Nitric oxide not superoxide radicals mediate neurovascular coupling during NMDA receptor activation.

NMDA receptors contribute to the cerebral blood flow (CBF) increase initiated by synaptic activity via nitric oxide (NO) (Circ Res. 72: , 1993). However, NMDA receptor activation generates reactive oxygen species (ROS), which, either directly or by scavenging NO, could modulate the CBF response. Therefore, we examined the role of NO and ROS in the CBF increase produced by NMDA. In anesthetized mice neocortical application of NMDA (40μM) increased CBF (21±3%), assessed by laser‐Doppler flowmetry, and ROS (41±6%; p<0.05), assessed with hydroethidine. CBF and ROS increases were blocked by the neuronal NO synthase (nNOS) inhibitor 7‐NI and were absent in nNOS−/− mice. ROS production, but not the CBF increase, was blocked by the ROS scavenger MnTBAP and was absent in mice lacking nox2, a NADPH oxidase subunit. The soluble guanylyl cyclase inhibitor ODQ attenuated the increase in CBF and ROS, an effect reversed by exogenous cGMP. KT5823, an inhibitor of the cGMP effector enzyme PKG, attenuated CBF and ROS increases. In neuronal cultures, NMDA increased ROS (60±17%; p<0.05), an effect blocked by MK801, MnTBAP, the NOS inhibitor L‐NNA, a peptide inhibitor of nox2, ODQ or KT5823. Thus, NMDA increases CBF through nNOS‐derived NO, and ROS through nox2. Both the vasodilation and ROS production are dependent on NO, cGMP and PKG, but neuronal NO is the critical factor mediating the hyperemia. Supported by HL18974 and NS37853