VESTIBULAR AND VISUAL CLIMBING FIBER SIGNALS EVOKED IN THE UVULA-NODULUS OF THE RABBIT CEREBELLUM BY NATURAL STIMULATION. Barmack, N.H. and H. Shojaku. R.S. Dow Neurological Sciences Institute, Legacy Good Samaritan Hospital & Medical Center, Portland, Oregon, USA and Department of Otolaryngology, Toyama Medical & Pharmaceutical University, Toyama, JAPAN.
APStracts 2:0202N, 1995.
SUMMARY AND CONCLUSIONS
1. The cerebellar uvula-nodulus receives vestibular projections from primary and secondary vestibular afferents, as well as vestibularly-related climbing fibers . It also receives visually-related information from climbing fiber pathways. In this experiment we investigated how this information is mapped onto the uvula-nodulus. We studied the specificity, dynamics and the topographic distribution of climbing fiber responses, simple spike responses and mossy fiber terminal responses evoked by vestibular and optokinetic stimulation in rabbits anesthetized with à-chloralose. 2. Vestibularly-evoked climbing fiber responses were found in the ventral uvula and nodulus. These responses were evoked during static roll tilt of the rabbit about a longitudinal axis and by sinusoidal oscillation about the longitudinal axis. Purely static responses were attributed to stimulation of the utricular otolith by the linear acceleration of gravity. Climbing fiber responses that lacked a static component were attributed to activation of the semicircular canals. 3. Using a null technique we showed that the canal-sensitive climbing fiber responses were caused by stimulation of the anterior or posterior semicircular canals. 96% of the climbing fiber responses classified as canal- related could be attributed to stimulation of the vertical semicircular canals. 4. Increases in climbing fiber responses were correlated with decreases in simple spike responses in half the Purkinje cells from which we recorded. These climbing fiber-induced pauses in simple spikes occurred during spontaneous climbing fiber discharge, as well as during climbing fiber discharge evoked by vestibular stimulation. The duration of this pause was inversely proportional to the spontaneous level of simple spikes before the occurrence of a climbing fiber response. In the other half of the recorded population of Purkinje cells, vestibularly-driven climbing fiber responses did not alter the simple spike responses. 5. Vestibularly- and visually-mediated climbing fiber responses (CFRs) were topographically represented on the surface of the uvula-nodulus. CFRs driven by ipsilateral otolithic inputs were distributed over the entire medio-lateral surface of the uvula-nodulus. CFRs driven by the ipsilateral posterior semicircular canal were distributed in a sagittal strip approximately 1.5 mm wide, extending laterally from the midline of the nodulus. CFRs driven exclusively by horizontal, posterior anterior, optokinetic stimulation of the ipsilateral eye were distributed in a sagittal strip approximately 0.5 mm's wide located 0.5 - 1.0 mm from the midline and restricted to the ventral nodulus. CFRs driven by the ipsilateral anterior semicircular canal were found in a sagittal strip approximately 1.0 mm wide extending 1.0 - 2.0 mm from the midline. 6. The sagittal, topographically arrayed, climbing fiber strips effectively map a medio-lateral gradient of possible postural responses based upon vestibular and optokinetic information. 

Received 31 March 1995; accepted in final form 12 July 1995.
APS Manuscript Number J215-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 July 1995.