The effects of nitrite on the excitability of brain neurons in the common snail.

Electrophysiological studies were performed on the effects of sodium nitrite (0.01-1 mM) on identified command neurons in the brain of the common snail. These studies showed that short periods of exposure to nitrite (from a few minutes up to 30 min) had little effect, producing a low level of depolarization and increases in neuron spike activity in only a few cases. Incubation of isolated brains with nitrite (1 mM) for periods ranging from 2 h to several days reduced excitation thresholds, significantly increased spike activity, increases responses to stimulation, and increases the levels of synaptic activity of the neurons studied. These effects increased with time and were stable, but were reversible on washing and were accompanied by depolarization and increased input resistance. The action of nitrite was imitated by known NO donors, and blockers of NO synthesis had the opposite effect. The possible mediation of the effects of nitrite by NO synthesis and the development of hypoxia is discussed.