Age-related hair cell loss in spontaneously hypertensive and normotensive rats

In the spontaneously hypertensive (SH) rat, a hereditary form of hypertension and widespread vascular abnormalities develop. In the present study the inner ear degeneration pattern in SH and normotensive (N) rats not exposed to noise was investigated and correlated with frequency-specific auditory brainstem response (ABR) thresholds. Rats of both strains were found to have a spontaneous loss of apical hair cells, but this was slightly more pronounced in SH. In SH rats, but not in those of the N strain, there was an age-related progressive loss of outer hair cells in the region 3-5 mm from the stapes, and a slight additional loss at the most basal end. According to available frequency maps, the hair cell loss should correspond to hearing loss between 6 and 24 kHz. In the SH rats hearing loss was not observed in the whole of this range, only at 16 and 20 kHz. It cannot be determined to what extent the localized spontaneous loss of hair cells is caused by vascular factors and what other mechanisms are involved, but vascular factors probably only play a minor role.