A role of climbing fibers in regulation of flocculonodular lobe protein kinase C expression during vestibular compensation

The behavioral recovery from unilateral labyrinthectomy (UL) in rats is accompanied by asymmetric expression of Protein kinase C (PKC) in parasagittal regions of the flocculonodular lobe within 6 h after UL, which resolves to the control, symmetric pattern within 24 h. These changes consist of a regionally selective increase in the number of PKC-immunopositive Purkinje cells contralateral to the lesion. This study tested the hypotheses (1) that climbing fiber innervation inhibits PKC expression and (2) that climbing fibers are essential for the observed changes in PKC expression within 6 h after UL. The patterns of flocculonodular lobe Purkinje cell PKC delta expression were analyzed 6 h post-operatively in both UL and sham-operated that had been treated previously with 3-acetylpyridine to destroy the inferior olive. These data were compared with previous results from rats with an intact olive. The results suggest that at least two signals regulate the zonal distribution of Purkinje cell PKC delta expression in the flocculonodular lobe during the early period of compensation from UL. Climbing fiber activation appears to reduce PKC expression, while extraolivary mechanisms appear to up-regulate PKC expression. It is suggested that the climbing fiber signals may act as a molecular 'filter' or 'automatic gain control' which adjusts the contributions of these kinases to synaptic plasticity within the context of the background activity of climbing fibers. (C) 1998 Elsevier Science B.V. All rights reserved.