Serotonin storage and uptake by identified neurons in the leech Haementeria ghilianii

Characterization of serotonin-containing neurons in the glossiphoniid leech Haementeria ghilianii was undertaken to provide a reference for developmental studies of their differentiation and for comparative studies of their distribution and function. Five types of serotonin-containing neurons were identified with an antiserum against serotonin and by radioenzymatic assay of individual isolated somata. They contain high concentrations of serotonin (in some cases exceeding saturation in aqueous solution) and their serotonin content increases with growth of the animal. Each type is capable of taking serotonin up from the extracellular fluid, as demonstrated autoradiographically. They exhibit segment-specific, and on comparison with hirudinid leeches, species-specific, differences in distribution, morphology, and the expression of serotonin metabolism.