FIG 3 .

Loss of auditory function and hair cells in vivo. (A) Effect of chronic aminoglycoside treatment in vivo on ABR at 12 kHz. The threshold shift is the difference in the auditory threshold before and 3 weeks after treatment, calculated for individual animals. The threshold shift is given in decibels (dB) and corresponds to a logarithmic scale, i.e., a 10-dB difference indicates a difference in energy of 1 log₁₀ unit. The different treatments are indicated as follows: black bars, control; gray bars, gentamicin; white bars outlined in black, compound 10; white bars outlined in gray, compound 11. Data represent means plus standard errors of the means (SEM) (error bars) (n = 3 to 11 per drug concentration). (B) Quantitative evaluation of hair cell loss. Surface preparations of guinea pig cochlea were evaluated quantitatively by determining the presence or absence of hair cells along the entire length of the cochlea. Representative examples are shown. Red, green, and blue lines indicate outer hair cells from the first, second, and third row, respectively. y axis, missing hair cells (%); x axis, distance from apex (mm). (a) Control (no drug treatment). Typical low-level scattered loss of individual cells along the length of the cochlea was observed. (b) Gentamicin given at 140 mg/kg. A steep rise of hair cell loss from the middle cochlea to complete loss at the base was seen. (c) Compound 10 given at 400 mg/kg. There was some hair cell loss but only at the very base of the cochlea. (d) Compound 11 given at 400 mg/kg. There was no significant hair cell loss.