Cocaine cue in pigeons: time course studies and generalization to structurally related compounds (norcocaine, WIN 35,428 and 35,065-2) and (+)-amphetamine.
1 Pigeons trained to discriminate between the presence or absence of effects induced by cocaine hydrochloride (5.6 mg/kg) were tested for generalization with norcocaine and two phenyltropane analogues (WIN 35,428 and WIN 35,065-2). Separate dose-effect curves were obtained at different intervals after the injections so that possible changes both in potency and duration of action could be evaluated.2 Results showed that all of these drugs fully generalized to cocaine. The order of potency was WIN 35,428 > norcocaine > WIN 35,065-2 > cocaine when tested either at 15 or 60 min after injection. The cocaine-like effects were strongest for all drugs when tested 15 min after injection as compared to the tests at the 60 min interval. The decay of the cocaine-like stimulus effects occurred at about the same rate.3 Apomorphine (0.3, 0.56 and 1 mg/kg), morphine (3 and 5.6 mg/kg), Delta(9)-tetrahydrocannabinôl (0.3 and 0.56 mg/kg), and lysergic acid diethylamide (LSD-25, 0.056 and 0.1 mg/kg) did not induce more than 30% cocaine appropriate responses. (+)-Amphetamine produced 73% and 85% cocaine appropriate responses depending on the injection-test interval used, 15 and 30 min respectively.4 The amphetamine homologue, para-hydroxyamphetamine (3.8 mg/kg) did not generalize to cocaine. Tests with 30 mg/kg of procaine produced 40% cocaine appropriate responses. Cocaine is effective also when administered by gavage into the opening of the proventriculus.5 The use of the drug discrimination technique for studying structure activity relationships of drugs is discussed.