Noise-induced hearing loss (NIHL) as a target of oxidative stress-mediated damage: Cochlear and cortical responses after an increase in antioxidant defense

This study addresses the relationship between cochlear oxidative damage and auditory cortical injury in a rat model of repeated noise exposure. To test the effect of increased antioxidant defenses, a water-soluble coenzymeQ₁₀ analog (Q_ter) was used.Weanalyzed auditory function, cochlear oxidative stress, morphological alterations in auditory cortices and cochlear structures, and levels of coenzymes Q₉ and Q₁₀ (CoQ₉ and CoQ₁₀, respectively) as indicators of endogenous antioxidant capability. We report three main results. First, hearing loss and damage in hair cells and spiral ganglion was determined by noise-induced oxidative stress. Second, the acoustic trauma altered dendritic morphology and decreased spine number of II-III and V-VI layer pyramidal neurons of auditory cortices. Third, the systemic administration of the water-soluble CoQ₁₀ analog reduced oxidative-induced cochlear damage, hearing loss, and cortical dendritic injury. Furthermore, cochlear levels of CoQ₉ and CoQ₁₀ content increased. These findings indicate that antioxidant treatment restores auditory cortical neuronal morphology and hearing function by reducing the noise-induced redox imbalance in the cochlea and the deafferentation effects upstream the acoustic pathway.