Endothelial N-methyl-D-aspartate receptors mediate neurovascular coupling in mice

Local neuronal activity is coupled with local changes in cerebral blood flow. This neurovascular coupling process ensures that active brain regions receive proportional increases in local blood flow in order to meet the metabolic needs of neurons. Important mediators of vasodilation and hyperemic responses include neuronal N-methyl-D-aspartate receptors (NMDARs) functionally linked to neuronal nitric oxide synthase (nNOS) and NO production, as well as active perisynaptic astrocytes whose end-feet processes ensheathe local blood vessels. Neurovascular coupling requires multidirectional signaling between the cells of the neurovascular unit, including neurons, astrocytes, contractile mural cells and endothelial cells. Recent evidence suggests that changes in cerebral blood flow require both local vasodilatory events and propagation of vasomotor signals upstream. In peripheral vascular beds, endothelial cells are known regulators of local vascular tone and are important mediators of vasomotor responses. Similarly, cerebral endothelial cells are thought to be critical components of a full hyperemic response in brain, yet it is not well understood how vasoactive signals from the brain reach the vasculature to initiate vasomotor responses. Previously, we showed that astrocyte-mediated vasodilation involves both endothelial NOS (eNOS) and endogenous NMDAR agonists. We hypothesized that endothelial NMDARs (eNMDARs) activate eNOS and are necessary for neurovascular coupling. We demonstrated that eNMDARs are functionally linked to eNOS activity. Secondly, we provided the first evidence that eNMDARs are localized to the abluminal vascular surface in an orientation suitable for receiving vasodilatory signals from cellular elements of the neurovascular unit. In cortical slices, we demonstrated a novel vasodilatory signaling axis between perivascular astrocytes and endothelial cells that is dependent on eNMDARs and eNOS. To investigate this axis further, we developed an elegant, a