Fig. 2
From: Flow of cerebrospinal fluid is driven by arterial pulsations and is reduced in hypertension
Perivascular spaces (PVSs) are larger in vivo and collapse after fixation. a Fluorescent dextran in the CSF confirms the size of the PVS in vivo. b Cross-section at the dashed line in a, showing two PVSs with tracer. c Cross-sections proximal, across, and distal to a bifurcation show that the non-connecting PVS structure continues. d Average measurements of the width of the PVS from superimposed microsphere trajectories (e.g., Fig. 1b). Mean ± SEM, n = 13 mice. e To test whether the PVS and CSF tracer distribution were modified during tissue processing, we perfusion fixed a live anesthetized mouse with f phosphate-buffered saline (PBS) followed by g 4% paraformaldehyde (PFA) to h fix the tissue (Supplementary Movie 1). Diagrams are included below each image indicating our observations. Scale bar: 30 µm. i The vasculature was labeled with a lectin in the PBS perfusion solution and the same vessel in the same animal shown in a was imaged after fixation. It was necessary to remove dura to image the same vessels in situ due to the shrinkage of the brain. Small arrows point to a fold in the collapsed artery wall and tracer being redistributed around a pial vein. Overlapping lectin and dextran appear yellow. Scale bar: 40 µm. j Cross-section at the dashed line in i shows that after fixation, the vessel collapses and folds, and the tracer redistributes around the arterial wall. Scale bar: 20 µm. k To quantify the size of the PVS compared to that of the artery, we computed the ratios of the areas of the PVS and the adjacent artery for in vivo measurements utilizing tracked microspheres and dextran dye and after fixation (fixed). The lateral area of the PVS is roughly 1.4 ± 0.1 times larger than that of the artery itself in the live mice, and fixation reduces this ratio to about 0.14 ± 0.04. One-way analysis of variance (ANOVA) post hoc Tukey's test, ***P < 0.0002, ns not significant, mean ± SEM, n = 6–7/group
