An investigation of mechanism of permanent threshold shift (PTS) induced by noise exposure

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Summary Using 97 male albino guinea pigs and applying electrophysiological methods, the effects of a 6 kHz tone were investigated at moderate sound pressure level to the inner ear during a 24-h exposure time. Following exposure to the 6 kHz tone at 90 dB.cochleas showed decreased maximum output voltage of cochlear microphonics (CM) and action potential (AP). In the endolymph. K^+ ion and Na^+ ion concentrations remained unchanged during 40 min anoxia and 90 dB tone exposure. At 80 dB sound exposure decreases in maximum output voltage of CM and AP and decreases in the absolate value of EP could not be detected. Endolymph K^+-ion Na^+-ion concentrations were also unchanged. These finding indicate that diffusion potentials are induced at the same time as decreases of maximum output voltage in CM induced by exposure to sound at 90 dB.