ANATOMICAL INTERRELATIONSHIPS OF THE MEDIAL PREOPTIC AREA AND OTHER BRAIN-REGIONS ACTIVATED FOLLOWING MALE SEXUAL-BEHAVIOR - A COMBINED FOSAND TRACT-TRACING STUDY

The medial preoptic nucleus (MPN) is an essential site for the regulat ion of male sexual behavior. Previous studies using c-fos as a marker for neural activation have shown that copulation increased c-fos expre ssion in the MPN. Neural activation was also present in brain regions that are connected with the MPN and are involved in male sexual behavi or including the posteromedial bed nucleus of the stria terminalis (BN STpm), posterodorsal preoptic nucleus (PD), posterodorsal medial amygd ala (MEApd), and parvocellular subparafascicular thalamic nucleus (SPF p). The present study investigated whether the copulation-induced, act ivated neurons in these brain regions are involved in the bidirectiona l connections with the MPN. Therefore, mating-induced Fos expression w as combined with application of anterograde (biotinylated dextran amin e) or retrograde (cholera toxin B subunit) tracers in the MPN. The res ults demonstrated that neurons in the BNSTpm, PD, MEApd, and SPFp that project to the MPN were activated following copulation. However, in m ales that displayed sexual behavior but did not achieve ejaculation, f ew double-labeled neurons were evident, although both retrogradely lab eled neurons and Fos-immunoreactive cells,were present. In addition, r etrograde neurons that expressed Fos were located in discrete subdivis ions within the brain regions studied, where Fos is induced after ejac ulation. Likewise, anterogradely labeled fibers originating from the M PN were not distributed homogeneously but were particularly dense in t hese discrete subdivisions. These results demonstrate that copulation- induced Fos-positive neurons in specific subdivisions of the BNSTpm, P D, MEApd, and SPFp have bidirectional connections with the MPN. Taken together with previous findings, this supports the existence of a disc rete subcircuit within a larger neural network underlying male sexual behavior. J. Comp. Neurol. 397:421-435, 1998. (C) 1998 Wiley-Liss, Inc .