Mutant golden hamsters with an abnormal outer hair cell stereociliary arrangement.

A new malformation of the inner ear was found in golden hamster reared at our institute. It was studied using electron microscope and auditory electrophysiological measurements including auditory brainstem response (ABR), whole nerve action potential (AP) cochlear microphonic (CM) potential, and the summating potential (SP). The stereocilia on individual first row of outer hair cells in the hamsters with malformed inner ears (F-K hamsters) were arranged in a triple W form, but the entire bundle of stereocilia was irregular in orientation. These anomalies were seen in approximately 70 to 85% of sensory hairs, in all rotations, with no difference between the right and left sides. The cuticles of the first row of outer hair cells were displaced, but lower portions did not appear to be affected. ABR and SP revealed no differences from normal hamsters and it is believed that the F-K hamsters' hearing ability was normal. The CM potential and the amplitude of AP in the F-K hamsters were significantly lower, at 50 to 80 dB sound pressure level (SPL). The linear portions of the CM input-output relation curve were separated by 4 to 6 dBSPL and the saturating voltage levels differed by 2.5 to 3.0 microV. Based on these results, the actually-measured CM potentials were shown to represent a summation of the reaction of the three individual rows of outer hair cells.