Higher heart rate of laboratory mice housed individually vs in pairs

Many studies have shown that housing mice individually over a long period significantly alters their physiology, but in most cases measurement has required human interference and restraint for sampling. Using a radio-telemetry system with implantable transmitters, we recorded heart rate (HR), motor activity (ACT) and body temperature (BT) of freely moving male mice (NMRI) housed either individually or in pairs with an ovarectomized female. Data for each parameter were collected at 5 min intervals for two consecutive 24 h periods. Even after several weeks of habituation to the social conditions, HR was increased in mice housed individually compared with mice housed in pairs, although their measured ACT did not differ. Additionally, BT tended to be reduced in individually-housed mice. When the data were analysed according to different ACT levels, HR was increased in individually-housed mice during phases of low and high, but not intermediate, motor activity. Furthermore, individually-housed mice had more, but shorter, resting bouts, indicating disruption of the normal circadian sleep pattern. Enhanced HR in individually-housed mice does not necessarily indicate stress, but might be an important physiological indicator of discomfort. The fact that individual housing alters basic physiological parameters in laboratory mice highlights the need to control for housing-dependent variation, especially in experiments that are sensitive to changes in these parameters.     

Determining the Value of Social Companionship to Captive Tufted Capuchin Monkeys (Cebus apella)

In general, guidelines on housing and care of animals in the laboratory state that rats and mice should not be housed in the same room. Mice may perceive rats as predators. Although one theory says this can cause stress, there is little scientific evidence to support this theory. In the wild, rats and mice usually do not share the same microhabitat, but this appears to be true for most small rodent species. Furthermore, reports of predatory behavior of rats toward mice mainly originate from experimental settings using rats with high inbred levels of aggression. This experiment measured heart rate (HR), body temperature (BT), activity (AC), and urinary corticosterone in female C57BL/6 mice before, during, and after introducing Wistar rats into their room. The study found no chronic effects of rat introduction on any parameters. The study concluded that housing rats and mice in the same room is at least less disturbing than cage cleaning, which caused a temporary increase of HR, BT, and AC. Current results do not support legislation based on compromised welfare.     

Effects of wire-bottom caging on heart rate, activity and body temperature in telemetry-implanted rats

Some experimental procedures are associated with placement of animals in wire-bottom cages. The goal of this study was to evaluate stress-related physiological parameters (heart rate [HR], body temperature [BT], locomotor activity [LA], body weight [BW] and food consumption) in rats under two housing conditions, namely in wire-bottom cages and in bedding-bottom cages. Telemetry devices were surgically implanted in male Sprague-Dawley rats. HR, BT and LA were recorded at 5 min intervals. Analysis under each housing condition was performed from 16:00 to 08:00 h of the following day (4 h light, 12 h dark). During almost all of the light phase, the HR of rats housed in wire-bottom cages remained high (371 ± 35 bpm; mean ± SD; n = 6) and was significantly different from that of rats housed in bedding-bottom cages (340 ± 29 bpm; n = 6; P < 0.001; Student's t-test). In general, BT was similar under the two housing conditions. However, when rats were in wire-bottom cages, BT tended to fluctuate more widely during the dark phase. LA decreased when animals were housed in wire-bottom cages, in particular during the dark phase. Moreover, there was a significant difference with respect to the gain in BW: BW of rats housed in bedding-bottom cages increased 12 ± 2 g, whereas that of rats in wire-bottom cages decreased by 2 ± 3 g (P < 0.001). Our results demonstrate that housing rats in wire-bottom cages overnight leads to immediate alterations of HR, BW and LA, which might be related to a stress response.     

Impact of 'living apart together' on postoperative recovery of mice compared with social and individual housing

Social housing is the optimal way of housing female laboratory mice. However, individual housing may be required in experimental designs, for example after surgery. We therefore investigated whether housing two female mice in a cage, separated by a grid partition ('living apart together', LAT), counters the adverse effects of individual housing on postoperative recovery. Ten individually housed (IND) mice, nine socially housed (SOC) mice and nine mice, housed LAT, were surgically implanted with a telemetry transmitter. From one week prior to surgery until three weeks thereafter, several physiological and behavioural parameters were measured in the mice subjected to surgery. The telemetry transmitter measured heart rate (HR), body temperature and activity continuously. Body weight, food and water intake were scored regularly, as were wound healing, ease of handling, nest building and behaviour. Results indicated that SOC mice appear to be less affected by abdominal surgery than IND mice, as indicated by HR and behaviour. LAT, however, did not appear to be beneficiary to the mice. Increased HR levels and differences in behaviour as compared with both SOC and IND animals indicate that LAT may even be the most stressful of the three housing conditions. We therefore conclude that mice benefit most from social housing after surgery. If, however, social housing is not possible, individual housing appears to be a better option than separating mice by a grid partition.     

Do Male Mice Prefer or Avoid Each Other's Company? Influence of Hierarchy, Kinship, and Familiarity

In the laboratory, individual housing of male mice who otherwise show aggression is common practice. Because mice are a social species, the question arises whether this procedure is right from the animals' point of view. This study tested the preference of subordinate animals for their dominant cagemate, and vice versa, and the preference of subordinate animals for an unknown subordinate partner. Experiments that allowed male mice with different histories to choose either an inhabited or an empty cage have shown that the mice preferred the proximity of another male over individual housing. No differences in this respect were found between dominant and subordinate males, or between littermates and nonlittermates. The preference was most obvious when mice who were previously housed together were tested. The study concludes that separation and single housing for mice are not attractive solutions for overcoming aggression in group-housed male mice and that alternative approaches, such as improving the housing conditions, should be explored as a way of tempering intermale aggression.     

Do Male Mice Prefer or Avoid Each Other's Company? Influence of Hierarchy,Kinship, and Familiarity

In the laboratory, individual housing of male mice who otherwise show aggression is common practice. Because mice are a social species, the question arises whether this procedure is right from the animals' point of view. This study tested the preference of subordinate animals for their dominant cagemate, and vice versa, and the preference of subordinate animals for an unknown subordinate partner. Experiments that allowed male mice with different histories to choose either an inhabited or an empty cage have shown that the mice preferred the proximity of another male over individual housing. No differences in this respect were found between dominant and subordinate males, or between littermates and nonlittermates. The preference was most obvious when mice who were previously housed together were tested. The study concludes that separation and single housing for mice are not attractive solutions for overcoming aggression in group-housed male mice and that alternative approaches, such as improving the housing conditions, should be explored as a way of tempering intermale aggression.     

The effect of housing and environmental enrichment on stereotyped behavior of adult vervet monkeys (Chlorocebus aethiops)

Little information is available on the response of vervet monkeys to different housing conditions or on the suitability of enrichment devices or methods for vervet monkeys. In this study, the authors evaluated the occurrence of stereotyped behavior in adult vervet monkeys under various conditions of housing and enrichment. The variables included cage size, cage level (upper or lower), enrichment with a foraging log, enrichment with an exercise cage and presence of a mate. The authors first determined the incidence of stereotyped behavior in captive-bred, singly housed adult female and male vervet monkeys. They then exposed monkeys to different housing and enrichment situations and compared the incidence of stereotyped behavior among the monkeys. The authors found that more females than males engaged in stereotyped behavior and that females, on average, engaged in such behavior for longer periods of time than males. Stereotyped behavior was most often associated with a small, single cage. The average amount of observed stereotyped activity in monkeys housed in a small cage was significantly lower when the monkeys had access to either a foraging log or an exercise cage. Stereotyped behavior was also lower in female monkeys that were housed (either with a male or without a male) in a larger cage. The least amount of abnormal behavior was associated with the largest, most complex and enriched housing situation. Males and females housed in cages on the lower level of two-level housing engaged in more stereotyped behavior than did monkeys housed in the upper level, regardless of the presence or type of enrichment provided.     

Rapid effects of estradiol on male aggression depend on photoperiod in reproductively non-responsive mice

In three genuses and four species of rodents, housing in winter-like short days (8L:16D) increases male aggressive behavior. In all of these species, males undergo short-day induced regression of the reproductive system. Some studies, however, suggest that the effect of photoperiod on aggression may be independent of reproductive responses. We examined the effects of photoperiod on aggressive behavior in California mice (Peromyscus californicus), which do not display reproductive responsiveness to short days. As expected, short days had no effect on plasma testosterone. Estrogen receptor alpha and estrogen receptor beta immunostaining did not differ in the lateral septum, medial preoptic area, bed nucleus of the stria terminalis, or medial amygdala. However, males housed in short days were significantly more aggressive than males housed in long days. Similar to previous work in beach mice (Peromyscus polionotus), estradiol rapidly increased aggression when male California mice were housed in short days but not when housed in long days. These data suggest that the effects of photoperiod on aggression and estrogen signaling are independent of reproductive responses. The rapid action of estradiol on aggression in short-day mice also suggests that nongenomic mechanisms mediate the effects of estrogens in short days.     

Factors affecting pair compatibility in captive kangaroo rats,Dipodomys heermanni

Captive propagation is a critical component of the Morro Bay Kangaroo Rat Recovery Plan, but past attempts to breed this and other kangaroo rat species have had mixed success. In three experiments using a closely related surrogate species, the Lompoc kangaroo rat, we evaluated the effects of familiarity and long-term housing experience on the behavior of captive males and females during dyadic encounters in an attempt to devise husbandry methods most conducive to reproduction. Females exhibited less aggression with and were more likely to allow physical contact with familiar males, provided the males had had previous social experience, such as that provided by living in close sensory contact with female conspecifics. Socialized males (those housed adjacent to females, separated from them by a wire mesh screen) were cautious, rather than persistent, when interacting with unfamiliar or anestrous females. Males housed in isolation from conspecifics were persistent whether or not they were familiar to the female. Pairs with very long periods of familiarity exhibited more nonaggressive contact than newly acquainted pairs. Results suggest that housing structures allowing longterm sensory contact between potential mates may improve breeding success in kangaroo rats and other solitary, aggressive species. © 1995 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Impact of IVC housing on emotionality and fear learning in male C3HeB/FeJ and C57BL/6J mice

Housing conditions are known to influence laboratory animal behavior. However, it is not known whether housing mice in individually ventilated cages (IVCs) to maintain optimal hygienic conditions alters behavioral baselines established in conventional housing. This issue is important with regard to comparability and reproducibility of data. Therefore, we investigated the impact of IVC housing on emotionality and fear learning in male C3HeB/FeJ (C3H) and C57BL/6J (B6J) mice housed singly either in conventional type II cages with wire bar lids (Conventional), or in IVCs of the same size, but with smooth, untextured lids (IVC classic), thus acoustically attenuated from external stimuli and with limited climbing facilities compared to Conventional. To evaluate the role of climbing, additional mice were kept in IVCs with lids having wire bars ("grid") added to the inner surface (IVC grid). Spontaneous behavior, sensorimotor behavior, and fear learning were measured. IVC housing reduced activity and enhanced anxiety-related behavior in both strains, whereas grooming latency was reduced in B6J only. IVC housing increased Acoustic Startle Response in C3H but not in B6J mice. The "grid" did not compensate for these IVC housing effects. In contrast, B6J mice in IVC grid performed best in fear potentiated startle while B6J mice in IVC classic performed the worst, suggesting that climbing facilities combined with IVC housing facilitate FPS performance in singly-housed B6J males. Our data show that IVC housing can affect behavioral performance and can modulate behavioral parameters in a general and a strain-specific manner, thus having an impact on mouse functional genomics.     

Cooperative social coordination and aggression in male laboratory rats: effects of housing and testosterone

A cooperative behavior, coordinated shuttling by pairs of laboratory rats in a rectangular chamber, can be influenced strongly by an interaction between housing and sex. Males and females learn readily when housed together socially, but individual housing ("isolation") causes severe deficits selectively in males. The aim of the present study was to examine the role of testosterone in the differential effects of housing on cooperation learning. Males of a Sprague-Dawley derived strain were housed socially or individually and treated daily in one of three ways (six groups, n = 6 per group): (1) castrated, injected with oil vehicle (without testosterone); (2) castrated, injected with 500 micrograms testosterone propionate (exogenous TP); and (3) sham operated, injected with oil (intact, endogenous testosterone). Socially housed pairs learned readily in all treatment groups, using strategies of coordination in which stereotyped contact or aggressive interactions were interpolated. Individual housing was associated with a deficit, but only in the TP-treated and intact groups in which some pairs either did not learn or performed poorly. The deficit was associated with violent fighting and extreme and stable differentiation into dominants and subordinates, the latter exhibiting prolonged freezing. Oil-treated castrates, when housed individually, were unimpaired and actually surpassed their socially housed counterparts on some measures. Their success was associated with an increase only in low-level aggression. The housing-hormone interaction in male rats suggests that testosterone influences the capacity to develop cooperative behavior by modulating both aggression and its consequences for the relationship between partners. The use of social interaction models, including cooperation, for the study of behavior-hormone interactions was also discussed.     

Influence of environmental enrichment and handling on the acute stress response in individually housed mice

In this study we investigated the effect of environmental enrichment and handling on the acute physiological stress response caused by short periods of restraint in individually housed female mice. Heart rate (HR) and body temperature (BT) were measured by radiotelemetry and compared with plasma corticosterone (pCORT) levels. Also, postmortem thymus weight and tyrosine hydroxylase (TH) activity were assessed. The acute stress response was seen in both HR and BT. Enrichment and handling were found to increase rather than decrease this stress response, but pCORT values, measured 90 min after restraint, suggested a lower stress response in the enriched groups. No effect was found with thymus weight or TH as parameters.     

The use of radiotelemetry to assess the time needed to acclimatize guineapigs following several hours of ground transport

The objective of this study was to investigate the effect of ground transportation on guineapigs. Physiological parameters, i.e. heart rate (HR), body temperature (BT) and activity (ACT), were measured before and after transport, using previously implanted radiotelemetry transmitters. Body weight was measured before and after transport. After a postsurgical recovery period and data recording at the breeder's facility, the animals were transported for 2.25 h (Group 1) and for 7.5 h (Group 2) to a different animal facility. Data collection started immediately after arrival at the second animal facility. All parameters measured changed significantly after transport. These results suggest that a 10- to 12-day period is required for guineapigs to return to pre-transport levels of HR, BT and ACT.     

Changes in Paternal Responsiveness of Prairie Voles (Microtus ochrogaster) in Response to Olfactory Cues and Continuous Physical Contact with a Female

In mammals, paternal care is rarely displayed, and we know little about the mechanisms regulating this behavior. Prairie voles (Microtus ochrogaster) are ideal mammals for the study of paternal behavior because they are a monogamous, bi‐parental species that is easily raised in the laboratory. Paternal responsiveness occurs at moderate levels in sexually‐naive voles and is heightened following a short cohabitation period of 72 h with a female. To determine how increased levels of paternal care are maintained after the initial cohabitation period, we tested the paternal behavior of males that were housed in isolation, were in physical contact with a female, or were exposed to various olfactory cues. The results indicate that the absence of odor cues from a female did not diminish the male’s motivation to care for infants following the initial cohabitation period. In contrast, odor cues from a male appeared to negatively influence the male’s paternal tendencies. The data also show that males that had continuous physical contact with a female spent more time responding paternally and more time hovering over the young compared to males that were housed alone. Together, these results suggest that although paternal behavior is maximized in response to continuous physical contact with females, olfactory cues may not be necessary for the maintenance of heightened paternal behavior.     

Comparing the relative benefits of grooming-contact and full-contact pairing for laboratory-housed adult female Macaca fascicularis

Tactile social contact is the most effective form of environmental enrichment for promoting normal behavior in captive primates. For laboratory macaques housed indoors, pair housing is the most common method for socialization. Pairs can be housed either in full contact (FC), or in protected contact (PC). At Washington National Primate Research Center, PC is provided by grooming-contact (GC) cages whereby two partners are housed individually in adjacent cages with access to each other through widely spaced vertical bars. Grooming-contact has been used to accommodate research protocol restrictions and improve the likelihood of compatibility for various pairings, in part by enabling male-female pairs. This study compares the benefits between the two housing types by video recording 14 pairs of adult female Macaca fascicularis in four sequential housing phases following an ABBA design: baseline grooming-contact, full contact shortly after introduction, 1-month-later full contact, and after reversion to grooming-contact. Prior to this study, pairs had been housed compatibly in GC. Twelve of the 14 long-term pairs transitioned successfully to full contact and data presented exclude the two failed pairs. Allogrooming increased significantly when pairs first switched from GC to FC (P = 0.018), but the effect did not last through the on 1-month-later FC phase suggesting that the initial improvement in affiliative behavior was a transitory novelty response that did not persist. Self-grooming significantly decreased between the first GC and first FC phases (P = 0.016), likely due to redirected allogrooming. Non-contact affiliative behavior towards partner or other conspecifics in the room did not differ, nor did agonism towards partner or others in the room. Occurrence of abnormal, tension, manipulation, miscellaneous active, and inactive behaviors did not differ significantly across housing phases. Proximity measurements indicated that pairs were significantly out of arm's reach more often in protected contact than when in full contact (P ≤ 0.02). Proportion of time spent in physical contact significantly increased between the first GC and first FC phases (P = 0.002), but subsequently declined. For both FC phases, partners chose to spend about 50% of their time in the same cage. Few behavioral improvements were seen after pairs switched to full contact and no negative effects came of reversion to grooming contact. This study suggests that tactile contact provided through widely spaced bars (grooming-contact) is a viable alternative to full contact housing for adult female longtailed macaques. It provides a degree of social housing while allowing both partners choice and control, key concepts in contemporary animal welfare guidelines.     

Heterosexual housing increases the retention of courtship behavior following castration and elevates metabolic capacity in limbic brain nuclei in male whiptail lizards,Cnemidophorus inornatus

In male vertebrates the display of courtship behavior depends on the presence of testicular androgens. However, social experiences in adulthood can alter the hormonal dependence of courtship behavior in a variety of species, and we have previously proposed that these behavioral changes are linked to changes in neural metabolic capacity (cytochrome oxidase activity). Here we investigated the effects of prior social experience (housing with females vs housing in isolation) on the retention of courtship behavior following gonadectomy and on cytochrome oxidase (CO) activity in male little striped whiptail lizards, Cnemidophorus inornatus. In Experiment 1, we found that males that were previously housed with females (HWF males) continued to display courtship behavior longer after castration than males previously housed in isolation (ISOLATE males). This is similar to the behavioral plasticity found in rodents and cats. On the other hand, courtship behavior while gonadally intact was indistinguishable between HWF and ISOLATE males. Because all males were housed individually following castration, the difference is due to different social experiences prior to castration. In Experiment 2, we found that gonadally intact HWF males had significantly elevated CO activity in the preoptic area, amygdala, and anterior and ventromedial hypothalamic areas relative to intact ISOLATE males. No significant differences in metabolism were found in the lateral septum, lateral hypothalamus, and habenula or in hindlimb muscle, suggesting that the increase in metabolism is specific to brain nuclei involved in courtship behavior. Altogether, this demonstrates that elevations in metabolic capacity correlate with experience-dependent increases in robustness to castration.     

Diurnal fluctuations of heart rate, body temperature and locomotor activity in the house musk shrew (Suncus murinus).

Diurnal fluctuations of heart rate (HR), body temperature (BT) and locomotor activity (LA) in the unanaesthetized and unrestrained house musk shrew (Suncus murinus) were studied using a telemetry system. Six adult male shrews (Jic:SUN) weighing 60-70 g were used in the present study. They were housed under conditions of 24 C and a 12/12-hr light-dark cycle. HR, BT and LA were recorded over 10 days, following the post-implantation period (10 days or more) of the telemetric transmitter. A clear nocturnal rhythm of LA was shown, while intermittent and short-term LA were shown during the light period. The mean HR was 323.5 +/- 8.8 bpm in the light period and 354.3 +/- 5.2 bpm in the dark period, and the fluctuation of HR showed a nocturnal pattern. A nocturnal pattern was also observed in BT fluctuation, and all animals lowered their body temperature from 35-37 C to approximately 30 C or below, mostly during the light period. The fall of body temperature progressed over 2-3 hr, and then rose to the baseline temperature rapidly within approximately 30 min. While the body temperature fell, HR markedly decreased to approximately 100 bpm. These results suggest that the shrew has unique physiological properties in maintaining metabolic balance which are anticipated to be caused by the dramatic alteration of the autonomic nervous function.     

Aggression and preputial gland of male mice affected by the presence of other males

The level of aggressiveness and the weight of preputial gland and testis in male mice (Mus musculus) were influenced by housing condition, especially by the presence of cohabitant males. In this study, the relation between aggressiveness and the preputial gland and testis weight was studied for various housing conditions. The mouse individually housed in a cage that was linked to another cage containing another male separated by wire net was more aggressive than isolated or paired mice. The preputial gland weight also showed the same tendency, suggesting that the odor from other males promotes pituitary-gonadal activity in males, and that long-term cohabitance inhibits it.     

Social buffering in adult male rhesus macaques (Macaca mulatta): Effects of stressful events in single vs. pair housing

Background The purpose of this study was to test whether long‐term pair housing of male rhesus macaques ameliorated negative responses to stressful events that can occur in the course of routine husbandry or research procedures. Methods Twelve singly housed individuals were videotaped during two potentially stressful events before and after social introduction into pairs. During each stressor, abnormal behavior and anxiety‐related behavior were quantified from videotape. Results When visually exposed to the restraint and anesthesia of other monkeys, subjects showed significantly reduced frequencies of abnormal behavior when pair‐housed in comparison to their reactions when housed singly. Noisy and disruptive conversation between technicians standing immediately in front of the subjects’ cage did not elicit the same reduction in abnormal behavior. Neither test showed a significant difference across housing settings for anxiety‐related behaviors. Conclusions These findings suggest that pair housing buffers adult male rhesus macaques against common stressors in the laboratory setting.     

Effect of Group vs. Single Housing on Phenotypic Variance in C57BL/6J Mice

Objective: To determine if group housing affects the variance of body composition parameters in a highly inbred mouse strain. Research Methods and Procedures: Thirty 3‐week‐old male C57BL/6J mice were obtained from the Jackson Laboratory. Fifteen mice were housed individually, and 15 mice were housed in groups of 5/cage. Animals were fed ad libitum and maintained in the same room under a 12:12‐hour light/dark photoperiod at 22 °C for 9 weeks. Animals were killed, and fat mass, soft‐lean tissue mass, bone mineral density (BMD), and bone mineral content (BMC) were determined by DXA. At necropsy, weights of the paired epididymal fat pads, paired retroperitoneal fat pads, right inguinal fat pad, liver, kidneys, paired testes, and seminal vesicles were obtained. Results: Relative to mice housed singly, group‐housed mice showed significantly greater variance in percentage of body fat, testes weight, and BMC. Group‐housed mice tended to show greater variance in liver weights and BMD. Mice housed singly were smaller, had less soft‐lean tissue mass and BMC, and lower BMD when compared with group‐housed mice. Discussion: These results suggest that with respect to body composition parameters, mice housed singly are more similar to one another than are group‐housed mice, most likely because of a reduction in environmental (predominately behavioral/social) effects. Thus, mice housed singly may be more representative of genotypic effects on body composition than group‐housed mice. Whether other inbred strains of mice show similar responses to housing condition is unknown.