Susceptibility of DPOAEs to sound overexposure in inbred mice with AHL

The notion that three inbred strains of mice, i.e., C57BL/6J (C57), BALB/cB yJ (BALB), and WB/ReJ (WB), which exhibit differential rates of age-related hearing loss (AHL), may also exhibit differential susceptibility to noise- induced hearing loss was tested by comparing the effects of sound overexpos ure on these strains. The aftereffects of noise overstimulation on the dist ortion-product otoacoustic emissions (DPOAEs) of these three strains were c ompared and contrasted to those for the CBA/CaJ (CBA) strain, which does no t show changes in hearing threshold sensitivity up to 15 months of age. Two cohorts of mice, one at 2.5 and the other at 6 months of age, were first e xposed to a tonal overstimulation paradigm, were allowed to recover, and th en were later re-exposed to an octave band noise (OBN), at 3 or 7 months of age, respectively. The two sound exposure episodes were designed to produc e either a temporary (tonal exposure) or permanent (OBN exposure) reduction in the levels of the 2f(1) - f(2) DPOAE in the WB strain, which exhibited the fastest rate of AHL. Although the tonal paradigm resulted in a temporar y decrease in DPOAE levels for all strains at both ages, the 2.5-month BALB s showed the greatest susceptibility to this overexposure, while the 2.5-mo nth WBs exhibited the least effects on DPOAEs. At the older age of 6 months , tonal overexposure produced essentially the same reduction in DPOAE level s for all four strains. In addition, there were no differences noted betwee n CBAs and C57s, at either of the two ages. The OBN paradigm resulted in a permanent decrease in DPOAE levels in all the strains exhibiting early AHL, i.e., the C57, BALB, and WB mice, for frequencies about one-half to an oct ave higher than the exposure frequency, regardless of age. In contrast, the CBA strain was not significantly affected by the OBN overexposure.