Self-expanding intestinal expansion sleeves (IES) for short gut syndrome.

PURPOSE: Many disease processes (necrotizing enterocolitis, caustic esophageal injury, malrotation with volvulus), can result in short-gut syndrome (SGS), where remnant intestinal segments may dilate axially, but rarely elongate longitudinally. Here we mechanically characterize a novel model of a self-expanding mesh prototype intestinal expanding sleeve (IES) for use in SGS. METHODS: Gut lengthening was achieved using a proprietary cylindrical layered polyethylene terephthalate IES device with helicoid trusses with isometric ends. The IES is pre-contracted by diametric expansion, deployed into the gut and anchored with bioabsorbable sutures. IES expansion to its equilibrium dimension maintained longitudinal gut tension, which may permit remodeling, increased absorptive surface area while preserving vascular and nervous supplies. We performed mechanical testing to obtain the effective force-displacement characterization achieved on these prototypes and evaluated minimal numbers of sutures needed for its anchoring. Furthermore, we deployed these devices in small and large intestines of New Zealand White rabbits, measured IES length-tension relationships and measured post-implant gut expansion ex vivo. Histology of the gut before and after implantation was also evaluated. RESULTS: Longitudinal tension using IES did not result in suture failure. Maximum IES suture mechanical loading was tested using 4-6 sutures; we found similar failure loads of 2.95 ± 0.64, 4 ± 1.9 and 3.16 ± 0.24 Newtons for 4, 6 and 8 sutures, respectively (n = 3, n.s). Pre-contracted IES tubes were deployed at 67 ± 4% of initial length (i.l.); in the large bowel these expanded significantly to 81.5 ± 3.7% of i.l. (p = 0.014, n = 4). In the small bowel, pre-contracted IES were 61 ± 3.8% of i.l.; these expanded significantly to 82.7 ± 7.4% of i.l. (p = 0.0009, n = 6). This resulted in an immediate 24 ± 7.8% and 36.2 ± 11% increase in gut length when deployed in large and small bowels, respectively, with maintained longitudinal tension. Maintained IES induced tension produced gut wall thinning; gut histopathological evaluation is currently under evaluation. CONCLUSION: IES is a versatile platform for gaining length in SGS, which may be simply deployed via feeding tubes. Our results need further validation for biocompatibility and mechanical characterization to optimize use in gut expansion.

Neurolymphatic biomarkers of brain endothelial inflammatory activation: Implications for multiple sclerosis diagnosis.

AIMS: Multiple sclerosis (MS) is the leading cause of non-traumatic neurological disability in young adults, and its diagnosis is often delayed due to the lack of diagnostic markers. Initiation of disease -modifying therapy in the early stages of MS is especially critical because currently available therapy mostly target relapsing-remitting MS, and is less effective as disease progresses into the more chronic form of secondary-progressive MS. Therefore, exploring specific and sensitive biomarkers will facilitate an expedited and more accurate diagnosis to allow currently available therapies to be more effective. MAIN METHODS: Western blotting was conducted to detect the expression of neurolymphatic proteins in human brain endothelial cells in culture. Additionally, using a cohort of 150 patients with relapsing remitting MS, 26 with secondary progressive MS, and 60 healthy control samples, neurolymphatic protein expression was detected in serum samples using dot blot analysis. KEY FINDINGS: Human brain microvascular endothelial cells express neurolymphatic markers. Neurolymphatic protein abundance increases with tumor necrosis factor (TNF)-α stimulation but decreases with interferon (IFN)- γ or combined (TNF + IFN) treatment. Circulating neurolymphatic protein levels is significantly lower in MS patients. Further, one of the markers, FOXC2, is associated with the clinical stages of MS, with significantly lower expression in secondary progressive MS compared to relapsing remitting MS. SIGNIFICANCE: Our findings describe brain endothelial expression of neurolymphatic proteins, which is altered under inflammatory stress, and provide a possibility of using a collective pool of circulating neurolymphatic proteins as a diagnostic and prognostic biomarker of MS.

Blood circulating microparticle species in relapsing-remitting and secondary progressive multiple sclerosis. A case-control, cross sectional study with conventional MRI and advanced iron content imaging outcomes.

BACKGROUND: Although multiple sclerosis (MS) is thought to represent an excessive and inappropriate immune response to several central nervous system (CNS) autoantigens, increasing evidence also suggests that MS may also be a neurovascular inflammatory disease, characterized by endothelial activation and shedding of cell membrane microdomains known as 'microparticles' into the circulation. OBJECTIVE: To investigate the relationships between these endothelial biomarkers and MS. METHODS: We examined the relative abundance of CD31(+)/PECAM-1, CD51(+)CD61(+) (αV-ß3) and CD54(+) (ICAM-1) bearing microparticles in sera of healthy individuals, patients with relapsing-remitting MS, and secondary-progressive MS. We also investigated the correlation among circulating levels of different microparticle species in MS with conventional MRI (T2- and T1-lesion volumes and brain atrophy), as well as novel MR modalities [assessment of iron content on susceptibility-weighted imaging (SWI)-filtered phase]. RESULTS: Differences in circulating microparticle levels were found among MS groups, and several microparticle species (CD31(+)/CD51(+)/CD61(+)/CD54(+)) were found to correlate with conventional MRI and SWI features of MS. CONCLUSION: These results indicate that circulating microparticles' profiles in MS may support mechanistic roles for microvascular stress and injury which is an underlying contributor not only to MS initiation and progression, but also to pro-inflammatory responses.

Progressive multifocal leukoencephalopathy: a review of the neuroimaging features and differential diagnosis.

Progressive multifocal leukoencephalopathy (PML) is an uncommon and often fatal demyelinating disease of human central nervous system, which is caused by reactivation of the polyomavirus JC (JCV). PML generally occurs in patients with profound immunosuppression such as AIDS patients. Recently, a number of PML cases have been associated with administration of natalizumab for treatment of multiple sclerosis (MS) patients. Diagnosis and management of PML became a major concern after its occurrence in multiple sclerosis patients treated with natalizumab. Diagnosis of PML usually rests on neuroimaging in the appropriate clinical context and is further confirmed by cerebrospinal fluid polymerase chain reaction (PCR) for JCV DNA. Treatment with antiretroviral therapies in HIV-seropositive patients or discontinuing natalizumab in MS patients with PML may lead to the development of immune reconstitution inflammatory syndrome (IRIS) which presents with deterioration of the previous symptoms and may lead to death. In patients under treatment with monoclonal antibodies in routine practice, or new ones in ongoing clinical trials, differentiating PML from new MS lesions on brain MRI is critical for both the neurologists and neuroradiologists. In this review, we discuss the clinical features, neuroimaging manifestations of PML, IRIS and neuroimaging clues to differentiate new MS lesions from PML. In addition, various neuroimaging features of PML on the non-conventional MR techniques such as diffusion-weighted imaging (DWI), diffusion tensor imaging (DTI), and MR spectroscopy (MRS) are discussed.

Dalfampridine: review of its efficacy in improving gait in patients with multiple sclerosis.

Multiple sclerosis (MS) is a progressive immune-mediated neurodegenerative disease of human central nervous system (CNS), which causes irreversible disability in young adults. The cause and cure for MS remain unknown. Pathophysiology of MS includes two arms: inflammatory demyelination and neurodegeneration. The inflammatory demyelination of MS which is mainly promoted by a massive activation of the immune system against putative CNS antigen(s) leads to loss of oligodendrocyte/myelin complex which slows down or halts impulse conduction in denuded axons. Practically, loss of myelin significantly reduces signal conduction along the demyelinated axons through alterations in the distribution of axonal ion channels. Dalfampridine (4-aminopyridine or 4-AP) is an oral potassium channel blocker, which was recently approved by FDA for symptomatic treatment of MS. Dalfampridine, which acts at the central and peripheral nervous systems, enhances conduction in demyelinated axons and improves walking ability of MS patients. A number of clinical trials have evaluated the safety and efficacy of fampridine in MS patients with the degree of gait improvement as the main outcome. The objective of this manuscript is to provide an overview of the pharmacology, pharmacokinetics, clinical trials, side effects and interactions of dalfampridine used in treatment of MS patients.

Differential cytokine responses in human and mouse lymphatic endothelial cells to cytokines in vitro.

BACKGROUND: Inflammatory cytokines dysregulate microvascular function, yet how cytokines affect lymphatic endothelial cells (LEC) are unclear. METHODS AND RESULTS: We examined effects of TNF-α, IL-1 beta, and IFN-gamma on LEC proliferation, endothelial cell adhesion molecule (ECAM) expression, capillary formation, and barrier changes in murine (SV-LEC) and human LECs (HMEC-1a). RESULTS: All cytokines induced ICAM-1, VCAM-1, MAdCAM-1, and E-selectin in SV-LECs; TNF-α, IL-1 beta; and IFN-gamma induced ECAMs (but not MAdCAM-1) in HMEC-1a. IL-1 beta increased, while IFN-gamma and TNF-α reduced SV-LEC proliferation. While TNF-α induced, IFN-gamma decreased, and IL-1 beta did not show any effect on HMEC-1a proliferation. TNF-α, IL-1 beta, and IFN-gamma each reduced capillary formation in SV-LEC and in HMEC-1a. TNF-α and IL-1 beta reduced barrier in SV-LEC and HMEC-1a; IFN-gamma did not affect SV-LEC barrier, but enhanced HMEC-1a barrier. Inflammatory cytokines alter LEC growth, activation and barrier function in vitro and may disturb lymphatic clearance increasing tissue edema in vivo. CONCLUSION: Therapies that maintain or restore lymphatic function (including cytokines blockade), may represent important strategies for limiting inflammation.

Alterations in serum MMP-8, MMP-9, IL-12p40 and IL-23 in multiple sclerosis patients treated with interferon-beta1b.

BACKGROUND: Interferon-beta1b (IFN-beta1b), an effective treatment for multiple sclerosis (MS), lessens disease severity in MS patients. However, the mechanisms of its immunoregulatory and anti-inflammatory effects in MS remain only partially understood. Matrix metalloproteinases (MMP) and tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) are involved in blood brain barrier disruption and formation of MS lesions. Th1/Th17 cytokines e.g. interleukins IL-12p40, IL-17, and IL-23, are associated with MS disease activity and are significant players in pathogenesis of MS. OBJECTIVE: During a 1-year prospective study, we serially measured serum MMP-8, MMP-9, TIMP-1, IL-12p40, IL-17, and IL-23 in 24 patients with relapsing-remitting MS. We compared the results to clinical course and to brain magnetic resonance imaging. IFN-beta1b decreased serum MMP-8 and MMP-9 (not TIMP-1). RESULTS: The sustained treatment with IFN-beta1b attenuated the pro-inflammatory environment by significantly reducing the serum IL-12p40, IL-23, and showed a trend for decreasing IL-17. Decreased serum MMP-8, MMP-9, IL-12 and IL-23 levels were correlated with a decrease in the number of contrast-enhanced T2-weighted lesions. CONCLUSION: Early treatment of MS with IFN-beta1b may stabilize clinical disease by attenuating levels of inflammatory cytokines and MMPs. Serial measurement of inflammatory mediators may serve as sensitive markers to gauge therapeutic responses to IFN-beta1b during the first year of treatment.

Increasing female preponderance of multiple sclerosis in Isfahan, Iran: a population-based study.

There is an overall increase in the worldwide prevalence and incidence of multiple sclerosis (MS). Studies from several countries also demonstrated an increase of female/male ratio over time denoting an increase in the incidence of MS particularly in women. In this study we sought to assess the trends in MS incidence and prevalence in males and females over recent decades in Isfahan, Iran, which differs from other regions in terms of environmental and lifestyle changes. We determined female/male ratio by year of birth (YOB) in 1584 patients with MS registered with Isfahan Multiple Sclerosis Society (IMSS) from April 2003 to August 2007. A comparison of sex ratio of MS patients by YOB showed a significant, progressive, gradual increase, with an apparent interruption in the late 1960s. In this study year of birth is a significant predictor for sex ratio (p < 0.001, chi(2) = 17.130, Spearman's rank correlation r = 0.893). Our findings show that there is a significant increase in the incidence of MS among females for the the last decades in the Isfahan province of Iran. This rapid increase may be related to changes in environmental interactions rather than genetic factors, and among them vitamin D insufficiency, enhanced diagnosis, and lifestyle changes appear to be more plausible causative factors.

Pathophysiology of the lymphatic drainage of the central nervous system: Implications for pathogenesis and therapy of multiple sclerosis.

In most organs of the body, immunological reactions involve the drainage of antigens and antigen presenting cells (APCs) along defined lymphatic channels to regional lymph nodes. The CNS is considered to be an immunologically privileged organ with no conventional lymphatics. However, immunological reactions do occur in the CNS in response to infections and in immune-mediated disorders such as multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). Here, we review evidence that cervical lymph nodes play a role in B and T cell mediated immune reactions in the CNS. Then we define the separate pathways by which interstitial fluid (ISF) and CSF drain to cervical lymph nodes. ISF and solutes drain from the brain along the 100-150nm-wide basement membranes in the walls of capillaries and arteries. In humans, this perivascular pathway is outlined by the deposition of insoluble amyloid (Abeta) in capillary and artery walls in cerebral amyloid angiopathy in Alzheimer's disease. The failure of APCs to migrate to lymph nodes along perivascular lymphatic drainage pathways may be a major factor in immunological privilege of the brain. Lymphatic drainage of CSF is predominantly through the cribriform plate into nasal lymphatics. Lymphatic drainage of ISF and CSF and the specialised cervical lymph nodes to which they drain play significant roles in the induction of immunological tolerance and of adaptive immunological responses in the CNS. Understanding the afferent and efferent arms of the CNS lymphatic system will be valuable for the development of therapeutic strategies for diseases such as MS.

Gray matter pathology in (chronic) MS: modern views on an early observation.

Involvement of the gray matter (GM) in the pathology of multiple sclerosis (MS) was already recognized in the early days of MS research, but the detection of (cortical) GM lesions under the microscope and with magnetic resonance imaging (MRI) techniques was initially suboptimal and could only recently be enhanced. The visualization of GM lesions in vivo opens new doors for studies focusing on clinical, especially cognitive, effects of GM pathology, as well as for monitoring of neuroprotective treatment. However, so far little is known about what causes GM pathology. In this review, several pathogenetic mechanisms will be discussed, affecting the MS brain both from the 'outside-in' and from the 'inside-out'. Also, the use and reliability of MRI atrophy measures as a monitoring tool for GM damage in the therapeutic setting will be reviewed.

Volumetric Examination of MS Plaques and Correlation with EDSS Ratings.

This study is a retrospective analysis of 17 patients with multiple sclerosis. The total volume of plaques from three different MR image sets of the brain was correlated with the EDSS ratings of the patients. Each of the correlations showed a positive relationship, but none was statistically significant. A more extensive study is required in order to give significance to these relationships.

Mechanisms of action of disease-modifying agents and brain volume changes in multiple sclerosis.

Disease-modifying agents (DMAs), including interferon beta (IFNbeta) and glatiramer acetate (GA), are the mainstays of long-term treatment of multiple sclerosis (MS). Other potent anti-inflammatory agents like natalizumab and different types of chemotherapeutics are increasingly being used for treatment of MS, particularly in patients with breakthrough disease activity. Brain volume (BV) loss occurs early in the disease process, accelerates over time, and may be only partially affected by DMA therapy. Low-dose, low frequency IFNbeta administered once weekly and GA appear to partially reduce BV decline over the second and third years of treatment. High dose, high frequency IFNbeta demonstrated no clear effect on BV loss during this time period. Current evidence suggests that changes in BV after immunoablation may not be due entirely to the resolution of edema but may be related to potential chemotoxicity of high dose cyclophosphamide. Natalizumab reduces the development of BV decline in the second and third years of treatment. IV immunoglobulin showed a positive effect on decelerating BV reduction in relapsing and advanced stages of MS. These differences between DMAs may be explained by the extent of their therapeutic effects on inflammation and on the balance between inhibition or promotion of remyelination and neuronal repair in the CNS. We described the mechanisms of action by which DMAs induce accelerated, non-tissue-related BV loss (pseudoatrophy) in the short term but, in the long run, may still potentially lead to permanent BV decline. The effects of corticosteroid therapy on changes in BV in patients with MS help clarify the mechanisms through which potent anti-inflammatory treatments may prevent, stabilize, or induce BV loss.

MAdCAM-1 expression and regulation in murine colonic endothelial cells in vitro.

BACKGROUND: Although the mucosal addressin cell adhesion molecule-1 (MAdCAM-1) is associated with the etiology of inflammatory bowel diseases, few studies have directly examined MAdCAM-1 using microvascular endothelium derived from the colon. This study measured the expression of MAdCAM-1 in a novel colon endothelial line MJC-1, as well as MAdCAM-1 regulation and function in vitro. METHODS: We cloned microvascular endothelial cells from primary colon cultures using ImmortoMice mice (whose cells express a temperature-sensitive SV40 large T antigen, H-2Kb-tsA58 mice). Expression of MAdCAM-1 after stimulation with cytokines [tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, or interferon (IFN)-gamma] was determined by Western blotting. Signal paths regulating MAdCAM-1 expression were examined using pharmacological blockers before cytokines. We also examined lymphocyte adhesion using lymphocytes that constitutively express alpha4beta7 integrin. RESULTS: TNF-alpha induced MAdCAM-1 in a dose-dependent manner by 24 hours. MAdCAM-1 induction was protein kinase C, tyrosine kinase, p38 mitogen activated protein kinase, and nuclear-factor kappa-B/poly adenosine diphosphate ribose polymerase dependent. Lymphocyte adhesion was increased 2.6-fold after TNF-alpha stimulation and was inhibited by anti-MAdCAM-1 antibody before treatment (P < 0.05 control versus TNF-alpha). CONCLUSIONS: In vitro, MAdCAM-1 can be induced on colon endothelial cells by TNF-alpha stimulation and may represent a useful model to study microvascular injury in the large intestine.

N-methyl-D-aspartate receptor activation in human cerebral endothelium promotes intracellular oxidant stress.

Cerebral endothelial cells in the rat, pig, and, most recently, human have been shown to express several types of receptors specific for glutamate. High levels of glutamate disrupt the cerebral endothelial barrier via activation of N-methyl-d-aspartate (NMDA) receptors. We have previously suggested that this glutamate-induced barrier dysfunction was oxidant dependent. Here, we provide evidence that human cerebral endothelial cells respond to glutamate by generating an intracellular oxidant stress via NMDA receptor activation. Cerebral endothelial cells loaded with the oxidant-sensitive probe dihydrorhodamine were used to measure intracellular reactive oxygen species (ROS) formation in response to glutamate receptor agonists, antagonists, and second message blockers. Glutamate (1 mM) significantly increased ROS formation compared with sham controls (30 min). This ROS response was significantly reduced by 1) MK-801, a noncompetitive NMDA receptor antagonist; 2) 8-(N,N-diethylamino)-n-octyl-3,4,5-trimethoxybenzoate, an intracellular Ca(2+) antagonist; 3) LaCl(3), an extracellular Ca(2+) channel blocker; 4) diphenyleiodonium, a heme-ferryl-containing protein inhibitor; 5) itraconazole, a cytochrome P-450 3A4 inhibitor; and 6) cyclosporine A, which prevents mitochondrial membrane pore transition required for mitochondrial-dependent ROS generation. Our results suggest that the cerebral endothelial barrier dysfunction seen in response to glutamate is Ca(2+) dependent and may require several intracellular signaling events mediated by oxidants derived from reduced nicotinamide adenine dinucleotide oxidase, cytochrome P-450, and the mitochondria.

Analytic approaches to differential gene expression in AIDS versus control brains.

We previously showed that specific strains of human immunodeficiency virus (HIV)-1 infect the brain and contribute to Neuropathology, Cognitive Distress, and Neuropsychiatric Disease. To study further brain disease that results from HIV-1 infection, we commenced analysis of changes in gene expression in brain. We analyzed RNA purified from Frontal Cortex of 5 HIV-1 infected and 4 HIV-1 negative control subjects RNA was amplified and Affymetrix technology was used to analyze gene expression using the 12,585 gene Affymetrix Human Genome U95A chip. The expressed genes showed highly significant Pearsons correlations with each other within the two groups. Expression intensities were transferred to Microsoft Excel and Spotfire was used to analyze the results. Twenty-group K-means cluster analysis was done for HIV+ and HIV- subjects. Genes that were expressed in the same cluster numbers in the two groups were removed from further analysis. Analysis of Gene expression in the top 13 HIV+ clusters showed expression in the 40 gene categories designated in our prior studies. Genes from several categories occurred in more than one K-means cluster. Genes identified in these lists included several genes that have been previously studied: MBP, Myelin-PLP, NMDA receptor, MAG, astrocytic protein, Notch 3, APP, Senescence, proteasome, Ferritin, signaling, cell cycle, iNOS, Chemokine, splicing, synapse, protein tags, and ribosomal proteins. The first (primary significant) axis of both Principal Component Analyses ordered the genes in the same patient groups as the K-means cluster analysis for the respective patient groups. PCA was thus not more informative than K-Means cluster analysis. Ratios of HIV+ to HIV- intensities were calculated for all the averaged gene expression intensities. The ratio range was 0.14 to 9.26. The genes at the extremes (ad extrema) did not correspond to the gene order by K-means clustering (or PCA). The genes in the top 13 K-means clusters showed low-level changes by expression ratio. Genes ad extrema by ratio were in clusters with very large memberships. Mann-Whitney analysis confirmed expression ratio results. Several inferences result from our preliminary study. First, study design will be different in future studies involving additional replicates. Second, ratios inform us of the extent of changes in gene expression quantitatively. Third, Cluster methodology provides us with more subtle information, how bunches (clusters) of genes behave in terms of their centroids (attractors). Fourth, genes that change extensively by ratio tend to be in the larger k-Means clusters. We conclude that ranking gene expression with the use of expression ratio or by K-means clustering, yield different representations of the data.

An occipital lobe epileptogenic focus in a patient with West Nile encephalitis.

Although most human cases of West Nile (WN) fever are benign, approximately 1% produce severe neurological illness. Meningitis and/or encephalitis comprise 75% of hospitalized cases with seizures in 10-15%. Occipital lobe seizures, often mimicking other primary seizure types due to extra-occipital spread, is uncommon in adults and especially so from an infectious origin. A case of WN encephalitis presenting with a simple partial seizure, focal motor, resulting from an occipital epileptogenic focus is reported. The atypical epileptogenic location of the case and the observed frequency of seizures in WN encephalitis suggest that this virus is particularly irritative to cortical neuronal networks. Thus when seizures especially with atypical EEG patterns present during an acute febrile illness in the warmer months, WN encephalitis should be considered.

Human neuroepithelial cells express NMDA receptors.

L-glutamate, an excitatory neurotransmitter, binds to both ionotropic and metabotropic glutamate receptors. In certain parts of the brain the BBB contains two normally impermeable barriers: 1) cerebral endothelial barrier and 2) cerebral epithelial barrier. Human cerebral endothelial cells express NMDA receptors; however, to date, human cerebral epithelial cells (neuroepithelial cells) have not been shown to express NMDA receptor message or protein. In this study, human hypothalamic sections were examined for NMDA receptors (NMDAR) expression via immunohistochemistry and murine neuroepithelial cell line (V1) were examined for NMDAR via RT-PCR and Western analysis. We found that human cerebral epithelium express protein and cultured mouse neuroepithelial cells express both mRNA and protein for the NMDA receptor. These findings may have important consequences for neuroepithelial responses during excitotoxicity and in disease.

Glutamate causes a loss in human cerebral endothelial barrier integrity through activation of NMDA receptor.

l-Glutamate is a major excitatory neurotransmitter that binds ionotropic and metabotropic glutamate receptors. Cerebral endothelial cells from many species have been shown to express several forms of glutamate receptors; however, human cerebral endothelial cells have not been shown to express either the N-methyl-D-aspartate (NMDA) receptor message or protein. This study provides evidence that human cerebral endothelial cells express the message and protein for NMDA receptors. Human cerebral endothelial cell monolayer electrical resistance changes in response to glutamate receptor agonists, antagonists, and second message blockers were tested. RT-PCR and Western blot analysis were used to demonstrate the presence of the NMDA receptor. Glutamate and NMDA (1 mM) caused a significant decrease in electrical resistance compared with sham control at 2 h postexposure; this response could be blocked significantly by MK-801 (an NMDA antagonist), 8-(N,N-diethylamino)-n-octyl-3,4,5-trimethyoxybenzoate (an intracellular Ca2+ antagonist), and N-acetyl-L-cystein (an antioxidant). Trans(+/-)-1-amino-1,3-cyclopentanedicarboxylic acid, a metabotropic receptor agonist (1 mM), did not significantly decrease electrical resistance. Our results are consistent with a model where glutamate, at excitotoxic levels, may lead to a breakdown in the blood brain barrier via activation of NMDA receptors.