DO NITRIC OXIDE-PRODUCING NEURONS OCCUR I N INVERTEBRATE ANIMALS

NADPH-diaphorase (NADPHd) has been shown to be identical to nitric oxi de (NO) synthase in the mammalian nervous system and is, therefore, us ed as. a marker of NO-producing neurons. Using histochemical reaction for NADPHd, we searched for such neurons in a variety of invertebrates belonging to principal taxonomic groups. No specific neuronal stainin g was found in coelenterates, turbellarians, nematodes, and ascidians. In annelids, molluscs, and arthropods, some neurons were selectively stained. In pulmonate molluscs, the reaction was especially strong. NA DPHd-positive neuron perikarya and processes occupied mostly the bucca l ganglia. It appears thus that NO can be used as a signal molecule by specific neurons in advanced invertebrates.