Background: Ear surgery using mastoid drills can lead to noise-induced hearing loss (NIHL). We investigated whether inhaled anesthetics or pentobarbital could have protective effects on NIHL in mice.
Methods: Mice were exposed to broad band white noise for 3 h per day for 3 consecutive days, with or without anesthesia, using halothane, isoflurane, or pentobarbital. The hearing level of each mouse was analyzed before exposure, and 1 day, 1, 2, and 3 Wk, and 1 mo after noise exposure by measuring auditory brainstem response thresholds. At 1 Wk after noise exposure, the organ of Corti was stained with a fluorescent isothiocyanate-conjugated phalloidin probe and a TUNEL kit.
Results: In the unanesthetized control group, the hearing threshold increased to 77.5 +/- 8.0 dB hearing level (HL) after noise stimulation. In the pentobarbital, isoflurane, and halothane groups, hearing threshold increased to 62.5 +/- 6.3 dB HL, 45.5 +/- 9.8 dB HL, and 39.3 +/- 6.2 dB HL, respectively, with all anesthetized groups of mice showing significantly preserved hearing compared with the control group (P < 0.05). But, in mice anesthetized with pentobarbital, hearing loss was more severe than in those treated with the inhaled anesthetics (P < 0.05). Hair cell survival was reduced in unanesthetized control mice and somewhat reduced in pentobarbital-treated mice, but largely unaffected in mice treated with inhaled anesthetics.
Conclusions: These findings indicate that, while halothane, isoflurane and pentobarbital could protect mice against NIHL and hair cell damage, inhaled anesthetics were more effective.