Survival and growth of fetal catecholamine neurons transplanted into primate brain

Dopamine and norepinephrine neuroblasts of the ventral mesencephalon, hypothalamus, and dorsolateral pons were transplanted from fetal African green monkeys into multiple brain sites in adult (host) African green monkeys. Tissue was grafted from both early and late gestational age fetuses. Immunohistochemical analysis, with antibodies to tyrosine hydroxylase, a marker of catecholamine-containing neurons, showed large numbers of transplanted catecholamine neurons in host cerebral cortex, corpus striatum and lateral ventricles up to 69 days after transplantation. Serial reconstructions revealed extensive outgrowth of neuronal processes from large numbers of transplanted neurons as well as expansion of the size of transplanted (solid) grafts of fetal brain tissue in the host brain. Some grafts extended from the caudate nucleus into the adjacent lateral ventricles or from the cerebral cortex into the underlying corpus callosum and ventricle. There were dense networks of varicose fibers emanating from the tyrosine hydroxylase positive neurons within intraparenchymal and intraventricular grafts. The size and shape of transplanted neurons retained characteristics common to catecholaminergic neurons from the dissected regions of fetal brain. Thus, a variety of fetal, catecholamine-containing neurons survive transplantation to primate brain and produce extensive neuritic outgrowths. Moreover, rejection of transplanted tissue was not apparent. These findings provide essential information on nerve cell grafting in a species closely related to humans as a prerequisite in the consideration of neural transplants as therapeutic measures in neurological disease.