Electrophysiological determinations of the effects of 1 kHz noise exposure on the high-frequency hearing of guinea pigs.

The effects of noise were studied in 90 5-week-old albino Hartley guinea pigs with normal hearing. The following experimental setup was used: (1) exposure to 1 kHz tones at 100 dB for 4 h, 20 h and 40 h; (2) exposure to 1 kHz tones at 110 dB for 20 h and 40 h. In order to investigate the effects of the noise exposures on the hearing of the guinea pigs, cochlear microphonics (CM), whole nerve action potentials (AP) and endocochlear potentials (EP) were examined. We obtained the following results. With a high sound pressure, a decrease was observed in the CM maximum output voltage in the test frequencies from 2 kHz to 6 kHz while the CM threshold increased ("pseudo threshold"). Intensity function of the N1 potential of the AP using a 7 kHz tone burst decreased; the threshold of the N1 potential also increased considerably by exposure to chronic high sound pressure. An extension of latency and a decrease in the absolute value of the negative potential in EP were induced by chronic noise exposure.