Sex differences in function of a pheromonally stimulated pathway: role of steroids and the main olfactory system

Exposure to the pheromones contained in female hamster vaginal secretions (FHVS) produces stereotypic, sex-specific behaviors in Syrian hamsters. Using Fos as a marker of neuronal stimulation we have found that (1) FHVS stimulates neurons in the posterior subdivision of the medial nucleus of the amygdala (MeP), the posterior medial subdivision of the bed nucleus of the stria terminalis (BNSTpm), and the magnocellular subdivision of the medial preoptic nucleus (MPN mag); (2) this stimulation is mediated by the main olfactory system; (3) stimulation of the MPN mag is regulated by testosterone in males; (4) stimulation of the BNSTpm and MeP is regulated by testosterone in females; and (5) FHVS does not induce Fos production in the MPN mag in females regardless of the hormonal state. These results support the hypothesis that the main olfactory system plays an important role in the regulation of pheromonally driven behaviors, identifies functional sex differences in pathways that regulate these behaviors, and emphasizes the different roles of the BNSTpm, MeP, and MPN mag in the regulation of male copulatory behavior.