The mammalian inner ear contains two types of sensory cells, inner hair cells (IHCs) and outer hair cells (OHCs). A great deal is known about the deleterious effects that OHC damage has on auditory function; however, almost nothing is known about the functional deficits that are associated with IHC damage. We have developed a preparation in which it is possible to use carboplatin, an anti-neoplastic agent, to selectively destroy the IHCs in the chinchilla while retaining a functionally intact population of OHCs. We will use this preparation to determine how IHC damage affects the discharge patterns of single auditory nerve fibers and how the selective loss of IHCs and type I afferent neurons affects behavioral measures of hearing. The specific questions that will be addressed are: (1) Do the spontaneous discharge rates, driven discharge rates and the adaptation and recovery of discharge rate eventually recover to their normal levels following carboplatin treatment? (2) Is the elevation of threshold in auditory nerve fibers linked to stereocilia damage on IHCs? (3) Does partial IHC loss alter behavioral thresholds? (4) Does partial IHC loss lead to abnormal intensity discrimination? (5) Does partial IHC loss lead to abnormal frequency distribution? (6) Does partial IHC loss lead to abnormal temporal resolution? The proposed experiments have the potential to clarify the functional role of IHCs at the level of the cochlea and to increase our understanding of how IHC damage alters our ability to hear critical features of acoustic stimuli.
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