Effects of pair-housing after social defeat experience on elevated plus-maze behavior in rats

Social defeat experience in male rats causes an increase in anxiety-like behavior in the elevated plus-maze. Some researchers have suggested that housing rats socially following social defeat attenuates and/or prevents an increase in anxiety-like behavior. However, many other studies have shown that individual housing per se enhances anxiety-like behavior even in the absence of social defeat. In the present study, we assessed the relative contributions of the experience of social defeat and housing conditions on animals’ performance in the elevated plus-maze. Rats were assigned to one of the following four groups: defeat/individual housing, defeat/pair-housing, non-defeat/individual housing, and non-defeat/pair-housing. The elevated plus-maze test was conducted 2 weeks after the defeat experience. Our results demonstrated that the defeat/individual housing group spent less time than the other groups in the open arms: moreover, there were no differences between the other three groups. These results confirm the claim that the group-housing of rats prevents an increase in anxiety-like behavior caused by defeat.     

Sensitiveness to social stress in female rats with alteration of the pituitary-adrenal axis stress reactivity

The sensitiveness of female rats to social stress induced by increasing group density, was investigated. It was shown that female rats were housed in groups of 9-10 animala per cage in pubertal period and demonstrated significant alteration of oestrous cycle duration and anxiety level. This housing condition increased basal level of corticostcrone in prenatal stressed female rats who have high stress reactivity of the hypothalamic-pituitary-adrenal axis, as well as a more profound effect on anxiety level and oestrous cycle. Prenatal stressed rats retained impairment of oestrous cycle and behavior after optimization of housing condition, whereas control rats demonstrated normalization of oestrous cycle duration and anxiety level. These data suggest that high stress reactivity females rats are more sensitive to crowding-induced stress.     

Social Environment Affects Peripheral Oxytocin and Cortisol during Stress Responses in Guinea-Pigs

Numerous studies have demonstrated interactions between oxytocin (OT) secretion, adrenal activity, an animal's social environment, and stress responses. In the present study, we hypothesized that partner preference and pair bonding cause increased peripheral OT, which down‐regulates the adrenal and behavioral response in stress. In addition, we tested whether these interactions depended on sex, the social environment of the individual, or the type of stressor. Experiments were carried out on guinea‐pigs held in sexual‐pairs or stressed by isolation. Among the paired individuals choice tests were carried out to document partner preference. Female preference for a male was expressed by spatial cohesion. Stress responses to abiotic stimuli were examined and compared between isolated and cohabited animals with or without preference. Results show that OT of cohabited animals was significantly higher than during isolation. OT levels were further increased in males preferred by females. Cortisol (CORT) levels were elevated in isolated animals. There were no significant differences between pairs with and without female preference. Behaviorally, partner preferences were expressed by high amounts of tactile contact. The stress‐induced behavioral immobility response after exposure to a noise stressor was significantly reduced in preferred males and to a lesser extent in their female partners. Only females with preferences showed an endocrine stress response. Their levels of OT increased. There was no consistent post‐stressor release of CORT. The data indicate that the social environment of an individual, here expressed as preference or isolation, influences peripheral OT secretion. Behavioral stress responses were similarly affected by social factors without a clear involvement of peripheral CORT or OT.     

Contrasting effects of opposite- versus same-sex housing on hormones,behavior and neurogenesis in a eusocial mammal

Competitive interactions can have striking and enduring effects on behavior, but the mechanisms underlying this experience-induced plasticity are unclear, particularly in females. Naked mole-rat (NMR) colonies are characterized by the strictest social and reproductive hierarchy among mammals, and represent an ideal system for studies of social competition. In large matriarchal colonies, breeding is monopolized by one female and 1–3 males, with other colony members being socially subordinate and reproductively suppressed. To date, competition for breeding status has been examined in-colony, with female, but not male, aggression observed following the death/removal of established queens. To determine whether this sex difference extends to colony-founding contexts, and clarify neural and endocrine mechanisms underlying behavioral change in females competing for status, we examined neurogenesis and steroid hormone concentrations in colony-housed subordinates, and NMRs given the opportunity to transition status via pair-housing. To this end, Ki-67 and doublecortin immunoreactivity were compared in the hippocampal dentate gyrus (DG) and basolateral amygdala (BLA) of colony-housed subordinates, and subordinates housed with a same-sex (SS) or opposite-sex (OS) conspecific. Results suggest that OS pairing in eusocial mammals promotes cooperation and enhances hippocampal plasticity, while SS pairing is stressful, resulting in enhanced HPA activation and muted hippocampal neurogenesis relative to OS pairs. Data further indicate that competition for status is confined to females, with female-female housing exerting contrasting effects on hippocampal and amygdalar neurogenesis. These findings advance understanding of social stress effects on neuroplasticity and behavior, and highlight the importance of including female-dominated species in research on aggression and intrasexual competition.     

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.     

Social isolation and the inflammatory response: sex differences in the enduring effects of a prior stressor

Numerous epidemiological studies have demonstrated an association between persistent social isolation and "all-cause" morbidity and mortality. To date, no causal mechanism for these findings has been established. Whereas animal studies have often reported short-term effects of social isolation on biological systems, the long-term effects of this adverse psychological state have been understudied. This is the first animal study to examine the effects of long-term social isolation from weaning through young adulthood on an innate inflammatory response linked to numerous disease processes. Results presented here offer a plausible link between vulnerability to disease and social neglect. For socially isolated male and female Sprague-Dawley rats, a naturally gregarious species, formation of a granuloma in response to a subcutaneous injection of carrageenin (seaweed) was significantly delayed compared with the response of animals housed in single-sex groups of five. Significant sex differences, however, emerged when an acute prior stressor was superimposed on the experience of chronic social isolation. In this context, isolated females produced a more robust inflammatory response than isolated males. This sexual dimorphism at the nexus of chronic social isolation, acute stress, and inflammatory processes may account for the observation in humans that men with low levels of social integration are more vulnerable to disease and death than women.     

Sex differences in compatibility of pair-housed adult longtailed macaques

This research was designed to evaluate the effects of same-sex pair housing on the psychological well-being of adult wild-born longtailed macaques (Macaca fascicularis). We studied behavioral compatibility and stress as measured by urinary cortisol excretion in 15 pairs of each sex. Before they were housed together, the pairs were categorized by noncontact pairedpreference testing as preferred, nonpreferred, or randomly assigned partners. Every aspect of data analysis indicated that the success of pairing was strongly related to gender. Whereas 100% of female pairs were compatible, only eight of the 15 male pairs were still together after two weeks, and only five (33%) showed a degree of compatibility resembling that of females. The psychological well-being of virtually all females seemed to be improved during the physical contact paired-housing conditions; they spent more than one-third of the day engaged in social grooming. Paired adult males had much lower interaction rates than adult females. On average, males were initially somewhat stressed by the introduction to a cagemate as indicated by increased urinary cortisol excretion. The noncontact preference testing procedure was no more predictive of pair success than random assignment. For males, the presence of fighting combined with the absence of grooming during the first 90 min opportunity for physical contact (“introduction”) was associated with pair incompatibility, but not to a statistically significant extent. For research protocols permitting social grouping of this species, the social contact requirement of the USDA Animal Welfare Rules usually can be met for adult females by pair housing. For males, pairing with other adult males often is unsuccessful; by our estimates, at least 20% of males cannot be pair-housed with other males. These sex differences in response to same-sex adults are consistent with the known socioecology of macaques. Further research is necessary to determine whether adult males have a lower need for social contact than females, or whether their needs are better met by other types of social contact. © 1994 Wiley-Liss, Inc.     

Solitary is not Asocial: Effects of Social Contact in Kangaroo Rats (Heteromyidae: Dipodomys heermanni)

Social interactions in solitary animals, such as Heermann's kangaroo rat ( Dipodomys heermanni ), have been little studied. In three experiments, the effect of social housing on levels of aggression and maintenance of estrous cycling was studied as part of a captive breeding program for an endangered form of this species. Expt 1 demonstrated that mixed-sex pairs of rats that were neighbors in social housing were no friendlier during staged encounters than unfamiliar pairs also housed socially. In expt 2, rats that had been isolated for several months were transferred to social housing and paired at weekly intervals with an opposite-sex neighbor. Initial encounters were highly aggressive and socialized partners retreated from previously isolated rats more often than vice versa, regardless of sex. By the third week, encounters resembled pairings of fully socialized rats, as in expt 1. Thus, social exposure may produce a general socializing effect rather than promote familiarity between specific individuals. In expt 3, the clear, perforated barriers that separated rats in social housing were replaced with solid, opaque barriers for 6 wk. Estrous cycle length immediately doubled and cycles of most females were disrupted for months. Taken together, the results reveal the influential role of social contact in this solitary species and highlight the need for more such work both for developing comprehensive theories of sociality and for guiding captive propagation efforts.     

The Effect of Social Stress on Chronic Pain Perception in Female and Male Mice

The current investigations on social stress primarily point to the negative health consequences of being in a stressful social hierarchy. The repetitive nature of such stressors seems to affect behavioral response to pain both in rodents and humans. Moreover, a large discrepancy in the possibility of social stresses affecting pain perception in the two genders exists. The present study examined the effect of chronic social stress on nociceptive responses of both sexes by implementing of food deprivation, food intake inequality and unstable social status (cage-mate change every 3 days) for a period of 14 days in 96 Balb/c mice. In this regard we injected 20 µl formalin 2% into the plantar surface of hind paw at the end of stress period and scored pain behaviors of all subjects, then serum concentrations of proinflammatory cytokines were measured. Our results showed that there was significant difference in chronic phase of formalin test following implementation of food deprivation and inequality (P<0.05) as compared to control group, so that pain perception was decreased considerably and this decline in inequality exposed subjects was well above isolated ones (P<0.05); whereas unstable social situation did not affect pain perception. Moreover, IL-1 and IL-6 concentrations in serum of stressed mice of both genders were well above control group (p<0.05). Finally, despite chronic pain perception in control and unstable male subjects was larger than females; the decrease of chronic pain perception in male stressed animals (poverty and inequality experienced subjects) was much more than stressed females. These results revealed that although food deprivation and social inequality can induce hypoalgesia, some socioeconomic situations like social instability don''t affect pain sensation, whereas there were similar increases of proinflammatory cytokines level in all socially stressed subjects. In addition, males display larger hypoalgesic responses to inequality as compared with females.     

Annual physiological changes in individually housed squirrel monkeys (Saimiri sciureus)

This study investigated whether annual changes in physiology occur in individually housed squirrel monkeys (Saimiri sciureus). Physiological measures were monitored for 20 months. Over the course of the study, all individually housed males and females exhibited clear annual changes in gonadal and adrenal hormone levels, and males exhibited species‐typical changes in body weight. Females exhibited a typical pattern of hormonal changes, with elevations in gonadal steroids occurring during the same months as elevations in cortisol. Males, however, exhibited an atypical pattern, as elevations in hormone levels were not synchronized with each other; rather, elevations in testosterone occurred out of phase with changes in cortisol and body weight. The timing of annual events in individually housed subjects was compared to that in nearby social groups, in which the timing of the breeding season from year to year was determined by social group formations and was outside the naturally occurring breeding season. Elevations of ovarian and adrenocortical hormones in individually housed females were synchronized with indices of breeding in heterosexual social groups. Similarly, weight gain in males was associated with elevations in cortisol and, as with socially housed males, tended to precede seasonal breeding in the social groups. In contrast, annual testosterone elevations for individually housed males were not synchronized with breeding in nearby social groups. We conclude that direct physical interaction is not required for the annual expression of breeding readiness. Synchrony of seasonality among squirrel monkeys may be accomplished by distant social cues in females, but males may require physical interaction for complete synchrony of annual physiological changes. Am. J. Primatol. 47:93–103, 1999. © 1999 Wiley‐Liss, Inc.     

Effects of social and inanimate enrichment on the behavior of yearling rhesus monkeys

Certain types of inanimate environmental enrichment have been shown to positively affect the behavior of laboratory primates, as has housing them in appropriate social conditions. While social housing is generally advocated as an important environmental enhancement, few studies have attempted to measure the influence of social conditions on the effects of inanimate enrichment or to compare the relative merits of social and inanimate enhancements. In the present study, inanimate enrichment (predominately physical and feeding enhancements) resulted in increased species-typical behavior for socially restricted subjects. However, social enrichment (living in groups) appeared to be more beneficial for young rhesus monkeys, leading to increased species-typical activities and decreased abnormal activities. The behavior of one cohort of yearling rhesus monkeys (Macaca mulatta) housed in small peer groups was compared with the behavior of four yearling cohorts housed in single cages. Half the animals in each cohort received a three-phase enrichment program and the rest served as controls. Group-housed yearlings spent significantly more time feeding and exploring and significantly less time behaving abnormally, self-grooming, and drinking than did singly housed yearlings. Enriched subjects spent significantly more time playing by themselves, and significantly less time self-grooming and exploring than did controls. Among group-housed subjects only, there were no differences between enriched and control monkeys. Captive primates should be housed socially, whenever appropriate, as the first and most important step in an enrichment program, with the provision of inanimate enhancements being considerably less important. Limited resources for inanimate enrichment programs instead should be focused on those individuals who can not be housed socially. © 1996 Wiley-Liss, Inc.     

Juvenile social subjugation induces a sex-specific pattern of anxiety and depression-like behaviors in adult rats

Child abuse is the most significant environmental risk factor for the development of mood disorders, which occur twice as frequently in women as in men. To determine whether juvenile social subjugation (JSS) of rats induces mood disorder-like symptoms, we exposed 28 day-old male and female rats to daily aggressive acts from aggressive male residents. Each rat received pins, kicks, and dominance postures from the resident for 10 min per day for 10 days. When the rats were adults, we tested their anxiety- and depression-like behaviors. In addition, we measured circulating basal and stress-evoked corticosterone (CORT) levels, and weighed the adrenal glands. Although the amount of JSS was indistinguishable between males and females, females were nonetheless more severely affected by the experience. Subjugated females became immobile more quickly during forced swim tests, and made fewer investigatory approaches during the social interaction test than control females. Juvenile social subjugation increased closed arm time in the elevated plus maze of males and females, but the effect of social subjugation was greater in females. Finally, stress-evoked CORT levels were significantly higher, and adrenal gland weights were significantly heavier, in subjugated females relative to their controls and to subjugated males. Our results demonstrate that JSS increases depression- and anxiety-like behaviors and sensitizes the stress response system in a sex-specific manner.     

Effect of prenatal stress on the hormonal response to acute and chronic stress and on immune parameters in the offspring

The effect of prenatal stress on the time course of the corticosterone response to acute and chronic stress and on hematological and immunological parameters in the offspring were analized in the present study. Pregnant Sprague-Dawley rats were stressed daily for 2 hours during the last week of gestation, and female and male off-spring were studied during adulthood. Corticosterone response to acute immobilization stress was not significantly different in either control or prenatally stressed rats. However, after 10 days of immobilization stress the corticosterone response completely disappeared in the control animals but not in the prenatally stressed group: high levels of corticosterone were found during the first hour of stress, although they were lower than those found in acutely stressed rats. Adrenal hypertrophy in response to prenatal stress was observed in females but not in male offspring, and chronic stress only increased adrenal weights in the male control group. Prenatal stress decreased the total peripheral leukocyte count, altered its diferential count decreasing lymphocytes and increasing neutrophil and eosinhophil counts, and significantly reduced the percentage of peripheral lymphocyte T CD8+ subset in male offspring. Chronic stress also reduced the percentage of the peripheral T CD8+ lymphocyte subset in the control group but not in the prenatally stressed group. These results suggest that the exposure to stress during pregnancy alters the adaptative response of the hypothalamus-pituitary-adrenocortical axis to chronic stress and presumably the immune competence in the offspring.     

Effect of Post-Weaning Individual Housing on Autonomic Responses in Male Rats to Sexually Receptive Female Rats

Post-weaning individual housing induces significant alterations in the reward system of adult male rats presented with sexually receptive female rats. In this study, we examined the effects of post-weaning individual housing on autonomic nervous activity in adult male rats during encounters with sexually receptive female rats to assess whether different affective states depending on post-weaning housing conditions are produced. Changes in heart rate and spectral parameters of heart rate variability indicated that in post-weaning individually housed male rats, both sympathetic and parasympathetic activity increased with no change in the sympathovagal balance, while in post-weaning socially housed male rats, both sympathetic and parasympathetic activity decreased with a predominance of parasympathetic activity. These two patterns of shifts in sympathovagal balances closely resembled changes in autonomic nervous activity with regard to classical appetitive conditioning in male rats. The autonomic changes in male rats housed individually after weaning corresponded to changes associated with the reward-expecting state evoked by the conditioned stimulus, and the autonomic changes observed in male rats housed socially after weaning corresponded to changes associated with the reward-receiving state evoked by the unconditioned stimulus. These results suggest that different affective states were induced in adult male rats during sexual encounters depending on male–male social interactions after weaning. The remarkable change caused by post-weaning individual housing may be ascribed to alteration of the reward system during sexual encounters induced by deficiency of intermale social communication after weaning.     

Altered stress responsiveness and hypothalamic‐pituitary‐adrenal axis function in male rat offspring of socially isolated parents

Social isolation in male rats at weaning results in reduced basal levels of the neuroactive steroid 3α,5α‐tetrahydroprogesterone (3α,5α‐TH PROG) in the brain and plasma as well as increased anxiety‐like behavior. We now show that socially isolated female rats also manifest a reduced basal cerebrocortical concentration of 3α,5α‐TH PROG as well as an anxiety‐like profile in the elevated plus‐maze and Vogel conflict tests compared with group‐housed controls. In contrast, despite the fact that they were raised under normal conditions, adult male offspring of male and female rats subjected to social isolation before mating exhibited an increased basal cerebrocortical level of 3α,5α‐TH PROG but no difference in emotional reactivity compared with the offspring of group‐housed parents. These animals also showed an increased basal activity of the hypothalamic‐pituitary‐adrenal axis as well as reduced abundance of corticotropin‐releasing factor in the hypothalamus and of corticotropin‐releasing factor receptor type 1 in the pituitary. Moreover, negative feedback regulation of hypothalamic‐pituitary‐adrenal axis activity by glucocorticoid was enhanced in association with up‐regulation of glucocorticoid receptor expression in the hippocampus. There was also attenuation of corticosterone release induced by foot‐shock stress in the offspring of socially isolated parents. The increase in the brain concentration of 3α,5α‐TH PROG induced by acute stress was also blunted in these animals. Our results thus show that a stressful experience before mating can influence neuroendocrine signaling in the next generation.     

Daily fecal sex steroid hormonal changes and mating success in captive female cheetahs (Acinonyx jubatus) in Japan

Daily fecal estrogen and progestin concentrations were measured by enzyme immunoassay in five female cheetahs (Acinonyx jubatus) for 4-6 months. The animals were housed under different conditions: (1) a female always housed in a group including one or more males; (2) two females isolated individually for short or long periods; (3) the other two females housed together. These females were separately housed with males for mating around the time of the estrogen peaks. The hormone profiles were similar in all five females regardless of the housing conditions. However, only the female that had been isolated from other cheetahs for over a year mated and reproduce cubs successfully, whereas the remaining four did not (one was isolated for only 6 weeks, another was always housed with males and the other two were housed together). In all females, the estrogen peaks were obtained at regular intervals of approximately 8-15 days. Unlike estrogen, the progestin concentrations were always low in all females except during pregnancy and they did not increase following the estrogen surges. These results showed that female cheetahs are typically reflex ovulators and female receptiveness may not be reflected to her hormonal states. It was also suspected that individual housing and long-term separation are advantageous for breeding this wild cat in captivity, mimicking the ecological/behavioral patterns in the wild, though housing condition might have no effect on the estrous cycle.     

Improved behavioral indices of welfare in continuous compared to intermittent pair-housing in adult female rhesus macaques (Macaca mulatta)

Limiting opportunities for captive nonhuman primates (NHPs) to express species-specific social behaviors may disrupt the adaptive drive for social companionship and may lead to increases in coping behaviors and inactivity. While captive NHPs show improved welfare when moving to pair-housing from single-housing, the impact of daily separation of pair-mates, as is implemented in intermittent pair-housing, is not fully understood. We compared behavioral indices of welfare exhibited by adult female rhesus macaques (Macaca mulatta) in two conditions: (1) intermittent pair-housing, involving daily overnight separation of pair-mates, and (2) continuous pair-housing, involving little separation of pair-mates. A within-subjects study design tested two groups of females experiencing both pairing conditions in an alternate order, switching either from continuous to intermittent pair-housing, or from intermittent to continuous pair-housing. Behavioral observations, recording activity state, self-directed, abnormal, and social behaviors, were conducted at midday when all females were paired, and in the afternoon when intermittent pairs were separated. Females exhibited higher levels of inactivity and self-directed behavior when separated due to intermittent pair-housing in comparison to continuous pair-housing. In addition, intermittently paired females showed higher levels of grooming and other types of affiliation when paired, than during the same time frame when they were continuously paired. These results suggest that females in the continuous presence of a social partner experience improved levels of activity and do not need to elevate levels of behavioral coping mechanisms (e.g., self-scratching, increased affiliation) as they receive the benefits associated with social companionship consistently throughout the day. Overall, this study provides the first evidence that continuous pair-housing affords better welfare than intermittent pair-housing in adult female rhesus macaques. Pair-housing options, such as continuous pairing, that reduce reliance on behavioral coping mechanisms and promote adaptive social behavior throughout the entirety of the day should be prioritized over husbandry care scheduled for convenience.     

Facilitation of hypothalamic-pituitary-adrenal responses to novel stress following repeated social stress using the resident/intruder paradigm

Our goal in these studies was to characterize some specific aspects of hypothalamic-pituitary-adrenal (HPA) activity in rats exposed to repeated social stress. We used a modification of the resident/intruder paradigm in which male intruder rats were subjected to defeat and then separated from the resident by an enclosure for a total of 30 min on Day 1. On Days 2-7, intruder rats were exposed to different resident rats every day through a wire mesh enclosure for 30 min in order to minimize injurious physical contact between the two rats. The intruder rats gained significantly less weight than controls over the 7-day period of stress though basal corticosterone levels and adrenal and thymus weights were not significantly different between the two groups. On Day 8, repeatedly stressed rats exhibited facilitation of HPA responses to novel restraint compared to controls but no differences in negative feedback sensitivity to dexamethasone (0.05 or 0.2 mg/kg) were observed. Thus, the HPA axis of socially stressed rats remains responsive to a stimulus that has never been encountered. Using this type of repeated presentation to an aggressive resident allows us to examine the neuroendocrine and behavioral consequences, and their underlying neural mechanisms, of exposure to a stressor that is social in nature and naturalistic for rodents.     

The Andean bear alopecia syndrome may be caused by social housing

The Andean bear alopecia syndrome is a progressive and chronic condition documented in ex situ populations. Recent advances focus on treating symptoms, not preventing future cases. We therefore explored the epidemiology of this syndrome through an analysis of husbandry and veterinary conditions of 63 Andean bears (26M:37F) housed in North and South American zoos and other ex situ circumstances. We had the most complete information for the North American population and found that 29% of females (n = 24) were affected. No males (n = 26) were affected. An analysis of generalized linear models indicated that three models were competitive in describing the occurrence of the condition (i.e., ΔAIC_c ≤ 2): the model including only the individual's sex (χ² = 13.41, df = 1, p < .001), the model including both individual sex and social housing status (χ² = 1.36, df = 2, p < .001), and the model including both individual sex and the expression of stereotypical behaviors (χ² = 13.82, df = 2, p = .001). Stereotypical behaviors were common among both males (50%, n = 26) and females (51.9%, n = 27) whether or not they were affected, but the syndrome was seen only in females who had been socially housed. Therefore, we suggest that the Andean bear alopecia syndrome is a symptomatic response to the long‐term social housing of bears that would otherwise not live socially. To prevent new cases, we recommend that female Andean bears be housed with adult conspecifics only when females choose to cohabitate.     

Social instability in adolescence differentially alters dendritic morphology in the medial prefrontal cortex and its response to stress in adult male and female rats

Adolescence is an important period for HPA axis development and synapse maturation and reorganization in the prefrontal cortex (PFC). Thus, stress during adolescence could alter stress‐sensitive brain regions such as the PFC and may alter the impact of future stressors on these brain regions. Given that women are more susceptible to many stress‐linked psychological disorders in which dysfunction of PFC is implicated, and that this increased vulnerability emerges in adolescence, stress during this time could have sex‐dependent effects. Therefore, we investigated the effects of adolescent social instability stress (SIS) on dendritic morphology of Golgi‐stained pyramidal cells in the medial PFC of adult male and female rats. We then examined dendritic reorganization following chronic restraint stress (CRS) with and without a rest period in adult rats that had been stressed in adolescence. Adolescent SIS conferred long‐term alterations in prelimbic of males and females, whereby females show reduced apical length and basilar thin spine density and males show reduced basilar length. CRS in adulthood failed to produce immediate dendritic remodeling in SIS rats. However, CRS followed by a rest period reduced apical dendritic length and increases mushroom spine density in adolescently stressed adult males. Conversely, CRS followed by rest produced apical outgrowth and decreased mushroom spine density in adolescently stressed adult females. These results suggest that stress during adolescence alters development of the PFC and modulates stress‐induced dendritic changes in adulthood.