Cochlear origin of 2f1-f2 distortion products assessed by using 2 types of mutant mice.

Mutant mice with a particular type of cochlear pathology are excellent models to study the functional role of various structures in the cochlea. In order to assess the contribution of inner and outer hair cells to the generation of distortion product emissions (DPEs) we have recorded the 2f1-f2 DPE in a control group of CBA mice, which have normal numbers of inner and outer hair cells and two different types of mutant mice: the Bronx-waltzer mice and the Wv/Wv mice. In the Bronx waltzer mutant mice, 70% of inner hair cells are missing whereas the outer hair cells are present in normal number. The distortion product emissions 2f1-f2 is clearly recordable with a 10-20 dB lower magnitude as compared to normal CBA control mice. The homozygous Wv/Wv mutant mice on the other hand present a selective outer hair cell loss as a constant defect with no progressive degeneration of the organ of Corti and an essentially normal inner hair cell population. The cubic distortion products 2f1-f2 could not be detected in all but one animal. Therefore, the present study strongly suggests, that the outer hair cells are critically involved in the production of DPEs.