PUTATIVE NO-SYNTHESIZING NEURONS OF LYMNAEA IN-VIVO AND IN-VITRO

The distribution of putative nitric oxide synthase- (NOS) containing n eurons in the CNS and peripheral tissues of the freshwater pulmonate m olluscs, Lymnaea stagnalis, Helisoma trivolvis and Biomphalaria sp. wa s investigated using NADPH-diaphorase (NADPH-d) histochemistry and NOS -immunolabelling. NADPH-d-positive cells were found in most of the cen tral ganglia but their distribution was different from that of other n eurotransmitters. Comparison of NADPH-d-positive neurons in the CNS of Lymnaea, Helisoma and Biomphalaria showed that bulinid snails contain ed more NADPH-d positive neurons in the CNS, especially in the cerebra l ganglia, compared to Lymnaea. Some of previously identified neurons were found to be NADPH-d-positive (e.g. a buccal gut motoneuron B2 in Lymnaea and its homologues B5 in the bulinids). In addition, the right parietal 'light yellow' cluster cells (LYC) were also weakly stained in Lymnaea both with NOS antibodies and NADPH-d. Neurons B2 and LYC we re isolated and maintained in culture under conditions that support ne urite outgrowth. In culture, both B2 and LYC were stained by NADPH-d s imilar to that observed in whole mount preparations. In addition to ce ll somata, intense NADPH-d positive staining was observed in the growt h cone and at the tips of filopodia of B2 neurons. We suggest that NO (or related substances) is involved in neuronal signalling in mollusca n species.