The activity of cerebellar neurones of an elasmobranch fish (Scyliorhinus canicula) during a reflex movement of a fin

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Abstract
Response of neurons in the corpus cerebelli of S. canicula (Elasmobranchii) were recorded in decerebrate unanesthetized fish during the performance of pectoral fin reflexes (p.f.r.) evoked by electrical stimulation of the fins. Of 421 single units recorded in the posterior dorsal quadrant of the corpus, 111 (26%) had their discharges modulated when the reflex was evoked; 59 were Purkinje (P) cells discharging single spikes, 13 were P cells discharging complex responses, 36 were stellate (S) cells and 3 were not positively identified. The responses of 51 units (37 P cells and 14 S cells) were analyzed in detail. In 31 of the P cells and all the S cells the initial response was excitatory, 6 P cells gave an inhibitory response only and a further 3 were inhibited after the initial excitation. Only 1 S cell had an inhibitory component in its response. The discharges of the S cells completely overlapped the inhibitory responses of the P cells. Only 1 cell (a P cell) was evoked at a latency shorter than that of the p.f.r. In 1 other P cell discharging single spikes spontaneously, the evoked response was a long latency (146 ms) complex response. Four other P cells discharged only complex responses but the pattern of their response to the p.f.r. was similar to that of P cells discharging single spikes only. No cerebellar responses were evoked if the fin stimulus was below the threshold necessary to evoke a p.f.r. In curarized fish, unit responses were recorded that were qualitatively similar to those recorded in unparalyzed fish. Because of the long latency of the responses, the cerebellum is unlikely to have a role in the initiation of the p.f.r. The responses during the p.f.r. were evoked via a mossy fiber-parallel fiber pathway. The responses were correlated with motor activity rather than sensory input.