Naloxone potentiates the disruptive effects of mescaline on operant responding in the rat.

Food-deprived male rats were trained to press a lever on a fixed ratio-40 (FR-40) operant schedule for food reinforcement. Administration of mescaline (4.0--10.0 mg/kg) immediately before the start of the operant session resulted in a cessation of responding for some portion of the 40-min period ("hallucinatory pause"). The duration of this pause was found to be dose-dependent. Although administration of naloxone alone (1.0-8.0 mg/kg, five minutes prior to the start of the session) had no effect on FR-40 responding per se, pretreatment with this agent significantly potentiated the disruptive effects of mescaline. This potentiation by naloxone was further shown to be dose-dependent. These data suggest that the effects of the phenethylamine hallucinogen mescaline are potentiated by pretreatment with the narcotic antagonist naloxone.