Effects of a D antagonist and of sexual experience on copulation-induced

Ž . Ž . The medial preoptic nucleus MPN of the medial preoptic area MPOA and the medial amygdala are two brain regions in which Ž . male rat sexual behavior increased Fos-like immunoreactivity Fos-Li . Dopamine is released in the MPOA during male rat sexual behavior and facilitates copulation. Psychostimulants, which increase dopamine levels, induce Fos-Li in the striatum through D1 receptors. We examined whether copulation-induced Fos-Li in the MPN was also mediated through D receptors. In Experiment 1, 1 sexually inexperienced male rats that received the D antagonist Schering 39166 prior to their first sexual experience had fewer Fos-Li 1 cells in the MPN than did those that received vehicle. In Experiment 2, no significant effect of the D antagonist was observed on 1 copulation-induced Fos-Li in male rats that had received repeated sexual experiences prior to the drug test day. Sexual experience increases copulatory efficiency; the mechanisms by which this improvement 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 was positively correlated with the Ž . post-ejaculatory interval. These experiments indicate that 1 stimulation of D receptors may contribute to the transient copulation-in1 Ž . duced increase in Fos-Li in the MPN, and 2 repeated sexual experiences enhanced copulation-induced Fos-Li in the MPN, which may represent a marker of altered responsiveness of neurons in the MPN to sexual or conditioned stimuli. q 1999 Published by Elsevier Science B.V. All rights reserved.