title: Noise-induced aspartate and glutamate efflux in the guinea pig cochlea and hearing loss.
abstract: Aspartate and glutamate were monitored in the scala tympani of the guinea pig cochlea using in vivo microdialysis before and during noise exposure. Moderate level broad band noise [105 dB sound pressure level (SPL), 30 min] neither altered the levels of aspartate or glutamate, nor auditory brainstem response (ABR) thresholds. High level noise exposure (135 dB SPL, 30 min) caused a large increase in aspartate (330%), a smaller increase in glutamate (150%), and a permanent ABR threshold shift of 60-75 dB between 2.0 and 12.5 kHz. Morphological analysis of the cochlea revealed a collapse of supporting structures, swelling of the afferent dendrites under the inner hair cells, and outer hair cell loss. Pretreatment with the NMDA antagonist, MK 801 (1 mg/kg body weight, i.p.) 1 h before noise exposure protected the afferent dendrites from swelling but did not protect the collapse of supporting structures, outer hair cell loss, or auditory thresholds. In conclusion, the noise-induced increase in aspartate and glutamate release in the cochlea and the protective effect of NMDA antagonism suggest that these two neurotransmitters are involved in noise-induced hearing loss.
authors.affiliation: Department of Otolaryngology, Huddinge University Hospital, Sweden. wanje.jager@telia.com
authors.forename: W
authors.initials: W
authors.lastname: Jäger
authors.forename: M
authors.initials: M
authors.lastname: Goiny
authors.forename: M
authors.initials: M
authors.lastname: Herrera-Marschitz
authors.forename: L
authors.initials: L
authors.lastname: Brundin
authors.forename: A
authors.initials: A
authors.lastname: Fransson
authors.forename: B
authors.initials: B
authors.lastname: Canlon
mesh_terms: D000161:Acoustic Stimulation; D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D003051:Cochlea / Q000502:physiology* / Q000503:physiopathology; D016057:Evoked Potentials, Auditory, Brain Stem; D018698:Glutamic Acid / Q000378:metabolism*; D006168:Guinea Pigs; D006317:Hearing Loss, Noise-Induced / Q000503:physiopathology*; D009622:Noise
chemical_list: D001224:Aspartic Acid; D018698:Glutamic Acid