ULTRASTRUCTURAL-CHANGES IN CONTRALATERAL VESTIBULOOCULAR NEURONS FOLLOWING VESTIBULAR NEURECTOMY IN THE CAT

Twenty contralateral superior vestibular vestibulo-ocular neurons (SVON) from 4 cats were studied morphologically 8 weeks after a right vestibular neurectomy. Nine SVON demonstrated a 35% loss of somal synaptic profiles (SP), normal nuclear and cytoplasmic size, but a slight decrease in organelles responsible for protein synthesis (rough endoplasmic reticulum and polyribosomes). Eleven SVON showed an 82% loss of SP, decrease in cell and nuclear size, and significant reduction in rough endoplasmic reticulum (RER) and polyribosomes. These transneuronal SVON changes are presumed to be the result of commissural pathway degeneration caused by the vestibular neurectomy.