A novel environment disrupts copulation in sexually naive but not experienced male rats: reversal with naloxone.

Relative to sexually experienced male rats, sexually naive males typically display a pattern of copulatory behavior that is characterized by a larger proportion of rats that do not copulate: those that do copulate during their first exposure to a sexually receptive female have longer mount, intromission, and ejaculation latencies, and longer postejaculatory intervals. A male rat's first sexual experience often coincides with the first exposure to handling and to the novel testing apparatus. Because handling or exposure to novel environments is stressful and can induce the release of endogenous opioids, and because the opioid antagonist naloxone can facilitate the copulatory behavior of sexually naive male rats, we examined whether preexposure to handling alone, or to handling and a novel testing chamber, would diminish the magnitude of the relative disruption observed in sexually naive male rats. Handling alone did not increase the proportion of males that mounted or intromitted, whereas preexposure to the chamber increased these proportions significantly and decreased the mount and intromission latencies, and the number of mounts without intromission. Naloxone hydrochloride (10 mg/kg) facilitated the display of mounts and intromissions in rats that were preexposed to handling alone, but had no effect in rats that had been additionally preexposed to the testing chambers. In contrast, the copulatory behavior of rats with extensive sexual experience was not adversely affected in a novel testing chamber. Novelty disrupts the copulatory behavior of sexually naive males and may do so by increasing endogenous opioid activity. However, sexual experience appears to diminish or eliminate the disruptive effect of a novel environment.