Auditory function recovery following acoustic overstimulation.

OBJECTIVE: To examine electrophysiological data from auditory brainstem responses (ABRs) and distortion product otoacoustic emissions (DPOAEs) in chickens following acoustic overstimulation. MATERIAL AND METHODS: 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. RESULTS: 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. CONCLUSION: Recovery of the DPgram response was detected 5 days after acoustic overstimulation, whereas the normal ABR threshold appeared on the 15th day.

[The study of ototoxicity in Gallus domesticus by recording distortion products]. / Estudio de la toxicidad auditiva en el Gallus domesticus mediante el registro de los productos de distorsión.

Distortion products (DP) were recorded and a morphological cochlear study was made of a sample of 60 ears from chickens (Gallus domesticus. Leghorn breed) and the ages of 15, 23, 29 and 60 days, after intoxication by intramuscular gentamicin injection (40 mg per kg weight and day for 8 days). Spontaneous or transitory otoacoustic emissions were not obtained in any case. DP recordings showed a 2F1-F2 response in every frequency band ranging from 0.7 to 6 KHz. The DP incidence shifted with the age of the chickens and differed significantly (p < 0.001) in the groups of 29 and 60 day-old chickens (m = 100%) and in the 29-day-old (m = 64%) and 60-day-old (m = 62%) intoxicated chickens. We found no significant differences in DP amplitude in subpopulations. In the intoxicated groups, the proximal segment of the ototic membrane disappeared in the macula lagenae and a loss of contact with the hair cells appeared. Degenerative vacuolar phenomena were observed in the support cells and cellular loss in the spiral ganglion.