Abstract
Histological analysis of cochleas from 100 albino guinea pigs (Hartley strain) obtained from Charles River Laboratories revealed an apparently congenital anomaly in 24% of animals, with roughly equal prevalence in males and females. In affected animals, 15–50% of the first-row outer hair cells (OHCs) showed distinctly abnormal orientation of the W-shaped stereociliary array. These abnormal hair bundles could be rotated by up to 180° from the normal quasi-radial orientation. Second- and third-row OHCs appeared normal in all cases. Cochlear sensitivity was assayed in a subset of animals via compound action potentials (CAPs): CAP thresholds in affected animals were, on average, elevated by 5–10 dB with respect to normal controls. If the contributions of individual OHCs to cochlear ‘amplification’ add linearly, and if the total OHC contribution corresponds to ∼45 dB of ‘gain’, a quantitative correlation of the degree of stereociliary rotation and the degree of threshold shift in these ears suggests that first-row OHCs make a larger contribution to the cochlear amplifier than either of the other OHC rows.
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