Noise-induced hearing loss (NIHL) relates closely to auditory cortex (AC) injury, so countermeasures aiming at the AC recovery would be of benefit. In this work, the effect of hyperbaric oxygen treatment on NIHL was elucidated, which was imposed on mice before (HBOP), during (HBOD) or after (HBOA) noise exposure. Morphology of neurons was assayed by hematoxylin-eosin or Nissl staining. Ceramide (Cer) level was measured through immunohistochemistry analysis. Apoptotic neurons were counted using transferase-mediated dUTP nick end labeling (TUNEL) staining. We demonstrated that the intense, broad band noise raised the threshold of auditory brainstem response, evoked neuronal degeneration or apoptosis and triggered the Cer accumulation in AC, all of which were restored significantly by HBOP, but not HBOD or HBOA. Cer over-generation reversed the advantages of HBOP significantly, while its curtailment recapitulated the effect. Next, noise exposure raised the superoxide or malondialdehyde (MDA) production which was blocked by HBOP or Cer repression. Oxidative control not only attenuated the hearing loss or neurodegeneration but, in turn, reduced the Cer formation significantly. In summary, mutual regulation between Cer and oxidative stress underlies the HBOP's curative effect on hearing loss and neuronal damage in noise-exposed mice.
Keywords: acid ceramidase; acid sphingomyelinase; ceramide; hearing loss; hyperbaric oxygen therapy; noise; oxidative stress.