Age-related changes in cochleas of mongolian gerbils.
The effects of aging on the gerbil cochlea were studied in 16 animals raised in a quiet environment. Animals were tested at ages ranging from 33 to 36 months, the approximate average lifespan of gerbils in our colony. Hearing sensitivity was assessed by measures of whole-nerve compound action potential (CAP) thresholds and surface preparations of the organ of Corti were subsequently examined by light microscopy for losses of sensory hair cells. These quiet-aged animals showed a wide range of hair-cell losses and threshold shifts. Outer hair cells often showed significant losses while inner hair cells were rarely absent. All animals had some threshold shift, especially at frequencies above 4 kHz. These shifts ranged from 1 to 68 dB. At high frequencies, threshold shifts often occurred without hair-cell losses at corresponding cochlear locations. At low frequencies, threshold shifts seldom reflected the losses of hair cells commonly found in the cochlear apex. Thus, the correlation of specific hair-cell losses and CAP threshold shifts at corresponding frequencies was poor. On the other hand, the total number of missing hair cells, irrespective of location, was a good, general indicator of the hearing capacity in a given ear. It appears that the factor or factors that makes cochleas susceptible to hair-cell loss with increasing age also affects other cochlear mechanisms that are necessary for normal functioning of the ear.
Department of Otolaryngology and Communicative Sciences, Medical University of South Carolina, Charleston 29425.
B I
BI
Tarnowski
R A
RA
Schmiedt
L I
LI
Hellstrom
F S
FS
Lee
J C
JC
Adams
D000200:Action Potentials; D000375:Aging / Q000473:pathology / Q000502:physiology*; D000818:Animals; D002452:Cell Count; D003051:Cochlea / Q000473:pathology / Q000502:physiology*; D005260:Female; D005849:Gerbillinae; D006198:Hair Cells, Auditory / Q000473:pathology; D008297:Male