Cardiac inhibitory neurons in gastropod snail Achatina fulica.

Two inhibitory heart motor neurons (HI-1, HI-2) were identified in the visceral ganglion of the snail Achatina fulica. Both motor neurons were connected monosynaptically with the myocardium. Irregular action potentials composed a typical pattern of neuronal spontaneous electrical activity. The neurons shared common excitatory synaptic inputs, and were connected through electrical synapses. Neuronal endings of these cells responded to tactile stimulation and to cardiac stretching when the chemical synapses were blocked. HI-1 and HI-2 neurons both elicited inhibitory post synaptic potentials in the myocardium with a constant delay and thereby modulated cardiac spikes frequency and amplitude. Staining with the dye Lucifer yellow revealed that these two neurons were unipolar cells which had dendrites only in the visceral ganglion.