Nitric oxide-mediated cGMP synthesis in Helix neural ganglia.

The central nervous system of the mollusc Helix pomatia was stimulated with NO donors sodium nitroprusside (SNP), S-nitroso-N-acetylpenicillamine (SNAP) or hydroxylamine, in the presence of a phosphodiesterase inhibitor 1-methyl-3-isobutylxanthine (IBMX). Radioimmunoassay revealed that all of the three NO donors significantly increased cGMP levels by 22-27-fold above basal levels. Compared with controls, strong cGMP immunoreactivity was observed in axons and cytoplasm of the stimulated neurons. About 80% of cGMP-immunoreactive neurons colocalized with NADPH-diaphorase activity. Some glial cells and giant neurons were not stained by NADPH-diaphorase histochemistry but were cGMP-immunoreactive. The results suggest the existence of a NO/cGMP pathway and indicate NO as an intra- and intercellular signaling molecule in the Helix central nervous system.