NEURONAL CONTROL OF CILIARY LOCOMOTION IN A GASTROPOD VELIGER (CALLIOSTOMA)

Intracellular recordings from pre-oral ciliated cells of competent Calliostoma ligatum veligers were used to demonstrate the mechanisms of neuronal control of ciliary locomotion. During normal ciliary beating at 5-7 Hz, the membrane potential shows no oscillations or spiking activity. It remains at a resting potential of about -60 mV. Depolarization from resting potential is due to excitatory input from the CNS and, depending upon the kind of input, veligers appear to show two types of locomotory behavior. In one type, normal ciliary beating is periodically interrupted by rapid, velum-wide ciliary arrests. These arrests are caused by a propagated, Ca⁺⁺-dependent action potential in the pre-oral ciliated cells. The second type is characterized by either a velum-wide or local slowing of normal ciliary beating, and appears to result from a slow depolarization of the ciliated cell membrane. Pre-oral ciliated cells are electrically coupled to each other. This property may ensure the synchrony of velum-wide ciliary arrests or differential velar slowing of ciliary beating. These findings demonstrate some of the mechanisms ofthe fine control veligers possess over their locomotory and feeding behavior.