Early hair-cell degeneration in the extreme apex of the guinea pig cochlea.

Guinea pigs, aged from 3 weeks before term to 31 weeks after birth, were prepared for scanning electron microscopy. Examination of the extreme apex of the cochlea showed apparently pathological hair cells, even 3 weeks before term. The pathologies included loss and fusion of stereocilia, and the formation of giant stereocilia. The pathologies were most prevalent on row 3 of outer hair cells, declining to outer hair cell rows 2 and 1, with the inner hair cells being least affected. The abnormalities increased with time, increasing rapidly over the first few weeks of life, and more slowly thereafter. It is suggested that early degeneration in the extreme cochlear apex forms a novel model for spontaneous hair cell degeneration, with applicability to other types of spontaneous hair cell degeneration.