Effect of Cerebellar Inactivation by Lidocaine Microdialysis on the
Vestibulo-ocular Reflex in Goldfish.
James G. McElligott, Phyllis Beeton, and Jeffrey Polk.
Dept. of Pharmacology, Temple University School of Medicine, Philadelphia,
PA 19140.
APStracts 4:347N, 1997.
ABSTRACT
Vestibulo-ocular performance and adaptation were examined during vestibulo-
cerebellar inactivation by localized lidocaine microdialysis or injection in
goldfish. In the light, eye velocity perfectly compensated for head velocity
(Vis-VOR) during sinusoidal yaw rotation (1/8 Hz 20). In the dark, the
reflex (VOR) gain was slightly reduced (gain 0.8 - 0.9). In neither case,
Vis-VOR and VOR, was gain altered following 1 hour of lidocaine microdialysis
in the vestibulo-cerebellum. Prior to adaptation of reflex gain, the initial
suppression or augmentation of Vis-VOR reflex gain produced by in-phase or
out-of -phase visual-vestibular stimulation was also unaffected by cerebellar
inactivation. Subsequently, three hours of adaptive reflex training in either
the in-phase or out-of-phase paradigm (acquisition phase) respectively
decreased (0.30 0.09) or increased (1.60 0.08) VOR gain during artificial
cerebral spinal fluid (CSF) microdialysis. However, microdialysis of lidocaine
completely blocked adaptive gain changes during a 3-4 hour period of
continuous application. This effect was reversible since VOR gain changes were
produced 1 hour after lidocaine was replaced with CSF as the dialysate. After
adaptive training, bilateral CSF injections (0.25 l/side) into the vestibulo-
cerebellum did not alter the normal retention or decay of adapted gain changes
during a 3 hour period in the dark (retention phase). However, injection of
lidocaine into the vestibulo-cerebellum completely blocked retention of the
adapted VOR gain returning the gain to values recorded prior to adaptation. In
contrast to either acute or chronic surgical removal, lidocaine inactivation
of the cerebellum by microdialysis did not alter either Vis-VOR and VOR
behavior or interactive Vis-VOR performance over a wide range of gain
extending from 0.3 to 1.4. Thus, short term VOR motor learning is a dynamic
process requiring either continuous operation of brainstem cerebellar loops
or, alternatively, modifiable sites within or directly influenced by the
cerebellum. Our data supports the latter hypothesis, because the direct
brainstem VOR pathways appear to be unaltered after cerebellar inactivation,
and, hence, independent of the VOR adapted state.
Received 11 January 1997; accepted in final form 28 November 1997.
APS Manuscript Number J25-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 12 December 1997