NEOVASCULARIZATION AND THE APPEARANCE OF MORPHOLOGICAL-CHARACTERISTICS OF THE BLOOD-BRAIN-BARRIER IN THE EMBRYONIC MOUSE CENTRAL-NERVOUS-SYSTEM

Vascularization and expression of blood-brain barrier (bbb)-associated morphological characteristics during the embryonic development of the mouse cnetral nervous system (CNS) was studied by ultrastructural ana lysis. At embryonic day 9 (E9) capillaries were only found in the peri neural mesenchymal tissue. These capillaries showed fenestrations, and pericyte like cells (PC) were found joined to the vessel walls. Aroun d E10 endothelial cells (EC) together with PC started invading the int raneural section. At this stage, the immigrating endothelial cells los t their fenestrations and exhibited numerous, partly extended junction al complexes, which appeared 'tight' in some places. A first intraneur al anastomotic plexus was observed at E10, as evidenced by the presenc e of blood cells in all capillary lumens. While the number of junction al complexes remained constant in intraneural capillaries, the frequen cy of pinocytotic vesicles decreased significantly from E10 to E17. Th ese findings indicate that from the first day of intraneural vasculari zation onwards, the morphological properties of the bbb are present in the early embryonic mouse cerebral cortex.