Discriminative stimulus properties of narcotic and non-narcotic drugs in rats trained to discriminate opiate kappa-receptor agonists.

The purpose of this study was to evaluate the discriminative stimulus properties of some narcotic and non-narcotic drugs in rats trained to discriminate the effect of the proposed opiate kappa-receptor agonists ethylketocyclazocine and bremazocine. Male Sprague-Dawley rats were trained in a two-lever food-reinforced paradigm to discriminate between the effect of ethylketocyclazocine (0.32 mg/kg) or bremazocine (0.04 mg/kg) and saline. Both groups of trained rats showed dose-dependent generalization to the effect of the proposed kappa-agonist MRZ-2033 and some animals generalized the effect of nalorphine and pentazocine. Some ethylketocyclazocine - but no bremazocine - trained rats generalized the effect of buprenorphine. The effect of dextrorphan, phencyclidine, and ketamine was generalized by some bremazocine -, but no ethylketocyclazocine-trained rats. Neither group of rats generalized the effect of etorphine, haloperidol, diazepam, or pentobarbital. These data suggest the usefulness of this procedure to evaluate the kappa-like properties of opioid drugs.