Similar effects of antidepressant and non-antidepressant drugs on behavior under an interresponse-time greater than 72-s schedule.

Antidepressant drugs were reported to decrease responses and increase reinforcements in water-deprived male albino rats pressing a lever for water on a schedule requiring a pause of at least 72 s between responses (IRT greater than 72). Subsequently other investigators, using food-deprived ovariectomized hooded rats pressing a lever for food, showed that antipsychotic drugs produced the same effect as antidepressants. Because methodologies differed somewhat, the present study was designed to replicate closely the experimental conditions of the original studies, e.g., same strain and sex, same reinforcer, similar baseline behavior. In this study the antidepressant imipramine, the antipsychotics chlorpromazine and haloperidol, and to some extent the anxiolytic buspirone produced qualitatively similar effects - decreased responses and increased reinforcements - although there were some quantitative differences. This result, and other results showing that some antidepressants increase responses and decrease reinforcements, suggest that the IRT greater than 72-s task lacks specificity as a screening method for antidepressants.