Local IP3 receptor–mediated Ca2+ signals compound to direct blood flow in brain capillaries

Healthy brain function depends on the finely tuned spatial and temporal delivery of blood-borne nutrients to active neurons via the vast, dense capillary network. Here, using in vivo imaging in anesthetized mice, we reveal that brain capillary endothelial cells control blood flow through a hierarchy of IP3 receptor–mediated Ca2+ events, ranging from small, subsecond protoevents, reflecting Ca2+ release through a small number of channels, to high-amplitude, sustained (up to ~1 min) compound events mediated by large clusters of channels. These frequent (~5000 events/s per microliter of cortex) Ca2+ signals are driven by neuronal activity, which engages Gq protein–coupled receptor signaling, and are enhanced by Ca2+ entry through TRPV4 channels. The resulting Ca2+-dependent synthesis of nitric oxide increases local blood flow selectively through affected capillary branches, providing a mechanism for high-resolution control of blood flow to small clusters of neurons.

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Imaging the construction of capillary networks in the neonatal mouse brain

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2100866118 ◽

2021 ◽

Vol 118 (26) ◽

pp. e2100866118

Author(s):

Vanessa Coelho-Santos ◽

Andrée-Anne Berthiaume ◽

Sharon Ornelas ◽

Heidi Stuhlmann ◽

Andy Y. Shih

Keyword(s):

Blood Flow ◽

Brain Diseases ◽

Brain Capillary ◽

Capillary Networks ◽

Two Photon ◽

Capillary Bed ◽

Flow Through ◽

And Function ◽

Blood Brain Barrier Integrity

Capillary networks are essential for distribution of blood flow through the brain, and numerous other homeostatic functions, including neurovascular signal conduction and blood–brain barrier integrity. Accordingly, the impairment of capillary architecture and function lies at the root of many brain diseases. Visualizing how brain capillary networks develop in vivo can reveal innate programs for cerebrovascular growth and repair. Here, we use longitudinal two-photon imaging through noninvasive thinned skull windows to study a burst of angiogenic activity during cerebrovascular development in mouse neonates. We find that angiogenesis leading to the formation of capillary networks originated exclusively from cortical ascending venules. Two angiogenic sprouting activities were observed: 1) early, long-range sprouts that directly connected venules to upstream arteriolar input, establishing the backbone of the capillary bed, and 2) short-range sprouts that contributed to expansion of anastomotic connectivity within the capillary bed. All nascent sprouts were prefabricated with an intact endothelial lumen and pericyte coverage, ensuring their immediate perfusion and stability upon connection to their target vessels. The bulk of this capillary expansion spanned only 2 to 3 d and contributed to an increase of blood flow during a critical period in cortical development.

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Electro-Metabolic Sensing Through Capillary ATP-Sensitive K+ Channels and Adenosine to Control Cerebral Blood Flow

10.1101/2021.03.12.435152 ◽

2021 ◽

Author(s):

Maria Sancho ◽

Nicholas R. Klug ◽

Amreen Mughal ◽

Thomas J. Heppner ◽

David Hill-Eubanks ◽

...

Keyword(s):

Endothelial Cells ◽

Blood Flow ◽

Cerebral Blood Flow ◽

Vascular Function ◽

Brain Activity ◽

List Type ◽

Capillary Endothelial Cells ◽

Metabolic Sensing ◽

Cellular Components

SUMMARYThe dense network of capillaries composed of capillary endothelial cells (cECs) and pericytes lies in close proximity to all neurons, ideally positioning it to sense neuro/glial-derived compounds that regulate regional and global cerebral perfusion. The membrane potential (VM) of vascular cells serves as the essential output in this scenario, linking brain activity to vascular function. The ATP-sensitive K+ channel (KATP) is a key regulator of vascular VM in other beds, but whether brain capillaries possess functional KATP channels remains unknown. Here, we demonstrate that brain capillary ECs and pericytes express KATP channels that robustly control VM. We further show that the endogenous mediator adenosine acts through A2A receptors and the Gs/cAMP/PKA pathway to activate capillary KATP channels. Moreover, KATP channel stimulation in vivo causes vasodilation and increases cerebral blood flow (CBF). These findings establish the presence of KATP channels in cECs and pericytes and suggest their significant influence on CBF.HIGHLIGHTSCapillary network cellular components—endothelial cells and pericytes—possess functional KATP channels.Activation of KATP channels causes profound hyperpolarization of capillary cell membranes.Capillary KATP channels are activated by exogenous adenosine via A2A receptors and cAMP-dependent protein kinase.KATP channel activation by adenosine or synthetic openers increases cerebral blood flow.

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Cellular Control of Brain Capillary Blood Flow: In Vivo Imaging Veritas

Trends in Neurosciences ◽

10.1016/j.tins.2019.05.009 ◽

2019 ◽

Vol 42 (8) ◽

pp. 528-536 ◽

Cited By ~ 12

Author(s):

Jaime Grutzendler ◽

Maiken Nedergaard

Keyword(s):

Blood Flow ◽

In Vivo Imaging ◽

Capillary Blood ◽

Capillary Blood Flow ◽

Brain Capillary ◽

Cellular Control

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Studies of the Hemopoietic Microenvironment. II. Effect of Erythropoietin on the Splenic Microvasculature of Polycythemic CF1 Mice

Blood ◽

10.1182/blood.v39.6.809.809 ◽

1972 ◽

Vol 39 (6) ◽

pp. 809-813 ◽

Cited By ~ 13

Author(s):

Robert S. McCuskey ◽

Howard A. Meineke ◽

Stephen M. Kaplan

Keyword(s):

Stem Cells ◽

Blood Flow ◽

Single Dose ◽

Pancreatic Tissue ◽

Linear Velocity ◽

Hemopoietic Microenvironment ◽

Microvascular Response ◽

Flow Through

Abstract The effect of erythropoietin on the splenic microvascular system of polycythemic CF1 mice was studied using in vivo microscopic methods. Administration of a single dose (3 U) of erythropoietin resulted in an increase in the linear velocity of blood flow through the splenic sinusoids and a reduction in the number of sinusoids storing blood. This response was first seen 4-6 hr after injection; it persisted for 48 hr and was reduced markedly by 72 hr. By 120 hr the spleens were indistinguishable from controls. The response was specific for erythrogenic tissue, since no response was seen in the adjacent nonerythropoietic pancreatic tissue. The results suggest that the splenic microvascular response to erythropoietin may be indirect and may be mediated by the release of a vasoactive metabolite from the erythrogenic tissues surrounding the sinusoids. Erythropoietin-sensitive stem cells are suggested to be the source of such a metabolite.

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Internalization of targeted quantum dots by brain capillary endothelial cells in vivo

Journal of Cerebral Blood Flow & Metabolism ◽

10.1177/0271678x15608201 ◽

2015 ◽

Vol 36 (4) ◽

pp. 731-742 ◽

Cited By ~ 17

Author(s):

Sarah Paris-Robidas ◽

Danny Brouard ◽

Vincent Emond ◽

Martin Parent ◽

Frédéric Calon

Keyword(s):

Drug Delivery ◽

Quantum Dots ◽

Endothelial Cells ◽

Transferrin Receptor ◽

Volume Of Distribution ◽

Electron Microscopic ◽

Brain Capillary ◽

Brain Capillary Endothelial Cells ◽

Capillary Endothelial Cells

Receptors located on brain capillary endothelial cells forming the blood–brain barrier are the target of most brain drug delivery approaches. Yet, direct subcellular evidence of vectorized transport of nanoformulations into the brain is lacking. To resolve this question, quantum dots were conjugated to monoclonal antibodies (Ri7) targeting the murine transferrin receptor. Specific transferrin receptor-mediated endocytosis of Ri7-quantum dots was first confirmed in N2A and bEnd5 cells. After intravenous injection in mice, Ri7-quantum dots exhibited a fourfold higher volume of distribution in brain tissues, compared to controls. Immunofluorescence analysis showed that Ri7-quantum dots were sequestered throughout the cerebral vasculature 30 min, 1 h, and 4 h post injection, with a decline of signal intensity after 24 h. Transmission electron microscopic studies confirmed that Ri7-quantum dots were massively internalized by brain capillary endothelial cells, averaging 37 ± 4 Ri7-quantum dots/cell 1 h after injection. Most quantum dots within brain capillary endothelial cells were observed in small vesicles (58%), with a smaller proportion detected in tubular structures or in multivesicular bodies. Parenchymal penetration of Ri7-quantum dots was extremely low and comparable to control IgG. Our results show that systemically administered Ri7-quantum dots complexes undergo extensive endocytosis by brain capillary endothelial cells and open the door for novel therapeutic approaches based on brain endothelial cell drug delivery.

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Quantification of in vitro and in vivo energy metabolism of the gastrointestinal tract of fed or fasted sheep

Canadian Journal of Animal Science ◽

10.4141/cjas93-088 ◽

1993 ◽

Vol 73 (4) ◽

pp. 855-868 ◽

Cited By ~ 9

Author(s):

J. M. Kelly ◽

B. G. Southorn ◽

C. E. Kelly ◽

L. P. Milligan ◽

B. W. McBride

Keyword(s):

Blood Flow ◽

Gastrointestinal Tract ◽

Portal Blood Flow ◽

Whole Body ◽

Hepatic Portal Vein ◽

Flow Through ◽

Hepatic Portal ◽

Ouabain Inhibition

The effect of level of nutrition on in vitro and in vivo O2 consumption by the gastrointestinal tract in four nonlactating, nonpregnant ewes catheterized in the anterior mesenteric vein, hepatic portal vein and mesenteric artery with duodenal cannulae was investigated. Animals were fed a pelleted ration at maintenance (M) or twice maintenance (2M) or fasted (F) subsequent to the M measurement. Duodenal in vitro O2, ouabain-sensitive O2 (OSO2) and cycloheximide-sensitive O2 (CSO2) consumption was determined polarographically using a YSI O2 monitor; whole-gut O2 consumption was determined as (arterio-venous difference of O2 concentration) × (blood flow through the PV). Whole-body O2 consumption was determined using indirect calorimetry. Ewes fed 2M exhibited higher (P < 0.10) whole-body O2 consumption than either M or F ewes. Ewes fed M and 2M had higher (P < 0.10) duodenal in vitro O2 and ouabain-insensitive O2 (OIO2) consumption than F ewes. Hepatic portal blood flow was directly proportional to level of intake (P < 0.10): it was lowest for F ewes (81.0 L h−1), intermediate for M ewes (97.7 L h−1) and highest for 2M ewes (122.5 L h−1). Ouabain inhibition of O2 consumption by portal-drained viscera (PDV) was highest in M ewes and lowest in 2M ewes (P < 0.10). CSO2 consumption by the entire PDV was not affected by level of intake, corresponding to no change in OIO2 consumption by the PDV. As a proportion of whole-body O2 consumption, total O2, OSO2 and cycloheximide-insensitive O2 consumption by the PDV was higher in F ewes than in 2M ewes (P < 0.10). Fasted ewes expended a greater proportion of whole-body O2 consumption on gastrointestinal energetics than did 2M ewes. Key words: Sheep, gastrointestinal oxygen consumption, sodium–potassium ATPase, protein synthesis

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Studies of the Hemopoietic Microenvironment. I. Changes in the Microvascular System and Stroma During Erythropoietic Regeneration and Suppression in the Spleens of CF1 Mice

Blood ◽

10.1182/blood.v39.5.697.697 ◽

1972 ◽

Vol 39 (5) ◽

pp. 697-712 ◽

Cited By ~ 45

Author(s):

Robert S. McCuskey ◽

Howard A. Meineke ◽

Samuel F. Townsend

Keyword(s):

Bone Marrow ◽

Blood Flow ◽

Linear Velocity ◽

Proliferating Cells ◽

Hemopoietic Microenvironment ◽

Murine Spleen ◽

Flow Through ◽

Tissue Compartments ◽

Red Pulp

Abstract Specific alterations in the microvascular and connective tissue compartments of the hemopoietic microenvironment have been examined during erythropoietic regeneration and suppression in the murine spleen and bone marrow using in vivo microscopic and histochemical methods. The results have confirmed the concept of specific hemopoietic microenvironments and have demonstrated specific alterations in the microenvironment during erythropoietic stimulation and repression. Elevated erythropoiesis in the splenic red pulp is accompanied by an elevation in blood flow through the microvascular system. Both the linear velocity of flow and the number of sinusoids with blood flow in them increased significantly. In contrast, erythropoietic repression was accompanied by a decreased linear velocity of blood flow, as well as a marked increase in the amount of blood being stored in the splenic sinusoids. This also was the picture when diffuse granulopoiesis was present in the red pulp, or when granuloid or undifferentiated colonies were present. The chemical composition of the stroma in the spleen and bone marrow also varied during states of hemopoietic activity and, in addition, there were differences in the composition of the stroma between these two organs. In both organs, foci of early proliferating cells were enveloped by a coating of sulfated acid mucopolysaccharide. This coat persisted on cells in later stages of granulopoiesis but not on cells in the later stages of erythropoiesis. The latter were enveloped with a coating of neutral mucopolysaccharide. A tentative hypothesis to explain the mechanisms involved in producing these changes is discussed.

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Blood-brain barrier permeability of 11C-labeled alcohols and 15O-labeled water

American Journal of Physiology-Legacy Content ◽

10.1152/ajplegacy.1976.230.2.543 ◽

1976 ◽

Vol 230 (2) ◽

pp. 543-552 ◽

Cited By ~ 217

Author(s):

ME Raichle ◽

JO Eichling ◽

MG Straatmann ◽

MJ Welch ◽

KB Larson ◽

...

Keyword(s):

Blood Flow ◽

Cerebral Blood Flow ◽

Time Course ◽

Brain Capillary ◽

Permeability Characteristics ◽

Permeability Surface ◽

Brain Barrier Permeability ◽

The Individual ◽

The Brain

The extraction of 11C-labeled methanol, ethanol, and isopropanol, as well as 15O-labeled water by the brain during a single capillary transit, was studied in vivo in six adult rhesus monkeys by external detection of the time course of these tracers subsequent to their internal carotid artery injection. The data demonstrate the feasibility of accurately measuring brain permeability of highly diffusible substances by this technique and show that neither water nor the alcohols studied freely equilibrate with brain when the cerebral blood flow exceeds 30 ml/100 g min-1. At a cerebral blood flow of 50 ml/100 g min-1 only about 93% of an injected bolus of labeled water freely exchanges with brain, compared with methanol (93%), ethanol (97%), and isopropanol (99%). The brain capillary permeability-surface area (PS) products computed from these data were 0.023 cm3/s g-1 (water), 0.024 cm3/s g-1 (methanol), 0.030 cm3/s g-1 (ethanol), and 0.062 cm3/s g-1 (isopropanol). This sequence of PS products is consistent with the individual lipid solubilities of the alcohols studied and underscores the unique brain permeability characteristics of lipid-insoluble water.

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