Hearing losses in mongolian gerbil after 300 days of continuous exposure to noise

Abstract

As part of a large, long‐term study of noise‐induced hearing loss, pres‐byacusis, and the interactions of the two, groups of mongolian gerbils are being exposed for their entire life to a wideband noise. The A‐weighted sound pressure level is 85 dB. Control groups are being raised in an acoustic environment where the average sound level is less than 35 dBA. Hearing is estimated from electrical potentials arising from the auditory nerve and brainstem and recorded with noninvasive electrodes. Now, we report results from a pilot group of gerbils during the course of 300 days of continuous exposure to noise. Estimated threshold shifts were largest, about 40 dB, between 2 and 8 kHz and decreased at lower and higher frequencies. Threshold shifts at 4.0 and 8.0 kHz did not appear to increase (± 5 dB) between 30 and 300 days of exposure whereas at other test frequencies threshold shifts increased by as much as 20 dB between 60 days and 180 days. Aging control animals appear to develop hearing losses first at 16 and 20 kHz whereas noise‐exposed animals develop their hearing losses first at 4 and 8 kHz. [Work supported by NIEHS.]