Control of feeding movements in the pteropod mollusc, Clione limacina.

(1) The buccal apparatus of the pteropod marine mollusc Clione limacina, isolated together with buccal ganglia, could perform rhythmic feeding movements. Movements of the radula and the hooks (which the Clione inserts into the body of its prey) as well as the electroneurogram of the radular nerve were recorded. Usually one could observe rhythmic radula movements alone, while the hooks were motionless. But sometimes the hooks also performed rhythmic movements which were more or less synchronous with those of the radula. The radula movement cycle consisted of the protraction and the retraction phases, which were occasionally followed by a quiescent phase. Corresponding to each radula movement was a burst of activity in the radular nerve, consisting of the protractor and the retractor components. (2) Isolated buccal ganglia were capable of feeding rhythm generation. Most of the buccal neurons exhibited rhythmic activity correlating with the activity in the radular nerve. According to the phase of activity in the feeding cycle, rhythmic neurons were divided into two groups - the protractor and the retractor ones. The neurons within each of the groups were electrically coupled with each other. The protractor and retractor neurons inhibited each other. (3) Protractor and retractor neurons were extracted from buccal ganglia by means of a microelectrode. Many isolated cells generated slow oscillations of membrane potential and bursts of spikes, the pattern of this activity being similar to that before isolation. (4) A model of the feeding rhythm generator is discussed. It consists of two (protractor and retractor) groups of neurons with mutual inhibitory connections, neurons of each group being endogenous bursters.