Differences between alcohol-preferring and alcohol-nonpreferring rats in ethanol generalization.

Alcohol-preferring (P rats) and alcohol-nonpreferring rats (NP rats) were trained to discriminate intraperitoneal injections of 0.5 g/kg ethanol, or subcutaneous injections of 0.6 mg/kg nicotine from saline. P rats learned the ethanol discrimination more rapidly and made a higher percentage (88%) of their responses on the ethanol lever after ethanol and a lower percentage (7%) after saline than NP rats (78 and 15%, respectively). In substitution tests, increasing doses of ethanol produced increases in the percentage of responses on the ethanol lever with similar ED50s (0.43 and 0.44 g/kg) in P and NP rats. P rats trained to discriminate ethanol from saline made more responses on the ethanol lever after nicotine (80%) and d-amphetamine (63%) than NP rats (33 and 40%). The ethanol stimulus did not generalize to morphine in either P or NP rats. NP rats trained to discriminate ethanol from saline responded more on the ethanol lever after bupropion (77%) than P rats (49%). In rats trained to discriminate nicotine from saline, the nicotine discriminative stimulus did not generalize to ethanol in either P or NP rats, suggesting that the genetic difference in the stimulus generalization of ethanol was not symmetrical.