PubMed · 8562081
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R Hen. 1996. Mean genes.. https://doi.org/10.1016/s0896-6273(00)80019-7
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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.
The impact of chronic confrontation on behavior, body weight, and aspects of blood cellular immunity was investigated in 24 Long Evans intruder rats. At the beginning of a 1-week confrontation period, an adult male was introduced into a one male-one female resident group which resulted in fights for dominance. Although most intruders became losers in this situation, their specific behavior differed. Two groups of losers were defined: subdominant (N = 11) and submissive intruders (N = 9). In contrast to subdominant intruders, submissive males often displayed behaviors indicating social defeat. They were frequently involved in agonistic interactions and lost 7% of their initial body weight. Confrontation provoked marked changes in many measures of blood cellular immunity. Importantly, the immunological effects differed significantly in magnitude and direction depending on the individuals' behavior. Submissive males reacted with reduction in lymphocyte proliferation in response to ConA and shifts in lymphocyte subsets (decline in percentage of CD4 and CD8 T cells, increase of B cells), but with little change in lymphocyte numbers. In addition, a pronounced increase in granulocytes was evident. In contrast, in subdominant males lymphocyte, T cell, and B cell counts were lowered but no change in subset composition occurred. The effects on T and B cell composition were not fully reversible within 7 days after end of the confrontation period indicating long-term consequences for migration of lymphocyte subsets. These data show that a detailed behavioral analysis is required for a meaningful biological evaluation of social stress-induced immune changes in rats, because different coping strategies result in different immunological consequences.
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