Pattern of gentamicin-induced cochlear degeneration in the guinea pig. A morphological and electrophysiological study.

Gentamicin-induced cochlear degeneration in the guinea pig was studied by complete hair-cell counting (cytocochleograms) and phase-contrast and interference microscopical examination of the stria vascularis and Reissner's membrane. Gentamicin (100 mg/kg/day) was administered over a period of 7-17 days. The first loss of hair cells (OHC) occurred in a region 6-8 mm from the round window. From this 'degeneration point', the loss of haircells progressed towards the round window (fast) and the apex (slowly). The stria vascularis showed no signs of degeneration. Reissner's membrane, on the other hand, showed intracellular vacuolization of the endolymphatic cells over the complete length of the cochlea after 12 or more days intoxication. Hearing loss was measured by electrocochleography with skin electrodes. The histologic findings were compared with the objective audiograms.