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The influence of bedding depth on behaviour in golden hamsters (Mesocricetus auratus) /
Abstract
Diss. med. vet. Bern. Literaturverz. Universität, Bern
Hamsters are very willingly kept in homes as companion animals. However, despite this, very hard to find reliable information on the requirements associated with the maintenance of these rodents. However, this does not change the fact that accommodation for a hamster must meet its normal physiological and behavioral needs, including resting, nesting, grooming, exploration, climbing, hiding, digging, searching, storing and chewing food. In order to check whether the level of public knowledge about keeping hamsters and their needs is adequate to the popularity of these rodents and whether it is sufficient to provide them with appropriate conditions in an average amateur breeding farm, a questionnaire survey was used in which as many as 80.3% of the respondents admitted to having or owning a hamster, and when asked about the appropriate size of the cage, they preferred larger sizes such as 80 x 40 cm (34.7%) or 90 x 45 cm (25.1%). However, noting that housing in small cages causes chronic stress in hamsters, the rule of thumb should be: the bigger the better. As many as 619 (80.1%) respondents state that a good amount of litter significantly improves hamster welfare. It has been proven that at least 40 cm of bedding really increases the level of hamster welfare. In addition, the absolute majority of respondents stated that the satisfaction of behavioral needs affects (22.6%) or is even dependent on hamster welfare (69.7%).The results obtained from the survey data highlight the need for new studies that would provide the opportunity to update the knowledge already available and correct unclear guidelines related to hamster housing. This would allow us to optimize the conditions of keeping hamsters in amateur breeding conditions and ensure their good or even high welfare.
Although rodents have been in captivity for centuries, they still express many of their natural behaviors. As their popularity in the pet trade increases, it becomes important to address their welfare, including the avoidance of abnormal and detrimental behaviors. Inappropriate husbandry practices may lead to psychological and physical disorders. The extensive amount of information available, as well as the large number of rodent species maintained as pets, makes it difficult to apply a broad set of behavior rules for rodents. Nonetheless, there are basic behavior models that should be considered for all rodent species. This article presents basic concepts of behavior of rodents with enclosure and nutritional enrichment techniques that can be used to support a fulfilling and interactive life. Copyright 2011 Elsevier Inc. All rights reserved.
In order to determine a stress response, two groups of twenty male golden hamsters were either exposed to a ferret or handled by a human. The hamsters’ body temperature and running wheel activity were measured as stress correlates. Half of the hamsters’ cages were equipped with a functional running wheel to determine whether the presence of a running wheel might reduce stress. Exposure to the ferret was followed by a significant increase in body temperature and running wheel revolutions; however, running wheel activity did not change after handling. Body temperature increased less after handling in hamsters living in a cage with a functional running wheel than in those with a non-revolving running wheel. This suggests that hamsters with a functional running wheel reacted less strongly to acute stress caused by handling. On the other hand, temperature increase after the exposure to a ferret was not affected by the presence of a running wheel. Both exposure to a ferret and handling caused stress in golden hamsters, as demonstrated by an increase in body temperature (emotional fever). Stress caused by handling was much milder than stress caused by the ferret.
Consideration of the human-animal bond typically focuses on the benefits of companion animals to human health and well-being, but it is essential that in realizing these benefits the welfare needs of the animals, both physical and mental, are also met. Positive emotional relationships with animals are likely to increase recognition of animal sentience and so help create positive attitudes toward animals at the societal level, but, at the individual level, the animals to which humans are bonded should also benefit from the human-animal relationship. A strong human-animal bond may benefit animal welfare (e.g., by motivating an owner to commit time and funds to necessary veterinary medical treatment), but may also be the source of compromised welfare. Highly bonded owners may, for example, be reluctant to permit euthanasia on humane grounds, and the anthropomorphic nature of many human-companion animal bonds can contribute to the development of problem behaviors and obesity. The challenge for the veterinary profession is to ensure that widespread positive sentiment toward animals, which the human-animal bond generates, is translated in to human behavior and actions that are conducive to good animal welfare. This, it is suggested, can be achieved through adequate veterinary education in veterinary and animal welfare science, ethics, and communication.
The present study investigated the effects of bedding material (pine shavings versus beta chip) and running wheel surfaces (standard metal bars versus metal bars covered with a plastic mesh) on the occurrence of wounds on the paws of male and female Syrian (golden) hamsters, Mesocricetus auratus. Four groups of 10 males and 10 females were each assigned to one of the following treatments: pine/no mesh, pine/mesh, chips/no mesh and chips/mesh. Each hamster paw was observed at 1-3-day intervals for 60 days. A total of 1-3 wounds, separate in time, developed on the paws (mostly the hind ones) of almost all animals. Wounds appeared as small pinpricks, cuts or scabs, mostly on the palms. Females ran 15% less than males, yet their front paws were more commonly affected and their wounds tended to last longer. Hamsters with plastic mesh inside their wheels took longer to develop wounds but once they appeared, the wounds were larger and lasted longer. Hamsters on pine shavings developed fewer wounds and had more wound-free days. Hamsters kept running at high levels and many wounds did not heal during the study, suggesting a need for veterinary intervention.
Compared running wheels and spring-suspended cages as measurement devices for evaluating circadian locomotor activity rhythm. 12 golden hamsters were tested individually in a spring-suspended cage; 6 also had access to running wheels. Ss were exposed to 5 different levels of constant illumination, each condition lasting for several wks, and to a light-dark cycle. The onset of activity in the spring-suspended cage preceded the onset of activity in the running wheel by an amount which is a function of the circadian period. The increment by which the period changes in response to changes in light intensity equals, approximately, the changes of the interval between the 2 onsets. Animals with access to a running wheel show a tendency towards longer circadian periods. (16 ref.)
Investigated the effects of cage size and cage surface texture as factors in environmental enrichment. 79 C57BL/6J mice were reared in 1 of 4 types of cages: small wire, small Plexiglas, large wire, or large Plexiglas. Dependent measures included gross body weight at 38 and 50 days of age, open-field activity and defecation, running-wheel activity, exploration, and water consumption. Cage size significantly affected 38-day gross body weight, open-field activity and defecation, and water consumption. These findings indicate that cage size is an important factor in the enriched environment experience, and they are in accordance with data reported previously by the authors. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Two expeditions were carried out during September 1997 and March 1999 to confirm the current existence of Mesocricetus auratus in northern Syria. Six females and seven males were caught at different sites near Aleppo. One female was pregnant and gave birth to six pups. Altogether, 30 burrows were mapped and the structures of 23 golden hamster burrows investigated. None of the inhabited burrows contained more than one adult. Burrow depths ranged from 36 to 106 cm (mean 65 cm). Their structure was simple, consisting of a single vertical entrance (gravity pipe) that proceeded to a nesting chamber and at least one additional food chamber. The mean length of the entire gallery system measured 200 cm and could extend up to 900 cm. Most burrows were found on agricultural fields preferentially on leguminous cultures. The distribution of golden hamsters is discussed in association with historical data, soil types, geography, climate and human activities. All 19 golden hamsters were transferred to Germany and, together with three wild individuals supplied by the University of Aleppo, form a new breeding stock.
The study investigated whether nonphotic cues that alter the phase of overt circadian rhythms do so by causing instantaneous shifts in the underlying, light-sensitive clock. Wheel-running activity in Syrian hamsters was studied under free-running conditions of constant dim red light as an overt marker of circadian phase, the daily onset of activity being defined as circadian time 12 (CT 12). Exposure to a 15 min pulse of bright light at CT 12.20 caused a phase delay in activity onset, whereas pulses delivered at CT 11.20 had no effect upon the overt rhythm. Correlated with their effect on behavior, light pulses delivered at CT 12.20 induced expression of c-fos-like immunoreactivity in the retinorecipient regions of the suprachiasmatic nuclei of the hypothalamus (SCN), whereas pulses delivered at CT 11.20 had no effect upon the expression of c-fos. Expression of this immediate-early gene therefore provided a second marker of circadian phase, because its induction by light is closely correlated with the onset of subjective night (CT 12). To establish a suitable protocol for nonphotic shifts of the activity rhythm, animals were handled and received a subcutaneous injection of saline at different circadian phases. Injections at CT 8 or CT10 caused an immediate bout of wheel-running activity, and a consequent phase advance in the activity rhythm as assessed by the earlier onsets of activity in successive days. Handling and injections at other circadian phases were without effect. Despite shifting the overt rhythm, these procedures at CT 10 did not lead to the expression of c-fos in the SCN.(ABSTRACT TRUNCATED AT 250 WORDS)
This paper reviews the discovery and characterization of a behavioural system for entrainment of circadian rhythms. This behavioural system depends on non-photic inputs but interacts with the light-entrainment system. Non-photic stimuli can be powerful quantitatively: behavioural events can shift rhythms by several hours. Non-photic entrainment offers scope for rephasing biological rhythms in circumstances where light input from the environment is inadequate.
Circadian rhythms in the Syrian hamster can be markedly phase shifted by 3 h of wheel running or arousal stimulation during their usual daily rest period ("subjective day"). Continuous wheel running is predictive but not necessary for phase shifts of this "nonphotic" type; hamsters aroused by gentle handling without running can also show maximal shifts. By contrast, physical restraint, a standard stress procedure and thus presumably arousing, is ineffective. To resolve this apparent paradox, phase-shifting effects of 3-h sessions of restraint or other stress procedures were assessed. In a preliminary study, phase shifts to arousal by gentle handling were significantly potentiated by the cortisol synthesis inhibitor metyrapone, suggesting that stress-related cortisol release may inhibit phase shifts to arousal. Next, it was confirmed that restraint in the subjective day does not induce phase shifts, but behavioral observations revealed that it also does not sustain arousal. Restraint combined with noxious compressed air blasts did sustain arousal and induced a significant cortisol response compared with arousal by gentle handling but did not induce shifts. Restraint combined with continuous horizontal rotation was also ineffective, as was EEG-validated arousal via confinement to a pedestal over water. However, 3 h of resident-intruder interactions (an intense psychosocial stress) or exposure to an open field (a mild stress) did induce large shifts that were positively correlated with indexes of forward locomotion. The results indicate that large phase shifts associated with arousal in the usual sleep period are neither induced nor prevented by stress per se, but are dependent on the expression of at least low levels of locomotor activity. Sustained arousal alone is not sufficient.
Some species - ring-tailed lemurs and snow leopards, for example - apparently thrive in captivity, whereas others, such as Asian elephants and polar bears, are prone to problems that include poor health, repetitive stereotypic behaviour and breeding difficulties. Here we investigate this previously unexplained variation in captive animals' welfare by focusing on caged carnivores, and show that it stems from constraints imposed on the natural behaviour of susceptible animals, with wide-ranging lifestyles in the wild predicting stereotypy and the extent of infant mortality in captivity. Our findings indicate that the keeping of naturally wide-ranging carnivores should be either fundamentally improved or phased out.
Of the three defining properties of circadian rhythmicity--persisting free-running rhythm, temperature compensation, and entrainment--the last is often poorly understood by many chronobiologists. This paper gives an overview of entrainment. Where have we been? Where are we now? Whence should we be going? Particular emphasis is given to a discussion of the Discrete vs. Continuous models for entrainment. We provide an integrated mechanism for entrainment from a limit-cycle perspective.
Although there are many studies on the running wheel in laboratory animals, it is not clear if a running wheel should be provided for golden hamsters kept as pets. Unlike laboratory animals, golden hamsters kept as pets usually have larger cages, more varied food, and are kept singly. In this study, 10 sister-pairs of golden hamsters were kept singly in large enriched cages with a functional or a non-functional large running wheel. Using video-recordings, the behaviour of hamsters of both groups was compared. Hamster females with a functional wheel showed significantly less climbing and stereotypical bar-mouthing than females with non-functional wheels.In order to compare the physical condition of the females, they were regularly mated and raised up to four litters before they stopped reproducing. Body masses did not differ between the groups, but females with functional wheels had significantly larger litters. Offspring growth did not differ, probably because the females decreased running in the wheel during pregnancy and stopped running completely during lactation. Therefore, we conclude that a large well-constructed running wheel will have no detrimental effect on golden hamsters kept in large and enriched cages with ad libitum access to adequate food and water. On the contrary, the running wheel may have had a beneficial effect on the well-being of the hamsters since it significantly decreased stereotypic bar-mouthing.
Several species of mice build burrows, however, little is known about the motivation underlying this behaviour. This study had two aims: (1) to investigate whether burrowing constitutes a behavioural need, that is, whether mice were motivated to perform the behaviour of burrowing per se, or whether it is the functional consequences of burrowing that motivate the behaviour; (2) to determine the strength of motivation that laboratory mice have for burrowing. In Experiment 1, eight BALB/c mice were placed individually into a start cage connected to two burrowing compartments containing peat. During Phase 1, the mice had access to only one compartment, and during Phase 2, access to only the second. At the beginning of Phase 3, the burrows in one of the compartments were destroyed and the mice given access to both. The duration of burrowing remained unchanged throughout all three phases, and the number of burrowing bouts significantly increased. During Phase 3, there was no significant difference between burrowing in the compartments containing the intact or the destroyed burrows. These data confirmed that laboratory mice readily build burrows when given the opportunity, and indicate this behaviour constitutes a ‘behavioural need’. In Experiment 2, the strength of motivation for burrowing was examined in five CB57 mice using an operant technique in which a single mouse within a group could work to gain access to burrowing substrate. Despite increasing cost of gaining access, the mice continued to work to visit the burrowing substrate. The slope and area under the demand function indicated that the motivation to build burrows was high. These findings indicate that if studies require laboratory mice to express a full behavioural repertoire, or to avoid compromises of welfare, mice should be provided with the opportunity to perform burrowing wherever practicable.
A variety of recent rodent studies have suggested the use of an enriched environment as a strategy to increase the welfare of captive animals. However, a number of standard procedures of environmental enrichment are applied without taking into account the etho-ecological, species-specific, needs of laboratory animals. The aim of the present study was to evaluate the age and sex differences in the utilisation of a physically-enriched environment, consisting of four differently-shaped plastic compartments: a central chamber, a circle, a running wheel and a tower. These compartments are characterised by features (e.g. size, lightness, presence of food, opportunity to perform physical activity) of eco-ethological relevance for the mouse, the most common laboratory species. Presence and activity in each cage compartment during 5 consecutive days were assessed in juvenile (35 days old) and adult (90 days old) CD-1 mice of both sexes. Mice explored all the compartments, spending most of the time in the central chamber and making an extensive use of the running wheel. Juveniles of both sexes and adult males showed a prominent occupation of the central chamber, where food and sawdust were located, and they widely used it to sleep, suggesting that food availability might be a relevant factor in driving their choice of the resting location. Conversely, adult females displayed a more complex utilisation profile and preferentially stayed in the tower while inactive, suggesting that safety needs, that the covered structure of this compartment probably cater for, may be more relevant for them than availability of food and water resource. These findings indicate that in laboratory mice the features of an enriched environment are differentially relevant according to age and sex and, thus, may exert a different impact on their psycho-physical welfare.
This study compared the capability for social entrainment of the circadian locomotory rhythms of solitary versus socially living nocturnal small mammals. Therefore single adult golden hamsters and Mongolian gerbils of both sexes were kept under LD 12:12 and then transferred in their cages to a dark chamber (DD), which was covered with an opaque material, but located permanently in a room with other conspecifics exposed to a light regime (LD 12:12). The animal in the chamber was able to detect acoustical and olfactorial stimuli of the conspecifics outside the chamber. Under these experimental conditions all the golden hamsters and gerbils investigated developed free-running rhythms of activity with an individual-specific spontaneous period. In golden hamsters these free-running rhythms were never entrained or masked. In 5 out of 6 gerbils the free-running of activity rhythms stopped after a few days and the rhythms were more or less pronounced entrained or masked. Unexpectedly the response was not induced via signals from the conspecifics but quite probably by the caretaking procedures in the animal room. Therefore, our results suggest that in neither investigated species did social entrainment of the circadian activity rhythms occur.
Claims about animal welfare based on data regarding the pituitary-adrenocortical axis should be viewed with scepticism because of the lack of consistency between the results of different studies. Occasional sampling of blood does not give an accurate description of the episodic nature of corticosteroid secretion. Too little is known about how chronic stress affects the activity of the pituitary-adrenocortical axis, or whether changes in mean daily level or in the nature of the secretory episodes are most important. More attention should be paid to basic research to understand the nature of this biological system rather than to premature attempts to “measure” animal welfare by corticosteroid values.
To determine the factors that cause the development of stereotypic digging, features in the captive environment of young Mongolian gerbils, Meriones unguiculatus , were varied. It was hypothesized that stereotypic digging develops because stimuli that control digging motivation are lacking. A regulatory model of motivation was used to examine whether digging motivation is decreased by the performance of the motor pattern `digging' or by the consequences of digging. Young gerbils that could dig in a sand area developed stereotypic digging. In contrast, young gerbils that could not dig in sand but had access to an artifical burrow, which was presumed to be the consequence of digging, showed less non-stereotypic digging than gerbils from the sand treatment and did not develop stereotypic digging. Therefore, the mere perception of the stimulus `burrow' by a retreating animal decreased digging motivation. The complexity of the artifical burrow was reduced to a few elements to analyse in detail the stimuli that control digging motivation. A dark and narrow chamber at the end of a tube connected to the cage provided the stimuli that elicited retreating and prevented the development of stereotypic digging. The tube was a necessary feature: a chamber alone did not prevent the development of stereotypic digging. Such a stimulus situation seems to match the stimuli of a natural burrow which is built to buffer climatic fluctuations and to provide shelter from predators. The results show that stereotypic digging develops when a young gerbil cannot achieve a stimulus situation that is efficient in decreasing digging motivation.
We estimate that stereotypies are currently displayed by over 85 million farm, laboratory and zoo animals worldwide. This paper investigates their reliability as welfare indicators, by surveying studies relating stereotypy to other welfare measures and by analysing the mechanisms underlying this behaviour. Where data exist, most (approximately 68%) situations that cause/increase stereotypies also decrease welfare. Stereotypy-eliciting situations are thus likely to be poor for welfare, although exceptions exist. Within such an environment, however, most (approximately 60%) accounts link individual stereotypy performance with improved welfare (cf approximately 20% linking it with reduced welfare). Thus, in a sub-optimal environment, non-stereotyping or low-stereotyping individuals could well have the poorest welfare, although again exceptions exist. Examining the mechanisms underlying stereotypy performance, we discuss four processes that could account for these complex links between stereotypy and welfare. Beneficial consequences from performing the specific source-behaviour of the stereotypy ('do-it-yourself enrichment'), or arising from repetition per se ('mantra effects'), may ameliorate welfare in poor environments. In addition, stereotypies that have become centrally controlled (habit-like), or that arise from autistic-like changes in the control of all behaviour (perseveration), are likely to be unreliable indicators of current state because they can be elicited by, or persist in, circumstances that improve welfare. To refine the role of stereotypy in welfare assessment, we suggest the collection of specific additional data to reveal when any of these four processes is acting. Until such research increases our understanding, stereotypies should always be taken seriously as a warning sign of potential suffering, but never used as the sole index of welfare; non-stereotyping or low-stereotyping individuals should not be overlooked or assumed to be faring well; simple measures of frequency should not be used to compare stereotypies that differ in age, form, or the biological or experiential characteristics of the performing animal; enrichments that do not immediately reduce stereotypies should not be assumed failures with respect to welfare; and finally, stereotypies should not be reduced by means other than tackling their underlying motivations.
To be able to assess animal welfare the researcher must presuppose a number of background assumptions that cannot be tested by means of ordinary empirical data collection. In order to substantiate these assumptions two sorts of inferences have to be relied upon, which the authors designate by the terms ‘analogies’ and ‘homologies’. Analogies are evaluative, philosophical reflections by means of which it is made clear what provisions or states constitute the welfare of humans and other animals. By means of analogies it may, for example be argued that animal welfare consists of subjective experiences such as pain, boredom, pleasure and expectation. Also by means of analogies the relative ‘weight’ of these states can be decided. Homologies are part of theoretical science. They serve to clarify how the relevant experiences are linked to measurable anatomical, physiological and behavioural parameters.
An account is given of the steps which have to be taken to give a full answer to a question concerning the welfare of animals. In the account only farm animals are mentioned, but the same steps, of course, also have to be taken to answer questions concerning the welfare of other kinds of animals be they companion, laboratory, zoo or wild. Eight steps are described, and it is argued that both analogies and homologies are needed at very fundamental levels. Therefore, if animal welfare science is to provide relevant, rational and reliable answers to questions concerning animal welfare, it must be an interdisciplinary inquiry involving philosophical reflections and theoretical biology.
Although the physiological and behavioural changes that can indicate poor welfare are generally agreed upon, using these measures in practice sometimes yields results that are hard to interpret. For example, different types of measure may suggest quite different things about an animal's welfare. Such contradictions are often due to the differing properties of the variables being measured. How each variable responds to a stressor can be affected by several factors - the type of unpleasant stimulus to which the animal is exposed; when and for how long exposure occurs; the animal's psychological state, eg does it feel that it is in control?; and the time at which the measurement is made, relative to the stressor. Typical responses also often differ between species and between individuals, and may even change in a single individual over time. Furthermore, some responses used to assess welfare lack specificity: they can be elicited by neutral or even pleasant events as well as by aversive ones. Appreciating these factors is vital when designing experiments, when choosing what to measure along with each welfare variable, and when interpreting results. Even after taking these factors into consideration, interpreting a result can still be difficult. One approach then is to consider the effects on welfare of the changes measured, eg if there is immunosuppression, does the animal succumb to disease? Another is to use the animal's behaviour to indicate its preference for, or aversion to, particular environments. Ultimately, however, interpreting welfare measures involves subjective judgements which will be influenced by the nature of our concern for the animal under consideration. By raising these problems, we hope that this review will highlight and clarify the apparent contradictions that sometimes emerge in scientific studies of animal welfare, and help researchers improve the designs of their experiments for the benefit of the animals concerned.
Prolonged interaction with cage bars by captive mammals (usually classed as stereotypic) may reflect poor welfare. Such behaviour may arise from motivation to investigate the external environment or to escape captivity. However, these hypotheses have not been explicitly tested. We raised mice, Mus musculus, to adulthood in modified laboratory cages with two sets of bars at the top and side of the cage. One set provided a potential escape route, and half of each set was backed by Perspex to reduce cues from the external environment. We predicted where mice should interact with the bars according to their motivational priorities. Body weights were recorded weekly to study the relationship between physical development and bar-related behaviour. Serum corticosterone was measured to monitor the effect of bar-related behaviour on stress physiology. Mice preferred to interact with bars where external cues were detectable. As adults, mice responded more to the bars providing a potential exit, though this was affected by the exit location. Corticosterone titres were higher in mice whose potential exit was situated at the cage top. Response to the bars was apparently restricted by the physical development of mice, particularly among those whose potential exit was situated in the cage top. © 1999 Elsevier Science B.V. All rights reserved.
Stereotypies are repetitive, invariant behaviour patterns with no obvious goal or function. They seem to be restricted to captive animals, mentally ill or handicapped humans, and subjects given stimulant drugs. In this respect they are abnormal, although possibly the product of normal behavioural processes. Stereotypies are often associated with past or present sub-optimal aspects of the environment, and have been used as a welfare indicator. It has been hypothesized that stereotypies have beneficial consequences which reinforce their performance, although other means, such as positive feedback, may equally explain their persistence. Empirical evidence links them with lowered awareness of external events, and reduced arousal and distress. However, as most of this evidence is correlational it remains uncertain that the stereotypies are themselves the cause of coping. Furthermore, they are heterogeneous in source of origin, proximate causation and physical characteristics, and they change over time in important respects, becoming more readily elicited by a wider range of circumstances. Therefore the properties of one stereotypy are not necessarily those of another.
Three groups of six pairs of adult male laboratory mice of the ICR-strain kept in standard laboratory cages were selectively prevented from stereotypic wire-gnawing for 1, 5 or 10 days, respectively. Behaviour was observed throughout the 12 h dark period one day prior to prevention, on day 1, 4 or 9 (depending on the group) during the period of prevention and on post-inhibitory day 1 and 3. Prior to prevention wire-gnawing was positively correlated (P<0.05) with total activity and climbing. During prevention all three groups showed a significant reduction in total activity (non-stationary; P<0.05) and climbing (P<0.001) and significantly enhanced inactivity (lying motionless; P<0.05). However, the decrease in total activity was positively correlated with base levels of wire-gnawing only on day 1 (P<0.01) but not at later stages of prevention. Similarly, climbing during prevention was positively correlated (P<0.05) with base levels of wire-gnawing on day 1 and 4 but not on day 9 of prevention. These results indicate that the mice only gradually adapted to the new situation. On post-inhibitory day 1 all three groups resumed wire-gnawing at pre-treatment base levels with performance following the same time course throughout the dark period but with significantly reduced peak performance (P<0.05). In the light of motivational theory these results shed doubt on the general validity of the coping hypothesis. Two alternative explanations are discussed.
Artificial weaning in laboratory mice elicits increased levels of exploratory and escape behaviour. Under barren housing conditions patterns of exploration and escape subsequently develop into stereotypic behaviour. Weaning weight in wild house mice,Mus musculus domesticus, is known to affect offspring fitness, thus reduced weaning weight represents a risk to fitness. In male ICR-mice,Mus musculus, precocious weaning 3 days prior to standard weaning age tended to decrease growth rate in the long term, and differences in weaning weight of mice weaned at the standard age persisted into adulthood. Both plasma corticosterone levels 48 h after weaning and adult stereotypy levels were higher in precociously weaned mice, but also in animals weaned at the usual age but at a low weight. These results suggest that potential costs in terms of fitness may affect stress levels at the onset of stereotypy development and predispose ICR-mice to perform stereotypies at a high level when adult.
The importance of a commodity, as perceived by animals, can be determined by measuring the amount of work animals are prepared to perform to gain access to that commodity. In the present study, this method is extended to establish how animals perceive the importance of increasing amounts of one commodity, that is, additional space. The behavioural demand functions of caged laboratory mice,Mus musculusfor additional space ranging from 196 cm2to 1600 cm2on fixed-ratio schedules ranging from 5 to 80 switch operations were determined. At all fixed-ratio values, the mice worked economically and gained access to additional space on several occasions within each 1-h observation session. The amount of access gained decreased as the work required increased, but the slope of the function (−0.347) was sufficiently shallow to indicate that additional space was regarded by the mice as a highly important commodity. The frequency of visits and the time spent in the additional space were significantly different between the sizes of additional space offered, but unexpectedly, these differences were small. In addition, the elasticity coefficients were not significantly different between the sizes of additional space. The absence of large differences in response to disparate sizes of additional space may indicate that the mice may have (1) been motivated to escape their home-cage, (2) been motivated to search for unavailable resources, or (3) perceive the different amounts of additional space as nearly equally (non-)rewarding. Time of day had a significant effect on the responses of the mice in that towards the end of the active phase, the additional space was visited less frequently and for shorter periods indicating a temporally based change in motivational status or efficiency of behaviour. It is argued that these results support previous evidence that laboratory mice are highly motivated to explore and subsequently monitor areas made accessible to them, regardless of size and, to some extent, content.
The pervasive role of circadian clocks in regulating physiology and behavior is widely recognized. Their adaptive value is their ability to be entrained by environmental cues such that the internal circadian phase is a reliable predictor of solar time. In mammals, both light and nonphotic behavioral cues can entrain the principal oscillator of the hypothalamic suprachiasmatic nuclei (SCN). However, although light can advance or delay the clock during circadian night, behavioral events trigger phase advances during the subjective day, when the clock is insensitive to light. The recent identification of Period (Per) genes in mammals, homologues of dperiod, which encodes a core element of the circadian clockwork in Drosophila, now provides the opportunity to explain circadian timing and entrainment at a molecular level. In mice, expression of mPer1 and mPer2 in the SCN is rhythmic and acutely up-regulated by light. Moreover, the temporal relations between mRNA and protein cycles are consistent with a clock based on a transcriptional/translational feedback loop. Here we describe circadian oscillations of Per1 and Per2 in the SCN of the Syrian hamster, showing that PER1 protein and mRNA cycles again behave in a manner consistent with a negative-feedback oscillator. Furthermore, we demonstrate that nonphotic resetting has the opposite effect to light: acutely down-regulating these genes. Their sensitivity to nonphotic resetting cues supports their proposed role as core elements of the circadian oscillator. Moreover, this study provides an explanation at the molecular level for the contrasting but convergent effects of photic and nonphotic cues on the clock.
The 24-h patterns of circulating cortisol and corticosterone were determined in male hamsters housed under a 14:10 light-dark cycle. Corticoid levels varied significantly over the 24-h sampling period with peak levels of both hormones occurring near the onset of the daily dark phase. The ratio of cortisol to corticosterone changed dramatically during the day. Corticosterone levels were significantly higher than cortisol during the early part of the light phase; however, cortisol levels became significantly higher than corticosterone when both hormones began their daily rise. To examine whether the circadian rhythm of cortisol secretion could be involved in the physiological control of hamster circadian organization, cortisol was infused at approximately physiological levels into adrenalectomized hamsters either continuously or in a 24-h rhythm. No significant differences were observed in the timing of circadian wheel-running rhythms in hamsters housed in LD 16:8, LD 14:10, or LL when cortisol was infused continuously, in a 24-h rhythm that mimicked the cortisol rhythm of intact hamsters, or in a 24-h rhythm several hours out of phase with the rhythm of intact hamsters. Provision of cortisol in a 24-h rhythm appeared to promote the survival of adrenalectomized hamsters since hamsters receiving a 24-h pattern of cortisol survived the experimental protocol significantly longer than those receiving the same dose of cortisol continuously.
Because some recent studies of hamster adrenocortical function have depended on older studies that may have been inadequate or misinterpreted, the present study re-examined plasma corticosterone and cortisol concentrations in hamsters under several conditions to determine which plasma glucocorticoid predominated in this animal. Sensitive radioimmunoassays were used to measure separately the two glucocorticoids in the basal condition, after adrenocorticotropin (ACTH) treatment, after acute stress, and after chronic stress. In the basal condition, corticosterone concentrations were 3-4 times higher than those of cortisol. After stimulation, this difference disappeared, but rarely were any hamster's cortisol levels higher than their corticosterone levels. Both ACTH and acute stress elevated plasma corticosterone and cortisol concentrations, but only plasma cortisol concentrations were elevated following chronic stress. The dissociation between cortisol and corticosterone concentrations after chronic stress suggests that the two glucocorticoid hormones in the hamster may be regulated independently. The data also indicate that both corticosterone and cortisol should be measured when assessing adrenocortical function in the hamster.
Sleep/wake expression in mice varies predictably with circadian phase. Such circadian rhythms are known to depend on intact suprachiasmatic nuclei (SCN) in the hypothalamus, but the mechanism by which SCN activity modulates sleep/wake expression is unknown. This paper examines the possibility that circadian patterns of sleep/wake derive partly from circadian timing of waking behaviors that are incompatible with sleep, such as locomotor activity. Voluntary locomotor activity was restricted in five mice adapted to a running wheel by locking the wheel in place. Continuous electrographic monitoring of sleep and wakefulness over multiple circadian cycles revealed: (1) during the active phase, shorter wake bouts and more frequent bouts of sleep, resulting in greater sleep/wake fragmentation and more time spent asleep; (2) during the rest phase, a small compensatory reduction in NREM sleep; (3) reduced amplitude of circadian sleep/wake rhythms and a greater amount of sleep overall. Thus, voluntary locomotor activity has an important influence on sleep/wake expression in mice, and the normal circadian pattern of sleep/wake depends on circadian timing of activity. Previous reports of damped circadian sleep/wake rhythms in rodents may therefore be explained by coincident diminutions in locomotor activity associated with age or health status. Our results also support analogous findings in human subjects, and we propose that elderly humans may benefit from therapies that augment daytime activity.
Behavioral aspects of photoentrainment of circadian locomotor activity rhythms were recorded for a nocturnal den-dwelling rodent, the flying squirrel,Glaucomys volans. Methods included both telemetric monitoring and infrared observations of animals under constant dark (DD) or light-dark (LD) schedules in either standard wheel cages or in newly developed simulated den cages. By means of the den cages, several aspects of a circadian activity cycle could be simultaneously measured emphasizing the arousal from rest, the light-sampling behavior by which a squirrel assessed the environmental photoregimen, and the phase-shifting by which photoentrainment was achieved. Each animal in a den cage remained for 12 or more hours of its rest period almost exclusively in the darkened nest box, then at an abrupt arousal time moved to the light-sampling porthole. In darkness each animal initiated wheel activity immediately after arousal; light at arousal time, however, induced a return to the nest box for a nap and a delay phase-shift in onset of activity of approximately 40 min. On subsequent days, each animal appeared to be free-running (τ
FR< 24 h) until onset again advanced into the light period. A squirrel usually viewed only a few minutes light per day, and on free-running days occasionally saw none of the 12-h light period. The significance of these data for theories of circadian photoentrainment is discussed.
The adrenocortical response to increasing periods of exposure to a novel cage, as well as the effects of returning hamsters to their familiar home cages, were examined. We found that a five min exposure to a novel cage was insufficient to activate the pituitary-adrenal system, but that cortisol levels increased significantly as duration of exposure increased from 15 to 30 min. In contrast, returning hamsters to their home cages for at least 15 min following the 15 min novel cage exposure produced a significant drop in plasma levels of cortisol. Finally we found that males exhibit a greater cortisol response to novelty than females, indicating a sexual dimorphism which is the reverse of that reported in other rodents.
Male Syrian hamsters were housed in simulated burrows in order to investigate (a) how these nocturnal, fossorial rodents entrain to the prevailing light:dark cycle in this semi-natural habitat and (b) the response of the reproductive system to environmental illumination. The burrow emergence activity of hamsters housed in simulated burrows was compared to the running wheel activity of animals maintained in standard cage conditions. The activity rhythm was similar in both measuring devices. The data suggested that in a natural environment hamsters are only exposed to light for short amounts of time each day. To determine whether brief photoperiodic stimulation could alter the phase angle of entrainment and/or the reproductive condition, burrow housed animals were exposed to a supplemental 30-second light pulse during specified clock hours of the dark period on a daily basis. These light pulses induced a phase shift and maintained a long day reproductive response in what was otherwise a short photoperiod.
Isolated Golden hamsters of both sexes were compared with animals which had been grouped in tens for a period of 62 days, with respect to fighting behavior, and adrenal and gonadal function regardless of sex. The isolated animals were found to show more agonistic behavior toward young female opponents, but the isolated females were more aggressive than their male counterparts. Isolation had no effect on adrenal, ovarian or hemiuterus weight in the female but such treatment caused an increased weight in both the adrenal gland and the ventral prostate gland in the male, the latter change being indicative of higher androgen levels. It is argued that the increased aggressiveness of female hamsters following isolation cannot be attributed merely to changes in the production of sex steroids as it has in the house mouse. The established sex difference in adrenal weight, the male having a heavier adrenal than the female, was confirmed and was not changed by isolation/grouping but atypically the males appeared to have lower plasma cortisol levels than the females, an effect which may be due to treatment differing in the two categories. It is argued that certain of the adrenal changes can be attributed to an increase in androgen level in the isolated male.
Wheel-running and direct observation of animals in their home cages were used to measure the activity of golden hamsters through the oestrous cycle, pregnancy and pseudopregnancy. Both methods showed that the pro-oestrous and oestrous days of the cycle were days of increased activity. Levels of hweel-running fell immediately after copulation and were low throughout pregnancy and pseudopregnancy. Except for bar-chewing, categories of behaviour scored in the home cages did not show a comparable decline. Nest-building increased during pregnancy. Sleeping was reduced on days 5 and 10 of pregnancy. The differences between the two methods of recording activity are discussed, as are the physiological bases of the changes in behaviour.
Some of the main themes in this review are as follows. 1. The notion that non-photic zeitgebers are weak needs re-examining. Phase-shifts to some non-photic manipulations can be as large as those to light pulses. 2. As well as being able to phase-shift and entrain free-running rhythms, non-photic events have a number of other effects: these include after-effects of entrainment, period changes, and promotion of splitting. 3. The critical variable for non-photic shifting is unknown. Locomotor activity is more likely to be an index of some other necessary state rather than being causal itself. This index may be better when tendencies to move are channelled into easily measured behaviours like wheel-running. 4. Given ignorance about the critical variable, quantification of activity may be the best presently available measure of zeitgeber intensity. Therefore, the behaviour during non-photic manipulations must be examined as carefully as the shifts themselves. When no phase-shifting follows manipulations such as IGL lesions or serotonin depletion, if the animals are inactive, then little can be inferred. 5. Lack of information on the critical variable(s) for non-photic shifting makes it problematic to compare data from studies using different non-photic manipulations. However, the presence of locomotor activity (or its correlate) does appear to be necessary for triazolam to produce shifts. 6. Novelty-induced wheel-running in hamsters depends on the NPY projection from the IGL to SCN. It remains to be determined how important NPY is in other species or in clock-resetting by other manipulations, but methods are now available to study this. 7. Interactions between photic and non-photic zeitgebers remain virtually unexplored, but it is evident that photic and non-photic stimuli can attenuate the phase-shifting effects of each other. Interactions are not purely additive or predictable from PRCs. 8. The circadian system does more than synchronize free-running rhythms to the solar day. Its non-photic functions and their interactions with photic inputs probably account for some of the anatomical complexity of circadian circuitry.
Phase shifts resulting from nonphotic events can be accompanied by sizable changes in the free-running period. This study examined the relationship between tau changes and phase shifts produced by confining Syrian hamsters to a novel running wheel in the mid-subjective day. Both phase shifting and tau lengthening were higher in animals that made a high number of wheel turns in the 3 h in the novel wheel. Hamsters that ran little during the activity pulse, and did not subsequently exhibit either phase shifts or tau lengthening, had low baseline activity and long taus before the pulse. However, long taus did not preclude hamsters from running in a novel wheel and subsequently phase shifting. This was demonstrated by finding the phase shifts after activity pulses in animals whose tau had already been lengthened by previous activity pulses in novel wheels. The possibility is discussed that feedback from locomotor activity influences the period of the clock in hamsters, but it is concluded that, in addition, there must be other mechanisms accounting for the relationships between activity and tau.
Voluntary wheel running by animals is an activity that has been observed and recorded in great detail for almost a century. This review shows that it is performed, often with startling intensity and coordination, by a wide variety of wild, laboratory and domestic species with diverse evolutionary histories. However, despite the plethora of published studies on wheel running, there is considerable disagreement between many findings, thus leading to a lack of consensus on explanations of the causality and function. In the initial part of this review, I discuss the internal and external factors that may be involved in the causality of this behaviour, with an emphasis on disparities in both the factual and theoretical development of the subject. I then address the various proposed functions of wheel running, again highlighting evidence to the contrary. This leads to the conclusion that any single theory on the basis of wheel running is likely to be simplistic with little generality. I then present a novel, behaviour-based interpretation in which it is argued that wheel running has no directly analogous naturally occurring behaviour, it is (sometimes) performed for its own sake per se rather than as a redirected or substitute activity, and studies on motivation show that wheel running is self-reinforcing and perceived by animals as 'important'. This review proposes that wheel running may be an artefact of captive environments or of the running-wheel itself, possibly resulting from feedback dysfunction. I also discuss the ubiquity and intensity of its performance, along with its great plasticity and maladaptiveness, all indicating that if it is an artefact, it is nevertheless one of great interest to behavioural science. Copyright 1998 The Association for the Study of Animal Behaviour.
What are phase-response curves (PRCs)? How can they be measured? How should they be plotted? These questions and many other fascinating facets of PRCs are addressed in this review, including research topics in which phase-resetting data have provided crucial insights: entrainment, phototransduction, pacemaker mechanism, phase markers of the pacemaker, and gauges of oscillator amplitude. PRCs have enlightened us and will continue to be a valuable tool in clock research.
Stressful events are known to initiate a cascade of physiological mechanisms that are potentially costly for metabolic processes. Although these mechanisms are well understood, the long-term costs and the potential implications for individual condition and behaviour have been considered only recently. Combining information from physiological, ecological and behavioural studies can help us to understand the implications of stress for individual life history strategies. Furthermore, the concept of individual variation in stress tolerance has implications for the immunocompetence handicap hypothesis and the evolution of secondary sexual signals.
Since consistent data on endogenous circadian rhythms of Mongolian gerbils are not available, the main aim of our study was to identify suitable conditions to receive stable and reproducible free-running rhythms of activity under different light intensities. Another objective was to determine the role of social cues as an exogenous zeitgeber in the absence of a light-dark (LD) cycle. We performed two long-term sets of experiments with adult male gerbils kept in climatic chambers under various photoperiods of at least 30 days each. In all cases, the time of lights on in the chambers differed from the daily starting hour of work in the animal house. Always, two animals per chamber were kept separately in cages with a running wheel while their activity was monitored continuously. During the first set, only three of eight animals developed intra- and interindividual variable free-running rhythms. The activity patterns seemed to be influenced by human activities outside, indicating high sensitivity to external factors. Subsequently, we damped the chambers and the room and restricted access to the room. In the following noise-reduced set, all gerbils developed comparable free-running rhythms of activity. We determined the mean of the free-running period tau, the activity-rest relationship alpha/theta and the amount of running wheel activity per day: tau = 23.7h +/- 0.08h under low light (5 lux) and 25.5h +/- 0.19h under high light intensities (450 lux); alpha/theta = 0.53 +/- 0.08 under 5 lux and 0.34 +/- 0.04 under 450 lux. The amount of daily activity was 12 times as high under 5 lux as under 450 lux. There was no indication that the two animals in one chamber socially synchronized each other. In conclusion, the pronounced rhythm changes in accordance with Aschoff's theory support the view that gerbils are mainly nocturnal animals.
Rodents used in biomedical research are typically reared in small cages that lack key features of their natural habitats. These conditions impose constraints on behaviour and brain development, resulting in altered brain functions. In this article, evidence for three different ways in which barren housing conditions interfere with brain development and behaviour is reviewed. Early environmental deprivation, thwarting of behavioral response rules, and disruption of habitat-dependent adaptation processes are shown to result in aberrant or maladaptive brain functions. Current standard housing conditions could therefore compromise the utility of rodents for research, especially in behavioural neuroscience. However, a better understanding of the animals' needs and of the environmental factors involved in the control of behaviour could offer a biological basis for refinement.
Stressors, both physical and psychological, can activate the hypothalamic-pituitary-adrenal (HPA) axis, leading to a wide range of physiological responses including increased glucocorticoid release and suppression of immune function. The majority of studies published to date have focused on the effects of physical stressors (e.g., cold exposure, electric shock) on immunity. The present study examined the role of a stressor, social defeat, on humoral immune function of Syrian hamsters (Mesocricetus auratus). Specifically, adult male Syrian hamsters experienced social defeat (i.e., exposure to a dominant animal in that animal's home cage) that was either acute (i.e., a single exposure) or chronic (i.e., daily exposures across 5 days). A control group of animals was placed in a resident's home cage without the resident animal present and did not experience defeat. After the last encounter, blood samples were drawn and animals were subsequently injected with keyhole limpet hemocyanin (KLH). Blood samples were again taken 5 and 10 days postimmunization and serum was analyzed to determine serum cortisol and anti-KLH immunoglobulin G (IgG) concentrations. Cortisol concentrations were elevated in both acutely and chronically defeated hamsters compared with control animals. In contrast, serum IgG concentrations were significantly reduced in both groups of defeated hamsters compared with control animals. Collectively, these results demonstrate that both acute social defeat and chronic social defeat lead to activation of the HPA axis and suppression of humoral immune function. These data suggest that social defeat is an important, ecologically relevant model with which to examine stress-induced immune suppression in rodents.
The golden hamster (Mesocricetus auratus) is one of the most frequently used laboratory animals, particularly in chronobiological studies. One reason is its very robust and predictable rhythms, although the question arises whether this is an inbreeding effect or rather is typical for the species. We compared the daily (circadian) activity rhythms of wild and laboratory golden hamsters. The laboratory hamsters were derived from our own outbred stock (Zoh:GOHA). The wild hamsters included animals captured in Syria and their descendants (F1). Experiments were performed under entrained (light: dark [LD] 14h:0h) and under free-running (constant darkness, DD) conditions. Locomotor activity was recorded using passive infrared detectors. Under entrained conditions, the animals had access to a running wheel for a certain time to induce additional activity. After 3 weeks in constant darkness, a light pulse (15 min, 100 lux) was applied at circadian time 14 (CT14). Both laboratory and wild hamsters showed well-pronounced and very similar activity rhythms. Under entrained conditions, all hamsters manifested about 80% of their total 24h activity during the dark portion of the LD cycle. The robustness of the daily rhythms was also similar. However, interindividual variability was higher in wild hamsters for both measures. All animals used the running wheels almost exclusively during the dark portion of the LD cycle, although the wild hamsters were three times more active. The period length, measured in constant darkness, was significantly shorter in wild (23.93h +/- 0.10h) than in laboratory hamsters (24.06 +/- 0.07h). The light-induced phase changes were not different (about 1.5h). In summary, these results indicate that the laboratory hamster is not much different from the wild type.
Spontaneously occurring abnormal behaviors in animals have recently received considerable attention, both in veterinary medicine and as a potential model for abnormal behavior in several human mental disorders. Stereotypies are abnormal repetitive, unvarying, and functionless behaviors that are often performed by captive and domesticated animals housed in barren environments. They closely resemble the stereotypies of autistic and mentally retarded patients, stereotypies of unmedicated chronic schizophrenic patients, certain classes of simple tic in Tourette's syndrome, and several drug-induced behaviors. However, evidence for a common mechanism has been lacking. Stereotypies in human mental disorders are indicative of profound brain dysfunction involving the basal ganglia, and are associated with pervasive voluntary-motor impairments and psychological distress. Here we show that stereotypy in captive Orange-Wing Amazon Parrots (Amazona amazonica) is correlated with poor performance on the same psychiatric task (the 'gambling task') as stereotypy in autistic and schizophrenic patients. The task measures recurrent perseveration-the tendency to inappropriately repeat responses. Thus, the more stereotypy a parrot performed, the more likely it was to inappropriately repeat itself from trial-to-trial on the task; and the more rapidly it made repeated, but not switched, responses. These results parallel the executive motor impairments seen in human patients, and therefore suggest that, like in human patients, stereotypy in caged parrots reflects a general disinhibition of the behavioral control mechanisms of the dorsal basal ganglia. If this result holds true in other laboratory species, stereotypic animals are likely to be of questionable utility in behavior, neuroscience, and neuropharmacological experiments. In humans, stereotypies and obsessive-compulsive behaviors are considered to be mutually exclusive categories of behavior, with different neural substrates, and different treatment strategies. These results, therefore, suggest that the pharmacological treatment of stereotypies in veterinary medicine based on the assumption that they are equivalent to human Obsessive-Compulsive Disorder may be inappropriate. As stereotypies in captive animals develop in response to the captive environment, these results also emphasize the role that the environment may play in eliciting or exacerbating stereotypy in human patients. Finally, by parallel to human patients, there is a potential psychological distress in animals showing these behaviors.
In male golden hamsters, repeated social subjugation during puberty accelerates the development of adult aggressive behavior and enhances its intensity in the presence of smaller individuals. The current study is focused on the characterization of the hormonal and behavioral responses to social subjugation during puberty. Subjugation consisted of daily exposure to an aggressive adult for 20-min periods from postnatal day 28 (P-28) to P-42, while controls were placed into an empty clean cage. Plasma cortisol levels were measured prior to or immediately after treatment on P-28 and P-42. On P-28, exposure to an aggressive adult or a clean and empty cage caused an increase in plasma cortisol levels. However, only social subjugation resulted in elevated cortisol levels on P-42, showing that juvenile hamsters habituate to an unfamiliar environment but not to social subjugation. In addition, we found a relationship between the frequency of submissive responses during social subjugation and the development of aggressive behavior. The transition from play fighting to adult aggression was most accelerated in the least submissive animals. These data show that behavioral response to social subjugation determines the development of aggressive behavior in golden hamsters. Our data also suggest that submissive behavior is a form of coping that attenuates the behavioral consequences of social subjugation in male golden hamsters.
Running wheels are frequently used in behavioural and physiological experiments. The function of wheel-running activity in laboratory animals is controversial. In the present long-term study, the influence of this activity was evaluated in male golden hamsters over a period of 52 weeks. Four months after the start of the experiment, hamsters with access to running wheels were significantly heavier than those without these wheels. In addition, food consumption nearly doubled. The absolute values of fat-free mass (FFM), total body water (TBW) and crude fat mass (CFM) increased. However, in contrast to these absolute differences, the relative values were never different and general body composition was therefore unaffected by running-wheel activity. Different organ masses were established for absolute values of kidneys, testes and epididymis; possible effects on reproduction are discussed. The present data indicating improved physical condition leads to the assumption that a running wheel is a useful enrichment, enhancing animal welfare in the golden hamster.
In male golden hamsters, agonistic behavior matures during puberty, changing from play fighting to adult-like aggression. In addition, this transition is accelerated by repeated social subjugation early in puberty. However, little is known about the development of agonistic behavior in females. In the present study, we compared the development of agonistic behavior in male and female golden hamsters. Furthermore, we also tested the effects of repeated social subjugation on the development of agonistic behavior during puberty. Hamsters were tested for agonistic behavior in the presence of a smaller intruder at different intervals during puberty. Several observations were made. First, the frequency of attacks remained stable in females, while varying in males. Second, the transition from play fighting to adult-like aggression occurred at earlier time periods in females than in males. Finally, a clear transitional period marked by attacks focused on the flanks was observable in males around mid-puberty. However, this transitional period was not apparent in females. In addition, juvenile females were exposed to aggressive adult males or females. In both cases, repeated exposure to stress had no statistically significant effect on the development of agonistic behavior. After 2 weeks of subjugation, exposure to aggressive adults had no effect on serum cortisol levels, indicating that juvenile females habituate to repeated social stress. These data show significant sex differences in the development of agonistic behavior and adaptation to repeated stress in juvenile golden hamsters.
This paper introduces automated observations in a modular home cage system as a tool to measure the effects of wheel running on the time distribution and daily organization of cage floor locomotor activity in female C57BL/6 mice. Mice (n = 16) were placed in the home cage system for 6 consecutive days. Fifty percent of the subjects had free access to a running wheel that was integrated in the home cage. Overall activity levels in terms of duration of movement were increased by wheel running, while time spent inside a sheltering box was decreased. Wheel running affected the hourly pattern of movement during the animals' active period of the day. Mice without a running wheel, in contrast to mice with a running wheel, showed a clear differentiation between novelty-induced and baseline levels of locomotion as reflected by a decrease after the first day of introduction to the home cage. The results are discussed in the light of the use of running wheels as a tool to measure general activity and as an object for environmental enrichment. Furthermore, the possibilities of using automated home cage observations for e.g. behavioural phenotyping are discussed.