The physiology of social conflict in rats: what is particularly stressful?

The involvement of the opponent's behavior in the aggression-induced stress response was tested. Subjects (male Wistar rats) faced stimulus rats previously submitted either to mediobasal hypothalamic lesion (MBHL) or to sham operation. MBHL intruders were more aggressive but were also more ready to submit compared with sham-operated rats; as residents they were more efficient in inducing submissive behavior in the opponent. The subject's stress response at 15 min was neither dependent on the intensity of aggressive behavior nor on residence status but on dominant-submissive relationships. The submission of the stimulus rat reduced corticosterone plasma levels in the subjects, while the subjects' own submissive behavior elicited a very significant increase in its plasma corticosterone. In contrast, plasma glucose seemed to depend on residence status, whereas plasma free fatty acids reacted to any novel event (including cage switch).