Morphologic changes in contralateral superior vestibulo-ocular neurons following labyrinthectomy in the cat

Ultrastructural changes were measured in 22 contralateral superior vestibulo-ocular neurons (SVONs) from four cats painlessly sacrificed at 8 weeks and 25 contralateral SVONs from four cats sacrificed at 1 year following unilateral labyrinthectomy. The SVONs at 8 weeks showed a 43% decrease in somal size, a 34% loss in rough endoplasmic reticulum (RER), a 48% loss of ribosomes, and a 47% decrease in the number of synaptic profiles (SPs) contacting the soma. At 1 year the SVONs had a 31% decrease in size, a 43% decrease in RER, a 50% loss of ribosomes, and a 71% decrease in SPs. Synaptic vesicles (SVs) in both groups of SVONs showed no change in size or shape compared to control SVs. These findings resemble the contralateral SVON changes that occur following excision of the vestibular ganglion.