Naloxone blocks place preference conditioning after paced mating in female rats.

Sexual behavior in male rats induces a positive affect as evaluated by conditioned place preference (CPP). In addition, when females control or "pace" the rate of sexual interaction, a clear CPP is also observed. The reward state induced by mating in male rats is blocked by the injection of the opioid antagonist naloxone. In the present experiment, a dose of 4 mg/kg of naloxone completely blocked the CPP induced in females by paced mating. It appears that a common opioid system is involved in the positive affect induced by sexual behavior in both male and female rats.