Stimulus control by diazepam of behavior maintained under fixed-ratio stimulus-shock termination schedules in rats

The stimulus control of behavior by diazepam (1.0 mg/kg) was investigated where responding was maintained under fixed-ratio (FR) schedules of stimulus-shock termination in rats. The size of the FR requirement was either 1, 5, 10, or 20 responses. At each FR requirement, dose-effect curves were determined for diazepam, flurazepam, pentobarbital and cyproheptadine. Diazepam-like discriminative stimuli were produced by flurazepam and pentobarbital but not by cyproheptadine. The magnitude of the FR requirement had no significant effect on the dose-effect curves for percentage of responses emitted on the diazepam-appropriate choice lever for any of the four drugs. On the other hand, the effects of these drugs on rates of responding depended on the magnitude of the FR requirement. None of the drugs altered response rates under the FR1 schedule. Diazepam tended to increase response rates under the FR5 schedule, but had no effect or decreased rates under the FR10 and FR20 schedules. Flurazepam and pentobarbital predominantly decreased rates at FR requirements of 5, 10 or 20 responses. Cyproheptadine had no significant effect on response rates at any schedule parameter. Together with previous reports, the present results indicate that the discriminative effects of diazepam are similar under schedules employing noxious (this study) or non-noxious (other reports) consequences, even though the effects on response rates of diazepam-like drugs differ depending on the schedule of reinforcement and consequent event maintaining the behavior.