The effects of the opioid antagonist naloxone were examined on the development of conditioned partner preference induced by paced copulation in female rats. In Experiment 1, ovariectomized, hormone-primed rats were conditioned to associate scented and unscented male rats with paced and nonpaced copulation, respectively. Female rats in Experiment 2 associated albino or pigmented male rats with paced or nonpaced copulation. Naloxone or saline was administered before each conditioning trial. During a final drug-free preference test, female rats could choose to copulate with either a pacing related or unrelated male. Saline-trained female rats in the paired group copulated preferentially with the pacing-related male rat, whereas naloxone-trained female rats did not show a preference. The authors concluded that opioids mediated the conditioned partner preference induced by paced copulation.

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