Expression of platelet-derived growth factor in and around intrastriatal embryonic mesencephalic grafts

The expression of platelet-derived growth factor (PDGF) was investigated in the embryonic donor tissue and surrounding host brain before and after intracerebral transplantation in a rat model of Parkinson's disease (PD). Ventral mesencephalic tissue from E13-E15 rat embryos was dissociated and implanted into adult rats with unilateral lesions of the mesostriatal dopamine system. Immunohistochemical studies showed that the majority of the grafted cells were PDGF-positive at early time points after grafting. However, the immunostaining gradually decreased, and had disappeared almost completely 3 wk after transplantation. These results were in agreement with in situ hybridization data demonstrating detectable levels of mRNA for PDGF chains in graft cells after 1, but not after 6 wk. In contrast, a large number of PDGF-immunoreactive cells was observed in the host brain adjacent to the grafts from 1 wk after transplantation, and increasing with time. Increased expression of PDGF was also observed in response to a sham-operation (injection of vehicle), although the number of PDGF-positive cells seemed lower than after grafting of embryonic tissue. Double immunofluorescence labeling of these cells with an anti-glial fibrillary acidic protein (GFAP) antiserum and a monoclonal antibody against PDGF B-chain, indicated that the PDGF-positive cells were astrocytes. The dynamic expression of PDGF in and around intrastriatal embryonic mesencephalic implants has several, potentially important, implications for graft survival and function. Glial cells could utilize the elevated levels of PDGF to proliferate in a reactive gliosis, and PDGF might also augment immune responses. It is also possible that PDGF increases the survival of, and promotes neurite outgrowth from, grafted dopaminergic neurons.