title: Complementary distribution of NADPH-diaphorase and l-arginine in the snail nervous system.
abstract: Since the interneuronal messenger nitric oxide (NO) can not be stored in neurones, the regulation of the NO-producing enzyme nitric oxide synthase (NOS) is crucial. Neuronal NOS metabolises L-arginine to nitric oxide (NO) and L-citrulline in a Ca(2+)-dependent manner. Thus, availability of L-arginine to NOS may modulate NO production. In this study, we examined the cellular distribution of reduced nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase, L-arginine and L-citrulline. Using NADPH-diaphorase histochemistry to visualise putative NO-producing cells and immunocytochemistry to localise L-arginine, we showed that the distribution of L-arginine-immunoreactive neurones correlates well with those of NADPH-diaphorase-positive neurones in cerebral ganglia of the pulmonate Helix pomatia. However, substrate and enzyme were visualised in separate but adjacent neurones. We further examined whether NADPH-diaphorase-labelled cells contain the L-citrulline. Following elevation of intracellular Ca(2+) by the Ca(2+) ionophore, ionomycin, or by a high-K(+) solution, the number of L-citrulline-immunoreactive neurones in mesocerebrum and pedal lobe increased up to tenfold. Preincubation of ganglia with the NOS inhibitor N(G)-nitro-L-arginine prevented ionomycin or high-K(+) solution-induced L-citrulline synthesis. Most L-citrulline-immunoreactive neurones contain NADPH-diaphorase activity. In conclusion, these experiments indicate a complementary distribution of NOS and L-arginine and suggest an unknown signalling pathway between neurones to maintain L-arginine and NO homeostasis.
authors.affiliation: Department of Molecular Neurobiology and Cell Physiology, Institute of Zoology, University of Salzburg, Hellbrunnerstr. 34, 5020 Salzburg, Austria.
authors.forename: Mingqiang
authors.initials: M
authors.lastname: Xie
authors.forename: Anton
authors.initials: A
authors.lastname: Hermann
authors.forename: Hubert H
authors.initials: HH
authors.lastname: Kerschbaum
mesh_terms: D000818:Animals; D001120:Arginine / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002956:Citrulline / Q000378:metabolism; D017952:Ganglia, Invertebrate / Q000166:cytology / Q000378:metabolism; D006372:Helix, Snails / Q000033:anatomy & histology / Q000378:metabolism*; D006706:Homeostasis; D009252:NADPH Dehydrogenase / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000378:metabolism*
chemical_list: D002956:Citrulline; D009569:Nitric Oxide; D001120:Arginine; D019001:Nitric Oxide Synthase; D009252:NADPH Dehydrogenase; D002118:Calcium