Auditory function recovery following acoustic overstimulation

To examine electrophysiological data from auditory brainstem responses (ABRs) and distortion product otoacoustic emissions (DPOAEs) in chickens following acoustic overstimulation.

A total of 15 white 15-day-old Leghorn chickens were used. The animals were anesthetized with Equithensin, and placed with their heads in a special holder. Click stimuli were generated by a Nicolet CA1000 device and ABRs were recorded subcutaneously using three stainless-steel electrodes. An ILO 92/DP analyzer was used to determine DPOAEs. The noise was generated by a Promax GB 212 device. The acoustic exposure was provoked with a 2-kHz pure tone at 120 dB SPL for 24 h. ABRs and DPOAEs were determined before and immediately post-exposure and 5, 15, 21 and 30 days after the traumatic exposure.

In our control DPgram response, the maximum amplitudes (dB SPL) occurred at 1, 1.5, 2, 3 and 4 kHz and the minimum amplitudes at 0.7, 5 and 6 kHz. Immediately following acoustic overstimulation an amplitude loss in all frequencies was detected (p < 0.001). Five days after noise exposure only the amplitude loss at 3 kHz remained. Three waves with positive and negative peaks appeared in our control ABR recordings. An important threshold shift was detected in the ABR response immediately after acoustic overstimulation. Its complete recovery occurred 15 days after the acoustic trauma.

Recovery of the DPgram response was detected 5 days after acoustic overstimulation, whereas the normal ABR threshold appeared on the 15th day.