Fig. 5

Arterial wall permeability is bi-directional. Tracer introduced into the CSF travel along the Glymphatic path and can penetrate from the perivascular space across arteriolar walls towards the luminal direction. a, b 30 min CSF tracer challenges with Alexa-647 conjugated dextran (10 kDa, cisterna magna injections) and immunostaining for SMA and CD31 of wild-type adult brain sections. (L) marks the vessel lumen. Dashed arrows marks tracer direction towards the lumen. Scale bars 10 µm a Precise nano-scale localization with dSTORM imaging shows tracer signals located along the CSF-blood trajectory. Inset (a’ scale bars 2 µm) magnifications demonstrating tracer signals between smooth-muscle and endothelium markers (arrows), and at the endothelium luminal side (arrowhead). b Based on tracer signal distribution, especially at high magnification (inset b’ scale bars 100 nm), we identify tracer clusters that fit the dimensions of transcytosis vesicles. These vesicle-like structures are located in smooth muscle cells (arrowheads, in 1 and 2). Elongated distribution might represent tracer filled basement membrane between the smooth muscle and the endothelial cell (arrow, in 2). Vesicle-shaped structures that are connected to the basement membrane resemble the ultrastructure of flask shape membrane pits (astrix); n = 3 mice, 12 arterioles