Survival of lesioned axons is critically dependent upon an ability to repair the damage (seal off small hole or cut ends) within minutes to hours after lesioning. However, very little is currently known about the cellular mechanisms responsible for short-term repair of damaged axons. To obtain such data, we have used several unmyelinated and myelinated, both invertebrate and vertebrate, axons to demonstrate that the cut ends of severed axons are sealed by a tightly-packed plug of vesicles, some of which arise from endocytosis of the axolemma. We now propose to describe specific cellular/ biochemical/ molecular/ biophysical mechanisms responsible for the sealing of a small axonal hole or a complete axonal transection using data obtained from various techniques, including photomicroscopy (DIC, confocal fluorescence), electron microscopy, vibrating probe measures of injury current, ID and 2D SDS gels or Western transfers, and patch voltage clamp analysis of ion channels and transporters in membranes obtained from injury-induced vesicles. More specifically, we now propose to determine (1) the Ca2+ distribution in axons ms to hrs after a lesion (small hole or complete transection), (2) the origins and mechanisms of formation of vesicles that seal a lesioned (small hole or completely transected) axon, (3) the mechanisms that move vesicles to an axonal lesion site (small hole or complete transection) (4) the mechanisms by which vesicles seal small holes or completely transected cut axonal ends, and (5) whether the same cellular mechanisms seal small holes vs complete transections in a given axon or seal similar lesions in axons with different characteristics. These studies should be significant for several reasons (1) data on cellular repair mechanisms and the consequences of their failure should be of general interest to cell biologists and neurobiologists, (2) data on cellular mechanisms for sealing of lesioned (small hole or completely transected) axons might lead to procedures which increase axonal survival after injury, and (3) lack of repair in the axon studied may be helpful as a simple model of complicated neurodegenerative processes in mammalian fibers.
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