Figure 2.

Schematic of glymphatic and perivascular waste clearance routes. According to the glymphatic model, cerebrospinal fluid (CSF) flows along para-arterial spaces (1), mixes with interstitial fluid (ISF) and solutes (2), and is cleared from the brain along para-venous spaces (3). Efficient glymphatic clearance of waste and solutes is dependent on fluid movement across aquaporin-4 (AQP4) channels located on astrocytic endfeet surrounding the parenchymal vasculature. In contrast, perivascular drainage of ISF and solutes occurs along the middle layers of the basement membrane of arterial smooth muscle cells and, as indicated by arrows, flows in a direction opposite to that of glymphatic clearance. Reprinted with permission from Macmillan Publishers Ltd: © Tarasoff-Conway et al. (2015).