title: Effects of acoustic trauma on the auditory system of the rat: The role of microglia.
abstract: Exposure to loud, prolonged sounds (acoustic trauma, AT) leads to the death of both inner and outer hair cells (IHCs and OHCs), death of neurons of the spiral ganglion and degeneration of the auditory nerve. The auditory nerve (8cn) projects to the three subdivisions of the cochlear nuclei (CN), the dorsal cochlear nucleus (DC) and the anterior (VCA) and posterior (VCP) subdivisions of the ventral cochlear nucleus (VCN). There is both anatomical and physiological evidence for plastic reorganization in the denervated CN after AT. Anatomical findings show axonal sprouting and synaptogenesis; physiologically there is an increase in spontaneous activity suggesting reorganization of circuitry. The mechanisms underlying this plasticity are not understood. Recent data suggest that activated microglia may have a role in facilitating plastic reorganization in addition to removing trauma-induced debris. In order to investigate the roles of activated microglia in the CN subsequent to AT we exposed animals to bilateral noise sufficient to cause massive hair cell death. We studied four groups of animals at different survival times: 30 days, 60 days, 6 months and 9 months. We used silver staining to examine the time course and pattern of auditory nerve degeneration, and immunohistochemistry to label activated microglia in the denervated CN. We found both degenerating auditory nerve fibers and activated microglia in the CN at 30 and 60 days and 6 months after AT. There was close geographic overlap between the degenerating fibers and activated microglia, consistent with a scavenger role for activated microglia. At the longest survival time, there were still silver-stained fibers but very little staining of activated microglia in overlapping regions. There were, however, activated microglia in the surrounding brainstem and cerebellar white matter.
authors.affiliation: Department of Physiology & Biophysics, University at Buffalo, United States. Electronic address: baizer@buffalo.edu.
authors.forename: J S
authors.initials: JS
authors.lastname: Baizer
authors.affiliation: Department of Physiology & Biophysics, University at Buffalo, United States.
authors.forename: K M
authors.initials: KM
authors.lastname: Wong
authors.affiliation: Center for Hearing and Deafness, University at Buffalo, Buffalo, NY 14214, United States.
authors.forename: S
authors.initials: S
authors.lastname: Manohar
authors.affiliation: Center for Hearing and Deafness, University at Buffalo, Buffalo, NY 14214, United States.
authors.forename: S H
authors.initials: SH
authors.lastname: Hayes
authors.affiliation: Center for Hearing and Deafness, University at Buffalo, Buffalo, NY 14214, United States.
authors.forename: D
authors.initials: D
authors.lastname: Ding
authors.affiliation: Center for Hearing and Deafness, University at Buffalo, Buffalo, NY 14214, United States.
authors.forename: R
authors.initials: R
authors.lastname: Dingman
authors.affiliation: Center for Hearing and Deafness, University at Buffalo, Buffalo, NY 14214, United States.
authors.forename: R J
authors.initials: RJ
authors.lastname: Salvi
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism; D015703:Antigens, CD / Q000378:metabolism; D015214:Antigens, Differentiation, Myelomonocytic / Q000378:metabolism; D001306:Auditory Pathways / Q000473:pathology* / Q000503:physiopathology*; D039481:CD11b Antigen / Q000378:metabolism; D004195:Disease Models, Animal; D006198:Hair Cells, Auditory / Q000473:pathology / Q000648:ultrastructure; D006317:Hearing Loss, Noise-Induced / Q000150:complications / Q000209:etiology / Q000473:pathology*; D008297:Male; D008562:Membrane Glycoproteins / Q000378:metabolism; D017628:Microglia / Q000378:metabolism* / Q000648:ultrastructure; D009410:Nerve Degeneration / Q000209:etiology / Q000473:pathology; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009622:Noise / Q000009:adverse effects; D011571:Psychoacoustics; D051381:Rats; D017207:Rats, Sprague-Dawley; D016622:Silver Staining; D000097382:CD68 Molecule
chemical_list: D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D039481:CD11b Antigen; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; C067980:CD68 antigen, human; D000097382:CD68 Molecule; C116337:OX-6 monoclonal antibody; C489618:Sv2a protein, rat
keywords: deafness; inflammation; macrophages; noise exposure; synaptic stripping