The relation between social rank and plasma corticosterone levels in mice

Abstract

Male CFW mice that had been isolated since weaning were placed in groups of four for six hours and 24 hours and observed for the development of aggressive behavior patterns and dominance hierarchies. Control animals were maintained in individual cages. At the end of the grouping period the animals were sacrificed by decapitation and plasma corticosterone levels and adrenal weight recorded. There was a distinct relation between position in a dominance hierarchy and plasma corticosterone levels with dominant animals having significantly lower levels than subordinate ones. Thus these data corroborate the findings of earlier workers who used indirect criteria for adrenocortical activity. The results further support the hypothesis that the psychological factor of defeat after fighting is important in eliciting adrenocortical activity. Thus subordinate mice were frequently defeated and chased resulting in a high frequency of wounding on the tail and rump. Dominant animals, on the other hand, were not frequently defeated and showed very few injuries to the tail and rump.