The ability of d-amphetamine and ethanol to alter discriminative stimulus control by pentobarbital was examined in pigeons. Saline and pentobarbital (5.6 mg/kg) were established as discriminative stimuli for food-maintained responding in six birds. Dose-response functions for stimulus control and response rate were determined for pentobarbital alone and in combination with selected doses of d-amphetamine or ethanol. In tests of stimulus generalization, d-amphetamine alone did not exert pentobarbital-like stimulus control, while ethanol alone evoked variable degrees of pentobarbital-like stimulus control. d-Amphetamine attenuated pentobarbital stimulus control. Doses of 1.0 or 3.2 mg/kg d-amphetamine increased the dose of pentobarbital required for stimulus control in five of six birds. Combinations of high d-amphetamine and pentobarbital doses yielded less than additive rate suppression. Ethanol produced variable effects on pentobarbital stimulus control, with moderate doses generally decreasing, and high doses increasing, the dose of pentobarbital required for stimulus control. A high ethanol dose decreased the pentobarbital dose required for rate suppression. Taken together, these data demonstrate that pentobarbital stimulus control can be altered by drugs within or without the sedative hypnotic class.
