Testosterone Differentially Influences Sex-Specific Pheromone-Stimulated Fos Expression in Limbic Regions of Syrian Hamsters

The results of the present study indicate that (1) pheromones differentially stimulate neurons in males and females within a pathway that regulates copulatory behavior; and (2) testosterone (T) differentially regulates these sex differences. Exposure to the pheromones in FHVS (female hamster vaginal secretions) induces Fos immunoreactivity (Fos-IR) in the posterior subdivision of the medial nucleus of the amygdala (MeP) and the posteromedial subdivision of the bed nucleus of the stria terminalis (BNSTpm) of both sexes and stimulates the magnocellular subdivision of the medial preoptic nucleus (MPNmag) in males but not in females. Males also show more Fos in the MeP and BNSTpm than females. In the absence of T, gonadectomized males show greater FHVS-stimulated Fos-IR in the BNSTpm and MeP than gonadectomized females. T in females eliminates the sex difference in these regions. Only T-treated males show FHVS-stimulated Fos-IR within the MPNmag, and T has no effect on FHVS-stimulated Fos-IR within MPNmag in females. Thus, T influences FHVS-stimulated Fos-IR in the BNSTpm and MeP of females and the MPNmag of males. T also increases investigation (sniffing and licking) of FHVS in both males and females, but increases copulatory responses only in males. Our results indicate that T in the adult hamster differentially influences neural and behavioral responses to pheromone exposure in males and females. T only partially accounts for observed sex differences, and it is likely that neural organization during development also plays a role in influencing responses to pheromones.