Fig. 1

General representation of structural and cellular differences between GM and WM: the brain is approximately segmented in equal volumes of GM and WM, where the cellular composition differs considerably. GM has a high non-myelinated neuronal content and lesser extent of myelinated axons. WM is composed of both myelinated and non-myelinated axons; with higher myelin content is responsible for its whitish appearance. Similarly, GM and WM also exhibit differences in other resident brain cell types, including astrocytes, glial cells in number and morphology. These differences in the immediate environment of the vasculature may confer specific differential WM and GM vascular phenotypes that may be reflected in amount and organization of tight junctions, expression of various receptors, transporters and responses to stimuli in neurovascular diseases