Facilitatory effects of pituitary transplants on intraspecific aggression in female hamsters

Abstract

To help clarify the relationship between prolactin (PRL) secretion and aggression in the hamster, the aggressiveness of ovariectomized females given two ectopically grafted pituitary glands was compared to that of ovariectomized control females which underwent a sham transplantation procedure. In a series of three neutral territory tests with male partners, female-initiated attacks, chasing, and fighting were more frequent in the pituitary-grafted group than in the controls. Male partners of pituitary-grafted females responded by exhibiting more submissive behavior than did males paired with control females. In a final test in which pituitary-grafted females were paired with control female partners, control females were found to be more submissive and less aggressive than experimentals despite a significant body weight advantage. These results demonstrate a facilitatory effect of pituitary transplantation on aggression which is independent of gonadal hormones. Because an association between heightened aggressiveness and reported elevations in PRL secretion is observed in pituitary-grafted females and in pregnant and lactating females, these findings lend further support to the hypothesis that PRL promotes aggression during the hamster reproductive cycle.