(A) Red blood cells were detected in embryonic brains using an antibody against TER119. Ventricles are delineated by green dotted lines. Boxes indicate magnified areas. Hemorrhages are identified by the presence of TER119⁺ cells outside of CD31⁺ areas, as shown in Tgfbr2^ΔiEC/ΔiEC embryos. Representative image of 2 Tgfbr2^ΔiEC/ΔiEC embryos. Scale bars: 100 μm. (B) Embryos were injected intrahepatically with 10 kDa dextran labeled with TMR at E18.5. The fluorescence of the labeled dextran was observed in brain sections stained for GFP and CD31 to test the ability of the tracer to leak into the brain parenchyma. Scale bar: 100 μm. (C) Endogenous mouse IgG was detected in brain sections at E18.5 with a fluorescently labeled antibody. Sections representative of brain parenchyma of the indicated number of embryos are shown. Scale bar: 100 μm. (D) Flvcr2 inactivation was induced by injecting tamoxifen in the indicated number of adult mice, and animals were perfused with sulfo-NHS-biotin 10 days after the last induction. (E) Biotin presence was detected with fluorescently labeled streptavidin in brain, and localization outside of CD31⁺ cells was assessed. Scale bar: 100 μm. (F) Recombination was induced in adult mice, and Evans blue was injected i.p. 10 days later. Brains were collected after perfusion and photographed intact. n = 3. (G and H) Fluorescently labeled cadaverine was injected i.v. into WT and Flvcr2^ΔiEC/ΔiEC mice, and brains were collected 3 hours later. The brain from one animal was sectioned to visualize dye localization. Scale bar: 100 μm. Brains from cadaverine-injected mice were homogenized and tissue fluorescence was quantified. n = 4.