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Elevation of Reactive Oxygen Species following Ischemia-Reperfusion in Mouse Cochlea Observed in vivo

An in vivo method for assessment of changes in hydroxyl radical levels in cochlear perilymphatic spaces is described and applied to cochlear ischemia-reperfusion in the mouse. Cochlear blood flow was reversibly reduced by compression of the anterior inferior cerebellar arterial network. Changes in the production of hydroxyl radicals, used as an index of tissue production of reactive oxygen species (ROS), were determined by measuring the conversion of salicylate to 2,3-dihydroxybenzoic acid. Low levels of salicylate (0.1 mM) in artificial perilymph were applied by perfusion of the cochlea using a round window entry and apical exit. Perfusate was collected and analyzed by high-performance liquid chromatography. Forty minutes of partial ischemia led to a > 10-fold average increase over baseline in the concentration of hydroxyl radical, which increase persisted for at least 40–80 min following reperfusion. Our observations support previous results obtained using less direct methods, indicating that cochear ischemia-reperfusion and related damage is associated with elevated ROS levels. Development of an in vivo method for assessing changes in cochlear ROS in mice will facilitate the study of the relation between deafness genes, vulnerability to insults and dynamics of cellular processes that produce and regulate ROS.