Sexual reinforcement is blocked by infusion of naloxone into the medial preoptic area.

The present experiment was designed to determine whether infusions of naloxone into specific brain sites can block sexual reinforcement as evaluated with the conditioned place preference procedure. Methylnaloxonium (5 micrograms/cannula) was infused bilaterally either into the medial preoptic area (MPOA) or into the nucleus accumbens (NAC) of sexually experienced male rats. We chose the MPOA because it is important for sexual behavior, and several opioid peptides have been shown to modify sexual behavior when infused there. The NAC appears to be a critical structure for drug-induced reward. Methylnaloxonium blocked place preference produced by ejaculation after infusion into the MPOA without affecting sexual behavior. Infusion of the antagonist into the NAC did not reduce the reinforcing properties of ejaculation. These data suggest that the MPOA may be a site where sexual reward is produced.