Fig. 3: Variability in intimal pial and epipial relationships give rise to distinct PAS architectures in superficial brain regions.

As shown on volumetric lightsheet image of a tissue-cleared (CLARITY) specimen, the intimal pia and epipia adjoin at the brain surface and create a basket-like sieve around penetrating arterioles (a). The anatomy is further delineated on confocal Z-stack images of longitudinal and axial cortical mouse brain sections (b). Heterogeneous relationships of the intimal pia and epipia around penetrating arterioles result in a spectrum of periarteriolar space (PAS) anatomy, with three primary structures in healthy young mouse brains: Type A (c), Type B (d), or Type C (e); white arrows represent separate pial sheaths (i.e., the intimal pia and epipia), while arrowheads mark sites of pial coalescence with the tunica media. The variable anatomy are depicted in longitudinal images with enlargements of boxed areas (c–e, left-hand side) and axial schematics (c–e, right-hand side) that depict deeper levels, from left to right (labeled 1–4, respectively). Type A PAS is shown in relation to an unsheathed arteriole (i.e., an arteriole lacking epipial coverage at the site of brain penetration). The distribution of PAS types at the brain surface is summarized in (f). PAS types are further characterized according to brain region (g) and vessel size (h and i); one-way ANOVA with Tukey’s multiple comparisons test; n = 57 vessels from 6 mice. a–e Red/CY3, SMA; green/FITC, ERTR7; blue, DAPI or lectin; violet/CY5, aquaporin 4; scale bars = a, e 50 μm; b, c 10 μm; d 30 μm. Source data are provided as a Source Data file.