PROLIFERATION AND DIFFERENTIATION OF TRANSPLANTED EMBRYONIC DIENCEPHALON IN THE BRAIN OF ADULT-RATS

The survival, proliferation potential, differentiation, and host tissu e reaction of allografts of undifferentiated embryonal diencephalic ti ssue (E12.5, E17.5) transplanted into or around the third ventricle of adult rats were investigated. Rats harboring grafts were sacrificed a t three, six, and nine weeks after transplantation. The proliferative activity of the grafts was assessed by injection of 5'-bromo-2'-deoxyu ridine (BrdU) into pregnant rats before the removal of fetuses for tra nsplantation, and staining the grafts using an anti-BrdU antibody. The proliferative activity of the transplanted grafts was evaluated by im munostaining using an anti-proliferating cell nuclear antigen (PCNA) a ntibody. The differentiation of the grafts into neurons was estimated by double immunostaining using anti-BrdU and anti-neuron-specific enol ase (NSE) antibodies. The survival rate of the grafts was strongly rel ated to the proliferative activity of the graft. Surviving E17.5 graft s contained immunoreactive BrdU cells. E12.5 grafts could survive with out immunoreactive BrdU cells. Undifferentiated E12.5 grafts prolifera ted up to six weeks after transplantation. Thereafter, most graft cell s differentiated into mature neurons. E12.5 diencephalic allografts su rvived well with minimal rejection reactions and resulted in substanti al neurite ingrowth into the host brain, while E17.5 allografts caused substantial reactive gliosis and little ingrowth.