QUANTITATIVE MEASURES OF HAIR CELL LOSS IN CBA AND C57BL 6 MICE THROUGHOUT THEIR LIFE SPANS/

The CBA mouse shows little evidence of hearing loss until late in life , whereas the C57BL/6 strain develops a severe and progressive, high-f requency sensorineural hearing loss beginning around 3-6 months of age . These functional differences have been linked to genetic differences in the amount of hair cell loss as a function of age; however, a prec ise, quantitative description of the sensory cell loss is unavailable. The present study provides mean values of inner hair cell (IHC) and o uter hair cell (OHC) loss for CBA and C57BL/6 mice at 1, 3, 8, 18, and 26 months of age. CBA mice showed little evidence of hair cell loss u ntil 18 months of age. At 26 months of age, OHC losses in the apex and base of the cochlea were approximately 65% and 50%, respectively, and IHC losses were approximately 25% and 35%. By contrast, C57BL/6 mice showed approximately a 75% OHC and a 55% IHC loss in the base of the c ochlea at 3 months of age. OHC and IHC losses increased rapidly with a ge along a base-to-apex gradient. By 26 months of age. more than 80% o f the OHCs were missing throughout the entire cochlea; however, LHC lo sses ranged from 100% near the base of the cochlea to approximately 20 % in the apex. (C) 1997 Acoustical Society of America.