Effects of imipramine on responding reduced by methadone

Interactions between methadone and acute and chronic imipramine were studied in pigeons key pecking under a multiple variable interval 15-sec variable interval 150-sec schedule of food presentation. Both drugs decreased response rates at the highest doses. The VI 15-sec schedule was slightly more sensitive to acute drug administration than was the variable interval 150-sec schedule. Acute combinations of the two drugs neither ameliorated nor exacerbated the effects of either drug alone. Chronic imipramine alone had no lasting effect on responding. Unlike acute combinations, chronic imipramine lessened the rate reducing effect of methadone.