AGE-RELATED DEGENERATION OF THE ORGAN OF CORTI IN 2 GENOTYPES OF MICE

Degenerative changes in the organ of Corti were investigated in two ge notypes of mice, CBA/Ca (moderate age-related late-onset hearing loss) and 7BL/6J (spontaneous early-onset auditory deterioration), ranging in age from 1 to 21 months (C57BL) and from 1 to 33 months (CBA). Ligh t, transmission and scanning electron microscopes were used for qualit ative and quantitative analyses. Alterations of deterioration in the C BA-mouse cochlea showed a late-onset loss of hair cells, lipofuscin in the outer hair cells (OHCs), giant stereocilia on the inner hair cell s and elevated pillar heads. In C57BL mice, the primary lesions of the organ of Corti include early damage of stereocilia on OHCs, missing O HCs, 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 Cor ti. The results indicate that the patterns of degeneration of the orga n of Corti are different between CBA/Ca and C57BL/6J mice, probably un der the control of different genes.