title: α-Synuclein deficiency and efferent nerve degeneration in the mouse cochlea: a possible cause of early-onset presbycusis.
abstract: OBJECTIVE
  Efferent nerves under the outer hair cells (OHCs) play a role in the protection of these cells from loud stimuli. Previously, we showed that cochlear α-synuclein expression is localized to efferent auditory synapses at the base of the OHCs. To prove our hypothesis that α-synuclein deficiency and efferent auditory deficit might be a cause of hearing loss, we compared the morphology of efferent nerve endings and α-synuclein expression within the cochleae of two mouse models of presbycusis.
  
  
  METHODS
  Comparative animal study of presbycusis.
  
  
  METHODS
  The C57BL/6J(C57) mouse strain, a well-known model of early-onset hearing loss, and the CBA mouse strain, a model of relatively late-onset hearing loss, were examined. Auditory brainstem responses and distortion product otoacoustic emissions were recorded, and cochlear morphology with efferent nerve ending was compared. Western blotting was used to examine α-synuclein expression in the cochlea.
  
  
  RESULTS
  Compared with CBA mice, C57 mice showed earlier onset high-frequency hearing loss and decreased function in OHCs, especially within high-frequency regions. C57 mice demonstrated more severe pathologic changes within the cochlea, particularly within the basal turn, than CBA mice of the same age. Weaker α-synuclein and synaptophysin expression in the efferent nerve endings and cochlear homogenates in C57 mice was observed.
  
  
  CONCLUSIONS
  Our results support the hypothesis that efferent nerve degeneration, possibly due to differential α-synuclein expression, is a potential cause of early-onset presbycusis. Further studies at the cellular level are necessary to verify our results.
authors.affiliation: Department of Otolaryngology-Head & Neck Surgery, The Catholic University of Korea, College of Medicine, St. Mary's Hospital, 505 Banpodong, Seochogu, Seoul 137-701, Republic of Korea. snparkmd@catholic.ac.kr
authors.forename: S N
authors.initials: SN
authors.lastname: Park
authors.forename: S A
authors.initials: SA
authors.lastname: Back
authors.forename: Y H
authors.initials: YH
authors.lastname: Choung
authors.forename: H L
authors.initials: HL
authors.lastname: Kim
authors.forename: O
authors.initials: O
authors.lastname: Akil
authors.forename: L R
authors.initials: LR
authors.lastname: Lustig
authors.forename: K H
authors.initials: KH
authors.lastname: Park
authors.forename: S W
authors.initials: SW
authors.lastname: Yeo
mesh_terms: D017668:Age of Onset; D000818:Animals; D003051:Cochlea / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D004195:Disease Models, Animal; D018450:Disease Progression; D004525:Efferent Pathways / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D018072:Hair Cells, Auditory, Outer / Q000378:metabolism / Q000473:pathology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D009410:Nerve Degeneration / Q000235:genetics* / Q000378:metabolism / Q000503:physiopathology*; D011304:Presbycusis / Q000235:genetics* / Q000378:metabolism* / Q000503:physiopathology; D051844:alpha-Synuclein / Q000172:deficiency* / Q000235:genetics
chemical_list: D051844:alpha-Synuclein