Distortion-product Otoacoustic Emissions Study of the Noise-induced Toughening Effect in Rats

Abstract

Objective—To compare the toughening effects in rats induced by pure tones and a broadband noise (BBN). Material and Methods—Sprague–Dawley female albino rats (n=148; 8–10 weeks old) were used. Three experimental groups were established as follows. Toughening only: 38 rats, divided into 3 subgroups, were exposed to different conditioning sounds (2 and 4 kHz and a BBN of 0.25–6 kHz, respectively) at 75–85 dB sound pressure limit (SPL) for 8 h/day for 10 days. Acoustic trauma only: 54 rats, divided into 3 subgroups, were exposed to different conditioning sounds as above for 24 h at 100–110 dB SPL. Toughening plus acoustic trauma: 56 rats, divided into 3 subgroups, were exposed to different conditioning sounds as above, followed 8 h later by traumatic exposure to the conditioning sound at 110 dB SPL for 24 h. 2f1–f2 distortion-product (DP) otoacoustic emission measurements were obtained from the right ear of each animal pre-exposure, immediately post-exposure and after 8 h of the traumatic or conditioning exposure. Results—In our control DPgram response, the maximum amplitude occurred at the highest frequencies (2, 3, 4, 5 and 6 kHz). No statistical differences between the control DPgram and the DP toughening (2 and 4 kHz and BBN) responses were found. Only 2 and 4 kHz frequencies induced a protective effect against traumatic sound exposures to the same frequencies, and this finding was statistically significant. Conclusion—The toughening phenomenon induced using 2 and 4 kHz pure tones and BBN in rats does not modify the DPgram response. Nevertheless, only 2 and 4 kHz frequencies induce a protective effect against traumatic sound exposures to the same frequencies.

• conditioning
• distortion-product otoacoustic emissions
• noise resistance
• threshold shift
• toughening

Sánchez Fernández JM, Martínez Ibargüen A, Orbegozo Etxebarría E, Sánchez del Rey A, Santaolaya Montoya F. Distortion-product otoacoustic emissions study of the noise-induced toughening effect in rats. Acta Otolaryngol 2003; 123: 154–159.

Sánchez Fernández JM, Martínez Ibargüen A, Orbegozo Etxebarría E, Sánchez del Rey A, Santaolaya Montoya F. Distortion-product otoacoustic emissions study of the noise-induced toughening effect in rats. Acta Otolaryngol 2003; 123: 154–159.