Structural Analyses Core

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Abstract: Core C will assist the overall goal of the Projects to test the unifying hypothesis that aging auditory neurons and their subcellular components develop defined structural alterations, leading to profound neural circuit re-wiring and aberrant structure/function plasticity along the auditory pathway. Core C will leverage the National Center for Microscopy and Imaging Research (NCMIR; Dr. Perkins) resources and Dr. Fritzsch's confocal microscopy and deep neuroanatomy expertise. Core C will use computer resources to integrate large-volume, micro- and nano-scale structural investigations through serial block-face scanning electron microscopy (SBEM) and confocal microscope z-series of fluorescent-tagged proteins (biomarkers), into each Project in deciphering the structural correlates of age-related hearing loss (ARHL). Core C will provide structural support for: Project 1: Studies of structural (anatomic) projections of spiral ganglion neurons (SGN) from inner hair cells (HCs) to the brainstem cochlear nucleus (CN), which show age-dependent demyelination and synaptopathy using SBEM; SGN subtype-specific projection tracing from cochlear HCs to the CN, and determination of the age-dependent re-wiring using fluorescent-tags of SGN-subtype biomarkers. Core C will analyze axonal nodes and internodes along the peripheral auditory neurons (AN) using Nav or Kv3.1 and CASPR immunofluorescence labeling. Other sub-cellular changes in the aging SGN will be examined. Project 2: Studies of aging on the cochlear nucleus (CN) using SBEM; investigation of synaptic vesicle densities and mitochondrial structure, with profound age- dependent synaptic plasticity in ARHL models. Project 3: Connectomic analysis of nerve fibers, synapses, dendrites, and mitochondrial networks that are altered in aging in the CN and the medial nucleus of the trapezoid body (MNTB) using SBEM; tracking myelin thickness and the length of the internodes over relatively long tracts of myelinated axons (central portion of the AN and axons of bushy cells to the MNTB). For all projects, the typically large confocal and SBEM volumes will be placed in the NCMIR Cell Image Library (CIL), allowing Core and Project researchers to annotate features in the volumes and share the annotations across sites to view in the CIL web application interactively, and with approved researchers elsewhere. Core C will support the overall goal in providing new insights into the current knowledge gaps in synaptic and neural overtures in aging auditory neurons, to determine the mechanism and treatment of ARHL.