AUDITORY DEGENERATION AFTER ACOUSTIC TRAUMA IN 2 GENOTYPES OF MICE

Two strains of mice, CBA/Ca and C57BL/6J, were exposed to a steady noi se (27 kHz) of 120 dB SPL for 5 min at 1, 3, 6, or 12 months of age. T hreshold shifts were determined by recording auditory brainstem respon se 1 month after exposure and thereafter up to the age of 16 months (C 57BL) or 23-27 months (CBA). With increasing age of exposure, suscepti bility to acoustic truama at middle frequencies (6.3-12.5 kHz) 1 month after exposure decreased in CBA mice but remained constant in C57BL m ice. With increasing age after exposure, threshold shifts were retaine d at the middle frequencies in CBA mice exposed at 1 month of age and in C57BL mice of all exposed groups. The progress of the interaction b etween the previous noise damage and aging effects was generally the s ame for the two strains, first an additivity and then a blocking-like interaction. The rate of the progress in post-noise hearing did not ex ceed the spontaneous rate of aging. The differences between exposed an d non-exposed groups decreased with advancing age. The results indicat e that the interaction of noise trauma and aging effects depends on th e susceptibility of the individual to acoustic trauma, affected freque ncies. and the severity of noise-induced PTS. A previous noise damage did not potentiate the auditory degeneration either in CBA/Ca or in C5 7BL/6J mice.