Age as a factor in susceptibility to hearing loss: young versus adult ears.

Abstract

In order to test the relative susceptibility of young and adult ears to loss from intense stimulation, losses in round window cochlear microphonic (CM) sensitivity and hair cell losses were compared in series of experiments using 52 eight-week old kittens and 59 adult cats. In acute experiments, ears of deeply anesthetized animals were exposed to 50 min of 5.0-kHz pure tone stimulation at that intensity necessary to produce a maximum CM output (MAX+0), or 10 dB(MAX+10) or 30 dB(MAX+30) higher than that. In chronic experiments, similar measures were made and the animals were allowed to recover for six weeks before their sensitivity was remeasured and their cochleas examined by surface preparation histology. Losses were the same at MAX+0, but at MAX+10 the kittens lost significantly more sensitivity than the cats. At MAX+30 the losses were large (45–50 dB) but not significantly different. The chronic experiments showed that some CM recovery did occur and that hair cell losses were orderly and generally confined to the areas of the basilar membrane involved in the displacement pattern for a 5.0-kHz tone. Subject Classification: [43]65.64, [43]65.40.