Tryptophan metabolism and the occurrence of amino acids and serotonin in the leech (Hirudo medicinalis) nervous system.

The occurrence and distribution of serotonin (5-HT) and amino acids along the central nerve chain of the leech, Hirudo medicinalis, was analyzed using dansyl-chloride in order to obtain information on the functional roles of amines and amino acids. There was no statistical variation in the occurrence of most of the amino acids or serotonin in the different parts of the dorsal nerve chain of the leech. A variation in the serotonin content was found during the year with the highest level occurring in winter. Leech ganglia also accumulated 3H-tryptophan and metabolized part of it to form 5-HTP, 5-HT, and 5-HIAA. The results are discussed from the point of view of 5-HT being a transmitter substance.