Dopamine in a molluscan nervous system: synthesis and fluorescence histochemistry

The nervous system of the pond snail, Helisoma trivolvis, was investigated for its ability to synthesize and accumulate 3H-catecholamines from 3H-tyrosine. 3H-Dopamine, but not 3H-norepinephrine, was synthesized by several ganglia. The highest accumulations were found in the cerebral, pedal, and buccal ganglia. The Falck-Hillarp and glyoxylic acid fluorescence histochemical techniques were applied to the buccal ganglia to visualize dopamine-containing cells. Fluorescing cells were found on both dorsal and ventral sides of the ganglion. Peripheral nerves of the buccal ganglia also displayed catecholamine fluorescence and accumulated 3H-dopamine. However, no 3H-dopamine synthesis occurred in the cerebral-buccal connectives, which connect the buccal ganglia with the rest of the central nervous system. Therefore, we conclude that there is a dopaminergic system intrinsic to the buccal ganglia and their peripheral targets.