The blood-brain barrier: cellular basis

Viral inhibitory potential of hyoscyamine in Japanese encephalitis virus-infected embryonated chicken eggs involving multiple signaling pathways

Japanese encephalitis virus (JEV) is the leading cause of viral encephalitis worldwide. The emergence of new genotypes of the virus and a high rate of mutation make it necessary to develop alternative treatment strategies against this deadly pathogen. Although the antiviral properties of Atropa belladonna and some of its active components, such as atropine and scopolamine, have been studied, the effect of another important component, hyoscyamine, against JEV infection has not yet been investigated. In this study, we investigated the antiviral effect of hyoscyamine against JEV and its immunomodulatory activity in embryonated chicken eggs. Pretreatment with hyoscyamine sulphate resulted in a significant decrease in the viral load in both chorioallantoic membrane (CAM) and brain tissues at 48 and 96 hours postinfection. In silico studies showed stable binding and interaction between hyoscyamine and non-structural protein 5 (NS5), suggesting that this could be the basis of its antiviral effect. Embryonated eggs pretreated with hyoscyamine sulphate showed upregulation of Toll-like receptor 3 (TLR3), TLR7, TLR8, interleukin 4 (IL-4), and IL-10 as well as interferons and regulatory factors. Hyoscyamine sulphate was also found to cause significant downregulation of TLR4. The potential use of hyoscyamine for controlling JEV replication and its dissemination to the brain suggest that it may be a promising therapy option against JEV in the future.

Pre-treatment with Scopolamine Naturally Suppresses Japanese Encephalitis Viral Load in Embryonated Chick Through Regulation of Multiple Signaling Pathways

Suitable recognition of invasive microorganisms is a crucial factor for evoking a strong immune response that can combat the pathogen. Toll-like receptors (TLRs) play a pivotal role in the induction of this innate immune response through stimulation of interferons (IFNs) that control viral replication in the host via distinct signaling pathways. Though the antiviral property of Atropa belladonna has been established, yet the role of one of its active components scopolamine in modulating various factors of the innate immune branch has not yet been investigated until date. Thus, the present study was conducted to assess the antiviral effects of scopolamine and its immunomodulatory role against Japanese encephalitis virus (JEV) infections in embryonated chick. Pre-treatment with scopolamine hydrobromide showed a significant decrease in the viral loads of chorioallantoic membrane (CAM) and brain tissues. Molecular docking analysis revealed that scopolamine hydrobromide binds to the active site of non-structural protein 5 (NS5) that has enzymatic activities required for replication of JEV, making it a highly promising chemical compound against the virus. The binding contributions of different amino acid residues at or near the active site suggest a potential binding of this compound. Pre-treatment with the scopolamine hydrobromide showed significant upregulation of different TLRs like TLR3, TLR7, and TLR8, interleukins like IL-4, and IL-10, as well as IFNs and their regulatory factors. However, virus-infected tissues (direct infection group) exhibited higher TLR4 expression as compared to scopolamine hydrobromide pre-treated, virus-infected tissues (medicine pre-treated group). These results indicate that scopolamine hydrobromide contributes much to launch antiviral effects by remoulding the TLR and IFN signaling pathways that are involved in sensing and initiating the much-needed anti-JEV responses.

The study of the function of AQP4 in cerebral ischaemia-reperfusion injury using poroelastic theory

Brain oedema is thought to form and to clear through the use of water-protein channels, aquaporin-4 (AQP4), which are found in the astrocyte endfeet. The model developed here is used to study the function of AQP4 in the formation and elimination of oedema fluid in ischaemia-reperfusion injury. The cerebral space is assumed to be made of four fluid compartments: astrocyte, neuron, ECS and blood microvessels, and a solid matrix for the tissue, and this is modelled using multiple-network poroelastic theory. AQP4 allows the movement of water between astrocyte and the ECS and the microvessels. It is found that the presence of AQP4 may help in reducing vasogenic oedema shown by a decrease in brain tissue extracellular pressure. However, the astrocyte pressure will increase to compensate for this decrease, which may lead to cytotoxic oedema. In addition, the swelling will also depend on the ionic concentrations in the astrocyte and extracellular space, which may change after ischaemic stroke. Understanding the role of AQP4 in oedema may thus help the development of a treatment plan in reducing brain swelling after ischaemia-reperfusion.

Retinal microvascular network alterations: potential biomarkers of cerebrovascular and neural diseases

Increasing evidence suggests that the conditions of retinal microvessels are indicators to a variety of cerebrovascular, neurodegenerative, psychiatric, and developmental diseases. Thus noninvasive visualization of the human retinal microcirculation offers an exceptional opportunity for the investigation of not only the retinal but also cerebral microvasculature. In this review, we show how the conditions of the retinal microvessels could be used to assess the conditions of brain microvessels because the microvascular network of the retina and brain share, in many aspects, standard features in development, morphology, function, and pathophysiology. Recent techniques and imaging modalities, such as optical coherence tomography (OCT), allow more precise visualization of various layers of the retina and its microcirculation, providing a "microscope" to brain microvessels. We also review the potential role of retinal microvessels in the risk identification of cerebrovascular and neurodegenerative diseases. The association between vision problems and cerebrovascular and neurodegenerative diseases, as well as the possible role of retinal microvascular imaging biomarkers in cerebrovascular and neurodegenerative screening, their potentials, and limitations, are also discussed.

Application of the chick embryo chorioallantoic membrane in neurosurgery disease

The chick embryo chorioallantoic membrane (CAM) is a highly vascularized extraembryonic membrane. Because of its ease of accessibility, extensive vascularization and immunodeficient environment, the CAM has been broadly used in the oncology, biology, pharmacy, and tissue regeneration research. The present review summarizes the application of the CAM in neurosurgery disease research. We focused on the use of the CAM as an assay for the research of glioma, vascular anomalies, Moyamoya Disease, and the blood-brain barrier.

Generation of primary astrocyte cultures devoid of contaminating microglia

Microglia, resident phagocytic cells of the central nervous system, are frequent contaminants of astrocyte cultures. Unfortunately and not always fully appreciated, contamination by microglia can confound results of studies designed to elucidate the molecular mechanisms underlying astrocyte-specific responses. The paradigm described herein employs the mitotic inhibitor, cytosine β-D: -arabinofuranoside, followed by the lysosomotropic agent, leucine methylester, to maximally deplete microglia, thereby generating highly enriched astrocyte monolayers that remain viable and functional. Successful removal of microglia from confluent monolayers of primary astrocyte cultures is achieved without the need for cell passage and successful reduction is confirmed by depletion of microglial-specific markers.

Isolation and culture of neurons and astrocytes from the mouse brain cortex

Many experimental animal models of human neurodegenerative diseases have been developed to understand the events leading toward neuronal dysfunction and death. However, definitive comprehension of the molecular and cellular mechanisms in these animal models is problematic because of the complexity of the intact nervous tissue. Primary neuronal cultures prepared from rodent nervous tissues represent a powerful tool not only to study the individual contribution of different cell types (such as neurons or glia) to disease progression, but also to investigate the role of neuron-glia interactions during development and pathogenesis of disease. Here, we describe a method to isolate and culture neurons and astrocytes from the mouse cerebral cortex, and we also present a practical application for transfection and subsequent immunofluorescence.

Evaluation of the selected barrier properties of retinal pigment epithelial cell line ARPE-19 for an in-vitro blood-brain barrier model

In-vitro models that maintain complex transport mechanisms and structural properties associated with the blood-brain barrier in vivo would be useful in drug permeability and neurotoxicological studies. To evaluate the suitability of a human retinal pigment epithelial cell line for a blood-brain barrier model, we have compared the barrier properties of the human retinal pigment epithelial cell line ARPE-19, the human colonic adenocarcinoma cell line Caco-2, and primary porcine microvessel endothelial cells. The tight junction proteins occludin and ZO-1 were stained immunocytochemically. The paracellular ionic permeability was evaluated by measuring the trans-epithelial or trans-endothelial electric resistance. To evaluate the active transport mechanisms, the existence and the activity of the efflux transporters, P-glycoprotein and multidrug resistance-associated proteins, were studied. All the cell types in this study stained positively for occludin and ZO-1. However, the trans-endothelial electric resistance of ARPE-19 cells was low compared with that of primary porcine microvessel endothelial cell and Caco-2 cells. In addition, both the P-glycoprotein expression and its activity in ARPE-19 cells were low. In conclusion, the barrier properties of the human ARPE-19 cell line were not satisfactory for a blood-brain barrier model. For future studies, it is important to develop a human brain endothelial cell line with expression of the complex in-vivo properties of the blood-brain barrier.

Manganese neurotoxicity: a focus on the neonate

Manganese (Mn) is an essential trace metal found in all tissues, and it is required for normal amino acid, lipid, protein, and carbohydrate metabolism. While Mn deficiency is extremely rare in humans, toxicity due to overexposure of Mn is more prevalent. The brain appears to be especially vulnerable. Mn neurotoxicity is most commonly associated with occupational exposure to aerosols or dusts that contain extremely high levels (>1-5 mg Mn/m(3)) of Mn, consumption of contaminated well water, or parenteral nutrition therapy in patients with liver disease or immature hepatic functioning such as the neonate. This review will focus primarily on the neurotoxicity of Mn in the neonate. We will discuss putative transporters of the metal in the neonatal brain and then focus on the implications of high Mn exposure to the neonate focusing on typical exposure modes (e.g., dietary and parenteral). Although Mn exposure via parenteral nutrition is uncommon in adults, in premature infants, it is more prevalent, so this mode of exposure becomes salient in this population. We will briefly review some of the mechanisms of Mn neurotoxicity and conclude with a discussion of ripe areas for research in this underreported area of neurotoxicity.

Differential expression of cell fate determinants in neurons and glial cells of adult mouse spinal cord after compression injury

Cellular responses after spinal cord injury include activation of astrocytes, degeneration of neurons and oligodendrocytes, and reactions of the ependymal layer and meningeal cells. Because it has been suggested that tissue repair partially recapitulates morphogenesis, we have investigated the expression of several developmentally prominent molecules after spinal cord injury of adult mice where neurogenesis does not occur after injury. Cell fate determinants Numb, Notch-1, Shh and BMPs are abundantly expressed during development but mostly decline in the adult. In the present study, we investigated whether these genes are triggered by spinal cord injury as a sign of attempted recapitulation of development. Expression of Numb, Notch, Shh, BMP2/4 and Msx1/2 was analysed in the adult mouse spinal cord after compression injury by in situ hybridization up to 1 month after injury. The mRNA expression levels of Notch-1, Numb, Shh, BMP4 and Msx2 increased in the grey matter and/or white matter and in the ependyma rostral and caudal to the lesion site after injury. However, BMP2 and Msx1 were not up-regulated. Combining immunohistochemistry of cell type-specific markers with in situ hybridization we found that all the up-regulated genes were expressed in neurons. Moreover, Numb, BMP4 and Msx2 were also expressed by GFAP-positive astrocytes, while Shh was expressed by MBP-positive oligodendrocytes. In conclusion, the cell fate determinants Notch-1, Numb, Shh, BMP4 and Msx2 are expressed in neurons and/or glial cells after injury in a time-dependent manner, suggesting that these genes reflect to some extent an endogenous self-repair potential by recapitulating some features of development.

Manganese transport by rat brain endothelial (RBE4) cell-based transwell model in the presence of astrocyte conditioned media

Manganese (Mn), an essential nutrient, is neurotoxic at high levels and has been associated with the development of a parkinsonian syndrome termed manganism. Currently, the mechanisms responsible for transporting Mn across the blood-brain barrier (BBB) are unknown. By using rat brain endothelial 4 (RBE4) cell monolayers cultured in astrocyte-conditioned media (ACM), we examine the effects of temperature, energy, proton (pH), iron (Fe), and sodium (Na(+)) dependence on Mn transport. Our results suggest that Mn transport is temperature, energy, and pH dependent, but not Fe or Na(+) dependent. These data suggest that Mn transport across the BBB is an active process, but they also demonstrate that the presence of ACM in endothelial cell cultures decreases the permeability of these cells to Mn, reinforcing the use of ACM or astrocyte cocultures in studies examining metal transport across the BBB.

Characterization of an improved procedure for the removal of microglia from confluent monolayers of primary astrocytes

Cultures of astrocytes can be readily established and are widely used to study the biological functions of these glial cells in isolation. Unfortunately, contamination by microglia can confound results from such studies. Herein, a simple and highly effective modification of a common procedure to remove microglia from astrocyte cultures is described. After becoming confluent, astrocytes were exposed to a mitotic inhibitor for 5-6 days then treated with 50-75 mM l-leucine methyl ester (LME) for 60-90 min. Unlike previous protocols that employed lower LME concentrations on subconfluent cultures or during passage of astrocytes, this protocol effectively depleted microglia from high-density astrocyte monolayers. This was evidenced by the selective depletion of microglial-specific markers. Purified monolayers appeared morphologically normal 24h after LME treatment and expressed nitric oxide synthase-2 (NOS-2) and cyclooxygenase-2 (COX-2) proteins upon stimulation with LPS plus IFNgamma, albeit to a lower level than unpurified monolayers. This difference could be attributed to removal of contaminating microglia from monolayers and not to astrocyte dysfunction, since LME treatment did not alter global protein synthesis and a reactive phenotype could be induced in the purified monolayers. Thus, this modified protocol selectively depletes microglia from high-density primary astrocyte monolayers without compromising their functional integrity.

Basic Principles of Cerebrospinal Fluid Metabolism and Intracranial Pressure Homeostasis

Significant progress has been made in understanding the production,circulation, and absorption of CSF. In part because of autoregulation, rapid changes in arterial pressure produce parallel but significantly dampened changes in CSF pressure. Chronic arterial hypertension rarely affects ICP,but changes in venous pressure are transmitted directly into the CSF, taking precedence over arterial effects. An understanding of basic CSF physiology,particularly in relation to ICP homeostasis, is important for surgeons treating intracranial hypertension, low ICP pressure, and spontaneous,traumatic, or iatrogenic CSF leakages. The principles discussed in this article are valuable to remember when planning surgical procedures in the head and neck, both to prevent and to treat potential complications related to increased or decreased CSF pressure.

Retinal vascular image analysis as a potential screening tool for cerebrovascular disease: a rationale based on homology between cerebral and retinal microvasculatures

The retinal and cerebral microvasculatures share many morphological and physiological properties. Assessment of the cerebral microvasculature requires highly specialized and expensive techniques. The potential for using non-invasive clinical assessment of the retinal microvasculature as a marker of the state of the cerebrovasculature offers clear advantages, owing to the ease with which the retinal vasculature can be directly visualized in vivo and photographed due to its essential two-dimensional nature. The use of retinal digital image analysis is becoming increasingly common, and offers new techniques to analyse different aspects of retinal vascular topography, including retinal vascular widths, geometrical attributes at vessel bifurcations and vessel tracking. Being predominantly automated and objective, these techniques offer an exciting opportunity to study the potential to identify retinal microvascular abnormalities as markers of cerebrovascular pathology. In this review, we describe the anatomical and physiological homology between the retinal and cerebral microvasculatures. We review the evidence that retinal microvascular changes occur in cerebrovascular disease and review current retinal image analysis tools that may allow us to use different aspects of the retinal microvasculature as potential markers for the state of the cerebral microvasculature.

Role for the α7β1 integrin in vascular development and integrity

The alpha7beta1 integrin is a laminin receptor that has been implicated in muscle disease and the development of neuromuscular and myotendinous junctions. Studies have shown the alpha7beta1 integrin is also expressed in nonskeletal muscle tissues. To identify the expression pattern of the alpha7 integrin in these tissues during embryonic development, alpha7 integrin chain knockout mice were generated by a LacZ knockin strategy. In these mice, expression from the alpha7 promoter is reported by beta-galactosidase. From embryonic day (ED) 11.5 to ED14.5, beta-galactosidase was detected in the developing central and peripheral nervous systems and vasculature. The loss of the alpha7 integrin gene resulted in partial embryonic lethality. Several alpha7 null embryos were identified with cerebrovascular hemorrhages and showed reduced vascular smooth muscle cells and cerebral vascularization. The alpha7 null mice that survived to birth exhibited vascular smooth muscle defects, including hyperplasia and hypertrophy. In addition, altered expression of alpha5 and alpha6B integrin chains was detected in the cerebral arteries of alpha7 null mice, which may contribute to the vascular phenotype. Our results demonstrate for the first time that the alpha7beta1 integrin is important for the recruitment or survival of cerebral vascular smooth muscle cells and that this integrin plays an important role in vascular development and integrity.

Neuropathological features of mitochondrial disorders

Genetic defects affecting the mitochondrial respiratory chain comprise an important cause of encephalomyopathies. Considering the structural complexity of the respiratory chain, its dual genetic control, and the numerous nuclear genes required for proper assembly of the enzyme complexes, the phenotypic heterogeneity is not surprising. From a neuropathological view point, application of in situ hybridization and immunohistochemistry to study the choroid plexus and brain-blood barrier in "prototypes" of mitochondrial encephalopathies have revealed alterations that we think are important in the pathogenesis of central nervous system dysfunction in these disorders. As the role of the blood-cerebrospinal fluid (CSF) and brain-blood barriers in mitochondrial encephalopathies is better understood, manipulation of their functions offers promises for therapeutic interventions.

Toxin-induced vasogenic cerebral oedema in a rat model

Vasogenic cerebral oedema (VCO) was induced in Hooded Wistar rats by intraperitoneal injection of Clostridium perfringens type D epsilon prototoxin. Animals were killed, 1 h to 14 d postinjection, by perfusion fixation under general anaesthesia. VCO was detected by the presence of endogenous albumin in the brain, visualised by immunocytochemistry. As early as 1 h postinjection, albumin was detected in the walls of cerebral microvessels. Maximal diffuse leakage within the neural parenchyma was seen at 24 and 48 h and immunoreactivity was still present at 4 d. At 7 d only few foci were seen, and at 14 d albumin distribution was similar to that in controls. Ultrastructural assessment of the microvessels showed swelling of many astrocytic processes and abnormalities of the endothelial cells varying from swelling with loss of cytoplasmic organelles to cells showing increased electron density. Immunostaining for the endothelial barrier antigen (EBA) showed strongly immunoreactive vessels throughout normal brains. Experimental animals showed partial reduction in EBA expression, most evident at 24 and 48 h, with gradual recovery to normal by 14 d. The exact role that EBA plays in the intact BBB remains obscure.

Cerebral microvascular pathology in aging and Alzheimer's disease

The aging of the central nervous system and the development of incapacitating neurological diseases like Alzheimer's disease (AD) are generally associated with a wide range of histological and pathophysiological changes eventually leading to a compromised cognitive status. Although the diverse triggers of the neurodegenerative processes and their interactions are still the topic of extensive debate, the possible contribution of cerebrovascular deficiencies has been vigorously promoted in recent years. Various forms of cerebrovascular insufficiency such as reduced blood supply to the brain or disrupted microvascular integrity in cortical regions may occupy an initiating or intermediate position in the chain of events ending with cognitive failure. When, for example, vasoconstriction takes over a dominating role in the cerebral vessels, the perfusion rate of the brain can considerably decrease causing directly or through structural vascular damage a drop in cerebral glucose utilization. Consequently, cerebral metabolism can suffer a setback leading to neuronal damage and a concomitant suboptimal cognitive capacity. The present review focuses on the microvascular aspects of neurodegenerative processes in aging and AD with special attention to cerebral blood flow, neural metabolic changes and the abnormalities in microvascular ultrastructure. In this context, a few of the specific triggers leading to the prominent cerebrovascular pathology, as well as the potential neurological outcome of the compromised cerebral microvascular system are also going to be touched upon to a certain extent, without aiming at total comprehensiveness. Finally, a set of animal models are going to be presented that are frequently used to uncover the functional relationship between cerebrovascular factors and the damage to neural networks.

Calcium antagonists decrease capillary wall damage in aging hypertensive rat brain

Chronic hypertension during aging is a serious threat to the cerebral vasculature. The larger brain arteries can react to hypertension with an abnormal wall thickening, a loss of elasticity and a narrowed lumen. However, little is known about the hypertension-induced alterations of cerebral capillaries. The present study describes ultrastructural alterations of the cerebrocortical capillary wall, such as thickening and collagen accumulation in the basement membrane of aging spontaneously hypertensive stroke-prone rats. The ratio of cortical capillaries with such vascular pathology occurred significantly more frequently in hypertensive animals. Nimodipine and nifedipine are potential drugs to decrease blood pressure in hypertension but their beneficial effects in experimental studies reach beyond the control of blood pressure. Nimodipine and nifedipine can alleviate ischemia-related symptoms and improve cognition. These drugs differ in that nifedipine, but not nimodipine reduces blood pressure at the here-used concentration while both drugs can penetrate the blood-brain barrier. Here we show that chronic treatment of aging hypertensive stroke-prone rats with nimodipine or nifedipine could preserve microvascular integrity in the cerebral cortex.

Qualitative and quantitative analysis of monocyte transendothelial migration by confocal microscopy and three-dimensional image reconstruction

A novel method for qualitative and quantitative analysis of monocyte transendothelial migration is described. By labeling monocytes and endothelial cells with different fluorophores, and utilizing confocal microscopy and three-dimensional image reconstruction, transmigrating monocytes were resolved and quantified within a subendothelial collagen gel. Comparison of monocyte migration across endothelial monolayers derived from human brain microvessels versus umbilical veins revealed diapedesis across brain endothelium to be significantly delayed. Inclusion of astrocytes within the subendothelial collagen gel resulted in the formation of an array of astrocytic processes that simulated the glia limitans surrounding brain microvessels in situ, thus yielding a more physiologic paradigm of the blood-brain barrier. By virtue of its unique capacity to provide information on the total number of migrating cells, this analytic approach overcomes significant caveats associated with sampling only aspects of the migration process. The potential adaptability of this method to computer-assisted analysis further enhances its prospective use in high-throughput screening.

Confocal microscopic study of glial-vascular relationships in the retinas of pigmented rats

Astroglia are interposed between the cerebral vasculature and neurons, where they may mediate the transfer of substances from the circulation to neurons and couple changes in neuronal activity to changes in cerebral blood flow. The retina is a particularly advantageous model system for studying glial-vascular interactions in situ. Confocal microscopy and three-dimensional image reconstruction were used to study the anatomical relationships between glia and the surface vasculature in retinas acutely isolated from adult pigmented rats. Retinas were immunostained using antibodies directed against the basal lamina surrounding the vasculature as well as antibodies directed against glial fibrillary acidic protein. Surface vessels of all calibers were contacted by the processes of astrocytes. The vitreal surfaces of the large retinal vessels were covered by a meshwork of immunoreactive astrocyte processes of a variety of shapes, whereas the scleral surfaces of the vessels were supported by thick bundles of astrocyte processes. In addition, glial cells were filled intracellularly with the gap junction-permeable tracers Lucifer yellow and Neurobiotin. Intracellular fills clearly demonstrated the presence of astrocytes with somata that were closely apposed to the large retinal vessels. Tracer-filled astrocytes displayed a variety and complexity of shapes that was not apparent in immunostained material. Gap junctional coupling was stronger between astrocytes adjacent to the same artery than between periarterial astrocytes and astrocytes located away from arteries. Significantly fewer Müller cells were labeled when Neurobiotin was injected into astrocytes associated with arteries than when Neurobiotin was injected into astrocytes that were distant from arteries.

Vascular endothelial growth factor up-regulates ICAM-1 expression via the phosphatidylinositol 3 OH-kinase/AKT/Nitric oxide pathway and modulates migration of brain microvascular endothelial cells

Endothelium of the cerebral blood microvessels, which constitutes the major component of the blood-brain barrier, controls leukocyte and metastatic cancer cell adhesion and trafficking into the brain parenchyma. In this study, using rat primary brain microvascular endothelial cells (BMEC), we demonstrate that the vascular endothelial growth factor (VEGF), a potent promoter of angiogenesis, up-regulates the expression of the intracellular adhesion molecule-1 (ICAM-1) through a novel pathway that includes phosphatidylinositol 3 OH-kinase (PI3K), AKT, and nitric oxide (NO), resulting in the migration of BMEC. Upon VEGF treatment, AKT is phosphorylated in a PI3K-dependent manner. AKT activation leads to NO production and release and activation-deficient AKT attenuates NO production stimulated by VEGF. Transfection of the constitutive myr-AKT construct significantly increased basal NO release in BMEC. In these cells, VEGF and the endothelium-derived NO synergistically up-regulated the expression of ICAM-1, which was mediated by the PI3K pathway. This activity was blocked by the PI3K-specific inhibitor, wortmannin. Furthermore, VEGF and NO significantly increased BMEC migration, which was mediated by the up-regulation of ICAM-1 expression and was dependent on the integrity of the PI3K/AKT/NO pathway. This effect was abolished by wortmannin, by the specific ICAM-1 antibody, by the specific inhibitor of NO synthase, N(G)-l-monomethyl-arginine (l-NMMA) or by a combination of wortmannin, ICAM-1 antibody, and l-NMMA. These findings demonstrate that the angiogenic factor VEGF up-regulates ICAM-1 expression and signals to ICAM-1 as an effector molecule through the PI3K/AKT/NO pathway, which leads to brain microvessel endothelial cell migration. These observations may contribute to a better understanding of BMEC angiogenesis and the physiological as well as pathophysiological function of the blood-brain barrier, whose integrity is crucial for normal brain function.

Cerebral microvascular endothelial cell tube formation: role of astrocytic epoxyeicosatrienoic acid release

Cerebral microvascular endothelial cells (CMVEC) form tubes when cocultured with astrocytes (AS). Therefore, it appears that AS may be important in mediating angiogenesis in the brain. We hypothesized that AS modulate CMVEC tube formation by releasing a soluble factor. Thymidine incorporation in cultured CMVEC increased 305% when incubated with 50% conditioned AS medium for 24 h [control: 52,755 +/- 4,838 counts per minute (cpm) per well, conditioned 161,082 +/- 12,099 cpm/well, n = 8]. Because our laboratory has previously shown that AS can produce epoxyeicosatrienoic acids (EETs), which are known mitogens, we investigated whether release of EETs by AS is responsible for tube formation in the CMVEC-AS coculture. AS were seeded on Lab-Tek slides, CMVEC were seeded on the AS the next day, and cultures were allowed to progress for another 5 days with and without cytochrome P-450 epoxygenase blockade by 17-octadecynoic acid (17-ODYA). Tube formation in cocultures receiving 17-ODYA was significantly inhibited compared with control (93.8%). These data suggest that tube formation requires the release of EETs by AS.

An integrative approach to neurotoxicology

Exposure of human populations to a wide variety of chemicals has generated concern about the potential neurotoxicity of new and existing chemicals. Experimental studies conducted in laboratory animals remain critical to the study of neurotoxicity. An integrative approach using pharmacokinetic, neuropathological, neurochemical, electrophysiological, and behavioral methods is needed to determine whether a chemical is neurotoxic. There are a number of factors that can affect the outcome of a neurotoxicity study, including the choice of animal species, dose and dosage regimen, route of administration, and the intrinsic sensitivity of the nervous system to the test chemical. The neurotoxicity of a chemical can vary at different stages of brain development and maturity. Evidence of neurotoxicity may be highly subjective and species specific and can be complicated by the presence of systemic disease. The aim of this paper is to give an overview of these and other factors involved in the assessment of the neurotoxic potential for chemicals. This article discusses the neurotoxicity of several neurotoxicants (eg, acrylamide, trimethyltin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, manganese, and ivermectin), thereby highlighting a multidisciplinary approach to the assessment of chemically induced neurotoxicity in animals. These model chemicals produce a broad range of effects that includes peripheral axonopathy, selective neuronal damage within the nervous system, and impaired neuronal-glial metabolism.

Neuroglial activation repertoire in the injured brain: graded response, molecular mechanisms and cues to physiological function

Damage to the central nervous system (CNS) leads to cellular changes not only in the affected neurons but also in adjacent glial cells and endothelia, and frequently, to a recruitment of cells of the immune system. These cellular changes form a graded response which is a consistent feature in almost all forms of brain pathology. It appears to reflect an evolutionarily conserved program which plays an important role in the protection against infectious pathogens and the repair of the injured nervous system. Moreover, recent work in mice that are genetically deficient for different cytokines (MCSF, IL1, IL6, TNFalpha, TGFbeta1) has begun to shed light on the molecular signals that regulate this cellular response. Here we will review this work and the insights it provides about the biological function of the neuroglial activation in the injured brain.

Vasopressin and sensory circumventricular organs

The subfornical organ, the area postrema and the organum vasculosum of the lamina terminalis are considered to be sensory circumventricular organs as they contain neuronal somata which are located outside the blood-brain barrier and are thus capable of serving as 'sensors' for blood-borne humoral messengers. The endocrine hormone, vasopressin (VP), not only causes strong antidiuresis by acting on the kidney, but also exerts centrally mediated effects as a neuromodulator. Several lines of evidence suggest that VP can influence regulatory functions mediated by the sensory circumventricular organs, since vasopressinergic somata and terminals as well as VP receptors have been reposted to be present in these structures. These biochemical prerequisites offer the possibility that blood-borne VP might on the one hand act as a feedback signal from the periphery and, on the other hand, synaptically released or locally produced VP could modulate the known functions of sensory circumventricular organs, such as thirst, fever or cardiovascular regulation. This review focuses on the possible physiological relevance of VP acting on sensory circumventricular organs in view of recent evidence obtained from biochemical and electrophysiological studies at the cellular level.

Late onset and increasing expression of the gap junction protein connexin30 in adult murine brain and long-term cultured astrocytes

In rat brain, expression of the gap junction protein connexin30 increased during the first 3 weeks after birth and reached its maximum after 4 weeks, as shown by analysis with specific connexin30 antibodies. This contrasts with the prenatal onset of connexin43 expression. On cryosections of rat brain, connexin30 immunoreactivity was found near blood vessels and in ependymal as well as in leptomeningeal cells. Expression in the neuropil was first noticed 3 weeks after birth, showing the same spatial pattern of immunoreactivity as connexin43. This late onset of connexin30 expression in astrocytes was also seen in long-term glial cell cultures, where connexin30 was coexpressed with the astrocytic marker proteins S-100beta and glial fibrillary acid protein. In acute brain slices, connexin30 immunofluorescent signals were detected on processes of functionally identified astrocytes. Thus, our results show that connexin30 is expressed in three different cell types of the rodent brain. The late onset of connexin30 expression in astrocytes suggests that this gap junctional protein fulfills a role in intercellular communication among mature astrocytes.

Astrocyte-Derived Monocyte-Chemoattractant Protein-1 Directs the Transmigration of Leukocytes Across a Model of the Human Blood-Brain Barrier

The migration of leukocytes across the blood-brain barrier (BBB) into the central nervous system is critical in the pathogenesis of central nervous system inflammatory diseases. The production of chemokines, such as monocyte-chemoattractant protein-1 (MCP-1), by endothelial cells (EC) and astrocytes may initiate and amplify this process. Using a coculture of human EC and astrocytes to model the BBB, we demonstrated that exogenous MCP-1 induces the transmigration of monocytes in a dose-dependent manner. TNF-α, IFN-γ, or IL-1β treatment of cocultures also induced significant migration of monocytes that correlates with the induction of MCP-1 protein. TGF-β, previously shown to induce MCP-1 expression in astrocytes, but not in EC, caused migration of monocytes across cocultures, but not across EC grown alone. Monocytes and lymphocytes transmigrated across cytokine-treated cocultures in greater numbers than across EC alone. Astrocytes were the main source of cytokine-induced MCP-1, supporting a role for astrocytes in facilitating leukocyte transmigration. A blocking Ab to MCP-1 inhibited MCP-1- and cytokine-induced transmigration of monocytes by 85–90%. Cytokine treatment of cocultures also resulted in the transmigration of activated, CD69-positive lymphocytes. The MCP-1-mediated transmigration of monocytes across cocultures was blocked using an Ab to ICAM-1 and inhibited by 55% using an Ab to E-selectin. These data suggest a central role for astrocyte-derived MCP-1 in directing the migration of monocytes and lymphocytes across the BBB.

Astrocyte expression of monocyte chemoattractant protein-1 is differentially regulated by transforming growth factor beta

The pathophysiology of central nervous system (CNS) inflammatory disease is dependent, in part, on leukocyte recruitment across the blood-brain barrier. The expression of cytokines and chemokines by astrocytes may contribute to this process. Astrocytes express monocyte chemoattractant protein-1 (MCP-1), an activator of monocytes and a chemoattractant for monocytes and activated T cells. We examined the regulation of MCP-1 expression in human fetal astrocytes following cytokine treatment in the presence and absence of transforming growth factor beta (TGF-beta). TGF-beta, TNFalpha and IL-1beta, but not IFNgamma, induced MCP-1 mRNA and protein. TGF-beta, in cotreatment with TNFalpha caused an additive increase in MCP-1 mRNA, but not protein. In combination with IFNgamma, TGF-beta significantly increased MCP-1 mRNA and protein, as compared to either untreated, TGF-beta- or IFNgamma-treated astrocytes. However, TGF-gamma in cotreatment with IL-1beta decreased MCP-1 mRNA and protein, as compared to IL-1beta alone. Treatment of astrocytes with TGF-beta prior to TNFalpha, IFNgamma or IL-1beta treatment significantly increased MCP-1 expression. The kinetics of cytokine expression in the CNS may differentially regulate astrocyte-derived MCP-1 expression and subsequent recruitment and activation of leukocytes.

Microglia in cell culture and in transplantation therapy for central nervous system disease

The central nervous system (CNS) is host to a significant population of macrophage-like cells known as microglia. In addition to these cells which reside within the parenchyma, a diverse array of macrophages are present in meningeal, perivascular, and other peripheral locations. The role that microglia and other CNS macrophages play in disease and injury is under intensive investigation, and functions in development and in the normal adult are just beginning to be explored. At present the biology of these cells represents one of the most fertile areas of CNS research. This article describes methodology for the isolation and maintenance of microglia in cell cultures prepared from murine and feline animals. Various approaches to identify microglia are provided, using antibody, lectin, or scavenger receptor ligand. Assays to confirm macrophage-like functional activity, including phagocytosis, lysosomal enzyme activity, and motility, are described. Findings regarding the origin and development of microglia and results of transplantation studies are reviewed. Based on these data, a strategy is presented that proposes to use the microglial cell lineage to effectively deliver therapeutic compounds to the CNS from the peripheral circulation.

Cultured astrocytes express regional heterogeneity of the immunoreactive phenotype under basal conditions and after gamma-IFN induction

Cerebral astrocytes are known to show a region-specific phenotype, concerning the expression of several receptors and the synthesis of secreted substances. In order to find out whether this heterogeneity also exists for the immunological activation, we studied several parameters that are known to characterize activated astroglia on cultured primary rat astrocytes originating from cortex, hippocampus, striatum, septum and brain stem: major histocompatibility complex (MHC) class II and intercellular adhesion molecule (ICAM)-1 expression, nitric oxide (NO) production and interleukin-6 (IL-6) synthesis. Unstimulated cultures show a baseline expression of MHC class II molecules that differs from one region to another, hippocampus and brain stem showing the highest values. These differences are strongly enhanced after a 48-h incubation with gamma-interferon (gamma-IFN). NO production is also induced by a 72-h incubation with gamma-IFN, showing similar patterns of regional specialization. The baseline expressions of ICAM-1 and IL-6 also show major regional differences, with the brain stem and the striatum showing elevated values for ICAM-1, and the septum and the brain stem producing the largest amounts of IL-6. The expressions of ICAM-1 and IL-6 are not affected by an incubation with gamma-IFN. Our results demonstrate that the immunological activities of astroglial cells show regional heterogeneities. This specialization may be implicated in the pathophysiological pathways of several neurodegenerative disorders.

Ciliary muscle capillaries have blood-tissue barrier characteristics

It was determined whether the capillaries in the ciliary muscle are of the blood-tissue barrier or of the permeable non-barrier type. Ciliary body and iris of normal human and animal eyes were examined by electron microscopy and by immunohistochemical staining with a panel of antibodies recognizing endothelial blood-brain barrier markers. In addition, horseradish peroxidase (HRP) tracer studies of the anterior segment were carried out in rabbits. Our results demonstrated that the capillary endothelium in human and rabbit ciliary muscle has few luminal pinocytotic vesicles and a morphological aspect suggesting the presence of tight junctions. Ciliary muscle and iris capillaries stained positive for the blood-brain barrier markers Glucose-Transporter-1 and P-Glycoprotein, while staining for the PAL-E antigen and the transferrin receptor was absent. In the rabbit ciliary muscle, vascular leakage of exogenous HRP tracer was absent. It was concluded that this functional barrier and the observed phenotype of ciliary muscle capillaries are consistent with a blood-tissue barrier function similar to that of the iris microvasculature.

The development of the blood-brain barrier in alcohol-exposed rats

Circulating horseradish peroxidase (HRP) was used as a tracer to determine if the blood-brain barrier to protein was altered by dietary prenatal alcohol exposure. Animals were prepared for light microscopic visualization of HRP after HRP infusion on gestational days 16, 18, 20, 22 and postnatal day 4. There was no consistent evidence of HRP leakage through the BBB in the alcohol-exposed animals compared to control animals. Capillary endothelial cells and perivascular astrocytic endfeet were morphologically characterized by electron microscopy in rat optic nerve and cerebellum following dietary prenatal and postnatal ethanol exposure. Photomontages of optic nerve capillaries from G20 and P5 animals and cerebellar capillaries from P15 animals were examined for evidences of effects of alcohol on the development of the capillaries and adjacent astroglial endfeet. There was no consistent evidence of any alcohol-induced effect that could indicate a disruption of the vessel, the endothelial tight junctions, the perivascular glial limiting membranes, or the extent of vascular ensheathment by astrocytic endfeet.

Age-related changes in the blood-brain barrier

Aging of the cerebral microcirculation results in significant alteration in the blood-brain barrier (BBB). The barrier function appears to remain intact in older animals, although it may be more susceptible to disruption by external factors (hypertension) and drugs (haloperidol). While overall transport processes do not change with age, aging animals and humans have altered BBB function of select carrier mediated transport systems including the transport of choline, glucose, butyrate and triiodothyronine. These age-related changes are the result of either alteration in the carrier molecules or the physiochemical properties of the cerebral microvessels. At the present time, it is not known whether changes in the BBB contribute to the age-related neurodegenerative diseases or are merely epiphenomena of aging.

Enriched immune-environment of blood-brain barrier deficient areas of normal adult rats

The circumventricular organs (CVOs) in the brain are without a blood-brain barrier (BBB) and as such directly exposed to blood plasma constituents and blood-borne pathogens. In light of previous studies showing discrepancies regarding the immunocompetence of these organs, we initiated the present study to provide a comprehensive immunohistochemical analysis of the cellular expression of immune-associated antigens within the pineal gland, area postrema and the subfornical organ. In all CVOs, subpopulations of cells morphologically similar to complement receptor type 3 immunoreactive microglial/macrophage cells expressed major histocompatibility complex (MHC) class II antigen, leucocyte common antigen (LCA/CD45), as well as CD4 and ED1 antigen. Based on morphological criteria the MHC class II antigen expressing cells could be grouped into a major population of classical parenchymal and perivascular ramified microglial cells and a minor population presenting itself as scattered or small groups of rounded macrophage-like cells. CD4 and ED1 antigen were expressed by both cell types. CD45 was preferentially expressed by macrophage-like cells. MHC class I antigen was expressed by the vascular endothelium in both BBB-protected and BBB-deficient areas and was additionally present as a lattice-like network throughout the BBB-deficient parenchyma in all CVOs. The results suggest that the BBB-free areas of the brain besides being constantly surveyed by blood-borne macrophages, possess an intrinsic immune surveillance system based on resting and activated microglial cells, which may function as a non-endothelial, cellular barrier against blood-borne pathogens.

A co-evolutionary theory of sleep

Based on recent experimental evidence, a novel theory of sleep function and regulation is advanced, stating that sleep primarily evolved to protect the brain against a wakefulness-dependent increase in the permeability of the blood-brain barrier. A restitutional mechanism for the blood-brain barrier had to co-evolve against the omnipresent gut-derived bacterial cell wall constituents, because these and their elicited cellular responses increase blood-brain barrier permeability and potentially harm nervous tissue. Thus, in order to develop a highly organized cerebral structure, an immune-like response specific for the brain co-evolved during the phylogeny of the symbiosis between animals and gut bacteria to control the detrimental effects of bacterial cell wall constituents. In the course of further evolution, the sleep-associated 'controlled inflammatory state' of the brain employed the growth-factor activities of locally activated cytokines to enforce cerebral development and the maintenance of cognitive functions.

Direct and astrocyte-mediated effects of ethanol on brain-derived endothelial cells

The effects of ethanol have been studied in the central nervous system, however there exists only scarce information about the effects of ethanol on endothelial cells forming the blood-brain barrier. As some properties of brain endothelial cells are modulated by underlying astrocytes, the effect of ethanol on cerebral microvasculature might be indirect and mediated by astrocytes. To analyse this question, we added to rat brain-derived endothelial cells (rbEC) in culture either only ethanol (0, 15 and 150 mM) or ethanol conjointly with soluble factors secreted by astrocytes. Alternatively, astrocytes were exposed to ethanol and the medium was added to rbEC. The effects of treatments were evaluated on cell growth and expression of specific proteolytic markers of rbEC. The experiments showed that while the addition of ethanol alone to rbEC increased the expression of gamma-glutamyltranspeptidase and cell growth following an initial toxic effect, the most significant effects were seen when ethanol was added to rbEC together with astrocytic factors or when medium conditioned by astrocytes exposed to ethanol was added to rbEC. In particular, the expression of angiotensin converting enzyme in endothelial cells was dose-dependently increased. These results indicate that the hypertensive and toxic effects of ethanol are mediated by ethanol and soluble factor(s) secreted by astrocytes and dependent on the expression of angiotensin converting enzyme in the brain endothelium. Thus, when evaluating in vitro the effects of toxic substances such as ethanol on the cerebral endothelium, the modulating effect of cells surrounding cerebral vessels must be accounted for.

Metabolism-dependent binding of the heterocyclic amine Trp-P-1 in endothelial cells of choroid plexus and in large cerebral veins of cytochrome P450-induced mice

Trp-P-1 (3-amino-1,4-dimethyl-5H-pyrido(4,3-b)indole) is known to be metabolized by cytochrome P4501A (P4501A) to reactive intermediates which may bind irreversibly to tissue macromolecules. The irreversible binding of [3H]Trp-P-1 in the brain of NMRI-mice was studied by microautoradiography. There was a selective irreversible binding of radioactivity in endothelial cells following an i.v. or i.p. injection of [3H]Trp-P-1 (100 micrograms/kg or 1.5 mg/kg) in mice treated with the P4501A-inducing agent beta-naphthoflavone (BNF). The binding of radioactivity was highest in capillary loops of the choroid plexus, less marked in large cerebral veins and in arachnoidal veins whereas no binding was observed in cerebral capillaries, arteries, neurons or in other brain cells. In endothelial cells of vehicle-treated control mice injected with [3H]Trp-P-1 no binding of radioactivity was observed. At incubation of brain slices with [3H]Trp-P-1, there was a marked irreversible binding of radioactivity in endothelial cells in the choroid plexus of BNF-treated mice but not in vehicle-treated control mice. The P4501A inhibitor ellipticine abolished the BNF-induced endothelial binding of [3H]Trp-P-1-derived radioactivity in vivo and in vitro. The marked binding of Trp-P-1-derived radioactivity in endothelial cells of the choroid plexus of BNF-treated mice demonstrate that a BNF-responsive enzyme activity, possibly P4501A, may be induced at this site and suggests that a P450-dependent enzyme activity be part of the blood-cerebrospinal fluid barrier regulating the transendothelial passage of compounds.