Effect of serotoninergic drugs on positive and negative reinforcing systems in cats.

Administration of tryptophan and 5-hydroxytryptophan produced inhibition of self-stimulation through hypothalamic electrodes which was accompanied by drowsiness and decrease of motor activity. In cats pretreated with Ro 4-4602, an inhibitor of peripheral decarboxylase, both drugs did not produce drowsiness and markedly activated self-stimulation. Both drugs prolonged the latency of the escape reaction and inhibited the punishment reaction. The data suggest an activating effect of serotonin on the system of reward and an inhibitory effect on the system of punishment.