Olivo-Cochlear Bundle in the Guinea Pig Cochlea After Central Transsection of the Crossed Bundle: Electron Microscopic Study on Origin and Distribution of Unmyelinated Efferent Fibers by Axonal Degeneration

Abstract

In order to clarify origin and distribution of unmyelinated efferent fibers in the guinea pig cochlea, the olivo-cochlear bundle (OCB) was electron microscopically traced from the internal auditory meatus to the organ of Corti at various intervals after central transsection of the crossed bundle. In othx animals the organ of Corti was destroyed in order to induce retrograde degeneration of the co-chlear nerve fibers. The resultant Wallerian degeneration occurred in a majority of myelinated and unmyelinated fibers in the fascicles of OCB after nerve section, whereas the fascicles survived after destruction of the organ of Corti. These findings indicate that both the crossed and uncrossed OCBs consist of myelinated and unmyelinated fibers. Both the myelinated and unmyelinated fibers of the crossed OCB originate in the brain stem. Both the crossed and uncrossed fibers are intermingled in the fascicles distal to the internal auditory meatus. It is probable that the unmyelinated efferents would be different from the myelinated efferents in the functional role in hearing.