Influence of genotype and age on acute acoustic trauma and recovery in CBA/Ca and C57BL/6J mice.

Two inbred strains of mice, CBA/Ca (with a moderate auditory impairment starting late in life) and C57BL/6J (with a progressive auditory degeneration starting during young adulthood), were exposed to a 120 dB SPL broadband noise (2-7 kHz) for 5 min at the age of 1, 3, or 6 months. Compound and permanent threshold shifts (CTS and PTS) were determined by auditory brainstem response during the first day (CTS) and 1 month (PTS) after exposure. With increasing age, susceptibility to CTS at middle frequencies (8 and 12.5 kHz) decreased in CBA mice, yet was retained in C57 mice. C57 mice were more severely affected by CTS than age-matched CBA mice. Noise-induced CTS was positively correlated to pre-exposure thresholds in C57 mice and to PTS over all ages and strains. The amount of recovery from CTS to PTS was, however, independent of age and strain. There was only a 2% risk of classifying CBA mice as C57 mice by pre-exposure thresholds at high frequency, while there was about 40% risk by CTS. The results indicate that genetic predisposition can affect susceptibility to auditory degeneration and noise impairment in a systematic manner, allowing the identification of susceptible individuals by pre-exposure audiometric examination, especially at high frequencies.