Vascular morphology and permeability in fetal CNS grafts to the renal capsule

According to conventional neovascularization concepts, due to local tissue factors, a viable graft of central nervous (CNS) tissue should be expected to retain a complete blood-brain barrier (BBB) in its new site. In order to determine if grafted CNS would alter the phenotype of ingrowing peripheral vessels we have used an uncomplicated model. Rat fetal cortex, which already has a BBB to protein, was grafted to the subcapsular space of the host rat kidney. After postoperative times between 4 weeks and 3 months, horseradish peroxidase was injected systemically for periods between 90 s and 4 min. Correlative electron microscopy depicted vascular morphology. Each graft contained protein exudation particularly around large vessels in the neuropil. At the EM level some of the vascular endothelia had fenestrations, were invested with collagen, and were not contacted by astroglia. Capillaries indigenous to the CNS grafts and related normally to astroglial end feet were also prominent. The presence of non-CNS vessels with peripheral ultrastructural and permeability characteristics would appear to contradict conventional theory in that CNS grafts can be vascularized by vessels of a different phenotypic and physiologic nature.