The discriminative stimulus properties of cocaine in the rhesus monkey

Abstract

Three rhesus monkeys were trained to discriminate IM injections of cocaine (0.25 mg/kg) from saline under conditions where responding was maintained on one of two levers under a fixed-ratio 30 schedule of food delivery. The ability of other doses of cocaine and other compounds to substitute for the training dose of cocaine in controlling cocaine-appropriate responding was assessed. Cocaine (0.008–0.5 mg/kg), d-amphetamine (0.03–0.25 mg/kg) and l-cathinone (0.03–0.5 mg/kg) produced dose dependent increases in the percent of cocaine-appropriate responding in test sessions. At the highest doses tested, these three compounds produced more than 90% cocaine-appropriate responding suggesting that they share discriminative stimulus properties. When nicotine (0.125–16 mg/kg) and procaine (0.06–8.0 mg/kg) were tested, some of the monkeys responded 90% or more on the cocaine-appropriate lever; in other cases there was a trend towards generalization at lower doses but when higher doses were administered, responding was suppressed. These data suggest that these two compounds have discriminative stimulus properties which differ to some extent from cocaine. Finally, when pentobarbital (2–16 mg/kg) was administered, responding occurred on the saline-appropriate lever indicating that this drug does not share the discriminative stimulus properties of cocaine.