MATING-INDUCED FOS-LIKE IMMUNOREACTIVITY IN THE RAT FOREBRAIN - A SEXCOMPARISON AND A DIMORPHIC EFFECT OF PELVIC NERVE TRANSECTION

Previous research has shown that mating induces the expression of the immediate-early gene, c-fos, as detected by the increased presence of nuclear FOS-like immunoreactivity (FOS-IR), in specific forebrain regi ons of both male and female rats. In the male both olfactory/vomeronas al (O/V) and genital/somatosensory (G/S) inputs appear to contribute t o the neural FOS response to mating whereas in the female G/S input ca rried by the pelvic nerves appears to mediate the forebrain FOS respon se. To date, however, no direct sex comparison of the mating-induced f orebrain FOS response has been made in rats maintained under the same steroidal conditions nor has the contribution of afferent sensory inpu t from the pelvic nerves been assessed in males. We first compared the level of FOS-IR in brain regions of mated and unpaired gonadectomized male and female rats given 5 mug/kg estradiol benzoate (EB) for 7 day s and 500 mug progesterone (P) 4 h prior to testing. One h after exper iencing 1 ejaculation, both sexes showed increased FOS-IR in the media l preoptic area (MPOA), bed nucleus of the stria terminalis (BNST), me dial amygdala, the ventro-lateral portion of the ventromedial nucleus of the hypothalamus (VMN), and the midbrain central tegmental field (C TF). This increase was significantly greater in the MPOA and medial am ygdala of mated females than of males. Bilateral transection of the pe lvic nerves significantly attenuated the increase in FOS-IR after mati ng in the CTF of male rats and in the MPOA, BNST, VMN, medial amygdala and CTF of females. Thus, following mating there is no sex difference in the brain regions which express c-fos, but there is a dimorphism i n the contribution of afferent information conveyed by the pelvic nerv es to the mating-induced FOS response, The neural FOS response of the female to mating is heavily dependent upon the G/S afferent inputs car ried by the pelvic nerves whereas the male's neural c-fos response may depend on O/V input plus G/S input conveyed via other afferent pathwa ys such as the pudendal nerves.