title: Hyperbaric oxygen upregulates cochlear constitutive nitric oxide synthase.
abstract: BACKGROUND
  Hyperbaric oxygen therapy (HBOT) is a known adjuvant for treating ischemia-related inner ear diseases. Controversies still exist in the role of HBOT in cochlear diseases. Few studies to date have investigated the cellular changes that occur in inner ears after HBOT. Nitric oxide, which is synthesized by nitric oxide synthase (NOS), is an important signaling molecule in cochlear physiology and pathology. Here we investigated the effects of hyperbaric oxygen on eardrum morphology, cochlear function and expression of NOS isoforms in cochlear substructures after repetitive HBOT in guinea pigs.
  
  
  RESULTS
  Minor changes in the eardrum were observed after repetitive HBOT, which did not result in a significant hearing threshold shift by tone burst auditory brainstem responses. A differential effect of HBOT on the expression of NOS isoforms was identified. Upregulation of constitutive NOS (nNOS and eNOS) was found in the substructures of the cochlea after HBOT, but inducible NOS was not found in normal or HBOT animals, as shown by immunohistochemistry. There was no obvious DNA fragmentation present in this HBOT animal model.
  
  
  CONCLUSIONS
  The present evidence indicates that the customary HBOT protocol may increase constitutive NOS expression but such upregulation did not cause cell death in the treated cochlea. The cochlear morphology and auditory function are consequently not changed through the protocol.
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, China Medical University Hospital, and Graduate Institute of Clinical Medical Science, Department of Anatomy, School of Medicine, China Medical University, Taichung, Taiwan.
authors.forename: Chia-Der
authors.initials: CD
authors.lastname: Lin
authors.forename: I-Hua
authors.initials: IH
authors.lastname: Wei
authors.forename: Chih-Ho
authors.initials: CH
authors.lastname: Lai
authors.forename: Te-Chun
authors.initials: TC
authors.lastname: Hsia
authors.forename: Ming-Ching
authors.initials: MC
authors.lastname: Kao
authors.forename: Ming-Hsui
authors.initials: MH
authors.lastname: Tsai
authors.forename: Ching-Hsiang
authors.initials: CH
authors.lastname: Wu
authors.forename: Mang-Hung
authors.initials: MH
authors.lastname: Tsai
mesh_terms: D000818:Animals; D016923:Cell Death; D003051:Cochlea / Q000201:enzymology*; D006168:Guinea Pigs; D006320:Hearing Tests; D006931:Hyperbaric Oxygenation / Q000379:methods; D008297:Male; D052248:Nitric Oxide Synthase Type I / Q000378:metabolism*; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism*; D038781:Otoscopy / Q000379:methods; D018709:Statistics, Nonparametric; D015854:Up-Regulation / Q000502:physiology*
chemical_list: D052248:Nitric Oxide Synthase Type I; D052250:Nitric Oxide Synthase Type III