Female rats in a competitive situation: medial hypothalamic lesions increase and ovariectomy decreases success and...

Competition for food was observed between pairs of ovariectomized female rats with medial hypothalamic lesions or sham lesions. A second series of tests observed food-competition between ovariectomized and sham-ovariectomized females. Competing pairs were continuously housed together and maintained on a 23-hr food-deprivation schedule. Competition occurred as each rat attempted to maintain access to a spout containing liquid food that only one animal could lick at a time. Female rats made hyperdefensive by medial hypothalamic lesions maintained access to a food spout significantly longer than their sham-lesioned cagemates. The lesioned animals were also significantly more aggressive than their sham-lesioned cagemates. Sham-ovariectomized rats maintained access to the food spout significantly longer than their ovariectomized cagemates. The intact cagemates were also more aggressive. These results suggest that defensive aggression heightened by medial hypothalamic lesions is displayed in a competitive situation by females as has been demonstrated previously with males. Further, ovariectomy in females appears to decrease aggression and success in a competitive situation as does gonadectomy in males. These results suggest that homologous biological mechanisms modulate aggressive behavior in male and female rats.