Increased drug sensitivity in the drug discrimination procedure afforded by drug versus drug training.

Rats were trained to discriminate norfenfluramine (NF) 1.4 mg/kg from its vehicle or amphetamine (AMPH) 0.8 mg/kg or pentobarbital (PB) 6.0 mg/kg in order to determine the role that drug combination training plays in the rate of learning and sensitivity to lower drug doses. The results suggest that drug versus drug training can increase the rate of drug discrimination learning for some drugs that are learned slowly when trained in a drug versus vehicle training procedure, whereas drug versus drug training does not increase the rate of learning for other drugs that are learned rapidly. Drug versus drug training does, however, appear to increase the level of stimulus control of the training drug for all drugs examined in this study.