Distribution of Fos immunoreactivity following mating versus anogenital investigation in the male rat brain.

In the present study a detailed quantitative analysis was made using Fos as a marker for neural activation to define which subregions in the neural circuitry underlying male sexual behavior are involved in display of anogenital investigation versus copulation. Neural activity was differentially distributed following anogenital investigation versus mating and was restricted to specific subdivisions that form a heavily interconnected network. Chemosensory investigation increased neural activity in the posteromedial subdivision of the bed nucleus of the stria terminalis and the posterodorsal subdivision of the medial amygdala, brain regions that receive chemosensory signals processed through the olfactory bulbs, presumably reflecting the acquisition of chemosensory signals or the display of anogenital investigation. However, other sensory signals or sexual experience may also have contributed to the induction of neural activation in these brain areas. Moreover, consummatory behavior increased neural activity in the subparafascicular nucleus, a brain region that receives genital sensory inputs. In turn, this brain region projects to the medial preoptic nucleus and posterior nucleus of the amygdala, where neural activity was also abundant only following copulation. In addition, clusters of neurons were activated in the posteromedial subdivision of the bed nucleus of the stria terminalis and posterodorsal subdivision of the medial amygdala following consummatory behavior. The present study provides an anatomically detailed picture about the distribution of neural activation following sexual behavior in the rat, specifically in relation to differences following anogenital investigation versus mating.