Neurovascular coupling and briefCO ₂ interrogate distinct vascular regulations

Neurovascular coupling (NVC), which mediates rapid increases in cerebral blood flow in response to neuronal activation, is commonly used to map brain activation or dysfunction. Here we tested the reemerging hypothesis that CO ₂ generated by neuronal metabolism contributes to NVC. We combined functional ultrasound and two-photon imaging in the mouse barrel cortex to examine specifically the onsets of local changes in vessel diameter, blood flow dynamics, vascular/perivascular/intracellular pH, and intracellular calcium signals along the vascular arbor in response to briefCO ₂ , a short and strong hypercapnic challenge (10 s, 20%) and whisker stimulation. We report that briefCO ₂ reversibly acidifies all cells of the arteriole wall and the periarteriolar space 3-4 seconds prior to the arteriole dilation. During this prolonged lag period, NVC triggered by whisker stimulation is not affected by the acidification of the entire neurovascular unit. As it also persists under condition of continuous inflow of CO ₂ , we conclude that CO ₂ is not involved in NVC.