Ultrastructural changes in contralateral superior vestibulo-ocular neurons one year after vestibular neurectomy in the cat.

Twenty contralateral superior vestibulo-ocular neurons (SVON) from 3 cats were studied morphologically one year after a right vestibular neurectomy. Eighteen SVON contained a smooth or slightly crenated nuclear membrane, a 63% loss of synaptic profiles (SP) and a 22% decrease in size compared to control SVON. Two cells contained nuclear membrane invaginations, a 40% loss of SP and a 31% size decrease compared to control SVON. The volume fractions of rough endoplasmic reticulum and ribosomes were decreased in these two cell groups but no change was noted in Golgi apparatus and mitochondria. These contralateral SVON reached a size, innervation density and content of organelles similar to ipsilateral SVON at one year following vestibular neurectomy.