[Growth of the graft and astrocytic reaction following transplantation of fetal brain to adult rat's brain. Part I: Tissue transplantation into cerebral cortex, lateral ventricle, subarachnoid space and cerebral cortical cavity].
Brain transplantation has been examined as one of the therapeutic methods in the animal models of Alzheimer's disease. Among a lot of problems inherent to therapeutic brain transplantation, we have investigated implanting techniques and methods. Small pieces of fetal basal forebrain tissue containing cholinergic neurons were transplanted into adult rats' cerebral cortex, lateral ventricle, subarachnoid space, and the cerebral cortical cavity which had been made 10 days before transplantation (delayed cavity technique). Two to 3 months after transplantation, growth of the grafts, neurites elongation and astrocytic reaction were observed by Nissl staining, histochemical staining for acetylcholinesterase and immunocytochemical staining for glial fibrillary acidic protein (GFAP). Intracortical grafts were small and surrounded by thick glial scar formation, but there was found a partial lack of glial scar and host-graft neuronal integration was also observed. Both intraventricular and subarachnoid grafts grew relatively well. GFAP-immunoreactive cells had a tendency to gather near the margin of the graft and perivascularly. These facts seemed to suggest that reactive astrocytes were also taking part in support of the homeostasis of environments in the graft tissue. By delayed cavity technique, better growth of the grafts was observed, but dense glial and connective tissue scar tissues developed and prevented the outgrowth of neuronal processes. Nevertheless, hyperinnervation from graft to host cortex was partially noticed. It should be stressed that although the hyperinnervation may be effective for recovery of the host from the central nervous system damages, it may possibly damage the host's neuronal circuits.