The present work seeks to advance quantitative understanding of semicircular canal biophysics and biomechanics and is organized around three specific aims: 1) Examine sulfated glycosaminoglycans (GAGs) in vivo by tracking the time-course of expression in the cupula and extracellular space around stereocilia following mechanical and aminoglycoside insults. Inner ear GAGs are known to play essential roles in development, mechanics, regeneration, repair, and protection. Our experimental approach using new xyloside conjugates is revealing entirely new information about this important process. 2) Map the spatial distribution of hair bundle displacements across the sensory epithelium in response to physiological stimuli in vivo. The diverse temporal response properties of afferent neurons correlate with projections in the crista ampullaris, but we do not yet know how or if responses depend upon spatial maps of hair bundle displacements. We will measure micromechanical displacement fields while recording afferent responses innervating the same region of the crista. 3) Detail mechano-electrical transduction (MET) current adaptation and its relationship to active amplification by semicircular canal hair cells. Our recent results suggest that the most sensitive semicircular canal afferent neurons rely on hair cell amplification to increase sensitivity to low strength stimuli. We will investigate the role of MET adaptation and electrical mechanisms in this important process by tracking bundle displacements and recording from hair cells in vivo. Results are expected to have long-term impact by enhancing understanding of semicircular canal micromechanics, cupulogenesis and self-repair, amplification by hair cells, and efferent control of motion sensation by the brain.
Disorders of the vestibular system are debilitating and common, afflicting approximately 30% of the population over the age of 65 (Schappert, 1994). The present application is directly relevant to the biomechanical and biophysical substrates underlying sensitivity of semicircular canals under both physiological and pathological conditions. Unique in vivo experimental techniques will be applied to examine cupulogenesis/self-repair, glycosaminoglycan expression following damage, micromechanics, hair cell amplification, and efferent control.
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