Selective inner hair cell loss does not alter distortion product otoacoustic emissions

Outer hair cells (OHC) are believed to be the dominant source of distortion product otoacoustic emissions (DPOAE) in mammals; however, some studies in genetic mutants suggest that inner hair cell (IHC) loss may lead to a significant reduction of DPOAE amplitude. In the present study, we determined the extent to which IHC loss altered DPOAE amplitude by using carboplatin to destroy selectively the IHCs in the chinchilla while sparing virtually all of the OHCs. IHC losses of 80-100% with normal retention of OHCs did not reduce the amplitude of the DPOAEs or the cochlear microphonic potential (CM); however, it completely abolished the compound action potential (CAP). The only time that the amplitude of the DPOAEs and CM were reduced was in cases where both the IHCs and OHCs were destroyed in the base of the cochlea. We conclude that the total loss of IHCs does not lead to a significant change in DPOAE amplitude. DPOAE amplitude was only reduced when there was a significant loss of OHCs.