Interaction of hypothalamic structures in the mediation of male sexual behavior

A series of studies was conducted in which the influences of medial forebrain bundle (MFB) and medial preoptic area (MPOA) lesions on the copulatory behavior of the male rat were investigated. Previous findings that bilateral electropytic lesions in parafornical MFB or the MPOA abolish sexual behavior were confirmed. Further, it was found that MFB lesions as far anterior as the MPOA, but not rostral to this area, were also effective in abolishing male sexual behavior. Asymmetrical hypothalamic lesions were also employed in an attempt to ascertain the degree of interaction between the MPOA and the MFB in the mediation of male sexual behavior. Unilateral lesions in the MFB combined with contralateral destruction of the MPOA were also found to effectively suppress mating. These findings were interpreted as supporting suggestions that portions of the MFB function as a caudally directed pathway from the MPOA in the mediation of sexual behavior. Attempts to reverse the effects on sexual behavior of MFB lesions by the administration of dl-5-hydroxytryptophan were not successful. On the contrary, this chemical was found to be inhibitory to male sexual behavior.