Temporal Analysis of Snail Feeding Rhythms: a Three-phase Relaxation Oscillator

1. Rhythmic fictive feeding was recorded from the motoneurones of the buccal ganglia of Lymnaea stagnalis. The times of the action potentials were recorded by microcomputer and the lengths of the three phases (Nl, N2 and N3) making up each feeding cycle were determined. 2. During spontaneous rhythmic fictive feeding in Lymnaea stagnalis the cycle period varied randomly. 3. Most of the variation in cycle period arose from alterations in the duration of the N3 (swallowing) phase of the rhythm; the Nl (protraction) and N2 (rasp) phases were fixed in length. 4. The firing rates of feeding motoneurones active in the Nl and N3 phases increased with feeding rate: this was not true of those active in the N2 phase. 5. In rhythms produced by stimulating the SO modulatory interneurone, both the Nl and N3 phases varied in duration. The N2 duration remained constant. 6. The temporal analysis is accounted for by the neuronal model based on the synaptic interactions recorded by Elliott and Benjamin (1985a,Z>; J. Neurophysiol. 54, 1396-1421).