The brain dynamically regulates its blood supply presumably to meet neuronal metabolic demands. We identified a sparse, long-projecting population of inhibitory neurons expressing NOS and Tachykinin receptor 1 (Tacr1) that strongly regulate cerebral blood flow. They respond to excitatory feed-forward input and their processes come in close contact with astrocytic end-feet and blood vessels, suggesting that Tacr1 neurons integrate cortical activity to regulate blood supply.