Transneuronal down regulation of vestibulo-ocular neurons following vestibular ablation.

Unilateral ablation of vestibular input causes lasting morphological changes bilaterally in superior vestibulo-ocular neurons (SVON). The present study was performed to see if these changes in SVON are more pronounced after bilateral vestibular neurectomy. Twenty-three SVON from both vestibular nuclei of 2 cats sacrificed 8 weeks after bilateral ablation were examined utilizing morphometric ultrastructural techniques. There was a significantly greater somal atrophy, loss of synaptic profiles, rough endoplasmic reticulum and polyribosomes compared to unilateral neurectomy. These changes indicate a down regulation that is proportional to the level of deafferentation and may account for functional deficits seen in the vestibulo-ocular reflex after peripheral ablation.