TTS Accompanied by Sustained Reduction of AP Amplitudes in Noise-Exposed Guinea Pigs

Abstract

Guinea pigs were fitted with permanent recording macroelectrodes having tips located in the auditory-nerve-cochlear-nucleus region. After recording detection levels and input-output functions for clicks or pure-tone bursts under waking conditions using computer-averaging techniques, the animals were exposed to 115 dB SPL of broad-band noise for 1 h. Postnoise measurements were made within the hour following exposure and for at least four weeks thereafter. VDLs shifted for clicks and midfrequency tonal stimuli, although corresponding suprathreshold AP responses showed sustained reduction of peak-to-peak amplitudes. The altered form of the AP input-output functions is characteristic of nerve fiber depopulation conditions and suggests that damage occurred to the ear in spite of the fact that VDLs returned to prenoise levels.