Discriminative stimulus properties of the mixed agonist-antagonist pentazocine in the rat using two-choice discrete-trial avoidance paradigm.

The discriminative stimulus effects of pentazocine were evaluated in the rat trained to discriminate 3.0 mg/kg of pentazocine from vehicle in a two-choice discrete-trial avoidance paradigm. The rats used could discriminate 3.0 mg/kg of pentazocine from vehicle within 20 sessions after the start of discrimination training. The stimulus effects lasted 30 to 90 min and disappeared thereafter except for one rat in which the discriminative effects lasted 30 to 150 min. Pentazocine produced dose-dependent stimulus effects at 0.3 to 3.0 mg/kg doses. The stimulus effects of pentazocine were fully reversed by higher doses of naltrexone. Butorphanol, nalorphine, morphine, levorphanol, SKF 10,047, and methamphetamine generalized to pentazocine cue. However, ethylketocyclazocine, dextrorphan or pentobarbital did not produce stimulus effects in common with pentazocine. These results suggest that the discriminative stimulus effects of pentazocine (3.0 mg/kg) are mediated through an opioid but non-mu and nonspecific mechanism.