Influence of age on noise-induced permanent threshold shifts in CBA/Ca and C57BL/6J mice.

Two inbred strains of mice, CBA/Ca (showing a moderate hearing loss with onset late in life) and C57BL/6J (undergoing spontaneous auditory degeneration with onset during young adulthood), were exposed to a broad-band noise of 120 dB SPL (2-7 kHz) for 5 min at 1,2,3,6 or 12 (only for CBA) months of age. Permanent threshold shifts (PTS) were determined by recording auditory brainstem response (ABR) 1 month after exposure. C57 mice were more severely affected by acoustic trauma than age-matched CBA mice. With increasing age, susceptibility to PTS decreased in CBA mice but remained constant in C57 mice. Results indicate that the auditory system of CBA mice undergoes a progressive resistance to noise damage, whereas the persistent high susceptibility to acoustic trauma in C57 mice may be related to their genetic predisposition to rapid auditory degeneration.