Some effects of desmethylimipramine and amitriptyline on the schedule-controlled behavior of pigeons and rats

The effects of desmethylimipramine and amitriptyline on schedule-controlled behavior of pigeons and rats were examined. Pigeons responded under either a multiple (mult) fixed-interval (FI) 600-sec, fixed-ratio (FR) 30-response schedule of food presentation or a mult FI 200-sec, FI 200-sec schedule, in which responding during one component was punished with electric shock. Rats responded under a mult FI 300-sec, FR 30-response schedule of food presentation. Under the mult FI, FR schedules, desmethylimipramine and amitriptyline decreased overall rates of FI and FR responding in both species. Overall rates of responding were decreased to similar extents under both the FI and FR components of the schedule. In the pigeon, but not in the rat, the effects of desmethylimipramine and amitriptyline on responding under the FI component of the mult FI, FR schedule depended on the control-rate of responding, i.e. desmethylimipramine and amitriptyline increased more or decreased less the low rates of FI responding at the beginning of the FI compared to the higher rates of FI responding at the end of the FI. In contrast, in the rat desmethylimipramine and amitriptyline did not differentially affect the low rates of responding at the beginning of the FI compared to the higher rates of responding at the end of the FI. Correspondingly, in the pigeon, but not in the rat, desmethylimipramine and amitriptyline decreased the fixed-interval quarter-life at relatively low doses. In the pigeon neither desmethylimipramine nor amitriptyline differentially affected the overall rate of punished as compared to unpunished responding.