick or imbibe some compounds before it can detect them (Brennan & Keverne, 2004). Here ‘olfaction’ includes both systems, because in most cases the specific odorant or detection mechanism is currently unknown. The focus is on olfactory communication, but some significant scents within laboratory environments are also discussed. 4.1 Overview of rat olfactory communication

Rat olfactory communication is well-developed, yet remains little understood by humans. Much communication is mediated through urine, but rats have many scent glands, including the sebaceous, preputial, clitoral, perineal, salivary, anal, plantar, and Harderian glands. Through scent, rats can gain information about each others’ gender (Alberts & Galef, 1973; Moore, 1985; Brown, 1992; Garcia-Brull et al., 1993), reproductive state (Gawienowski et al., 1975; Manzo et al., 2002; Zala et al., 2004),

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genetic relatedness (Wills, 1983; Hurst et al., 2005), dominance (Krames et al., 1969), health status (Zala et al., 2004), and individual identity (Hopp et al., 1985; Gheusi et al., 1997). Rats also recognise familiar conspecifics using olfaction (Burman & Mendl, 2003), not through a shared ‘colony scent’, but through remembering individual odours (Alberts & Galef, 1973; Carr et al., 1976). These odours can be determined genetically or be acquired from the environment (Schellinck et al., 1991; Schellinck & Brown, 2000; Hurst et al., 2005). Laboratory rats may not be completely isolated from conspecifics even when individually housed, because scents from neighbouring cages, or experimental apparatus and instruments can influence them (unless they are in individually ventilated cages). These scents can profoundly affect rats, as described below, although it should be mentioned that isolation itself also affects these social animals (e.g. Day et al., 1982; Hurst et al., 1997; Sharp et al., 2002; Westenbroek et al., 2005). 4.2 Scent and reproduction

Much sexual behaviour in rodents is olfactorily mediated. The ‘Bruce effect’, whereby female mice abort their offspring upon encountering the volatile scent of unfamiliar males (Bruce & Parrott, 1960), seems not to occur in rats. However, the ‘Whitten effect’, in which volatile male scents trigger oestrus in females (Whitten, 1959), and the ‘Lee–Boot effect’, when females housed without males show suppressed, irregular oestrus cycles (Van Der Lee & Boot, 1956) do occur relatively weakly in rats. In rats and mice, male odour accelerates the onset of puberty in females, in a phenomenon labelled the ‘Vandenbergh effect’ (Vandenbergh, 1969, 1976). The scent of female rats, especially those in oestrus, stimulates male sexual behaviour, but also urinary-marking (Manzo et al., 2002) and competitive aggression (Alberts & Galef, 1973). It is possible therefore, that housing males where they can smell females could affect their physiology and behaviour, affecting research, and
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might affect their welfare either way. The vomeronasal system, probably responsible for detecting these scents, habituates to stimuli less easily than most sensory systems (Holy et al., 2000), so the effects might be persistent. However, since the vomeronasal organ requires direct physical contact to detect some pheromones (Brennan & Keverne, 2004), the problem might only exist if the scent is volatile. Other important scents here include those mediating the mother–pup relationship. For example, diodecyl proprionate, a pup preputial gland pheromone, induces maternal licking (Brouettelahlou et al., 1991). Mother rats produce various odours aiding pup survival, including those guiding pups to the nipples, and those deposited in the bedding that reduce pup activity, keeping them in the nest (Porter & Winberg, 1999). Also, pregnant females release a non-volatile pheromone that prevents infanticide by cohabiting males (Mennella & Moltz, 1988). Perhaps it is the removal of these scents that increases the likelihood of pups being cannibalised when rats’ cages are cleaned within the first few days of birth (Burn & Mason, in press). 4.3 Olfactory modulation of aggression

Aggression in male rodents can be triggered by novel (usually male) scents, so rats rendered anosmic show little aggression in resident–intruder tests (Alberts & Galef, 1973). Habituation to familiar or self-scents plays a large role in reducing aggression between familiar or related individuals. For example, aggression is reduced between more familiar individuals (Alberts & Galef, 1973; Garcia-Brull et al., 1993) and between more closely related individuals (Nevison et al., 2003). Some inbred mouse strains cannot discriminate between familiar and unfamiliar conspecific odours, resulting in reduced aggression (Nevison et al., 2003). This could also be true for rats. In fact, unfamiliar male scents not only stimulate aggression, but also defensive behaviour in subordinate males encountering dominant male odours. Rats defeated by an alpha-male, subsequently show avoidance and fear behaviour upon encountering the scent of other alpha-males (Williams & Groux, 1993; Williams, 1999).
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This said, while cage-cleaning – which removes scent marks – provokes aggression in male mice (Gray & Hurst, 1995; Van Loo et al., 2000), in familiar rats it merely provokes non-aggressive skirmishing (Burn et al., 2006a; Burn et al., 2006b); perhaps for this reason cage-cleaning frequency seemingly has no long-term effects on male rat welfare. When unfamiliar rats are to be housed together, exposing them to each other’s scents for a few days before allowing physical contact may prevent aggression (e.g. Bulla, 1999). Alternatively, aggression can sometimes be prevented by masking unfamiliar conspecifics using another unfamiliar, neutral scent. In rats evidence is anecdotal, but in a controlled study of mice, chocolate or sheep’s wool odours reduced resident–intruder aggression (Kemble et al., 1995). Finally, it is worth mentioning that odour-mediated aggression does not only occur between males. For example, mother rats able to smell their own pups show aggression towards intruders – neither visual, tactile, nor auditory cues from the pups elicit this aggression (Ferreira & Hansen, 1986). 4.4 Communication about experiences

Rats are generally attracted to areas smelling of conspecifics (e.g. Galef & Heiber, 1976; Mackay-Sim & Laing, 1980), but scents released during negative or positive experiences, can make those areas aversive or more attractive, respectively. Rats produce ‘alarm’ odour when they experience electric shocks (Mackay-Sim & Laing, 1980; Abel & Bilitzke, 1990; Williams & Groux, 1993; Kiyokawa et al., 2004), transport between rooms (Beynen, 1992), and the events and disturbances accompanying carbon dioxide euthanasia (Ware & Mason, 2003). They probably also produce it in forced-swim tests (Abel & Bilitzke, 1990), but no unstressed controls were used so rats may simply have been responding to odours left by an unfamiliar male. Alarm odour is more powerful with more severe stressors (Mackay-Sim & Laing, 1980). The molecule(s) involved have not yet been identified, but a candidate
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is 2-heptanone; more of this is present in urine from stressed rats, but diazepam during the stressor does not reduce the amount produced (Gutiérrez-García et al., 2006). In recipients, alarm odour increases freezing behaviour (Williams, 1999; Kikusui et al., 2001), activity (Mackay-Sim & Laing, 1980; Abel & Bilitzke, 1990; Kikusui et al., 2001; Ware & Mason, 2003), body temperature (Kikusui et al., 2001), hypothalamic–pituitary–adrenal activity (Takahashi et al., 1990; but see Mackay-Sim & Laing, 1980), urination (Stevens & Koster, 1972), and latency to approach rewards (Mackay-Sim & Laing, 1981; Ware & Mason, 2003). It also causes avoidance compared with the scent of unstressed conspecifics (Mackay-Sim & Laing, 1980). Experience can affect responses to alarm odour, with rats avoiding the odour of shocked rats more if they have experienced shock themselves, but not necessarily if they have experienced defeat by an alpha-male (Williams & Groux, 1993). A somewhat separate body of literature describes ‘frustration’ or ‘non-reward’ odour, produced when anticipated rewards are withheld (Collerain & Ludvigson, 1972; Ludvigson et al., 1985; Taylor & Ludvigson, 1987). Again this odour causes avoidance, but unlike alarm odour, no fear responses to it have been reported. It seems not to exist in urine (Collerain & Ludvigson, 1972), unlike alarm odour (Mackay-Sim & Laing, 1981), but both are also produced from other bodily sources yet to be identified (Mackay-Sim & Laing, 1981; Weaver et al., 1982). Rats probably also produce a ‘reward’ odour, although this has mainly been tested against non-reward situations (i.e. frustration odour), with no neutral rat odour control. Nevertheless, a rat’s trail is more attractive if laid down after the rat receives a reward than before (Galef & Buckley, 1996), and when it perceives a signal that reliably predicts reward (Ludvigson et al., 1985). However, the attraction of rats to reward odour is much weaker than the avoidance of frustration odour, when compared against the same ‘no odour’ control (Taylor & Ludvigson, 1980).

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The release of alarm odour means that rat welfare and experimental aims might be compromised if neighbouring conspecifics are distressed by illness, injury, or experimental procedures (Beynen, 1992). Any of these odours can bias rats’ decisions in choice tests (Collerain & Ludvigson, 1972; Aoyama & Okaichi, 1994; Mitchell et al., 1999), increase ‘baseline’ stress in subsequently tested rats or supposed control ones (Beynen, 1992; Kikusui et al., 2001), and alter behaviour in tests such as swim tests (Abel & Bilitzke, 1990), and open field or novelty tests (Mackay-Sim & Laing, 1981; Takahashi et al., 1990; Ware & Mason, 2003). There has apparently been no evaluation of effective ways to clean experimental apparatus; various cleaning agents are used, which probably vary in efficacy and may have intrinsic odours that affect rats. Alcohol is commonly used, but in pigs, its volatile components can reduce cortisol levels in open field tests (Thodberg et al., 2006). 4.5 Communication about food

Rats can learn about specific foods from conspecific odours. Carbon disulphide, present in rats’ breath (Galef et al., 1988), causes rats to strongly prefer novel foods eaten by their cagemates versus other novel foods (e.g. Strupp & Levitsky, 1984). The preferences can persist for at least 30 days, even without opportunity to sample the foods during that time (Galef & Whiskin, 2003b). Aversion to novel foods can be caused by the ‘poisoned partner effect’ (Lavin et al., 1980). Here if a novel food is eaten by a rat, which then encounters the odour of a poisoned conspecific, the healthy rat will subsequently avoid the novel food, even if the poisoned rat did not eat it (Stierhoff & Lavin, 1982). Strangely, the healthy rat only avoids food that it itself has eaten, rather than that eaten by the poisoned rat, and therefore not necessarily the poisonous food (Galef et al., 1990). In fact, exactly as described above, the healthy rat actually prefers novel foods after smelling them on the poisoned rat’s breath (Galef et al., 1990).
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Lactating rats also avoid novel foods ingested just before their pups become ill, because of an odour released by pups with gastrointestinal illness (Gemberling, 1984). The odour causes no aversion in males or nulliparous females, and is not released by pups stressed in other ways, so it seems more specific than the poisoned partner effect. 4.6 Scents in the laboratory

Most of the scents relevant to laboratory rats are those within the cage itself. Apart from those produced by conspecifics or food, others could include detergent residues, bedding materials, and microbial products from the breakdown of food or excreta. Cage-cleaning abruptly changes the olfactory environment, which might contribute to post-cleaning changes in rat behaviour and physiology (Burn et al., 2006a). Also, like gerbils, rats might more accurately discriminate scents in a test arena on days when their cages are clean rather than soiled (Dagg et al., 1971). Another salient source of smell for laboratory rodents might be their human handlers. Rats respond differently towards different humans (McCall et al., 1969; Morlock et al., 1971; Davis et al., 1997; van Driel & Talling, 2005), mostly because of differences in odour (McCall et al., 1969). People smell different due to genetic factors and environmental ones, such as diet, smoking, perfume, soap, and deodorant. Regular rodent handlers may also be ‘marked’ with odours from previously handled rodents, sometimes including reward or alarm odours. Additionally, rats might fear humans carrying scents from their pets, especially if the pet is a predatory species. Rats innately fear predator odours, including cats and mustelids (reviewed in Blanchard et al., 2003), but apparently not dogs. Rats cannot easily habituate to predator odours (Blanchard et al., 1998), showing increased corticosterone, freezing and vigilance, elevated plus-maze anxiety and endogenous opioid analgesia, and suppressed electric-prod burying, and impaired working memory (Williams, 1999; Blanchard et al., 2003). Predator odours also elicit fear26

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related fast-waves and reduce cell-proliferation in the dentate gyrus (Heale et al., 1994; Tanapat et al., 2001). It is even possible that rats would instinctively fear human odour – wild rats usually avoid close human contact, and any such fear of humans might have escaped our notice, of course, it would require a controlled experiment not involving human presence. Many odours from synthetic products used in laboratories could affect rodents. While several reviews compare the efficacy of detergents for cleaning animal cages (e.g. Heuschele, 1995), none discuss their potential olfactory impacts on the animals. Yet, some organic solvents (e.g. xylene, toluene, diethyl ether, and methyl methacrylate) cause avoidance and fast-waves in the dentate gyrus, just as predator odours do (Heale et al., 1994). These solvents constitute many everyday substances, including some inks, glues, and paints; indeed, identification-marking rodents with inks or dyes can affect their anxiety profiles (Burn et al., in press) and cause them to become submissive to unmarked cagemates (Lacey et al., 2007). Many odorants that smell subjectively pleasant to humans, often therefore being present in perfumed products or human diets, can also influence hypothalamopituitary-adrenal activity and immune responsiveness, positively or negatively (Komori et al., 2003). Rose oil (de Almeida et al., 2004) and ‘green odour’, trans-2hexenal (Nakashima et al., 2004), are anxiolytic to rats. Citrus oils are analgesic (Aloisi et al., 2002), but can have complex effects on rodent anxiety (Komori et al., 2003; Ceccarelli et al., 2004). In rat pups, peppermint increases mortality and decreases activity (Pappas et al., 1982), and rats avoid the scent of garlic (Keeler, 1942) and rosemary (R. M. J. Deacon, personal communication). Many of these effects could inadvertently introduce variation between experiments, but some could be used as non-nutritive environmental enrichments or rewards. Also, anxiolytic

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scents could be easily administered to rats in mildly stressful situations (de Almeida et al., 2004; Nakashima et al., 2004).

5

Gustation

Like us, rats are opportunistic omnivores; their ecological niche is characterised by sampling diverse food substances and remembering their nutritional consequences (e.g. Capaldi, 1996). They rapidly learn aversions to harmful novel foods, which can be a problem in pest control situations when they ingest sub-lethal quantities of bait. Rats, particularly wild strains, are neophobic, being reluctant to consume novel food (Galef & Whiskin, 2003a). They initially sample only small amounts of novel food (if any at all), but if it proves safe, they later readily consume it, often in preference to more familiar foods (Calhoun, 1963). Under natural conditions, this cautious but explorative behaviour might help them obtain a full nutritional complement, reducing reliance on any one food type, while avoiding poisoning. Rats detect similar taste dimensions to humans, i.e. sweetness (carbohydrates and artificial sweeteners), saltiness (sodium salts), sourness (hydrogen ions), bitterness (quinine, caffeine, most natural toxins, and some others) (Grill & Norgren, 1978), and umami (amino acids, such as glutamate) (e.g. Smith & Margolskee, 2001). As with humans, sweetness and umami are rewarding, bitterness is usually aversive, and saltiness and sourness are only pleasant at low concentrations (Grill & Norgren, 1978; Berridge, 2000). They also initially strongly avoid capsaicin, the ‘hot’ taste of chilli, but often consume it readily once it becomes familiar (Jensen et al., 2003). However, rats do not perceive certain artificial sweeteners as being ‘sweet’ (Sclafani & Abrams, 1986; Dess, 1993; Sclafani & Clare, 2004), and they may have separate receptors for sugars and starch (Sclafani, 1987). Their bitterness thresholds for some compounds differ from ours (Glendinning, 1994; Mueller et al., 2005), allowing denatonium benzoate – which tastes less bitter to rats than to humans and some other animals – to be added to baits to prevent its consumption by non-target species
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(Hansen et al., 1993). There are also some strain and sex differences in rat gustation (Boakes et al., 2000; Clarke et al., 2001). In fact, ‘flavour’ involves not only gustation, but also olfaction and tactile sensations (Smith & Margolskee, 2001). For completeness, these senses are not separated here when discussing the practical implications of rat gustatory biases. 5.1 Taste in the laboratory

Laboratory rodents usually have no opportunity to sample different foods, typically being fed a palatable, dry, nutritionally complete diet, in powder form or as pellets. These diets are easily stored, inexpensive, and require little preparation (Lane-Petter, 1975), and they aid standardisation between experiments. Laboratory rats will also taste their mothers’ milk, bodily secretions from themselves or conspecifics (if socially housed), their cage surfaces, and perhaps human hands or gloves, and bedding material (if provided). Hence, scope for learning taste–nutrient associations is very limited, rendering the gustatory sense largely redundant in laboratories. For other sensory modalities, sensory deprivation reduces the volume and functioning of the associated brain regions. For example, the visual cortices of rats reared in darkness are permanently underdeveloped (Fagiolini et al., 1994), while sensory deprivation only temporarily limits olfactory bulb (Cummings et al., 1997) and barrel cortex development (Polley et al., 2004; but see Rema et al., 2003). However, despite rats frequently being used as models in taste research, precisely because their gustatory perception is supposedly similar to ours, the effects of gustatory deprivation on the brain and behaviour are apparently unknown. The effects may be minimal if taste is tightly genetically controlled, but alternatively, lack of gustatory experience could, for example, exaggerate rats’ neophobia or diminish their gustatory learning abilities.

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5.2

Nutritional regulation

It is unclear whether rats can appropriately self-regulate their nutritional intake, given the opportunity. Most discrepancies between findings are probably due to differences between the diets offered to rats (Naim et al., 1985; Sclafani, 1987; Prats et al., 1989), and circadian variations in intake patterns (Larue-Achagiotis et al., 1992). Rats generally do select foods appropriate for their changing nutritional needs, but like humans, they are biased towards sugary or fatty foods. They are consequently also prone to obesity if offered palatable, calorific diets (Naim et al., 1985; Sclafani, 1987; Prats et al., 1989). Because laboratory rodent diets are homogenous, they allow no qualitative nutritional regulation. Generally, this is unproblematic because the diets have sustained rodent populations for many decades, without apparent negative effects on breeding, health, or longevity. However, although special formulations are available, many widely used diets cover all age and sex categories: oestrus females, weanling pups, and elderly males alike. Moreover, they are often common to rats and mice. Thus, within this diversity, individuals might sometimes have different nutritional requirements from that provided. In standardising diets to this extent, we might inadvertently increase, rather than decrease, variation in rodents’ internal nutritional states because they have no opportunity to regulate them. Some dietary supplements can enhance laboratory rat health, calling into question the completeness of homogenous diets. For example, blueberries, high in antioxidants, prevent cognitive deficits in aging rats (Casadesus et al., 2004), and as mentioned previously, other dietary supplements prevent retinal damage (Li et al., 1985). Also, in hamsters, supplementation with seeds and rabbit chow increased pup growth, and reduced cannibalism by the mothers (Day et al., 2002).

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5.3

Refinement within the homecage

Palatable diets may provide rats with ‘enjoyment’ (Lane-Petter, 1975) or hedonic experiences, with palatable and unpalatable foods eliciting distinctive behavioural expressions that are homologous to human gustatory expressions (Berridge, 2000). Most welfare efforts concentrate on reducing negative welfare, but facilitating positive welfare, such as pleasure from food or foraging, should not be neglected (e.g. Balcombe, 2005). Food-related environmental enrichments might be particularly relevant for generalists, like rats, because their natural ecology incorporates diverse food types, varying through time and space. However, the idea of food-related enrichment has been little explored for laboratory rats, and yet it could improve their welfare (Johnson & Patterson Kane, 2003), provided obesity is avoided (e.g. Mattson, 2005). There are three main aspects of food that could be varied for enrichment purposes: nutritional content, flavour, and physical presentation. 5.3.1 Nutritional content

Providing rodents with very nutritionally diverse diets may be undesirable for practical reasons (Lane-Petter, 1975; Key, 2004), and because they encourage obesity (Mattson, 2005), and may increase variation. Nevertheless, offering some opportunity to nutritionally self-regulate could be beneficial, as suggested above. In some animal facilities, seeds and nuts are scattered onto rats’ bedding; rats become very active upon hearing them being scattered in neighbouring cages, and continue foraging for many hours (Key, 2004). Since the seeds would constitute only a very small proportion of the diet, they are unlikely to impact heavily on nutritional regulation, but could allow some relevant gustatory stimulation and regular hedonic experiences. Proper evaluation of the effects is necessary however; the most relevant study so far seems to be one, mentioned earlier, when seed supplements enhanced hamster pup growth and decreased cannibalism (Day et al., 2002).

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5.3.2

Flavour

Even without nutritional value, gustatory enrichment could be achieved; providing daily non-nutritional pina-colada flavour treats to breeding mice increased the number of pups weaned (Inglis et al., 2004), suggesting that the hedonistic aspects alone of scatter-feeding are beneficial. Domesticated rats value variety, and will substitute a preferred food that has been their sole diet for several days for a less preferred, newly available food (Galef & Whiskin, 2003a, 2005). They also consume more food if provided as a succession of varied ‘meals’ rather than homogenous meals (Treit et al., 1983; Clifton et al., 1987; Le Magnen, 1999b). These preferences exist even when foods differ primarily in flavour not nutritional value, such as when cinnamon, cocoa, ‘all spice’, or marjoram are added to normal chow (as in the above five studies). These additives presumably have negligible bioactivity, being common non-nutritive components of human diets, but confirmation in rats is required. The above studies suggest that obesity might be a risk because of the increased food consumption, but they were all relatively short-term, so rats might down-regulate their intake of variable food over time. Le Magnen (1999b) found that if ‘variable days’ were alternated with ‘homogenous days’, rats ate less food than normal on homogenous days, perhaps compensating for over-eating on variable days. 5.3.3 Physical presentation

Finally, enrichment might be achieved through varying dietary presentation. Soft ‘wet mash’ (chow soaked in water) is often used to help sick or weak rats gain weight, and usually any healthy cage-mates also prefer the mash to freely available pellets. However, it is an impractical enrichment for healthy rats, being messy and encouraging microbial growth (Lane-Petter, 1975). Occasionally scattering chow pellets within the cage allows rats to eat in their natural posture, holding the pellet in

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their forepaws (Bruce, 1965), and they more readily consume these pellets than those in the hopper (personal observation). Captive rats also ‘contra-freeload’, choosing food that requires handling and preparation, even when prepared food is available (Carder & Berkowitz, 1970). This may be because most of a wild rat’s time and effort would be devoted to foraging (Johnson & Patterson Kane, 2003). Scattering small food items, such as the aforementioned seed mixes or chow pellets, in bedding allows rats to forage, which may be rewarding in itself. Scatter-feeding rarely triggers competitive aggression because the food is spatially distributed. Commercially available rodent puzzlefeeders are also available, although they are uncommon in laboratories and are not always easily sourced. 5.4 Refinement of experiments

The generalist feeding habits of rats can be exploited in research, improving experiments ethically, enhancing rats’ cooperation, and reducing interference from stress. Drugs and inoculants are often delivered by gavage, a tube inserted via the mouth into the stomach, which can be technically difficult, and causes stress, respiratory distress, and occasionally even death (Balcombe et al., 2004). However, substances can be successfully delivered within palatable vehicles that rats will voluntarily consume, provided there is no interference with the active ingredient. Fruit- or beef-flavoured gelatine is commonly used but some rats only reluctantly consume it, so it can be worth trying several alternatives (Hawkins et al., 2004). Another example is to use small amounts of chocolate (Huang-Brown & Guhad, 2002). Taste aversion can develop if the vehicle becomes associated with illness, but giving rats prior experience with the unadulterated food can prevent this. Some substances can also be microencapsulated and added to chow for long-term studies (Melnick et al., 1987; Dieter et al., 1993; Yuan et al., 1993).

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Preferred rewards can often be used to motivate rats to perform tasks in experiments, rather than using punishments or prior deprivation. Deprivation is a powerful motivator, but can undesirably affect behaviour, physiology, neurochemistry, and drug efficacy (Slawecki & Roth, 2005). Moreover, it is sometimes unnecessary, because undeprived rats will often work – albeit to a limited extent – for preferred rewards, including commercially available reward pellets, sucrose solution (Slawecki & Roth, 2005), or breakfast cereals (e.g. Ellis, 1984). Prats and colleagues (1989) found that rats did not readily consume cheese, chocolate or fruit-candy, and instead preferred other foods offered, including banana, cookies, standard chow pellets, and liver pâté. Large quantities of dairy products (DiBattista, 1990) and chocolate (Huang-Brown & Guhad, 2002) should be avoided as they harm rodent health. Undeprived rats are particularly motivated to earn rewards if experiments coincide with their active period (Hyman & Rawson, 2001), with a shifted light cycle enabling practical working hours (see the section on Vision). Neophobia can be eliminated by providing the palatable incentive in the homecages of rats several days before experiments. Finally, food must often be withheld overnight before surgery or intraperitoneal injections. This deprivation causes weight loss, and reduced hepatic weight and blood glucose, and potentially, emotional distress from hunger. However, providing sugar cubes to the rats can prevent these problems, while gastrointestinal volume is still reduced, as required (Levine & Saltzman, 1998).

6

Somatosensation

Rat somatosensation could be considered from many different angles. Here, the focus is on that relating to the ability of rats to explore and interact with their environments. In the rat somatosensory cortex, the vibrissae (sensory whiskers), nose and mouth, forepaws, and sinus hairs on its wrists, are particularly well-represented. In fact, the forepaws are represented twice each, and the whiskers and sinus hairs have
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specialised granular aggregates devoted to them (Hermer-Vazquez et al., 2005). In general, rat and human somatosensation seem similar, but there are two main differences that noticeably affect rat behaviour. Firstly, rats’ vibrissae are extremely sensitive (Arabzadeh et al., 2005), being comparable to primate fingertips (Carvell & Simons, 1990). Rats can whisk them independently of each other across surfaces to make fine tactile discriminations (Guic-Robles et al., 1989; Carvell & Simons, 1990). In a study investigating rats’ numerical competencies, subjects could not discriminate between two, three or four tactile stimuli delivered to the body, but they succeeded when the stimuli were delivered to a single vibrissal hair (Davis et al., 1989). The vibrissae also detect differences in mechanical resonant frequencies, with the shorter anterior vibrissae detecting higher frequencies than the longer posterior ones (Neimark et al., 2003). The second obvious difference from humans relates to thigmotaxis; the bias of rats towards maintaining physical contact with vertical surfaces. In fact, thigmotaxis underlies many tests of ‘anxiety’ (Treit & Fundytus, 1988), because when rats perceive environments as threatening, they stay closer to vertical surfaces, such as the boundaries of open field arenas, or the closed arms of elevated plus-mazes. The thigmotactic bias may not be strictly somatosensory, perhaps also incorporating visual preferences for avoiding light exposure. Rats that lack vibrissae on one side prefer to maintain wall-contact on their intact side, suggesting the vibrissae play a role (Meyer & Meyer, 1992). The implications of rat somatosensation include the impact of environmental enrichment on rat somatosensory development generally, and implications of the vibrissal sense for experiments and housing. 6.1 Environmental enrichment and somatosensation

Environmental enrichment profoundly affects the somatosensory and barrel cortices. In rats kept in enriched rather than barren environments, the primary somatosensory
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cortex representing the forepaws becomes 1.5 times larger (Xerri et al., 1996; Coq & Xerri, 1998, 2001). The barren cages in these studies contained bedding, exerting their effect despite rats being able to dig with their forepaws, so the difference might be even more pronounced in rats housed on wire floors. Environmental enrichment seemingly does not enhance textural discrimination abilities, but it does increase the rate of learning such discriminations (Bourgeon et al., 2004). Enrichment can also counteract age-related declines in hind-paw representation in the somatosensory cortex, which is otherwise associated with impaired walking in aged rats (Godde et al., 2002). Finally, in naturalistic environments, the representation of each whisker in the barrel cortex becomes dramatically more well-defined compared with standard cages (Polley et al., 2004). The above studies combined several enrichment types, including social contact, foraging opportunities, structural features and novelty, so it is unclear what relative contributions were made by each enrichment type. It is lack of tactile contact with conspecifics that apparently leads to the self-biting and tail manipulation seen in isolated rats (Day et al., 1982; Hurst et al., 1997). 6.2 Vibrissae and the laboratory environment

The sensitivity of the vibrissal sense (Davis et al., 1989; Guic-Robles et al., 1989; Carvell & Simons, 1990; Arabzadeh et al., 2005) is probably under exploited in learning tasks, where less salient visual cues are currently more widely used (Dymond, 1995; Dymond et al., 1996; Birrell & Brown, 2000). However, laboratory rats can sometimes lack vibrissae for various reasons, including ‘barbering’, when hairs and often whiskers are removed by conspecifics (Garner et al., 2004). This occurs in rats, albeit to a much lesser extent than in mice (Bresnahan et al., 1983; Wilson et al., 1995). Other rats may lack whiskers due to their strain; some nude rodent strains have no whiskers at all (e.g. Sundberg et al., 2000), but most have short, kinked whiskers, giving a limited sensory range (e.g. Festing et al., 1978; Moemeka et

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al., 1998). Nude strains also lack the sensitive guard hairs otherwise dispersed through the coat, and which would convey proprioceptive information. Both vibrissal absence and barrel cortex impairment through lack of environmental enrichment (as described above), could have practical consequences. Rats lacking vibrissae show impaired orientation towards tactile stimuli, and – provided they have environmental enrichment – compensate by orienting towards visual stimuli more than controls (Symons & Tees, 1990). Whiskers also aid swimming, enabling animals to keep their heads above water (Ahl, 1986; Meyer & Meyer, 1992), and consequently, rats lacking vibrissal sensation can drown in water mazes and swim tests (Hughes et al., 1978). Finally, vibrissae are important in social interactions, with whiskerless rats being unable to avoid bites to their faces during fighting (Blanchard et al., 1977a; Blanchard et al., 1977b). Because aggression between familiar rats is uncommon (Burn et al., 2006b), whiskerless rats need not be socially isolated, except in cases where aggression is observed. However, whiskerless rats may be injured if introduced to unfamiliar conspecifics, when fighting is more likely.

7

Summary

It is impossible for us to know what it is like to be a `rat` (Nagel, 1974), but knowledge of their sensory biases allows us to imagine what it might be like, as a human, to have those biases within a laboratory rat’s environment. This insight, while imperfect, could help predict how rats might be affected by different situations, improving our experimental design and their welfare. In summing up then, an overall theoretical picture of a rat’s perception of the laboratory could be as follows. The rat’s sensitive eyes, shunning the intense artificial light, provide it with a hazy view in predominantly grey, ultra-violet and green hues. From within its cage, it hears the chirps, squeaks and whines of its neighbours, gaining information that we
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cannot hear unaided and are yet to understand. Background noise consists of the low babbles and hisses of distinctively scented humans, and the unregulated drones and blasts of ultrasonic sounds. Scents provide visceral warnings and enticements, induce new motivations, and inform the rat about social possibilities outside the cage. The environment wafts a succession of scents, from pleasant, calming fragrances to the innately alarming odours of intangible predators. The rat tastes little apart from its dry, satiating homogenous diet. Its vibrissae provide a protective, finely tuned forcefield to feel the details of the cage surfaces; with the rat perceiving security from close contact with the solid walls.

8

Conclusion
Knowledge of the sensory gulfs and similarities between ourselves and this

commonly used research animal can improve science and enhance rat welfare. More work is still necessary to understand rat perception, and even more so for less wellresearched species. The aim of this review is to make current knowledge accessible to researchers, rat caretakers and rodent specialists, in the hope that it will enable tangible improvements in experimental design and rat welfare.

Acknowledgements
Many thanks to Georgia Mason for her detailed comments and encouragement, and also to Robert Deacon, Mark Ungless, Jennifer Bizley, and Alex Weir for their comments.

References
Abel, E. L., Bilitzke, P. J., 1990. A possible alarm substance in the forced swimming test. Physiol. Behav. 48, 233-239. Ahl, A. S., 1986. The role of vibrissae in behavior: a status review. Vet. Res. Commun. 10, 245-268. Akula, J. D., Lyubarsky, A. L., Naarendorp, F., 2003. The sensitivity and spectral identity of the cones driving the b-wave of the rat electroretinogram. Vis. Neurosci. 20, 109-117.
38

1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053

Alberts, J. R., Galef, B. G., 1973. Olfactory cues and movement: stimuli mediating intraspecific aggression in the wild Norway rat. J. Comp. Physiol. Psychol. 85, 233-242. Allin, J. T., Banks, E. M., 1972. Functional aspects of ultrasound production by infant albino rats (Rattus norvegicus). Anim. Behav. 20, 175-185. Aloisi, A. M., Ceccarelli, I., Masi, F., Scaramuzzino, A., 2002. Effects of the essential oil from citrus lemon in male and female rats exposed to a persistent painful stimulation. Behav. Brain Res. 136, 127-135. Andrade, M. M., Tome, M. F., Santiago, E. S., Lucia-Santos, A., de Andrade, T. G., 2003. Longitudinal study of daily variation of rats' behavior in the elevated plus-maze. Physiol. Behav. 78, 125-133. Aoyama, K., Okaichi, H., 1994. The influence of conspecific distress responses on the lever choice behavior in the rat. Jpn. J. Psychol. 65, 286-294. Arabzadeh, E., Zorzin, E., Diamond, M. E., 2005. Neuronal encoding of texture in the whisker sensory pathway. PLoS Biology 3, e17. Artal, P., Herreros De Tejada, P., Muñoz Tedó, C., Green, D. G., 1998. Retinal image quality in the rodent eye. Vis. Neurosci. 15, 597-605. Balcombe, J., 2005. Pleasure: the neglected experience (Poster presentation). Paper presented at From Darwin to Dawkins: the science and implications of animal sentience, London. Balcombe, J. P., Barnard, N. D., Sandusky, C., 2004. Laboratory routines cause animal stress. Contemp. Top. Lab. Anim. Sci. 43, 42-51. Bartoletti, A., Medini, P., Berardi, N., Maffei, L., 2004. Environmental enrichment prevents effects of dark-rearing in the rat visual cortex. Nat. Neurosci. 7, 215216. Bellhorn, R. W., 1980. Lighting in the animal environment. Lab. Anim. Sci. 30, 440450. Bennett, A. T., Cuthill, I. C., 1994. Ultraviolet vision in birds: what is its function? Vision Res. 34, 1471-1478. Berdoy, M. (2002). The laboratory rat: a natural history. Retrieved 24th Feb 2006, from www.ratlife.org Berridge, K. C., 2000. Measuring hedonic impact in animals and infants: microstructure of affective taste reactivity patterns. Neurosci. Biobehav. Rev. 24, 173-198. Berson, E. L., 2000. Nutrition and retinal degenerations. Int. Ophthalmol. Clin. 40, 93-111. Beynen, A. C., 1992. Communication between rats of experiment-induced stress and its impact on experimental results. Anim. Welf. 1, 153-160. Birrell, J. M., Brown, V. J., 2000. Medial frontal cortex mediates perceptual attentional set shifting in the rat. J. Neurosci. 20, 4320-4324. Björk, E., Nevalainen, T., Hakumäki, M., Voipio, H.-M., 2000. R-weighting provides better estimation for rat hearing sensitivity. Lab. Anim. 34, 136-144. Blanchard, D. C., Griebel, G., Blanchard, R. J., 2003. Conditioning and residual emotionality effects of predator stimuli: Some reflections on stress and emotion. Prog. Neuro-Psychopharmacol. Biol. Psychiatry 27, 1177-1185. Blanchard, R. J., Blanchard, D. C., Takahashi, T., Kelley, M. J., 1977a. Attack and defensive behaviour in the albino rat. Anim. Behav. 25, 622-634. Blanchard, R. J., Takahashi, L. K., Fukunaga, K. K., Blanchard, D. C., 1977b. Functions of the vibrissae in the defensive and aggressive behavior of the rat. Aggress. Behav. 3, 231-240.
39

1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103

Blanchard, R. J., Blanchard, D. C., Agullana, R., Weiss, S. M., 1991. Twenty-two kHz alarm cries to presentation of a predator, by laboratory rats living in visible burrow systems. Physiol. Behav. 50, 967-972. Blanchard, R. J., Nikulina, J. N., Sakai, R. R., McKittrick, C., McEwen, B., Blanchard, D. C., 1998. Behavioral and endocrine change following chronic predatory stress. Physiol. Behav. 63, 561-569. Blom, H. J. M., Van Tintelen, G., Baumans, V., Van Den Broek, J., Beynen, A. C., 1995. Development and application of a preference test system to evaluate housing conditions for laboratory rats. Appl. Anim. Behav. Sci. 43, 279-290. Boakes, R. A., Boot, B., Clarke, J. V., Carver, A., 2000. Comparing albino and hooded Wistar rats of both sexes on a range of behavioral and learning tasks. Psychobiology 28, 339-359. Bourgeon, S., Xerri, C., Coq, J.-O., 2004. Abilities in tactile discrimination of textures in adult rats exposed to enriched or impoverished environments. Behav. Brain Res. 153, 217-231. Brainard, G. C., Barker, F. M., Hoffman, R. J., Stetson, M. H., Hanifin, J. P., Podolin, P. L., Rollag, M. D., 1994. Ultraviolet regulation of neuroendocrine and circadian physiology in rodents. Vision Res. 34, 1521-1533. Brennan, P. A., Keverne, E. B., 2004. Something in the air? New insights into mammalian pheromones. Curr. Biol. 14, R81-R89. Bresnahan, J. F., Kitchell, B. B., Wildman, M. F., 1983. Facial hair barbering in rats. Lab. Anim. Sci. 33, 290-291. Brouettelahlou, I., Amouroux, R., Chastrette, F., Cosnier, J., Stoffelsma, J., Vernetmaury, E., 1991. Dodecyl propionate, attractant from rat pup preputial gland - characterization and identification. J. Chem. Ecol. 17, 1343-1354. Brown, R. E., 1992. Responses of dominant and subordinate male-rats to the odors of male and female conspecifics. Aggress. Behav. 18, 129-138. Bruce, H. M., Parrott, D. M., 1960. Role of olfactory sense in pregnancy block by strange males. Science 131, 1526. Bruce, H. M., 1965. Comments on the design of food hoppers in current use for laboratory animals. J. Anim. Technicians Assoc. 16, 32-33. Brudzynski, S. M., Chiu, E. M., 1995. Behavioural responses of laboratory rats to playback of 22 kHz ultrasonic calls. Physiol. Behav. 57, 1039-1044. Brudzynski, S. M., Pniak, A., 2002. Social contacts and production of 50-kHz short ultrasonic calls in adult rats. J. Comp. Psychol. 116, 73-82. Bulduk, S., Canbeyli, R., 2004. Effect of inescapable tones on behavioral despair in Wistar rats. Prog. Neuro-Psychopharmacol. Biol. Psychiatry 28, 471-475. Bulla, G., 1999. Fancy rats: a complete pet owner's manual (E. A. Bye, Trans.). New York: Barrons Educational Series Inc. Burgdorf, J., Knutson, B., Panksepp, J., 2000. Anticipation of rewarding electrical brain stimulation evokes ultrasonic vocalization in rats. Behav. Neurosci. 114, 320-327. Burgdorf, J., Knutson, B., Panksepp, J., Shippenberg, T. S., 2001. Evaluation of rat ultrasonic vocalizations as predictors of the conditioned aversive effects of drugs. Psychopharmacology 155, 35-42. Burgdorf, J., Panksepp, J., 2001. Tickling induces reward in adolescent rats. Physiol. Behav. 72, 167-173. Burman, O. H. P., Mendl, M., 2003. The influence of preexperimental experience on social discrimination in rats (Rattus norvegicus). J. Comp. Psychol. 117, 344349.
40

1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151

Burman, O. H. P., Ilyat, A., Jones, G., Mendl, M., 2007. Ultrasonic vocalizations as indicators of welfare for laboratory rats (Rattus norvegicus). Appl. Anim. Behav. Sci. 104, 116-129. Burn, C. C., 2006. Effects of husbandry manipulations and the laboratory environment on rat health and welfare. Unpublished D.Phil. thesis, University of Oxford, Oxford, UK. Burn, C. C., Peters, A., Mason, G. J., 2006a. Acute effects of cage cleaning at different frequencies on laboratory rat behaviour and welfare. Anim. Welf. 15, 161-172. Burn, C. C., Day, M. J., Peters, A., Mason, G. J., 2006b. Long-term effects of cagecleaning frequency and bedding type on laboratory rat health, welfare, and handleability: a cross-laboratory study. Lab. Anim. 40, 353-370. Burn, C. C., Deacon, R., Mason, G. J., in press. Marked for life? Effects of early cage cleaning frequency, delivery batch and identification tail-marking on adult rat anxiety profiles. Dev. Psychobiol. Burn, C. C., Mason, G. J., in press. Effects of cage-cleaning frequencies on rat reproductive performance, infanticide, and welfare. Appl. Anim. Behav. Sci. Calhoun, J. B., 1963. The ecology and sociology of the Norway rat (Vol. 1008). Bethesda, Md., USA: U.S. Department of Health Education and Welfare Public Health Service. Calvino, B., Besson, J. M., Boehrer, A., Depaulis, A., 1996. Ultrasonic vocalization (22-28 kHz) in a model of chronic pain, the arthritic rat: Effects of analgesic drugs. Neuroreport 7, 581-584. Campbell, B. A., Messing, R. B., 1969. Aversion thresholds and aversion difference limens for white light in albino and hooded rats. J. Exp. Psychol. 82, 353-359. Cancedda, L., Putignano, E., Sale, A., Viegi, A., Berardi, N., Maffei, L., 2004. Acceleration of visual system development by environmental enrichment. J. Neurosci. 24, 4840-4848. Capaldi, E. D., 1996. Conditioned food preferences. In E. D. Capaldi (Ed.), Why we eat what we eat (pp. 53-82). Washington: American Psychological Association. Cardenas, F., Lamprea, M. R., Morato, S., 2001. Vibrissal sense is not the main sensory modality in rat exploratory behavior in the elevated plus-maze. Behav. Brain Res. 122, 169-174. Carder, B., Berkowitz, K., 1970. Rats' preference for earned in comparison with free food. Science 167, 1273-1274. Carr, W. J., Yee, L., Gable, D., Marasco, E., 1976. Olfactory recognition of conspecifics by domestic norway rats. J. Comp. Physiol. Psychol. 90, 821-828. Carvell, G. E., Simons, D. J., 1990. Biometric analyses of vibrissal tactile discrimination in the rat. J. Neurosci. 10, 2638-2648. Casadesus, G., Shukitt-Hale, B., Stellwagen, H. M., Zhu, X. W., Lee, H. G., Smith, M. A., Joseph, J. A., 2004. Modulation of hippocampal plasticity and cognitive behavior by short-term blueberry supplementation in aged rats. Nutr. Neurosci. 7, 309-316. Ceccarelli, I., Lariviere, W. R., Fiorenzani, P., Sacerdote, P., Aloisi, A. M., 2004. Effects of long-term exposure of lemon essential oil odor on behavioral, hormonal and neuronal parameters in male and female rats. Brain Res. 1001, 78-86.

41

1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201

Chase, J., 1980. Rat echolocation: correlations between object detection and click production. In R. G. Busnel, J. F. Fish (Eds.), Animal Sonar Systems (pp. 875877). New York: Plenum Press. Cicerone, C. M., 1976. Cones survive rods in the light-damaged eye of the albino rat. Science 194, 1183-1185. Clarke, S. N. D. A., Koh, M. T., Bernstein, I. L., 2001. NaCl detection thresholds: comparison of Fischer 344 and Wistar rats. Chem. Senses 26, 253-257. Clenet, F., Bouyon, E., Hascoet, M., Bourin, M., 2006. Light/dark cycle manipulation influences mice behaviour in the elevated plus maze. Behav. Brain Res. 166, 140-149. Clifton, P. G., Burton, M. J., Sharp, C., 1987. Rapid loss of stimulus-specific satiety after consumption of a second food. Appetite 9, 149-156. Collerain, I., Ludvigson, H. W., 1972. Aversion of conspecific odor of frustrative nonreward in rats. Psychon. Sci. 27, 54-56. Commission of the European Communities. 2003. Third report from the Commission to the Council and the European Parliament on the statistics on the number of animals used for experimental and other scientific purposes in the member states of the European Union (No. COM/2003/0019). Brussels: Commission of the European Communities. Coq, J. O., Xerri, C., 1998. Environmental enrichment alters organizational features of the forepaw representation in the primary somatosensory cortex of adult rats. Exp. Brain Res. 121, 191-204. Coq, J. O., Xerri, C., 2001. Sensorimotor experience modulates age-dependent alterations of the forepaw representation in the rat primary somatosensory cortex. Neuroscience 104, 705-715. Creel, D. J., Dustman, R. E., Beck, E. C., 1970. Differences in visually evoked responses in albino versus hooded rats. Exp. Neurol. 29, 246-260. Cummings, D. M., Henning, H. E., Brunjes, P. C., 1997. Olfactory bulb recovery after early sensory deprivation. J. Neurosci. 17, 7433-7440. D'Eath, R. B., 1998. Can video images imitate real stimuli in animal behaviour experiments? Biol. Revs 73, 267-292. Dagg, A. I., Bell, W. L., Windsor, D. E., 1971. Urine marking of cages and visual isolation as possible sources of error in behavioural studies of small mammals. Lab. Anim. 5, 163-167. Datesand Ltd. 2005. Environmental enrichment. In Product Catalogue (pp. 23-26). Manchester: Datesand Ltd. Davis, H., MacKenzie, K. A., Morrison, S., 1989. Numerical discrimination by rats (Rattus norvegicus) using body and vibrissal touch. J. Comp. Psychol. 103, 45-53. Davis, H., Taylor, A. A., Norris, C., 1997. Preference for familiar humans by rats. Psychon. Bull. Rev. 4, 118-120. Day, D. E., Mintz, E. M., Bartness, T. J., 2002. Diet choice exaggerates food hoarding, intake and pup survival across reproduction. Physiol. Behav. 75, 143-157. Day, H. D., Seay, B. M., Hale, P., Hendricks, D., 1982. Early social deprivation and the ontogeny of unrestricted social behavior in the laboratory rat. Dev. Psychobiol. 15, 47-59. de Almeida, R. N., Motta, S. C., de Brito Faturi, C., Catallani, B., Leite, J. R., 2004. Anxiolytic-like effects of rose oil inhalation on the elevated plus-maze test in rats. Pharmacol. Biochem. Behav. 77, 361-364.
42

1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249

Dess, N. K., 1993. Saccharin's aversive taste in rats - evidence and implications. Neurosci. Biobehav. Rev. 17, 359-372. Deutschlander, M. E., Freake, M. J., Borland, S. C., Phillips, J. B., Madden, R. C., Anderson, L. E., Wilson, B. W., 2003. Learned magnetic compass orientation by the Siberian hamster, Phodopus sungorus. Anim. Behav. 65, 779-786. DiBattista, D., 1990. Conditioned taste avoidance induced by lactose ingestion in adult rats. Physiol. Behav. 47, 253-257. Dieter, M. P., Goehl, T. J., Jameson, C. W., Elwell, M. R., Hildebrandt, P. K., Yuan, J. H., 1993. Comparison of the toxicity of citral in F344 rats and B6C3F1 mice when administrated by microencapsulation in feed or by corn-oil gavage. Food Chem. Toxicol. 31, 463-474. Dilsaver, S. C., Majchrzak, M. J., 1988. Bright artificial light produces subsensitivity to nicotine. Life Sci. 42, 225-230. Doty, R. L., 1986. Odor-guided behavior in mammals. Experientia 42, 257-271. Dulac, C., 1997. Molecular biology of pheromone perception in mammals. Semin. Cell Dev. Biol. 8, 197-205. Dymond, S., 1995. Conditional discrimination responding in non-humans. Ir. J. Psych. 16, 334-345. Dymond, S., Gomez-Martin, S., Barnes, D., 1996. Multi-modal conditional discrimination in rats: Some preliminary findings. Ir. J. Psych. 17, 269-281. Ellis, M. E., 1984. Exhaustive memory scanning in Rattus norvegicus: recognition for food items. J. Comp. Psychol. 98, 194-200. Emes, R. D., Beatson, S. A., Ponting, C. P., Goodstadt, L., 2004. Evolution and comparative genomics of odorant- and pheromone-associated genes in rodents. Genome Res. 14, 591-602. Engineer, N. D., Percaccio, C. R., Pandya, P. K., Moucha, R., Rathbun, D. L., Kilgard, M. P., 2004. Environmental enrichment improves response strength, threshold, selectivity, and latency of auditory cortex neurons. J. Neurophysiol. 92, 73-82. European Union, 2003. Directive 2003/10/EC on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (noise), The European Parliament and the Council of the European Union Fagiolini, M., Pizzorusso, T., Berardi, N., Domenici, L., Maffei, L., 1994. Functional postnatal development of the rat primary visual cortex and the role of visual experience: dark rearing and monocular deprivation. Vision Res. 34, 709-720. Farrell, W. J., Alberts, J. R., 2002. Stimulus control of maternal responsiveness to Norway rat (Rattus norvegicus) pup ultrasonic vocalizations. J. Comp. Psychol. 116, 297-307. Ferreira, A., Hansen, S., 1986. Sensory control of maternal aggression in Rattus norvegicus. J. Comp. Psychol. 100, 173-177. Festing, M. F., May, D., Connors, T. A., Lovell, D., Sparrow, S., 1978. An athymic nude mutation in the rat. Nature 274, 365-366. Fleshler, M., 1965. Adequate acoustic stimulus for startle reaction in the rat. J. Comp. Physiol. Psychol. 60, 200-207. Forsman, K. A., Malmquist, M. G., 1988. Evidence for echolocation in the common shrew. J. Zool. 216, 655-662. Fox, S., 1997. The guide to owning a rat. Neptune City: TFH Publications Inc.

43

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Galef, B. G., Jr., Heiber, L., 1976. Role of residual olfactory cues in the determination of feeding site selection and exploration patterns of domestic rats. J. Comp. Physiol. Psychol. 90, 727-739. Galef, B. G., Jr., Mason, J. R., Preti, G., Bean, N. J., 1988. Carbon disulfide: A semiochemical mediating socially-induced diet choice in rats. Physiol. Behav. 42, 119-124. Galef, B. G., Jr., McQuoid, L. M., Whiskin, E. E., 1990. Further evidence that Norway rats do not socially transmit learned aversions to toxic baits. Anim. Learn. Behav. 18, 199-205. Galef, B. G., Jr., Buckley, L. L., 1996. Use of foraging trails by Norway rats. Anim. Behav. 51, 765-771. Galef, B. G., Jr., Whiskin, E. E., 2003a. Preference for novel flavors in adult Norway rats (Rattus norvegicus). J. Comp. Psychol. 117, 96-100. Galef, B. G., Jr., Whiskin, E. E., 2003b. Socially transmitted food preferences can be used to study long-term memory in rats. Learn. Behav. 31, 160-164. Galef, B. G., Jr., Whiskin, E. E., 2005. Differences between golden hamsters (Mesocricetus auratus) and Norway rats (Rattus norvegicus) in preference for the sole diet that they are eating. J. Comp. Psychol. 119, 8-13. Gamble, M. R., Clough, G., 1976. Ammonia build-up in animal boxes and its effect on rat tracheal epithelium. Lab. Anim. 10, 93-104. Gamble, M. R., 1982. Noise and laboratory animals. J. Inst. Anim. Technicians 33, 515. Garcia-Brull, P. D., Nunez, J., Nunez, A., 1993. The effect of scents on the territorial and aggressive-behavior of laboratory rats. Behav. Process. 29, 25-36. Garcia, A. M. B., Cardenas, F. P., Morato, S., 2005. Effect of different illumination levels on rat behavior in the elevated plus-maze. Physiol. Behav. 85, 265-270. Garner, J. P., Dufour, B., Gregg, L. E., Weisker, S. M., Mench, J. A., 2004. Social and husbandry factors affecting the prevalence and severity of barbering ('whisker trimming') by laboratory mice. Appl. Anim. Behav. Sci. 89, 263-282. Gawienowski, A. M., Orsulak, P. J., Stacewicz-Sapuntzakis, M., Joseph, B. M., 1975. Presence of sex pheromone in preputial glands of male rats. J. Endocrinol. 67, 283-288. Gemberling, G. A., 1984. Ingestion of a novel flavor before exposure to pups injected with lithium chloride produces a taste aversion in mother rats (Rattus norvegicus). J. Comp. Psychol. 98, 285-301. Gheusi, G., Goodall, G., Dantzer, R., 1997. Individually distinctive odours represent individual conspecifics in rats. Anim. Behav. 53, 935-944. Gilad, Y., Man, O., Paabo, S., Lancet, D., 2003. Human specific loss of olfactory receptor genes. Proc. Natl. Acad. Sci. USA 100, 3324-3327. Giroux, M. L., Malatynska, E., Dilsaver, S. C., 1991. Bright light does not alter muscarinic receptor binding parameters. Pharmacol. Biochem. Behav. 38, 695697. Glendinning, J. I., 1994. Is the bitter rejection response always adaptive? Physiol. Behav. 56, 1217-1227. Godde, B., Berkefeld, T., David-Jurgens, M., Dinse, H. R., 2002. Age-related changes in primary somatosensory cortex of rats: evidence for parallel degenerative and plastic-adaptive processes. Neurosci. Biobehav. Rev. 26, 743-752. Graver, L., Mason, G. J., Burman, O. H. P., 2004. Do rats use ultrasound? Unpublished B.A. Honours dissertation, University of Oxford, Oxford.

44

1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347

Gray, S., Hurst, J. L., 1995. The effect of cage cleaning on aggression within groups of male laboratory mice. Anim. Behav. 49, 821-826. Grill, H. J., Norgren, R., 1978. The taste reactivity test: I. Mimetic responses to gustatory stimuli in neurologically normal rats. Brain Res. 143, 263-279. Guic-Robles, E., Valdivieso, C., Guajardo, G., 1989. Rats can learn a roughness discrimination using only their vibrissal system. Behav. Brain. Res. 31, 285289. Gutiérrez-García, A. G., Contreras, C. M., Mendoza-López, M. R., Cruz-Sánchez, S., García-Barradas, O., Rodríguez-Landa, J. F., Bernal-Morales, B., 2006. A single session of emotional stress produces anxiety in Wistar rats. Behav. Brain. Res. 167, 30-35. Hansen, S. R., Janssen, C., Beasley, V. R., 1993. Denatonium benzoate as a deterrent to ingestion of toxic substances: toxicity and efficacy. Vet. Hum. Toxicol. 35, 234-236. Hawkins, P., Grant, G., Raymond, R., Hughes, G., Morton, D., Mason, G. J., Playle, L., Hubrecht, R., Jennings, M., 2004. Reducing suffering through refinement of procedures: Report of the 2003 RSPCA/UFAW rodent welfare group meeting. Anim. Technol. Welf. 3, 79-85. Hawkins, P., Nicholson, J., Burn, C. C., Mean, J., Leach, M., Strudley, I., Van Loo, P., Bolam, S., Anderson, D., Hubrecht, R., Jennings, M., 2005. Report of the 2004 RSPCA/UFAW Rodent Welfare Group meeting. Anim. Technol. 4, 7989. Heale, V. R., Vanderwolf, C. H., Kavaliers, M., 1994. Components of weasel and fox odors elicit fast wave bursts in the dentate gyrus of rats. Behav. Brain Res. 63, 159-165. Heffner, R. S., Heffner, H. E., 1992a. Visual factors in sound localization in mammals. J. Comp. Neurol. 317, 219-232. Heffner, H. E., Heffner, R. S., 1992b. Auditory Perception. In P. Clive, D. Piggins (Eds.), Farm animals and the environment (pp. 159-184). Wallingford, UK: CAB International. Heffner, H. E., Heffner, R. S., Contos, C., Ott, T., 1994. Audiogram of the hooded Norway rat. Hear. Res. 73, 244-247. Hemsworth, P. H., 2003. Human-animal interactions in livestock production. Appl. Anim. Behav. Sci. 81, 185-198. Hermer-Vazquez, L., Hermer-Vazquez, R., Chapin, J. K., 2005. Somatosensation. In I. Q. Whishaw, B. Kolb (Eds.), The behavior of the laboratory rat: a handbook with tests (pp. 60-68). Oxford: Oxford University Press. Heuschele, W. P., 1995. Use of disinfectants in zoos and game parks. Revue Scientifique et Technique 14, 447-454. Hirsjarvi, P., Valiaho, T., 1995. Effects of gentling on open-field behaviour of Wistar rats in fear-evoking test situation. Lab. Anim. 29, 380-384. Hobson, J. A., 2005. Sleep is of the brain, by the brain and for the brain. Nature 437, 1254-1256. Holy, T. E., Dulac, C., Meister, M., 2000. Responses of vomeronasal neurons to natural stimuli. Science 289, 1569-1572. Home Office, 1989. Code of practice for the housing and care of animals used in scientific procedures, Home Office, UK Hopp, S. L., Owren, M. J., Marion, J. R., 1985. Olfactory discrimination of individual littermates in rats (Rattus norvegicus). J. Comp. Psychol. 99, 248-251.

45

1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397

Huang-Brown, K. M., Guhad, F. A., 2002. Chocolate, an effective means of oral drug delivery in rats. Lab Animal 31, 34-36. Hughes, C. W., Stein, E. A., Lynch, J. J., 1978. Hopelessness-induced sudden death in rats: Anthropomorphism for experimentally induced drownings? J. Nerv. Ment. Dis. 166, 387-401. Hugo, J., Krijt, J., Vokurka, M., Janousek, V., 1987. Secretory response to light in rat Harderian gland: possible photoprotective role of Harderian porphyrin. Gen. Physiol. Biophys. 6, 401-404. Humpel, C., Neudorfer, C., Philipp, W., Steiner, H. J., Haring, C., Schmid, K. W., Schwitzer, J., Saria, A., 1992. Effects of bright artificial-light on monoamines and neuropeptides in 8 different brain-regions compared in a pigmented and nonpigmented rat strain. J. Neurosci. Res. 32, 605-612. Hurst, J. L., Barnard, C. J., Nevison, C. M., West, C. D., 1997. Housing and welfare in laboratory rats: Welfare implications of isolation and social contact among caged males. Anim. Welf. 6, 329-347. Hurst, J. L., Thom, M. D., Nevison, C. M., Humphries, R. E., Beynon, R. J., 2005. MHC odours are not required or sufficient for recognition of individual scent owners. Proc. R. Soc. Lond. B 272, 715-724. Hyman, S., Rawson, N. E., 2001. Preliminary results of olfactory testing in rats without deprivation. Lab Animal 30, 38-39. Inglis, C. A., Campbell, E. R., Auciello, S. L., Sarawar, S. R., 2004. Effects of enrichment devices on stress-related problems in mouse breeding: Final report for The Centre for Alternatives to Animal Testing, John Hopkins University. Jacobs, G. H., Fenwick, J. A., Williams, G. A., 2001. Cone-based vision of rats for ultraviolet and visible lights. J. Exp. Biol. 204, 2439-2446. Jarvis, J. R., Prescott, N. B., Wathes, C. M., 2003. A mechanistic inter-species comparison of flicker sensitivity. Vision Res. 43, 1723-1734. Jensen, P. G., Curtis, P. D., Dunn, J. A., Austic, R. E., Richmond, M. E., 2003. Field evaluation of capsaicin as a rodent aversion agent for poultry feed. Pest Manag. Sci. 59, 1007-1015. Johnson, S. R., Patterson Kane, E. G., 2003. Foraging as environmental enrichment for laboratory rats: a theoretical review. Anim. Technol. Welf. 2, 13-22. Jourdan, D., Ardid, D., Chapuy, E., Eschalier, A., Lebars, D., 1995. Audible and ultrasonic vocalization elicited by single electrical nociceptive stimuli to the tail in the rat. Pain 63, 237-249. Kaltwasser, M. T., Schnitzler, H. U., 1981. Echolocation signals confirmed in rats. Zeit. Saugetierkunde 46, 394-395. Kaltwasser, M. T., 1990. Startle-inducing acoustic stimuli evoke ultrasonic vocalization in the rat. Physiol. Behav. 48, 13-17. Kaltwasser, M. T., 1991. Acoustic startle induced ultrasonic vocalization in the rat - a novel animal-model of anxiety. Behav. Brain Res. 43, 133-137. Keeler, C. E., 1942. The association of the black (non-agouti) gene with behavior in the Norway rat. J. Hered. 33, 371-384. Keller, C., Grimm, C., Wenzel, A., Hafezi, F., Reme, C. E., 2001. Protective effect of halothane anesthesia on retinal light damage: Inhibition of metabolic rhodopsin regeneration. Invest. Ophth. Vis. Sci. 42, 476-480. Kelly, J. B., Masterton, B., 1977. Auditory sensitivity of the albino rat. J. Comp. Physiol. Psychol. 91, 930-936. Kemble, E. D., Garbe, C. M., Gordon, C., 1995. Effects of novel odors on intermale attack behavior in mice. Aggress. Behav. 21, 293-299.
46

1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437 1438 1439 1440 1441 1442 1443 1444 1445 1446

Key, D., 2004. Environmental enrichment options for laboratory rats and mice. Lab Anim. Eur. 4, 30-38. Kikusui, T., Takigami, S., Takeuchi, Y., Mori, Y., 2001. Alarm pheromone enhances stress-induced hypothermia in rats. Physiol. Behav. 72, 45-50. Kiyokawa, Y., Kikusui, T., Takeuchi, Y., Mori, Y., 2004. Modulatory role of testosterone in alarm pheromone release by male rats. Horm. Behav. 45, 122127. Knutson, B., Burgdorf, J., Panksepp, J., 1998. Anticipation of play elicits highfrequency ultrasonic vocalizations in young rats. J. Comp. Psychol. 112, 6573. Knutson, B., Burgdorf, J., Panksepp, J., 1999. High-frequency ultrasonic vocalizations index conditioned pharmacological reward in rats. Physiol. Behav. 66, 639643. Knutson, B., Burgdorf, J., Panksepp, J., 2002. Ultrasonic vocalizations as indices of affective states in rats. Psychol. Bull. 128, 961-977. Komori, T., Miyahara, S., Yamamoto, M., Matsumoto, T., Zhang, K., Nakagawa, M., Nomura, S., Motomura, E., Shiroyama, T., Okazaki, Y., 2003. Effects of odorants on the hypothalamic-pituitary-adrenal axis and interleukin-6 (IL-6) and IL-6 receptor mRNA expression in rat hypothalamus after restraint stress. Chem. Senses 28, 767-771. Krames, L., Carr, W. J., Bergman, B., 1969. A pheromone associated with social dominance among male rats. Psychon. Sci. 16, 11-12. Krinke, G., 2000. The laboratory rat. London: Academic Press. La Vail, M. M., 1976. Survival of some photoreceptor cells in albino rats following long-term exposure to continuous light. Inv. Opthal. 15, 64-70. Lacey, J. C., Beynon, R. J., Hurst, J. L., 2007. The importance of exposure to other male scents in determining competitive behaviour among inbred male mice. Appl. Anim. Behav. Sci. 104, 130-142. Lane-Petter, W., 1975. Presentation of compound diets. Anim. Technol. 26, 83-85. Larue-Achagiotis, C., Martin, C., Verger, P., Louis-Sylvestre, J., 1992. Dietary selfselection vs. complete diet: body weight gain and meal pattern in rats. Physiol. Behav. 51, 995-999. Lashley, K. S., 1938. The mechanisms of vision III: The comparative visual acuity of pigmented and albino rats. J. Genet. Psych. 37, 481-484. Latham, N., Mason, G., 2004. From house mouse to mouse house: the behavioural biology of free-living Mus musculus and its implications in the laboratory. Appl. Anim. Behav. Sci. 86, 261-289. Lavin, M. J., Freise, B., Coombes, S., 1980. Transferred flavor aversions in adult rats. Behav. Neur. Biol. 28, 15-33. Le Magnen, J., 1999a. Efficacy of olfactory, tactile, and other food stimuli in the acquisition and manifestation of appetite in rats. Appetite 33, 43-51. Le Magnen, J., 1999b. Increased food intake induced in rats by changes in the satiating sensory input from food. Appetite 33, 33-35. Legg, C. R., Lambert, S., 1990. Distance estimation in the hooded rat: Experimental evidence for the role of motion cues. Behav. Brain Res. 41, 11-20. Lemmon, V., Anderson, K. V., 1979. Behavioral correlates of constant light-induced retinal degeneration. Exp. Neurol. 63, 35-49. Levine, S., Saltzman, A., 1998. An alternative to overnight withholding of food from rats. Contemp. Top. Lab. Anim. Sci. 37.

47

1447 1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466 1467 1468 1469 1470 1471 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494

Li, Z. Y., Tso, M. O., Wang, H. M., Organisciak, D. T., 1985. Amelioration of photic injury in rat retina by ascorbic acid: a histopathologic study. Invest. Ophth. Vis. Sci. 26, 1589-1598. Light Therapy ProductsTM. (2006). MI, USA. Retrieved 5th February 2006, from http://www.lighttherapyproducts.com/ Lindner, M. D., Plone, M. A., Schaller, T., Emerich, D. F., 1997. Blind rats are not profoundly impaired in the reference memory Morris water maze and cannot be clearly discriminated from rats with cognitive deficits in the cued platform task. Cogn. Brain Res. 5, 329-333. Ludvigson, H. W., Mathis, D. A., Choquette, K. A., 1985. Different odors in rats from large and small rewards. Anim. Learn. Behav. 13, 315-320. Mackay-Sim, A., Laing, D. G., 1980. Discrimination of odors from stressed rats by non-stressed rats. Physiol. Behav. 24, 699-704. Mackay-Sim, A., Laing, D. G., 1981. The sources of odors from stressed rats. Physiol. Behav. 27, 511-513. Maddocks, S. A., Cuthill, I. C., Goldsmith, A. R., Sherwin, C. M., 2001. Behavioural and physiological effects of absence of ultraviolet wavelengths for domestic chicks. Anim. Behav. 62, 1013-1019. Manzo, J., Garcia, L. I., Hernandez, M. E., Carrillo, P., Pacheco, P., 2002. Neuroendocrine control of urine-marking behavior in male rats. Physiol. Behav. 75, 25-32. Mason, G., Wilson, D., Hampton, C., Wurbel, H., 2004. Non-invasively assessing disturbance and stress in laboratory rats by scoring chromodacryorrhoea. Alt. Lab. Anim. 32, 153-159. Mason, R. K., 1969. The influence of noise on emotional states. J. Psychosom. Res. 13, 275-282. Mattson, M. P., 2005. Energy intake, meal frequency, and health: a neurobiological perspective. Annu. Rev. Nutr. 25, 237-260. McCall, R. B., Lester, M. L., Corter, C. M., 1969. Caretaker effect in rats. Dev. Psychol. 1, 771. McLennan, I. S., Taylor-Jeffs, J., 2004. The use of sodium lamps to brightly illuminate mouse houses during their dark phases. Lab. Anim. 38, 384-392. Melnick, R. L., Jameson, C. W., Goehl, T. J., Maronpot, R. R., Collins, B. J., Greenwell, A., Harrington, F. W., Wilson, R. E., Tomaszewski, K. E., Agarwal, D. K., 1987. Application of microencapsulation for toxicology studies. II. Toxicity of microencapsulated trichloroethylene in Fischer 344 rats. Fundam. Appl. Toxicol. 8, 432-442. Mennella, J. A., Moltz, H., 1988. Infanticide in rats: male strategy and female counter-strategy. Physiol. Behav. 42, 19-28. Meyer, M. E., Meyer, M. E., 1992. The effects of bilateral and unilateral vibrissotomy on behavior within aquatic and terrestrial environments. Physiol. Behav. 51, 877-880. Milligan, S. R., Sales, G. D., Khirnykh, K., 1993. Sound levels in rooms housing laboratory-animals - an uncontrolled daily variable. Physiol. Behav. 53, 10671076. Mitchell, C. J., Heyes, C. M., Gardner, M. R., Dawson, G. R., 1999. Limitations of a bidirectional control procedure for the investigation of imitation in rats: Odour cues on the manipulandum. Q. J. Exp. Psychol. B 52, 193-202.

48

1495 1496 1497 1498 1499 1500 1501 1502 1503 1504 1505 1506 1507 1508 1509 1510 1511 1512 1513 1514 1515 1516 1517 1518 1519 1520 1521 1522 1523 1524 1525 1526 1527 1528 1529 1530 1531 1532 1533 1534 1535 1536 1537 1538 1539 1540 1541 1542 1543 1544

Moemeka, A. N., Hildebrandt, A. L., Radaskiewicz, P., King, T. R., 1998. Shorn (shn): a new mutation causing hypotrichosis in the Norway rat. J. Hered. 89, 257-260. Moinard, C., Sherwin, C. M., 1999. Turkeys prefer fluorescent light with supplementary ultraviolet radiation. Appl. Anim. Behav. Sci. 64, 261-267. Moore, B. C. J., 2003. An introduction to the psychology of hearing (5th ed.). London: Academic Press. Moore, C. L., 1985. Sex differences in urinary odors produced by young laboratory rats (Rattus norvegicus). J. Comp. Psychol. 99, 336-341. Morlock, G. W., McCormick, C. E., Meyer, M. E., 1971. The effect of a stranger's presence on the exploratory behavior of rats. Psychon. Sci. 22, 3-4. Mueller, K. L., Hoon, M. A., Erlenbach, I., Chandrashekar, J., Zuker, C. S., Ryba, N. J. P., 2005. The receptors and coding logic for bitter taste. Nature 434, 225229. Muenzinger, K. F., Reynolds, H. E., 1936. Color vision in white rats: I. Sensitivity to red. J. Genet. Psych. 48, 58-71. Muheim, R., Edgar, N. M., Sloan, K. A., Phillips, J. B., 2006. Magnetic compass orientation in C57BL/6J mice. Learn. Behav. 34, 366-373. Munn, N. L., Collins, M., 1936. Discrimination of red by white rats. J. Genet. Psych. 48, 72-87. Nagel, T., 1974. What is it like to be a bat? Philos. Rev. 83, 435-450. Naim, M., Brand, J. G., Kare, M. R., Carpenter, R. G., 1985. Energy intake, weight gain, and fat deposition in rats fed flavored, nutritionally controlled diets in a multichoice ("cafeteria") design. J. Nutr. 115, 1447-1458. Nakashima, T., Akamatsu, M., Hatanaka, A., Kiyohara, T., 2004. Attenuation of stress-induced elevations in plasma ACTH level and body temperature in rats by green odor. Physiol. Behav. 80, 481-488. Neimark, M. A., Andermann, M. L., Hopfield, J. J., Moore, C. I., 2003. Vibrissa resonance as a transduction mechanism for tactile encoding. J. Neurosci. 23, 6499-6509. Nevison, C. M., Barnard, C. J., Hurst, J. L., 2003. The consequence of inbreeding for modulating social relationships between competitors. Appl. Anim. Behav. Sci. 81, 387-398. Noirot, E., 1968. Ultrasounds in young rodents. II. Changes with age in albino rats. Anim. Behav. 16, 129-134. O'Sullivan, D. J., Spear, N. E., 1964. Comparison of hooded and albino rats on the visual cliff. Psychon. Sci. 1, 87-88. Olsson, I. A. S., Nevison, C. M., Patterson-Kane, E. G., Sherwin, C. M., Van de Weerd, H. A., Wurbel, H., 2003. Understanding behaviour: the relevance of ethological approaches in laboratory animal science. Appl. Anim. Behav. Sci. 81, 245-264. Osteen, W. K., Spencer, R. L., Bare, D. J., Mcewen, B. S., 1995. Analysis of severe photoreceptor loss and Morris water-maze performance in aged rats. Behav. Brain Res. 68, 151-158. Otten, W., Kanitz, A. E., Puppe, B., Tuchscherer, M., Brüssow, K. P., Nürnberg, G., Stabenow, B., 2004. Acute and long term effects of chronic intermittent noise stress on hypothalamic-pituitary-adrenocortical and sympathoadrenomedullary axis in pigs. Anim. Sci. 78, 271. Otto, J., Brown, M. F., Long, W., 2002. Training rats to search and alert on contraband odors. Appl. Anim. Behav. Sci. 77, 217-232.
49

1545 1546 1547 1548 1549 1550 1551 1552 1553 1554 1555 1556 1557 1558 1559 1560 1561 1562 1563 1564 1565 1566 1567 1568 1569 1570 1571 1572 1573 1574 1575 1576 1577 1578 1579 1580 1581 1582 1583 1584 1585 1586 1587 1588 1589 1590 1591 1592 1593

Outside In Ltd. (2006). Cambridge, UK. Retrieved 5th February 2006, from http://www.outsidein.co.uk/ Overstreet, D. H., Pucilowski, O., Rezvani, A. H., Janowsky, D. S., 1995. Administration of antidepressants, diazepam and psychomotor stimulants further confirms the utility of Flinders sensitive line rats as an animal-model of depression. Psychopharmacology 121, 27-37. Panksepp, J., Burgdorf, J., 2000. 50-kHz chirping (laughter?) in response to conditioned and unconditioned tickle-induced reward in rats: Effects of social housing and genetic variables. Behav. Brain Res. 115, 25-38. Panksepp, J., 2006. Affective neuroscience and the ancestral sources of socioemotional feelings within animal minds. Paper presented at the 40th International Congress of the ISAE, Bristol. Pappas, B. A., Vickers, G., Buxton, M., Pusztay, W., 1982. Infant rat hyperactivity elicited by home cage bedding is unaffected by neonatal telencephalic dopamine or norepinephrine depletion. Pharmacol. Biochem. Behav. 16, 151154. Perez, J., Perentes, E., 1994. Light-induced retinopathy in the albino rat in long-term studies. An immunohistochemical and quantitative approach. Exp. Toxicol. Pathol. 46, 229-235. Petounis, A., Spyrakis, C., Varonos, D., 1977. Effects of infrasound on activity levels of rats. Physiol. Behav. 18, 153-155. Picciotto, M. R., Self;, D. W., Pohorecky;, L. A., Dawson, G. R., Flint, J., Wilkinson;, L. S., Hen;, R., Tordoff, M. G., Bachmanov, A. A., Friedman, M. I., Beauchamp;, G. K., Wahlsten, D., Crabbe, J., Dudek, B., 1999. Testing the genetics of behavior in mice. Science 285, 2067. Polley, D. B., Kvasnak, E., Frostig, R. D., 2004. Naturalistic experience transforms sensory maps in the adult cortex of caged animals. Nature 429, 67-71. Pons, F., 2006. The effects of distributional learning on rats' sensitivity to phonetic information. J. Exp. Psychol. Anim. Behav. Process. 32, 97-101. Porter, R. H., Winberg, J., 1999. Unique salience of maternal breast odors for newborn infants. Neurosci. Biobehav. Rev. 23, 439-449. Prats, E., Monfar, M., Castella, J., Iglesias, R., Alemany, M., 1989. Energy intake of rats fed a cafeteria diet. Physiol. Behav. 45, 263-272. Prior, H., 2006. Effects of the acoustic environment on learning in rats. Physiol. Behav. 87, 162-165. Prusky, G. T., Reidel, C., Douglas, R. M., 2000. Environmental enrichment from birth enhances visual acuity but not place learning in mice. Behav. Brain Res. 114, 11-15. Prusky, G. T., Harker, K. T., Douglas, R. M., Whishaw, I. Q., 2002. Variation in visual acuity within pigmented, and between pigmented and albino rat strains. Behav. Brain Res. 136, 339-348. Prusky, G. T., Douglas, R. M., 2005. Vision. In I. Q. Whishaw, B. Kolb (Eds.), The behavior of the laboratory rat: a handbook with tests (pp. 49-59). Oxford: Oxford University Press. Quignon, P., Giraud, M., Rimbault, M., Lavigne, P., Tacher, S., Morin, E., Retout, E., Valin, A. S., Lindblad Toh, K., Nicolas, J., Galibert, F., 2005. The dog and rat olfactory receptor repertoires. Genome Biol. 6, R83. Rajan, R., Clement, J. P., Bhalla, U. S., 2006. Rats smell in stereo. Science 311, 666670.

50

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Rao, G. N., 1991. Light intensity-associated eye lesions of Fischer-344 rats in longterm studies. Toxicol. Pathol. 19, 148-155. Rat Genome Sequencing Project Consortium. 2004. Genome sequence of the Brown Norway rat yields insights into mammalian evolution. Nature 428, 493-521. Rema, V., Armstrong-James, M., Ebner, F. F., 2003. Experience-dependent plasticity is impaired in adult rat barrel cortex after whiskers are unused in early postnatal life. J. Neurosci. 23, 358-366. Riley, D. A., Rosenzweig, M., 1957. Echolocation in rats. J. Comp. Physiol. Psychol. 50, 323-328. Robbins, K. (2004). Critter critiques - Bio-Serv’s Mouse Igloo and Crawl Ball. AFRMA Rat & Mouse Tales Magazine, 2004, http://www.afrma.org/cc_bioserv.htm. Robinson, L., Bridge, H., Riedel, G., 2001. Visual discrimination learning in the water maze: a novel test for visual acuity. Behav. Brain. Res. 119, 77-84. Rosenzweig, M. R., Riley, D. A., Krech, D., 1955. Evidence for echolocation in the rat. Science 121, 600. Routtenberg, A., Glickman, S. E., 1964. Visual cliff behavior in albino and hooded rats. J. Comp. Physiol. Psychol. 58, 140-142. Sales, G. D., 1972. Ultrasound and aggressive behaviour in rats and other small mammals. Anim. Behav. 20, 88-100. Sales, G. D., Wilson, K. J., Spencer, K. E. V., Milligan, S. R., 1988. Environmental ultrasound in laboratories and animal houses - a possible cause for concern in the welfare and use of laboratory animals. Lab. Anim. 22, 369-375. Sales, G. D., 1991. The effect of 22 kHz calls and artificial 38 kHz signals on activity in rats. Behav. Process. 24, 83-93. Sales, G. D., Milligan, S. R., Khirnykh, K., 1999. Sources of sound in the laboratory animal environment: A survey of the sounds produced by procedures and equipment. Anim. Welf. 8, 97-115. Saper, C. B., Scammell, T. E., Lu, J., 2005. Hypothalamic regulation of sleep and circadian rhythms. Nature 437, 1257-1263. Schellinck, H. M., Brown, R. E., Slotnick, B. M., 1991. Training rats to discriminate between the odors of individual conspecifics. Anim. Learn. Behav. 19, 223233. Schellinck, H. M., Brown, R. E., 2000. Selective depletion of bacteria alters but does not eliminate odors of individuality in Rattus norvegicus. Physiol. Behav. 70, 261-270. Schlingmann, F., De Rijk, S. H. L. M., Pereboom, W. J., Remie, R., 1993a. Light intensity in animal rooms and cages in relation to the care and management of albino rats. Anim. Technol. 44, 97-107. Schlingmann, F., Pereboom, W. J., Remie, R., 1993b. The sensitivity of albino and pigmented rats to light: a mini review. Anim. Technol. 44, 71-85. Schlingmann, F., De Rijk, S. H. L. M., Pereboom, W. J., Remie, R., 1993c. 'Avoidance' as a behavioural parameter in the determination of distress amongst albino and pigmented rats at various light intensities. Anim. Technol. 44, 87-96. Schnecko, A., Witte, K., Lemmer, B., 1998. Effects of routine procedures on cardiovascular parameters of Sprague-Dawley rats in periods of activity and rest. J. Exp. Anim. Sci. 38, 181-190. Sclafani, A., Abrams, M., 1986. Rats show only a weak preference for the artificial sweetener aspartame. Physiol. Behav. 37, 253-256.
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Sclafani, A., 1987. Carbohydrate taste, appetite, and obesity: An overview. Neurosci. Biobehav. Rev. 11, 131-153. Sclafani, A., Clare, R. A., 2004. Female rats show a bimodal preference response to the artificial sweetener sucralose. Chem. Senses 29, 523-528. Semple-Rowland, S. L., Dawson, W. W., 1987. Retinal cyclic light damage threshold for albino rats. Lab. Anim. Sci. 37, 289-298. Sharp, J. L., Zammit, T. G., Azar, T. A., Lawson, D. M., 2002. Stress-like responses to common procedures in male rats housed alone or with other rats. Contemp. Top. Lab. Anim. Sci. 41, 8-14. Shepherd, G. M., 2006. Behaviour: Smells, brains and hormones. Nature 439, 149151. Sherwin, C. M., 2002. Comfortable quarters for mice in research institutions. In V. Reinhardt, A. Reinhardt (Eds.), Comfortable Quarters for Laboratory Animals (9 ed., pp. 6-17). Washington: Animal Welfare Institute. Sherwin, C. M., Glen, E. F., 2003. Cage colour preferences and effects of home cage colour on anxiety in laboratory mice. Anim. Behav. 66, 1085-1092. Slawecki, C. J., Roth, J., 2005. Assessment of sustained attention in ad libitum fed Wistar rats: Effects of MK-801. Physiol. Behav. 85, 346-353. Smith, D. V., Margolskee, R. F., 2001. Making sense of taste. Sci. Am. 284, 32. Stevens, D. A., Koster, E. P., 1972. Open-field responses of rats to odors from stressed and nonstressed predecessors. Behav. Biol. 7, 519-525. Stierhoff, K. A., Lavin, M. J., 1982. The influence of rendering rats anosmic on the poisoned-partner effect. Behav. Neur. Biol. 34, 180-189. Strupp, B. J., Levitsky, D. A., 1984. Social transmission of food preferences in adult hooded rats (Rattus norvegicus). J. Comp. Psychol. 98, 257-266. Sundberg, J. P., Boggess, D., Bascom, C., Limberg, B. J., Shultz, L. D., Sundberg, B. A., King, L. E., Jr., Montagutelli, X., 2000. Lanceolate hair-J (lahJ): a mouse model for human hair disorders. Exp. Dermatol. 9, 206-218. Symons, L. A., Tees, R. C., 1990. An examination of the intramodal and intermodal behavioral consequences of long-term vibrissae removal in rats. Dev. Psychobiol. 23, 849-867. Szel, A., Rohlich, P., 1992. Two cone types of rat retina detected by anti-visual pigment antibodies. Exp. Eye Res. 55, 47-52. Takahashi, L. K., Kalin, N. H., Baker, E. W., 1990. Corticotropin-releasing factor antagonist attenuates defensive-withdrawal behavior elicited by odors of stressed conspecifics. Behav. Neurosci. 104, 386-389. Tanapat, P., Hastings, N. B., Rydel, T. A., Galea, L. A. M., Gould, E., 2001. Exposure to fox odor inhibits cell proliferation in the hippocampus of adult rats via an adrenal hormone-dependent mechanism. J. Comp. Neurol. 437, 496-504. Taylor, R. D., Ludvigson, H. W., 1980. Selective removal of reward and nonreward odors to assess their control of patterned responding in rats. Bull. Psychon. Soc. 16, 101-104. Taylor, R. D., Ludvigson, H. W., 1987. Airborne differences in odors emitted by Rattus norvegicus in response to reward and nonreward. J. Chem. Ecol. 13, 1147-1161. Thodberg, K., Malmkvist, J., Herskin, M. S., 2006. The acute effect of a synthetic pig appeasing hormone on open field and intruder test behaviour. Paper presented at the 40th International Congress of the ISAE, Bristol. Tong, T. Y. Y., Goh, V. H. H., 2000. Effect of selected wavelengths of light on the fertility status of rats. Anim. Technol. 51, 1-7.
52

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Toro, J. M., Trobalon, J. B., Sebastián-Gallés, N., 2003. The use of prosodic cues in language discrimination tasks by rats. Anim. Cogn. 6, 131-136. Treit, D., Spetch, M. L., Deutsch, J. A., 1983. Variety in the flavor of food enhances eating in the rat: A controlled demonstration. Physiol. Behav. 30, 207-211. Treit, D., Fundytus, M., 1988. Thigmotaxis as a test for anxiolytic activity in rats. Pharmacol. Biochem. Behav. 31, 959-962. Van Der Lee, S., Boot, L. M., 1956. Spontaneous pseudopregnancy in mice. II. Acta Physiol. Pharmacol. Neerl. 5, 213-215. Van der Poel, A. M., Miczek, K. A., 1991. Long ultrasonic calls in male-rats following mating, defeat and aversive-stimulation - Frequency-modulation and bout structure. Behaviour 119, 127-142. van Driel, K., Talling, J., Pickersgill, M., Hendrie, C., Lane, J., Owen, D., 2004. Effect of experience of the handler on stress in rats. Paper presented at the 9th FELASA Symposium: Internationalization and harmonization in laboratory animal care and use issues, Nantes, France. van Driel, K. S., Talling, J. C., 2005. Familiarity increases consistency in animal tests. Behav. Brain Res. 159, 243-245. Van Loo, P. L. P., Kruitwagen, C. L. J. J., Van Zutphen, L. F. M., Koolhaas, J. M., Baumans, V., 2000. Modulation of aggression in male mice: Influence of cage cleaning regime and scent marks. Anim. Welf. 9, 281-295. Vandenbergh, J. G., 1969. Male odor accelerates female sexual maturation in mice. Endocrinology 84, 658-660. Vandenbergh, J. G., 1976. Acceleration of sexual maturation in female rats by male stimulation. J. Reprod. Fertil. 46, 451-453. Vivian, J. A., Miczek, K. A., 1991. Ultrasounds during morphine-withdrawal in rats. Psychopharmacology 104, 187-193. Voipio, H.-M., 1997. How do rats react to sounds? Scand. J. Lab. Anim. Sci. 24, 1-80. Voipio, H.-M., Björk, E., Hakumäki, M., Nevalainen, T., 1998. Sound: from noise to communication. Paper presented at the Scand-LAS Symposium, Hafjell. Wallace, J., Steinert, P. A., Scobie, S. R., Spear, N. E., 1980. Stimulus modality and short-term memory in rats. Anim. Learn. Behav. 8, 10-16. Walton, W. E., 1933. Color vision and color preference in the albino rat. II. The experiments and results. J. Comp. Psychol. 15, 373-394. Walton, W. E., Bornemeier, R. W., 1938. Further evidence of color discrimination in rodents. J. Genet. Psych. 52, 165-181. Ware, N., Mason, G. J., 2003. Does euthanasia by CO2 elicit the production of fear odours in laboratory rats? Using conspecific reaction as a tool for data collection. Unpublished B.A. Honours dissertation, University of Oxford, Oxford. Weaver, M. S., Whiteside, D. A., Janzen, W. C., Moore, S. A., Davis, S. F., 1982. A preliminary investigation into the source of odor-cue production. Bull. Psychon. Soc. 19, 284-286. Westenbroek, C., Snijders, T. A. B., den Boer, J. A., Gerrits, M., Fokkema, D. S., Ter Horst, G. J., 2005. Pair-housing of male and female rats during chronic stress exposure results in gender-specific behavioral responses. Horm. Behav. 47, 620-628. Whishaw, I. Q., Kolb, B., 2005. The behavior of the laboratory rat: a handbook with tests. Oxford: Oxford University Press. Whitten, W. K., 1959. Occurrence of anoestrus in mice caged in groups. J. Endocrinol. 18, 102-107.
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Williams, J. L., Groux, M. L., 1993. Exposure to various stressors alters preferences for natural odors in rats (Rattus Norvegicus). J. Comp. Psychol. 107, 39-47. Williams, J. L., 1999. Effects of conspecific and predator odors on defensive behavior, analgesia, and spatial working memory. Psychol. Rec. 49, 493-536. Williams, R. A., Howard, A. G., Williams, T. P., 1985. Retinal damage in pigmented and albino rats exposed to low levels of cyclic light following a single mydriatic treatment. Curr. Eye Res. 4, 97-102. Wills, G. D., 1983. Discrimination by olfactory cues in albino rats reflecting familiarity and relatedness among conspecifics. Behav. Neur. Biol. 38, 139143. Wilson, A., Hubrecht, R., Bradley, W. A., Buist, D., Smith, D., Francis, R., James, R., 1995. Housing husbandry and welfare provision for animals used in toxicology studies: results of a UK questionnaire on current practice (1994). Report of the Toxicology and Welfare Working Group, Universities Federation for Animal Welfare. Wolf, N. S., Li, Y., Pendergrass, W., Schmeider, C., Turturro, A., 2000. Normal mouse and rat strains as models for age-related cataract and the effect of caloric restriction on its development. Exp. Eye Res. 70, 683-692. Woodhouse, R., Greenfeld, N., 1985. Responses of albino and hooded rats to various illumination choices in a six-chambered alleyway. Percept. Mot. Skills 61, 343-354. Xerri, C., Coq, J. O., Merzenich, M. M., Jenkins, W. M., 1996. Experience-induced plasticity of cutaneous maps in the primary somatosensory cortex of adult monkeys and rats. J. Physiol. 90, 277-287. Yuan, J., Dieter, M. P., Bucher, J. R., Jameson, C. W., 1993. Application of microencapsulation for toxicology studies. III. Bioavailability of microencapsulated cinnamaldehyde. Fundam. Appl. Toxicol. 20, 83-87. Zala, S. M., Potts, W. K., Penn, D. J., 2004. Scent-marking displays provide honest signals of health and infection. Behav. Ecol. 15, 338-344.

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Figure 1
Visual perception of rat strains in visual-based behavioral tasks, reprinted from Prusky and colleagues (2002) (with permission from Elsevier and the authors). The original image (top-left) has been blurred to model the perception of rats with acuities of 1.5 c/d (top-right; Fisher–Norway), 1.0 c/d (bottom-left; Dark Agouti, Long-Evans, wild) and 0.5 c/d (bottom-right; Fisher-344, Sprague–Dawley, Wistar) when the image subtends 10 degrees. This approximates the size of the image if it were used as a visual cue in a typical visuo-behavioural task (see Prusky et al., 2002 for details).

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