Abstract
In the freshwater pulmonate pond snail and flateye snail, contact of the pneumostoma (the respiratory organ) with the water surface and tactile stimulation of the mantle induced phase-coordinated excitation and inhibition of activation of symmetrical pedal neurons RPeD1 (the GDC--giant dopamine cell) and LPeD1 (the GSC--giant serotonin cell). GDC and GSC are not primary sensory neurons and the mechanism by which their actions are coordinated is polysynaptic. Injections of depolarizing current into the GDC or GSC induced spike discharges in one of the columellar nerves. It is suggested that coordination the activities of the GDC and GSC is functionally important for controlling the right and left halves of the columellar complex of muscles during respiration.