The author described the electron-microscopic changes observed in the hair cells and nerve endings of the organ of Corti in the guinea pig after exposure to white noise at 120db.
The significant changes were found in the outer hair cells.
The mitochondria normally located inside the plasma membrane were displaced to the axial part by the sound stimulation. Numerous small granules (50-100Å) were found in the mitochondria in the infracuticular region after short exposure. After long exposure the mitochondria in this region lost their double cristal membrane, inclosed the agglomeration of osmiophilic granules and began to swell and degenerate. Sometimes degenerate mitochondria were seen to supranuclear region.
Next pronounced change seen was in the membranous layer, consisting of smooth surfaced Endoplasmic Reticulum (ER) arranged in lamellae. After exposure the axial ER system (Hensen body) increased in number and varied in form. Chains of spherical and irregular forms in upper half of hair cells were often found. On the other hand, the peripheral ER system beneath the plasma membrane often became anomalously thickened, consisting of the series of membranous layer.
The golgi-complex increased in supra nuclear zone after exposure.
A number of electron dense granules (200Å) were seen inside the plasma membrane and the outer membrane of the hairs after exposure.
The structural changes of cytoplasmic organella in the outer hair cells described above were more pronounced in the upper part of the cells, but in the infranuclear part no change were found even after long noise exposure.
In the inner hair cells, structual changes were less noticeable than in the outer hair cells.
The nerve endings under the outer hair cell showed two different kinds of nerve terminations, a small and a large one. The small nerve endings were found swollen with indistinct mitochondrial cristae after exposure, but the mitochondria in the large nerve ending less affected. No certain signs of reduction in number of synaptic vesicle in nerve endinge were seen.
The morphological changes in the hair cells and nerve endings became more marked with increase in duration of noise exposure.