Parameters affecting the survival of cultured and grafted embryonic neurons

Abstract: The extent of behavioral recovery following neural transplantation in part depends on the amount of surviving graft tissue. The main objective of this thesis was to study parameters affecting the survival of embryonic striatal and mesencephalic neurons in experimental models of Huntington's and Parkinson's disease. Firstly, we studied the survival and maturation of embryonic striatal neurons that could be suitable to replace striatal neurons lost in Huntington's disease. Neuronal phenotypes specific for the striatum were most likely to develop in human embryonic cell cultures and xenografts prepared from the lateral ganglionic eminence, although striatal-specific "P-zones" comprised less than 30% of total graft volumes. Positive immunostaining for proliferating cell nuclear antigen and growth-associated protein-43 suggests that the paucity in P-zones was most likely due to an incomplete maturation of human striatal xenografts still 3-6 months following transplantation. Secondly, in order to ensure the procurement of sufficient amounts of embryonic donor tissue for transplantation at a given timepoint, we established different tissue preservation techniques. Rat striatal transplants exhibited unimpaired survival following 5 days preservation at 4° ("hibernation" medium with a "lazaroid", and inhibitor of lipid peroxidation, mesencephalic dopamine neurons survived 8 days hibernation without major loss in viability upon subsequent culturing or grafting. Thirdly, we attempted to increase the number of dopamine neurons harvested from one embryonic brain. In human diencephalic transplants, only low numbers of faintly tyrosine hydroxylase-immunoreactive neurons were retreived. Inhibition of lipid peroxidation by lazaroids prior to and during transplantation significantly enhanced the survival of mesencephalic dopamine neurons. Finally, we characterized three models of induced cell death and found that mesencephalic neurons are highly susceptible to serum-deprivation, nitrogen monoxide toxicity and glutathione depletion. The administration of a lazaroid efficiently prevented neurotoxicity in these insult models suggesting that lipid peroxidation is a crucial factor in dopamine neuron death. In the future, lazaroids might exert beneficial effects as neuroprotective agents in clinical transplantation trials or the progressive neurodegenerative process underlying Parkinson's disease.