title: Systemic immunity influences hearing preservation in cochlear implantation.
abstract: OBJECTIVE
  To determine whether a systemic immune response influences hearing thresholds and tissue response after cochlear implantation of hearing guinea pigs.
  
  
  METHODS
  Guinea pigs were inoculated with sterile antigen (Keyhole limpet hemocyanin) 3 weeks before cochlear implantation. Pure-tone auditory brainstem response thresholds were performed before implantation and 1 and 4 weeks later. Dexamethasone phosphate 20% was adsorbed onto a hyaluronic acid carboxymethylcellulose sponge and was applied to the round window for 30 minutes before electrode insertion. Normal saline was used for controls. Cochlear histology was performed at 4 weeks after implantation to assess the tissue response to implantation. To control for the effect of keyhole limpet hemocyanin priming, a group of unprimed animals underwent cochlear implantation with a saline-soaked pledget applied to the round window.
  
  
  RESULTS
  Keyhole limpet hemocyanin priming had no significant detrimental effect on thresholds without implantation. Thresholds were elevated after implantation across all frequencies tested (2-32 kHz) in primed animals but only at higher frequencies (4-32 kHz) in unprimed controls. In primed animals, dexamethasone treatment significantly reduced threshold shifts at 2 and 8 kHz. Keyhole limpet hemocyanin led to the more frequent observation of lymphocytes in the tissue response to the implant.
  
  
  CONCLUSIONS
  Systemic immune activation at the time of cochlear implantation broadened the range of frequencies experiencing elevated thresholds after implantation. Local dexamethasone provides partial protection against this hearing loss, but the degree and extent of protection are less compared to previous studies with unprimed animals.
authors.affiliation: Department of Otolaryngology, University of Melbourne, Royal Victorian Eye and Ear Hospital, East Melbourne, Australia.
authors.forename: Melanie
authors.initials: M
authors.lastname: Souter
authors.forename: Hayden
authors.initials: H
authors.lastname: Eastwood
authors.forename: Paul
authors.initials: P
authors.lastname: Marovic
authors.forename: Gordana
authors.initials: G
authors.lastname: Kel
authors.forename: Sarin
authors.initials: S
authors.lastname: Wongprasartsuk
authors.forename: Allen F
authors.initials: AF
authors.lastname: Ryan
authors.forename: Stephen John
authors.initials: SJ
authors.lastname: O'Leary
mesh_terms: D000276:Adjuvants, Immunologic / Q000494:pharmacology; D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology; D001301:Audiometry, Pure-Tone; D001309:Auditory Threshold / Q000187:drug effects; D019929:Cochlear Implantation / Q000009:adverse effects; D003054:Cochlear Implants / Q000009:adverse effects; D003907:Dexamethasone / Q000494:pharmacology; D004195:Disease Models, Animal; D004333:Drug Administration Routes; D006168:Guinea Pigs; D034381:Hearing Loss / Q000188:drug therapy / Q000276:immunology*; D006433:Hemocyanins / Q000276:immunology / Q000494:pharmacology; D012405:Round Window, Ear / Q000187:drug effects
chemical_list: D000276:Adjuvants, Immunologic; D000893:Anti-Inflammatory Agents; D003907:Dexamethasone; D006433:Hemocyanins; C032808:keyhole-limpet hemocyanin