Discriminative stimulus properties of cocaine in pigeons

The present study was designed to assess the discriminative stimulus properties of cocaine in pigeons. Six pigeons were trained to discriminate IM injections of cocaine (2 mg/kg) from saline with responding maintained under a fixed-ratio 30 schedule of food delivery. Cocaine, d-amphetamine, and l-cathinone substituted completely for the training dose of cocaine in all pigeons. When nicotine (0.25-4.0 mg/kg), apomorphine (0.03-1.0 mg/kg), procaine (4-32 mg/kg), and lidocaine (4-16 mg/kg) were substituted, both partial substitutions and individual differences between pigeons were observed. Oxazepam (0.5-4.0 mg/kg) and pentobarbital (2-8 mg/kg) failed to substitute for the training dose of cocaine. Discriminative stimulus control by cocaine was greatest when the drug was administered 10-40 min prior to the session and the effects disappeared after 2 h. The substitution results indicate drug class specificity of the cocaine cue but, in addition, suggest its multidimensional nature.