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Neurosci Res. 2011 Nov;71(3):303-10. doi: 10.1016/j.neures.2011.07.1835. Epub 2011 Aug 5.

α-Synuclein deficiency and efferent nerve degeneration in the mouse cochlea: a possible cause of early-onset presbycusis.

Author information

1
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

Abstract

OBJECTIVES/HYPOTHESIS:

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.

STUDY DESIGN:

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.

PMID:
21840348
DOI:
10.1016/j.neures.2011.07.1835
[Indexed for MEDLINE]

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