Age-related de-efferentation in the murine organ of Corti

Introduction The acquired and progressive auditory deterioration with increasing age affects approximately one third of the world population over 65 years of age. The emerging evidence of a protective effect underlying a proper efferent auditory function is suggestive for a direct or indirect influence of the efferent auditory system in the onset and/or progression of age-related hearing decline.

Materials and methods The loss of myelinated efferent medial olivocochlear (MOC) fibers contacting outer hair cells (OHC) was analyzed in relation to the degeneration of type I myelinated afferent nerve fibers contacting inner hair cells (IHC) along the lifespan of CBA/J mice. 75 mice were grouped in 7 age groups between 3 and 20 months. For each mouse, cochlear apical, middle and basal turns were characterized for the integrity of OHC efferent synapses, responsible for OHC modulation, and IHC afferent ribbon synapses using immunohistochemistry. Confocal microscopy was chosen for image acquisition. Intact synapses were defined as those, in which pre-/ and post-synaptic markers colocalized.

Results Intact MOC efferent synapses showed a significant age-dependent reduction in the middle and basal cochlear turns (p < 0.05). For afferent IHC ribbon synapses a significant age-related loss was observed in the apical and middle turns (p < 0.05), as well as in the base (p < 0.1).

Conclusion Results obtained from afferent IHC ribbon synapses are in concordance with the literature. A significant age-dependent de-efferentation of OHC was observed in the middle and basal turns. This is the first time, to our knowledge, that the integrity of OHC efferent MOC synapses is being analyzed in direct relation to the loss of afferent IHC synapses along lifespan.

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Conflict of interest

Der Erstautor gibt keinen Interessenskonflikt an.

Publication History

Article published online:
13 May 2021