INFLUENCE OF COMBINED ESTRADIOL AND TESTOSTERONE IMPLANTS ON THE AGGRESSIVENESS OF NONAGGRESSIVE FEMALE RATS

Female rats that had been cohabiting with a sterile male or with anoth er female for 6 weeks were tested for aggression toward an unfamiliar female once each week for 3 weeks. Females that were not aggressive as a result of cohabitation with a sterile male were ovariectomized. Hal f were implanted with a Silastic tube containing estradiol (1 mm long hormone-filled space) and a tube containing testosterone (5 mm long ho rmone-filled space). The other half were implanted with empty tubes. A ll females that had been cohabiting with another female were ovariecto mized and implanted with an estradiol- and a testosterone-filled tube. Three additional weekly tests of aggression were given beginning 1 we ek postoperatively. Females given hormone replacement displayed only a slight increase in aggression postoperatively. Females not given horm one replacement declined in aggressiveness. These results indicate tha t hormone replacement levels sufficient to maintain aggression in high ly aggressive females following ovariectomy are not sufficient to prod uce a high level of aggression in females that have not become aggress ive following cohabitation with a sterile male or that have been cohab iting with another female.