Neuronal Control of Mucus Secretion by Leeches: Toward a General Theory for Serotonin

Abstract

The large Retzius cells are serotonin-containing neurons whose impulse activity controls the secretion of mucus from the skin of leeches. Serotonin elicits the secretion of mucus without any apparent synaptic transfers in either the central or peripheral nervous systems. Such a secretogogue function may be more general as serotonin controls the secretion of mucus from the gastrointestinal tract of mammals and from the ciliated gills of bivalved molluscs. Furthermore, the qualitative and quantitative distribution of serotonin in molluscs, annelids, arthropods, and vertebrates corresponds approximately with mucosecretory structures. Serotonin appears also to control other secretory functions in some of these animals. It is proposed therefore that serotonin might often function in controlling secretion.