Damage and threshold shift resulting from cochlear exposure to Paraquat-generated superoxide

• Published in: Hearing research Vol. 207; no. 1; pp. 35 - 42
• Main Authors: Bielefeld, Eric C., Hu, Bo Hua, Harris, Kelly Carney, Henderson, Donald
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.09.2005; Elsevier
• Subjects: Animals; Auditory Threshold - drug effects; Biological and medical sciences; Chinchilla; Cochlea; Cochlea - drug effects; Cochlea - pathology; Cochlea - physiopathology; Dose-Response Relationship, Drug; Drug toxicity and drugs side effects treatment; Ear, auditive nerve, cochleovestibular tract, facial nerve: diseases, semeiology; Evoked Potentials, Auditory - drug effects; Hair Cells, Auditory, Inner - drug effects; Hair Cells, Auditory, Inner - pathology; Hair Cells, Auditory, Outer - drug effects; Hair Cells, Auditory, Outer - pathology; Hearing Loss - chemically induced; Hearing Loss - pathology; Hearing Loss - physiopathology; Herbicides - administration & dosage; Herbicides - toxicity; Medical sciences; NADPH oxidase; NADPH Oxidases - metabolism; Non tumoral diseases; Otorhinolaryngology. Stomatology; Paraquat; Paraquat - administration & dosage; Paraquat - toxicity; Pharmacology. Drug treatments; Superoxide; Superoxides - metabolism; Superoxides - toxicity; Toxicity: respiratory system, ent, stomatology; PBS; PQ; IHC; TDT; SOD; Superoxide; OHC; PTS; TTS; NADPH oxidase; ROS; Cochlea; Paraquat; IC; EVP; Noise; Central nervous system; Electrophysiology; Auditory disorder; Recovery; Inner ear; Outer hair cell; Chinchilla; Organ of hearing; Encephalon; ENT disease; Drug; Hair cell of the ear; Oxygen; Implant; Rodentia; Hearing loss; Vertebrata; Mammalia; Round window; Colliculus inferior; Evoked potential; Threshold shift; Auditory pathway; Superoxide: NADPH oxidase
• ISSN: 0378-5955; 1878-5891
• DOI: 10.1016/j.heares.2005.03.025

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.