The effects of 5-HT uptake- and MAO-inhibitors on L-5-HTP-induced excitation in rats.

The behavioural syndrome caused by L-5-HTP in rats was used for the study of effects of selective 5-HT uptake inhibitors and inhibitors of MAO on central 5-HT receptors. A good correlation was found between the relative potencies of drugs in inhibiting the 5-HT uptake in the rat brain and in intensifying L-5-HTP-induced behavioural stimulation. The potentiation of the L-5-HTP syndrome by the MAO inhibitors correlated with the inhibition of the A- but not of the B-form of the brain monoamine oxidase. In rats treated with the maximally inhibiting dose of a 5-HT uptake inhibitor, MAO inhibitors were still able to increase the intensity of the L-5-HTP syndrome, while the combination of maximal doses of two 5-HT uptake inhibitors did not produce a more intense syndrome than that produced by one 5-HT uptake inhibitor alone. The L-5-HTP-induced behavioural syndrome in rats seems to afford an experimental model allowing the quantification and characterization of the interaction of drugs with serotonin metabolism in the brain.