Control of locomotion in marine mollusc Clione limacina. VI. Activity of isolated neurons of pedal ganglia.

In the pteropodial mollusc Clione limacina, the rhythmic locomotor wing movements are controlled by the pedal ganglia. The locomotor rhythm is generated by two groups of interneurons (groups 7 and 8) which drive efferent neurons. In the present paper, the activity of isolated neurons, which were extracted from the pedal ganglia by means of an intracellular electrode, is described. The following results have been obtained: Isolated type 7 and 8 interneurons preserved the capability for generation of prolonged (100-200 ms) action potentials. The frequency of these spontaneous discharges was usually within the limit of locomotor frequencies (0.5-5 Hz). By de- or hyperpolarizing a cell, one could usually cover the whole range of locomotor frequencies. This finding demonstrates that the locomotor rhythm is indeed determined by the endogenous rhythmic activity of type 7 and 8 interneurons. Type 1 and 2 efferent neurons, before isolation, could generate single spikes as well as high-frequency bursts of spikes. These two modes of activity were also observed after isolating the cells. Thus, the bursting activity of type 1 and 2 neurons, demonstrated during locomotion, is determined by their own properties. Type 3 and 4 efferent neurons generated only repeated single spikes both before and after isolation. The activity of the isolated axons of type 1 and 2 neurons did not differ meaningfully from the activity of the whole cells. Furthermore, in the isolated pedal commissure, we found units whose activity (rhythmically repeating prolonged action potentials) resembled the activity of type 7 and 8 interneurons.(ABSTRACT TRUNCATED AT 250 WORDS)