The long term goal of this project is to elucidate axonal elongation and the navigation of growing axons to synaptic targets. The focus of these studies is the elongating nerve fiber tip, the growth cone. The behavior of growth cones and their role in formation of axonal pathways will be examined by studying two major aspects of growth cone activity. (1) Intracellular events at the front of a growth cone that are directly involved in the elongation, turing and branching of neurites. (2) The adhesive interactions of growth cones migrating on substrata containing components of extracellular matrices. This information will help understand how axons regenerate and why some do not, and may aid in planning stategies to improve recovery from damage to the nervous system. Information about the adhesive interactions of growing axons with extracellular matrices may be used to modify the environment of growing axons to stimulate regeneration. The proposed studies will use tissue culture, immunocytochemistry, and high resolution computer-enhanced videomicroscopy to examine relationships between microtubule distribution and the advancement of neurite components. The three dimensional ultrastructure of neuritic components will be examined by computer aided reconstructions of serial sections or tomographic reconstructions of whole mounted growth cones. The immunocytochemical distributions of several cytoskeletal and associated proteins in cultured growth cones will be examined. The dynamics of microtubule organization will be analyzed in cultured neurons microinjected with fluorescent tubulin. Interference reflection microscopy will be used to reveal the adhesive contacts of growth cones on surfaces treated with fibronectin and laminin. Neurons will be cultured on continuous and discontinuous adhesive pathways to examine the control of growth cone migration by differential adhesivity. Molecular and biochemical methods will be used to examine the specific domains of fibronectin that promote attachment and neutite outgrowth by CNS and PNS neurons and identify the cell surfaces receptors for these domains.
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