The effect of isoflurane, halothane and pentobarbital on noise-induced hearing loss in mice

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.

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.

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.

These findings indicate that, while halothane, isoflurane and pentobarbital could protect mice against NIHL and hair cell damage, inhaled anesthetics were more effective.