Histamine in the nervous system of Macoma balthica (Bivalvia).

The distribution of histamine(HA)-immunoreactivity of the molluscan species Macoma balthica was mapped with an antiserum against a histamine-protein conjugate. The main ganglia of the central nervous system of M. balthica, the cerebropleural ganglia, the pedal ganglion and the visceral ganglion all contained strongly HA-positive fluorescent cell bodies. The positive cell bodies were situated in clusters in the outer region of the ganglia. Immunoreactive fibres were located in the inner neuropil region of the ganglia. Also the commissure and the connectives of the ganglia as well as many nerve roots contained HA-positive fibres. These results agree well with the recent finding of the wide distribution of histamine in the nervous system of two marine gastropod molluscs, Aplysia and Pleurobranchaea supporting the thought that histamine has an important role in many physiological function of molluscs.