Neovascularization of the dorsal root ganglia transplanted into the olfactory bulb of neonatal rats

Dorsal root ganglia (DRG), whose vessels are permeable to blood-born proteins, were syngenically transplanted into 2-5 day old Wistar albino rats after partial unilateral bulbectomy. Our aim was to follow survival and vascularization of the DRG, transplanted into a new environment, the developing olfactory bulb (OB). Three months after grafting the DRG graft was found fused with the spared portion of the OB. Only a subpopulation of the transplanted neurons survived the transplantation. Cholinesterase histochemistry showed BuChE positive vessels of host origin around the surviving DRG neurons. The majority of the vessels was impermeable to i.v. applied fluorescent dyes (Evans blue and lucifer yellow) and only few (1-3 vessel profiles/section) of them were labeled at the graft surface. By lanthanum nitrate tracing at the ultrastructural level, tight junctions were seen in the majority of the blood vessels of the graft. Our study shows that during the neovascularization the transplanted DRG is invaded by the host-derived blood vessels which possess blood brain barrier properties - they are impermeable to applied micro - and macromolecules. The newly formed/reestablished circulation appeared to be sufficient for maintaining a subpopulation of the transplanted sensory neurons.