Distortion-product otoacoustic emissions study of the noise-induced toughening effect in rats.
OBJECTIVE
To compare the toughening effects in rats induced by pure tones and a broadband noise (BBN).


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.


CONCLUSIONS
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.
Sánchez Fernandez
J M
JM
Otorhinolaryngology Department, Basurto Hospital, School of Medicine, Basque Country University, Bilbao, Spain. infojaime@camaranet.com
Martínez Ibargüen
A
A
Orbegozo Etxebarría
E
E
Sánchez Del Rey
A
A
Santaolalla Montoya
F
F
D000222:Adaptation, Physiological; D000818:Animals; D001300:Audiometry, Evoked Response; D001309:Auditory Threshold; D003213:Conditioning, Psychological; D004195:Disease Models, Animal; D005260:Female; D006317:Hearing Loss, Noise-Induced; D009622:Noise / Q000009:adverse effects*; D017084:Otoacoustic Emissions, Spontaneous / Q000502:physiology*; D010469:Perceptual Distortion / Q000502:physiology*; D011336:Probability; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012016:Reference Values; D012680:Sensitivity and Specificity