Genetic Progressive Hearing Loss in the C57/M6 Mouse: Relation of Behaviorial Responses to Cochlear Anatomy

Abstract

Mice (strain C57/bl6) were studied using light microscopy. The inner ear developed normally. However, at the age of 3 months, degeneration began in the organ of Corti, beginning in the basal portion and progressing gradually to involve all of the cochlea. By the end of one year, the organ of Corti had disappeared from the basal turn and persisted only in a degenerative form in the apical portion.

Behaviorally, the hearing of this animal was near normal at the age of 2-3 months, except for the frequencies 30 Kc and above. As the animal grew older, hearing gradually deteriorated and the high frequencies were totally lost; the low frequencies were preseived, but at an elevated threshold.

Interestingly enough, at the time when this animaľs threshold of hearing above 30 Kc was higher than normal, the organ of Corti appeared normal. Similarly, at the end of one year, light microscopy revealed an atrophic and disorganized organ of Corti, present only in the apical turn of the cochlea (the rest of the cochlea having degenerated totally) and yet this animal maintained hearing for the low frequencies although at an elevated threshold. It appears that light microscopy alone cannot discriminate between the functional and non-functional state of the cochlea.