title: Damage and threshold shift resulting from cochlear exposure to paraquat-generated superoxide.
abstract: Superoxide has been implicated as a contributing factor to cochlear pathology from a number of sources, including noise and ototoxic drugs. The effects of NADPH oxidase-dependent superoxide on the cochlea were investigated in the current study using paraquat (PQ). PQ is a toxic herbicide that causes tissue damage by generating superoxide through reduction of molecular oxygen in a reaction catalyzed by NADPH oxidase. The current study examined the effects of round window PQ administration on inferior colliculus (IC) evoked potential thresholds (EVP) and hair cell damage. Using implanted IC electrodes, chinchillas were tested for IC EVP thresholds before and after PQ exposure. Ears were exposed to PQ at one of four concentrations: 10, 5, 3 mM, and vehicle control. Thresholds were increased in a dose-dependent manner, and peaked between one and seven days post-exposure. Thresholds then showed a small amount of recovery before reaching PTS by Day 22. Outer and inner hair cell losses were consistent with PTS. The similarities between PQ ototoxicity and noise-induced hearing loss suggest the possibility of similar biochemical pathways involving superoxide.
authors.affiliation: Department of Communicative Disorders and Sciences, Center for Hearing and Deafness, State University of New York at Buffalo, 137 Cary Hall, 3435 Main Street, Buffalo, NY 14214, USA. ecb2@buffalo.edu
authors.forename: Eric C
authors.initials: EC
authors.lastname: Bielefeld
authors.forename: Bo Hua
authors.initials: BH
authors.lastname: Hu
authors.forename: Kelly Carney
authors.initials: KC
authors.lastname: Harris
authors.forename: Donald
authors.initials: D
authors.lastname: Henderson
mesh_terms: D000818:Animals; D001309:Auditory Threshold / Q000187:drug effects; D002682:Chinchilla; D003051:Cochlea / Q000187:drug effects* / Q000473:pathology / Q000503:physiopathology; D004305:Dose-Response Relationship, Drug; D005072:Evoked Potentials, Auditory / Q000187:drug effects; D006199:Hair Cells, Auditory, Inner / Q000187:drug effects / Q000473:pathology; D018072:Hair Cells, Auditory, Outer / Q000187:drug effects / Q000473:pathology; D034381:Hearing Loss / Q000139:chemically induced / Q000473:pathology / Q000503:physiopathology; D006540:Herbicides / Q000008:administration & dosage / Q000633:toxicity*; D019255:NADPH Oxidases / Q000378:metabolism; D010269:Paraquat / Q000008:administration & dosage / Q000633:toxicity*; D013481:Superoxides / Q000378:metabolism / Q000633:toxicity*
chemical_list: D006540:Herbicides; D013481:Superoxides; D019255:NADPH Oxidases; D010269:Paraquat