Ouabain-Induced Cochlear Degeneration in Rat

Abstract

Objective: To elucidate the neurodegenerative effects of ouabain in vitro and in vivo in rat.

Method: Ouabain applied in organotypic cultures. Phalloidin and neurofilament antibody used to label hair cells and nerve tissue. In vivo, 1 mM or 10 mM ouabain applied to round window. ABR and DPOAE were recorded 7 days posttreatment. Cochlea sections were used to count SGN and nerve fibers. TUNEL staining were used to assess apoptosis.

Results: In vitro, low concentrations of ouabain only damaged spiral ganglion neurons; however, high doses destroyed both spiral ganglion neurons and cochlear hair cells. Application of 1 mM ouabain to the rat round window membrane only altered ABR thresholds and DPOAE amplitudes at higher frequencies. In contrast, 10 mM ouabain significantly increased ABR thresholds and decreased DPOAE amplitudes at almost all frequencies. Consistent with physiological results, both spiral ganglion neurons and hair cells were missing or damaged in the basal turn of the cochlea and both hair cells and neurons showed signs of apoptotic cell death.

Conclusion: In vitro and vivo, ouabain damage was dose and time-dependent; SGN were more vulnerable than HCs. ABR thresholds increased at high frequencies with 1mM ouabain and increased at all frequencies with 10 mM ouabain.DPOAE amplitude minimally affected with 1 mM ouabain and got large reduction at all frequencies with 10 mM oubain.