Figure 3.

Hair cell counts in the basal turn of the organ of Corti of Htu/+ mutants revealed a large decrease in the number of outer hair cells (OHC) and a smaller increase in the number of hair cells in the inner row when compared with controls. Counts varied for each cochlea but averaged approximately 1,000 μm per cochlea. (A) The number of total outer hair cells is decreased significantly, largely because of the striking loss of hair cells in the third row. (B) The total number of inner hair cells is increased slightly (but significantly) in Htu/+ mutants. This increase is due to a significant increase in the number of cells in the second row (which are seen occasionally in controls), rather than a change in the packing density, as there was no difference in the number of hair cells within the normal (first) row of inner hair cells. Atypical cells, which were never observed in control cochleas and were not included in the inner hair cell counts, occurred at about the same frequency as the extra inner hair cells (*, P < 0.05; **, P < 0.01; ***, P < 0.001; Student's two-tailed t test). (C) Compound action potential thresholds from the five littermate controls (solid line ± SEM) and the five mutants (dashed line ± SEM), aged 60–83 days, showing that thresholds were slightly higher for the mutants at all frequencies, although these differences were not significant (P > 0.05; Student's two-tailed t test).