Distribution of NADPH-diaphorase reactivity and effects of nitric oxide on feeding and locomotory circuitry in the pteropod mollusc, Clione limacina.

The action of nitric oxide (NO) and the distribution of putative nitric oxide synthase-containing cells in the pelagic pteropod mollusc Clione limacina were studied using nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry and conventional microelectrode techniques in the isolated central nervous system and in semi-intact preparations. The majority of NADPH-d-reactive neuronal somata were restricted to the cerebral ganglia. The labeled cells were small in diameter (20-30 microm) and were located in the medial areas of the ganglia. A pair of symmetrical neurons was found in the peripheral "olfactory organ." NADPH-d-reactive non-neuronal cells were detected in the periphery and were mainly associated with secretorylike cells and organs of the renopericardial system. The NO donor, diethylamine NO complex sodium salt (10-100 microM), activated neurons from both feeding and locomotory circuits. The cGMP analog, 8-Br-cGMP, mimicked the effects of NO on neurons. We suggest that NO is an endogenous neuromodulator involved in the control of some aspects of feeding and locomotor behavior of Clione.