Age-related degeneration of the organ of Corti in two genotypes of mice.

Degenerative changes in the organ of Corti were investigated in two genotypes of mice, CBA/Ca (moderate age-related late-onset hearing loss) and C57BL/6J (spontaneous early-onset auditory deterioration), ranging in age from 1 to 21 months (C57BL) and from 1 to 33 months (CBA). Light, transmission and scanning electron microscopies were used for qualitative and quantitative analyses. Alterations of deterioration in the CBA-mouse cochlea showed a late-onset loss of hair cells, lipofuscin in the outer hair cells (OHCs), giant stereocilia on the inner hair cells and elevated pillar heads. In C57BL mice, the primary lesions of the organ of Corti include early damage of stereocilia on OHCs, missing OHCs, and a ruptured reticular lamina. Giant cilia and elevated pillar heads were not evident in C57BL mice. In the aged C57BL mouse cochlea, the whole organ of Corti was collapsed and replaced by the supporting cells, whilst in the oldest CBA mice, completely normal-looking OHCs still remained even in severely deteriorated areas of the organ of Corti. The results indicate that the patterns of degeneration of the organ of Corti are different between CBA/Ca and C57BL/6J mice, probably under the control of different genes.