[The properties of NADPHd-positive neurons in the brain of the snail]

Studies of NADPH-diaphorase (NADPHd) histochemistry in Helix brain indicate a number of discrete populations of putative NO-producing neurons in different ganglia. It has been shown that NADPHd-positive neurons (4 populations) have similar morphological, electrical, and plastic properties. These neurons are small (about 20 mcm), silent, with low threshold of excitability and low synaptic activity. They don't habituate to stimulation by impulses of depolarizing current and demonstrate low sensitivity to neurotransmitters. Serotonin, dopamine, and opioid peptides hyperpolarize, and glutamate, NMDA, and acetylcholine depolarize them. The evidence has been obtained that NO regulates the electrical and plastic properties of NADPHd-positive neurons in Helix brain and potentiates their sensitivity to glutamate. The properties of putative NO-producing Helix neurons have been compared with the known properties of vertebrate NO-producing neurons. The possible mechanisms are discussed of regulation by NO of the plastic properties of these neurons.