Purinergic glio-endothelial coupling during neuronal activity: role of P2Y1 receptors and eNOS in functional hyperemia in the mouse somatosensory cortex

Impairment of moment-to-moment adjustment of cerebral blood flow (CBF) via neurovascular coupling is thought to play a critical role in the genesis of cognitive impairment associated with aging and pathological conditions associated with accelerated cerebromicrovascular aging (e.g., hypertension, obesity). Although previous studies demonstrate that endothelial dysfunction plays a critical role in neurovascular uncoupling in these conditions, the role of endothelial NO mediation in neurovascular coupling responses is not well understood. To establish the link between endothelial function and functional hyperemia, neurovascular coupling responses were studied in mutant mice overexpressing or deficient in endothelial NO synthase (eNOS), and the role of P2Y1 receptors in purinergic glioendothelial coupling was assessed. We found that genetic depletion of eNOS (eNOS−/−) and pharmacological inhibition of NO synthesis significantly decreased the CBF responses in the somatosensory cortex evoked by whisker stimulation and by administration of ATP. Overexpression of eNOS enhanced NO mediation of functional hyperemia. In control mice, the selective and potent P2Y1 receptor antagonist MRS2179 attenuated both whisker stimulation-induced and ATP-mediated CBF responses, whereas, in eNOS−/− mice, the inhibitory effects of MRS2179 were blunted. Collectively, our findings provide additional evidence for purinergic glio-endothelial coupling during neuronal activity, highlighting the role of ATP-mediated activation of eNOS via P2Y1 receptors in functional hyperemia.

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Role of endothelium-pericyte signaling in capillary blood flow response to neuronal activity

Journal of Cerebral Blood Flow & Metabolism ◽

10.1177/0271678x211007957 ◽

2021 ◽

pp. 0271678X2110079

Author(s):

Wenri Zhang ◽

Catherine M Davis ◽

Douglas M Zeppenfeld ◽

Kirsti Golgotiu ◽

Marie X Wang ◽

...

Keyword(s):

Blood Flow ◽

Neuronal Activity ◽

Functional Hyperemia ◽

Neuronal Activation ◽

Two Photon Microscopy ◽

Tightly Coupled ◽

Whisker Stimulation ◽

Optical Microangiography ◽

Hyperemic Response

Local blood flow in the brain is tightly coupled to metabolic demands, a phenomenon termed functional hyperemia. Both capillaries and arterioles contribute to the hyperemic response to neuronal activity via different mechanisms and timescales. The nature and specific signaling involved in the hyperemic response of capillaries versus arterioles, and their temporal relationship are not fully defined. We determined the time-dependent changes in capillary flux and diameter versus arteriolar velocity and flow following whisker stimulation using optical microangiography (OMAG) and two-photon microscopy. We further characterized depth-resolved responses of individual capillaries versus capillary networks. We hypothesized that capillaries respond first to neuronal activation, and that they exhibit a coordinated response mediated via endothelial-derived epoxyeicosatrienoates (EETs) acting on pericytes. To visualize peri-capillary pericytes, we used Tie2-GFP/NG2-DsRed mice, and to determine the role of endothelial-derived EETs, we compared cerebrovascular responses to whisker stimulation between wild-type mice and mice with lower endothelial EETs (Tie2-hsEH). We found that capillaries respond immediately to neuronal activation in an orchestrated network-level manner, a response attenuated in Tie2-hsEH and inhibited by blocking EETs action on pericytes. These results demonstrate that capillaries are first responders during functional hyperemia, and that they exhibit a network-level response mediated via endothelial-derived EETs’ action on peri-capillary pericytes.

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Critical Role of the Astrocyte for Functional Remodeling in Contralateral Hemisphere of Somatosensory Cortex after Stroke

Journal of Neuroscience ◽

10.1523/jneurosci.2657-12.2013 ◽

2013 ◽

Vol 33 (11) ◽

pp. 4683-4692 ◽

Cited By ~ 39

Author(s):

Y. Takatsuru ◽

K. Eto ◽

R. Kaneko ◽

H. Masuda ◽

N. Shimokawa ◽

...

Keyword(s):

Somatosensory Cortex ◽

Critical Role ◽

Contralateral Hemisphere ◽

Functional Remodeling

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Suppression of Basal Spontaneous Gonadotropin-Releasing Hormone Neuronal Activity during Lactation: Role of Inhibitory Effects of Neuropeptide Y

Endocrinology ◽

10.1210/en.2008-0962 ◽

2008 ◽

Vol 150 (1) ◽

pp. 333-340 ◽

Cited By ~ 31

Author(s):

Jing Xu ◽

Melissa A. Kirigiti ◽

Michael A. Cowley ◽

Kevin L. Grove ◽

M. Susan Smith

Keyword(s):

Neuropeptide Y ◽

Neuronal Activity ◽

Fluorescent Protein ◽

Resting Membrane Potential ◽

Inhibitory Effects ◽

Gnrh Neurons ◽

Cell Current ◽

Green Fluorescent ◽

Hypothalamic Slices

Increased neuropeptide Y (NPY) activity drives the chronic hyperphagia of lactation and may contribute to the suppression of GnRH activity. The majority of GnRH neurons are contacted by NPY fibers, and GnRH cells express NPY Y5 receptor (Y5R). Therefore, NPY provides a neurocircuitry for information about food intake/energy balance to be directly transmitted to GnRH neurons. To investigate the effects of lactation on GnRH neuronal activity, hypothalamic slices were prepared from green fluorescent protein-GnRH transgenic rats. Extracellular loose-patch recordings determined basal GnRH neuronal activity from slices of ovariectomized control and lactating rats. Compared with controls, hypothalamic slices from lactating rats had double the number of quiescent GnRH neurons (14.51 ± 2.86 vs. 7.04 ± 2.84%) and significantly lower firing rates of active GnRH neurons (0.25 ± 0.02 vs. 0.37 ± 0.03 Hz). To study the NPY-postsynaptic Y5R system, whole-cell current-clamp recordings were performed in hypothalamic slices from control rats to examine NPY/Y5R antagonist effects on GnRH neuronal resting membrane potential. Under tetrodotoxin treatment, NPY hyperpolarized GnRH neurons from −56.7 ± 1.94 to −62.1 ± 1.83 mV; NPY’s effects were blocked by Y5R antagonist. To determine whether increased endogenous NPY tone contributes to GnRH neuronal suppression during lactation, hypothalamic slices were treated with Y5R antagonist. A significantly greater percentage of GnRH cells were activated in slices from lactating rats (52%) compared with controls (28%). These results suggest that: 1) basal GnRH neuronal activity is suppressed during lactation; 2) NPY can hyperpolarize GnRH neurons via postsynaptic Y5R; and 3) increased inhibitory NPY tone during lactation is a component of the mechanisms responsible for suppression of GnRH neuronal activity. Neuropeptide Y (NPY) directly hyperpolarizes GnRH neurons via postsynaptic NPY Y5 receptor. Increased inhibitory NPY tone during lactation is an important component of the suppression of GnRH neuronal activity.

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Compensatory role of NO in cerebral circulation of piglets chronically treated with indomethacin

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00256.2001 ◽

2002 ◽

Vol 282 (2) ◽

pp. R400-R410 ◽

Cited By ~ 8

Author(s):

Yifan Zhang ◽

C. W. Leffler

Keyword(s):

Nitric Oxide ◽

Cerebrospinal Fluid ◽

Methyl Ester ◽

Cerebral Circulation ◽

No Synthase ◽

Inhibitory Effects ◽

Circulatory Control ◽

Pial Arterioles ◽

Indomethacin Treatment

We hypothesize that inhibitory effects exist between prostanoids and nitric oxide (NO) in their contributions to cerebral circulation. Piglets (1–4 days old) were divided into three chronically treated (6–8 days) groups: control piglets, piglets treated with indomethacin (75 mg/day), and piglets treated with N ω-nitro-l-arginine methyl ester (l-NAME, 100 mg · kg−1 · day−1). Pial arterioles dilated in response to hypercapnia similarly among the three groups (41 ± 4, 40 ± 6, and 45 ± 11%). Cerebrospinal fluid cAMP increased in control piglets, while cGMP increased in indomethacin-treated piglets. l-NAME, but not 7-nitroindazole, inhibited the response to hypercapnia only in indomethacin-treated piglets (40 ± 6 vs. 17 ± 5%). Topical sodium nitroprusside or iloprost restored dilation in response to hypercapnia. Similar results were obtained when the dilator was bradykinin. Pial arterioles of control and l-NAME-treated piglets constricted in response to ACh (−24 ± 3%). However, those of indomethacin-treated piglets dilated in response to ACh (15 ± 2%). This dilation was inhibited by l-NAME. NO synthase activity, but not endothelial NO synthase expression, increased after chronic indomethacin treatment. These data suggest that chronic inhibition of cyclooxygenase can increase the contribution of NO to cerebrovascular circulatory control in piglets.

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Angiotensin II attenuates functional hyperemia in the mouse somatosensory cortex

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00464.2003 ◽

2003 ◽

Vol 285 (5) ◽

pp. H1890-H1899 ◽

Cited By ~ 65

Author(s):

Ken Kazama ◽

Gang Wang ◽

Kelly Frys ◽

Josef Anrather ◽

Costantino Iadecola

Keyword(s):

Angiotensin Ii ◽

Somatosensory Cortex ◽

Neural Activity ◽

Brain Regions ◽

Synaptic Activity ◽

Nitric Oxide Donor ◽

Ang Ii ◽

Functional Hyperemia ◽

Doppler Flowmetry ◽

Whisker Stimulation

We investigated whether angiotensin II (ANG II), a peptide that plays a central role in the genesis of hypertension, alters the coupling between synaptic activity and cerebral blood flow (CBF), a critical homeostatic mechanism that assures adequate cerebral perfusion to active brain regions. The somatosensory cortex was activated by stroking the facial whiskers in anesthetized C57BL/6J mice while local CBF was recorded by laser-Doppler flowmetry. Intravenous ANG II infusion (0.25 μg·kg–1·min–1) increased mean arterial pressure (MAP) from 82 ± 2 to 102 ± 3 mmHg ( P < 0.05) without affecting resting CBF ( P > 0.05). ANG II attenuated the CBF increase produced by whisker stimulation by 65% ( P < 0.05) but did not affect the response to hypercapnia or to neocortical application of the nitric oxide donor S-nitroso- N-acetyl penicillamine ( P > 0.05). The effect of ANG II on functional hyperemia persisted if the elevation in MAP was offset by controlled hemorrhage or prevented by topical application of the peptide to the activated cortex. ANG II did not reduce the amplitude of the P1 wave of the field potentials evoked by whisker stimulation ( P > 0.05). Infusion of phenylephrine increased MAP ( P > 0.05 from ANG II) but did not alter the functional hyperemic response ( P > 0.05). The data suggest that ANG II alters the coupling between CBF and neural activity. The mechanisms of the effect are not related to the elevation in MAP and/or to inhibition of the synaptic activity evoked by whisker stimulation. The imbalance between CBF and neural activity induced by ANG II may alter the homeostasis of the neuronal microenvironment and contribute to brain dysfunction during ANG II-induced hypertension.

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Regulation of blood flow in diabetic retinopathy

Visual Neuroscience ◽

10.1017/s0952523820000036 ◽

2020 ◽

Vol 37 ◽

Author(s):

Amy R. Nippert ◽

Eric A. Newman

Keyword(s):

Blood Flow ◽

Diabetic Retinopathy ◽

Neuronal Activity ◽

Neurovascular Coupling ◽

Functional Hyperemia ◽

Retinal Neurons ◽

Adequate Supply ◽

Oxygen Levels ◽

Signaling Mechanisms ◽

Diabetic Brain

Abstract Blood flow in the retina increases in response to light-evoked neuronal activity, ensuring that retinal neurons receive an adequate supply of oxygen and nutrients as metabolic demands vary. This response, termed “functional hyperemia,” is disrupted in diabetic retinopathy. The reduction in functional hyperemia may result in retinal hypoxia and contribute to the development of retinopathy. This review will discuss the neurovascular coupling signaling mechanisms that generate the functional hyperemia response in the retina, the changes to neurovascular coupling that occur in diabetic retinopathy, possible treatments for restoring functional hyperemia and retinal oxygen levels, and changes to functional hyperemia that occur in the diabetic brain.

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Role of Peoxisome Proliferator Activator Receptor on Blood Retinal Barrier Breakdown

PPAR Research ◽

10.1155/2008/679237 ◽

2008 ◽

Vol 2008 ◽

pp. 1-4 ◽

Cited By ~ 6

Author(s):

Yasuo Yanagi

Keyword(s):

Diabetic Retinopathy ◽

Pigment Epithelium ◽

Retinal Pigment ◽

Critical Role ◽

Blood Retinal Barrier ◽

Early Diabetes ◽

Pathological Conditions ◽

Barrier Breakdown ◽

Brb Breakdown

The retinal vessels have two barriers: the retinal pigment epithelium and the retinal vascular endothelium. Each barrier exhibits increased permeability under various pathological conditions. This condition is referred to as blood retinal barrier (BRB) breakdown. Clinically, the most frequently encountered condition causing BRB breakdown is diabetic retinopathy. In recent studies, inflammation has been linked to BRB breakdown and vascular leakage in diabetic retinopathy. Biological support for the role of inflammation in early diabetes is the adhesion of leukocytes to the retinal vasculature (leukostasis) observed in diabetic retinopathy. is a member of a ligand-activated nuclear receptor superfamily and plays a critical role in a variety of biological processes, including adipogenesis, glucose metabolism, angiogenesis, and inflammation. There is now strong experimental evidence to support the theory that inhibits diabetes-induced retinal leukostasis and leakage, playing an important role in the pathogenesis of diabetic retinopathy. Therapeutic targeting of may be beneficial to diabetic retinopathy.

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Relative Changes in Cerebral Blood Flow and Neuronal Activity in Local Microdomains during Generalized Seizures

Journal of Cerebral Blood Flow & Metabolism ◽

10.1097/01.wcb.0000131669.02027.3e ◽

2004 ◽

Vol 24 (9) ◽

pp. 1057-1068 ◽

Cited By ~ 51

Author(s):

Hrachya Nersesyan ◽

Peter Herman ◽

Ersan Erdogan ◽

Fahmeed Hyder ◽

Hal Blumenfeld

Keyword(s):

Visual Cortex ◽

Somatosensory Cortex ◽

Neuronal Activity ◽

Barrel Cortex ◽

Similar Distribution ◽

Somatosensory Stimulation ◽

Doppler Flowmetry ◽

Absence Seizures ◽

Generalized Seizures ◽

Whisker Stimulation

There is broad agreement that generalized tonic–clonic seizures (GTCS) and normal somatosensory stimulation are associated with increases in regional CBF. However, the data regarding CBF changes during absence seizures are controversial. Electrophysiologic studies in WAG/Rij rats, an established animal model of absence seizures, have shown spike-wave discharges (SWD) that are largest in the perioral somatosensory cortex while sparing the visual cortex. Recent functional magnetic resonance imaging (fMRI) studies in the same model have also shown localized increases in fMRI signals in the perioral somatosensory cortex during SWD. Because fMRI signals are only indirectly related to neuronal activity, the authors directly measured CBF and neuronal activity from specific microdomains of the WAG/Rij cortex using a specially designed probe combining laser-Doppler flowmetry and extracellular microelectrode recordings under fentanyl/haloperidol anesthesia. Using this approach, parallel increases in neuronal activity and CBF were observed during SWD in the whisker somatosensory (barrel) cortex, whereas the visual cortex showed no significant changes. For comparison, these measurements were repeated during somatosensory (whisker) stimulation, and bicuculline-induced GTCS in the same animals. Interestingly, whisker stimulation increased neuronal activity and CBF in the barrel cortex more than during SWD. During GTCS, much larger increases that included both the somatosensory and visual cortex were observed. Thus, SWD in this model produce parallel localized increases in neuronal activity and CBF with similar distribution to somatosensory stimulation, whereas GTCS produce larger and more widespread changes. The normal response to somatosensory stimulation appears to be poised between two abnormal responses produced by two physiologically different types of seizures.

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Mechanisms Mediating Functional Hyperemia in the Brain

The Neuroscientist ◽

10.1177/1073858417703033 ◽

2017 ◽

Vol 24 (1) ◽

pp. 73-83 ◽

Cited By ~ 27

Author(s):

Amy R. Nippert ◽

Kyle R. Biesecker ◽

Eric A. Newman

Keyword(s):

Nitric Oxide ◽

Arachidonic Acid ◽

Final Section ◽

Neurovascular Coupling ◽

Functional Hyperemia ◽

Generating Functional ◽

Signaling Mechanisms ◽

The Brain ◽

Astrocyte Endfeet

Neuronal activity within the brain evokes local increases in blood flow, a response termed functional hyperemia. This response ensures that active neurons receive sufficient oxygen and nutrients to maintain tissue function and health. In this review, we discuss the functions of functional hyperemia, the types of vessels that generate the response, and the signaling mechanisms that mediate neurovascular coupling, the communication between neurons and blood vessels. Neurovascular coupling signaling is mediated primarily by the vasoactive metabolites of arachidonic acid (AA), by nitric oxide, and by K+. While much is known about these pathways, many contentious issues remain. We highlight two controversies, the role of glial cell Ca2+ signaling in mediating neurovascular coupling and the importance of capillaries in generating functional hyperemia. We propose signaling pathways that resolve these controversies. In this scheme, capillary dilations are generated by Ca2+ increases in astrocyte endfeet, leading to production of AA metabolites. In contrast, arteriole dilations are generated by Ca2+ increases in neurons, resulting in production of nitric oxide and AA metabolites. Arachidonic acid from neurons also diffuses into astrocyte endfeet where it is converted into additional vasoactive metabolites. While this scheme resolves several discrepancies in the field, many unresolved challenges remain and are discussed in the final section of the review.

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The Role of Dll4/Notch Signaling in Normal and Pathological Ocular Angiogenesis: Dll4 Controls Blood Vessel Sprouting and Vessel Remodeling in Normal and Pathological Conditions

Journal of Ophthalmology ◽

10.1155/2018/3565292 ◽

2018 ◽

Vol 2018 ◽

pp. 1-8 ◽

Cited By ~ 6

Author(s):

Ivan Lobov ◽

Natalia Mikhailova

Keyword(s):

Blood Vessel ◽

Transmembrane Protein ◽

Mammalian Species ◽

Vascular Development ◽

Critical Role ◽

Notch Pathway ◽

The Body ◽

Therapeutic Effects ◽

Pathological Conditions

Background. Retina is the highest oxygen-demanding and vascularized tissue in the body. Retinal development and function require proper vascularization and blood vessel function and integrity. Dll4 is most prominently expressed in the endothelium of angiogenic blood vessels and in quiescent arteries and capillaries in all tissues and organs of the mammalian species, and it is the key regulator of blood vessel sprouting.Results. Dll4 is a transmembrane protein that acts as a ligand for Notch receptors 1 and 4. Genetic deletion of Dll4 causes severe abnormalities in embryonic and postnatal vascular development. Deletion of even a single Dll4 allele results in almost complete embryonic lethality due to severe vascular abnormalities, the phenomenon called haploinsufficiency indicating the critical role of Dll4/Notch in vascular development. Dll4/Notch pathway interplays at multiple levels with other signaling pathways including VEGF, Wnt/Fzd, and genes controlling vascular toning. Multiple studies of the effects of Dll4 inhibition were performed in the developing retina to elucidate the key functions of Dll4 in normal and pathological angiogenesis. Several genetic approaches and therapeutic molecules were tested to evaluate the biological and therapeutic effects of acute and prolonged Dll4 inhibition in the eye and oncology.Conclusions. All current studies demonstrated that Dll4 controls blood vessel sprouting, growth, and remodeling in normal and pathological conditions as well as arterial-venous differentiation. Genetic and therapeutic Dll4 modulation studies show that Dll4 inhibition can promote blood vessel sprouting and might be useful to stimulate vessel growth in the ischemic retina and Dll4 is the key modulator of the postangiogenic vascular remodeling that ultimately defines vascular patterning.

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