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Aggressive behavior in female golden hamsters: Development and the effect of repeated social stress

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Abstract

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.

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... Although males and females did not differ in the overall rate of attacks and supine postures, juvenile forms of playful aggression peaked during PD29-35 in both males and females. These findings are consistent with reports in male rats and hamsters that attacks, particularly those directed at the head and neck, decrease with age (Pellis and Pellis, 1987;Taravosh-Lahn and Delville, 2004). However, a juvenile peak in the rate of attacks and pins is less clear in female hamsters. ...
... Open circles indicate males (n = 18) and closed circles indicate females (n = 18), although circles may represent more than one animal. (Guerra et al., 1992;Taravosh-Lahn and Delville, 2004). Overall, these findings indicate that the transition from play fighting to adult-like forms of aggression occurs earlier in female hamsters than in males. ...
... Adult females were also much more likely than males to show aggression toward a novel, same-sex intruder in adulthood. Together, these results are consistent with previous research showing that male hamsters display more social play than females as young juveniles, whereas females display more territorial aggression than males as adults (Huhman et al., 2003;Taravosh-Lahn and Delville, 2004). ...
Article
In several rodent species social play appears to be necessary for proper deployment of species-specific patterns of aggressive and reproductive behavior. Specifically, in male Syrian hamsters (Mesocricetus auratus), play has been linked to the development of adult aggression. We quantified several types of social play behavior in same-sex peer groups of Syrian hamsters three times per week for three consecutive weeks after weaning, which included postnatal days 22–42 (PD22 to PD42). Male hamsters increased playful contact during PD36-PD42, whereas females showed peak playful contact during PD29-PD35. These findings suggest that the motivation for social play increases during mid-adolescence in males, but dissipates in females. To investigate the effects of social play deprivation, one hamster per litter remained pair-housed with its mother for three weeks after weaning its littermates. In adulthood, both play-deprived and play-exposed animals received acute social defeat stress followed by social interaction testing. Play deprivation led to increased defeat-induced social avoidance in both males and females. In males, play deprivation increased fighting back during social defeat stress, whereas in females it reduced aggressive behavior during conditioned defeat testing. We suggest that social play deprivation disrupts neural circuits regulating aggression in a sex-specific manner, perhaps related to sex differences in territorial defense, but has similar effects on neural circuits regulating stress responsivity. Overall, these findings suggest that juvenile social play functions to promote coping with stress and appropriate social behavior in adulthood.
... Por outro lado, estudos mais recentes mostram que machos e fêmeas de hamster reagem de modo diferente ao estresse social. Enquanto a condição de derrotado modifica de maneira profunda e persistente o comportamento dos machos, inibindo totalmente a agressão territorial e estimulando a exibição frequente de comportamentos de submissão e defesa, não induz nenhuma alteração durável no comportamento agonístico das fêmeas Taravosh-Lahn;Delville, 2004). Em particular, elas se mostram muito menos propensas do que eles a estabelecer relações claramente polarizadas e estáveis entre dominante e dominada . ...
... Por outro lado, estudos mais recentes mostram que machos e fêmeas de hamster reagem de modo diferente ao estresse social. Enquanto a condição de derrotado modifica de maneira profunda e persistente o comportamento dos machos, inibindo totalmente a agressão territorial e estimulando a exibição frequente de comportamentos de submissão e defesa, não induz nenhuma alteração durável no comportamento agonístico das fêmeas Taravosh-Lahn;Delville, 2004). Em particular, elas se mostram muito menos propensas do que eles a estabelecer relações claramente polarizadas e estáveis entre dominante e dominada . ...
... On the other hand, more recent studies suggested sex differences in the reaction of Syrian hamsters to social stress. Whereas in males social defeat leads to profound and persistent behavioral changes, characterized by a total absence of territorial aggression and by the frequent display of submissive and defensive behaviors, it does not cause any long-lasting effect on the agonistic behavior of females Taravosh-Lahn & Delville, 2004). Specially, the group-housing-induced dominance hierarchy, which is stable in males, is unstable among females . ...
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Article
A flexibilidade da socialidade presente em muitas espécies sugere que muitos dos traços comportamentais e fisiológicos presentes em grupos sociais complexos possam existir em estado latente em indivíduos de espécies solitárias. Hierarquia de dominância e assimetria reprodutiva são traços característicos de espécies sociais. O hamster Sírio é um excelente modelo para o estudo do estresse social e dos seus efeitos fisiológicos e comportamentais. Na presente pesquisa foram enfocados os efeitos do alojamento em grupo antes e no início da gestação na fêmea de hamster Sírio. Investigou-se se o estresse social produz algum grau de assimetria reprodutiva nesta espécie solitária e se o sucesso reprodutivo e o comportamento materno das fêmeas variam em função do seu status social. Dois experimentos foram realizados envolvendo respectivamente 34 fêmeas de hamster criadas em grupo do desmame até o início do estudo e 76 fêmeas criadas isoladamente. Em cada experimento, um terço dos animais foram alojados em gaiolas individuais, enquanto pares de fêmeas desconhecidas umas das outras eram formados com os outros dois terços. O comportamento dos pares foi observado ao longo de 10 dias para determinar o status social de cada fêmea. Todas as fêmeas foram acasaladas neste período. Quatro dias após o parto, os filhotes foram contados, sexados e pesados e as ninhadas padronizadas a seis filhotes, três machos e três fêmeas. As mães e suas ninhadas foram observadas diariamente durante sessões de 40min e 13 categorias comportamentais foram registradas. No intuito de esclarecer os mecanismos fisiológicos subjacentes à relação entre estresse social e fertilidade, os níveis dos hormônios reprodutivos e dos glicocorticóides foram monitorados ao longo da gestação por métodos não-invasivos, previamente validados, de quantificação dos seus metabólitos nas fezes. Foi demonstrada, pela primeira vez, a adequação de um enzimaimunoensaio e de um conjunto diagnóstico comercial de radioimunoensaio para a quantificação respectiva dos metabólitos fecais de glicocorticóides em hamsters Sírios dos dois sexos e de testosterona no hamster Sírio macho, mas não da fêmea. As variações das concentrações de metabólitos fecais de progesterona, estrógenos e glicocorticóides, refletiram os perfis séricos descritos na literatura para hamsters gestantes. Os resultados mostram que quando fêmeas de hamster Sírio são alojadas individualmente após o desmame, sua fertilidade não é afetada pelo estresse social. Em contraste, quando as fêmeas são criadas em grupo, o estresse social tanto de isolamento como de subordinação a uma fêmea dominante induz um grau significante de assimetria reprodutiva, traço característico de espécies sociais que criam seus filhotes em comunidade. A manutenção de hamsters cativos adultos em grupos parece despertar traços comportamentais e fisiológicos presentes em grupos sociais complexos e que se encontram em estado latente nesta espécie solitária. A socialidade parece flexível no hamster e modulada pelas condições ecológicas. The flexibility of sociality found in many species suggests that many of the behavioral and physiological mechanisms responsible for highly developed social interactions are present as latent traits, even in species usually considered as solitary. Social hierarchy and reproductive skew are typical features of social species. Syrian hamsters (Mesocricetus auratus) are an ideal model for the investigation of social stress and its physiological, neuroendocrine, and behavioral effects. The present research focused on the effects of group-housing prior to mating and on the first days of gestation of the female hamster. We investigated if social stress produces some degree of reproductive skew in this solitary species, and if female reproductive success varies as a function of social rank. Two experiments were carried out. The first one involved 34 females group-raised from weaning until the beginning of the trial and the second one 76 singly raised females. In each case one third of the animals were singly housed. Pairs of unrelative females were formed with the remaining animals. Pair behavior was observed through 10 days for assessment of the social rank of each female. All females were mated during this period. On day 4 post-partum, pups were counted, sexed, and weighed and litters were culled to six, three males and three females. Litters and dams were observed daily through 40-min sessions and 13 behavioral categories recorded. In order to assess the physiological relationship between social stress and fertility, we monitored reproductive hormones and glucocorticoids of solitary and pair-housed females during pregnancy by utilizing recently established non-invasive methods for measuring the respective hormone metabolites in the feces. The suitability of an enzyme immunoassay and of a commercial radioimmunoassay for respective quantification of fecal glucocorticoid metabolites of hamsters of both sexes and fecal testosterone metabolites in the male but not in the female was proven for the first time. The patterns of fecal progesterone, estrogen, and glucocorticoid metabolites were similar to blood profiles reported in the literature for pregnant hamsters. Our results showed that when female hamsters are singly housed from weaning, social stress did not affect their fertility. However, when females are group-raised, both isolation and subordination stress induced a significant reproductive skew, which is a characteristic feature of cooperative breeders. It seems that group-keeping of adult hamsters evokes social physiological and behavioral mechanisms present as latent traits in this solitary species. As in other rodents, sociability seems flexible in the Syrian hamster and our findings support the idea that social interactions may be a function of ecological conditions.
... Three different aspects of offensive responses have been shown to undergo changes during puberty in male hamsters. The frequency of attacks during agonistic encounters peaks around Postnatal Day 35 (P-35) and decreases into late puberty and early adulthood (Postnatal Day 70 [P-70]; Goldman & Swanson, 1975;Pellis & Pellis, 1988;Taravosh-Lahn & Delville, 2004;Wommack et al., 2003). Furthermore, the areas on the body of the protagonists initially targeted during attacks also undergo a gradual transition during this period (Taravosh-Lahn & Delville, 2004;. ...
... The frequency of attacks during agonistic encounters peaks around Postnatal Day 35 (P-35) and decreases into late puberty and early adulthood (Postnatal Day 70 [P-70]; Goldman & Swanson, 1975;Pellis & Pellis, 1988;Taravosh-Lahn & Delville, 2004;Wommack et al., 2003). Furthermore, the areas on the body of the protagonists initially targeted during attacks also undergo a gradual transition during this period (Taravosh-Lahn & Delville, 2004;. In early puberty, during the peak of play-fighting activity, attacks are predominantly directed at the cheeks and face of the opponents (play-fighting attacks). ...
... Offensive responses in hamsters undergo several changes during the course of development (Cervantes, Taravosh-Lahn, & Delville, 2005;Taravosh-Lahn & Delville, 2004;Wommack et al., 2003). On the basis of these observations, it was hypothesized that juvenile hamsters would be less responsive to serotonin than adults. ...
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Article
In male golden hamsters (Mesocricetus auratus), attack frequency decreases during puberty. As serotonin inhibits offensive responses in adult hamsters, it is hypothesized that the serotonin system becomes upregulated in the hypothalamus during puberty. This hypothesis was tested through acute treatment with fluoxetine, a serotonin reuptake inhibitor, as well as through analysis of serotonin innervation in specific brain areas. In adults, fluoxetine treatment inhibited aggressive behavior. In juveniles, high doses of fluoxetine only reduced offensive responses (i.e., frequency and repetition of attacks), whereas low doses enhanced them. Juveniles also showed a dose-specific maturation of attack targets. In addition, the density of serotonin innervation of the hypothalamus was 20% higher in adult hamsters compared with juveniles. On the basis of these data, it is proposed that the developing serotonergic system shapes the development of offensive behaviors in male golden hamsters.
... By late puberty and early adulthood (P-55 to P-70), attacks become focused on the lower belly and rump (Pellis & Pellis, 1988a,b;Wommack et al., 2003). Quantitatively, the frequency of attacks, bites, and pins as well as the duration of contact time peak during early puberty around P-35 and then decrease gradually until stabilization in late puberty around P-55 (Cervantes, David, Loyd, & Delville, 2005;Goldman & Swanson, 1975;Taravosh-Lahn & Delville, 2004;Wommack et al., 2003). ...
... Offensive Responses. The behavioral data collected for this study were comprised from previously videotaped and analyzed experimental sets from three previous experiments in our laboratory and described below Taravosh-Lahn & Delville, 2004;Wommack et al., 2003). Within 2 days of weaning, male hamsters were first observed for a few seconds in the presence of an adult animal to test for inherent fearfulness. ...
... The attack frequency compared across test dates showed a significant peak of attack frequency on P-35 followed by a gradual decrease throughout puberty Taravosh-Lahn & Delville, 2004;Wommack et al., 2003). This decrease in agonistic behavior during puberty concurred with previous studies in golden hamsters (Goldman & Swanson, 1975). ...
Article
In hamsters, the maturation of aggression during puberty is associated with a gradual reduction of offensive responses. The purpose of this study was to analyze the changes during this decrease to provide an enhanced description of the behavior. During early puberty, play-fighting is characterized by long and continuous contact duration throughout the encounter and repetitive attacks within bouts of agonistic interaction. By mid-puberty, adult patterns of offensive behavior emerge. Contact time becomes shorter in duration and shifts to the beginning of the test, while attacks become less repetitive per bout. In late puberty, animals show an enhanced efficiency of behavior, as indicated by an increased percentage of attacks followed by bites. This study provides a better understanding of the development of aggression by characterizing the differences between juvenile play-fighting and adult aggression and the process of the maturation of aggression.
... Syrian hamsters (Mesocricetus auratus) are territorial and solitary animasl 1,2 that exhibit aggressive behavior when housed with other hamsters. 3,11 As observed in the present study, maintaining one female animal per cage will reduce the aggressiveness of hamsters during handling. We housed hamsters in groups with a maximum of 4 animals (80 to 120g per cage in cages measuring 490 mm × 340 mm × 160 mm) because this number is stated in Normative Resolution Number 15 of CONCEA 4 for this cage size. ...
... Groups of 2 or 3 hamsters were not tested because having one or 2 fewer hamsters in the cage was did not reduce aggression. 1 Previous studies have reported that male hamsters are less aggressive than female hamsters. 1,2,11 In the present study, group-housed females were more aggressive (intraspecific aggression or aggression during handling) than males, regardless of age, and individually housed females were less aggressive than females housed in groups of 4 per cage. We therefore suggest individual housing of females used for experimentation, assuming this is feasible depending on available space in the animal facility. ...
Article
The Syrian hamster (Mesocricetus auratus) is a solitary and naturally territorial animal, with female hamsters being moreaggressive than males. This behavior makes handling difficult because they are usually housed in groups, which can leadto aggressive behavior. The objective of this study was to refine the management of Syrian hamsters in order to minimizeaggressiveness, reduce the animal injuries, and lessen the risk of accidents among laboratory animal technicians due to the hamster aggression during handling. The experiment was conducted at the Center for Animals Experimentation, OswaldoCruz Institute. Four groups of hamsters were observed by video recording: group 1 (group-housed males, 6 to 8 wk of age),group 2 (group-housed females 6 to 8 wk of age), group 3 (group-housed female, 3 to 4 wk of age), and group 4 (individually housed females, 6 to 8 wk of age). Group 1 animals were less aggressive and agitated both during housing and during handling by the animal technician as compared with groups 2 and 3. Groups 2 and 3 showed greater agitation and aggression. Marked reduction in the level of aggressiveness and agitation was observed in group 4 as compared with all other groups evaluated during handling by the animal technician. Male hamsters housed in groups of 4 and females housed individually has reduced risks of accident during handling, thereby averting distress and consequent physiologic alterations. Avoiding these risks is essential to obtaining reliable experimental results.
... At P25, all animals were weaned and single-housed in Plexiglas cages (19 W ϫ 43.2 D ϫ 26.5 H cm) enriched with food piles and cotton pads. Only males were kept for the present experiments as early exposure to social stress in females does not affect the development of agonistic behavior Taravosh-Lahn & Delville, 2004). Training in conditioning chambers started between P50 and P60 and the animals were tested between P70 and P90. ...
... Injured individuals would have been removed from the study, but as typical of hamsters (Blanchard, Wall, & Blanchard, 2003) no injuries were reported. Nevertheless, this experience is known to impact juvenile hamsters as shown by consistent cortisol responses (Taravosh-Lahn & Delville, 2004), learned avoidance and enhanced risk assessment behavior (Bastida et al., 2009). ...
Article
In hamsters, individuals attacked by adults during puberty become aggressive adults. Perhaps, enhanced aggression observed as repeated attacks toward opponents is associated with a lack of impulse control. We examined impulsive action in male golden hamsters exposed daily to aggressive adults from postnatal Day 28 to 42. These animals were trained in conditioning chambers and tested during adulthood in a go-no-go task addressing action inhibition. Overall, previously stressed hamsters were less likely to inhibit a conditioned lever pressing response during no-go trials. Because this effect could be the result of an extinction impairment, additional animals were tested to evaluate their response to omission of reward associated with conditioned lever pressing. In this experiment, all animals were equally capable of inhibiting their conditioned response. The capacity to inhibit a conditioned response was further addressed by testing responses to a 60-s reward delay after lever pressing. In this case, previously stressed animals were faster to inhibit lever pressing and stopped showing a preference for the proximity of the lever. These studies show selective condition-dependent effects on lever pressing activity and support the possibility that stress in early puberty enhances impulsive action in adulthood. These experiments may be relevant to the study of mental disorders associated with early trauma in humans. (PsycINFO Database Record
... Differences in aggression patterns were observed in some animal species [40], generally with females more aggressive than males due its dominant role in social hierarchies [14,22,32,42] and due to mating and social systems [42]. In some fish species, females can be more aggressive, mainly in monogamous or polyandrous systems [21]. ...
... On the other hand, females seem to be more aggressive than males, suggesting an effect of UCS protocol. Studies have already observed that females were capable of adapting to repeated social subjugation, even under more severe conditions, whereas males were not able to adapt to these situations [15,40,41]. We consider the MIA test as an additional stressor, since this protocol consists of the transfer fish from the UCS treatment aquarium to the test tank. ...
... Female Syrian hamsters not only display significantly more aggressive behaviour than males [76], but also tend to dominate males in heterosexual encounters [77]. This sex difference may be attributable to relative differences in steroid metabolism between the sexes [76]. ...
... Female Syrian hamsters not only display significantly more aggressive behaviour than males [76], but also tend to dominate males in heterosexual encounters [77]. This sex difference may be attributable to relative differences in steroid metabolism between the sexes [76]. Neonatal androgen and oestrogen exposure, as well as variation in steroid and neuropeptide levels in adulthood, have been implicated in the expression of female intrasexual social aggression. ...
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Article
Dimorphism on dominance and agonistic behaviour in mammals tends to be strongly biased toward males. In this review, we focus on a select few species of mammals in which females are as or more aggressive than males, and/or are dominant to males, and explore the role of androgenic hormones in mediating this important difference. While the data are not as clear-cut as those published on traditional laboratory mammals, our review highlights important endocrine substrates for both organizational and activational influences of steroids on female aggressive behaviour. We highlight areas in which further observations and experiments are crucial, especially the potential facilitative effects of androgens on female aggression. Finally, new and innovative techniques, including molecular genetics and receptor pharmacology, portend important insights into the ways in which androgenic hormones regulate aggressive behaviour in 'atypical' female mammals.
... There was a significant main effect of gender for systolic blood pressure [F(1,89) = 59. 43 The interaction between bullying and time was not significant for women [F(2,50) = .24, p = .78] ...
... This finding can be explained by two different findings in the animal literature. In regards to chronic stress, this finding is consistent with animal studies showing that females are not as affected by chronic stressors as males [18,43]. If females are not as affected by chronic stress as males, then it would explain why there is no difference between women with and without experience of chronic stress. ...
Article
Peer victimization in the form of bullying is a chronic social stressor experienced by many humans during development. Exposure to bullying has been associated with a variety of mental disorders, such as anxiety and depression. Participants pre-selected for the presence or absence of a history of being bullied were brought into a laboratory and placed in a stressful situation. Blood pressure, heart rate, and salivary cortisol levels were measured before the introduction of the stressor (Time 1), at the end of the stressor (Time 2), and after its removal (Time 3). Men with a history of exposure to frequent bullying showed blunted blood pressure responses at Time 2 compared to control men. Bullied and Non-bullied women did not show any differences in any of the measures. Men and women in both groups showed an increase in heart rate in response to the stressor. There were no significant differences in salivary cortisol levels between Bullied and Non-bullied participants. However, salivary cortisol levels and systolic blood pressure were lower in Bullied male participants who reported having no feelings of anger about their experience compared to controls and those who did report anger. These data show altered sympathetic responses to stress in men with a history of victimization as well as suggesting long-term effects on the HPA axis in the most affected individuals.
... Play fighting attacks of juvenile hamsters are targeted at the face of the protagonist, while attacks by adults are focused on the lower belly and rump (Pellis and Pellis, 1988a,b;Wommack et al., 2003). Quantitatively, juvenile hamsters are more active and perform many more attacks during agonistic contacts than adults Taravosh-Lahn and Delville, 2004). In particular, attacks and bouts of contact are much more repetitive in play fighting than in adult aggression (Cervantes et al., 2006). ...
... Their body weights were measured weekly and recorded to monitor their development. The studies were conducted in early puberty (P-35) around the time of peak play fighting activity in this species (Goldman and Swanson, 1975;Taravosh-Lahn and Delville, 2004;Cervantes et al., 2006). All procedures were performed according to National Institutes of Health guidelines approved by the Institutional Animal Care and Use Committee of the University of Texas at Austin and conducted in an AALAC-accredited facility. ...
Article
In hamsters, play fighting matures gradually into adult aggression. As these two behaviors share many similarities in this species, we predicted that a single neural circuitry controls their offensive component. The goal of the present study was to identify neural systems associated with offensive play fighting in male juvenile golden hamsters. The neural circuitry related to this behavior was identified through quantification of c-Fos immunolabeling. We also looked for vasopressin cells possibly associated with play fighting. We found that areas previously associated with offensive aggression in adult hamsters, including the ventrolateral hypothalamus, the medial amygdala, and the bed nucleus of the stria terminalis, also showed enhanced c-Fos expression after play fighting. In addition, vasopressin neurons in the nucleus circularis and the medial division of the supraoptic nucleus expressed enhanced c-Fos immunolabeling in juveniles after play fighting, as previously reported in adult hamsters after aggression. Finally, enhanced c-Fos expression associated with play fighting was also found in areas previously unexplored in adult hamsters, such as the prefrontal cortex. Together, our results support the hypothesis of a single core neural circuitry controlling the offensive components of play fighting and adult aggression throughout puberty in hamsters.
... Animals were tested for offensive responses on P-35, P-45, and P-56. As shown before (Goldman & Swanson, 1975;Wommack et al., 2003;Taravosh-Lahn & Delville, 2004), attack frequencies were highest on P-35 (Fig. 2) and decreased over time in most groups. The decrease was statistically significant for animal exposed to 0, 25 and 100 ppm lead acetate, but was only a trend in animals exposed to 400 ppm [0 ppm: X 2 (2) ¼ 11.4, p < 0.01; 25 ppm: X 2 (2) ¼ 12.2, p < 0.01; 100 ppm: X 2 (2) ¼ 8.3, p < 0.05; 400 ppm: X 2 (2) ¼ 4.9, p < 0.1]. ...
... Lead exposure affects the peri-pubertal maturation of agonistic behavior from play-fighting to adult aggression. During puberty, offensive responses (attacks) shift from the face and cheeks (Play-Fighting attacks), to the flanks (Side attacks), and finally to the lower belly and rump (Adult attacks) Taravosh-Lahn & Delville, 2004). Our data show a dose-specific effect of lead exposure on this maturation. ...
Article
We tested the effects of exposure to different doses of lead acetate (either 0, 25, 100, or 400 ppm) on the development of aggressive behavior in male golden hamsters. Pups were tested for offensive responses across puberty, as they were maturing from play fighting to adult aggression. Our data show a dose-specific effect of lead exposure on the development of aggression during puberty at doses resulting in blood levels well below 20 microg/dl. Animals exposed to 25 ppm lead acetate were faster and performed more than twice as many attacks on intruders by late puberty. They were also twice as likely to initiate adult instead of play-fighting attacks around mid-puberty. These observations were independent of any effect on growth. Thus, exposure to low doses of lead enhanced aggression and accelerated its maturation. As such, our data support the association between exposure to low doses of lead and aggressive behavior in boys.
... 28 Among laboratory rodents, Syrian hamsters (Mesocricetus auratus) are widely used for behavioral and stress-related studies. 4,7,24,30 In this species, as in most mammals, environmental stimuli activate the hypothalamic-pituitary-adrenal cortex axis, increasing the plasma levels of glucocorticoids, mainly cortisol in the hamster. 24 Measuring the activity of this system can be useful for attempting to assess how an animal copes with stressful events. ...
... 4,7,24,30 In this species, as in most mammals, environmental stimuli activate the hypothalamic-pituitary-adrenal cortex axis, increasing the plasma levels of glucocorticoids, mainly cortisol in the hamster. 24 Measuring the activity of this system can be useful for attempting to assess how an animal copes with stressful events. 17 A conventional means of measuring stress hormones is the analysis of blood. ...
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Article
Noninvasive techniques to monitor reproductive or stress hormones are now widely used in captive and free-ranging wildlife. These methods offer great advantages and deserve to be used also in laboratory rodents. However, we remain naïve about factors that may influence the accuracy of these techniques. The aim of this study was to evaluate the adequacy of measuring the concentration of cortisol fecal metabolites to assess the physiologic stress response. Ten adult female Syrian hamsters were ovariectomized, and all feces voided were collected daily for 4 d before and 5 d after surgery. Cortisol fecal metabolites were extracted and quantified by radioimmunoassay. We determined per-gram fecal cortisol metabolite concentrations, total 24-h fecal output and total 24-h fecal cortisol metabolite production. Surgery considerably affected fecal output, and using per-gram versus total cortisol metabolites led to different conclusions: whereas concentrations increased significantly just after ovariectomy and decreased on subsequent days, the total excreted cortisol metabolites varied in a symmetrical pattern. Therefore, the relative per-gram measure of hormones may not reflect the total amount of circulating hormones, because these measures are comparable only if the volume of the material in which the hormone is contained is the same in the 2 groups.
... Females have been shown to develop adult-like attack styles earlier in life than males and they are less affected by early social defeat than males are. These data suggest that sex differences in aggression and responses to agonistic encounters are present early in life (Lahn and Delville, 2004). Previous studies with adult hamsters, however, showed no sex differences in measures of aggressive behavior in like-sex encounters (Floody & Pfaff, 1977). ...
... We interpret these data to mean that males that lost maintained a stronger fear-avoidance response than females. These data support recent findings by Huhman et al (2004) showing that adult females fail to exhibit conditioned defeat and results from Lahn & Delville (2004), indicating that females were less affected by repeated defeat than males were. Our results were obtained in very different conditions than the studies of conditioned defeat; the fear/avoidance response in females was lost despite the conditions in which they were tested, namely that subjects were tested with the same stimulus animal and in the same environment where previous agonistic encounters took place. ...
Article
In the majority of mammalian species, males are dominant over and more aggressive than females. In contrast, some reports suggest that female golden hamsters are more aggressive than males but systematic comparisons using the same methods for both sexes are rare. We observed same-sexed pairs of hamsters over repeated trials to assess whether sex differences existed in the level of agonistic behavior and in the development and maintenance of dominant-subordinate relationships with familiar partners. There were no sex differences in measures of agonistic behavior or fear responses (fleeing) during the initial series of three trials on the first day of testing. Following a four-day interval, males that had lost in session 1 showed fearful responses to a familiar dominant male and were not likely to engage in a fight with him. In contrast, females that lost the initial fights were not fearful and fought vigorously with the familiar winner in subsequent encounters. Although the amount of agonistic behavior engaged in by females did decrease over the course of the three sessions, females that lost did not demonstrate an increase in fear, as measured by the latency to flee. Males that lost fights did show increased fear during later trials and sessions. These results suggest that female hamsters are less affected by losing fights than males are and thus that females are less likely than males to develop highly polarized dominant-subordinate relationships. Further work is needed to understand the mechanisms underlying these sex differences.
... Therefore, it is difficult to study sex differences in mechanisms and responses to social stress in ethologically meaningful ways using these animal models. In Syrian hamsters (Mesocricetus auratus), however, both sexes readily engage in agonistic behavior with a same-sex conspecific in the wild and in the laboratory [18][19][20]. Both males and females use the same agonistic behaviors to rapidly establish stable dominantsubordinate relationships allowing for the study of Bwinners( dominants) and Blosers^(subordinates) in both sexes. ...
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Article
The basolateral amygdala (BLA) is a critical nucleus mediating behavioral responses after exposure to acute social conflict. Male and female Syrian hamsters both readily establish a stable dominant-subordinate relationship among same-sex conspecifics, and the goal of the current study was to determine potential underlying genetic mechanisms in the BLA facilitating the establishment of social hierarchy. We sequenced the BLA transcriptomes of dominant, subordinate, and socially neutral males and females, and using de novo assembly techniques and gene network analyses, we compared these transcriptomes across social status within each sex. Our results revealed 499 transcripts that were differentially expressed in the BLA across both males and females and 138 distinct gene networks. Surprisingly, we found that there was virtually no overlap in the transcript changes or in gene network patterns in males and females of the same social status. These results suggest that, although males and females reliably engage in similar social behaviors to establish social dominance, the molecular mechanisms in the BLA by which these statuses are obtained and maintained are distinct.
... The limited studies performed support a lack of loser effect in female rodents. For example, it was found that juvenile female hamsters subjected to daily attack by adult females and males developed similar agonistic behaviors as unattacked controls [60]. Defeated female rats show similar levels of aggression in future agonistic encounters as winners [61]. ...
Article
Aggression is a fundamental social behavior that is essential for competing for resources and protecting oneself and families in both males and females. As a result of natural selection, aggression is often displayed differentially between the sexes, typically at a higher level in males than females. Here, we highlight the behavioral differences between male and female aggression in rodents. We further outline the aggression circuits in males and females, and compare their differences at each circuit node. Lastly, we summarize our current understanding regarding the generation of sexually dimorphic aggression circuits during development and their maintenance during adulthood. In both cases, gonadal steroid hormones appear to play crucial roles in differentiating the circuits by impacting on the survival, morphology, and intrinsic properties of relevant cells. Many other factors, such as environment and experience, may also contribute to sex differences in aggression and remain to be investigated in future studies.
... First, play fighting and adult fighting have different topographies. In play fighting, attacks are initiated toward the head and nape, whereas in serious fighting, attacks are initiated toward the rump (Pellis and Pellis, 1988;Wommack et al., 2003;Taravosh-Lahn and Delville, 2004). Defensive maneuvers during play and adult fighting differ as well. ...
Chapter
Aggressive behaviors range from lethal to subtle and typically arise whenever the interests of two or more individuals conflict. The relationship between the testes and aggression has been known since antiquity, but the relationship between testosterone and such behavior has some surprising twists. We review interactions between aggression, hormones, receptors, and brain structures in mammals. We examine the ontogeny of aggressive behavior and how hormones and experience shape the trajectory of adult sex differences in aggression. We compare rodent models with data on human aggression with the goal of emphasizing where further research is needed to understand pathological aggression.
... First, play fighting and adult fighting have different topographies. In play fighting, attacks are initiated toward the head and nape, whereas in serious fighting, attacks are initiated toward the rump (Pellis and Pellis, 1988;Wommack et al., 2003;Taravosh-Lahn and Delville, 2004). Defensive maneuvers during play and adult fighting differ as well. ...
Chapter
Aggression may be defined as overt behavior with the intention of inflicting harm or the threat of harm upon another individual. Aggressive behaviors range from lethal to subtle, and typically arise whenever the interests of two or more individuals conflict. Species- and situation-specific rules exist to regulate aggression. Males, particularly males engaged in territorial or courtship activities, are more aggressive than females in most situations and in most species. The relationship between the testes and aggression has been known since antiquity and castration helps maintain docility among nonbreeding livestock. The long-held relationship between testosterone and aggression has some surprising twists, including the importance of estrogens and their receptors in the regulation of aggression. This chapter outlines what is known about the interactions among aggression and sex steroid hormones, peptides, hormone receptors, neurochemistry, and brain structures in mammals. The ontogeny of aggressive behavior and how hormones and experience shape the trajectory of adult sex differences in aggression is also examined here. Throughout the chapter, a comparison is made between the regulation of rodent animal models of aggression and human aggression with the goal of emphasizing where further research is needed to understand nonadaptive or pathological aggression.
... Other early manipulations of the social environment during development such as social subjugation during puberty also show differential effects on female and male aggression. Whereas males respond to social ( Delville et al ., 1998 ), female aggression is not affected by this treatment ( Taravosh-Lahn & Delville, 2004 ). ...
Chapter
Series of experiments with Peromyscus combined with studies from other species reveal interesting effects of parental behavior on aggression. Both paternal pup retrievals and some aspect(s) of maternal separation (MS) appear to influence aggression of offspring. Paternal retrievals, however, may have a unique effect on offspring aggression that function in part through changes to the arginine vasopressin neurochemical system associated with the bed nucleus of the stria terminalis. In comparison, MS and paternal huddling and grooming may function through the paraventricular nucleus as a result of stress, although effects on aggression appear to vary depending on species. The effects of paternal behavior were not uniform such that pup retrievals, but not huddling and grooming appeared to influence aggression. Thus, paternal effects on aggression may operate through mechanisms different than those traditionally associated with stress. This is also supported by preliminary data indicating a change in testosterone levels of pups in response to paternal retrievals. Despite the lack of an effect of changes in paternal huddling and grooming of offspring on aggression, it is possible that paternal separation in California mice may cause changes in aggression similar to those of MS in either rats or house mice. A careful comparison of aspects of aggression that are influenced by paternal retrievals vs. parental separation could be very illuminating in that one might predict different outcomes for different types of aggression.
... In contrast to males, female Syrian hamsters displayed a stable frequency of attacks through puberty and into adulthood, there was no obvious mid-puberty transitional period, and cortisol habituated to repeated exposures to aggressive adults. 89 Male hamsters do not appear to habituate to repeated exposure to social subjugation. 87 After 2 weeks of repeated exposure to aggressive adults, male hamsters persistently displayed elevated plasma cortisol concentrations e an endocrine marker of the maturation of agonistic behavior from play fighting to adult-like attacks. ...
Chapter
This chapter explains how aggression is a social interaction to determine the outcome of a conflict over resources. Aggressive behaviors take many forms, despite evidence that the regulatory factors and brain mechanisms are conserved across vertebrate species. Castrated animals are expected to show reduced aggression levels, whereas castrated animals with testosterone replaced via an implant are expected to display aggression levels similar to those of intact animals. Androgens such as testosterone can be converted to estrogens by the aromatase enzyme, and many brain regions known to regulate aggression express aromatase. Thus, in some cases, the effects of testosterone on aggression may actually be mediated by estrogenic metabolites. Dehydroepiandrosterone (DHEA) is an endogenous steroid that circulates at relatively high concentrations among humans. Similar to androgens, the relationship between glucocorticoids and aggressive behaviors is complex. The neuropeptides vasopressin and oxytocin have complex effects on aggressive behaviors. Vasopressin neurons in the bed nucleus of the stria terminalis (BNST) and medial amygdala send projections to the lateral septum.
... However, in the current study, our animals are tested for adolescent AAS-induced offensive aggression on postnatal day 57, i.e., a time at which the behavioral response pattern comprises nearly equal parts frontal:belly/rear attacks (Wommack and Delville, 2003). In our animal model of adolescent AAS-induced offensive aggression, the majority of AAS-treated adolescents target their offensive responses to the flank and rear regions of intruders (Ricci et al., 2013;Schwartzer and Melloni, 2010a;Schwartzer and Melloni, 2010b), i.e., a hallmark characteristic of the adult aggressive phenotype (Taravosh-Lahn and Delville, 2004;Wommack and Delville, 2003), although some frontal attack behavior is still observed. Thus AAS-treated animals display the adult form of offensive aggression in the absence of social learning, indicating that the AAS treatment regimen circumvents the learning of mature fighting behavior. ...
Article
Male Syrian hamsters (Mesocricetus auratus) treated with anabolic/androgenic steroids (AAS) during adolescence (P27-P56) display highly escalated and mature forms of offensive aggression correlated with increased γ-aminobutyric acid (GABA) afferent development as well as decreased GABAA receptors in the lateroanterior hypothalamus (LAH) - an area of convergence for developmental and neuroplastic changes that underlie offensive aggressive behaviors in hamsters. This study investigated whether microinfusion of a GABAA receptor agonist (muscimol; 0.01-1.0 pmol/l) or antagonist (bicuculline; 0.04-4.0 pmol/l) directly into the LAH modulate adolescent AAS-induced offensive aggression. Activation of LAH GABAA receptors enhanced adolescent AAS-induced offensive aggression, beginning at the 0.1 pmol/l dose, when compared with AAS-treated animals injected with saline into the LAH. Importantly, GABAA receptor agonism within the LAH significantly increased the frequency of belly/rear attacks, while simultaneously decreasing the frequency of frontal attacks. These data identify a neuroanatomical locus where GABAA receptor activation functions to enhance aggression in adolescent AAS-treated animals, while also promoting the display of mature forms of aggression and suppressing juvenile play behaviors.
... Desde então, estes roedores conquistaram um lugar de destaque entre as espécies utilizadas para a pesquisa médica e biológica graças a algumas características únicas que os tornam modelo para o estudo de diversas doenças humanas nas áreas de odontologia (Dale et al. 1944), cardiologia (Bajusz 1969, Missihoun et al. 2009), oncologia (Zheng et al. 2009) por exemplo. Ademais, espécie estritamente territorial, de hábitos solitários na natureza (Gattermann et al. 2001), o hamster tem sido objeto de numerosos estudos comportamentais e envolvendo estresse e/ou comportamento agonístico (Cain et al. 2004, Cordner et al. 2004, Taravosh-Lahn & Delville 2004, Wommack et al. 2004, Gebhardt-Heinrich et al. 2007, Zhang et al. 2008. A investigação dos mecanismos fisiológicos subjacentes ao comportamento supõe muitas vezes o monitoramento das flutuações hormonais nos indivíduos envolvidos. ...
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Article
Besides being models for a variety of human diseases, hamsters have been object of numerous behavioral studies about stress and agonistic behavior. Such studies usually involve hormone change monitoring. The aim of the present study was to confirm the suitability of a commercial kit for human serum testosterone analysis to quantify testosterone metabolites in the feces (MFT) of male and female Syrian hamsters. Ten males were submitted to a GnRH challenge test to stimulate testicular activity and increase circulating testosterone levels. Five females received a testosterone injection and five other females were given a saline injection. Fecal samples collected before and after the procedures, and fecal samples collected from 20 pregnant females through gestation were analyzed for MFT with a commercial radioimmunoassay. The detection of a MFT peak 12 h after GnRH administration followed by a decrease under baseline showed that, in males, changes in the levels of MFT are related to respective changes of testosterone concentrations in the blood. Again in males a circadian cycle of MFT similar to the circadian rhythm described in literature for blood concentrations was detected. The administration of exogenous testosterone caused in females a dramatic peak of MFT. However, the concentrations measured through gestation did not reflect the pattern of endogenous testosterone blood levels as described in the literature. Therefore, the use of a radioimmunoassay for human blood testosterone was validated in male Syrian hamster, but a more specific assay would be necessary for female hamsters.
... This finding is consistent with the concept that sexual experience during puberty triggers anxiety-and depressive-like behaviors in Siberian hamsters ( Morris et al., 2013). Perhaps juvenile males prefer NR females because they are more likely to interact with them, as these animals are still engaging in play fighting (Taravosh Lahn and Delville, 2004;Wommack et al., 2003). Thus, appetitive male sexual behavior in hamsters appears to mature from seeking females for play fighting. ...
Article
Repeated social subjugation in early puberty lowers testosterone levels. We used hamsters to investigate the effects of social subjugation on male sexual behavior and metabolic activity within neural systems controlling social and motivational behaviors. Subjugated animals were exposed daily to aggressive adult males in early puberty for postnatal days 28 to 42, while control animals were placed in empty clean cages. On postnatal day 45, they were tested for male sexual behavior in the presence of receptive female. Alternatively, they were tested for mate choice after placement at the base of a Y-maze containing a sexually receptive female in one tip of the maze and an ovariectomized one on the other. Social subjugation did not affect the capacity to mate with receptive females. Although control animals were fast to approach females and preferred ovariectomized individuals, subjugated animals stayed away from them and showed no preference. Cytochrome oxidase activity was reduced within the preoptic area and ventral tegmental area in subjugated hamsters. In addition, the correlation of metabolic activity of these areas with the bed nucleus of the stria terminalis and anterior parietal cortex changed significantly from positive in controls to negative in subjugated animals. These data show that at mid-puberty, while male hamsters are capable of mating, their appetitive sexual behavior is not fully mature and this aspect of male sexual behavior is responsive to social subjugation. Furthermore, metabolic activity and coordination of activity in brain areas related to sexual behavior and motivation was altered by social subjugation.
... Thus, there is also a clear sex difference in the behavioral response to social defeat in Syrian hamsters. This finding is consistent with a recent study which demonstrated that following repeated social stress, female hamsters were less likely to display alterations in the development of agonistic behavior and were quicker to habituate to repeated social stress than were males (Taravosh-Lahn & Delville, 2004). There are very few field data available about the natural environment of Syrian hamsters. ...
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Article
Following social defeat, male hamsters exhibit behavioral changes characterized by a breakdown of normal territorial aggression and an increase in submissive/defensive behaviors in the presence of a non-aggressive intruder (NAI). We have termed this phenomenon conditioned defeat (CD). By contrast, only a small subset of defeated females exhibit submissive/defensive behavior in the presence of a NAI. We hypothesized that fluctuations in gonadal hormones might contribute to differences in the display of submissive behavior in intact female hamsters. Following social defeat, proestrous females (higher endogenous estradiol) were more likely to display conditioned defeat compared with diestrous 1 (lower endogenous estradiol) females. This finding suggests that there is an estrous cycle-dependent fluctuation in the display of CD in female hamsters and suggests that increased estradiol might contribute to increased submissive behavior. We then demonstrated that ovariectomized females given estradiol prior to CD testing exhibited significantly higher submissive behavior in the presence of a NAI suggesting that estradiol increases the expression of CD in female hamsters. We have also shown that castrated males that were singly housed for four weeks displayed
... In addition to the elevated aggression observed in winning hamsters, it is important to consider that the stimulus intruders were repeatedly exposed to subjugation stress in the resident-intruder paradigm. Previous research on agonistic encounters in hamsters has shown that repeated social subjugation alters behavioral responses to future encounters (Delville, Melloni, et al., 1998;Taravosh-Lahn & Delville, 2004;Wommack & Delville, 2003) and, like the winner effect, repeated losing experiences can increase the probability for losing future encounters (i.e., the loser effect; Dugatkin, 1997). Therefore, it is possible that the correlation between repeated training sessions and winning aggressive encounters may be a result of changes in the behavioral responses of the intruders. ...
Article
Winning an aggressive encounter enhances the probability of winning future contests. This phenomenon, known as the winner effect, has been well studied across vertebrate species. While numerous animal models have been developed to study the winner effect in the laboratory setting, large variation in experimental design, choice of species, and housing conditions have resulted in conflicting reports on the behavioral outcomes. The Syrian hamster (Mesocricetus auratus) presents as a novel species with face validity to study the effects of repeated fighting on subsequent agonistic encounters. After a 14-day training period, "trained fighter" hamsters displayed elevated fighting behaviors characterized by more intense and severe displays of aggression along with increased displays of dominant postures compared to naïve residents with no prior social experience. To determine whether these phenotypic changes in fighting behavior reflect alterations in neurochemistry, brains of aggressive and naïve hamsters were examined for changes in dopaminergic innervation in key regions known to control social and motivational behavior. Interestingly, changes in tyrosine hydroxylase, the rate limiting enzyme for dopamine production, were observed in brain regions within the social decision-making network. These increases in aggression observed after repeated winning may reflect a learned behavior resulting from increases in neurotransmitter activity which serve to reinforce the behavior. The data implicate the presence of a winner effect in hamsters and provide evidence for a neural mechanism underlying the changes in aggressive behavior after repeated agonistic encounters. Aggr. Behav. 9999:XX-XX, 2013. © 2013 Wiley Periodicals, Inc.
... Rodent models indicate enhanced stress susceptibility during puberty (Bingham et al., 2011), suggesting a physiological rather than psychological element to this risk factor. Social stress exposure during puberty also alters the formation of agonistic behaviors in female golden hamsters (Taravosh-Lahn and Delville, 2004). In addition, social stress during puberty can alter subsequent stress responses (McCormick and Mathews, 2007), as well as substance abuse behaviors in animals (Ferris and Brewer, 1996;McCormick et al., 2004). ...
Article
The genetic, biological, and environmental backgrounds of an organism fundamentally influence the balance between risk and resilience to stress. Sex, age, and environment transact with responses to trauma in ways that can mitigate or exacerbate the likelihood that post-traumatic stress disorder will develop. Translational approaches to modeling affective disorders in animals will ultimately provide novel treatments and a better understanding of the neurobiological underpinnings behind these debilitating disorders. The extant literature on trauma/stress has focused predominately on limbic and cortical structures that innervate the hypothalamic-pituitary-adrenal axis and influence glucocorticoid-mediated negative feedback. It is through these neuroendocrine pathways that a self-perpetuating fear memory can propagate the long-term effects of early life trauma. Recent work incorporating translational approaches has provided novel pathways that can be influenced by early life stress, such as the glucocorticoid receptor chaperones, including FKBP51. Animal models of stress have differing effects on behavior and endocrine pathways; however, complete models replicating clinical characteristics of risk and resilience have not been rigorously studied. This review discusses a four factor model that considers the importance of studying both risk and resilience in understanding the developmental response to trauma/stress. Consideration of the multifactorial nature of clinical populations in the design of preclinical models and the application of preclinical findings to clinical treatment approaches comprise the core of translational reciprocity which is discussed in the context of the four factor model.
... It is interesting to note, this level of aggression met or exceeded that of trained fighters (Ferris et al., 1997;Schwartzer, Ricci, & Melloni, 2012), suggesting that aggression may be maximized in adolescent animals administered fluoxetine. Importantly, fluoxetine-treated adolescents targeted their offensive responses, that is, a hallmark feature of mature, adult aggressive behavior (Taravosh-Lahn & Delville, 2004). Yet, here, adolescent hamsters were tested for aggression in the absence of prior social experience, therefore, fluoxetine exposure alone was sufficient to generate adolescent animals with a mature, highly escalated offensive aggressive phenotype. ...
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Article
Fluoxetine is the only selective serotonin reuptake inhibitor registered for the treatment of major depressive disorder in pediatric populations, despite reports that it is disproportionately associated with an array of adverse side effects that include agitation, hostility, and overt acts of pathological aggression and violence in youth. This study examined the effects of repeated adolescent fluoxetine administration on offensive aggression and the development of the serotonin (5HT) and vasopressin (AVP) neural systems modulating this behavior using pubertal Syrian hamsters (Mesocricetus auratus) as an adolescent-animal model. Adolescent hamsters administered fluoxetine were tested for offensive aggression using the resident/intruder test, sacrificed the following day, and, using immunohistochemistry, examined for 5HT and AVP afferent innervation/development to areas of the brain implicated in aggression control. Repeated exposure to a low dose (0.3 mg/kg/day) of fluoxetine during adolescence increased nearly all measures of offensive aggression (i.e., upright offensive attacks, lateral attacks, flank/rump bites, pursuits, flank marks), whereas measures of social interest (i.e., olfactory investigation, contact time), comfort (i.e., grooming), and locomotion (i.e., contact time, cage climbing) remained constant. Fluoxetine exposure also increased 5HT and AVP afferent development to brain areas implicated in aggressive behavior, most notably the latero-anterior hypothalamus (LAH)-an area of convergence for developmental and neuroplastic changes correlated with offensive aggression in hamsters. These data indicate that repeated administration of clinically relevant doses of fluoxetine during adolescent development directly stimulates aggressive behavior and alters LAH 5HT and AVP development, yet only alterations in AVP afferent development within the LAH correlate with the fluoxetine-induced aggressive behavioral phenotype.
... On the other hand, more recent studies suggested that the exposure to social stress causes no long-lasting effects on the agonistic behavior of the female hamster [14,15]. Specifically, the group-housing-induced dominance hierarchystable in malesis unstable among females [16]. ...
Article
In many mammal species, reproduction is not shared equally among the members of a social unit. Even though reproductive skew seems unlikely in females of solitary species, this phenomenon could result from environmental factors. Although solitary in the wild, captive Syrian hamsters (Mesocricetus auratus) are generally housed in groups. We investigated whether social stress produces some degree of reproductive skew in this solitary species and whether female reproductive success varies as a function of social rank. To assess the physiological relationship between social stress and fertility, we monitored reproductive hormones and glucocorticoids of solitary and pair-housed females during pregnancy by means of recently established non-invasive methods for measuring hormone metabolites in the feces. The patterns of fecal progesterone, estrogen and glucocorticoid metabolites were similar to those found in blood and reported in the literature for pregnant hamsters. As expected, dominant females had higher breeding success than subordinate females. However the rate of reproductive failure was also very high among the singly housed females of our control group. The number of pups per litter, the average sex-ratio in each group, and the mean weight of pups did not differ significantly among groups. Glucocorticoid concentrations were unaffected by housing and social rank and the few differences between the endocrine profiles of singly- and pair-housed females are not sufficient to explain the observed difference in breeding success. It is likely that social isolation impairs reproduction in the same manner as subordination. Our findings suggest that social isolation of animals accustomed to group living was equally as disturbing as cohabitation with an unknown conspecific.
... In such cases, flight initiation distance by females is predicted to be unaffected by presence of conspecific males or females. In some species and reproductive states, however, females are aggressive to conspecifics of one or both sexes (e.g., Cooper and Crews 1987;Langmore et al. 2002;Taravosh-Lahn and Delville 2004). Courtship opportunities may be rare or subject to competition (Langmore et al. 2002;Mays and Hopper 2004). ...
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Article
As a predator approaches, prey base decisions about when to flee on a balance between degree of predation risk and costs of escaping. Lost opportunities to perform activities that may increase fitness are major escape costs. Paramount among these are chances to increase fitness by courting and mating and by driving away sexual rivals. Because sexual selection imposes different social demands on the sexes, social opportunities can have different consequences for males and females, but effects of sex differences in social opportunity costs on escape behavior are unknown. We conducted a field experiment showing that male striped plateau lizards (Sceloporus virgatus) given the opportunity to court or perform aggressive behavior permit closer approach before fleeing, but females do not. Males allowed a simulated predator to approach closer before initiating escape if a tethered male or female rather than a control stimulus was introduced to them, but females initiated escape at similar distances in all conditions. For males, a trade-off between the greater predation risk accepted before fleeing due to the likelihood of enhancing fitness by sexual or aggressive behavior accounts for closer approach allowed in the presence of conspecifics. Mating opportunities are not limiting for females in most species and females often have little to gain by interacting aggressively with other females. Therefore, presence of a conspecific male or female may not justify taking greater risk. Results confirm the prediction of optimal escape theory that flight initiation decreases as cost of escaping increases. The sex difference in effect of presence of conspecifics on flight initiation distance is a consequence of the sex difference in costs of escaping. Copyright 2007, Oxford University Press.
... Moreover, these solitaryliving and strictly territorial animals (Gattermann et al. 2001) have been widely used as models for behavioral and stress-related studies (e.g. Cain et al. 2004;Cordner et al. 2004;Gebhardt-Henrich et al. 2007;Taravosh-Lahn and Delville 2004;Touma and Palme 2005;Wommack et al. 2004;Zhang et al. 2008) for which measuring the activity of the hypothalamic-pituitary-adrenal axis is a basic tool . Classically, such studies have relied on blood sampling and the measurement of serum cortisol or corticosterone, depending upon which glucocorticoid is predominantly secreted in each species . ...
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Article
We verified the relevance of measuring fecal glucocorticoid metabolites (FGM) to assess the stress response of the Syrian hamster. Male and female hamsters (n = 10 each) were submitted to an adrenocorticotropic hormone (ACTH) challenge test, whereas animals in the control group received 0.5 mL of sterile isotonic saline solution. All feces voided by each animal were collected at 4 h intervals from 24 h before (baseline) until 48 h after injections. FGM were quantified using an 11-oxoetiocholanolone enzyme immunoassay (EIA). Basal concentrations of FGM were almost four times higher in males than in females. Following ACTH administration, FGM levels started rising from 8 h onwards, reaching peak concentrations 20 or 28 h post injection in males and females, respectively. Despite the much higher absolute concentrations present in males, the relative increase (500%) in response to the ACTH stimulation was similar in both sexes. Sex differences in FGM levels are in accordance with results reported by others regarding the hamster adrenal physiology. The comparison of the adrenocortical response of males and females to an ACTH challenge provided new information about the amplitude and the timing of such a response and the excretion of glucocorticoids in both sexes. We demonstrated for the first time in the Syrian hamster that adrenocortical activity can be monitored in fecal samples in a noninvasive way. Our study provides a humane, practical, and noninvasive alternative to blood removal and therefore a powerful tool for stress-related studies in a species frequently used as an animal model in medical research.
... While our data suggest that chronic passive exposure to aggression predisposes an observer to be aggressive [14], it still remains unclear whether the observer's aggressive behavior results from a stress-related or learned mechanism. Stress-induced aggression has been reported in male rats [17,18] and golden hamsters [19] although there are gender and species-type differences in stressinduced aggression [20,21]. Neurochemical effects of stress include an increase in dopamine D 2 receptor levels in (the shell of) the nucleus accumbens (Acb) [22][23][24][25], as well as an increase in corticosterone levels [22,[25][26][27][28][29]. ...
Article
It has been recently reported that passive exposure to aggression induces aggressive behavior in a rodent model. However, it remains unclear whether this response is correlated with neurochemical changes that correspond either to stress-induced aggression or non-stressed, learned aggression. Stress-induced aggression has been shown to result in increased brain dopamine D(2) receptor and serum corticosterone levels. In contrast, learned aggression is probably associated with reward deficiency syndrome, characterized by low dopamine D(2) receptor levels, without stress effects (i.e., high corticosterone levels). We hypothesized that chronic passive exposure to aggression would produce learned aggression, represented by low levels of dopamine D(2) receptor binding but normal levels of stress hormone. The present study additionally focused on serum testosterone and serotonin 5-HT(1B) receptor density that has been associated with aggression/reward circuits. Hormonal results indicated that there were no differences between the "observer" rats that had been passively exposed to aggression and non-aggression for 10 min/day for 23 consecutive days. However, receptor binding autoradiography identified lower densities of dopamine D(2) receptors in the cortical-accumbal regions (shell of the nucleus accumbens and cingulate and motor cortices) and lower 5-HT(1B) receptor densities in the tegmental regions (ventral tegmental area, substantia nigra pars compacta, and periaqueductal gray) among observers exposed to aggression, compared to controls. Changes in dopamine D(2) receptor densities due to chronic exposure to aggression do not resemble those patterns reported for stress-induced aggressive behavior. Our evidence suggests that the development of aggressive behavior among passive observers occurs through a learned, and not a stress-induced, mechanism.
... In fact, aggression and learning behaviors are common themes across various species. Specifically, aggressive behavior has been investigated not only in rats [e.g., Blanchard and Blanchard, 1990;Blanchard et al., 1993Blanchard et al., , 1995Blanchard et al., , 2001Miczek, 1974;Mikics et al., 2004;Tamashiro et al., 2004;van Erp and Miczek, 2000] but also mice [e.g., Caramaschi et al., 2007;Chiavegatto et al., 2001;Feldker et al., 2006;Fish et al., 1999Fish et al., , 2001, golden hamsters [e.g., Ferris et al., 1997;Taravosh-Lahn and Delville, 2004;Wommack and Delville, 2003], birds [Wingfield et al., 1990[Wingfield et al., , 2000, and fish [Clotfelter and Paolino, 2003]. In addition, animal models have also been used to understand bystander effects [for review, see Bonnie and Earley, 2007]. ...
Article
Previous studies have documented that exposure to aggression increases aggressiveness of human witnesses. However, the question of whether passive exposure to aggression can exclusively cause a risk of aggressive inclination for observers through a learning process, rather than mimicry effect, has not been readily addressed in the clinical literature. This study aimed to investigate this question by using a simple animal model to test the behavioral effect of chronic passive exposure to aggression. Our results indicate that observer rats that had been passively exposed to aggression for 10 min per day for 23 consecutive days exhibited more aggressive behavior than controls or those groups undergoing a single exposure to passive aggression. Furthermore, aggression levels in the group of 23-day chronic exposure to aggression lasted 16 days after the recovery from exposure to aggression. These data suggest that the development of aggression in this model occurred through a learning process because only chronic exposure to aggression resulted in this behavioral outcome in the long run.
... Corticosterone values peaked 1 hour after the injection with a maximum of 53 ng/ml (Fig. 5). Wommack and Delville, 2003;Taravosh-Lahn and Delville, 2004), duration ( Ottenweller et al. 1985), time of day ( Albers et al. 1985), and experience (Weinberg and Wong, 1986). Different methods could explain the discrepant values. ...
... Rodent models also indicated enhanced stress susceptibility during puberty, suggesting that it is a physiological and not psychological phenomenon. Social stress exposure during puberty alters the formation of agonistic behaviors in female golden hamsters (Taravosh-Lahn & Delville, 2004). In addition, social stress during puberty can alter subsequent stress responses (McCormick & Mathews, 2007) as well as substance abuse behaviors in animals (Ferris & Brewer, 1996;McCormick, Robarts, Gleason, & Kelsey, 2004). ...
Article
Exposure to interpersonal violence or abuse affects the physical and emotional well-being of affected individuals. In particular, exposure to trauma during development increases the risk of psychiatric and other medical disorders beyond the risks associated with adult violence exposure. Alterations in the hypothalamic-pituitary-adrenal (HPA) axis, a major mediating pathway of the stress response, contribute to the long-standing effects of early life trauma. Although early life trauma elevates the risk of psychiatric and medical disease, not all exposed individuals demonstrate altered HPA axis physiology, suggesting that genetic variation influences the consequences of trauma exposure. In addition, the effects of abuse may extend beyond the immediate victim into subsequent generations as a consequence of epigenetic effects transmitted directly to offspring and/or behavioral changes in affected individuals. Recognition of the biological consequences and transgenerational impact of violence and abuse has critical importance for both disease research and public health policy.
... It is well known that female hamsters are more aggressive than males. 11 In our case, male hamsters only showed aggressive behavior during the first days of stabulation, however, at sixty days of the stabulated period our female hamsters displayed much more aggressive comportment than males. Moreover, this conduct was maintained and constant. ...
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Article
The flank organ of the Syrian hamster, which shows a biodynamic response to androgen stimulation, is considered a good model for studying the androgen effect on sebaceous gland and hair. This organ is susceptible to programmed cell death (PCD), a prominent feature associated with sexual organ adjustment. We have recently shown the first direct evidence of a relationship between autophagy and morphological changes in androgen-dependent organs. In this work, animals were stabulated (housed) for two months under control conditions and, after sacrifice, autophagy markers, Beclin 1 and LC3-II, were evaluated. The results revealed autophagic processes in the flank organ of both sexes, especially in females, and no detectable caspase-3 activity. Therefore, these data indicated that macroautophagy, and not apoptosis, was the main mechanism by which the flank organ responds to androgen. Here, we present additional data on the flank organ, showing that the intensity of autophagy between genders depends on the length of stabulation. These data could indicate a role for autophagy in response to behavioral influences. A possible explanation and its implication in Syrian hamster social defeat are discussed in this addendum.
... Intense aggression can be provoked by the stress and frustration produced by removing reward (Azrin et al., 1966; Cherek and Pickens, 1970; Gallup, 1965). These effects may be influenced by the development of both aggression and stress circuitries, as repeated or chronic stress applied during puberty alters the progression of development of aggressive behaviors in male (Delville et al., 2003; Wommack et al., 2003) but not female hamsters (Lahn and Delville, 2004), accelerating the onset of adult aggression. In mammals, the circuitries of neural and endocrine stress responses, and those mediating aggressive behavior appear to converge in the hypothalamus, from where the ultimate output is directed. ...
Article
Socially aggressive interaction is stressful, and as such, glucocorticoids are typically secreted during aggressive interaction in a variety of vertebrates, which may both potentiate and inhibit aggression. The behavioral relationship between corticosterone and/or cortisol in non-mammalian (as well as mammalian) vertebrates is dependent on timing, magnitude, context, and coordination of physiological and behavioral responses. Chronically elevated plasma glucocorticoids reliably inhibit aggressive behavior, consistent with an evolutionarily adaptive behavioral strategy among subordinate and submissive individuals. Acute elevation of plasma glucocorticoids may either promote an actively aggressive response via action in specialized local regions of the brain such as the anterior hypothalamus, or is permissive to escalated aggression and/or activity. Although the permissive effect of glucocorticoids on aggression does not suggest an active role for the hormone, the corticosteroids may be necessary for full expression of aggressive behavior, as in the lizard Anolis carolinensis. These effects suggest that short-term stress may generally be best counteracted by an actively aggressive response, at least for socially dominant proactive individuals. An acute and active response may be evolutionarily maladaptive under chronic, uncontrollable and unpredictable circumstances. It appears that subordinate reactive individuals often produce compulsorily chronic responses that inhibit aggression and promote submissive behavior.
Article
In hamsters, exposure to stress in adulthood causes increased body weight. We addressed how social stress during puberty would impact food intake and body weight. Stressed hamsters started gaining significantly more weight than controls after only two days of stress exposure. Over a two-week period, stressed subjects gained 10% more weight and consumed more food than controls. At the end of the stress period, stressed hamsters collected nearly twice as many palatable sugar pellets from an arena than controls. Stressed subjects presented 15–20% more body fat in mesenteric, inguinal, and retroperitoneal fat pads. In order to assess the duration of these effects, we analyzed data from previous studies keeping hamsters for over two months past the stress period in puberty. Our analysis shows that stressed hamsters stopped gaining more weight after the stress period, but their body weights remained elevated for over two months, consistently weighing 10% more than their non-stressed counterparts. We also analyzed conditioning training data collected after the period of stress in late puberty and early adulthood (P56 to P70) that was part of the original studies. Training consisted of lever pressing for palatable food rewards. At these times, previously stressed hamsters retrieved similar numbers of food pellets from the conditioning chambers, suggesting no difference in appetite after the stress period. These data showing a long-lasting effect of stress on body weight may be relevant to studies on the ontogeny of lifelong obesity.
Article
Various forms of early life adversity (ELA) have been linked with increased risk for negative health outcomes, including neuropsychiatric disorders. Understanding how the complex interplay between types, timing, duration, and severity of ELA, together with individual differences in genetic, socio-cultural, and physiological differences can mediate risk and resilience has proven difficult in population based studies. Use of animal models provides a powerful toolset to isolate key variables underlying risk for altered neural and behavioral maturational trajectories. However, a lack of clarity regarding the unique features of differing forms of adversity, lab differences in the implementation and reporting of methods, and the ability compare across labs and types of ELA has led to some confusion. Here, we highlight the diversity of approaches available, current challenges, and a possible ways forward to increase clarity and drive more meaningful and fruitful implementation and comparison of these approaches.
Article
Although many people think of aggression as a negative or undesirable emotion, it is a normal part of many species’ repertoire of social behaviors. Purposeful and controlled aggression can be adaptive in that it warns other individuals of perceived breaches in social contracts with the goal of dispersing conflict before it escalates into violence. Aggression becomes maladaptive, however, when it escalates inappropriately or impulsively into violence. Despite ample data demonstrating that impulsive aggression and violence occurs in both men and women, aggression has historically been considered a uniquely masculine trait. As a result, the vast majority of studies attempting to model social aggression in animals, particularly those aimed at understanding the neural underpinnings of aggression, have been conducted in male rodents. In this review, we summarize the state of the literature on the neurobiology of social aggression in female rodents, including social context, hormonal regulation and neural sites of aggression regulation. Our goal is to put historical research in the context of new research, emphasizing studies using ecologically valid methods and modern sophisticated techniques. This article is part of the Special Issue entitled ‘Current status of the neurobiology of aggression and impulsivity’.
Article
Syrian hamsters readily display territorial aggression; if they lose even a single agonistic encounter, however, hamsters show striking reductions in aggressive behavior and increases in submissive behavior, a distinct behavioral change that we have previously termed conditioned defeat. This acute social defeat stressor is primarily psychological and is effective in both males and females. Therefore, we maintain that this procedure presents an ideal model for studying behavioral and physiological responses to social stress. Here, we demonstrate that social avoidance following social defeat is a particularly useful dependent measure because of its sensitivity and stability between sexes and across the estrous cycle. In addition, we demonstrate that peripubertal hamsters exposed to a single, 15min social defeat exhibit significantly more social avoidance 24h later when compared with no-defeat controls. Later, defeated and non-defeated hamsters displayed similar agonistic behavior in adulthood indicating that the peripubertal defeat did not alter adult territorial aggression. After experiencing an additional social defeat in adulthood, however, the hamsters that experienced the pubertal defeat responded to the adult defeat with increased social avoidance when compared with hamsters that were defeated only in adulthood and with no-defeat controls. These data are the first to show that a single social defeat in puberty increases susceptibility to later social defeat in both males and females.
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In the last decade much progress has been made in research using animal models of developmental psychopathology. The field has moved from the demonstration of long-term impacts of early adversity on behavioral and physiological development and the role of genetic risks for vulnerability, to including transgenerational transmission of stress-induced phenotypes through epigenetic modifications. Additional and critical paradigm shifts have also taken place, including increased focus on ecologically and ethologically valid animal models, research on resilience, the adolescent transition as a period of brain and behavioral reorganization, and sex differences. In this chapter we review recent literature using rodent and nonhuman primate animal models that examines the biological mechanisms through which the early environment programs neurobehavioral, cognitive, and physiological development. We discuss the evolutionary role of this plasticity on behavioral development, as it has an adaptive value in changing environments. Because of maternal care's critical role in early environment, we focus on models that study the effects of mother–infant relationship disruption and dissect the mechanisms by which maternal care regulates the development of brain circuits that control emotional and social behaviors of relevance for developmental psychopathology. Finally, we discuss developmental sensitive/critical periods as windows of opportunity for plastic adaptation of developing organisms to the environment that, if taken too far—as in the case of early traumatic experiences such as childhood maltreatment—lead to maladaptive developmental trajectories (psychopathology, pathophysiology). Animal models of early life adversity are paramount to understand the basic mechanisms and principles that translate early experience into developmental outcomes in our own species.
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Hamsters are an ideal animal model for a variety of biomedical research areas such as cancer, virology, circadian rhythms, and behavioural neuroscience. The use of hamsters has declined, however, most likely due to the dearth of genetic tools available for these animals. Our laboratory uses hamsters to study acute social stress, and we are beginning to investigate the genetic mechanisms subserving defeat-induced behavioural change. We have been limited, however, by the lack of genetic resources available for hamsters. In this study, we sequenced the brain transcriptome of male and female Syrian hamsters to generate the necessary resources to continue our research. We completed a de novo assembly and after assembly optimization, there were 113,329 transcripts representing 14,530 unique genes. This study is the first to characterize transcript expression in both female and male hamster brains and offers invaluable information to promote understanding of a host of important biomedical research questions for which hamsters are an excellent model.
Noninvasive techniques to monitor reproductive or stress hormones are now widely used in captive and free-ranging wildlife. These methods offer great advantages and deserve to be used also in laboratory rodents. However, we remain naive about factors that may influence the accuracy of these techniques. The aim of this study was to evaluate the adequacy of measuring the concentration of cortisol fecal metabolites to assess the physiologic stress response. Ten adult female Syrian hamsters were ovariectomized, and all feces voided were collected daily for 4 d before and 5 d after surgery. Cortisol fecal metabolites were extracted and quantified by radioimmunoassay. We determined per-gram fecal cortisol metabolite concentrations, total 24-h fecal output and total 24-h fecal cortisol metabolite production. Surgery considerably affected fecal output, and using per-gram versus total cortisol metabolites led to different conclusions: whereas concentrations increased significantly just after ovariectomy and decreased on subsequent days, the total excreted cortisol metabolites varied in a symmetrical pattern. Therefore, the relative per-gram measure of hormones may not reflect the total amount of circulating hormones, because these measures are comparable only if the volume of the material in which the hormone is contained is the same in the 2 groups.
Article
In pubertal male Syrian hamsters, exposure to anabolic/androgenic steroids (AAS) during adolescence facilitates a high level of offensive aggression modulated by the enhanced development and activity of the vasopressin (AVP) and dopamine (DA) neural systems within the latero-anterior hypothalamus (LAH), that is, a brain region implicated in the control of aggression. The present studies provide a detailed report of the pharmacologic interactions between AVP and DA D2 receptor signaling within the LAH in the control of adolescent AAS-induced offensive aggression. Male Syrian hamsters were treated with AAS throughout adolescence and tested for aggression after local infusion of the DA D2 receptor antagonist eticlopride (ETIC) alone, or in combination with AVP in the LAH in an effort to determine the influence of DA D2 receptors relative to AVP-receptor mediated aggression mechanisms. As previously shown, ETIC infusion into the LAH suppressed adolescent AAS-induced aggressive responding; however, the AAS-induced aggressive phenotype was rescued by the coinfusion of AVP into the LAH. These behavioral data indicate that interactions between AVP and DA neural systems within the LAH modulate the control of aggression following adolescent exposure to AAS and that DA D2 receptor signaling functions upstream of AVP in the LAH to control this behavioral response. (PsycINFO Database Record (c) 2015 APA, all rights reserved).
Article
Studies on the behaviour of the common hamster are very rare and fragmentary. From August till the middle of September 2005 we observed behaviour of six individuals of the common hamster (one female and five juveniles: three males and two females) and from the second part of September till October 2005 we observed behaviour of two juvenile males after they were separated from the group. The “Focal animal sampling” was used as an observation method, and the total time of observation amounted to 75 hours. During our observation 7707 bouts of behaviour were recorded. Both social and non-social behaviour were categorised. The number of the non-social behaviour prevailed significantly over the number of the social behaviour (n=496; 6.4%). The most frequent observed non-social behaviour was: head rearing (n=2019; 28%). Among interindividual interactions “escape” (45.4%; n=225) and “vocalisation” (15.7%; n=78) were noticed most frequently. Play-fighting, direct identification, following and hugging were the only aspects of the social behaviour characteristic of the young.The behaviour repertoire of the common hamster seems to be similar to the behaviour of the golden hamster (Mesocricetus auratus).
Article
Although early paternal deprivation significantly affects offspring behavioral and neuroendocrine development, the link between paternal deprivation and social play behavior remains unclear. Mandarin voles (Microtus mandarinus) are socially monogamous and display bi-paternal care. The present study examined the development of social play in juvenile male mandarin voles and the paternal influence on play-fighting, vasopressin- and oxytocin-immunoreactive neurons and serum corticosterone and testosterone levels. The results show that social play was more pronounced during postnatal days 28-35, differing from the ontogenetic pattern of other forms of social behavior. On postnatal day 35, the peak in play-fighting activity, paternal deprivation reduced boxing/wrestling levels and vasopressin-immunoreactive neurons in the anterior hypothalamus and oxytocin-immunoreactive neurons in the paraventricular nucleus, but increased vasopressin-immunoreactive neurons in the paraventricular nucleus and corticosterone levels. These results suggest that mandarin voles engage in social play according to an inverted U-shaped curve in ontogeny, and paternal deprivation influences the development of offspring play-fighting; hypothalamic vasopressin, oxytocin and serum corticosterone may play a modulatory role in the alteration of play-fighting elicited by paternal deprivation; decreased play-fighting may correlate with depressed vasopressin levels in the anterior hypothalamus.
Article
This study was focused on determining the possible role of corticotropin-releasing hormone (CRH) on play fighting in juvenile golden hamsters. As no specific neural sites have been proposed, we looked for changes in CRH innervations at the peak of play-fighting activity on postnatal day 35 (P-35) from a week before on P-28. We noted that the increase in play-fighting activity between these two dates was associated with a 100% increase of the density of CRH fibers within the lateral septum. We, then, tested the possible role of CRH receptors on play fighting within the lateral septum through microinjections of alpha-helical CRH, a CRH receptor antagonist (either 0, 30, or 300 ng), directly into the area. The treatments inhibited play-fighting attacks and pins as well as reduced the duration of time that the resident hamsters spent in contact with the intruders, though locomotor activity remained unaffected. The possible source of CRH release in the lateral septum was addressed by quantification of CRH neurons also labeled with a marker of cellular activity, c-Fos, after consummation of play fighting. CRH neurons in the horizontal part of the diagonal band, an area reciprocally connected with the lateral septum, showed a 75% increase in double labeling with c-Fos as compared to controls. Together, these data show that CRH receptors in the lateral septum have a general role on play fighting, not just facilitating its consummation, but also likely enhancing appetitive aspects as well. In addition, this effect is associated with enhanced CRH availability in the area and enhanced neuronal activity within interconnected areas.
Article
Vasopressin facilitates aggression in adult hamsters. Whether this neuropeptide has a similar role in play fighting remains unknown. The goal of the present study was to identify whether vasopressin controls play fighting in juvenile golden hamsters as well. Juvenile male golden hamsters were tested for play fighting after microinjections of a vasopressin V1A-receptor antagonist, Manning compound, either 0, 9, or 90 microM, into the anterior hypothalamus. The treatment selectively inhibited offensive aspects of play fighting in experimental animals. Attack frequencies were significantly decreased by both doses of Manning compound. In addition, the high dose of the receptor antagonist increased attack latencies, decreased bite frequencies, and decreased the averaged number of attacks per contact bout. Together, these results show that vasopressin controls offensive behaviors throughout development from play fighting in juveniles to aggression in adults.
Article
During puberty, the agonistic behaviour of male golden hamsters undergoes a transition from play fighting to adult aggression. Repeated exposure to social stress early in puberty accelerates this transition. The present study investigated the possible role of glucocorticoids on the maturation of agonistic behaviour. First, we compared serum cortisol levels following a 20-min restraint stress during early puberty, mid-puberty or adulthood. Across puberty, animals exhibited a two-fold increase in post-restraint cortisol levels. We also compared corticotrophin-releasing hormone (CRH) immunoreactive fibres projecting to the median eminence between animals in early puberty and adulthood. The CRH fibre density was two-fold greater in adults compared to juveniles. Furthermore, we investigated the effects of stress hormones on the maturation of agonistic behaviour. Male hamsters were injected daily with dexamethasone, a corticosteroid receptor type II agonist (0, 10 or 40 microg/100 g), early in puberty from postnatal day 31 (P-31) to P-36. When paired with a smaller and younger intruder on P-37, attack frequency did not differ between groups. However, dexamethasone-treated animals showed a dose-dependent decrease in the percentage of play-fighting attacks and an increase in the percentage of adult attacks. In summary, puberty can be described as a period of increasing hypothalamic-pituitary-adrenal activity in male golden hamsters. Moreover, increasing glucocorticoid levels influence the maturation of agonistic behaviour. These data shed new light on the neuroendocrine mechanisms that regulate the maturation of social behaviours during puberty.
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Studies in several species of rodents show that arginine vasopressin (AVP) acting through a V1A receptor facilitates offensive aggression, i.e., the initiation of attacks and bites, whereas serotonin (5-HT) acting through a 5-HT1B receptor inhibits aggressive responding. One area of the CNS that seems critical for the organization of aggressive behavior is the basolateral hypothalamus, particularly the anterior hypothalamic region. The present studies examine the neuroanatomical and neurochemical interaction between AVP and 5-HT at the level of the anterior hypothalamus (AH) in the control of offensive aggression in Syrian golden hamsters. First, specific V1A and 5-HT1B binding sites in the AH are shown by in vitro receptor autoradiography. The binding for each neurotransmitter colocalizes with a dense field of immunoreactive AVP and 5-HT fibers and putative terminals. Putative 5-HT synapses on AVP neurons in the area of the AH are identified by double-staining immunocytochemistry and laser scanning confocal microscopy. These morphological data predispose a functional interaction between AVP and 5-HT at the level of the AH. When tested for offensive aggression in a resident/intruder paradigm, resident hamsters treated with fluoxetine, a selective 5-HT reuptake inhibitor, have significantly longer latencies to bite and bite fewer times than vehicle-treated controls. Conversely, AVP microinjections into the AH significantly shorten the latency to bite and increase biting attacks. The action of microinjected AVP to increase offensive aggression is blocked by the pretreatment of hamsters with fluoxetine. These data suggest that 5-HT inhibits fighting, in part, by antagonizing the aggression-promoting action of the AVP system.
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Septal ablation in 19 male golden hamsters produced no increases in affective reactivity as scored on a six test rating schedule of emotionality. Examination of the comparative data shows that appearance of a septal syndrome, such as that seen in the rat, is relatively rare and suggests that it may be independent of other effects of septal lesions common to a number of species.
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This chapter begins with a discussion of the development of agonistic behavior in mammals. It then discusses the adaptive value of play and play fighting, sex differences and hormonal control of play fighting, neural control of play fighting, and controlling the time course of the maturation of agonistic behavior. It shows a correlation between that maturation of aggressive behavior and maturation of the the hypothalamic-pituitaryadrenal axis (HPA). The HPA axis controls the maturation of aggressive behavior during puberty. It is also likely that adrenarche, the onset of the activity of the HPA axis, controls the appearance of aggressive responses before puberty. This regulation mechanism may provide an explanation for interactions between genes and the environment, as the activity of the HPA axis differs between individuals and can be affected by external stimuli, such as stress.
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In golden hamsters, offensive aggression is facilitated by vasopressin and inhibited by serotonin. We tested whether these neurotransmitter systems respond to modifications resulting from the stress of threat and attack (i.e., social subjugation) during puberty. Male golden hamsters were weaned at postnatal day 25 (P25), exposed daily to aggressive adults from P28 to P42, and tested for offensive aggression as young adults (P45). The results showed a context-dependent alteration in aggressive behavior. Subjugated animals were more likely to attack younger and weaker intruders than nonsubjugated controls. Conversely, subjugated animals were less likely to attack animals of similar size and age. After testing, the animals were killed, and their brains were collected to determine whether these behavioral changes are underlined by changes in the vasopressin and serotonin systems. Social subjugation resulted in a 50% decrease in vasopressin levels within the anterior hypothalamus, a site involved in the regulation of aggression. Furthermore, whereas the density of vasopressin-immunoreactive fibers within the area was not significantly altered in subjugated animals, the number of serotonin-immunoreactive varicosities within the anterior hypothalamus and lateral septum was 20% higher in subjugated animals than in their controls. These results establish puberty as a developmental period sensitive to environmental stressors. Furthermore, the results show that changes in the vasopressin and serotonin systems can correlate with behavioral alterations, supporting the role of these two neurotransmitters in the regulation of aggression.
Chapter
In most research involving Syrian golden hamsters, the species is used as an animal model or “subject” and as such is totally unidimensional. There is no consideration of its evolution, of its domestication history, or of its ecology and ethology; nor is there any obvious need for these factors to be considered. We know that the hamster comes from the breeder, or comes from a cage, and that is enough. This situation was indeed the way in which I first encountered the hamster, but I soon found the relationship to be incomplete. My search for the real hamster began after my first talk at a scientific convention when I was “informed” by a member of the audience that the hamster was a cross between a rat and a guinea pig, and although there were many doubts expressed, neither I nor any other of those present were confident enough to challenge this absurd hybrid notion.
Chapter
In this chapter, I concentrate on the analysis of specific signals and their behavioral functions. More integrative treatments concerning sexual and aggressive behavior and their endocrine mechanisms can be found in other chapters of this volume. Section 2, on postures used during social interactions, should be useful for anyone beginning behavioral studies of hamsters. In Sections 3, 4, and 5 I have summarized and evaluated the more extensive literature on auditory and chemical communication.
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The study of aggressive behavior in hamsters has focused on five major areas and this chapter is organized accordingly. The first topic involves a description of the aggressive and submissive behaviors associated with intraspecific encounters. As will be seen, the effectiveness of a variety of experimental treatments is in part determined by which behaviors are chosen for measurement. The second section discusses the different testing conditions that have been used because these too represent potential sources of discrepancy among investigators. The third section analyzes the role of hormones, those administered exogenously and those secreted normally during the reproductive cycle. The effect of damage to central nervous system structures is the fourth topic and the final section includes peripheral influences (e.g., role of the flank glands, harderian glands, and so forth).
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Study of behavioral development in hamsters had its formal beginnings in German ethology in the work of Dieterlen, Eibl-Eibesfeldt, and others. These studies offered some of the first descriptions of hamster pup behavior and established an important precedent for experimental inquiries into developmental mechanisms by the use of hamsters reared in isolation—the so-called Kaspar-Hauser animals (Dieterlen, 1959)—to test the importance of environmental stimuli on behavioral development.
Article
Play behavior, as indicated by frequency and duration of pinning behavior, was studied in young rats between 18 and 64 days of age. The incidence of play was markedly increased by social isolation. Play increased from 18–28 days of age, peaked between 32 and 40 days of age, and gradually declined thereafter. Animals developed stable “dominance hierarchies” during the course of testing so that one animal pinned the other on the average 70% of the time. Also, “dominant” animals exhibited the longer pin durations. The data indicate that social play can be efficiently studied in the laboratory rat and, further, that one function of play may be to establish stable social relationships.
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Play-fighting (PF) in 6 pairs of deer mice (DM), prairie voles (PVs), and montane voles (MVs) was compared with that of laboratory rats. Play in rats appeared more complex for 2 reasons: (1) more of the playful contacts elicited defensive behaviors and (2) more of these defenses led to counterattacks and role reversals between attackers and defenders. Neither high levels of defense, as shown by MVs, nor high levels of counterattack, as shown by PVs, produced rat-like PF. This only occurred when high rates of defense involving turning to face the attacker and counterattack were combined, as in rats. Findings suggest that DM rarely exhibit rat-like PF. Playful counterattack appeared to arise from playful attack and not from an escalation of defense. More complex forms of social play may have evolved via the escalation of defense in response to playful attack. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
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The development of behavior in Sprague-Dawley descendants was observed in 13 litters, and detailed qualitative and quantitative descriptions are reported. Results include information on postural development, (lying, sitting, standing), reflex figures (twitching, head waving, stretching and yawning, body flexion, righting reaction, freezing, sniffing, auditory orientation reactions, visual orientating reactions), functional activities (sleeping, consummatory behavior, locomotor activity, climbing, grooming, exploration, manipulation, digging, defecation) and social behavior. (19 ref.) (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Article
Play-fighting appears to involve the behavior patterns of attack and defense otherwise seen in serious fighting. The degree of similarity, however, depends on the body targets attacked and defended during these forms of fighting. For many taxa, including diverse mammalian families and some birds, the same targets are attacked and defended during both play-fighting and serious fighting. However, for several species of muroid rodents, the targets of play-fighting are not the same as those of serious fighting. In these cases, the tactics of attack and defense are also different. It is argued that for these muroid species the playful targets have arisen from amicable behavior (e.g., social investigation, greeting, allogrooming) rather than, as appears to be the case in so many other taxa, from agonistic behavior. These data strongly suggest that “play-fighting” has evolved from different precursors in different taxa and thus has multiple origins. Furthermore, these data have an important bearing on the universal applicability of many of the suggested functions of play-fighting and also on how such behavior is to be described and classified.
Article
Play fighting in the Syrian Golden hamster Mesocricetus auratus can be distinguished from serious fighting by the targets attacked in each case. In play fighting, the animals attack and defend the cheeks and cheek pouches, whereas in serious fighting they attack and defend the rump and lower flanks. Since play typically involves the use of behaviors borrowed from other functional contexts, this paper investigates the origin of the cheek target during play fighting. Comparison of resident-intruder serious fighting with awake and anesthetized intruders does not reveal the cheek to be an inhibited target for serious attack. Similarly, analysis of social investigation and allog-rooming, while revealing the ears to be important targets, do not show the cheeks to be targets in these behaviors. Sniffing, licking, and nibbling of the cheek area appear to occur mainly during sexual encounters by males. This area, seemingly a sexual target, may be the one utilized during play fighting.
Article
Play-fighting is often difficult to differentiate from inhibited or immature serious fighting because both may utilize many of the same behavior patterns. In the rat the two behaviors involve different targets of attack. During play-fighting, snout or oral contact is directed at the opponent's nape of the neck, whereas during serious fighting, male residents mostly direct their bites at the intruder's rump. Although similar to those used in serious fighting, the behavior patterns used during play-fighting are modified to achieve the different targets of attack. Even though the tactics of attack and defense appear more adult-like with increasing age, the playful targets persist well into adulthood.
Article
Golden hamsters start displaying flank marking behavior (a form of scent marking) around postnatal day 20 (P-20). Because the behavior is dependent upon the central activity of arginine vasopressin (AVP), the present study was conducted to correlate this activation with changes in the vasopressinergic system. A first set of experiments was performed to compare flank marking activity between P-18 and P-22. A second set of experiments was performed to compare the density of AVP receptors between the age periods and assess responsiveness to AVP microinjection. Finally, a third set of experiments incorporated immunocytochemistry, radioimmunoassay, in situ hybridization, and Northern blot analysis to determine the location and numbers of AVP immunoreactive neurons and the level of mRNA correlating with the developmental onset of flank marking behavior. Our results show that flank marking develops between P-18 and P-22. Male and female hamsters do not display odor-induced flank marking anytime before P-19. However, all animals show odor-induced flank marking by P-22. The onset of flank marking does not appear to be associated with any change in AVP receptor binding in the anterior hypothalamus. Indeed, flank marking can be triggered in hamsters on P-18 by the microinjection of AVP in the anterior hypothalamus. This would suggest that the postsynaptic mechanisms contributing to the transduction of the AVP signal and the motor control of flank marking are intact prior to the onset of odor-induced flank marking. In contrast, AVP levels in the hypothalamus and pituitary increase by two to threefold between P-18 and P-22, suggesting that changes in AVP synthesis and release from presynaptic sites may contribute to the onset of flank marking. Interestingly, there is no change in AVP mRNA between P-18 and P-22, which raises questions about posttranslational processing during this developmental period. These results suggest that heightened synthesis and release of AVP between P-18 and P-22 may contribute to the developmental onset of flank marking. © 1996 John Wiley & Sons, Inc.
Article
Vasopressin-sensitive neurons in the region of the anterior hypothalamus are necessary for the mediation of flank marking behavior in the Golden hamster. The precise nature of the vasopressinergic innervation to the anterior hypothalamus is unknown. In this study we seek to examine the potential sources of this innervation by mapping and counting the vasopressin-immunoreactive neurons that contribute to the hypothalamo-neurohypophysial system, and those that do not. Vasopressin-immunoreactive neurons in the hypothalamus were visualized by immunocytochemistry. Sections were mapped with a computer-aided microscope system, and labeled neurons counted. Two-dimensional maps were stacked into a three-dimensional wireframe model which could be manipulated for further examination. The average number of vasopressin neurons was 3,135, with over 60% of all perikarya localized to the lateral supraoptic nucleus. In a double-labeling study, neurons contributing to the hypothalamo-neurohypophysial system were retrogradely labeled by the injection of horseradish peroxidase into the neurohypophysis. The enzyme reaction product was visualized by treatment with tetramethylbenzidine followed by nickel-conjugated diaminobenzidine. Sections were subsequently stained for vasopressin by immunocytochemistry. Single- and double-stained neurons from serial sections were mapped and counted. Wireframe and contoured three-dimensional representations were generated. The average number of neurons projecting to the neurohypophysis was 5,619. However, an average of 981 neurons was immunoreactive to vasopressin but devoid of horseradish peroxidase. The greatest number of these non-projecting perikarya were found in and around the anterior hypothalamus, localized primarily in the lateral and medial aspect of the supraoptic nuclei, the ventral area of the paraventricular nucleus, and the nucleus circularis. By comparing the number of non-projecting neurons found by double-staining to the total cell count of the entire vasopressin system, it was estimated that approximately 30% of all vasopressin neurons in and around the anterior hypothalamus did not project to the neurohypophysis. Based on the distribution and localization of the non-projecting perikarya, it is speculated that these neurons may provide neurotransmitter for vasopressin-dependent flank marking in the male Golden hamster.
Article
Nine female and 10 male adult golden hamsters were tested intact and gonadectomized with identical doses of heterologous and homologous gonadal hormones for mating behavior, investigatory behavior, aggressive patterns, and “marking.” All experimental animals were tested under all hormone treatments with both intact male and estrous female test partners.Lordosis responses were shown by females under conditions of natural and induced estrus. Lordosis responses were shown by castrated males after administration of estrogen and progesterone, estrogen alone, and testosterone propionate. The males showed lordoses most consistently after estrogen and progesterone, but even under this condition the lordoses were of significantly shorter duration than those shown by females.Mounting behavior of males was independent of hormonal state, although intromissions and ejaculations were only seen when the males had some source of androgen. Only one female hamster displayed mounting behavior. These data are interpreted in light of the “organizational theory of sexual behavior” as currently proposed.
Article
The effects of social deprivation schedules and days of testing on the play-fighting of juvenile golden hamsters were investigated. In Experiment 1, subjects totally (individually housed) or partially isolated (individually housed, but separated by a wire mesh 2 cm from another animal) for a period of 48 h spent significantly increased peer-peer bodily contact, play fighting, and play-fighting relative time (% of bodily contact time spent in play fighting), but exhibited decreased locomotor activity on the 1st day of testing. In Experiment 2, subjects reared since the 10th postnatal day with their mothers alone (chronically deprived of peer-peer social interactions) exhibited similar performances, except that locomotor activity was not affected. All dyads exhibited increased pinning turbulence (number of pinnings divided by time spent in play fighting) on the 1st day of testing, and the interactions between variables (deprivation schedules and days of testing) were statistically significant in most cases, suggesting that unfamiliarity between interactors also affect the performances of animals. We conclude that golden hamsters are sensitive to social deprivation, mothers do not substitute peer companions, animals reared in single-infant litters basically behave like socially-isolated animals, and the effects of induced social deprivation are reversible and disappear on days following testing.
Article
The present study was done to determine whether the vasopressinergic neurons in the hypothalamus controlling flank marking behavior are distinct from the magnocellular neurons comprising the hypothalamo-neurohypophysial system. Animals were either hypophysectomized or injected with a suicide transport lectin, volkensin, into the neurohypophysis. Both procedures resulted in a pronounced loss of vasopressin-immunoreactive perikarya throughout the hypothalamus concomitant with increases in water intake and urine output and decreases in circulating levels of vasopressin. The loss of the hypothalamo-neurohypophysial system was most pronounced in volkensin-treated animals that presented with frank diabetes insipidus and exceedingly low levels of plasma vasopressin. However, the vasopressinergic fibers and magnocellular neurons in and around the anterior hypothalamus implicated in the control of flank marking survived the volkensin treatment. Volkensin-treated animals exhibited levels of flank marking typical of untreated animals. These data suggest the presence of anatomically and functionally distinct populations of vasopressinergic magnocellular neurons in the hypothalamus of the golden hamster.
Article
This paper considers the functional significance of the testosterone-dependent vasopressinergic neurons of the medial amygdala (Ame) in intermale aggressive behavior of rats. Local microinfusion of vasopressin into the medial amygdala causes an increase in offensive behavior both in gonadally intact males and in animals that were castrated 1 week or 6 months prior to the experiment. The absolute level of offense after arginine-vasopressin (AVP) treatment declined with time after castration indicating that the behavioral consequences of AVP in the Ame are at least partially independent of testosterone. The discussion considers the possibility that AVP in the medial amygdala is involved in the modulatory role of this structure in social learning and memory processes.
Article
Abstract It is well established that flank marking behavior in the Golden hamster is controlled by vasopressin-sensitive neurons localized to the anterior hypothalamus; however, the source(s) of vasopressinergic innervation to this area is unknown. Previous analysis by immunocytochemistry showed distinct populations of vasopressinergic magnocellular neurons localized to the supraoptic nucleus, paraventricular nucleus and the nucleus circularis that did not project to the neurohypophysis. In the present study, these same hypothalamic nuclei were lesioned by microinjection of kainic acid to determine which, if any, of these populations of vasopressin neurons are involved in the control of flank marking. Unilateral lesions in the areas of the nucleus circularis and supraoptic nucleus at the rostro-caudal plane of the anterior hypothalamus abolished odor-induced flank marking behavior. Lesions in the paraventricular nucleus at the level of the anterior hypothalamus did not consistently inhibit flank marking, while lesions of magnocellular neurons rostral or caudal to the anterior hypothalamus were ineffective. The microinjection of vasopressin into the anterior hypothalamus following lesion of the paraventricular and supraoptic nuclei stimulated flank marking, evidence that treatment with kainic acid did not damage the efferent component of this behavior. However, animals with lesions in the nucleus circularis did not respond to the microinjection of vasopressin; hence, it is uncertain whether lesions in this area disrupt vasopressinergic innervation to the anterior hypothalamus or simply destroy the motor neurons controlling flank marking. In summary, the data clearly demonstrate that vasopressin neurons localized primarily to the medial aspect of the supraoptic nucleus are necessary for sensory integration of odor-induced flank marking, and as such, may be one possible source of neurotransmitter controlling this behavior.
Article
A procedure has been developed which reliably engenders agonistic behavior between alpha males of small colonies of laboratory rats and intruder rats. Drugs were administered either to the alpha resident male rat, who showed the pattern of attack and threat behavior, or to the intruder rat, who engaged in defensive, submissive, and flight reactions. The 5-min test also permitted assessment of drug effects on nonagonistic social and solitary behavior. Administration of d-amphetamine at a very low dose (0.063 mg/kg) to resident alpha rats increased the frequency of their attacks, sideways threats, and pursuits, while low doses of cocaine (0.5, 2.0 mg/kg) failed to alter any of these behaviors significantly. Attack and threat behavior was effectively decreased by 0.25–1.0 mg/kg d-amphetamine and by 8 and 32 mg/kg cocaine. The antiaggressive effects of amphetamine, but not cocaine, were accompanied by a marked increase in nonagonistic rearing and walking. Amphetamine administration to intruder rats produced an increase in nonagonistic locomotor activity and caused the intruders to be attacked more frequently, to escape more often, and to emit fewer ultrasonic vocalizations. Cocaine did not alter significantly the intruders' behavior. The resident-intruder situation appears to be a reliable, easy-to-use procedure detecting differential behavioral effects of psychomotor stimulants, such as d-amphetamine and cocaine, while avoiding the confounding influence of aversive stimulation, conditioning, and screening of suitable subjects typically associated with aggression tests in the laboratory.
Article
Male (1--60 days old) and female (1--30 days old) hamsters were decapitated and serum levels of LH, FSH, PRL, progesterone, androgens (males), and estradiol (females) were measured by RIA. Males and females had similar levels of LH until 15 days of age and of FSH until 12 days of age, at which times gonadotropin levels increased significantly in females. Peak levels for females occurred on days 19--21 for LH and on days -2--24 for FSH, later than the times reported for female rats. Adjusting female gonadotropin peaks for gestation length places these peaks for hamsters and rats at the same time in postmating age. In female hamsters, large variations occur in LH between 16--25 days of age, as reported for female rats. Males reached peak serum levels of LH and FSH on day 40, just before the first motile epididymal sperm. Serum PRL levels were identical in male and female hamsters until at least day 30. PRL levels sharply increased in both sexes after day 18 and remained elevated until at least day 30. In males, serum androgens were low until 30 days of age, in contrast to high levels reported for infantile rats. Androgens rose sharply in male hamsters after day 30 to peak levels on day 50. Progesterone in males also remained low until after day 30. Serum estradiol in females did not attain the extremely high elevations seen in rats. Some fluctuations occurred between 10--30 days of age, which presumably represent maturational changes in the ovary. Serum progesterone in females followed a pattern of development similar to estradiol.
Article
Social subordination, which suppresses gonadal function in juvenile and adult male house mice, also suppresses the activity of an androgen-dependent urinary pheromone that accelerates the rate of sexual maturation in juvenile females. Pheromone production may also be suppressed by the presence of pregnant or lactating females. This suggests that the social environment may influence the fertility of population females by altering urinary pheromone activity in the male.
Article
The aggressive behaviour of female hamsters was studied while they were housed in large enclosures with males and in brief tests with males or females. Some females are not aggressive with any male, whereas others are very aggressive toward all males in both testing conditions. Females that are not aggressive toward intact males may be very aggressive toward castrated males or females. When the animals are housed together for long periods of time, males dominate only if they are much heavier. Male dominance takes a relatively long time to establish and often there is an equivocal period characterized by reversals of dominance. Female dominance is rapidly established. Unless the male is much heavier, the female determines the presence or absence of agonistic behaviour.
Article
Social, olfactory, and oestrous cycle influences on the frequency of flank-marking and vaginal marking were studied in female hamsters. Vaginal marking was more frequent in the presence of males or their odours than females or their odours. Vaginal marking frequency was greatest the day before oestrus (day 4), intermediate on days 2 and 3, and zero on the oestrous day. The probable sexual advertisement functions of vaginal marking were discussed. In contrast, flank-marking by females was stimulated more by other female odours than by male odours. The frequency of flank-marking was elevated by agonistic encounters and was reduced by sexual encounters. Flank-marking seems to have functions related to functions of aggression among hamsters.
Article
Im Band 37, Heft 2, Seite 213, soll der erste Satz des Abstract wie folgt verbessert werden: 8 male golden hamsters were observed two at a time in a plexiglas cage (area roughly 11 sg. ft.) subdivided into 47 connected compartments. 8 malexj golden hamsters were observed two at a time in a plexiglas cage (area roughly 11 sp. ft.) subdivided into 47 connected compartments. Each pair spent 2–3 weeks in this cage, observations lasting 1–2 weeks. Dominance relationships, food hoarding and marking behaviour in this situation are described.
Article
Eight litters of hamsters living in a large enclosure were observed from birth to 120 days. For the first 65 days each litter was confined to a separate compartment. Basic motor coordination was reached by the 3rd week. Marking was seen during the 6th week when males began to mount their mothers sexually, but lordosis was not seen in female pups before the 7th week. Fighting appeared at this time with the females being the more aggressive. At 65 days the litters were combined into 2 groups of 4.A gradual shift followed in the relative aggressiveness of the sexes. Females, which had previously initiated over 90% of attacks, became less aggressive, whereas attacks by males increased to the former female level. This unusual behavior for hamsters, where females are normally dominant, may have been due to crowding. Also, severe disruption of maternal behavior occurred with marked infanticidal tendencies.
Article
Play fighting of homosexual and heterosexual dyads in golden hamsters was studied. The behaviors of male-male (MM), female-female (FF), and female-male (FM) dyads were recorded from the 25th to the 31st day of age. Play fighting activity of heterosexual dyads was depressed since MF and FM dyads exhibited a significantly high physical contact time and engaged in less play fighting, with a significantly lower time spent on such activity. Alternation ratio in the pinning posture was very high and subjects did not differ in the mean number of active (top) and passive pinning (under) in each dyad, showing an inexistence of sex dominance. In most cases, differences in the performances of MM and FF dyads were not significant. We have concluded that play fighting in golden hamsters may be predominantly modulated by environmental stimuli (sex of the partner) rather than by endogenous stimuli (androgen level).
Article
Syrian hamsters can communicate using a distinctive form of scent marking called flank marking. Vasopressin-sensitive neurons within the medial preoptic-anterior hypothalamic continuum (MPOA-AH) play a critical role in the control of this form of olfactory communication. Extrahypothalamic regions may also mediate hamster flank marking. Since the MPOA-AH and the periaqueductal gray (PAG) are reciprocally connected, the present study investigated whether PAG neurons are involved in the control of flank marking. The first study found that microinjection of vasopressin, but not oxytocin or saline, into the PAG induced high levels of flank marking in male (n = 8) and female (n = 5) hamsters (P less than 0.01). The second study demonstrated that microinjection of vasopressin into the PAG stimulated flank marking in a dose-dependent manner in both male (n = 7) and female (n = 11) hamsters (P less than 0.01). These data suggest that vasopressin-responsive neurons within the periaqueductal gray participate in the control of hamster flank marking.
Article
Monoclonal antibodies to oxytocin (OT) and vasopressin (VP) revealed some positively staining stromal cells in the subcapsular cortex and in the medulla of the human thymus. We further demonstrated that these cells are a subset of epithelial endocrine cells and also contain immunoreactive interleukin-1 together with the neuropeptides. In addition, the thymic cells stained by monoclonal antibodies directed to the cyclic part of oxytocin or vasopressin also contained some immunoreactive neurophysins. These data support the concept of intrathymic synthesis of neurohypophyseal-like peptides fitting the hypothalamic model. However, we observed that, contrary to the situation in the brain, OT- and VP-like peptides colocalized in the same thymic cells. Furthermore, one monoclonal antibody, specific for the tail part of oxytocin, did not label thymic cells. Therefore, thymic neuropeptide(s) could be related to, but distinct from, authentic OT and VP. These observations suggest some molecular differences between hypothalamic and thymic oxytocin biosynthetic pathways which need to be further investigated.