Repeated social stress and the development of agonistic behavior: individual differences in coping responses in male golden hamsters.

In male golden hamsters, repeated social subjugation during puberty accelerates the development of adult aggressive behavior and enhances its intensity in the presence of smaller individuals. The current study is focused on the characterization of the hormonal and behavioral responses to social subjugation during puberty. Subjugation consisted of daily exposure to an aggressive adult for 20-min periods from postnatal day 28 (P-28) to P-42, while controls were placed into an empty clean cage. Plasma cortisol levels were measured prior to or immediately after treatment on P-28 and P-42. On P-28, exposure to an aggressive adult or a clean and empty cage caused an increase in plasma cortisol levels. However, only social subjugation resulted in elevated cortisol levels on P-42, showing that juvenile hamsters habituate to an unfamiliar environment but not to social subjugation. In addition, we found a relationship between the frequency of submissive responses during social subjugation and the development of aggressive behavior. The transition from play fighting to adult aggression was most accelerated in the least submissive animals. These data show that behavioral response to social subjugation determines the development of aggressive behavior in golden hamsters. Our data also suggest that submissive behavior is a form of coping that attenuates the behavioral consequences of social subjugation in male golden hamsters.