Summary

Abstract

AChE activity was localized in the inner ear of guinea pig and chinchilla with the electron microscope using Karnovsky's method. The material was fixed by perilymphatic per-fusion with glutaraldehyde or formaldehyde, followed by postfixation with an OsO₄ solution. The following controls were performed: (a) incubation without substrate; (b) pre-incu-bation and incubation in the presence of inhibitors (eserine, DFP, iso-OMPA, BW 284 C 51); (c) incubation of frozen and thawed material.

In the organ of Corti the reaction was positive in the following sites: small efferent fibers and presynaptic enlargements in the inner spiral bundle; upper tunnel radial fibers; large efferent nerve endings in contact with the base of the outer hair cells and with afferent dendrites. The reaction product appeared deposited on the plasma membrane of these structures and filled the synaptic gap of the axosomatic and axodendritic synapses. The controls indicated that in these sites the reaction was due to AChE activity.

The reaction product was absent at the large afferent radial fibers innervating the inner hair cells; at the lower tunnel radial fibers, at most of the outer spiral fibers and at the afferent nerve endings in contact with the outer hair cells. A small quantity of amorphous precipitate was found on the hairs and cuticle of inner and outer hair cells and on the free surface of the body of the outer hair cells and pillars. The controls indicated that in these zones the precipitate was due to an artefact.

In the vestibular sensory areas the reaction was positive on the plasma membrane of the efferent nerve fibers and endings. The reaction product filled the synaptic gap between these endings and the afferent dendrites and nerve chalices. The controls indicated that the reaction was due to AChE activity.

The possible artefacts in the localization of AChE activity and the significance of AChE in the organ of Corti and vestibular sensory areas were discussed.