We plan to investigate myelinated and amyelinated nerves during development, degeneration, and regeneration, to determine the mechanisms underlying the dynamic cellular transactions between myelinating cells and axons. We shall concentrate on those morphological specializations relating to the nodes of Ranvier and the paranodal regions where elaborate, intimate contacts between glia and neuron occur. We shall employ freeze-fracture, thin section and thick section (using high voltage) electron microscopy, and inserting molecular-specific labels to localize and characterize membrane proteins, cytoskeletal proteins, and extracellular matrix components in these functionally specialized regions. Our objectives are to determine the cellular mechanisms involved in the creation, maintenance and regulation of supramolecular organization existing through, within and surrounding glial and axonal membranes in myelinated nerves during development or during recovery from injury. The node of Ranvier is intimately involved in conduction of the nerve impulse and is the site where at least two macromolecules, the Na+ channel and the Na++K+ ATPase, crucial for axonal excitability, are concentrated. We suspect the node to be a nexus or focus of cellular interactions occurring during development and regeneration. In these experiments we aim to: directly determine the densities of the Na+ channels and the Na++K+ ATPase molecules at nodes of Ranvier; examine the interactions and signaling between the axon and the Schwann cell; determine the involvement of their cytoskeletons in local differentiation of the axonal membrane; and examine the possible role of the extracellular matrix in determining the formation and placement of nodes of Ranvier. Basic data generated by studies specifically dedicated to defining the factors that contribute to nodal and paranodal membrane organization will be useful for understanding the dynamics of glial-axonal interactions during the development, maintenance, degeneration and regeneration of this vital structure. These data will also aid our efforts to improve the design of a prosthetic device (the silicone tube regeneration chamber) we now employ in experiments promoting regeneration and remyelination across large gaps in peripheral nerves. An increase in our understanding of the dynamic cellular interactions that establish, maintain, and control axonal membrane protein complexes requisite for conduction of action potentials unquestionably will be of value in recognizing the effects of disease processes at these sites.
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