Identified Neurones Involved in the Control of Rhythmic Buccal Motor Activity in the Snail Achat1na Fulica

In the land snail Achatinafulica, it has been suggested that two pairs of cerebral neurones, ventral cerebral distinct neurones (v-CDNs) and Cl neurones, and a pair of buccal motoneurones (BLs) are involved in the control of rhythmic motor activity (RMA) in the buccal ganglia. These neurones, when tonically fired by depolarizing current injection, could individually initiate and maintain RMA in previously quiescent isolated ganglia. The rhythm elicited by v-CDN persisted for several cycles after the firing of v-CDN stopped, while that elicited by Cl or Bl ceased immediately after the firing of these neurones stopped. RMA also occurred spontaneously and could be induced by labial nerve stimulation in a reduced preparation. Nevertheless, such rhythms were not always accompanied by the firing of v-CDN, Cl or BL. Thus, the firing of these neurones appears to be sufficient, but not essential, for rhythm generation in the experimental conditions. Taste stimulation of the lip in semi-intact preparations often induced RMA in the buccal ganglia. However, v-CDN and Bl were not tonically excited by the stimulation. It seems unlikely that v-CDN and Bl are critical elements in the generation of the feeding rhythm. Cl responded to taste stimuli with excitation after RMA had begun, suggesting that Cl is involved in the taste-induced buccal rhythm.