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Background Normal brain function depends on the ability of the vasculature to increase blood flow to regions with high metabolic demands. Impaired neurovascular coupling, such as the local hyperemic response to neuronal activity, may contribute to poor neurological outcome after stroke despite successful recanalization, that is, futile recanalization. Methods and Results Mice implanted with chronic cranial windows were trained for awake head‐fixation before experiments. One‐hour occlusion of the anterior middle cerebral artery branch was induced using single‐vessel photothrombosis. Cerebral perfusion and neurovascular coupling were assessed by optical coherence tomography and laser speckle contrast imaging. Capillaries and pericytes were studied in perfusion‐fixed tissue by labeling lectin and platelet‐derived growth factor receptor β. Arterial occlusion induced multiple spreading depolarizations over 1 hour associated with substantially reduced blood flow in the peri‐ischemic cortex. Approximately half of the capillaries in the peri‐ischemic area were no longer perfused at the 3‐ and 24‐hour follow‐up (45% [95% CI, 33%–58%] and 53% [95% CI, 39%–66%] reduction, respectively; P P =0.001). Whisker stimulation at the 3‐ and 24‐hour follow‐up led to reduced neurovascular coupling responses in the sensory cortex corresponding to the peri‐ischemic region compared with that observed at baseline. Conclusions Arterial occlusion led to contraction of capillary pericytes and capillary flow stalling in the peri‐ischemic cortex. Capillary dysfunction was associated with neurovascular uncoupling. Neurovascular coupling impairment associated with capillary dysfunction may be a mechanism that contributes to futile recanalization. Hence, the results from this study suggest a novel treatment target to improve neurological outcome after stroke.

Cerebral arterial networks match blood flow delivery with neural activity. Neurovascular response begins with a stimulus and a focal change in vessel diameter, which by themselves is inconsequential to blood flow magnitude, until they spread and alter the contractile status of neighboring arterial segments. We sought to define the mechanisms underlying integrated vascular behavior and considered the role of intercellular electrical signalling in this phenomenon. Electron microscopic and histochemical analysis revealed the structural coupling of cerebrovascular cells and the expression of gap junctional subunits at the cell interfaces, enabling intercellular signaling among vascular cells. Indeed, robust vasomotor conduction was detected in human and mice cerebral arteries after focal vessel stimulation; a response attributed to endothelial gap junctional communication, as its genetic alteration attenuated this behavior. Conducted responses was observed to ascend from the penetrating arterioles, influencing the contractile status of cortical surface vessels, in a simulated model of cerebral arterial network. Ascending responses recognisedin vivoafter whisker stimulation, were significantly attenuated in mice with altered endothelial gap junctional signalling confirming that gap junctional communication drives integrated vessel responses. The diminishment in vascular communication also impaired the critical ability of the cerebral vasculature to maintain blood flow homeostasis and hence tissue viability, after stroke. Our findings establish the integral role of intercellular electrical signalling in transcribing focal stimuli into coordinated changes in cerebrovascular contractile activity and expose, a hitherto unknown mechanism for flow regulation after stroke.SignificanceNeurovascular responses are viewed as a one step process whereby stimuli derived from neural cells focally diffuse to a neighboring vessel, altering its contractile state. While focal changes in tone can subtly tune flow distribution, they can’t substantively change “perfusion magnitude” as vascular resistance is broadly distributed along the cerebral arterial tree. We report that nature overcomes this biophysical constraint by conducting electrical signals among coupled vascular cells, along vessels, and across branch points. Our quantitative exploration of intercellular conduction illustrates how network coordination optimizes blood flow delivery in support of brain function. Diminishing the ability of vascular cells to electrically communicate, mitigates the brain’s ability to regulate perfusion during functional hyperemia and after stroke, the latter advancing tissue injury.

Objective— Inward rectifying K + (K IR ) channels are present in cerebral arterial smooth muscle and endothelial cells, a tandem arrangement suggestive of a dynamic yet undiscovered role for this channel. This study defined whether distinct pools of cerebral arterial K IR channels were uniquely modulated by membrane lipids and hemodynamic stimuli. Approach and Results— A Ba 2+ -sensitive K IR current was isolated in smooth muscle and endothelial cells of rat cerebral arteries; molecular analyses subsequently confirmed K IR 2.1/K IR 2.2 mRNA and protein expression in both cells. Patch-clamp electrophysiology next demonstrated that each population of K IR channels was sensitive to key membrane lipids and hemodynamic stimuli. In this regard, endothelial K IR was sensitive to phosphatidylinositol 4,5-bisphosphate content, with depletion impairing the ability of laminar shear stress to activate this channel pool. In contrast, smooth muscle K IR was sensitive to membrane cholesterol content, with sequestration blocking the ability of pressure to inhibit channel activity. The idea that membrane lipids help confer shear stress and pressure sensitivity of K IR channels was confirmed in intact arteries using myography. Virtual models integrating structural/electrical observations reconceptualized K IR as a dynamic regulator of membrane potential working in concert with other currents to set basal tone across a range of shear stresses and intravascular pressures. Conclusions— The data show for the first time that specific membrane lipid-K IR interactions enable unique channel populations to sense hemodynamic stimuli and drive vasomotor responses to set basal perfusion in the cerebral circulation.

Objective— To quantify structural and functional characteristics of the caudal artery from spontaneously hypertensive (SHR) and normotensive Wistar Kyoto (WKY) rats with particular reference to endothelium-derived hyperpolarizing factor (EDHF). Methods and Results— Ultrastructural studies showed that the number of myoendothelial gap junctions, smooth muscle cell (SMC) layers, and medial cross-sectional area were significantly greater in SHR than WKY. Intracellular dye labeling demonstrated hyperplasia of SMCs in SHR. Analysis of nerve-mediated excitatory junction potentials recorded in SMCs at the adventitial and luminal borders demonstrated decreased radial coupling of SMCs in SHR. In both SHR and WKY, in the presence of N G -nitro- l -arginine methyl ester and indomethacin, acetylcholine-elicited EDHF was abolished by charybdotoxin and apamin, while iberiotoxin had no effect, implicating the involvement of small and intermediate, but not large, calcium-activated potassium channels. EDHF was abolished by Gap-mimetic peptides, 18β-glycyrrhetinic acid, and endothelial removal but not affected by the NO scavengers hydroxocobalamin and carboxy-PTIO. Conclusions— Significant differences in SMC morphology and homocellular and heterocellular coupling exist between the caudal artery of SHR and WKY rats. In the caudal artery of SHR, significantly greater heterocellular coupling compensates for other structural changes in the media to maintain a functional role for EDHF.

Abstract —Although the chemical nature of endothelium-derived hyperpolarizing factor (EDHF) remains elusive, electrophysiological evidence exists for electrical communication between smooth muscle cells and endothelial cells suggesting that electrotonic propagation of hyperpolarization may explain the failure to identify a single chemical factor as EDHF. Anatomical evidence for myoendothelial gap junctions, or the sites of electrical coupling, is, however, rare. In the present study, serial-section electron microscopy and reconstruction techniques have been used to examine the incidence of myoendothelial gap junctions in the proximal and distal mesenteric arteries of the rat where EDHF responses have been reported to vary. Myoendothelial gap junctions were found to be very small in the mesenteric arteries, the majority being