Background-When challenged with extracellular fluid shear stress, vascular endothelial cells are known to release nitric oxide, an important vasodilator. Here, we show that the ability of cultured endothelial cells to sense a low range of fluid shear depends on apical membrane organelles, called cilia, and that cilia are compartments required for proper localization and function of the mechanosensitive polycystin-1 molecule. Methods and Results-Cells with the Pkd1null/null or Tg737 orpk/orpk mutation encoded for polycystin-1 or polaris, respectively, are unable to transmit extracellular shear stress into intracellular calcium signaling and biochemical nitric oxide synthesis. Cytosolic calcium and nitric oxide recordings further show that fluid shear sensing is a cilia-specific mechanism because other mechanical or pharmacological stimulation does not abolish calcium and nitric oxide signaling in polycystin-1 and polaris mutant endothelial cells. Polycystin-1 localized in the basal body of Tg737

The concept of the neurovascular unit as the key brain component affected by stroke is controversial, because current definitions of this entity neglect mechanisms that control perfusion and reperfusion of arteries and arterioles upstream of the cerebral microcirculation. Indeed, although definitions vary, many researchers consider the neurovascular unit to be restricted to endothelial cells, neurons and glia within millimetres of the cerebral capillary microcirculation. This Perspectives article highlights the roles of vascular smooth muscle, endothelial cells and perivascular innervation of cerebral arteries in the initiation and progression of, and recovery from, ischaemic stroke. The concept of the vascular neural network—which includes cerebral arteries, arterioles, and downstream neuronal and glial cell types and structures—is introduced as the fundamental component affected by stroke pathophysiology. The authors also propose that the vascular neural network should be considered the main target for future therapeutic intervention after cerebrovascular insult.

Hypoxia is one of the most common and severe challenges to the maintenance of homeostasis. Oxygen sensing is a property of all tissues, and the response to hypoxia is multidimensional involving complicated intracellular networks concerned with the transduction of hypoxia-induced responses. Of all the stresses to which the fetus and newborn infant are subjected, perhaps the most important and clinically relevant is that of hypoxia. Hypoxia during gestation impacts both the mother and fetal development through interactions with an individual's genetic traits acquired over multiple generations by natural selection and changes in gene expression patterns by altering the epigenetic code. Changes in the epigenome determine "genomic plasticity," i.e., the ability of genes to be differentially expressed according to environmental cues. The genomic plasticity defined by epigenomic mechanisms including DNA methylation, histone modifications, and noncoding RNAs during development is the mechanistic substrate for phenotypic programming that determines physiological response and risk for healthy or deleterious outcomes. This review explores the impact of gestational hypoxia on maternal health and fetal development, and epigenetic mechanisms of developmental plasticity with emphasis on the uteroplacental circulation, heart development, cerebral circulation, pulmonary development, and the hypothalamic-pituitary-adrenal axis and adipose tissue. The complex molecular and epigenetic interactions that may impact an individual's physiology and developmental programming of health and disease later in life are discussed.

We have examined age-related changes in segments of common carotid (Com), basilar (Bas), posterior communicating (PC), and middle cerebral (MC) arteries taken from 14 near-term fetal lambs, 62 newborn lambs 3-7 days old, and 42 adult nonpregnant sheep. Transition from fetal to newborn life was associated with a decreased water content in all arteries ranging from 0.6% (Com) to 2.3% (Bas), no change in the relative content of cellular protein, an increase in wall thickness ranging from 4% (MC) to 26% (Com), an increase in maximum contractile tension ranging from 18% (MC) to 82% (Com), an increase in stiffness, an increase in the maximum active stress ranging from 6% (Bas) to 43% (Com), a decrease in the amine-to-potassium ratio (calculated as the maximum response to 10 microM serotonin with 20 microM histamine divided by the maximum response to 122 mM K+) ranging from 8% (Bas) to 51% (Com), and a decrease in the norepinephrine-to-potassium ratio ranging from 2.1% (Bas) to 56% (Com). Thus developmental changes associated with the transition from fetal to newborn life were much more pronounced in the larger, more proximal Com than in the smaller, more distal cerebral arteries, suggesting that, at term, the cerebral arteries are more mature both functionally and structurally than the Com arteries. Similarly, the transition from newborn to adult life was associated with much greater changes in Com characteristics than with those of the cerebral arteries. These studies demonstrate that the effects of aging vary considerably along the cerebrovascular tree and that conclusions based on developmental studies of large systemic arteries cannot be freely extrapolated to the smaller arteries of the circle of Willis.

Background and Purpose-The present studies examined the hypothesis that the distribution of cerebral injury after a focal ischemic insult is associated with the regional distribution of nitric oxide synthase (NOS) activity. Methods-Based on previous studies that certain anatomically well-defined areas are prone to become either core or penumbra after middle cerebral artery occlusion (MCAO), we measured NOS activity in these areas from the right and left hemispheres in a spontaneously hypertensive rat filament model. Four groups were studied: (1) controls (immediate decapitation); (2) 1.5 hours of MCAO with no reperfusion (R0); (3) 1.5 hours of MCAO with 0.5 hour of reperfusion (R0.5); and (4) 1.5 hours of MCAO with 24 hours of reperfusion (R24). Three groups of corresponding isoflurane sham controls were also included: 1.5 (S1.5) or 2 (S2.0) hours of anesthesia and 1.5 hours of anesthesiaϩ24 hours of observation (S24). Results-Control core NOS activity for combined right and left hemispheres was 129% greater than penumbral NOS activity (PϽ0.05). Combined core NOS activity was also greater (PϽ0.05) in the three sham groups: 208%, 122%, and 161%, respectively. In the three MCAO groups, ischemic and nonischemic core NOS remained higher than penumbral regions (PϽ0.05). However, NOS activity was lower in the ischemic than in the nonischemic core in all three groups: R0 (29% lower), R0.5 (48%), and R24 (86%) (PϽ0.05). Addition of cofactors (10 mol/L tetrahydrobiopterin, 3 mol/L flavin adenine dinucleotide, and 3 mol/L flavin mononucleotide) increased NOS activity in all groups and lessened the decrease in ischemic core and penumbral NOS. Conclusions-Greater NOS activity in core regions could explain in part the increased vulnerability of that region to ischemia and could theoretically contribute to the progression of the infarct over time. The data also suggest that NOS activity during ischemia and reperfusion could be influenced by the availability of cofactors.

Fetal cerebrovascular responses to acute hypoxia are fundamentally different from those observed in the adult cerebral circulation. The magnitude of hypoxic vasodilatation in the fetal brain increases with postnatal age although fetal cerebrovascular responses to acute hypoxia can be complicated by age-dependent depressions of blood pressure and ventilation. Acute hypoxia promotes adenosine release, which depresses fetal cerebral oxygen consumption through action of adenosine on neuronal A1 receptors and vasodilatation through activation of A2 receptors on cerebral arteries. The vascular effect of adenosine can account for approximately half the vasodilatation observed in response to hypoxia. Hypoxia-induced release of nitric oxide and opioids can account for much of the adenosine-independent cerebral vasodilatation observed in response to hypoxia in the fetus. Direct effects of hypoxia on cerebral arteries account for the remaining fraction, although the vascular endothelium contributes relatively little to hypoxic vasodilatation in the immature cerebral circulation. In contrast to acute hypoxia, fetal cerebral blood flow tends to normalize during acclimatization to chronic hypoxia even though cardiac output is depressed. However, uncompensated chronic hypoxia in the fetus can produce significant changes in brain structure and function, alteration of respiratory drive and fluid balance, and increased incidence of intracranial hemorrhage and periventricular leukomalacia. At the level of the fetal cerebral arteries, chronic hypoxia increases protein content and depresses norepinephrine release, contractility, and receptor densities associated with contraction but also attenuates endothelial vasodilator capacity and decreases the ability of ATP-sensitive and calcium-sensitive potassium channels to promote vasorelaxation. Overall, fetal cerebrovascular adaptations to chronic hypoxia appear prioritized to conserve energy while preserving basic contractility. Many gaps remain in our understanding of how the effects of acute and chronic hypoxia are mediated in fetal cerebral arteries, but studies of adult cerebral arteries have produced many powerful pharmacological and molecular tools that are simply awaiting application in studies of fetal cerebral artery responses to hypoxia.

G protein-regulated Ca2+ sensitivity of vascular contractile proteins plays an important role in cerebrovascular reactivity. The present study examines the intracellular mechanisms that govern G protein-regulated Ca2+ sensitivity in cerebral arteries of different size and age. We studied β-escin-permeabilized segments of common carotid, basilar, and middle cerebral arteries from nonpregnant adult and near-term fetal sheep. Activation of protein kinase C (PKC) by (−)-indolactam V or a phorbol ester produced receptor-independent increases in Ca2+ sensitivity. Such increases were more marked in immature arteries and were inversely correlated with artery size in both mature and immature arteries. However, inhibitors of PKC did not significantly affect increases in Ca2+ sensitivity in responses to either serotonin (5-hydroxytryptamine, 5-HT) or guanosine 5′- O-(3-thiotriphosphate) (GTPγS). Alternatively, deactivation of rho p21, a small G protein associated with Rho kinase, by exotoxin C3 fully prevented increases in Ca2+ sensitivity in responses to 5-HT or GTPγS in both adult and fetal arteries of all types. Neither inhibitors of PKC nor exotoxin C3 altered baseline Ca2+ sensitivity. We conclude that patterns of receptor- and/or G protein-mediated modulation of Ca2+ sensitivity are dependent on an intracellular pathway that involves activation of small G proteins and Rho kinase. In contrast, PKC has little, if any, role in agonist-induced Ca2+ sensitization under the present experimental conditions.

Traumatic brain injuries (TBI) often involve vascular dysfunction that leads to longterm alterations in physiological and cognitive functions of the brain. Indeed, all the cells that form blood vessels and that are involved in maintaining their proper function can be altered by TBI. In this review, we focus on the different types of cerebrovascular dysfunction that occur after TBI, ranging from cerebral blood flow (CBF) alterations, autoregulation impairments, subarachnoid hemorrhage (SAH), vasospasms, blood-brain barrier (BBB) disruption and edema formation. We also discuss the mechanisms that mediate these dysfunctions, focusing on the cellular components of cerebral blood vessels (endothelial cells, smooth muscle cells, astrocytes, pericytes, perivascular nerves) and their known and potential roles in the secondary injury cascade.