Potential contributions of efferents from medial prefrontal cortex to neural activation following sexual behavior in the male rat.

The limbic system plays an important role in the regulation of sexual motivation and reward. At the core of this system is an interconnected mesocorticolimbic circuit, comprised of the ventral tegmental area, nucleus accumbens and medial prefrontal cortex. Previously, our laboratory showed that sexual behavior causes neural activation in the ventral tegmental area of male rats. The main goal of this study is to identify afferent inputs to ventral tegmental area neurons that may contribute to their activation during sexual behavior. Hence, the anterograde tracer biotinylated dextran amine was injected into subregions of the rat medial prefrontal cortex, which is known to project to the ventral tegmental area. Visualization of biotinylated dextran amine-labeled axons was combined with immunostaining for sex-induced Fos expression. Quantitative analysis showed that the majority of sex-activated ventral tegmental area neurons receive putative contacts from the infralimbic and prelimbic--but not the anterior cingulate--subregions of the medial prefrontal cortex. Thus, inputs from infralimbic area and prelimbic are in an anatomical position to provide a major source of input during sexual behavior. A second goal of this study was to determine if the medial prefrontal cortex projects to sex-activated neurons in other brain regions important for sexual behavior and motivation. Infralimbic area and prelimbic area sent projections to nucleus accumbens, medial preoptic area, principal nucleus of the bed nucleus of the stria terminalis, basolateral amygdala, and parvocellular subparafasicular thalamic nucleus. Thus, the infralimbic and prelimbic subregions of the medial prefrontal cortex may also influence sexual behavior and motivation via brain regions other than the ventral tegmental area.