Age-related hearing loss (ARHL) is one of the most prevalent disorders associated with aging. For over 30 years, the role of oxidative stress has been known in the aging literature. In the last 5 years, it has become apparent that oxidative stress is also a primary cause of acquired hearing loss from noise exposure and ototoxic drugs. This project is designed to evaluate the role of oxidative stress in ARHL and second, explore the possibility of preventing or reversing ARHL with antioxidant drugs that have been shown to prevent noise- or drug-induced hearing loss. The experiments will be conducted with Fischer 344 rats, ages 4, 12, 24 and 30 months. All animals will be evaluated for hearing function using evoked potentials and distortion product otoacoustic emission (DPOAE). The status of the endolymphatic potential and perilymph concentration of glutathione will be measured. The cochleas will then be harvested and morphological measures of sensory cell, VIII nerve cell bodies and stria vascularis will be done. In addition, some of the cochleas will be analyzed for oxidative stress using dichlorofluorescein (DCF) and succinic dehydrogenase (SDH). Finally, a third group of cochleas will be analyzed for the status of oxidative enzymes in strial, organ of Corti and spiral ganglion. The biochemical, morphological and histological measures will be correlated with hearing threshold.
