Discriminative stimulus properties of cocaine. Effects of apomorphine, haloperidol, procaine and other drugs.

In pigeons trained to discriminate between the presence and absence of 3 mg/kg of cocaine, combinations of intramuscularly injected (i.m.) procaine (0.7-7.0 mg/kg) plus cocaine (0.3-3.0 mg/kg) did not alter the drug (cocaine)-dose generalization curve as compared to cocaine alone although tests with large doses of procaine given alone (30.0 and 56.0 mg/kg) engendered dose-related responding appropriate to cocaine. Apomorphine (0.56 mg/kg, i.m.) also elicited more than 50% cocaine-appropriate responding, as did doses of 10 mg/kg of intragastrically administered cocaine, given by gavage at the opening of the proventriculus; of the two treatment-test intervals (15 and 30 min) examined the generalization effect was greater at 30 min as compared to 15 min after administration. D-Lysergic acid diethylamide (0.1 mg/kg) morphine (3.0 mg/kg), pentobarbital (10.0 mg/kg), and delta 9-tetrahydrocannabinol (0.3 mg/kg) caused less than 16% pecking responses on the cocaine-appropriate key. The discriminative stimulus effects of cocaine (3.0 mg/kg) were attenuated in a dose-related manner by the neuroleptic haloperidol (dose range tested: 0.1-1.0 mg/kg). Neither the antagonism, nor the substitution tests with haloperidol were accompanied by a significant change in the percentage of responding on the initially selected position (key) by the pigeons.