A small-molecule-inducible Nrf2-mediated antioxidant response provides effective prophylaxis against cerebral ischemia in vivo

The transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) coordinates expression of genes required for free radical scavenging, detoxification of xenobiotics, and maintenance of redox potential. Previously, activation of this pleiotropic response was neuroprotective in cell culture models that simulate components of stroke damage. However, the role of Nrf2 in limiting stroke damage in vivo remained unclear. We report that Nrf2 activation protects the brain from cerebral ischemia in vivo. Acute (1-3 d) intracerebroventricular or intraperitoneal pretreatment with tert-butylhydroquinone (tBHQ), an Nrf2 activity inducer, reduced cortical damage and sensorimotor deficit at 24 h and even 1 month after ischemia-reperfusion in rats. Cortical glutathione levels robustly increased with tBHQ administration to rats and Nrf2-expressing mice, but not Nrf2(-/-) mice. Basal and inducible activities of antioxidant/detoxification enzymes in Nrf2(-/-) mice were reduced when compared with Nrf2(+/+) controls. Interestingly, larger infarcts were observed in Nrf2(-/-) mice at 7 d after stroke, but not at 24 h, suggesting that Nrf2 may play a role in shaping the penumbra well after the onset of ischemia. Neuronal death caused by a "penumbral" model of stroke, using intracortical endothelin-1 microinjection, was attenuated by tBHQ administration to Nrf2(+/+), but not to Nrf2(-/-) mice, confirming the Nrf2-specific action of tBHQ in vivo. We conclude that Nrf2 plays a role in modulating ischemic injury in vivo. Accordingly, Nrf2 activation by small molecule inducers may be a practical preventative treatment for stroke-prone patients.

Two-photon microscopy as a tool to study blood flow and neurovascular coupling in the rodent brain

The cerebral vascular system services the constant demand for energy during neuronal activity in the brain. Attempts to delineate the logic of neurovascular coupling have been greatly aided by the advent of two-photon laser scanning microscopy to image both blood flow and the activity of individual cells below the surface of the brain. Here we provide a technical guide to imaging cerebral blood flow in rodents. We describe in detail the surgical procedures required to generate cranial windows for optical access to the cortex of both rats and mice and the use of two-photon microscopy to accurately measure blood flow in individual cortical vessels concurrent with local cellular activity. We further provide examples on how these techniques can be applied to the study of local blood flow regulation and vascular pathologies such as small-scale stroke.

NF-E2-related factor-2 mediates neuroprotection against mitochondrial complex I inhibitors and increased concentrations of intracellular calcium in primary cortical neurons

NF-E2-related factor-2 (Nrf2) regulates the gene expression of phase II detoxification enzymes and antioxidant proteins through an enhancer sequence referred to as the antioxidant-responsive element (ARE). In this study, we demonstrate that Nrf2 protects neurons in mixed primary neuronal cultures containing both astrocytes ( approximately 10%) and neurons ( approximately 90%) through coordinate up-regulation of ARE-driven genes. Nrf2-/- neurons in this mixed culture system were more sensitive to mitochondrial toxin (1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine or rotenone)-induced apoptosis compared with Nrf2+/+ neurons. To understand the underlying mechanism of this observed differential sensitivity, we compared the gene expression profiles using oligonucleotide microarrays. Microarray data showed that Nrf2+/+neuronal cultures had higher expression levels of genes encoding detoxification enzymes, antioxidant proteins, calcium homeostasis proteins, growth factors, neuron-specific proteins, and signaling molecules compared with Nrf2-/- neuronal cultures. As predicted from the microarray data, Nrf2-/- neurons were indeed more vulnerable to the cytotoxic effects of ionomycin- and 2,5-di-(t-butyl)-1,4-hydroquinone-induced increases in intracellular calcium. Finally, adenoviral vector-mediated overexpression of Nrf2 recovered ARE-driven gene expression in Nrf2-/- neuronal cultures and rescued Nrf2-/- neurons from rotenone- or ionomycin-induced cell death. Taken together, these findings suggest that Nrf2 plays an important role in protecting neurons from toxic insult.

The smallest stroke: occlusion of one penetrating vessel leads to infarction and a cognitive deficit

Microinfarctions are present in the aged and injured human brain. Their clinical relevance is controversial, with postulated sequelae ranging from cognitive sparing to vascular dementia. To address the consequences of microinfarcts, we used controlled optical methods to create occlusions of individual penetrating arterioles or venules in rat cortex. Single microinfarcts, targeted to encompass all or part of a cortical column, impaired performance in a macrovibrissa-based behavioral task. Furthermore, the targeting of multiple vessels resulted in tissue damage that coalesced across cortex, even though the intervening penetrating vessels were acutely patent. Post-occlusion administration of memantine, a glutamate receptor antagonist that reduces cognitive decline in Alzheimer's disease, ameliorated tissue damage and perceptual deficits. Collectively, these data imply that microinfarcts likely contribute to cognitive decline. Strategies that have received limited success in the treatment of ischemic injury, which include therapeutics against excitotoxicity, may be successful against the progressive nature of vascular dementia.

Cystine/glutamate exchange modulates glutathione supply for neuroprotection from oxidative stress and cell proliferation

The cystine/glutamate exchanger (xCT) provides intracellular cyst(e)ine for production of glutathione, a major cellular antioxidant. Using xCT overexpression and underexpression, we present evidence that xCT-dependent glutathione production modulates both neuroprotection from oxidative stress and cell proliferation. In embryonic and adult rat brain, xCT protein was enriched at the CSF-brain barrier (i.e., meninges) and also expressed in the cortex, hippocampus, striatum, and cerebellum. To examine the neuroprotective role of xCT, various non-neuronal cell types (astrocytes, meningeal cells, and peripheral fibroblasts) were cocultured with immature cortical neurons and exposed to oxidative glutamate toxicity, a model involving glutathione depletion. Cultured meningeal cells, which naturally maintain high xCT expression, were more neuroprotective than astrocytes. Selective xCT overexpression in astrocytes was sufficient to enhance glutathione synthesis/release and confer potent glutathione-dependent neuroprotection from oxidative stress. Moreover, normally nonprotective fibroblasts could be re-engineered to be neuroprotective with ectopic xCT overexpression indicating that xCT is a key step in the pathway to glutathione synthesis. Conversely, astrocytes and meningeal cells derived from sut/sut mice (xCT loss-of-function mutants) showed greatly reduced proliferation in culture attributable to increased oxidative stress and thiol deficiency, because growth could be rescued by the thiol-donor beta-mercaptoethanol. Strikingly, sut/sut mice developed brain atrophy by early adulthood, exhibiting ventricular enlargement, thinning of the cortex, and shrinkage of the striatum. Our results indicate that xCT can provide neuroprotection by enhancing glutathione export from non-neuronal cells such as astrocytes and meningeal cells. Furthermore, xCT is critical for cell proliferation during development in vitro and possibly in vivo.

Pericyte structure and distribution in the cerebral cortex revealed by high-resolution imaging of transgenic mice

Pericytes are essential for normal brain function, but many aspects of their physiology remain enigmatic due to a lack of tools to genetically target this cell population. Here, we characterize brain pericytes using two existing Cre-recombinase driver mouse lines that can serve distinct purposes in cerebrovascular research. One line expresses an inducible version of Cre under the NG2 proteoglycan promoter, which provides the sparse labeling necessary to define the morphology of single cells. These mice reveal structural differences between pericytes adjacent to arterioles versus those broadly distributed in the capillary bed that may underlie differential roles in control of vessel caliber. A second line expresses Cre constitutively under the platelet-derived growth factor receptor β promoter and provides continuous, highly specific and near-complete labeling of pericytes and myocytes along the entire cerebrovasculature. This line provides a three-dimensional view of pericyte distribution along the cortical angioarchitecture following optical clearing of brain tissue. In combination with recent reporter lines for expression of optogenetic actuators and activity-sensitive probes, these mice may be key tools for studying pericyte biology in the intact brain.

A novel surfactant nanoemulsion with a unique non-irritant topical antimicrobial activity against bacteria, enveloped viruses and fungi

A novel non-ionic surfactant nanoemulsion designated 8N8 has been tested for its biocidal activity. One percent 8N8 produced effective bactericidal activity against Bacillus cereus, Bacillus subtilis, Haemophilus influenzae, Neisseria gonorrhoeae, Streptococcus pneumoniae, and Vibrio cholerae in 15 minutes. In contrast, most enteric gram-negative bacteria were resistant to 8N8. One percent 8N8 was also virucidal within 15 minutes for all tested enveloped viruses, including Herpes simplex type 1, influenza A and vaccinia viruses. One percent 8N8 also demonstrated fungistatic activity on Candida albicans. The rapid and non-specific inactivation of vegetative bacteria and enveloped viruses, in addition to its fungistatic activity and low toxicity in experimental animals, makes 8N8 a potential candidate for use as a topical biocidal agent.

Induction of the Nrf2-driven antioxidant response confers neuroprotection during mitochondrial stress in vivo

NF-E2 related factor (Nrf2) controls a pleiotropic cellular defense, where multiple antioxidant/detoxification pathways are up-regulated in unison. Although small molecule inducers of Nrf2 activity have been reported to protect neurons in vitro, whether similar pathways can be accessed in vivo is not known. We have investigated whether in vivo toxicity of the mitochondrial complex II inhibitor 3-nitropropionic acid (3-NP) can be attenuated by constitutive and inducible Nrf2 activity. The absence of Nrf2 function in Nrf2(-/-) mice resulted in 3-NP hypersensitivity that became apparent with time and increasing dose, causing motor deficits and striatal lesions on a more rapid time scale than identically treated Nrf2(+/+) and Nrf2(+/-) controls. Striatal succinate dehydrogenase activity, the target of 3-NP, was inhibited to the same extent in all genotypes by a single acute dose of 3-NP, suggesting that brain concentrations of 3-NP were similar. Dietary supplementation with the Nrf2 inducer tert-butylhydroquinone attenuated 3-NP toxicity in Nrf2(+/-) mice, but not Nrf2(-/-), confirming the Nrf2-specific action of the inducer in vivo. Increased Nrf2 activity alone was sufficient to protect animals from 3-NP toxicity because intrastriatal adenovirus-mediated Nrf2 overexpression significantly reduced lesion size compared with green fluorescent protein overexpressing controls. In cultured astrocytes, 3-NP was found to increase Nrf2 activity leading to antioxidant response element-dependent gene expression providing a potential mechanism for the increased sensitivity of Nrf2(-/-) animals to 3-NP toxicity in vivo. We conclude that Nrf2 may underlie a feedback system limiting oxidative load during chronic metabolic stress.

Detection, risk factors, and functional consequences of cerebral microinfarcts

Cerebral microinfarcts are small lesions that are presumed to be ischaemic. Despite the small size of these lesions, affected individuals can have hundreds to thousands of cerebral microinfarcts, which cause measurable disruption to structural brain connections, and are associated with dementia that is independent of Alzheimer's disease pathology or larger infarcts (ie, lacunar infarcts, and large cortical and non-lacunar subcortical infarcts). Substantial progress has been made with regard to understanding risk factors and functional consequences of cerebral microinfarcts, partly driven by new in-vivo detection methods and the development of animal models that closely mimic multiple aspects of cerebral microinfarcts in human beings. Evidence from these advances suggests that cerebral microinfarcts can be manifestations of both small vessel and large vessel disease, that cerebral microinfarcts are independently associated with cognitive impairment, and that these lesions are likely to cause damage to brain structure and function that extends beyond their actual lesion boundaries. Criteria for the identification of cerebral microinfarcts with in-vivo MRI are provided to support further studies of the association between these lesions and cerebrovascular disease and dementia.

Entrainment of Arteriole Vasomotor Fluctuations by Neural Activity Is a Basis of Blood-Oxygenation-Level-Dependent "Resting-State" Connectivity

Resting-state signals in blood-oxygenation-level-dependent (BOLD) imaging are used to parcellate brain regions and define "functional connections" between regions. Yet a physiological link between fluctuations in blood oxygenation with those in neuronal signaling pathways is missing. We present evidence from studies on mouse cortex that modulation of vasomotion, i.e., intrinsic ultra-slow (0.1 Hz) fluctuations in arteriole diameter, provides this link. First, ultra-slow fluctuations in neuronal signaling, which occur as an envelope over γ-band activity, entrains vasomotion. Second, optogenetic manipulations confirm that entrainment is unidirectional. Third, co-fluctuations in the diameter of pairs of arterioles within the same hemisphere diminish to chance for separations >1.4 mm. Yet the diameters of arterioles in distant (>5 mm), mirrored transhemispheric sites strongly co-fluctuate; these correlations are diminished in acallosal mice. Fourth, fluctuations in arteriole diameter coherently drive fluctuations in blood oxygenation. Thus, entrainment of vasomotion links neuronal pathways to functional connections.

Organizational hierarchy and structural diversity of microvascular pericytes in adult mouse cortex

Smooth muscle cells and pericytes, together called mural cells, coordinate many distinct vascular functions. Canonically, smooth muscle cells are ring-shaped and cover arterioles with circumferential processes, whereas pericytes extend thin processes that run longitudinally along capillaries. In between these canonical mural cell types are cells with features of both smooth muscle cells and pericytes. Recent studies suggest that these transitional cells are critical for controlling blood flow to the capillary bed during health and disease, but there remains confusion on how to identify them and where they are located in the brain microvasculature. To address this issue, we measured the morphology, vascular territory, and α-smooth muscle actin content of structurally diverse mural cells in adult mouse cortex. We first imaged intact 3D vascular networks to establish the locations of major gradations in mural cell appearance as arterioles branched into capillaries. We then imaged individual mural cells occupying the regions within these gradations. This revealed two transitional cells that were often similar in appearance, but with sharply contrasting levels of α-smooth muscle actin. Our findings highlight the diversity of mural cell morphologies in brain microvasculature, and provide guidance for identification and categorization of mural cell types.

Dynamic Remodeling of Pericytes In Vivo Maintains Capillary Coverage in the Adult Mouse Brain

Direct contact and communication between pericytes and endothelial cells is critical for maintenance of cerebrovascular stability and blood-brain barrier function. Capillary pericytes have thin processes that reach hundreds of micrometers along the capillary bed. The processes of adjacent pericytes come in close proximity but do not overlap, yielding a cellular chain with discrete territories occupied by individual pericytes. Little is known about whether this pericyte chain is structurally dynamic in the adult brain. Using in vivo two-photon imaging in adult mouse cortex, we show that while pericyte somata were immobile, the tips of their processes underwent extensions and/or retractions over days. The selective ablation of single pericytes provoked exuberant extension of processes from neighboring pericytes to contact uncovered regions of the endothelium. Uncovered capillary regions had normal barrier function but were dilated until pericyte contact was regained. Pericyte structural plasticity may be critical for cerebrovascular health and warrants detailed investigation.

Pericyte Control of Blood Flow Across Microvascular Zones in the Central Nervous System

The vast majority of the brain's vascular length is composed of capillaries, where our understanding of blood flow control remains incomplete. This review synthesizes current knowledge on the control of blood flow across microvascular zones by addressing issues with nomenclature and drawing on new developments from in vivo optical imaging and single-cell transcriptomics. Recent studies have highlighted important distinctions in mural cell morphology, gene expression, and contractile dynamics, which can explain observed differences in response to vasoactive mediators between arteriole, transitional, and capillary zones. Smooth muscle cells of arterioles and ensheathing pericytes of the arteriole-capillary transitional zone control large-scale, rapid changes in blood flow. In contrast, capillary pericytes downstream of the transitional zone act on slower and smaller scales and are involved in establishing resting capillary tone and flow heterogeneity. Many unresolved issues remain, including the vasoactive mediators that activate the different pericyte types in vivo, the role of pericyte-endothelial communication in conducting signals from capillaries to arterioles, and how neurological disease affects these mechanisms.

Rapid determination of particle velocity from space-time images using the Radon transform

Laser-scanning methods are a means to observe streaming particles, such as the flow of red blood cells in a blood vessel. Typically, particle velocity is extracted from images formed from cyclically repeated line-scan data that is obtained along the center-line of the vessel; motion leads to streaks whose angle is a function of the velocity. Past methods made use of shearing or rotation of the images and a Singular Value Decomposition (SVD) to automatically estimate the average velocity in a temporal window of data. Here we present an alternative method that makes use of the Radon transform to calculate the velocity of streaming particles. We show that this method is over an order of magnitude faster than the SVD-based algorithm and is more robust to noise.

A polished and reinforced thinned-skull window for long-term imaging of the mouse brain

In vivo imaging of cortical function requires optical access to the brain without disruption of the intracranial environment. We present a method to form a polished and reinforced thinned skull (PoRTS) window in the mouse skull that spans several millimeters in diameter and is stable for months. The skull is thinned to 10 to 15 μm in thickness with a hand held drill to achieve optical clarity, and is then overlaid with cyanoacrylate glue and a cover glass to: 1) provide rigidity, 2) inhibit bone regrowth and 3) reduce light scattering from irregularities on the bone surface. Since the skull is not breached, any inflammation that could affect the process being studied is greatly reduced. Imaging depths of up to 250 μm below the cortical surface can be achieved using two-photon laser scanning microscopy. This window is well suited to study cerebral blood flow and cellular function in both anesthetized and awake preparations. It further offers the opportunity to manipulate cell activity using optogenetics or to disrupt blood flow in targeted vessels by irradiation of circulating photosensitizers.

Functional deficits induced by cortical microinfarcts

Clinical studies have revealed a strong link between increased burden of cerebral microinfarcts and risk for cognitive impairment. Since the sum of tissue damage incurred by microinfarcts is a miniscule percentage of total brain volume, we hypothesized that microinfarcts disrupt brain function beyond the injury site visible to histological or radiological examination. We tested this idea using a mouse model of microinfarcts, where single penetrating vessels that supply mouse cortex were occluded by targeted photothrombosis. We found that in vivo structural and diffusion MRI reliably reported the acute microinfarct core, based on spatial co-registrations with post-mortem stains of neuronal viability. Consistent with our hypothesis, c-Fos assays for neuronal activity and in vivo imaging of single vessel hemodynamics both reported functional deficits in viable peri-lesional tissues beyond the microinfarct core. We estimated that the volume of tissue with functional deficit in cortex was at least 12-fold greater than the volume of the microinfarct core. Impaired hemodynamic responses in peri-lesional tissues persisted at least 14 days, and were attributed to lasting deficits in neuronal circuitry or neurovascular coupling. These data show how individually miniscule microinfarcts could contribute to broader brain dysfunction during vascular cognitive impairment and dementia.

Two-photon imaging of glutathione levels in intact brain indicates enhanced redox buffering in developing neurons and cells at the cerebrospinal fluid and blood-brain interface

Glutathione is the major cellular thiol present in mammalian cells and is critical for maintenance of redox homeostasis. However, current assay systems for glutathione lack application to intact animal tissues. To map the levels of glutathione in intact brain with cellular resolution (acute tissue slices and live animals), we have used two-photon imaging of monochlorobimane fluorescence, a selective enzyme-mediated marker for reduced glutathione. Previously, in vitro experiments using purified components and cultured glial cells attributed cellular monochlorobimane fluorescence to a glutathione S-transferase-dependent reaction with GSH. Our results indicate that cells at the cerebrospinal fluid or blood-brain interface, such as lateral ventricle ependymal cells (2.73 +/- 0.56 mm; glutathione), meningeal cells (1.45 +/- 0.09 mm), and astroglia (0.91 +/- 0.08 mm), contain high levels of glutathione. In comparison, layer II cortical neurons contained 20% (0.21 +/- 0.02 mm) the glutathione content of nearby astrocytes. Neuronal glutathione labeling increased 250% by the addition of the cell-permeable glutathione precursor N-acetylcysteine indicating that the monochlorobimane level or glutathione S-transferase activity within neurons was not limiting. Regional mapping showed that glutathione was highest in cells lining the lateral ventricles, specifically ependymal cells and the subventricular zone, suggesting a possible function for glutathione in oxidant homeostasis of developing neuronal progenitors. Consistently, developing neurons in the subgranular zone of dentate gyrus contained 3-fold more glutathione than older neurons found in the neighboring granular layer. In conclusion, mapping of glutathione levels in intact brain demonstrates a unique role for enhanced redox potential in developing neurons and cells at the cerebrospinal fluid and blood-brain interface.

Pericyte Structural Remodeling in Cerebrovascular Health and Homeostasis

The biology of brain microvascular pericytes is an active area of research and discovery, as their interaction with the endothelium is critical for multiple aspects of cerebrovascular function. There is growing evidence that pericyte loss or dysfunction is involved in the pathogenesis of Alzheimer’s disease, vascular dementia, ischemic stroke and brain injury. However, strategies to mitigate or compensate for this loss remain limited. In this review, we highlight a novel finding that pericytes in the adult brain are structurally dynamic in vivo, and actively compensate for loss of endothelial coverage by extending their far-reaching processes to maintain contact with regions of exposed endothelium. Structural remodeling of pericytes may present an opportunity to foster pericyte-endothelial communication in the adult brain and should be explored as a potential means to counteract pericyte loss in dementia and cerebrovascular disease. We discuss the pathophysiological consequences of pericyte loss on capillary function, and the biochemical pathways that may control pericyte remodeling. We also offer guidance for observing pericytes in vivo, such that pericyte structural remodeling can be more broadly studied in mouse models of cerebrovascular disease.

Structural differences between soluble and membrane bound cytochrome P450s

The superfamily of cytochrome P450s forms a large class of heme monooxygenases with more than 13,000 enzymes represented in organisms from all biological kingdoms. Despite impressive variability in sizes, sequences, location, and function, all cytochrome P450s from various organisms have very similar tertiary structures within the same fold. Here we show that systematic comparison of all available X-ray structures of cytochrome P450s reveals the presence of two distinct structural classes of cytochrome P450s. For all membrane bound enzymes, except the CYP51 family, the beta-domain and the A-propionate heme side chain are shifted towards the proximal side of the heme plane, which may result in an increase of the volume of the substrate binding pocket and an opening of a potential channel for the substrate access and/or product escape directly into the membrane. This structural feature is also observed in several soluble cytochrome P450s, such as CYP108, CYP151, and CYP158A2, which catalyze transformations of bulky substrates. Alternatively, both beta-domains and the A-propionate side chains in the soluble isozymes extend towards the distal site of the heme. This difference between the structures of soluble and membrane bound cytochrome P450s can be rationalized through the presence of several amino acid inserts in the latter class which are involved in direct interactions with the membrane, namely the F'- and G'-helices. Molecular dynamics using the most abundant human cytochrome P450, CYP3A4, incorporated into a model POPC bilayer reveals the facile conservation of a substrate access channel, directed into the membrane between the B-C loop and the beta domain, and the closure of the peripheral substrate access channel directed through the B-C loop. This is in contrast to the case when the same simulation is run in buffer, where no such channel closing occurs. Taken together, these results reveal a key structural difference between membrane bound and soluble cytochrome P450s with important functional implications induced by the lipid bilayer.

Postnatal development of cerebrovascular structure and the neurogliovascular unit

The unceasing metabolic demands of brain function are supported by an intricate three-dimensional network of arterioles, capillaries, and venules, designed to effectively distribute blood to all neurons and to provide shelter from harmful molecules in the blood. The development and maturation of this microvasculature involves a complex interplay between endothelial cells with nearly all other brain cell types (pericytes, astrocytes, microglia, and neurons), orchestrated throughout embryogenesis and the first few weeks after birth in mice. Both the expansion and regression of vascular networks occur during the postnatal period of cerebrovascular remodeling. Pial vascular networks on the brain surface are dense at birth and are then selectively pruned during the postnatal period, with the most dramatic changes occurring in the pial venular network. This is contrasted to an expansion of subsurface capillary networks through the induction of angiogenesis. Concurrent with changes in vascular structure, the integration and cross talk of neurovascular cells lead to establishment of blood-brain barrier integrity and neurovascular coupling to ensure precise control of macromolecular passage and metabolic supply. While we still possess a limited understanding of the rules that control cerebrovascular development, we can begin to assemble a view of how this complex process evolves, as well as identify gaps in knowledge for the next steps of research. This article is categorized under: Nervous System Development > Vertebrates: Regional Development Vertebrate Organogenesis > Musculoskeletal and Vascular Nervous System Development > Vertebrates: General Principles.

The Neurovasculome: Key Roles in Brain Health and Cognitive Impairment: A Scientific Statement From the American Heart Association/American Stroke Association

BACKGROUND

Preservation of brain health has emerged as a leading public health priority for the aging world population. Advances in neurovascular biology have revealed an intricate relationship among brain cells, meninges, and the hematic and lymphatic vasculature (the neurovasculome) that is highly relevant to the maintenance of cognitive function. In this scientific statement, a multidisciplinary team of experts examines these advances, assesses their relevance to brain health and disease, identifies knowledge gaps, and provides future directions.

METHODS

Authors with relevant expertise were selected in accordance with the American Heart Association conflict-of-interest management policy. They were assigned topics pertaining to their areas of expertise, reviewed the literature, and summarized the available data.

RESULTS

The neurovasculome, composed of extracranial, intracranial, and meningeal vessels, as well as lymphatics and associated cells, subserves critical homeostatic functions vital for brain health. These include delivering O2 and nutrients through blood flow and regulating immune trafficking, as well as clearing pathogenic proteins through perivascular spaces and dural lymphatics. Single-cell omics technologies have unveiled an unprecedented molecular heterogeneity in the cellular components of the neurovasculome and have identified novel reciprocal interactions with brain cells. The evidence suggests a previously unappreciated diversity of the pathogenic mechanisms by which disruption of the neurovasculome contributes to cognitive dysfunction in neurovascular and neurodegenerative diseases, providing new opportunities for the prevention, recognition, and treatment of these conditions.

CONCLUSIONS

These advances shed new light on the symbiotic relationship between the brain and its vessels and promise to provide new diagnostic and therapeutic approaches for brain disorders associated with cognitive dysfunction.

Robust and fragile aspects of cortical blood flow in relation to the underlying angioarchitecture

We review the organizational principles of the cortical vasculature and the underlying patterns of blood flow under normal conditions and in response to occlusion of single vessels. The cortex is sourced by a two-dimensional network of pial arterioles that feeds a three-dimensional network of subsurface microvessels in close proximity to neurons and glia. Blood flow within the surface and subsurface networks is largely insensitive to occlusion of a single vessel within either network. However, the penetrating arterioles that connect the pial network to the subsurface network are bottlenecks to flow; occlusion of even a single penetrating arteriole results in the death of a 500 μm diameter cylinder of cortical tissue despite the potential for collateral flow through microvessels. This pattern of flow is consistent with that calculated from a full reconstruction of the angioarchitecture. Conceptually, collateral flow is insufficient to compensate for the occlusion of a penetrating arteriole because penetrating venules act as shunts of blood that flows through collaterals. Future directions that stem from the analysis of the angioarchitecture concern cellular-level issues, in particular the regulation of blood flow within the subsurface microvascular network, and system-level issues, in particular the role of penetrating arteriole occlusions in human cognitive impairment.

A guide to delineate the logic of neurovascular signaling in the brain

The neurovascular system may be viewed as a distributed nervous system within the brain. It transforms local neuronal activity into a change in the tone of smooth muscle that lines the walls of arterioles and microvessels. We review the current state of neurovascular coupling, with an emphasis on signaling molecules that convey information from neurons to neighboring vessels. At the level of neocortex, this coupling is mediated by: (i) a likely direct interaction with inhibitory neurons, (ii) indirect interaction, via astrocytes, with excitatory neurons, and (iii) fiber tracts from subcortical layers. Substantial evidence shows that control involves competition between signals that promote vasoconstriction versus vasodilation. Consistent with this picture is evidence that, under certain circumstances, increased neuronal activity can lead to vasoconstriction rather than vasodilation. This confounds naïve interpretations of functional brain images. We discuss experimental approaches to detect signaling molecules in vivo with the goal of formulating an empirical basis for the observed logic of neurovascular control.

A rapid staining technique for the detection of the initiation of germination of bacterial spores

AIMS

We propose to apply the Wirtz-Conklin staining technique to evaluate spore germination.

METHODS AND RESULTS

Spores at different stages of germination were stained with modified spore stain (Wirtz-Conklin) and evaluated for staining properties. Bacillus spores suspended in deionized water, which does not support germination, stained greenish-blue. Spores suspended in germination enhancers that did not form bacilli stained pink, indicating the initiation of germination. Spores suspended in culture media, which promotes bacterial outgrowth, formed bacilli and were also stained pink.

CONCLUSIONS

Modified spore stain (Wirtz-Conklin) was found to be useful to detect the initiation of spore germination as early as 30 min following incubation in a germination environment.

SIGNIFICANCE AND IMPACT OF THE STUDY

This simple staining procedure is useful in detecting the initiation of germination of bacterial spores.

Acute vascular disruption and aquaporin 4 loss after stroke

BACKGROUND AND PURPOSE

Ischemic protection has been demonstrated by a decrease in stroke-infarct size in transgenic mice with deficient Aquaporin 4 (AQP4) expression. However, it is not known whether AQP4 is rapidly reduced during acute stroke in animals with normal AQP4 phenotype, which may provide a potential self-protective mechanism.

METHODS

Adult male rats underwent transient occlusion of the middle cerebral artery (tMCAo) for 1 to 8 hours followed by reperfusion for 30 minutes. Protein and mRNA expression of AQP4 and glial fibrillary acidic protein (GFAP) were determined by Western blot and rtPCR. Fluorescence quantitation was obtained with laser scanning cytometry (LSC) for Cy5-tagged immunoreactivity along with fluorescein signals from pathological uptake of plasma-borne high-molecular-weight fluorescein-dextran. Cell death was assessed with in vivo Propidium Iodide (PI) nucleus labeling.

RESULTS

In the ischemic hemisphere in tissue sections, patches of fluorescein-dextran uptake were overlapped with sites of focal loss of AQP4 immunoreactivity after tMCAo of 1 to 8 hours duration. However, the average levels of AQP4 protein and mRNA, determined in homogenates of whole striatum, were not significantly reduced after 8 hours of tMCAo. Tissue section cytometry (LSC) of immunoreactivity in scan areas with high densities of fluorescein-dextran uptake demonstrated reductions in AQP4, but not in IgG or GFAP, after tMCAo of 2 hours or longer. Scan areas with low densities of fluorescein-dextran did not lose AQP4. There was sparse astrocyte cell death as only 1.7+/-0.85% (mean, SD) of DAPI labeled cells were PI- and GFAP-labeled after 8 hours of tMCAo.

CONCLUSIONS

During acute tMCAo, a rapid loss of AQP4 immunoreactivity from viable astrocytes can occur. However, AQP4 loss is spatially selective and occurs primarily in regions of vascular damage.