Thyroid gland responses to intermale aggression in an inherently aggressive wild rat

The aim of the present investigation was to ascertain whether intermale aggression (by fighting) affects thyroid gland activity in wild rat. Following intermale aggression for three hours, thyro-follicular epithelial height was significantly decreased and colloidal content in follicular lumen increased only in the subordinate rats whereas the thyroid gland of the dominant rats was not perceptibly changed. Thus, aggression inhibits thyroid gland activity only in the subordinate rats. It is suggested that this effect may be due to psychosomatic rather than physical stress during aggression.     

Intermale aggression of subordinate resident long-evans rats

Dominant male rats were separated from their colonies and subordinate residents were tested for aggression after a two week period. Subordinate animals showed significant increases in body weight and aggressive behavior toward intruders. Replacement of the previously dominant male led to rank reversals in three of six colonies. To assess whether two weeks of separation from the dominant male was necessary for subordinate males to exhibit aggression towards conspecifics, another intruder test was given following an additional two weeks of social housing. At the conclusion of this test, the more aggressive resident was removed and a naive intruder was immediately introduced into the colony with the subordinate male resident and again at 1, 5, and 10 day intervals. Aggressive posturing by the subordinate resident increased immediately following the removal of the dominant male, and remained at a high level throughout the subsequent intruder tests. In contrast, biting was initially low but increased steadily throughout the period of separation. These findings demonstrated that social or situational changes within a colony can greatly influence the aggression of subordinate males.     

布氏田鼠雄性的优势地位

在实验条件下对雄性成年布氏田鼠（Microtus brandti）相遇后的优势地位及生理指标的研究结果表明：布氏田鼠雄性之间存在严格的等级关系;优势雄鼠生理指标中睾丸重量和血清睾酮激素含量高于从属雄鼠,而血清中皮质醇激素的含量低于从属雄鼠。优势雄鼠的探究、攻击和修饰等行为频次显著高于从属雄鼠,而从属雄鼠在跳跃频次上多于优势雄鼠。随着观察时间的延长,不论优势个体还是从属个体,其探究频次都呈现明显的下降趋势,其他行为的频次则没有显著差异。相关性检验说明,除攻击行为可以作为判断区分雄鼠等级的依据之外,修饰行为也可以作为判断的依据。     

Effects of the probiotic strain Lactobacillus johnsonii strain La1 on autonomic nerves and blood glucose in rats

Oral administration of Lactobacillus casei reportedly reduces blood glucose concentrations in a non-insulin-dependent diabetic KK-Ay mouse model. In order to determine if other lactobacillus strains affect glucose metabolism, we evaluated the effect of the probiotic strain Lactobacillus johnsonii La1 (LJLa1) strain on glucose metabolism in rats. Oral administration of LJLa1 via drinking water for 2 weeks inhibited the hyperglycemia induced by intracranial injection of 2-deoxy-D-glucose (2DG). We found that the hyperglucagonemic response induced by 2DG was also suppressed by LJLa1. Oral administration of LJLa1 for 2 weeks also reduced the elevation of blood glucose and glucagon levels after an oral glucose load in streptozotocin-diabetic rats. In addition, we recently observed that intraduodenal injection of LJLa1 reduced renal sympathetic nerve activity and enhanced gastric vagal nerve activity, suggesting that LJLa1 might affect glucose metabolism by changing autonomic nerve activity. Therefore, we evaluated the effect of intraduodenal administration of LJLa1 on adrenal sympathetic nerve activity (ASNA) in urethane-anesthetized rats, since the autonomic nervous system, including the adrenal sympathetic nerve, may be implicated in the control of the blood glucose levels. Indeed, we found that ASNA was suppressed by intraduodenal administration of LJLa1, suggesting that LJLa1 might improve glucose tolerance by reducing glucagon secretion via alteration of autonomic nerve activities.     

Phenotypic differences in behavior, physiology and neurochemistry between rats selected for tameness and for defensive aggression towards humans

To better understand the biology of tameness, i.e. tolerance of human presence and handling, we analyzed two lines of wild-derived rats (Rattus norvegicus) artificially selected for tameness and defensive aggression towards humans. In response to a gloved human hand, tame rats tolerated handling, whereas aggressive rats attacked. Cross-fostering showed that these behavioral differences are not caused by postnatal maternal effects. Tame rats were more active and explorative and exhibited fewer anxiety-related behaviors. They also had smaller adrenal glands, larger spleens and lower levels of serum corticosterone. Blood glucose levels were lower in tame rats, whereas the concentrations of nine amino acids were higher. In the brain, tame rats had lower serotonin and higher taurine levels than aggressive rats. Our findings reinforce the notion that tameness is correlated with differences in stress response and will facilitate future efforts to uncover the genetic basis for animal tameness.     

The adrenocortical function of alloxan-induced diabetic rats

The purpose of this study is to investigate the adrenocortical function of alloxan-induced diabetic rats. Male rats of Wistar strain, weighing 200-250 gm were used. The results indicated that the adrenocortical response to stress and exogenous corticotropin (ACTH1-24) is decreased during the early diabetic stages (up to 6 days). Evidence from in vivo and in vitro studies shows that the depression is caused by the toxicity of alloxan on the adrenal cortex cells and not by the sudden rise of blood glucose levels. Streptozotocin (another diabetogen) has the same effect as alloxan on adrenal cortex cells.     

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

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

Behavioral and neuroendocrine correlates of displaced aggression in trout

In humans and other primates, violent actions performed by victims of aggression are often directed toward an individual or object that is not the source of provocation. This psychological phenomenon is often called displaced aggression. We demonstrate that displaced aggression is either rooted in evolutionarily conserved behavioral and neuroendocrine mechanisms, or represent a convergent pattern that has arisen independently in fish and mammals. Rainbow trout that briefly encountered large, aggressive fish reacted with increased aggression toward smaller individuals. There was a strong negative correlation between received aggression and behavioral change: Individuals subjected to intense aggression were subdued, while moderate assaults induced strong agitation. Patterns of forebrain serotonin turnover and plasma cortisol suggest that the presence of socially subordinate fish had an inhibitory effect on neuroendocrine stress responses. Thus, subordinate individuals may serve as stress-reducing means of aggressive outlet, and displaced aggression toward such individuals appears to be a behavioral stress coping strategy in fishes.     

The agonistic adrenal: melatonin elicits female aggression via regulation of adrenal androgens

Classic findings have demonstrated an important role for sex steroids as regulators of aggression, but this relationship is lacking within some environmental contexts. In mammals and birds, the adrenal androgen dehydroepiandrosterone (DHEA), a non-gonadal precursor of biologically active steroids, has been linked to aggression. Although females, like males, use aggression when competing for limited resources, the mechanisms underlying female aggression remain understudied. Here, we propose a previously undescribed endocrine mechanism regulating female aggression via direct action of the pineal hormone melatonin on adrenal androgens. We examined this in a solitary hamster species, Phodopus sungorus, in which both sexes are highly territorial across the seasons, and display increased aggression concomitant with decreased serum levels of sex steroids in short ‘winter-like'' days. Short- but not long-day females had increased adrenal DHEA responsiveness co-occurring with morphological changes in the adrenal gland. Further, serum DHEA and total adrenal DHEA content were elevated in short days. Lastly, melatonin increased DHEA and aggression and stimulated DHEA release from cultured adrenals. Collectively, these findings demonstrate that DHEA is a key peripheral regulator of aggression and that melatonin coordinates a ‘seasonal switch’ from gonadal to adrenal regulation of aggression by direct action on the adrenal glands.     

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

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

Inhibition of affective aggression and dominance in rats after thyrotropin-releasing hormone (TRH) microinjection into the nucleus accumbens

The effect of 10 micrograms TRH injected bilaterally into the nucleus accumbens septi on two models of affective aggression and on dominance in a water-competition task was investigated in pairs of male Wistar rats. TRH significantly suppressed affective shock-induced and apomorphine-induced fighting. It also decreased dominance when administered to dominant rats while no effect was noted upon injection into subordinate animals. The peptide influenced neither water consumption in thirsty rats nor the pain threshold in a hot plate test.     

Social aggressiveness of female and subordinate male crickets is released by opiate receptor antagonist

1. In the cricket Gryllus bimaculatus, effects of opiate receptor antagonist naloxone, 9 or 30 microg per animal, on aggressive behavior were investigated. 2. Naloxone had no significant impact on aggression of isolated and dominant males. In contrast, the drug caused a dramatic release of social aggression in female and subordinate male crickets. 3. The results suggest that activity of the opioid system contributes to suppress aggression in subordinate males, as well as in females, during social contacts.     

Sympatho-adrenal activity and metabolic responses in fasted rats--the role of interscapular brown adipose tissue

1. Sympatho-adrenal (SA) and metabolic responses to fasting were studied in sham-operated (SHAM) rats and in those with interscapular brown adipose tissue (IBAT) removed. 2. Fasting significantly increased adrenaline (A) excretion and serum free fatty acids (FFA), but decreased noradrenaline (NA) excretion and blood glucose level in SHAM rats. 3. IBAT removal did not change metabolic responses while it markedly altered the SA activity. Fasting in animals void of IBAT potentiated the activity of adrenal medulla, inhibited the FFA rise and prevented glucose reduction, which is normally observed in SHAM-fasted rats. 4. Results suggest the significance of IBAT in the regulation of the blood level of energy substrates in fasted rats and in maintaining the basal level of NA excretion.     

Evidence for centers in the central nervous system that selectively regulate fat mobilization in the rat

The blood sugar and plasma free fatty acid responses to administration of 2-deoxyglucose were determined in normal rats and in rats subjected to adrenodemedullation and/or hypothalamic deafferentation, as well as in rats with bilateral hypothalamic lesions. Adrenodemedullation of both intact and deafferentated rats reduced the 2-deoxyglucose-induced increase of blood sugar but did not affect the plasma free fatty acid response to 2-deoxyglucose in normal rats. The increases in blood sugar levels induced by the drug in intact rats were not significantly affected by deafferentation, but, in marked contrast, plasma free fatty acid mobilization after 2-deoxyglucose administration was completely suppressed in deafferentated rats, both in the presence and in the absence of the adrenal medulla. These results confirm previous observations indicating that the sympathetic nervous system and adrenalin release from the adrenal medulla participate in the production of hyperglycemia by 2-deoxyglucose. They provide, in addition, evidence for the existence, in the anterior hypothalamus or in limbic structures, of centers that can specifically influence mobilization of free fatty acids through a direct activation of the sympathetic fibers of adipose tissue without intervening in glucose homeostasis. The experiments in animals with bilateral hypothalamic lesions, although small in number, seem to support the above conclusions.     

The effects of temporary removal of the alpha male on the behavior of subordinate male vervet monkeys

The effects of temporary removal of the alpha male on the behavior of subordinate adult male vervet monkeys were evaluated. Twelve subordinate males from six captive multimale, multifemale vervet monkey groups were observed in two conditions: when all group members were present and when the alpha male was temporarily removed from each group. In the absence of the alpha male, subordinate males initiated more affiliative behavior and increased the amount of time spent in proximity to females but their rates of aggression were unaltered. Increased affiliative behavior was selectively directed to high-ranking females and their offspring. Under removal conditions, subordinate male behavior did not resemble that of alpha males in intact conditions: they differed in their proximity to and affiliative behavior towards other group members. In the absence of the alpha male, females increased their aggression towards subordinate males. These observations suggest that the presence of alpha males strongly inhibits subordinate males' behavior. When the constraints of the alpha male's presence are removed, subordinate males rapidly engage in behavior that may enhance their likelihood of attaining high rank. In combination with prior studies, the data also indicate that the behaviors involved in the maintenance of high rank by alpha males differ from those subordinates use to acquire dominance. Finally the current study supports the view that aggression by female vervets may be highly influential in determining male ascendency to dominant rank.     

Social stress,mortality and aggression in colonies and burrowing habitats

High mortality was found within six mixed-sex groups of Long-Evans rats living in burrowing habitats with 58% of subordinate males dying within 4 mo. of group formation. By contrast, no subordinate deaths occured during this time in six identical adult groups(3 males and 3 females) housed in similar (1 m square) colony cages without burrows. Although aggression against intruders was also much greater in habitats than colonies --through 400 days postformation--subordinate deaths did not appear to result from direct physical injury. It seems that mimicing key features of the rat's environment enhances intermale conflict and social stress, even while providing partial protection from biting attack. Behav. Proc.:     

Influence of reproductive season and rank on fecal glucocorticoid levels in free-ranging male Verreaux's sifakas (Propithecus verreauxi)

Studies in anthropoid primates and other mammals suggest that reproductive season, rank, reproductive skew, aggression received, and social support are the major factors influencing glucocorticoid output. In which way these are also affecting adrenal function in lemurid primates has been studied rarely. Here, we examine the influence of reproductive season and rank on glucocorticoid output in male sifakas (Propithecus verreauxi), a species characterized by high breeding seasonality, a hierarchy among males and extreme reproductive skew towards dominant males. We established a fecal assay for non-invasively monitoring adrenal activity and collected 315 fecal samples during the reproductive and birth season from 10 male sifakas living in 5 groups in Western Madagascar. We found a significant effect of season on glucocorticoid output, with males exhibiting higher fecal glucocorticoid levels during the reproductive compared to the birth season in conjunction with an increase in overall aggression rates during the former period. Moreover, our data indicate a significant effect of rank on adrenocortical activity with dominant males exhibiting higher glucocorticoid levels than subordinate males in the reproductive season. However, dominant males did not differ significantly in rates of initiated or received aggression and rates of affiliative behavior from subordinates but showed significantly lower rates of submission. Given their highly formalized dominance relationships, we conclude that higher glucocorticoid output in dominant males during the 4-month reproductive season is likely related to higher energetic demands necessary to cope with the challenges of male reproduction rather than to physical demands of increased fighting frequency to maintain dominance status. High rank in sifakas may thus carry high costs, which, however, may be outweighed by monopolization of almost all paternities. In sum, our data generally support the findings on the relationship between environmental and social factors and glucocorticoid output found in non-lemurid primates.     

Effect of corticoliberin fragment CRF4-6 on blood glucose level and body temperature of rats

The effects of tripeptide corticoliberin fragment CRF4-6 (Pro-Pro-Ile) on blood glucose level and the rat body temperatire were investigated. Intracerebroventricularly injected CRF4-6 (6, 30, 150 nmol/head) causes a dosedependent hyperglycemia and hyperthermia in anaesthetized animals. Corticotropin releasing factor antagonist alpha-helical CRF4-6 (6.5 nmol/head) abolishes the influence of tripeptide CRF4-6 (6 nmol/head) on blood glucose level and body temperature of rats. Bilateral adrenalectomy has no effect on tripeptide-induced hyperglycemia and hyperthemia. This result indicates that hyperglycemic and hyperthermal effects of tripeptide occur independently of adrenal gland catecholamines. In addition, non-pituitary corticoliberin receptors are involved in CRF4-6 influences on blood glucose level and body temperature.     

Postweaning environmental and social factors influencing the onset and expression of agonistic behavior in Norway rats

Two studies were conducted to determine the importance of the postweaning environment and social milieu in regulating the expression of intraspecific aggression in Norway rats. In Experiment 1, male rats were housed either individually or in pairs at 21 days of age. In addition, one-half of the singly housed and paired animals were given experiences with intruders during maturation. At 85 days of age, all animals were given a brief intruder test and then removed from their postweaning environment and provided individually with homecages for a two week period until tested for aggression toward intruders. Results of intruder tests given during maturation indicated agonistic exchanges appeared earlier and more frequently in cages housing a single resident than cages with cohabiting males. However, agonistic exchanges between singly reared residents and intruders had detrimental consequences in adulthood especially under long-term combat situations. That is, although individually reared animals, with early fighting experiences, were capable of initiating intraspecific aggression, such individuals were unable to defend their homecage over a long period of time as evidenced by the high number of wounds and tendency to lose body weight during adult fighting.In Experiment 2, male Norway rats were reared in pairs from 21 days of age and identified as dominant or subordinate on the basis of intracolony social interactions shown during maturation. At 80 days of age, animals were paired with individually reared males in an unfamiliar cage for a 20 day period and examined for agonistic behavior toward intruders at 100 days of age. Group-reared subordinate males exhibited defensive behavior during confrontations with individually reared animals and incurred more wounds and lost more body weight than their cohabiting partner. In addition, subordinate males showed significantly fewer offensive postures toward intruders than individually reared cohabitants. In contrast, group-reared dominant animals did not differ from individually reared males in display of agonistic patterns, in number of wounds, and body weight changes during the period of cohabitation. These findings demonstrate that early rearing factors have pronounced effects on agonistic behavior. Animals experiencing defeat during development are more likely to lose agonistic confrontations in unfamiliar territory than either animals dominant in their early social interactions or animals without the experience of winning or losing agonistic encounters. These results have implications for the understanding of agonistic behavior and predicting outcomes of animal contests, and reveal important differences in agonistic experiences among animals reared in groups.     

Reproductive skew in female common marmosets: what can proximate mechanisms tell us about ultimate causes?

Common marmosets are cooperatively breeding monkeys that exhibit high reproductive skew: most subordinate females fail to reproduce, while others attempt to breed but produce very few surviving infants. An extensive dataset on the mechanisms limiting reproduction in laboratory-housed and free living subordinate females provides unique insights into the causes of reproductive skew. Non-breeding adult females undergo suppression of ovulation and inhibition of sexual behaviour; however, they receive little or no aggression or mating interference by dominants and do not exhibit behavioural or physiological signs of stress. Breeding subordinate females receive comparable amounts of aggression to non-breeding females but are able to conceive, gestate and lactate normally. In groups containing two breeding females,however, both dominant and subordinate breeders kill one another's infants. These findings suggest that preconception reproductive suppression is not imposed on subordinate females by dominants, at a proximate level, but is instead self-imposed by most subordinates, consistent with restraint models of reproductive skew. In contrast to restraint models, however, this self-suppression probably evolved not in response to the threat of eviction by dominant females but in response to the threat of infanticide. Thus,reproductive skew in this species appears to be generated predominantly by subordinate self-restraint, in a proximate sense, but ultimately by dominant control over subordinates' reproductive attempts.