Cocaine-like discriminative stimulus effects of procaine, dimethocaine and lidocaine in rats

The discriminative stimulus effects of several local anesthetics and (+)-amphetamine were assessed in a drug discrimination based on the psychomotor stimulant cocaine. Two groups of adult male Sprague-Dawley rats were trained in two-lever operant chambers in a cocaine versus saline discrimination, or a cocaine versus procaine or saline discrimination, using a fixed ratio 20 schedule of food reinforcement. Cocaine, (+)-amphetamine and dimethocaine all dose-dependently substituted for the training dose of cocaine (10 mg/kg) in both procedures. While procaine and lidocaine showed partial substitution in the cocaine versus saline procedure, much less substitution occurred in the cocaine versus procaine or saline discrimination. These data demonstrate that it is possible to train rats to discriminate between cocaine and another local anesthetic procaine, resulting in an increased pharmacological specificity of cocaine discrimination. The fact that dimethocaine fully substituted for cocaine in both procedures indicates that this local anesthetic has more cocaine-like effects than others so far tested, which is consistent with results from other behavioral and neurochemical studies with this compound.