Susceptibility of the hair cells of the newborn rat cochlea to hypoxia and ischemia.

Hypoxia and ischemia are thought to be important pathogenetic factors in bringing about hearing loss. In order to study the effect of these determinants on the loss of inner and outer hair cells (IHCs/OHCs), we used an in vitro hypoxia and ischemia model of the newborn rat cochlea. The specimens of the organ of Corti were exposed either to hypoxia (10-20 mm Hg) or to normoxic glucose deprivation or to both (ischemia) in artificial perilymph for different exposure periods. The number of IHCs and OHCs was counted and the hair cell loss was compared to controls. Normoxic aglycemia did not cause significant hair cell loss as compared to controls. Hypoxia and ischemia led to hair cell loss in a dose-dependent manner, with the loss in the ischemia groups found to be markedly higher than that in the hypoxia groups. Hypoxia resulted in a mean loss of 8% OHC and of 14% IHC after an 8-h exposure. Ischemia increased the loss to 19% OHC and 39% IHC after the same exposure period of 8 h. Our findings suggest that IHCs are more susceptible to hypoxia/ischemia than OHCs.