Ultrastructural changes of the nerve elements following disruption of the organ of Corti. I. Nerve elements in the organ of Corti.

3-137 days after disruption of the guinea pig organ of Corti by perilymphatic perfusion with 20% streptomycin (SM), ultrastructural changes of the nerve fibers in the organ were observed. Most of nerve fibers began to degenerate after a latent period of 4 days. On the other hand, a number of fibers survived reactively enlarged and later developed into myelinated and unmyelinated fibers by becoming enclosed in Schwann cells which entered the organ of Corti through the habenula perforata. Regeneration and sprouting of the surviving nerve fibers also occurred. The fibers became mature, but atrophied after 60 days and then gradually disappeared. The regenerating fibers were mainly of the myelinated and unmyelinated efferent type. Retrograde degeneration occurred in both afferent and efferent fibers. In the less damaged organ of Corti perfused with 2% SM or Ringer's solution, Schwann cell invasion was not found.