Survival of the vestibular nerve after labyrinthectomy in the cat.

Temporal bone studies in cat, monkey, and man demonstrate that the cell bodies of the primary vestibular neurons located in Scarpa's ganglion persist after labyrinthectomy. However, it is not known whether the centrally directed axon process of deafferented vestibular neurons survive or degenerate after labyrinthectomy. If the central axon were to persist, then the primary vestibular neuron could influence vestibular compensation or produce symptoms of vestibular dysfunction. In the present study the temporal bones and brain stem of four cats were prepared for light microscopic examination with hematoxylin-eosin, silver, and trichrome connective tissue stains. Cell counts within Scarpa's ganglion were performed. After labyrinthectomy, many intact axons were demonstrated in the brain stem, a finding that correlated with survival of neurons in Scarpa's ganglion. This study provides anatomic evidence that primary vestibular neurons that survive labyrinthectomy may retain their central axon processes. The persistence of this neural pathway and data from behavioral studies in the cat suggest that vestibular neurons may affect vestibular compensation after labyrinthectomy. Deafferented vestibular neurons may play a role in human vestibular compensation and dysfunction.