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 typic ally display a pattern of copulatory behavior that is characterized by a larger proportion of rats that do not copulate; those that do copul ate during their first exposure to a sexually receptive female have lo nger mount, intromission, and ejaculation latencies, and longer postej aculatory intervals. A male rat's first sexual experience often coinci des with the first exposure to handling and to the novel testing appar atus. Because handling or exposure to novel environments is stressful and can induce the release of endogenous opioids, and because the opio id antagonist naloxone can facilitate the copulatory behavior of sexua lly naive male rats, we examined whether preexposure to handling alone , or to handling and a novel testing chamber, would diminish the magni tude of the relative disruption observed in sexually naive male rats. Handling alone did not increase the proportion of males that mounted o r intromitted, whereas preexposure to the chamber increased these prop ortions significantly and decreased the mount and intromission latenci es, and the number of mounts without intromission. Naloxone hydrochlor ide (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 con trast, the copulatory behavior of rats with extensive sexual experienc e was not adversely affected in a novel testing chamber. Novelty disru pts the copulatory behavior of sexually naive males and may do so by i ncreasing endogenous opioid activity. However, sexual experience appea rs to diminish or eliminate the disruptive effect of a novel environme nt.