gms | German Medical Science

Objective: The intratympanical application of gentamicin is widely used in the therapy of Ménière’s disease. Beside a wanted elimination of vestibular function, unwanted pathological processes are induced in the cochlea such as an increase in nitric oxide (NO). The aims of the present study were to clarify: 1.) if both the endothelial and inducible nitric oxide synthase (eNOS and iNOS) are involved in an increase in NO production and 2.) in which regions of the cochlea alterations in the specific expression patterns occur.

Material and methods: A single dose of gentamicin (10mg/kg body weight) was applied intratympanically into male guinea pigs (n=42). Hearing threshold was determined by recording auditory brainstem responses prior to and 1, 2 and 7 days after application of gentamicin. At these three different time points, the cochlea of the various experimental groups was prepared, fixed and embedded in paraffin. The expression patterns of eNOS and iNOS were localized by specific antibodies and the immuno staining intensities quantified by a computer program.

Results: After application of gentamicin, the immuno staining intensity of iNOS was increased in all regions of the cochlea whereas eNOS expression was altered differently with regional specificity. In the organ of Corti and in the spiral ganglion cells, eNOS expression was reduced, whereas there was an increase in the spiral ligament, the stria vascularis, and the interdental cells of the Limbus. In the nerve fibers of the osseous spiral ligament eNOS expression was unaltered.

Conclusion: The findings confirm the hypothesis, that gentamicin-induced NO production is not only influenced by iNOS induction but also by increased eNOS expression.