Peripheralaxons of auditory nerve fibers in homozygous mice degenerate between P10 and P20. A, Photomicrograph of a tangential section (inset) through the osseous spiral lamina in the basal turn of a homozygote cochlea aged 68 d. Scale bar, 50 μm. B, Higher magnification of the region in A indicated by the dotted box. C, Fractional survival of peripheral axons and hair cells obtained from 13 homozygote, 3 heterozygote, and 5 wild-type cochleas. Fractional survival is defined as the ratio of counts obtained in the transgenics to the mean value from the five wild types. All data are from the upper basal turn, i.e., the cochlear region corresponding to ∼18 kHz (Fig. 6, middle gray box).