FOS IMMUNOREACTIVITY IN THE RAT-BRAIN FOLLOWING CONSUMMATORY ELEMENTSOF SEXUAL-BEHAVIOR - A SEX COMPARISON

In the present study a comparison was made between the distribution of Fos immunoreactivity in the brain of female and male rats following s uccessive elements of sexual behavior. The distribution of Fos immunor eactivity following either mounting, eight intromissions or one or two ejaculations was compared with that in control animals. In both femal es and males, Fos immunoreactivity was induced in the medial preoptic nucleus, posteromedial part of the bed nucleus of the stria terminalis , posterodorsal part of the medial amygdala, and the parvicellular par t of the subparafascicular thalamic nucleus. In addition, Fos immunore activity in females was induced in the ventrolateral part and the most caudoventral part of the ventromedial nucleus of the hypothalamus and in the premammillary nucleus. Differences between females and males w ere detected in the phases of sexual activity that resulted in Fos imm unoreactivity in these brain areas, allowing more insight in the natur e of the sensory and hormonal stimuli leading to the induction of Fos immunoreactivity. The posteromedial bed nucleus of the stria terminali s appears to be involved in chemosensory investigation, while specific distinct subregions are only activated following ejaculation. In addi tion, the parvicellular subparafascicular nucleus and the lateral part of the posterodorsal medial amygdala appear to be involved in the int egration of viscero-sensory input. The neural circuitries underlying s exual behavior in males and females appear to be similar in terms of i ntegration of sensory information. In males the medial preoptic nucleu s may be regarded as the brain area where the integration of sensory a nd hormonal stimulation leads to the onset of male sexual behavior, wh ile in females the ventrolateral part of the ventromedial hypothalamic nucleus appears to have this function. In addition, Fos immunoreactiv ity Was distributed in distinct clusters in subregions within various brain areas in males and females. This was observed especially in the posteromedial bed nucleus of the stria terminalis and posterodorsal me dial amygdala, but also in the parvicellular subparafascicular nucleus , ventromedial hypothalamic nucleus and ventral premammillary nucleus. It appears that relatively small subunits within these nuclei seem to be concerned with the integration of sensory and hormonal information and may play a critical role in sexual behavior.