Pentazocine, cyclazocine, and nalorphine as discriminative stimuli.

Pentazocine, cyclazocine, and nalorphine are narcotic antagonists that also have analgesic activity of their own. The present investigation compared the stimulus properties of these three drugs in rats. Each drug was used as a discriminative stimulus for a separate group of rats. Depression of one lever resulted in food reinforcement following the administration of drug, and the opposite lever was reinforced after saline. Each drug readily acquired control of discriminated responding. The specific narcotic antagonist, naloxone, which antagonizes many of the effects of pentazocine, cyclazocine, and nalorphine, also antagonized the discrimination of these drugs. Stimulus generalization tests to each other narcotic antagonist, d-amphetamine, morphine, and LSD, showed that each narcotic antagonist has highly specific stimulus properties. Clear generalization occurred only to pentazocine and cyclazocine in the nalorphine-saline group, but neither cyclazocine nor pentazocine generalized to nalorphine.