Transplantation of polymer-encapsulated fetal hippocampal cells into ischemic lesions of adult rat hippocampus.

In a previous study we demonstrated that fetal hippocampal cells, when transplanted into ischemic lesions of the adult rat hippocampus, can survive in large numbers in the host brain and show the innervation of the transplants by cholinergic fibers originated from the host brain. The present study was undertaken in an attempt to elucidate the hypothesis that the fiber connections forming synapses between the transplanted fetal neurons and the host brain play an important role in the survival of the transplanted cells. We transplanted the polymer-encapsulated fetal hippocampal cells prepared from E17-18 rat fetuses into the ischemic lesions in the adult rat hippocampus at which the CA1 pyramidal cells selectively died, and examined both histochemically or immunohistochemically for their survival and the expression of the synaptic vesicle protein, synaptophysin, and dendritic cytoskeltal protein, microtubule-associated protein 2 (MAP 2) within them. In addition, the cholinergic fibers originated from the host brain were examined by acetylcholine esterase (AChE) histochemistry. The results demonstrated that the polymer-encapsulated hippocampal cells could survive in the brain; however, the number of surviving cells markedly decreased following the transplantation, whereas no host-derived cholinergic fibers penetrated the polymer membrane of the capsules following the transplantation. In the cluster of surviving cells, only slight synaptophysin expression and no extensive growth of the dendrites were detected. The present results indicate that the direct contact between the host brain tissue and the transplant play an important role in the survival of such allografted neurons.