Figure 7. Neurovascular signalling to capillaries in vivo is mediated by P2X₁ receptors.

(a) Two-photon stack (90 µm thick, maximum intensity projection) of FITC-dextran-filled vessels (green) in the somatosensory cortex of an anaesthetised rat. (b) Enlarged image showing a penetrating arteriole with a capillary branching off it. (c-d) Example traces of forepaw stimulation-evoked dilation of arterioles (c) and capillaries (d) in the presence of vehicle (aCSF, black traces) or the P2X₁ blocker NF449 (5 μM; red traces). Capillary dilations occurred faster than arteriole dilations (time to 10% dilation was 3.0±0.8s for 12 capillaries and 5.1±1.7s for 9 arterioles), as previously reported⁶; however, reflecting the smaller number of vessels studied, this effect did not reach significance in this study (p=0.3). (e) The percentage of arterioles (Art) and capillaries (Cap) that dilated in response to stimulation was not significantly different in NF449 and vehicle-treated animals. (f) Forepaw stimulation-evoked mean arteriolar dilation was similar in vehicle and NF449 treated animals, but capillary dilation was significantly inhibited by NF449. Data are shown as box and whisker plots as defined in the Statistics part of the Methods.