ASA 125th Meeting Ottawa 1993 May

4aBV2. The pathophysiology of presbyacusis: Does the aging cochlea need a jump start?

Richard A. Schmiedt

Dept. of Otolaryngol. Med., Univ. of South Carolina, 171 Ashley Ave., Charleston, SC 29425-2242

The Mongolian gerbil is used as an animal model to study the pathophysiology underlying presbyacusis. Gerbils are raised from birth in a quiet vivarium or are exposed to a long-duration wideband noise (0.5--4.0 kHz for 1--2 years at 85 dB SPL) at some time during their life. Quiet-aged ears have thresholds that are increased somewhat, especially above 4 kHz, but nonlinearities such as otoacoustic emissions and two-tone suppression are present and are largely unaffected by the aging process. Morphologically, hair cells in quiet-aged animals are highly conserved, whereas the lateral wall system degenerates, resulting in a decreased endocochlear potential (EP). Current injection to bolster the EP in these quiet-aged ears can enhance the response to low- and high-level stimuli. Noise-aged ears, while also showing increased thresholds, can be differentiated from their quiet-aged counterparts by a lack of nonlinear phenomena. Two-tone suppression is absent as are otoacoustic emissions. Thus, aging in quiet or in noise can have very different outcomes with regard to overall peripheral function, even when the respective audibility curves are similar. [Work supported by NIH P01 DC00422.]