Naloxone prevents the rapid reacquisition but not acquisition of alcohol seeking.

Opioid receptors are involved in reinstatement of alcohol seeking, yet there are no reports of their role in reacquisition of an extinguished alcohol seeking response. Here we investigated the effects of the opioid antagonist naloxone on reacquisition and compared these effects with those on acquisition. Rats were trained, extinguished, then retrained to respond for alcoholic beer. Upon retraining, a second group of rats with no prior experience with the contingency between response and reinforcer was trained under the same conditions. Reacquisition was faster than acquisition. Systemic injection of naloxone (1.25 or 5 mg/kg) reduced reacquisition but had no effect on acquisition. These results suggest that reacquisition and acquisition of alcohol seeking have dissociable neurochemical substrates.