Enhanced cochlear responses after sound exposure

Hensen’s cell alternating potentials were recorded in the gerbil cochlea by means of the approach developed previously in this laboratory. An intensity series of magnitude and phase transfer functions (TFs) and cochlear microphonic (CM) TFs from 125 Hz to 16 kHz were obtained at 40–90 dB sound pressure level (SPL) by means of frequency sweeps. Subsequently, the same frequency sweeps at either 80, 90, or 100 dB SPL were delivered to the ear for 10–40 min. CM, Hensen’s cell TFs, and EP were monitored periodically post-exposure. Hensen’s cell responses showed enhancement within 40–50 min post-exposure and a phase lead. There was no correlation between changes in peak response and changes in receptor potential or EP. The response enhancement and its associated phase lead is explained with the help of Zwislocki’s cochlear model [MechanicsandBiophysicsofHearing, edited by P. Dallos (Springer-Verlag, Berlin, 1990)]. Since Hensen’s cells cannot generate receptor potentials by themselves, and their AC potentials have been shown to be directly proportional to those of OHCs, the measured enhancement appears to reflect enhanced OHC responses. [Work supported by NIDCD.]