The DRL 72-second procedure is a highly predictive test for antidepressants. This is an operant procedure where the subjects are trained to withhold a lever-press for at least 72 seconds in order to obtain food reinforcement. Premature responses cause the clock to be reset and fewer reinforcements received. Response patterns of rats treated with antidepressant drugs from different classes (tricyclics, MAOIs, SSRIs and "atypical" antidepressants) are characterized by a decrease in response rate and an increase in reinforcement rate. Drugs that are not antidepressants do not have these effects.

Imipramine (at doses of 3.0 - 17.0 mg/kg) increases the reinforcement rate and decrease the response rate.