Tryptophan metabolism in characterized neurones of Helix

[(14)C]-Tryptophan perfused through the central nervous system of the snail Helix pomatia is taken up by both 5-hydroxytryptamine-containing (GSC) and non-5-hydroxytryptamine-containing cells. Only the GSCs have the capacity to metabolize [(14)C]-tryptophan to form some 5-hydroxytryptophan and slightly more 5-hydroxytryptamine. Electrical stimulation of the GSCs, strong enough to elicit a firing of spikes, resulted in more 5-hydroxytryptamine being produced, though there was also a slight increase in the amount of labelled tryptophan and 5-hydroxytryptophan. Doubling the length of stimulation and the amount of [(14)C]-tryptophan perfused through the central nervous system had no great influence on the content of radioactive substances found in the GSC. Pretreatment of snails with p-chlorophenylalanine, though not interfering with the uptake of tryptophan into the GSCs, almost completely prevented the formation of 5-hydroxytryptophan. As well as showing that the enzyme tryptophanhydroxylase is only present in cells containing 5-hydroxytryptamine, these experiments demonstrate the possibility of studying the metabolism of 5-hydroxytryptamine in characterized neurones.