Improving neural graft function in parkinsonian monkeys.

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The benefits of fetal neural transplantation in primate Parkinson's models have been partially confirmed by studies in patients, but transplantation may have significant problems which should be addressed. Functional improvement appears variable, less effective in older patients, and incomplete in spite of some apparent increases in dopamine production. The hypotheses are that transplantation's limitations result from inadequate grafts, due to poor survival of implanted cells, lack of critical growth factors, or nonphysiological graft placements and distribution. This program proposes to test these hypotheses with strategies which may improve functional benefits--the primary outcome measure of all studies in MPTP parkinsonian monkeys. Project One targets early cell death after grafting, with strategies to reduce oxidant stress, hypoxia/ischemia, and apoptosis using cell adhesion factors, the lazaroid tirilizad mesylate, melatonin, vascular endothelial growth factor, and cAMP. Project Two focuses on growth factors produced by fetal striatum enriched in astrocyte progenitor cells, or the growth factor, GDNF, delivered from encapsulated cells. An optimized method will be tested to determine benefits of combined methods in young adult and aged monkeys. Project Three aims to restore the relevant dopamine pathways by implantation of substantia nigra (SN) precursor tissue into SN and directing its outgrowth to the target areas, using co-grafted fetal striatal cells, or GDNF delivery. Duration of and stability of behavioral improvement, possible dyskinesias, or other toxic effects will be evaluated for three years and compared with striatal grafts. Quantitative behavioral effects will be correlated with biochemical and morphological measurements post-mortem. These studies may contribute to improving graft survival, reinnervation, and physiological restoration of the defective dopamine circuits and normalizing function. Although considerable preliminary work has been done in rodents, and because definitive controlled experiments with verifiable outcomes cannot be accomplished in humans, hypotheses and safety should be tested in the MPTP model in monkeys. The projects will be undertaken jointly by the program investigators, applying the resources of a unique primate transplantation laboratory (Core A) and shared outcome methodologies, all coordinated by a program support unit (Core B). Understanding of fetal precursor cell survival and outgrowth may also lead to improved understanding of the plasticity and function of other potential replacement cells, such as stem cells, and be relevant to other human neurodegenerative or traumatic conditions in addition to Parkinson's disease.