Astrocytic Gq-GPCR-Linked IP3R-Dependent Ca2+ Signaling Does Not Mediate Neurovascular Coupling in Mouse Visual Cortex In Vivo

Local blood flow is modulated in response to changing patterns of neuronal activity (Roy and Sherrington, 1890), a process termed neurovascular coupling. It has been proposed that the central cellular pathway driving this process is astrocytic Gq-GPCR-linked IP3R-dependent Ca2+ signaling, though in vivo tests of this hypothesis are largely lacking. We examined the impact of astrocytic Gq-GPCR and IP3R-dependent Ca2+ signaling on cortical blood flow in awake, lightly sedated, responsive mice using multiphoton laser-scanning microscopy and novel genetic tools that enable the selective manipulation of astrocytic signaling pathways in vivo. Selective stimulation of astrocytic Gq-GPCR cascades and downstream Ca2+ signaling with the hM3Dq DREADD (designer receptors exclusively activated by designer drugs) designer receptor system was insufficient to modulate basal cortical blood flow. We found no evidence of observable astrocyte endfeet Ca2+ elevations following physiological visual stimulation despite robust dilations of adjacent arterioles using cyto-GCaMP3 and Lck-GCaMP6s, the most sensitive Ca2+ indicator available. Astrocytic Ca2+ elevations could be evoked when inducing the startle response with unexpected air puffs. However, startle-induced astrocytic Ca2+ signals did not precede corresponding startleinduced hemodynamic changes. Further, neurovascular coupling was intact in lightly sedated, responsive mice genetically lacking astrocytic IP3R-dependent Ca2+ signaling (IP(3)R2 KO). These data demonstrate that astrocytic Gq-GPCR-linked IP3R-dependent Ca2+ signaling does not mediate neurovascular coupling in visual cortex of awake, lightly sedated, responsive mice.