GABA-ERGIC MODULATION OF COMPLEX SPIKE ACTIVITY BY THE CEREBELLAR NUCLEO- OLIVARY PATHWAY IN RAT. Lang, E. J., I. Sugihara and R. Llin[cedilla]cs. Department of Physiology and Neuroscience, New York University Medical Center, 550 First Avenue, New York, N. Y. 10016.
APStracts 3:0019N, 1996.
1) The role of GABA on the pattern generation properties of neuronal ensembles in the olivocerebellar system was studied utilizing multiple electrode recordings of complex spikes (CS) from rat crus 2a Purkinje cells (PC). Initially multiple electrode experiments were combined with micro-injections of picrotoxin into the inferior olive (IO). In order to corroborate the picrotoxin findings, the cerebellar nuclei, a major source of the GABAergic terminals in the IO, were chemically lesioned using micro-injections of kainic acid and NMDA. Both procedures generated comparable results. 2) Following intra-olivary picrotoxin injection there was an increase in the average firing rate, synchrony, and rhythmicity of spontaneous CS activity. In addition, the neuronal oscillation frequency tended to shift to lower frequencies. 3) The spatial distribution of synchronous CS activity in control conditions displayed a predominantly rostro-caudal orientation. Injection of picrotoxin to the IO disrupted this rostro-caudal organization, and led to synchronous CS activity amongst PCs throughout crus 2a. Similar effects were observed relating to the distribution of CSs evoked via the "climbing fiber reflex", in which antidromic activation of the climbing fibers is followed by a return excitation that is mediated by the gap junctions between olivary neurons. 4) Chemical lesions of the cerebellar nuclei resulted in increased CS average firing rates. The effect of the lesions on CS synchronicity was similar to that following the picrotoxin injections, but greater in magnitude. In contrast to the olivary picrotoxin injections, the cerebellar nuclear lesions did not lead to an enhanced CS rhythmicity. 5) Bilateral recordings from left and right crus 2a demonstrated significant interhemispheric synchronization of CS activity, consistent with previous reports. Both unilateral olivary injections of picrotoxin and unilateral cerebellar nuclear lesions resulted in increased synchronization of CS activity between the left and right crus 2a. 6) We conclude that the cerebellar nucleo-olivary projection to the olivary glomeruli modulates the effective electrotonic coupling between olivary neurons, and thereby carves out ensembles of neurons whose activity is synchronized. Thus, these two nuclei may form the basis for a flexible and sophisticated motor coordination system able to help generate the many distinct movements that organisms are capable of.

Received 12 October 1995; accepted in final form 9 January 1995.
APS Manuscript Number J681-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 29 January 96