Endocochlear potential in focal lesions of the guinea pig cochlea

To estimate the correlation between the cochlear lateral wall and endocochl ear potential (EP), the EP was measured at different time intervals up to 3 weeks at cochlear focal lesions made in the guinea pig. Lesions were produ ced by a photochemical reaction between systemically administered Rose Beng al and green light illumination in the second cochlear turn. Focal strial l esions (mean diameter 975 mu m) became apparent under a scanning electron m icroscope 60 min after illumination, and degeneration of the organ of Corti was recognized at 3 days. The EP was measured continuously for 1 h followi ng onset of the reaction in eight ears. In the other ears, EP measurements were done after various intervals of time up to 3 weeks. The EP showed two declines from pre-illumination level. The first started soon after illumina tion, reached a minimum value at 25 min, and then slightly recovered by 1 h . The second decline appeared at 3 days after illumination. In contrast to evident focal morphological degeneration 2 weeks post illumination, the EP values had recovered to almost normal. We suggest that the sequential chang es in the EP were produced depending on the degeneration and then repairing processes of the endolymphatic boundary tissues. (C) 1999 Elsevier Science B.V. All rights reserved.