Time- and pressure-dependent changes in blood-brain barrier permeability after temporary middle cerebral artery occlusion in rats

Pathogenic Mechanisms of a Stroke-like attack Elicited by Epidural Steroid Injection Therapy

BACKGROUND

The pathogenic mechanisms involved in a disastrous scenario, following epidural steroid injections (ESI), remain unclarified. Intra-arterial injection of steroids with needlepenetrating vascular injury would be the culprit, as particulate medicine elicits a brain or spinal cord stroke-like attack.

METHODS

On the other hand, the limited experimental approaches simulating an accidental steroid intra-arterial injection for ESI conflicted in their results: hemorrhage vs. ischemia.

RESULTS

This article dissects the potential pathogenic mechanisms at a neurovascular unit. Noticeably, a schematic representation provides an explanation of how emboli formed by particulate steroids elicit either hemorrhagic, or ischemic lesion.

CONCLUSION

In addition, the development of a rat model with intravertebral artery steroid injection is a proposal to address the unmet need in evaluating steroids and vascular injury in ESI.

Endothelin

The endothelins comprise three structurally similar 21-amino acid peptides. Endothelin-1 and -2 activate two G-protein coupled receptors, ETA and ETB, with equal affinity, whereas endothelin-3 has a lower affinity for the ETA subtype. Genes encoding the peptides are present only among vertebrates. The ligand-receptor signaling pathway is a vertebrate innovation and may reflect the evolution of endothelin-1 as the most potent vasoconstrictor in the human cardiovascular system with remarkably long lasting action. Highly selective peptide ETA and ETB antagonists and ETB agonists together with radiolabeled analogs have accurately delineated endothelin pharmacology in humans and animal models, although surprisingly no ETA agonist has been discovered. ET antagonists (bosentan, ambrisentan) have revolutionized the treatment of pulmonary arterial hypertension, with the next generation of antagonists exhibiting improved efficacy (macitentan). Clinical trials continue to explore new applications, particularly in renal failure and for reducing proteinuria in diabetic nephropathy. Translational studies suggest a potential benefit of ETB agonists in chemotherapy and neuroprotection. However, demonstrating clinical efficacy of combined inhibitors of the endothelin converting enzyme and neutral endopeptidase has proved elusive. Over 28 genetic modifications have been made to the ET system in mice through global or cell-specific knockouts, knock ins, or alterations in gene expression of endothelin ligands or their target receptors. These studies have identified key roles for the endothelin isoforms and new therapeutic targets in development, fluid-electrolyte homeostasis, and cardiovascular and neuronal function. For the future, novel pharmacological strategies are emerging via small molecule epigenetic modulators, biologicals such as ETB monoclonal antibodies and the potential of signaling pathway biased agonists and antagonists.

Src regulates angiogenic factors and vascular permeability after focal cerebral ischemia-reperfusion

Developing new strategies to treat cerebral ischemic-reperfusion injury will require a better understanding of the mechanisms that underlie vascular permeability. In this study we examined the temporal expression of Src and angiogenic factors in rat brain after focal cerebral ischemia and reperfusion and analyzed the relationships among those factors. We also investigated the effect of Src inhibitor PP1 (4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine) in ischemic reperfusion. Rats were subjected to middle cerebral artery occlusion for 90 min followed by reperfusion with or without PP1 treatment. Src mRNA increased at 3h after reperfusion and then gradually declined. Phosphorylation of Src at Y418 displayed a biphasic increase. Phosphorylation increased as early as 3h and peaked at 6h; after decreasing, it peaked again at 3-7 days. Increases in Src mRNA and phosphorylation correlated positively with levels of vascular endothelial growth factor (VEGF) and angiopoietin-2 (Ang-2), and negatively with levels of angiopoietin-1 (Ang-1) and zonula occludens-1 (ZO-1). Changes in the expression of these factors correlated with the progress of vascular permeability, especially early after reperfusion. Hence, dynamic temporal changes in Src Y418 phosphorylation may modulate vascular permeability after cerebral ischemia and reperfusion. PP1 effectively decreased Src Y418 phosphorylation and the expression of VEGF and Ang-2 and increased the expression of Ang-1 and ZO-1. It also reduced cerebral infarct size and neurologic dysfunction. Therefore, Src may represent a new therapeutic target for reducing tissue damage caused by increased vascular permeability.

[Dysfunction of the blood-brain barrier during ischaemia: a therapeutic concern]

Since it was discovered and its brain-protective role characterized, the blood-brain barrier (BBB), through the permeability-restricting action of the brain capillary endothelial cells, has been representing a hurdle for 95% of new medical compounds targeting the central nervous system. Recently, a BBB dysfunction is being found in an increasing number of pathologies such as brain ischaemic stroke, whose only therapy consists in a pharmacological thrombolysis limited to a small percentage of the admitted patients, because of the toxical effects of thrombolytics. And since the clinical failure of promising neuroprotectants, numerous studies of brain ischaemia were carried out, with physiopathological or pharmacological approaches refocused on the BBB, whose structural complexity is now expanded to perivascular cells, all forming a functional unit named the neurovascular unit (NVU). Nevertheless, in spite of the numerous molecular mechanisms identified, the process of BBB dysfunction in the ischaemia/reperfusion cascade remains insufficiently established to explain the pleiotropic action exerted by new pharmacological compounds, possibly protecting the entire NVU and representing potential treatments.

Therapeutic window of taurine against experimental stroke in rats

The dose-dependent protection of taurine against experimental stroke has been demonstrated previously. The objective of this study was to investigate the therapeutic window of taurine against experimental stroke, and the effects of delayed administration of taurine on inflammatory reaction in a rat model of stroke. Rats received 2-h ischemia by intraluminal filament, and then reperfused. Taurine (50 mg/kg) was administered intravenously 4 h, 8 h, 10 h, or 12 h after ischemia. The neurologic scores and the infarct volumes were evaluated 24 h after ischemia. Then, the effect of administration of taurine at 8 h after ischemia on the neutrophil infiltration in ischemic region was determined. Treatment with taurine 4 h or 8 h after ischemia significantly improved the neurologic function, and decreased the infarct volumes 24 h after ischemia. However, administration of taurine at 10 h or 12 h after ischemia had no significant neuroprotection. Further, taurine administered at 8 h after ischemia markedly reduced myeloperoxidase activity and attenuated neutrophil infiltration in ischemic region. Our data suggest that the therapeutic window of taurine against experimental stroke is of at least 8 h, and suppressing the neutrophil infiltration may be one of the mechanisms of delayed administration of taurine against experimental stroke.

Neuroprotective effect of L-serine against temporary cerebral ischemia in rats

To investigate the neuroprotective effect of L-serine and its underlying mechanisms, focal cerebral ischemia was induced in rats by occlusion of middle cerebral artery (MCAO) with a suture, and reperfusion was given by filament withdrawal 2 hr later. Meanwhile, rat hippocampal neurons were primarily cultured, and incubated in serum-free medium in an incubator containing 1% O(2) for hypoxic exposure of 5 hr, or incubated in serum-free medium containing 1 mM glutamate for glutamate exposure of 2 hr. Brain tissue injury and cell damage were then measured. L-serine dose-dependently decreased the neurology deficit score and infarct volume, elevated the cell viability and inhibited the leakage of lactate dehydrogenase. These effects were blocked by strychnine in both MCAO rats and cultured hippocampal neurons. Furthermore, L-serine (168 mg.kg(-1)) reduced the brain water content, permeability of blood-brain barrier, neuronal loss and the expression of activated caspase-3 in the cortex. In addition, L-serine effectively protected the brain from damage when it was administered within 6 hr after the end of MCAO. It is suggested that L-serine could exert a neuroprotective effect on the ischemic-reperfused brain and on the hypoxia- or glutamate-exposed hippocampal neurons, which may be mediated by activating glycine receptors.

Sleep deprivation attenuates experimental stroke severity in rats

Indirect epidemiological and experimental evidence suggest that the severity of injury during stroke is influenced by prior sleep history. The aim of our study was to test the effect of acute sleep deprivation on early outcome following experimental stroke. Young male Sprague-Dawley rats (n=20) were subjected to focal cerebral ischemia by reversible right middle cerebral artery occlusion (MCAO) for 90 min. In 10 rats, MCAO was performed just after 6-h of total sleep deprivation (TSD) by "gentle handling", whereas the other rats served as controls. Neurological function during the first week after stroke was monitored using a battery of behavioral tests investigating the asymmetry of sensorimotor deficit (tape removal test and cylinder test), bilateral sensorimotor coordination (rotor-rod and Inclined plane) and memory (T-maze and radial maze). Following MCAO, control rats had impaired behavioral performance in all tests. The largest impairment was noted in the tape test where the tape removal time from the left forelimb (contralateral to MCAO) was increased by approximately 10 fold (p<0.01). In contrast, rats subjected to TSD had complete recovery of sensorimotor performance consistent with a 2.5 fold smaller infarct volume and reduced morphological signs of neuronal injury at day 7 after MCAO. Our data suggest that brief TSD induces a neuroprotective response that limits the severity of a subsequent stroke, similar to rapid ischemic preconditioning.

Intra-arterial injection in the rat brain: evaluation of steroids used for transforaminal epidurals

STUDY DESIGN

Prospective in vivo experimental animal model.

OBJECTIVES

To determine the effect of intra-arterial injection of the steroids commonly used for transforaminal epidurals on the central nervous system. And to determine if all of the steroids have the same effect. SUMMARY OF BACKGROUND DATA.: Transforaminal epidural steroid injection is commonly employed to treat radicular pain. This approach is associated with complications, including stroke and death. While the mechanism is unknown, the leading hypothesis is that intravascular injection of particulate steroids leads to microembolization.

METHODS

To characterize the nature of steroid induced injury, a rodent model was employed. The internal carotid artery was dissected and its branches ligated. The external carotid artery was ligated, mobilized, cannulated, and injectate administered. Five solutions were tested: Depo-Medrol (N = 11), Depo-Medrol carrier (N = 6), Solu-Medrol (N = 6), Decadron (N = 8), and normal saline (N = 7). Drugs, in volume of 50 microL, were injected into the ICA via the ECA cannula at 25 microL/min. The extent of central nervous system injury was evaluated by analysis of coronal sections of the brain.

RESULTS

Cerebral hemorrhage occurred in test subjects with the following frequency: 8 of 11 in the Depo-Medrol group, 7 of 8 in the Solu-Medrol group, and 3 of 6 in the Depo-Medrol carrier group; no lesions were identified in the Decadron or saline groups (P < 0.01). Evan's blue dye leakage was detected in the Depo-Medrol and Solu-Medrol groups, but not the Decadron or saline groups.

CONCLUSION

This study presents the first in vivo evaluation of intra-arterial steroid injection. Data demonstrate Depo-Medrol, as well as its nonparticulate carrier, and Solu-Medrol can produce significant injury to the blood-brain barrier when injected intra-arterially. These results demonstrate that injury is produced not only by particulate obstruction of the cerebral microvasculature, but also by toxicity of the carrier or steroid (methylprednisolone).

Preconditioning with a TLR2 specific ligand increases resistance to cerebral ischemia/reperfusion injury

The brain's resistance to ischemic injury can be transiently augmented by prior exposure to a sub-lethal stress stimulus, i.e. preconditioning. It has been reported that Toll-like receptors (TLRs) are involved in the preconditioning-induced protective effect against ischemic brain injury. In this study, we investigated the effect of preconditioning with a TLR2 specific ligand, Pam3CSK4, on focal cerebral ischemia/reperfusion (I/R) injury in mice. Pam3CSK4 was administered systemically 24 h before the mice were subjected to focal cerebral ischemia (1 h) followed by reperfusion. Cerebral infarct size was determined, blood brain barrier (BBB) permeability was evaluated, and expression of tight-junction proteins were examined after focal cerebral I/R. Results showed that pre-treatment with Pam3CSK significantly reduced brain infarct size (1.9+/-0.5% vs 9.4+/-2.2%) compared with the untreated I/R group. Pam3CSK4 pre-treatment also significantly reduced acute mortality (4.3% vs 24.2%), preserved neurological function (8.22+/-0.64 vs 3.91+/-0.57), and attenuated brain edema (84.61+/-0.08% vs 85.29+/-0.09%) after cerebral I/R. In addition, Pam3CSK4 pre-treatment preserved BBB function as evidenced by decreased leakage of serum albumin (0.528+/-0.026 vs 0.771+/-0.059) and Evans Blue (9.23+/-0.72 microg/mg vs 12.56+/-0.65 microg/mg) into brain tissue. Pam3CSK4 pre-treatment also attenuated the loss of the tight junction protein occludin in response to brain I/R injury. These results suggest that TLR2 is a new target of ischemic preconditioning in the brain and preconditioning with a TLR2 specific ligand will protect the brain from I/R injury.

Changes in tissue factor and the effects of tissue factor pathway inhibitor on transient focal cerebral ischemia in rats

INTRODUCTION

To determine the contribution of tissue factor (TF) to focal cerebral ischemia/reperfusion injury, we investigated the changes in TF in rat brains with transient focal cerebral ischemia and also assessed the effect of TF pathway inhibitor (TFPI).

MATERIALS AND METHODS

Spontaneous hypertensive rats were subjected to 90-min of middle cerebral artery occlusion (MCAO) and then were reperfused for up to 24 h. Immediately after MCAO, recombinant human TFPI (rhTFPI) (50 or 20 microg/kg/min) was administered by means of a continuous intravenous injection for 4.5 h.

RESULTS AND CONCLUSIONS

TF immunoreactivity decreased or scattered in the ischemic area after reperfusion, however, an increased TF expression was observed in the microvasculature with the surrounding brain parenchyma and it peaked at 3 to 6 h, which coincided with the start of fibrin formation. On the other hand, total TF protein in ischemic area continued to exist and did not remarkably change until 24 h after reperfusion. At 24 h after reperfusion, the total infarct volume in the group treated with 50 microg/kg/min rhTFPI was significantly smaller than that in the controls (saline). Western blotting and immunohistochemical studies showed that rhTFPI treatment resulted in a decrease of fibrin in the ischemic brains and microvasculature. TF-mediated microvascular thrombosis is thus considered to contribute to focal cerebral ischemia/reperfusion injury. The continuous infusion of rhTFPI until a peak of TF-mediated microvascular thrombosis therefore attenuates the infarct volume by reducing fibrin deposition in the cerebral microcirculation.

Neuroprotective effect of taurine against focal cerebral ischemia in rats possibly mediated by activation of both GABAA and glycine receptors

To investigate the neuroprotective effect of taurine and the involved mechanisms, middle cerebral artery occlusion (MCAO) was induced with suture for 2h in rat, and the brain tissue was then reperfused. The infarct volume and cerebral damage area were measured, respectively, with 2,3,5-triphenyltetrazolium chloride (TTC) staining and MRI. Nissl staining was used for histological observation, and immunohistochemistry and Western-blot analysis for detecting the activated caspase-3 expression. Both pre- (200mgkg(-1)) and post-treatment of taurine decreased the neurology deficit score, infarct volume and brain water content. Taurine post-treatment (67, 200 and 600mgkg(-1)) showed a dose-dependent neuroprotective effect. Taurine (200mgkg(-1)) significantly decreased neuronal loss in the cerebral cortex and hippocampus, and reduced the expression of caspase-3 as well. The neuroprotective effect of taurine was partly blunted by strychnine or bicuculline alone, and almost completely blocked by coapplication of both antagonists of glycine and GABA(A) receptors. It is suggested that taurine exerts a neuroprotective role on the brain when administered before or after MCAO. Such effect is possibly mediated by the activation of both GABA(A) receptors and strychnine-sensitive glycine receptors. Moreover, inhibition of caspase-3 expression is involved in this neuroprotective effect. These results imply a potential therapeutic use of taurine for stroke.

Endothelin-1 overexpression leads to further water accumulation and brain edema after middle cerebral artery occlusion via aquaporin 4 expression in astrocytic end-feet

Stroke patients have increased levels of endothelin-1 (ET-1), a strong vasoconstrictor, in their plasma or cerebrospinal fluid. Previously, we showed high level of ET-1 mRNA expression in astrocytes after hypoxia/ischemia. It is unclear whether the contribution of ET-1 induction in astrocytes is protective or destructive in cerebral ischemia. Here, we generated a transgenic mouse model that overexpress ET-1 in astrocytes (GET-1) using the glial fibrillary acidic protein promoter to examine the role of astrocytic ET-1 in ischemic stroke by challenging these mice with transient middle cerebral artery occlusion (MCAO). Under normal condition, GET-1 mice showed no abnormality in brain morphology, cerebrovasculature, absolute cerebral blood flow, blood-brain barrier (BBB) integrity, and mean arterial blood pressure. Yet, GET-1 mice subjected to transient MCAO showed more severe neurologic deficits and increased infarct, which were partially normalized by administration of ABT-627 (ET(A) antagonist) 5 mins after MCAO. In addition, GET-1 brains exhibited more Evans blue extravasation and showed decreased endothelial occludin expression after MCAO, correlating with higher brain water content and increased cerebral edema. Aquaporin 4 expression was also more pronounced in astrocytic end-feet on blood vessels in GET-1 ipsilateral brains. Our current data suggest that astrocytic ET-1 has deleterious effects on water homeostasis, cerebral edema and BBB integrity, which contribute to more severe ischemic brain injury.

Calbindin D-28k is expressed in the microvascular basal lamina in the ventral horn at early time after transient spinal cord ischemia in the rabbit

Much evidence has been accumulated that the increased expression of calbindin D-28k (CB) is involved in the blockade of calcium-evoked excitotoxicity in cerebral ischemia. We investigated the expression of CB in the basal lamina of microvessels in the ventral horn of the rabbit spinal cord after transient spinal cord ischemia. Spinal cord sections at the level of L7 were immunostained using monoclonal antibody raised against CB at light and electron microscopic levels. CB immunoreactivity was detected in the basal lamina of microvessels at 30 min after ischemic insult. By 3 h after ischemia, CB immunoreactivity was increased in the basal lamina of the microvessels. CB immunoreactivity began to decrease at 6 h after ischemia and nearly disappeared at 48 h after ischemic insult. For calcium detection in the blood vessels of spinal cord, we conducted an alizarin red staining. Alizarin red reactivity was detected in some microvessels at 3 h after ischemic insult. Our results suggest that the ectopic expression of CB in the microvascular basal laminae may be associated with the buffering of calcium in the endothelial cells of microvessels after ischemic damage.

Postischemic reperfusion: ultrastructural blood-brain barrier and hemodynamic correlative changes in an awake model of transient forebrain ischemia

OBJECTIVE

In nonrecovery models of cerebral ischemia, blood-brain barrier (BBB) and cerebral blood flow (CBF) changes are known to occur during reperfusion. It is unknown, however, whether those CBF and BBB alterations occur after brief, transient ischemia with neurological recovery. The purpose of this study was to characterize the time course of CBF and BBB ultrastructural changes during reperfusion in an awake, recovery model of transient global forebrain ischemia (GFI).

METHODS

Forty-five adult Sprague-Dawley rats were subjected, while awake, to 10 minutes of GFI by the nine-vessel occlusion method. Thirty-five age-matched animals composed a sham-operated group. Normal control (n = 5), sham-operated (n = 5), and nine-vessel occlusion/reperfusion (n = 15) rats were selected for ultrastructural analysis. Electroencephalography was performed, and CBF, mean arterial blood pressure, and intracranial pressure were measured during ischemia and reperfusion up to 24 hours. Quantitative morphological analysis of cortical BBB capillaries was performed by transmission electron microscopy at the same time points at which specific CBF changes occurred during reperfusion.

RESULTS

CBF decreased to 6% of preocclusion values during GFI. This correlated with coma and decerebrate rigidity. During reperfusion, short-lived hyperemia (225 +/- 18%, P < 0.001) was characterized by increased intracranial pressure (28.3 +/- 2.6 mm Hg, P < 0.001) and isoelectric electroencephalogram. This was followed by hypoperfusion, which reached a nadir of 59.7% (59.7 +/- 8.8%, P < 0.01) from baseline by 90 minutes. At this time point, the electroencephalogram recovered, and intracranial pressure and mean arterial blood pressure showed no abnormalities. By 8.5 hours, CBF returned to normal, and this coincided with complete recovery of the animal. Ultrastructural BBB analysis revealed astrocyte end-foot process edema and patent capillaries during hyperemia. Severe interstitial BBB edema and capillary lumen collapse was observed during hypoperfusion. Detachment and migration of pericytes was observed during hypoperfusion and beyond.

CONCLUSION

A biphasic CBF response is elicited during reperfusion after brief nonlethal GFI under awake conditions.

The time course of ischemic damage and cerebral perfusion in a rat model of space-occupying cerebral infarction

We aimed to establish a rat model of space-occupying hemispheric infarction to evaluate potential treatment strategies. For adequate timing of therapy in future experiments, we studied the development of tissue damage, edema formation, and perfusion over time with different MRI techniques. Permanent middle cerebral artery (MCA) occlusion was performed in 32 Fisher-344 rats. Forty-six MRI experiments including diffusion weighted (DW), T2-weighted (T2W), flow-sensitive alternating inversion recovery (FAIR) perfusion-weighted, and T1-weighted (T1W) imaging before and after gadolinium were performed at 1, 3, 8, 16, 24, and 48 h of ischemia. MCA occlusion consistently led to infarction of the complete MCA territory. Mortality was 75%. Lesion volumes as derived from apparent diffusion coefficient (ADC) and T2 maps increased to maximum values of 400+/-48 mm3 at 24 h and 420+/-54 mm3 at 48 h of ischemia, respectively. Midline shift peaked at 24 h. The area with diffusion-perfusion deficit decreased to a minimum at 24 h after onset of ischemia and perfusion of the contralateral hemisphere dropped at the same time point. Leakage of gadolinium through the blood-brain barrier in the entire infarct occurred within 3 h of ischemia. Permanent intraluminal MCA occlusion in Fisher-344 rats is an adequate model for space-occupying cerebral infarction. Rats may benefit from intervention aimed at reducing tissue shift and intracranial pressure (ICP), and at improving cerebral blood flow, if initiated before 24 h after MCA occlusion. The value of treatment modalities depending on an intact blood-brain barrier should be questioned.

3-[2-[4-(3-chloro-2-methylphenyl)-1-piperazinyl]ethyl]-5,6-dimethoxy-1-(4-imidazolylmethyl)-1H-indazole dihydrochloride 3.5 hydrate (DY-9760e), a novel calmodulin antagonist, reduces brain edema through the inhibition of enhanced blood-brain barrier permeability after transient focal ischemia

An alteration of the blood-brain barrier (BBB) permeability contributes to the development of brain edema after stroke. In this study, we evaluated the effects of 3-[2-[4-(3-chloro-2-methylphenyl)-1-piperazinyl]ethyl]-5,6-dimethoxy-1-(4-imidazolylmethyl)-1H-indazole dihydrochloride 3.5 hydrate (DY-9760e), a novel calmodulin antagonist, on brain edema formation and BBB integrity in rats subjected to transient focal ischemia. DY-9760e (1 mg/kg/h) was intravenously infused for 6 h, starting immediately after reperfusion of a 1-h middle cerebral artery occlusion. Treatment with DY-9760e significantly suppressed the increase in water content and the extravasation of Evans blue dye after transient focal ischemia. Analysis of a magnetic resonance imaging method revealed that DY-9760e significantly prevented the development of brain edema in the cortical region of the ipsilateral hemisphere. Trifluoperazine, a calmodulin antagonist that is structurally different from DY-9760e, also attenuated brain edema elicited by transient focal ischemia. Furthermore, DY-9760e and trifluoperazine reduced tumor necrosis factor-alpha-induced hyperpermeability of inulin through a cultured brain microvascular endothelial cell monolayer, suggesting an involvement of calmodulin in the regulation of brain microvascular barrier function. The present results demonstrate that DY-9760e ameliorates brain edema formation and suggest that this effect may be mediated in part by the inhibition of enhanced BBB permeability after ischemic insults. Thus, DY-9760e is expected to be a therapeutic drug for treatment of acute stroke patients.

L-NAME reduces infarction, neurological deficit and blood-brain barrier disruption following cerebral ischemia in mice

The role of nitric oxide (NO) in the development of post-ischemic cerebral infarction has been extensively examined, but fewer studies have investigated its role in other outcomes. In the present study, we first determined the temporal evolution of infarct volume, NO production, neurological deficit and blood-brain barrier disruption in a model of transient focal cerebral ischemia in mice. We then examined the effect of the nonselective NO-synthase inhibitor N(omega)-nitro-L-arginine-methylester (L-NAME). L-NAME given at 3 mg/kg 3 h after ischemia reduced by 20% the infarct volume and abolished the increase in brain NO production evaluated by its metabolites (nitrites/nitrates) 48 h after ischemia. L-NAME with this protocol also reduced the neurological deficit evaluated by the grip test and decreased by 65% the extravasation of Evans blue, an index of blood-brain barrier breakdown. These protective activities of L-NAME suggest that NO has multiple deleterious effects in cerebral ischemia.

Ischaemic brain oedema

Ischaemic brain oedema appears to involve two distinct processes, the relative contribution and time course of which depend on the duration and severity of ischaemia, and the presence of reperfusion. The first process involves an increase in tissue Na+ and water content accompanying increased pinocytosis and Na+, K+ ATPase activity across the endothelium. This is apparent during the early phase of infarction and before any structural damage is evident. This phenomenon is augmented by reperfusion. A second process results from a more indiscriminate and delayed BBB breakdown that is associated with infarction of both the parenchyma and the vasculature itself. Although, tissue Na+ level still seems to be the major osmotic force for oedema formation at this second stage, the extravasation of serum proteases is an additional potentially deleterious factor. The relative importance of protease action is not yet clear, however, degradation of the extracellular matrix conceivably leads to further BBB disruption and softening of the tissue, setting the stage for the most pronounced forms of brain swelling. A number of factors mediate or modulate ischaemic oedema formation, however, most current information comes from experimental models, and clinical data on this microcosmic level is lacking. Clinically significant brain oedema develops in a delayed fashion after large hemispheric strokes and is a cause of substantial mortality. Neurological signs appear to be at least as good as direct ICP measurement and neuroimaging in detecting and gauging the secondary damage produced by stroke oedema. The neuroimaging characteristics of the stroke, specifically the early involvement of greater than half of the MCA territory, are, however, highly predictive of the development of severe oedema over the subsequent hours and days. None of the available medical therapies provide substantial relief from the oedema and raised ICP, or at best, they are temporizing in most cases. Hemicraniectomy appears most promising as a method of avoiding death from brain compression, but the optimum timing and manner of patient selection are currently being investigated. All approaches to massive ischaemic brain swelling are clouded by the potential for survival with poor functional outcome. It is possible to manage blood pressure, serum osmolarity by way of selective fluid administration, and a number of other systemic factors that exaggerate brain oedema. Broad guidelines for treatment of stroke oedema can therefore be given at this time.

Characteristics of sustained blood-brain barrier opening and tissue injury in a model for focal trauma in the rat

Minor stab wounding of rodent brain by needle or razor blade is a standard model for immunohistochemical investigations of secondary neuronal degeneration and scarring. Opening of the blood-brain barrier (BBB) to plasma molecules and inflammatory cells is integral to the secondary injury process. To facilitate quantitative study of these BBB phenomena, we tested the utility of a stereotaxic wire knife as a minimally invasive way for modeling of focal trauma and bleeding in brain parenchyma and substantial, reproducible BBB damage. Adult rats were anesthetized, and through a skull burr hole, the 0.3-mm dia guide cannula housing a laterally extendable tungsten wire (0.13 mm dia) was inserted into the right striatum. A layering of horizontal disk-like cuts (3 mm dia) was made, producing a cylindrical lesion of approximately 18 mm3 volume, approximately 2.7% of the cerebral hemisphere. Transfer constants (Ki) for blood to brain permeation of [3H]sucrose measured from 30 min to 2 weeks postlesion showed sustained BBB leakiness; for example, mean Ki +/- SEM (nL.g(-1) x s(-1)) for a standard, matrix-dissected forebrain sample enclosing the lesion were 7.2 +/- 1.2 (day 1 postlesion), 8.1 +/-1.4 (day 3), 5.4 +/- 0.8 (day 14) compared with values for contralateral nonlesioned forebrain ranging from 1.3 +/- 0.05 to 1.6 +/- 0.3 (n = 3-4 samples per time point). Analysis of the simultaneous transport of [14C]sucrose (MW = 342 Da) and [3H]inulin (MW approximately 5,000) showed significantly larger upward increments in Ki for sucrose than inulin, indicating a pore-like opening mechanism. Significant edema was measured 3 days postlesion. A reactive glial response was indicated by an increase in S100beta by 6 h and a glial scar forming around the lesion by 7 days. Secondary brain injury was indicated by a 10% loss of hemisphere mass, measured at 2 months. The wire knife enabled tailoring of interstitial trauma with a minimum of extraneous injury and supported reproducible measurements of sustained BBB injury using relatively few animals.

Biphasic opening of the blood-brain barrier following transient focal ischemia: effects of hypothermia

OBJECTIVE

Tracer constants (Ki) for blood-to-brain diffusion of sucrose were measured in the rat to profile the time course of blood-brain barrier injury after temporary focal ischemia, and to determine the influence of post-ischemic hypothermia.

METHODS

Spontaneously hypertensive rats were subjected to transient (2 hours) clip occlusion of the right middle cerebral artery. Reperfusion times ranged from 1.5 min to 46 hours, and i.v. 3H-sucrose was circulated for 30 min prior to each time point (1 h, 4 h, 22 h, and 46 h; n = 5-7 per time point). Ki was calculated from the ratio of parenchymal tracer uptake and the time-integrated plasma concentration. Additional groups of rats (n = 7-8) were maintained either normothermic (37.5 degrees C) or hypothermic (32.5 degrees C or 28.5 degrees C) for the first 6 hours of reperfusion, and Ki was measured at 46 hours.

RESULTS

Rats injected after 1.5-2 min exhibited a 10-fold increase in Ki for cortical regions supplied by the right middle cerebral artery (p < 0.01). This barrier opening had closed within 1 to 4 hours post-reperfusion. By 22 hours, the blood-brain barrier had re-opened, with further opening 22 and 46 hours (p < 0.01), resulting in edema. Whole body hypothermia (28 degrees C-29 degrees C) during the first six hours of reperfusion prevented opening, reducing Ki by over 50% (p < 0.05).

CONCLUSIONS

Transient middle cerebral artery occlusion evokes a marked biphasic opening of the cortical blood-brain barrier, the second phase of which causes vasogenic edema. Hypothermic treatment reduced infarct volume and the late opening of the blood-brain barrier. This opening of the blood-brain barrier may enhance delivery of low permeability neuroprotective agents.

Induced hypertension treatment to improve cerebral ischemic injury after transient forebrain ischemia

The effect of induced hypertension treatment on cerebral ischemia is still controversial. We investigated the preferred blood pressure manipulation level and pressor agent required to reduce cerebral ischemic injury following transient forebrain ischemia induced by bilateral occlusion of the common carotid arteries in anesthetized gerbils. Following 60-min cerebral ischemia, we evaluated the preferred blood pressure manipulation level and pressor agent required to treat cerebral ischemic injury after reperfusion by examining the effects of different levels of mean arterial blood pressure (MABP), increased with phenylephrine or angiotensin II or decreased by blood withdrawal, on cerebral blood flow (CBF), survival ratio, cerebral edema, and brain energy metabolism following transient forebrain ischemia in gerbils. Mild phenylephrine-induced hypertension treatment (21+/-4 mmHg) during post-cerebral ischemia-reperfusion improved the survival ratio and reduced cerebral edema, which was also associated with an increase in local CBF and a recovery of brain energy metabolism. However, intense phenylephrine-induced hypertension, angiotensin II-induced hypertension, or hypotension worsen the survival rate and produced extra cerebral edema, that were also associated with deterioration of brain energy metabolism. These results demonstrate that a mild induced hypertension with phenylephrine (21+/-4 mmHg above the baseline level) results in reduction of the cerebral edema and improves the survival ratio and brain energy metabolism. Furthermore, angiotensin II may have neurotoxic effect to use as the pressor agent for induced hypertension after cerebral ischemia.

Dynamics of cerebral injury, perfusion, and blood-brain barrier changes after temporary and permanent middle cerebral artery occlusion in the rat

By means of magnetic resonance imaging (MRI) we longitudinally monitored the evolution of ischemic injury, changes in cerebral hemodynamics and alterations of the blood-brain barrier (BBB) during permanent or temporary middle cerebral artery occlusion (MCAO) in rats. Using the intraluminal suture occlusion model, male Sprague-Dawley rats were subjected to either permanent MCAO (Group A, n = 6), reperfusion after 1 h (Group B, n = 5), or reperfusion after 3 h (Group C, n = 5). Diffusion- and perfusion-weighted MRI and Gd-DTPA enhanced T1-weighted images were performed at six time points from 0.5 to 6 h post-MCAO. The lesion volume increased progressively in group A, decreased significantly in group B (P<0.01), and only showed a tendency toward reduction in group C. Perfusion-weighted MRI delineated severe perfusion deficits in the ischemic core, confirmed early and late reperfusion, and was able to demonstrate postischemic hyperperfusion in group C. Gd-DTPA extravasation was found in all animals with permanent MCAO and initially became grossly visible between 4.5 and 6 h post-MCAO. While only 2 animals demonstrated contrast enhancement in group B, widespread BBB changes were detected immediately following late reperfusion (Group C). Our results demonstrate that with advanced MRI techniques, alterations of the BBB can be correlated with the hemodynamic and biophysical consequences of reperfusion.

Tumor necrosis factor alpha expression produces increased blood-brain barrier permeability following temporary focal cerebral ischemia in mice

Alteration of blood-brain barrier (BBB) function occurs in both permanent and temporary cerebral ischemia. Studies in vivo and in vitro have shown that tumor necrosis factor-alpha (TNFalpha) is involved in changes of BBB permeability. However, the relationship between TNFalpha expression and BBB disruption during reperfusion is unclear. The aim of this study is to find the cell source of TNFalpha and to determine the relationship between TNFalpha expression and BBB disruption following temporary focal cerebral ischemia in mice. Adult CD-1 mice received 1 h middle cerebral artery occlusion (MCAO) followed by 2 h, 6 h, 12 h, 24 h, and 48 h of reperfusion. MCAO was achieved using an intraluminal suture technique and reperfusion was performed by the suture withdrawal. Neutralizing monoclonal anti-mouse TNFalpha antibody was administrated intraventricularly immediately after reperfusion. TNFalpha expression was determined by double labeling immunohistochemistry. BBB permeability was determined by albumin immunostaining. TNFalpha immunoreactivity (IR) was observed in the ipsilateral hemisphere from 1 h MCAO with 2 h reperfusion. TNFalpha positive cells included neurons, astrocytes, and ependymal cells. BBB disruption was detected beginning at 6 h reperfusion but was not present at 2 h of reperfusion. The areas of BBB disruption were significantly enlarged at 12 h reperfusion and plateaued at 24 h to 48 h reperfusion. BBB disruptions were significantly attenuated in the anti-TNFalpha antibody treated mice (p<0.05). Our results demonstrate that TNFalpha IR existed in neurons, astrocytes, and ependymal cells during reperfusion. TNFalpha IR following temporary focal cerebral ischemia precedes increased BBB permeability. Treatment with TNFalpha antibody reduces BBB disruption, suggesting TNFalpha may be an important mediator in altering BBB permeability during reperfusion.

YM872, a highly water-soluble AMPA receptor antagonist, preserves the hemodynamic penumbra and reduces brain injury after permanent focal ischemia in rats

BACKGROUND AND PURPOSE

We recently described an image analysis technique based on the temporal correlation mapping (TCM) of injected contrast agents that can be used to distinguish the hemodynamic core and hemodynamic penumbra after focal ischemia. In this study we used this technique for the first time to investigate the effects of the water-soluble AMPA receptor antagonist YM872 in permanent focal ischemia.

METHODS

Fischer 344 rats were subjected to permanent occlusion of the middle cerebral artery. Approximately 30 minutes after ischemia, functional CT images were collected with the use of a dynamic scanning protocol with bolus injections of nonionic contrast agent iohexol (1 mL/kg). TCM analysis defined the distributions of hemodynamic core and hemodynamic penumbra. Cerebral perfusion indices were calculated on the basis of the area under the first-pass transit curves. One hour after ischemia, animals were randomly treated with YM872 (n=8, 20 mg/kg per hour over 4 hours) or normal saline (n=10). Twenty-four hours later, neurological deficits were evaluated, and conventional CT and triphenyltetrazolium chloride staining were used to define volumes of ischemic damage.

RESULTS

At 24 hours after ischemia, hypodense lesions were visible on conventional CT scans that were highly correlated with triphenyltetrazolium chloride lesion volumes. YM872 improved neurological deficits and reduced volumes of ischemic damage in cortex (90+/-14 versus 170+/-16 mm3 in controls) but not striatum (57+/-14 versus 79+/-6 mm3 in controls). Comparison of early TCM images with conventional CT scans of ischemic injury showed that the hemodynamic core was always damaged in all rats. In controls, 54% of the tissue within the hemodynamic penumbra evolved into ischemic damage compared with 24% in YM872-treated rats. Furthermore, the perfusion index corresponding to the ischemic damage threshold was significantly reduced by YM872 (28+/-2% versus 37+/-2% in controls).

CONCLUSIONS

These results indicate that YM872 is a neuroprotective compound that ameliorates the deterioration of the hemodynamic penumbra after focal ischemia.

Induced hypertension improves regional blood flow and protects against infarction during focal ischemia: time course of changes in blood flow measured by laser Doppler imaging

OBJECTIVE

To characterize changes in regional blood flow (rCBF) during and after a period of arterial occlusion and determine the effect on rCBF and on the extent of infarction when the mean arterial blood pressure is increased during the period of occlusion.

METHODS

rCBF in the middle cerebral artery (MCA) territory of rabbits was monitored using laser Doppler perfusion imaging before, during, and after a 1- or 2-hour period of MCA occlusion, and the size of the infarction was assessed by 2,3,5-triphenyltetrazolamine chloride staining after 2 hours of reperfusion. Test animals, the mean arterial blood pressure of which was increased by 65 mm Hg with intravenous phenylephrine during the ischemia, were compared with control animals that remained normotensive. The laser Doppler perfusion imager (Lisca Developments Co., Linköping, Sweden) scanned a 3-cm2 area of cortex with a resolution of 4 mm2 every 15 minutes.

RESULTS

MCA occlusion reduced rCBF to 71 +/- 2% of the control level (n = 24, P < 0.001). Hypertension (HTN) restored rCBF to 84 +/- 3% of the control level (n = 12, P < 0.01), but the HTN-induced improvement diminished with time, so that after 1 hour, there was no longer a significant difference between hypertensive and normotensive animals. HTN during the MCA occlusion caused a 97% reduction in infarct size (P < 0.05) in the animals subjected to 1 hour of occlusion but caused only a 45% reduction (P approximately 0.1) in the animals subjected to 2 hours of occlusion.

CONCLUSION

This study supports the use of HTN to minimize ischemic injury from short intervals of major intracranial vessel occlusion but fails to demonstrate protection when HTN is maintained during occlusions of more than 1 hour.

Immunologic tolerance to myelin basic protein decreases stroke size after transient focal cerebral ischemia

Immune mechanisms contribute to cerebral ischemic injury. Therapeutic immunosuppressive options are limited due to systemic side effects. We attempted to achieve immunosuppression in the brain through oral tolerance to myelin basic protein (MBP). Lewis rats were fed low-dose bovine MBP or ovalbumin (1 mg, five times) before 3 h of middle cerebral artery occlusion (MCAO). A third group of animals was sensitized to MBP but did not survive the post-stroke period. Infarct size at 24 and 96 h after ischemia was significantly less in tolerized animals. Tolerance to MBP was confirmed in vivo by a decrease in delayed-type hypersensitivity to MBP. Systemic immune responses, characterized in vitro by spleen cell proliferation to Con A, lipopolysaccharide, and MBP, again confirmed antigen-specific immunologic tolerance. Immunohistochemistry revealed transforming growth factor beta1 production by T cells in the brains of tolerized but not control animals. Systemic transforming growth factor beta1 levels were equivalent in both groups. Corticosterone levels 24 h after surgery were elevated in all sham-operated animals and ischemic control animals but not in ischemic tolerized animals. These results demonstrate that antigen-specific modulation of the immune response decreases infarct size after focal cerebral ischemia and that sensitization to the same antigen may actually worsen outcome.

Serum protein leakage in Alzheimer's disease revisited

Leakage of serum proteins into the brain parenchyma has been repeatedly used as evidence of blood-brain barrier (BBB) damage in experimental and human studies. However, there is no consensus in the literature concerning this phenomenon in Alzheimer's disease (AD). We have examined this question by comparing frontal lobe sections in seven groups of patients: Multi-infarct dementia (n = 6), AD with (n = 10) and without (n = 10) infarcts, age-matched controls with (n = 10) and without (n = 10) infarcts, controls with neurodegenerative diseases other than AD, and young controls (n = 10). An additional series compared prospectively followed patients with a diagnosis of either multi-infarct dementia (n = 5) or AD (n = 4). Albumin was detected in white-matter astrocytes in all cases, without significant variation in intensity. In addition, diverse combinations of neurons, astrocytes, and (in AD patients) senile plaques were present in the cerebral cortex in an inconsistent manner. Semiquantitative analysis showed no statistically significant differences among groups. Anti-IgG labeled astrocytes in infarcts only. Complement C3c component was detected in rare amyloid plaques in a minority (15%) of AD cases. Selective labeling of AD-specific lesions in a patchy manner was observed for serum amyloid P. We conclude that there is no immunohistochemical evidence of alteration of the BBB in Alzheimer's disease with or without vascular factors or in old age. Serum amyloid P binds avidly to AD lesions, but our findings are consistent with leakage through the BBB during the agonal or immediate postmortem period. Finally, no specific pattern of abnormality in the BBB was detected in multi-infarct dementia.

Duration threshold of induced hypertension on cerebral blood flow, energy metabolism, and edema after transient forebrain ischemia in gerbils

We have investigated whether there is a duration threshold for the effects of phenylephrine-induced hypertension on CBF, brain energy metabolism, and cerebral parenchymal specific gravity (SG) following transient forebrain ischemia in gerbils. Sixty gerbils were randomly assigned to one of the four treatment groups: one control group and three groups subjected to an increase of 25 mm Hg in MABP induced by treatment, 30 min after reperfusion, with phenylephrine for 15 min, 30 min, or 60 min. The local CBF was measured continuously, and the SG was evaluated 120 min after reperfusion. Sequential changes in brain energy metabolism, as shown by the ratio of phosphocreatine to inorganic phosphate (Pi), the beta-ATP/Pi ratio, and intracellular pH, were also measured. The 15-min induced hypertension regimen was most suited to the recovery of brain energy metabolism, which was associated with an increase in local CBF and a decrease in cerebral edema. These results demonstrate that a suitable duration can be chosen to optimize the beneficial effects of phenylephrine-induced hypertension on ischemic brain injury following transient forebrain ischemia.

Induced hypertension during ischemia reduces infarct area after temporary middle cerebral artery occlusion in rats

BACKGROUND

Induced hypertension is one of the few interventions available to reverse acute ischemic neurologic deficit. The purpose of this study was to determine the safety and efficacy of hypertension during prolonged temporary focal ischemia.

METHODS

Anesthetized rats underwent 2 hours of endovascular middle cerebral artery occlusion. Angiotensin was given to increase mean arterial blood pressure to 40%-60% above baseline during ischemia. Neurologic deficit and infarct size in hypertensive rats were assessed at 72 hours.

RESULTS

Hypertensive rats had smaller infarcts than normotensive controls (mean, 12.40 +/- 3.71% versus 24.19 +/- 2.89; p < 0.05) without hemorrhage. Neuroscores were comparable.

CONCLUSION

Hypertension safely reduces infarction after 2 hours of focal ischemia in rats.

Focal cerebral ischemia during anesthesia with etomidate, isoflurane, or thiopental: a comparison of the extent of cerebral injury

An investigation was performed to compare the cerebral protective properties of etomidate, isoflurane, and thiopental. In separate groups of spontaneously hypertensive rats, etomidate, isoflurane, or thiopental was administered to achieve and maintain burst-suppression of the electroencephalogram (3-5 bursts/min) for the duration of the experiment. A fourth group received 1.2 minimal alveolar concentration halothane. All groups underwent 3 hours of middle cerebral artery occlusion and then 2 hours of reperfusion. Thereafter, the animals were killed and the volume of injured brain was determined by staining with 2,3,5-triphenyltetrazolium. Physiological parameters did not differ among the four groups during the investigation, with the exception that hemolysis occurred in the etomidate group (free hemoglobin levels, approximately 0.4 g.dl-1). The volume of injured brain in the thiopental group (56 +/- 10 mm3) was significantly smaller than that in the halothane control group (99 +/- 13 mm3). The volumes of injured brain in the etomidate and isoflurane groups (145 +/- 11 mm3 and 139 +/- 14 mm3, respectively) were significantly larger than those in the control and thiopental groups. We speculate that the apparently detrimental effect of etomidate may be the result of the binding of nitric oxide of cerebral endothelial origin by the iron component of free hemoglobin. Intracranial pressure was not recorded, and in the isoflurane group, there may have been adverse effects on cerebral perfusion pressure associated with vasodilation caused by high concentrations of isoflurane. The results are consistent with a protective effect by barbiturates.

Blood-brain barrier breakdown and edema formation following frontal cortical contusion: does hormonal status play a role?

The present experiment was designed to evaluate and correlate the time course of blood-brain barrier (BBB) integrity and cerebral edema in adult male rats given medial frontal cortex contusions. The effect of sex hormones on BBB integrity in the same injury model was also examined, because previous work has shown that progesterone can reduce cerebral edema (Roof et al., 1993). BBB breakdown was assessed by Evans blue extravasation and albumin immunostaining while edema formation was measured by the wet weight dry weight technique. These processes were examined beginning 2 h and continuing up to 10 days after injury. Our findings show that medial frontal contusion in rats produces changes in cerebral water content and opening of the BBB that endures at least 7 days postinjury. Although pseudopregnancy has been shown to reduce cerebral edema at day 1 postinjury, we did not find any evidence that this hormonal state is associated with BBB repair.

Early entry of plasma proteins into damaged neurons in brain infarcts. An immunohistochemical study on experimental animals

Entry of plasma proteins into damaged neurons has previously been demonstrated in various pathological conditions, but little is known about brain infarcts in this respect. In the present study, focal ischemic lesions were produced in rats by permanent occlusion of the middle cerebral artery (MCA). The animals were killed from 1 to 48 h postlesion. Leakage of plasma proteins across the blood-brain barrier into the infarcted area was visualized with immunostaining 2-3 h after the occlusion. This is earlier than in most previous reports. Entry of plasma proteins into ischemic neurons was seen 3 h after permanent occlusion of the MCA, while reliable changes were not seen until 12-24 h in sections stained with hematoxylin and eosin (H & E). Ischemic neurons stained for plasma proteins irrespective of their morphological appearance. Even cells that appeared normal with H & E staining were positively labeled. The technique may be used to diagnose very early ischemic lesions.

Reperfusion-induced injury to the blood-brain barrier after middle cerebral artery occlusion in rats

BACKGROUND AND PURPOSE

The integrity of the blood-brain barrier may play an important pathophysiological role during postischemic reperfusion. To determine the factors that lead to exacerbation of brain injury by reperfusion, we investigated changes in cerebral blood flow, blood-brain barrier permeability, edema formation, and infarction in permanent or temporary middle cerebral artery occlusion in rats and studied the relation between local cerebral blood flow and blood-brain barrier disruption.

METHODS

Middle cerebral artery occlusion was performed with the rat suture model, allowing either permanent (6 hours) or temporary occlusion (3 hours of occlusion and 3 hours of reperfusion). We measured brain water, ion contents, and infarct volumes and determined cerebral blood flow using laser Doppler flowmetry and blood-brain barrier permeability with [3H] alpha-aminoisobutyric acid.

RESULTS

During occlusion, cerebral blood flow was reduced to 7% to 15% (permanent) and 10% to 17% (temporary) of the baseline. During 3 hours of reperfusion, it returned to 47% to 80% (lateral cortex) and 78% to 98% (medial cortex) of the baseline. Compared with the contralateral hemisphere, the water content in the ischemic area increased in both permanent and temporary groups (P < .05, P < .01). Both infarct volume and blood-brain barrier disruption were greater in the reperfusion group compared with the permanent occlusion group (P < .05). Blood-brain barrier disruption correlated with cerebral blood flow during reperfusion (P < .05).

CONCLUSIONS

These findings demonstrate that brain infarct and blood-brain barrier disruption are exacerbated after reperfusion in this model of focal ischemia. Blood-brain barrier disruption may relate to the degree of cerebral blood flow recovery. Thus, although early reperfusion in focal ischemia may preserve penumbra tissue, late reperfusion may increase the tissue injury.