title: Therapeutic Effect of Dexamethasone for Noise-induced Hearing Loss: Systemic Versus Intratympanic Injection in Mice.
abstract: OBJECTIVE
  Dexamethasone is commonly used clinically to treat noise-induced hearing loss (NIHL) because the drug exerts multiple anti-inflammatory effects. In the present study, we investigated the post-noise therapeutic effects of dexamethasone given systemically or via intratympanic injection in the mouse.
  
  
  METHODS
  Twenty-four C57BL/6J mice were used. Eighteen experimental mice were exposed to 110 dB sound pressure level white noise and then divided into three groups: the noise, intraperitoneal dexamethasone injection (IP), and intratympanic dexamethasone injection (IT) groups.
  
  
  METHODS
  Dexamethasone (3 mg/kg/d) was injected intraperitoneally for five successive days in the IP group. Intratympanic injections were given on post-noise days 1 and 4 in the IT group. We compared hearing levels, the architecture of the organ of Corti (OC), and the microscopic appearance of the medial olivocochlear efferent terminals (MOC ETs) among the groups.
  
  
  RESULTS
  Both the IP and IT groups exhibited hearing recovery as revealed by auditory brainstem responses (ABRs), but recovery was not apparent in distortion product otoacoustic emissions (DPOAEs). OC degeneration as revealed by light microscopy was most extensive in the noise group and least extensive in the IP group. Scanning electron microscopy showed that the OC ultrastructure was better preserved in the IP than the IT group. Confocal microscopy showed that the ETs were shrunken in all noise-exposed groups as compared to the control group, but more shrunken in the dexamethasone-treated groups. Transmission electron microscopy showed that the MOC ET-outer hair cell (OHC) synapses were damaged in all noise-exposed groups, but the extent of degeneration was less in the IT than in the noise group.
  
  
  CONCLUSIONS
  Dexamethasone exerts reliable therapeutic effects when used to treat NIHL. It seems that the protective effects may differ by the routes of administration as the OCs were better preserved in the IP group and the ET-OHC synapses were more intact in the IT group.
authors.affiliation: Department of Otorhinolaryngology-Head and Neck Surgery, College of Medicine, The Catholic University of Korea, Seoul, Korea.
authors.forename: Min Ah
authors.initials: MA
authors.lastname: Han
authors.forename: Sang A
authors.initials: SA
authors.lastname: Back
authors.forename: Hong Lim
authors.initials: HL
authors.lastname: Kim
authors.forename: So Young
authors.initials: SY
authors.lastname: Park
authors.forename: Sang Won
authors.initials: SW
authors.lastname: Yeo
authors.forename: Shi Nae
authors.initials: SN
authors.lastname: Park
mesh_terms: D000818:Animals; D000893:Anti-Inflammatory Agents / Q000008:administration & dosage*; D003907:Dexamethasone / Q000008:administration & dosage*; D004195:Disease Models, Animal; D004432:Ear, Middle / Q000187:drug effects; D016057:Evoked Potentials, Auditory, Brain Stem / Q000187:drug effects; D006198:Hair Cells, Auditory / Q000187:drug effects / Q000648:ultrastructure; D006317:Hearing Loss, Noise-Induced / Q000188:drug therapy* / Q000473:pathology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D008855:Microscopy, Electron, Scanning; D017084:Otoacoustic Emissions, Spontaneous / Q000187:drug effects
chemical_list: D000893:Anti-Inflammatory Agents; D003907:Dexamethasone