Considerable interest has been generated by recent studies which have utilized transplants to facilitate the regeneration of axons in the injured adult mammalian central nervous system (CNS). However, little is currently known about the cellular sources of the positive axonal growth promoting factors that appear to be present in peripheral nerve or embryonic CNS tissue. Thus, the long-term objectives of the proposed research are to identify and characterize factors which promote axonal regeneration from injured neurons in the adult mammalian CNS. The experimental paradigm to be used for the proposed studies is the transplantation of a variety of cellular and acellular substrates into bilateral intracephalic cavities in which all axonal connections are severed between the septum and hippocampus. Four experimental transplant preparations will be used: 1) specific non-neuronal PNS or CNS cells prepared in tissue culture, 2) control acellular substrates, 3) intact CNS or PNS nerves, and 4) extracellular matrix molecules.
The specific aims of these experiments are focused to determine the effects of the transplant environments on: 1) the rate of axonal regrowth, 2) the types of neurons generating axons, 3) specific cells and/or molecules which promote axonal regeneration, and 4) the morphological relationship between regenerating axons and the cellular terrain of the transplant. Several light microscopic neuroanatomical procedures will be utilized for identifying and tracing axonal connections between the transplant and host CNS. These will include retrograde tracing procedures (fluorescent dyes and horseradish peroxidase), anterograde tracing techniques (autoradiography, horseradish peroxidase, neurofibrillar and myelin stains), histochemical protocols for identifying specific axon types (catecholamine histofluorescence and acetylcholinesterase histochemistry), and immunohistochemical staining techniques for identifying selected cell components (laminin, fibronectin, glial fibrillary acidic protein, myelin basic protein, serotonin and C-4). In addition, those experiments which analyze cellular events in the transplant and at the transplant-host interface will utilize transmission electron microscopy. The results from the proposed research will provide important insight into the cellular and extracellular factors that can promote axonal regeneration in the adult mammalian CNS. The characterization of these axonal growth promoting factors should prove beneficial for developing therapies for treating traumatic brain and spinal cord injuries in man.
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