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 hypot hesis that the fiber connections forming synapses between the transpla nted fetal neurons and the host brain play an important role in the su rvival of the transplanted cells. We transplanted the polymer-encapsul ated fetal hippocampal cells prepared from E17-18 rat fetuses into the ischemic lesions in the adult rat hippocampus at which the CA1 pyrami dal cells selectively died, and examined both histochemically or immun ohistochemically for their survival and the expression of the synaptic vesicle protein, synaptophysin, and dendritic cytoskeletal protein, m icrotubule-associated protein 2 (MAP 2) within them. In addition, the cholinergic fibers originated from the host brain were examined by ace tylcholine esterase (AChE) histochemistry. The results demonstrated th at the polymer-encapsulated hippocampal cells could survive in the bra in; however, the number of surviving cells markedly decreased followin g the transplantation, whereas no host-derived cholinergic fibers pene trated the polymer membrane of the capsules following the transplantat ion. In the cluster of surviving cells, only slight synaptophysin expr ession and no extensive growth of the dendrites were detected. The pre sent results indicate that the direct contact between the host brain t issue and the transplant play an important role in the survival of suc h allografted neurons.