CONTRIBUTION OF TRYPTAMINE TO BEHAVIORAL-EFFECTS OF L-TRYPTOPHAN IN TRANYLCYPROMINE-TREATED RATS

Rats pretreated with the monoamine oxidase inhibitor tranylcypromine and given l-tryptophan develop a characteristic behavioural syndrome. A comparison of the behavioural effects of tranylcypromine plus l-tryptophan (50 and 100 mg/kg) showed a small increase in locomotor activity and a greater increase in the behavioural score with the higher dose. This was associated with a proportionately smaller increase in brain 5-hydroxytryptamine (5-HT) than in brain tryptamine and no change in spinal cord 5-HT. Tryptamine (1-5 mg/kg) in the presence of tranylcypromine produced behavioural effects very similar to those occurring when l-tryptophan is given to tranylcypromine-pretreated rats. Increasing brain tryptamine, by the injection of tryptamine (0.75 mg/kg), enhanced the behavioural effects of tranylcypromine plus l-tryptophan (50 mg/kg) without altering brain 5-HT. Para-chlorophenylalanine pretreatment, which reduced brain 5-HT, prevented the behavioural effects of tryptamine. Inhibition of peripheral decarboxylase with R04-4602 (50 mg/kg) reduced brain tryptamine and did not alter brain 5-HT, but reduced the locomotor activity and the behavioural score of rats given tranylcypromine and l-tryptophan (100 mg/kg). The results suggest that brain tryptamine changes are partly responsible for the behavioural effects of tranylcypromine plus l-tryptophan and that some of this tryptamine is of extracerebral origin. © 1978 Springer-Verlag.