Abstract
Preference for social odors in the rat is sexually dimorphic, i.e. they prefer odor derived from sexually active, opposite-sex conspecifics to that from sexually inactive or same-sex individuals. In addition, male rats show clear preference for odor of castrated males to that of sexually active males. This preference toward same-sex odor is not appeared in females, presumably due to the property as territorial animals. Since neuroendocrine basis of those preferences is still unclear, we examined effects of ibotenic-acid lesion in the medial amygdala or the preoptic area, both belonging to the vomeronasal systems, on male rat preference toward conspecific odors. Preference was measured by a 3-compartment apparatus, in which experimental males was presented with one of stimulus-odor pairs, receptive female and sexually active male, receptive female and ovariectomized female, or sexually active male and castrated male. Nose-poking time to explore each stimulus was compared among medial amygdala lesioned, preoptic lesioned and sham-operated male rats. Medial amygdala lesions disturbed preference for receptive females to ovariectomized females, while preoptic lesions eliminated preference for castrated males to sexually active males. Although ejaculation latency was increased in the medial amygdala and preoptic lesioned males, no male showed a complete suppression of sexual behavior. The results suggest that the medial amygdala and the preoptic area play different roles in regulation of social behavior. [J Physiol Sci. 2007;57 Suppl:S175]
