Age effects in susceptibility to noise-induced hearing loss

Several studies in recent years have suggested that susceptibility to noise-induced hearing loss is influenced by an animal's age at the time of acoustic overstimulation. In the present experiment an attempt was made to learn more about age effects by integrating into a single study observations of the initial effects of noise exposure and the time course of postexposure threshold changes. Mice were exposed to noise at one of two ages (18 or 28 days). The threshold of the auditory compound action potential was estimated from the scalp-recorded electrical response immediately after the exposure and again at 5- and 30-days postexposure. These measures were compared with identical measures from yoked control subjects to determine the effects of noise exposure. Results indicate an interaction of age with exposure intensity and postexposure interval. Specifically, an age effect is seen only at the higher of two exposure intensities and only after a 30-day postexposure interval. Individual data suggest further that the existence of an age effect is determined not by the initial postexposure threshold shift, but rather by subsequent changes in threshold following exposure.