Background and Purpose-Brain edema is a life-threatening consequence of stroke and leads to an extension of the affected tissue. The space-occupying effect due to brain edema can be quantified in rat stroke models with the use of MRI. The present study was performed to test 2 hypotheses: (1) Can quantification of the space-occupying effect due to brain edema serve as a noninvasive measure for brain water content? (2) Does morphometric assessment of brain swelling allow determination of true infarct size on MRI after correction for the space-occupying effect of edema? Methods-Thirty rats were subjected to permanent suture middle cerebral artery occlusion. MRI was performed after 6 or 24 hours, and hemispheric swelling was assessed morphometrically. Interobserver and intraobserver agreements were determined for MRI measurements. In study I, the space-occupying effect due to brain edema was correlated with the absolute brain water content by the wet/dry method. In study II, lesion volumes corrected and uncorrected for edema were calculated on MRI and on TTC staining and compared. Results-Interobserver and intraobserver agreements for MRI measurements were excellent (rՆ0.97). Brain water content and hemispheric swelling correlated well after 6 and 24 hours (rՆ0.95). Corrected lesion volumes correlated with rϭ0.78 between TTC staining and MRI. Without edema correction, lesion volumes were overestimated by 20.3% after 6 hours and by 29.6% after 24 hours of ischemia. Conclusions-Morphometric assessment of hemispheric swelling on MRI can determine the increase in absolute brain water content noninvasively and can also provide ischemic lesion volumes corrected for brain edema.

Cell injury leads to exposure of intracellular material and is associated with increased permeability of vessels in the vicinity of the damage. Here, we demonstrate that natural extracellular RNA as well as artificial RNA (poly- I IntroductionBrain homeostasis is maintained by the blood-brain barrier (BBB), which forms a mechanical and functional threshold between the central nervous system and the systemic circulation. The barrier is relatively impermeable to ions, many amino acids, small peptides, and proteins, and thus contributes to the maintenance of a specific neural tissue environment. In vertebrates, the BBB exists at the level of the endothelial cells that form brain capillaries 1 in order to regulate and limit the degree of trans-and paracellular flux. 2 The tight barrier properties of the BBB result from the absence of fenestrations, the low number of pinocytotic vesicles, and the presence of tight intercellular junctions between endothelial cells with extremely high electrical resistance. 3 Pathologic conditions associated with brain tumors, head injury, or ischemic stroke are accompanied by endothelial-cell dysfunction, leading to increased permeability across the BBB, which might lead to the development of vasogenic cerebral edema. 4,5 Vascular endothelial growth factor (VEGF) as a hypoxia/ischemia inducible protein in vitro and in vivo is one of the strongest natural permeability factors 6 and a likely candidate for the development of ischemia-and tumor-induced vasogenic brain edema. 7-9 VEGF stimulates endothelial-cell growth and migration in vitro 10,11 and angiogenesis in vivo. 6,12 VEGF was originally described as a potent vascular permeability factor responsible for the accumulation of plasma protein-rich fluid in the ascites of patients with tumors. 13 Structurally, VEGF exists as a dimeric glycoprotein of molecular weight (Mr) 34 000 to 42 000 and is related to the platelet-derived growth factor family of molecules. 14 Although VEGF is the product of a single gene, 6 differentially spliced isoforms between 121 and 206 amino acid residues exist in humans 15,16 that exhibit similar functional activities. Different isoforms are distinguished by their affinity for heparin: although VEGF 121 does not bind heparin, VEGF 165 has moderate affininity for heparin, whereas VEGF 189 and VEGF 206 bind heparin with high affinity. 17 VEGF exerts its multiple actions by ligation with tyrosine kinase receptors, VEGFreceptor 1 (VEGF-R1), as well as VEGF-R2, [18][19][20] which are expressed on vascular endothelial cells. A third member, VEGF-R3 is expressed on lymphatic endothelial cells. 21 During pathologic conditions of the brain associated with tumor burden, stroke, or head injury, nucleic acids might be released by damaged cells. RNA-proteolipid complexes were detected in the circulation of patients with cancer and were suggested to represent a specific secretory product of cancer cells. 22 Accordingly, circulating RNA is present in blood plasma of patients with tumors. 23 The presence of specific types ...

Transcranial direct current stimulation (tDCS) is increasingly being used in human studies as an adjuvant tool to promote recovery of function after stroke. However, its neurobiological effects are still largely unknown. Electric fields are known to influence the migration of various cell types in vitro, but effects in vivo remain to be shown. Hypothesizing that tDCS might elicit the recruitment of cells to the cortex, we here studied the effects of tDCS in the rat brain in vivo. Adult Wistar rats (n = 16) were randomized to either anodal or cathodal stimulation for either 5 or 10 consecutive days (500 µA, 15 min). Bromodeoxyuridine (BrdU) was given systemically to label dividing cells throughout the experiment. Immunohistochemical analyses ex vivo included stainings for activated microglia and endogenous neural stem cells (NSC). Multi-session tDCS with the chosen parameters did not cause a cortical lesion. An innate immune response with early upregulation of Iba1-positive activated microglia occurred after both cathodal and anodal tDCS. The involvement of adaptive immunity as assessed by ICAM1-immunoreactivity was less pronounced. Most interestingly, only cathodal tDCS increased the number of endogenous NSC in the stimulated cortex. After 10 days of cathodal stimulation, proliferating NSC increased by ∼60%, with a significant effect of both polarity and number of tDCS sessions on the recruitment of NSC. We demonstrate a pro-inflammatory effect of both cathodal and anodal tDCS, and a polarity-specific migratory effect on endogenous NSC in vivo. Our data suggest that tDCS in human stroke patients might also elicit NSC activation and modulate neuroinflammation.

Focal cerebral ischemia elicits strong inflammatory responses involving activation of resident microglia and recruitment of monocytes/macrophages. These cells express peripheral benzodiazepine receptors (PBRs) and can be visualized by positron emission tomography (PET) using [ 11 C]PK11195 that selectively binds to PBRs. Earlier research suggests that transient ischemia in rats induces increased [11 C]PK11195 binding within the infarct core. In this study, we investigated the expression of PBRs during permanent ischemia in rats. Permanent cerebral ischemia was induced by injection of macrospheres into the middle cerebral artery. Multimodal imaging 7 days after ischemia comprised (1) 18 F]FDG metabolic rate constant with accumulated activated microglia and macrophages. These results suggest that after permanent focal ischemia, neuroinflammation occurring in the normoperfused peri-infarct zone goes along with increased energy demand, therefore extending the tissue at risk to areas adjacent to the infarct.

Neural stem cells reside in two major niches in the adult brain [i.e., the subventricular zone (SVZ) and the dentate gyrus of the hippocampus]. Insults to the brain such as cerebral ischemia result in a physiological mobilization of endogenous neural stem cells. Since recent studies showed that pharmacological stimulation can be used to expand the endogenous neural stem cell niche, hope has been raised to enhance the brain's own regenerative capacity. For the evaluation of such novel therapeutic approaches, longitudinal and intraindividual monitoring of the endogenous neural stem cell niche would be required. However, to date no conclusive imaging technique has been established. We used positron emission tomography (PET) and the radiotracer 3Ј-deoxy-3Ј-[

Background and Purpose-Investigating focal cerebral ischemia requires animal models that are relevant to human stroke.Complications and side effects are common among these models. The present study describes potential pitfalls in 3 techniques for middle cerebral artery occlusion (MCAO) in rats using magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA). Methods-Rats were subjected to temporary MCAO for 90 minutes using the suture technique (group I; nϭ10) or to permanent MCAO using the suture technique (group II; nϭ10) or the macrosphere technique (group III; nϭ10). Clinical evaluation was performed after 3 hours and 24 hours. After 24 hours, animals underwent MRI and MRA to determine lesion size and the intracranial vascular status. Results-Hemispheric lesion volume was significantly smaller in group I (14.6%) compared with groups II (35.2%; PϽ0.01) and III (21.3%; PϽ0.05). Two animals (1 each in group II and III) did not demonstrate neurological deficits and had no lesion on MRI and a patent MCA main stem on MRA. Subarachnoid hemorrhage was detected in 2 animals (1 each in group I and II). MRA indicated a patent MCA main stem in 2 animals (group II), although both rats displayed neurological deficits. Hypothalamic infarction with subsequent pathological hyperthermia was detected in all animals in group II and in 1 rat in group III. Conclusions-Model failures occurred frequently in all groups. MRI and MRA helps to identify animals that need to be excluded from experimental stroke studies.

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Extracellular RNA has been shown to induce vascular endothelial growth factor (VEGF)-dependent hyperpermeability in vivo as well as in vitro. Studies were performed to investigate the mechanism of these effects. For permeability studies primary cultures of porcine brain-derived microvascular endothelial cells (BMECs) and for all other analytical studies the human brain endothelial cell line HCMEC/D3 or human umbilical vein endothelial cells (HUVECs) were used. RNA, but not DNA, initiated signaling events by binding of VEGF to neuropilin-1, followed by VEGF-R2 phosphorylation, activation of phospholipase C (PLC), and intracellular release of Ca(2+). Activation of these pathways by RNA also resulted in the release of von Willebrand Factor from Weibel-Palade bodies. Pretreatment of cells with heparinase totally abrogated the RNA-induced permeability changes, whereas RNA together with VEGF completely restored VEGF-R2-mediated hyperpermeability. Although poly:IC increased the interleukin-6 release via activation of toll-like receptor-3 (TLR-3), permeability changes mediated by poly:IC or RNA remained unchanged after blocking TLR-3 or NF-kB activation. These results indicate that extracellular RNA serves an important cofactor function to engage VEGF for VEGF-R2-dependent signal transduction, reminiscent of the coreceptor mechanism mediated by proteoglycans, which might be of relevance for the mobilization and cellular activities of RNA-binding cytokines in general.