The regulation of 5-hydroxytryptamine release from superfused synaptosomes by 5-hydroxytryptamine and its immediate precursors

Abstract

The effect ofl-tryptophan, 5-hydroxy-l-tryptophan (5-HTP), and 5-hydroxytryptamine (5-HT) on the K⁺-evoked release of [³H]5-HT from superfused rat brain synaptosomes was studied. 5-HT at concentrations above 10 nM significantly inhibited the K⁺-evoked release of [³H]5-HT. A slight enhancement of [³H]5-HT release was observed at a concentration of 5nM. In contrast tryptophan at a concentration of 10 nM significantly enhanced [³H]5-HT release with little effect at higher concentrations. 5-HTP did not significantly effect [³H]5-HT release. The results confirm previous findings that 5-HT inhibits its own release from nerve endings, and demonstrate that low concentrations of tryptophan in the synaptic region may act as a positive feedback regulator of 5-HT release.