Proliferation and differentiation of transplanted embryonic diencephalon in the brain of adult rats.

The survival, proliferation potential, differentiation, and host tissue reaction of allografts of undifferentiated embryonal diencephalic tissue (E12.5, E17.5) transplanted into or around the third ventricle of adult rats were investigated. Rats harboring grafts were sacrificed at three, six, and nine weeks after transplantation. The proliferative activity of the grafts was assessed by injection of 5'-bromo-2'-deoxyuridine (BrdU) into pregnant rats before the removal of fetuses for transplantation, and staining the grafts using an anti-BrdU antibody. The proliferative activity of the transplanted grafts was evaluated by immunostaining using an anti-proliferating cell nuclear antigen (PCNA) antibody. The differentiation of the grafts into neurons was estimated by double immunostaining using anti-BrdU and anti-neuron-specific enolase (NSE) antibodies. The survival rate of the grafts was strongly related to the proliferative activity of the graft. Surviving E17.5 grafts contained immunoreactive BrdU cells. E12.5 grafts could survive without immunoreactive BrdU cells. Undifferentiated El2.5 grafts proliferated up to six weeks after transplantation. Thereafter, most graft cells differentiated into mature neurons. E12.5 diencephalic allografts survived well with minimal rejection reactions and resulted in substantial neurite ingrowth into the host brain, while El7.5 allografts caused substantial reactive gliosis and little ingrowth.