BEHAVIOR AS A STIMULUS: JOINT EFFECTS OF d-AMPHETAMINE AND PENTOBARBITAL

¹ Laboratory of Psychopharmacology, University of Maryland, College Park, Maryland

Pigeons were trained on a procedure where the number of pecks required on a center key (fixed-ratio) signalled which of two side keys was "correct." The effects of d-amphetamine, pentobarbital and combinations of the drugs on both rate of responding and accuracy were examined. Response rates on the center key were increased by appropriate doses of pentobarbital, but only decreased by d-amphetamine. When given in combination, the two drugs antagonized each other's effects. Response rates on the side keys were increased by either d-amphetamine or pentobarbital, and combinations of the two drugs acted synergistically to incrcase rates more than either drug alone. Both drugs reduced accuracy in a dose-related fashion, and combinations of low doses of the drugs worked synergistically to decrease accuracy. The effects of amphetamine were little changed when the difficulty of the discrimination was increased. The nature of the joint effect of amphetamine and pentobarbital depended on both the current situation and on the aspect of behavior measured.