Exposure to the microgravity conditions of spaceflight alleviates the load normally imposed by the Earth’s gravitational field upon the inner ear utricular epithelia. Previous ultrastructural investigations showed that spaceflight induced an increase in synapse density within hair cells of the rat utricle. However, the utricle exhibits broad physiologic heterogeneity across different epithelial regions, and it is unknown whether capabilities for synaptic plasticity generalize to hair cells across its topography. To achieve systematic and broader sampling of the epithelium than previously conducted we used immunohistochemistry and volumetric image analyses to quantify synapse distributions across representative utricular regions in specimens from mice exposed to spaceflight (a 15-day mission of the space shuttle Discovery). These measures were compared to similarly-sampled Earth-bound controls. Following paraformaldehyde fixation and microdissection, immunohistochemistry was performed on intact specimens to label presynaptic ribbons (anti-CtBP2) and postsynaptic receptor complexes (anti-Shank1A) DOI: 10.1152/jn.00240.2016.
Mature vestibular hair cells retain capabilities for structural plasticity manifested through modulation of synapse density. Investigations are ongoing that are testing the hypothesis that synapse density increases may result from exposure to centrifugation-induced hypergravity, which would provide the foundation for future research into the molecular mechanisms through which these modifications are induced. This research will provide insight and strategies for inner ear rehabilitation through the induction of synapse density increases in conditions of vestibular paresis.
Maybe zero gravity will play a role in therapies for hearing loss?
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