Extended Data Fig. 4: Capillaries in the middle and on the venule side of the capillary bed are a major vascular compartment, covered by pericytes that generate contractile tone in response to laser injury (unlike pericytes and SMCs on the arteriole side of the vascular bed).

a 3D capillary tracing of barrel cortex microvasculature in vivo from the start of the 1^st capillary branch off a penetrating arteriole (star, also shown in (b) as a z projection without the overlying pial artery; note that in (a) the arteriole is hidden behind the artery) to the start of the venule (diamond) connecting to a pial vein in an NG2-Cre^ERT2-GCaMP5g WT mouse (with Texas Red given i.v.). Left bar graph: shortest capillary length between PA and AV. Right bar graph: capillaries of the >3^rd branch order comprise >90% of the total capillary length in WT and AD mice. b Left: low magnification in vivo two-photon z projection of capillaries branching from arteriole (star marking start of 1^st capillary branch as shown in 3D in (a)) in WT mouse. Branching orders in high magnification images on the right and in the bottom [Ca²⁺]_i traces are indicated as numbers; these images are color-framed (according to position in vascular bed, see inset) and shown pre- and post-laser injury. Bottom traces: laser injury evoked [Ca²⁺]_i rises increase with increasing vessel branching order (see also Fig. 3d–h and Supplementary Video 4). The 7th order capillary in the low power view is the same capillary rotated in Fig. 3e. c-d Laser injury does not significantly modulate [Ca²⁺]_i or diameter of arterioles (c) or 1^st-2^nd order capillaries (d) in WT mice (see also Supplementary Video 5). P-values are 2-tailed. Error bars are s.e.m.

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