d-Amphetamine and fixed-interval performance: effects of establishing the drug as a discriminative stimulus.

The effects of d-amphetamine were examined as a function of conditioning history. The compound (0.5 mg/kg) (1) increased the response rate of rats under a fixed-interval 60-sec schedule, (2) produced greater increases in responding under the fixed-interval schedule when drug administration had been explicitly paired with a fixed-ratio 20 schedule, and (3) decreased responding under the fixed-interval schedule when the drug had been paired with electric shock punishment. Randomly giving amphetamine before fixed-ratio or punishment sessions did not produce such modifications of drug effects under the fixed-interval schedule. These results, like earlier findings, indicate that drug effects can be modified by conditioning history.