Cardioexcitatory neurons in the snail Achatina fulica.

The excitatory motor unit of Achatina fulica is composed of five identified cardioregulatory motor neurons: three tonically active neurons (TAN-1, -2 and -3), a periodically oscillating neuron (PON) and a VG1 neuron. High frequency discharges in TAN neurons evoked slow depolarization waves. The PON elicited biphasic excitatory post synaptic potentials (EPSP). One spike in PON was sufficient to increase heart rate for several minutes. VG1 elicited discrete fast EPSP in the myocardium. Bursts of spikes from VG1 resulted in a summation of EPSP and transiently increased heart. VG1 inhibited spontaneous electrical activity in PON. Our results suggest that the use of semi-intact preparations allow elucidation of new functional cardioregulatory properties of intact neural networks.