INDUCTION OF FOS-LIKE IMMUNOREACTIVITY IN MUSK SHREWS AFTER MATING

In many mammalian species the neuroendocrine regulation of male and fe male reproductive behavior is sexually dimorphic. By contrast, many fe atures of female sexual behavior in the musk shrew (Suncus murinus) mo re closely resemble those of males than of females of other species. F emale musk shrews require testosterone (T), which is neurally aromatiz ed to estrogen, to induce sexual behavior. Aromatization occurs in the medial preoptic area (MPOA), and this region is critical for the expr ession of female receptivity. To compare neural responses to sexual be havior in females and males, we compared the number of Foe-like immuno reactive (Fos-ir) neurons after mating in musk shrews. In both males a nd females the number of Fos-ir neurons was increased by mating activi ty 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, th is response was only dimorphic in the ventral medial nucleus of the hy pothalamus (VMN), where mating significantly increased Fos-ir in femal es, but not in males. In both sexes, only the gr-AOB displayed an incr ease in Fos-ir after exposure to chemosensory cues alone. Thus, the pa ttern of Fos expression in the brain after mating is only sexually dim orphic in one region, the VMN. Further, in spite of past behavioral st udies done in this species, which show a role for pheromones in induct ion of receptivity, these data show that exposure to pheromones does n ot induce Fos in structures caudal to the olfactory bulbs. (C) 1998 Pu blished by Elsevier Science B.V. All rights reserved.