Copulatory analgesia is greater and longer lasting in early ejaculator rats than in intermediate and late ejaculators

Copulatory analgesia refers to the reduction of pain induced by copulatory sexual activity. The present study evaluated the duration and intensity of this effect after one ejaculation or only five intromissions without ejaculation in male rats with different ejaculatory latency endophenotypes (early, intermediate, and late). Pain sensitivity was assessed using the Vocalization Threshold to Tail Shock (VTTS) technique. In Experiment 1, VTTS was evaluated at 0, 5, 20, and 60 minutes after ejaculation; in Experiment 2, VTTS was measured after five intromissions without ejaculation. Results showed that ejaculation significantly increased VTTS, particularly in early phenotype males. Compared to the other groups of rats, these males required a stronger electric stimulus to elicit a vocal response, indicating a more intense and prolonged analgesic effect. Although five intromissions also increased VTTS, the magnitude and duration of the effect were lower, and no significant differences were found among ejaculatory phenotypes. All endophenotypes showed a post-ejaculatory decrease in the analgesic effect at 60 minutes. The neurobiological mechanisms involved could include GABA, serotonin, dopamine, and opioid systems, suggesting that early males may exhibit more activity within these neural pathways. These findings confirm that copulatory behavior induces analgesia in male rats, and provide a basis for future research on the pharmacological regulation of pain in reproductive contexts.