The aging vestibular hair cell.

The ultrastructure of aging vestibular hair cells of the guinea pig can be abnormal even though they appear morphologically normal by light microscopy. In only a few of the hair cells studied did nonspecific changes occur. In general, the age-related changes involved specific structures in the hair cells: aggregations of lipofuscin pigments, multivesiculated bodies, disintegration of the cuticular plate, and rod-shaped inclusions from the cuticle area into the hair cell. Furthermore, sensory hairs are generally present when the cuticular plate shows an advanced disintegration. Nerve calyces can be ultrastructurally changed without morphologic changes in the adjacent hair cell. Type I hair cells show age-related morphologic changes more often than do type II hair cells.