A nitric oxide synthase activity is involved in the modulation of acetylcholine release in Aplysia ganglion neurons: a histological, voltammetric and electrophysiological study.
The role of nitric oxide or related molecules as neuromodulators was investigated in the buccal and the abdominal ganglia of the mollusc Aplysia californica. In a first step we showed that reduced nicotinamide adenine dinucleotide phosphate-diaphorase histochemistry and specific nitric oxide synthase immunohistochemistry labelled the same neurons and fibres in both ganglia, pointing to the presence of a neuronal nitric oxide synthase. In a second step, we performed voltammetric detection of nitric oxide-related molecules using a microcarbon electrode in a reduction mode. A peak identified as N-nitroso-L-arginine was detected at -1.66 V in both ganglia. The identification of this compound as a product of endogenous nitric oxide synthase activity was reinforced by the fact that its peak amplitude was decreased in the presence of NG-monomethyl-L-arginine, an inhibitor of nitric oxide synthase, and increased with its substrate, L-arginine. An additional proof of a nitric oxide synthase activity was the detection of nitrites and nitrates in high concentrations (millimolar range) by capillary electrophoresis. We also showed that these nitric oxide-related molecules modulated acetylcholine release at two identified synapses in these ganglia. L-Arginine decreased acetylcholine release at the inhibitory synapse (buccal ganglion), whereas it increased acetylcholine release at the excitatory synapse (abdominal ganglion). The nitric oxide synthase inhibitors, N omega-nitro-L-arginine and NG-monomethyl-L-arginine, had opposite effects. Moreover, the exogenous nitric oxide donor, 3-morpholinosydnonimine hydrochloride mimicked the effects of L-arginine on both inhibitory and excitatory cholinergic synapses. The identification of two cholinergic synapses where nitric oxide affects acetylcholine release in opposite ways provides a useful tool to study the cellular mechanisms through which nitric oxide-related molecules modulate transmitter release.
Meulemans
A
A
Laboratoire de Biophysique, Faculté de Médecine Xavier-Bichat, Paris, France.
Mothet
J P
JP
Schirar
A
A
Fossier
P
P
Tauc
L
L
Baux
G
G
D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D001048:Aplysia; D002799:Cholinergic Fibers / Q000502:physiology; D019075:Electrophoresis, Capillary; D004594:Electrophysiology; D017952:Ganglia, Invertebrate / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D009252:NADPH Dehydrogenase / Q000378:metabolism; D009433:Neural Inhibition / Q000502:physiology; D009474:Neurons / Q000378:metabolism* / Q000502:physiology; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D013569:Synapses / Q000502:physiology
D019001:Nitric Oxide Synthase; D009252:NADPH Dehydrogenase; D000109:Acetylcholine