Deafness and cochlear pathology of <i>rda</i> and <i>rda^2J</i> mutant mice.

<p><b>A.</b> ABR thresholds (dB SPL) of <i>rda/rda</i> and <i>rda ^2J/rda^2J</i> mutant mice and non-mutant controls tested at 33–48 days of age. ABRs for 8, 16, and 32 kHz stimulus frequencies were not detected in any of the <i>rda/rda</i> (N = 9) and <i>rda^2J/rda^2J</i> (N = 8) mutant mice tested, even with the maximum stimulus presentation of 100 dB SPL. Heterozygous +/<i>rda</i> (N = 8) and +/<i>rda^2J</i> (N = 4) mice and homozygous +/+ B6 mice (N = 17) were combined as controls because their ABR thresholds did not significantly differ from one another. Error bars represent standard deviations of the threshold means. <b>B, C.</b> Cross sections through the basal turn of the cochlea from a +/<i>rda</i> heterozygous control mouse (B) and a littermate <i>rda/rda</i> mutant mouse (C) examined at 4 months of age. Note the complete degeneration of the organ of Corti (oc) and decreased density of spiral ganglion cells (sgc) in the <i>rda/rda</i> cochlea. Scale bars represent 100 microns. Cochlear cross sections of <i>rda^2J</i> mutant mice (not shown) exhibited this same pathology.