Vulnerability to noise-induced hearing loss in 'middle-aged' and young adult mice: a dose-response approach in CBA, C57BL, and BALB inbred strains

Vulnerability of the cochlea to noise induced permanent threshold shifts (N IPTS) was examined in young adult (1-2 months) and 'middle-aged' (5-7 month s) CBA/CaJ, C57BL/6J, and BALB/cJ inbred mice. For each age and strain, a d ose-response paradigm was applied, whereby groups of up to 12 animals were exposed to intense broadband noise (110 dB SPL) for varying durations. Expo sure durations reliably associated with < 10% and > 90% probability of a cr iterion amount of NIPTS (determined 2 weeks postexposure) were identified, and the minimum NIPTS exposure and the slope of the dose-response relation were then derived by numerical modeling. For all three strains, young adult mice were more susceptible to NIPTS than older adults; That is, a shorter exposure was able to cause NIPTS in the younger mice. Strain comparisons re vealed that C57 mice were more susceptible than CBAs in the older age group only. At both ages examined, however, BALE mice were most susceptible to N IPTS. When animals with a similar amount of NIPTS were compared, outer hair cell loss in the cochlear base was more widespread in the younger animals. BALE mice appear particularly susceptible to noise-induced outer hair cell loss throughout life. Our data suggest that the mechanism or site of noise injury differs between young adults and older adults, and may depend on ge netic background. The finding that both BALE and C57 mice, which show prono unced age-related hearing loss, are also especially vulnerable to noise sup ports the notion that genes associated with age-related hearing loss often act by rendering the cochlea susceptible to insults. (C) 2000 Elsevier Scie nce B.V. All rights reserved.