Changes in off-lesion endocochlear potential following localized lesion in the lateral wall

Endocochlear potential (EP) was measured at various off-lesion sites after a small focal lesion was made in the lateral wall of the guinea pig cochlea. Lesions were produced by a photochemical reaction between systemically administered rose bengal and focused green light illumination. In 21 ears, continuous measurement for 30 min after onset of the reaction at turns apical or basal to the site of illumination revealed no significant changes in EP compared with the control value (p < 0.01). In another group of 43 ears, EP was measured at 3 days post-illumination. A significant decline was seen at every site located apical to the lesion (p < 0.001). Conversely, no significant change was measured at any site located basal to the lesion. These findings suggest that the decrease in EP assumes the form of a gradient from the lower to upper turns in the guinea pig cochlea.