Ultrastructure of the terminals of an identified dopamine-containing neurone markedby intracellular injection of radioactive dopamine.

The terminal processes of an identified dopamine-containing neurone in the central nervous system of the water snail were located for study with the electron microscope. This was achieved by intracellular injection of 3-H-dopamine followed by light and electron microscope autoradiography. The neurone showed extensive branching in ganglia whereprevious electrophysiological work had shown the presence of postsynaptic neurones. The terminal processes in these ganglia contained dense-cored vesicles of 50-250 nm diametersimilar to those in the perikaryon. Vesicles were found in large numbers in certain lacalized regions which may be synaptic terminals. The vesicles, which appear to take updopamine, tended to be smaller in the presumed terminal regions than in the preterminals and the perikaryon. No membrane specializations associated with typical synapses were observed.