Age-dependent changes in susceptibility to ototoxic hearing loss.

Several species undergo age-dependent changes in susceptibility to noise-induced and drug-induced hearing loss. In this experiment 18-day-old mice were given 200 mg/kg kanamycin plus varying doses of bumetanide (20, 30 or 40 mg/kg). Thresholds of the scalp-recorded compound action potential of the auditory nerve indicated that diuretic doses of 30 and 40 mg/kg produced significant loss of hearing sensitivity. Thirty-eight-day-old mice were then treated with 200 mg/kg kanamycin plus 40 mg/kg bumetanide and demonstrated no loss of hearing sensitivity. These results confirm the existence of age-dependent changes in susceptibility to ototoxic hearing loss in mice. Furthermore, the treatment, consisting of two injections on the same day, offers promise as a means of defining the critical period of susceptibility in greater detail than has been possible with aminoglycosides alone.