Aggression by a female rat cohabiting with a sterile male declines within 27 h following ovariectomy

Females that had become aggressive as a result of cohabiting with a sterile male were ovariectomized and implanted with empty Silastic tubes. Control groups were either sham ovariectomized or ovariectomized and implanted with Silastic tubes providing replacement levels of estradiol and testosterone. Twenty-seven hours following surgery, all animals were tested for aggressiveness toward an unfamiliar female rat. The aggression of ovariectomized females without hormone replacement declined to a minimal level postoperatively and was significantly lower than that of sham-ovariectomized females or ovariectomized females with estradiol and testosterone replacement. Both sham-ovariectomized females and ovariectomized females given hormone replacement displayed a level of aggression close to that observed preoperatively. The aggression of a female rat cohabiting with a sterile male appears to be highly sensitive to the removal of gonadal hormones. This corresponds with observations made on pregnant females and contrasts with those made on lactating females.