Vascularization in the brain during development is
derived from a preformed perineural vascular plexus
and occurs almost exclusively through sprouting angiogenesis that starts at embryonic day 9 in vertebrates
[63]. Angiogenesis is the formation of new vessels from
existing vessels. Sprouting angiogenesis is an invasive
process that involves proteolytic activities required for
degradation of the basal lamina, with pericyte and
endothelial migration through tissue matrix [63]. During
vessel formation, the recruitment of pericytes and astrocytes to newly-forming vascular tubes is closely associated with the formation of tight junctions. At P4,