NEUROPATHOLOGICAL SEQUELAE OF LONG-TERM ALLOGENEIC AND SYNGENEIC NEURAL TRANSPLANTATION INTO THE HIPPOCAMPUS

The long-term fate of multiple intrahippocampal allogeneic transplants of fetal basal forebrain tissue was studied in neonatally tolerised a nd immunised groups of rats with lesions of the fimbria-fornix, Despit e the good survival of the allografts in all groups, unexpected transp lant-associated host hippocampal neuropathology was discovered 12 mont hs after transplantation, which consisted of (i) CA1 cell degeneration and (ii) abnormal accumulations of phosphorylated neurofilaments in n euronal perikarya and axonal swellings only within the host hippocampa l neuropil and not of the transplanted tissue, This neurofilament abno rmality, identified by RT97 immunohistochemistry, was significantly gr eater in the transplanted rats compared to the non-grafted lesion-only and sham-lesioned rats (p<0.01), The same type of neurofilament abnor mality was again observed in a second, separate experiment using unila teral and bilateral syngeneic and allogeneic transplants, The neuropat hology was significantly (p<0.05) greater in the transplanted side of the unilateral transplanted rats compared to the non-transplanted lesi on-only control side of the same animals, showing that transplantation per se was a major factor involved in the pathogenesis of this neurop athology, irrespective of the type of transplant (syngeneic or allogen eic), In addition, a small degree of neurofilament abnormality was als o found within the transplants in the second experiment, but not in th e first, The results show that, under certain conditions, specific loc al neuropathological damage to the surrounding host neural tissue can develop in long-surviving allografted and syngrafted animals.