Effects of a D-1 antagonist and of sexual experience on copulation-inducedFos-like immunoreactivity in the medial preoptic nucleus

The medial preoptic nucleus (MPN) of the medial preoptic area (MPOA) and th e medial amygdala are two brain regions in which male rat sexual behavior i ncreased Fos-like immunoreactivity (Fos-Li). Dopamine is released in the MP OA during male rat sexual behavior and facilitates copulation. Psychostimul ants, which increase dopamine levels, induce Fos-Li in the striatum through D-1 receptors. We examined whether copulation-induced Fos-Li in the MPN wa s also mediated through D-1 receptors. In Experiment 1, sexually inexperien ced male rats that received the D-1 antagonist Schering 39166 prior to thei r first sexual experience had fewer Fos-Li cells in the MPN than did those that received vehicle. In Experiment 2, no significant effect of the D-1 an tagonist was observed on copulation-induced Fos-Li in male rats that had re ceived repeated sexual experiences prior to the drug test day. Sexual exper ience increases copulatory efficiency; the mechanisms by which this improve ment occurs are unclear. In Experiment 3, copulation by highly experienced male rats led to greater Fos-Li in the MPN than did copulation by sexually naive males. Although there were no differences between groups in amygdala Fos-Li in these studies, in several groups Fos-Li in the medial amygdala wa s positively correlated with the post-ejaculatory interval. These experimen ts indicate that (1) stimulation of D-1 receptors may contribute to the tra nsient copulation-induced increase in Fos-Li in the MPN, and (2) repeated s exual experiences enhanced copulation-induced Fos-Li in the MPN, which may represent a marker of altered responsiveness of neurons in the MPN to sexua l or conditioned stimuli. (C) 1999 Published by Elsevier Science B.V. All r ights reserved.