[Generation of locomotor rhythms in Limacina helicina]

Two groups of neurons (motoneurons and putative interneurons), exhibiting periodic activity with the locomotory rhythm, were recorded in the pedal ganglia of the isolated nervous system of the mollusc Limacina helicina. Motoneurons periodically generated spike bursts, while interneurons generated only one prolonged (100-400 ms) action potential per cycle. Rhythmic generation persisted after blocking the spike discharges of motoneurons by means of tetrodotoxin. Rhythmic generation could be facilitated by application of serotonin.