Electron Microscopic Studies on the Changes of Cochlear Hair Cells by Acoustic Stimulation

Especially Referred to the Effects of Vitamin B₁ Administration

Abstract

The fine structural changes in the cochleas of guinea pigs, acoustically stimulated with or without vitamin B₁ administration, were observed under an electron microscope.
The observations were performed on the intermediate zone of the outer and inner hair cells, the nerve endings at the base of the outer hair cells and the myelinated nerve fibers in the osseous spiral lamina. The correlation between the structural changes by acoustic stimulation and the effects of vitamin Bi administration in relation with these changes were examined.
All the experimental animals of the first group were exposed to white noise at 110 phon without vitamin B₁ administration. The exposure time ranged from 15 min. to 24 hrs. In the second group the animals were given vitamin B₁ (10mg/day, for 7 days, intraperitoneally) and then were exposed to white noise as well as in the first group.
Immediately after the noise exposure, the cochleas were removed and fixed in glutaraldehyde and osmium tetroxide, dehydrated with aceton and then embedded in Epon 812. Ultrathin sections which were cut out of the blocks and stained with uranylacetate and then with lead hydroxide were examined under a HU-10A electron microscope.
The structural changes observed were as follows:
1. In the intermediate zone of the outer hair cells, some of the smoothsurfaced endoplasmic reticulums along the cell membrane showed swelling, their lamellae increasing in number and their lamellar arrangement coming out of order. Mitochondria in this zone began to swell and degenerate in the long exposed animals (over 6 hrs.). These changes were found to be more dominant in the group without vitamin Bi administration.
2. In the intermediate zone of the outer hair cells, some kinds of cell particles, all regarded as lysosomes, were found. With the shortly exposed animals (within 60 min.), electron dense inclusions in the cell particles appeared thicker in proportion to the exposure time. On the other hand, with long exposed animals (over 6 hrs.), these electron dense inclusions were found thick if vitamin B₁ was administered, while with the animals without vitamin B₁ administration, they were found remarkably thin.
3. In the intermediate zone of inner hair cells, structural changes were less noticeable than in that of the outer hair cells.
4. In the non-vesiculated (afferent) nerve endings at the base of the outer hair cells, the mitochondria showed swelling and degeneration in the long stimulated animals (over 6 hrs.), without vitamin Bi administration.
5. In the axon of myelinated nerve fibers in the osseous spiral lamina of some long exposed animals (over 6 hrs.), extraordinary membranous structures were found.
6. As finding of great interest, in the intermediate zone of outer hair cells of the two of all the experimental animals, a group of virus-like particles was discovered.