Alterations of auditory nerve responses by hypoxia in normal and hydropic ears of awake guinea pigs

Allopurinol attenuates endolymphatic hydrops in the guinea pig cochlea

Based on the hypothesis that Ca(2+) overload in the scala media may produce endolymphatic hydrops and generate free oxygen radicals (FOR), allopurinol, a xanthine oxidase inhibitor and free radical scavenger, was administered to guinea pigs after the surgical obliteration of the endolymphatic duct. Allopurinol was given intraperitoneally (50 mg/kg/day) for 15 days starting 1 day prior to the surgical blockage procedure. Measurements from histological serial sections of these temporal bones showed that the total volume of the scala media was significantly reduced (p = 0.007) compared with control hydropic ears. There was an indication of reduced incidence of atrophy in sensorineural structures and stria vascularis. These findings suggest that allopurinol may attenuate the development of endolymphatic hydrops and cell damage by preventing the formation of FOR or scavenging FOR. This study may lead to a new aspect of treatment for Menière's disease.

Ultrastructural changes in the hydropic cochlea of the guinea-pig

Transmission electron microscopy of the cochlear organ of Corti in experimental endolymphatic hydrops revealed two principal features. Starting 1 month after induction of hydrops, osmiophilic inclusions thought to represent lipofuscin accumulation were frequently observed in the subcuticular cytoplasm of the outer hair cells along the length of the cochlea. Starting 3 months after induction of hydrops the efferent terminals on the outer hair cells appeared to be vacuolated. These data suggest that oxidative insult is likely to contribute to the pathology associated with endolymphatic hydrops and thus that free radical scavengers might be useful in the treatment of Menière's disease patients. In addition the early modification of the efferent innervation of the hydropic cochlea might underlie the known hypersensitivity to various insults, including noise stimulation, glycerol administration and hypoxia.