Stimulation-induced increases in cerebral blood flow and local capillary vasoconstriction depend on conducted vascular responses

Significance Pericytes are located at the outside wall of capillaries. However, whether and how pericytes are involved in the regulation of blood flow in brain capillaries is still debated. We report that capillary vascular responses are mostly initiated and peak at near-arteriole capillaries. These vascular responses are conducted along capillaries at a speed of 5–20 µm/s. Conducted vascular responses in brain capillaries appear to involve pericytes, the mural cells of microvessels, and may be a novel modulator of vascular function in the brain. Functional neuroimaging, such as fMRI, is based on coupling neuronal activity and accompanying changes in cerebral blood flow (CBF) and metabolism. However, the relationship between CBF and events at the level of the penetrating arterioles and capillaries is not well established. Recent findings suggest an active role of capillaries in CBF control, and pericytes on capillaries may be major regulators of CBF and initiators of functional imaging signals. Here, using two-photon microscopy of brains in living mice, we demonstrate that stimulation-evoked increases in synaptic activity in the mouse somatosensory cortex evokes capillary dilation starting mostly at the first- or second-order capillary, propagating upstream and downstream at 5–20 µm/s. Therefore, our data support an active role of pericytes in cerebrovascular control. The gliotransmitter ATP applied to first- and second-order capillaries by micropipette puffing induced dilation, followed by constriction, which also propagated at 5–20 µm/s. ATP-induced capillary constriction was blocked by purinergic P2 receptors. Thus, conducted vascular responses in capillaries may be a previously unidentified modulator of cerebrovascular function and functional neuroimaging signals.