Stimulus control and the effects of d-amphetamine in the rat.

External discriminative stimuli can modify the behavioral effects of d-amphetamine. Previous work with the pigeon has demonstrated that some aspects of performance on the fixed consecutive number schedule are changed less if a discriminative stimulus indicates when reinforcement is available. This effect has now been replicated with the rat using both simple and multiple schedules. Moderate doses of d-amphetamine (0.56--1.0 mg/kg) usually produced large decreases in reinforced runs when no external cue indicated the possibility of reinforcement. Adding discriminative stimuli when the number requirement was met decreased the drug effect. As was true in the pigeon, response rate measures did not differ between the two stimulus control conditions. Thus, external stimulus control diminishes the drug effect in both species, despite the fact that key pecking was studied in the pigeon and lever pressing in the rat. Evidence was also seen of a possible increase in discriminative stimulus control by d-amphetamine.