title: Degeneration of auditory nerve fibers in guinea pigs with severe sensorineural hearing loss.
abstract: Damage to and loss of the organ of Corti leads to secondary degeneration of the spiral ganglion cell (SGC) somata of the auditory nerve. Extensively examined in animal models, this degeneration process of SGC somata following deafening is well known. However, degeneration of auditory nerve axons, which conduct auditory information towards the brainstem, and its relation to SGC soma degeneration are largely unknown. The consequences of degeneration of the axons are relevant for cochlear implantation, which is applied to a deafened system but depends on the condition of the auditory nerve. We investigated the time sequence of degeneration of myelinated type I axons in deafened guinea pigs. Auditory nerves in six normal-hearing and twelve deafened animals, two, six and fourteen weeks (for each group four) after deafening were histologically analyzed. We developed a semi-automated method for axon counting, which allowed for a relatively large sample size (20% of the total cross-sectional area of the auditory nerve). We observed a substantial loss of auditory nerve area (29%), reduction in axon number (59%) and decrease in axoplasm area (41%) fourteen weeks after deafening compared to normal-hearing controls. The correlation between axonal degeneration and that of the SGC somata in the same cochleas was high, although axonal structures appeared to persist longer than the somata, suggesting a slower degeneration process. In the first two weeks after induction of deafness, the axonal cross-sectional area decreased but the axon number did not. In conclusion, the data strongly suggest that each surviving SGC possesses an axon.
authors.affiliation: Department of Otorhinolaryngology and Head & Neck Surgery, University Medical Center Utrecht, Room G.02.531, P.O. Box 85500, 3508 GA, Utrecht, The Netherlands. Electronic address: stevenkroon1@gmail.com.
authors.forename: Steven
authors.initials: S
authors.lastname: Kroon
authors.affiliation: Department of Otorhinolaryngology and Head & Neck Surgery, University Medical Center Utrecht, Room G.02.531, P.O. Box 85500, 3508 GA, Utrecht, The Netherlands; Brain Center Rudolf Magnus, University Medical Center Utrecht, Utrecht, The Netherlands. Electronic address: d.ramekers@umcutrecht.nl.
authors.forename: Dyan
authors.initials: D
authors.lastname: Ramekers
authors.affiliation: Department of Otorhinolaryngology and Head & Neck Surgery, University Medical Center Utrecht, Room G.02.531, P.O. Box 85500, 3508 GA, Utrecht, The Netherlands. Electronic address: emmasmeets@gmail.com.
authors.forename: Emma M
authors.initials: EM
authors.lastname: Smeets
authors.affiliation: Department of Otorhinolaryngology and Head & Neck Surgery, University Medical Center Utrecht, Room G.02.531, P.O. Box 85500, 3508 GA, Utrecht, The Netherlands. Electronic address: f.hendriksen@umcutrecht.nl.
authors.forename: Ferry G J
authors.initials: FG
authors.lastname: Hendriksen
authors.affiliation: Department of Otorhinolaryngology and Head & Neck Surgery, University Medical Center Utrecht, Room G.02.531, P.O. Box 85500, 3508 GA, Utrecht, The Netherlands; Brain Center Rudolf Magnus, University Medical Center Utrecht, Utrecht, The Netherlands. Electronic address: s.klis@umcutrecht.nl.
authors.forename: Sjaak F L
authors.initials: SF
authors.lastname: Klis
authors.affiliation: Department of Otorhinolaryngology and Head & Neck Surgery, University Medical Center Utrecht, Room G.02.531, P.O. Box 85500, 3508 GA, Utrecht, The Netherlands; Brain Center Rudolf Magnus, University Medical Center Utrecht, Utrecht, The Netherlands. Electronic address: h.versnel@umcutrecht.nl.
authors.forename: Huib
authors.initials: H
authors.lastname: Versnel
mesh_terms: D000818:Animals; D001369:Axons / Q000473:pathology*; D003056:Cochlear Nerve / Q000473:pathology* / Q000503:physiopathology; D004195:Disease Models, Animal; D005260:Female; D006168:Guinea Pigs; D006309:Hearing; D006319:Hearing Loss, Sensorineural / Q000473:pathology* / Q000503:physiopathology; D009410:Nerve Degeneration; D012720:Severity of Illness Index; D013136:Spiral Ganglion / Q000473:pathology* / Q000503:physiopathology; D013997:Time Factors
keywords: Auditory nerve; Axon; Degeneration; Guinea pig; Hearing loss; Spiral ganglion cell