Interaction of the discriminative stimulus effects of phencyclidine with those of (+)-N-allylnormetazocine, pentobarbital and d-amphetamine.

Pigeons trained to discriminate 1.0 mg/kg phencyclidine from saline were used to study the interaction between the stimulus effects of phencyclidine and those of (+)-N-allylnormetazocine [(+) NANM], pentobarbital and d-amphetamine using a cumulative-dosing procedure. Both (+) NANM and pentobarbital enhanced the discriminative stimulus effects of phencyclidine. The enhancement of the phencyclidine stimulus by pentobarbital was predicted by adding the effects of the individual drugs, but the enhancement of the phencyclidine stimulus by (+) NANM was sometimes more than would have been expected from adding the effects of the individual drugs. d-Amphetamine did not enhance the discriminative stimulus effects of phencyclidine, but neither did it interfere with these effects. Combinations of (+) NANM or pentobarbital with phencyclidine also enhanced the rate-decreasing effects of phencyclidine, but to a lesser extent than they enhanced the discriminative stimulus effects of phencyclidine. d-Amphetamine only slightly enhanced the rate-decreasing effects of phencyclidine.