Sex-relevant connections of the medial preoptic area: A combined immunochemical and tract tracing study

In the male rat the medial preoptic area (MPOA) is involved in the integration of sex-relevant stimuli and coordination of female-directed sexual behaviors. Disruption of inputs to the MPOA decreases sexual activity and lesions of the MPOA or disruption of its efferents impairs sexual behavior. Fos-Like Immunoreactivity (FLI) has been observed in the MPOA of sexually active male rats. By combining FLI with retrograde tracing techniques, three experiments investigated the sex-relevant cells in the MPOA. In Experiment 1 male rats were placed into a novel environment, empty mating arena, or with a receptive female to determine whether FLI in the MPOA is mating specific. In Experiment 2, unilateral injections of the retrograde tracer FluoroGold into the MPOA and colocalization of sex-induced FLI and FluoroGold was examined in MPOA afferents. In Experiment 3, unilateral injections of FluoroGold into midbrain sites thought to be involved in the expression of sexual behavior. The results of the three experiments showed: (1) that Fos expression in the MPOA is sex-specific, (2) cells displaying FLI in the corticomedial amygdala, bed nucleus of the stria terminalis and lateral portion of the central tegmental field project to the MPOA and, (3) a majority of the cells labeled for FluoroGold in the MPOA were in the region lateral to the sex-specific region displaying FLI. These experiments confirm the importance of the MPOA for male sexual behavior and the inputs to the sex-specific region of the MPOA.