SENSORINEURAL HEARING-LOSS ALTERS RECOVERY FROM SHORT-TERM ADAPTATIONIN THE C57BL 6 MOUSE/

Several strains of laboratory mouse (Mus musculus) have a pattern of h earing loss which resembles that found in humans. The C57BL/6 strain o f mouse has a genetic defect that results in degeneration of the organ of Corti, originating in the basal, high-frequency region and then pr oceeding apically over time. The end result is a severe-to-profound se nsorineural hearing loss (SNHL) by 14 months of age. In contrast, audi tory function of the CBA strain remains normal through its early life span then slowly declines later in life, much like that typified by hu man presbycusis. The purpose of the present study was to compare ABR ( peak 5) forward masking recovery functions in young, normal-hearing CB A and C57BL/6 mice to hearing-impaired C57BL/6 mice. ABR audiograms we re obtained prior to collecting the tone-on-tone forward masking data. Masking was defined as a 50% reduction in the P5 component of the ABR , elicited and masked by 12 kHz tone bursts, using masker/probe time d elays from 0 to 100 ms. Time constants were computed from an exponenti al model fit to the recovery functions (masker level vs. time delay). In hearing-impaired animals there was a significant increase in recove ry from short-term adaptation as measured by the time constants, as we ll as a significant latency shift in the P5 component. The effects of SNHL on the recovery of the P5 component from short-term adaptation wa s comparable to that reported behaviorally for human hearing-impaired listeners and physiologically from the inferior colliculus (IC) of chi nchillas suffering permanent threshold shifts.