Monoamine precursor uptake in ganglia of a mollusc Anodonta cygnea L. (Bivalvia) An autoradiographic and ultrastructural study.

In vitro-uptake and localization of 3H-5 hydroxytryptophan and 3H-dihydroxyphenylalanine have been investigated by means of light microscopic autoradiography in the central nervous system of the freshwater mussel, Anodonta cygnea L. Accumulation of the labelled monoamine precursors could be observed both over neuronal perikarya and neuropil in the ganglia. 3H-5-hydroxytryptophan and 3H-dihydroxyphenylalanine were taken up by neurons characterized by a small size (10-20 micrometer), a polygonal form and an intense staining with toluidine blue. Labelled axon branches situated either in the neuropil or between nerve cells in the cortex exhibited only a moderate activity, frequently of a diffuse character. After pretreatment fro 24 h with colchicine, silver grains were also seen over a neuronal perikarya and some axon profiles. This shows that local uptake of the monoamine precursors and, presumably, the synthesis of the monoamines takes place both at perikaryal and axonal/terminal level. The nerve cells accumulating the monoamine precursors contain a nucleus with rich chromatin content and a deeply invaginate nuclear envelope. Further ultrastructural characteristics of these neurons are their well-developed rough endoplasmic reticulum system, a great number of mitochondria and glycogen granules, and the presence of dense-cored vesicles of different types. All those features are responsible for the electron-dense appearance of the cytoplasm.