Action of antidepressants, stimulants and depressants in the transition from a fixed ratio to a fixed interval schedule of reinforcement.

1. The modifications of rat behaviour caused by imipramine, amitriptyline, doxepin, amphetamine, chlorpromazine, caffeine and diazepam were studied. 2. The schedule of reinforcement was changed from a fixed ratio to a fixed interval schedule. 3. All the studied drugs caused a depression of the rat behaviour but only tricyclic antidepressants and caffeine caused virtually no damage to the ability of the animal to adapt its behaviour to the new experimental situation.