Abstract
The choice of sexual partners is sexually dimorphic: estrous female rats access males, while sexually mature males pursue receptive females to copulate. In order to investigate the neuroendocrine mechanism of sexual orientation, we examined their preference of conspecific odors, showing that sexually active males preferred estrous female odors than those of males or ovariectomized females (masculine pattern), and estrous females preferred male odors than those of females or orchidectomized males (feminine pattern). Gonadectomy results in no preference at all, although males show transiently the feminine preference (2 weeks) after castration. Estrogen treatment in males induces the feminine preference, whereas testosterone in females activates their own, feminine pattern. Medial amygdala lesions in females eliminate the preference for sexually active males, but the same lesions in males failed to affect the preference for estrous females. These facts suggest that the masculine and feminine neural circuits are different and independent. Males may have potentially neural circuits for both masculine and feminine preferences, whereas females have only feminine one because of a lack of neonatal androgen. [Jpn J Physiol 54 Suppl:S41 (2004)]
