... from the pia mater invade the brain and extend toward the ventricles [4] Like other vascular networks, brain vessels undergo formation, stabilization, branching, pruning and specialization In brief, ... transports water bidirectionally between the blood and the brain Astrocytes secrete water into the perivascular space via AQP4, thereafter maintaining water homeostasis in the brain environment ... vasoconstriction and vasodilation The thickness of the vSMC layer dif- Regulation of angiogenesis and barriergenesis fers according to the size of the vessels In the brain, pial arteries invade the brain parenchyma...