Influence of some drugs of abuse on the discriminative stimulus properties of amphetamine.

The present study assessed the utility of a drug interaction paradigm for measuring the effects of various psychoactive drugs on the stimulus properties of d-amphetamine. In the first experiment, rats trained to discriminate 1.0mg/kg d-amphetamine from saline were tested for generalization to a range of d-amphetamine doses (0.25, 0.50 and 1.0mg/kg) injected alone or with cocaine, apomorphine or haloperidol. When given alone d-amphetamine yielded an orderly dose-response function and this was altered by the test drugs in a manner consistent with the dopamine agonist or antagonist actions of each compound. In the second experiment, the cueing effects of d-amphetamine were potentiated by nicotine and attenuated by morphine and midazolam. Ethanol enhanced the cueing effects of the lower d-amphetamine doses but produced no drug-lever responding when given alone. These findings confirm the results of previous studies which have assessed the effects of these classes of drugs on the stimulus properties of amphetamine. However, the results are inconsistent with the hypothesis that all drugs of abuse possess psychomotor stimulant properties.