The aging cochlear hair cell.

Specimens from the organ of Corti were taken from regions which appeared normal in the cytocochleogram as evaluated with the Nomarski optics. Ultrastructural, qualitative analyses of aging cochlear hair cells in the guinea pig showed, however, principally five distinct types of pathological changes: (1) disintegration of the cuticle; (2) increased amounts of intracellular lamellar structures and submembrane cisternae; (3) aggregations of electron optically dense particles; (4) lysosome-like structures; and (5) vesiculation of cytoplasm. Stereocilia remained intact also in cells where the cuticular plate showed severe degeneration. Outer hair cells showed more extensive cytological changes than inner hair cells. The ultrastructural pathology in aging cochlear hair cells is specific and is a sign of dysdifferentiation of their specific morphology although the hair cells survive for a long time in a more or less dysdifferentiated state. Hair cell changes were primary, leaving afferent and efferent nerve terminals initially morphologically intact.