Induction of fos-like immunoreactivity in musk shrews after mating

In many mammalian species the neuroendocrine regulation of male and female reproductive behavior is sexually dimorphic. By contrast, many features of female sexual behavior in the musk shrew (Suncus murinus) more closely resemble those of males than of females of other species. Female musk shrews require testosterone (T), which is neurally aromatized to estrogen, to induce sexual behavior. Aromatization occurs in the medial preoptic area (MPOA), and this region is critical for the expression of female receptivity. To compare neural responses to sexual behavior in females and males, we compared the number of Fos-like immunoreactive (Fos-ir) neurons after mating in musk shrews. In both males and females the number of Fos-ir neurons was increased by mating activity in the granule layer of the accessory olfactory bulb (gr-AOB), the bed nucleus of the stria terminalis (BNST), MPOA, the medial amygdala (MeA), and the region corresponding to the midbrain central tegmental field (CTF). Although Fos was induced by mating in several regions, this response was only dimorphic in the ventral medial nucleus of the hypothalamus (VMN), where mating significantly increased Fos-ir in females, but not in males. In both sexes, only the gr-AOB displayed an increase in Fos-ir after exposure to chemosensory cues alone. Thus, the pattern of Fos expression in the brain after mating is only sexually dimorphic in one region, the VMN. Further, in spite of past behavioral studies done in this species, which show a role for pheromones in induction of receptivity, these data show that exposure to pheromones does not induce Fos in structures caudal to the olfactory bulbs.