Discriminative effects of cocaethylene in rats trained to discriminate cocaine or ethanol

Two groups of rats were trained to discriminate between the stimulus properties of either intraperitoneally administered 10.0 mg/kg cocaine or 60 mg/kg ethanol and its vehicle in a two-lever operant chamber. Once trained, both groups exhibited a dose-related decrease in discriminative performance when tested with lower doses. A dose of 10 mg/kg cocaine, as well as doses of 10-30 mg/kg cocaethylene, in the ethanol-trained animals produced no greater than 38.9% responding on the ethanol-appropriate lever. Combinations of the approximate ethanol ED50 dose with either 10 mg/kg cocaine or 20 mg/kg cocaethylene did not increase ethanol lever responding. In contrast, in the cocaine-trained animals, administration of cocaethylene produced dose-responsive cocaine-like discrimination with 30 mg/kg producing 88.9% responding on the cocaine-appropriate lever. In addition, 600 mg/kg ethanol co-administered with a (2.5 mg/kg) dose of cocaine that was poorly discriminated produced 85% of responses on the cocaine-appropriate lever. The peak effect of cocaine and cocaethylene were observed to occur in 15-30 min post-administration with cocaine choice behavior decreasing at a faster rate than seen for cocaethylene discrimination. Results are discussed in light of ethanol and cocaine producing a heightened, as well as prolonged, euphoria in humans.