Neovascularization and the Blood-Brain Barrier in Neural Transplantation

The formation of new blood vessels from existing vessels (angiogenesis) is mandatory for organ and tissue development, and differs in degree from vasculogenesis, which is the de novo formation of the rudimentary vasculature in the early embryo. Angiogenesis is a continuous event in digestive and reproductive systems, but, in the brain, the endothelial cells (ECs) that comprise the vasculature and proliferate at a moderate pace in development, essentially cease cell division by 2 wk postnatal. ECs, and thus the capillary beds, are entirely stable in the mature brain, and EC division is practically nil. Angiogenesis in the mature brain occurs only after conditions of injury or neuropathological event. Vascular growth has been documented following diverse injuries, such as penetrating wound, inflammation, or ischemic incident.