Cochlear structure and function after round window application of ototoxins

Topical round window application of ototoxic agents has been a useful method for studying ototoxicity and hearing loss in the mammalian cochlea. For example, species-specific differences in cochlear susceptibility to damage have been documented using this technique. Carboplatin has been characterized in the literature as a selective inner hair cell (IHC) toxin in chinchillas, while cisplatin has been characterized as a selective outer hair cell (OHC) toxin. The present experiment quantified dose-dependent damage to cochlear hair cells in the chinchilla after a single direct round window application of either cisplatin or carboplatin. Detailed cytocochleograms were obtained for the entire cochlear duct, for a range of doses, along with auditory brainstem response thresholds. In agreement with the literature, although there was variability, at the lowest concentrations tested (2 and 3 mg/ml), carboplatin produced substantial IHC damage with no OHC damage. In contrast, the effects of cisplatin were more variable, and contrary to published reports, across the range of doses producing OHC damage, IHC damage was always observed. Limitations of direct round window ototoxin treatments are discussed, in addition to their potential application in the study of tinnitus.