Subcellular localization of serotonin-immunoreactivity in the pedal ganglion of Mytilus galloprovincialis (Mollusca, Bivalvia).

Serotonin has been localized in neurons of the pedal ganglion of Mytilus galloprovincialis by means of colloidal gold immunostaining. Ultrastructural quantitative analysis shows that gold particles are concentrated over perikarya and fibers containing a unique vesicle population. The vesicles are round or elliptical with a diameter ranging from 100 to 180 nm and have a dense core with areas of minor density. Their intense labelling suggests that they are the main cellular compartment where serotonin is stored.