The role of inner hair cells in hearing

Abstract

DISCUSSION about functional differences between the inner and outer hair cells (IHCs and OHCs) in the mammalian organ of Corti^1–5, has arisen as a result of several anatomical and electrophysiological observations. The proportions of afferent and efferent fibres supplying the two types of cells are quite different^6–8; the afferent neurones associated with them are distinct cytologically as well as in their susceptibility to retrograde degeneration^6–8; the electrophysiological responses following preferential loss of OHCs are not what would be expected on the basis of a similarity of function^2,5,9–11. Attempts at the elucidation of these differences^2,9 have made use of the ototoxic antibiotic kanamycin, which causes preferential damage to OHCs. This technique is far from ideal: the damage may be patchy and IHCs may also be affected. As to the selective elimination of IHCs, no procedure has been available. Mutant genes frequently provide material that cannot be produced experimentally, but although a large number of genes affecting the inner ear in various ways are known in the mouse^12–14, there has been none so far that clearly discriminated between IHCs and OHCs. We now report a new mutation in the mouse which selectively eliminates IHCs. As the mutant animals are almost totally deaf, it would seem that hearing is predominantly dependent on IHCs.