Supplementary Figure 1: Schematic diagram of the mechanisms underlying neurovascular signalling to capillaries and arterioles.

Synaptic activity (top) evokes ATP release from post-synaptic neurons, which activates ionotropic ATP receptors containing P2X₁ subunits on astrocytes, leading to a rise in [Ca²⁺]_i via influx from the extracellular space. This rise in [Ca²⁺]_i activates PLD2, resulting in the formation of phosphatidic acid (PA) which is converted into diacylglycerol (DAG), which is then further metabolized by DAG lipase into arachidonic acid (AA). AA is then metabolized, by the consecutive activity of COX1 and PGES, to produce PGE₂, which dilates capillaries by acting on EP₄ receptors, presumably on pericytes. Synaptic activation of Ca²⁺ entry through NMDA receptors increases NOS activity in interneurons, resulting in NO release onto arterioles to dilate them. The neurovascular coupling pathways involved in signalling to capillaries and arterioles are highlighted in blue, while the enzymes and receptors ruled out by our experiments are shown in red with black crosses.