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These findings indicate that application of 4-16-fold diluted Omniscan could have depressant effects on the frog vestibular end organs. Based on cochlear studies on cytotoxicity using 8-fold diluted Omniscan, 16-fold diluted Omniscan is optimal for the inner ear and its application could be useful for visualization of endolymphatic hydrops as well as the control of vertiginous attacks in Meniere's disease.Endolymphatic hydrops could be visualized recently by intratympanic injection of Omniscan diluted 8- or 16-fold with saline using three-dimensional fluid attenuated inversion recovery (3-D FLAIR) MRI. However, the effects of the Omniscan on vestibular end organs are not clearly understood. The purpose of this study was to investigate the effects of Omniscan on vestibular end organs both morphologically and physiologically.Vestibular hair cells isolated from bullfrogs were loaded with 4-32-fold diluted Omniscan (gadolinium hydrate) and morphological changes were observed. Moreover, compound action potentials of posterior semicircular canals were also observed after application of Omniscan.Application of 4-16-fold diluted Omniscan caused morphological damage of isolated vestibular hair cells and decreased action potentials of the posterior semicircular canal. After application of 32-fold diluted Omniscan, no apparent changes were noted even after 20 min, both morphologically and physiologically.

Our findings indicate that oxidative stress induces morphological changes in vestibular hair cells and subsequently leads to cell death after 2.5 h.The aim of this study was to confirm the direct effects of oxidative stress on vestibular hair cells.Vestibular hair cells isolated from guinea pigs were loaded with 1 or 10 mM H2O2, and morphological changes were observed. In addition, in a viability/cytotoxicity assay system, the numbers of dead cells in isolated cristae ampullares were counted 1, 3, and 5 h after loading with H2O2 or artificial perilymph (control).Reactive oxygen, in the form of H2O2, directly affects the cell membrane of isolated vestibular hair cells and causes swelling of the cell body, bleb formation, and shortening of the neck region. Morphological changes occur within 30 min after loading with H2O2, but a significant increase in the number of dead cells is noted only after 3 h.