Control of locomotion in the freshwater snail Planorbis corneus. II, Differential control of various zones of the ciliated epithelium

In the freshwater snail Planorbis corneus , the neuronal mechanisms of the pedal ganglia that control ciliary locomotion were studied. The foot was attached to the bottom of a recording chamber with the ciliated epithelium facing upwards. To record the total motor effect produced by ciliary beating, a small disk with its edge lying on the sole of the foot was used. The ciliary beating forced the disk to rotate. In the pedal ganglia, efferent locomotor neurones (ELNs) were found, which control the locomotor activity of the ciliated epithelium. This locomotor activity increased with excitation of an ELN, and decreased with its inhibition. Axons of the ELNs, controlling the anterior, middle and posterior zones, traverse the corresponding pedal nerves. For the anterior zone, two ELNs were found. For the middle and posterior zones, only one ELN per zone was found. The activity of ELNs correlated with the intensity of ciliary beating during the following central and reflex influences upon the locomotor mechanisms: (1) spontaneous fluctuations of the locomotor activity, (2) changes of temperature, (3) transections of central connections (interganglionic connectives), (4) defensive reactions evoked by tactile stimuli or switching off the light, and (5) activation of feeding behaviour by natural stimuli. The data strongly suggest that ELNs are responsible for the differential control of locomotor activity in various zones of the ciliated epithelium during different behavioural acts.