Noise damage in the C57BL/CBA mouse cochlea

The present study was designed to determine the response to noise of the au ditory system of a genetically well-defined laboratory mouse in preparation for examining the effect of noise on mice with specific genetic mutations. The mice were C57BL/CBA F1 hybrids. Eight mice served as non-noise-exposed controls and 39 mice were exposed for 1-24 h to an octave band of noise wi th a center frequency of 2, 4 or 8 kHz and a sound pressure level of 100-12 0 dB. Auditory brainstem response thresholds were measured pre-exposure and several times post-exposure (i.e., 0-27 days) to determine the magnitude o f the temporary threshold shift (TTS) and permanent threshold shift (PTS). After Fixation by cardiac perfusion, the cochleas from each mouse were embe dded in plastic, dissected into quarter turns of the cochlear duct and anal yzed quantitatively. Immediately post-exposure, all mice had sizable TTSs a t the tested frequencies (i.e., 3-50 kHz). At this time, two mice were kill ed. Thresholds of the other 37 mice recovered somewhat in the first 4 days post-exposure. One mouse fully recovered from its TTS; 10 mice were left wi th PTSs at all frequencies; 26 mice recovered at some frequencies but not o thers. Most mice with PTSs for 30-50 kHz had focal losses of inner and oute r hair cells in the basal 20% of the organ of Corti, often with degeneratio n of adjacent myelinated nerve fibers in the osseous spiral lamina. On the other hand, mice with PTSs for the lower frequencies (i.e., 3-20 kHz) had s tereocilia disarray without significant hair cell losses in the second and first turns. Considerable variability was found in the magnitude of hair ce ll losses in those mice that received identical noise exposures, despite th eir genetic homogeneity. (C) 2000 Elsevier Science B.V. All rights reserved .