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Ethanol effects on the olivocerebellar system Harris, David Platt


The detrimental effect of ethanol on coordinated movement and the similarity of this effect to that of pathological damage to the cerebellum or the inferior olive (10) suggests that ethanol profoundly effects the olivocerebellar system. Each cerebellar Purkinje cell (PC) displays two distinct action potential responses: the simple spike (SS), evoked intrinsicly and via the parallel fibres, and the complex spike (CS), evoked via a solitary climbing fibre (CF) which originates from the 10. Ethanol (1.5 g/kg, i.v.) was found to have no significant effect on the CS activity evoked by direct electrical activation of CFs, while it significantly reduced, in parallel, that evoked by cerebral cortex stimulation and that occurring spontaneously. In addition, ethanol, applied both systemically and locally by micropressure, reduced the spontaneous activity of inferior olive (10) neurones. These results strongly suggest an action of ethanol local to the 10 nucleus, perhaps by a direct action on the 10 neurones themselves. Elimination of spontaneous CS activity by the electrolytic lesioning of the contralateral 10 did not significantly alter spontaneous SS firing rate. However, subsequent administration of ethanol i.v. did produce a significant increase of SS rate, indicating that only part of ethanol-evoked SS rate increase is dependant upon the reduction of CS activity. Simple spike regularity was not significantly altered by either 10 lesioning or i.v. ethanol. Ethanol applied locally to PC's by micropressure was found to reduce the period of inhibition evoked by local stimulation of the cerebellar cortex in the majority of the cells tested. This result is in agreement with the previously reported effects of intravenous ethanol on this inhibition, thought to be mediated by gamma-aminobutyric acid (GABA). Both intravenously and locally applied ethanol antagonized the inhibition of PC's evoked by locally applied GABA. These results, while in agreement, are contrary to the reported effects of ethanol in other systems. Intravenously administered ethanol did not significantly alter Golgi cell spontaneous firing, while it did significantly reduce the period of inhibition of Golgi cell firing evoked by 10 stimulation.

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