Quantitative measures of hair cell loss in CBA and C57BL/6 mice throughout their life spans

TLDR

CBA mice exhibit minimal hearing loss until late life, whereas C57BL/6 mice develop severe, progressive high‑frequency sensorineural loss beginning at 3–6 months, a difference attributed to genetic variation in age‑related hair cell loss, yet precise quantitative data are lacking. This study aims to quantify mean inner and outer hair cell loss in CBA and C57BL/6 mice at 1, 3, 8, 18, and 26 months. The authors measured inner and outer hair cell counts across the cochlea of both strains at the specified ages to generate mean loss values. CBA mice show negligible hair cell loss until 18 months, with 65% apex and 50% base OHC loss and 25–35% IHC loss at 26 months, whereas C57BL/6 mice exhibit 75% OHC and 55% IHC loss in the cochlear base already at 3 months, with rapid, base‑to‑apex increases culminating in >80% OHC loss and 100% base IHC loss by 26 months.

Abstract

The CBA mouse shows little evidence of hearing loss until late in life, whereas the C57BL/6 strain develops a severe and progressive, high-frequency 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 precise, quantitative description of the sensory cell loss is unavailable. The present study provides mean values of inner hair cell (IHC) and outer 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 until 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 cochlea at 3 months of age. OHC and IHC losses increased rapidly with age along a base-to-apex gradient. By 26 months of age, more than 80% of the OHCs were missing throughout the entire cochlea; however, IHC losses ranged from 100% near the base of the cochlea to approximately 20% in the apex.