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.     

去骨瓣减压术对大鼠局灶性脑缺血后脑水肿、血脑屏障、脑血流变化的影响

目的:观察去骨瓣减压术对局灶性脑缺血大鼠脑水肿、血脑屏障(BBB)及脑血流(CBF)的影响,探讨该手术对缺血性脑损害的保护机制。方法:改良Koizumi′s法制作脑缺血大鼠动物模型,脑缺血后6h行去骨瓣减压术,分别在术后3和7d观察脑水肿和血脑屏障的变化,另持续观察缺血1h 去骨瓣减压2h的CBF变化。结果:去骨瓣减压术后半暗区CBF增加更加持久和有效,在术后第3天时BBB破坏范围明显缩小,术后第7天时脑水含量明显降低。结论:去骨瓣减压术对局灶性脑缺血的保护作用可能与增加半暗区CBF、改善BBB破坏和减轻脑水肿有关。     

高血糖对大鼠脑缺血后血脑屏障葡萄糖转运蛋白1表达的影响

目的探讨高血糖对脑缺血后血脑屏障（BBB）葡萄糖转运蛋白1（GLUTl）表达的影响。方法采用链脲佐菌素法建立大鼠高血糖模型，线栓法制作大鼠大脑中动脉闭塞模型，用免疫组化法观察脑缺血后1h、3h、6h、12h、1d、2d、3d、7d时BBBGLUT1表达的变化。结果正常血糖组大鼠及高血糖组大鼠脑缺血后BBBGLUT1的表达均增加，除脑缺血后7d外，高血糖组脑缺血后各时间点GLUT1的表达均低于正常血糖组（P〈0．01）。结论高血糖可降低脑缺血后BBBGLUT1的表达，隆低BRB蒴菊搐接请活性     

Estradiol reduces activity of the blood-brain barrier Na-K-Cl cotransporter and decreases edema formation in permanent middle cerebral artery occlusion.

Estrogen has been shown to protect against stroke-induced brain damage, yet the mechanism is unknown. During the early hours of stroke, cerebral edema forms as increased transport of Na and Cl from blood into brain occurs across an intact blood-brain barrier (BBB). We showed previously that a luminal BBB Na-K-Cl cotransporter is stimulated by hypoxia and arginine vasopressin (AVP), factors present during cerebral ischemia, and that inhibition of the cotransporter by intravenous bumetanide greatly reduces edema in rats subjected to permanent middle cerebral artery occlusion (MCAO). The present study was conducted to determine whether estrogen protects in stroke at least in part by reducing activity of the BBB cotransporter, thereby decreasing edema formation. Ovariectomized rats were subjected to 210 mins of permanent MCAO after 7-day or 30-min pretreatment with 17beta-estradiol and then brain swelling and 2,3,5-triphenyltetrazolium chloride staining were assessed as measures of brain edema and lesion volume, respectively. Diffusion-weighed imaging was used to monitor permanent MCAO-induced decreases in apparent diffusion coefficient (ADC) values, an index of changes in brain water distribution and mobility. Na-K-Cl cotransporter activity of cerebral microvascular endothelial cells (CMECs) was assessed as bumetanide-sensitive K influx and cotransporter abundance by Western blot analysis after estradiol treatment. Estradiol significantly decreased brain swelling and lesion volume and attenuated the decrease in ADC values during permanent MCAO. Estradiol also abolished CMEC cotransporter stimulation by chemical hypoxia or AVP and decreased cotransporter abundance. These findings support the hypothesis that estrogen attenuates stimulation of BBB Na-K-Cl cotransporter activity, reducing edema formation during stroke.     

Effects of anti-VEGF antibody on blood-brain barrier disruption in focal cerebral ischemia

Since cerebral ischemia increases expression of vascular endothelial growth factor (VEGF) and exogenous VEGF can aggravate BBB disruption in cerebral ischemia, we hypothesized that inhibition of endogenous VEGF would attenuate BBB disruption. To test this hypothesis, rats were mechanically ventilated with isoflurane and a craniotomy (5 mm in diameter) was performed to expose the cerebral cortex. Anti-VEGF antibody was applied topically (75 mug) 1 h before middle cerebral artery (MCA) occlusion and additional anti-VEGF antibody was applied (25 mug) immediately after MCA occlusion (anti-VEGF group). For the control animals, normal saline was applied instead of anti-VEGF antibody on the surface of the cortex (control group). One hour after MCA occlusion, the transfer coefficient (K(i)) of (14)C-alpha-aminoisobutyric acid and volume of (3)H-dextran (70,000 Da) distribution were determined to measure the degree of BBB disruption. There was no significant difference in vital signs, blood gases, and pericranial temperature between the control and the anti-VEGF group. In both of the groups, the K(i) of the ischemic cortex (IC) was higher than that of the corresponding contralateral cortex (CC) (p<0.05). The K(i) of the IC of the anti-VEGF group was significantly lower than that of the IC of the control group (-34%, p<0.05). The K(i) of the CC and pons were similar between these two groups. The data of volume of dextran distribution followed the same pattern as that of K(i) but without a statistical significance. Our data demonstrated that inhibition of endogenous VEGF by topical application of anti-VEGF antibody in the ischemic cortex decreased the K(i) of (14)C-AIB and suggest that endogenous VEGF is in part responsible for the BBB disruption during the early stage of focal cerebral ischemia.     

Depression and anxiety in a Portuguese MS population: associations with physical disability and severity of disease

In cerebral ischemia, transmission by the inhibitory neurotransmitter, γ-aminobutyric acid (GABA) is altered. This study was performed to determine whether blockade of GABA(A) receptor would affect regional cerebral blood flow (rCBF) and blood-brain barrier (BBB) permeability in a focal ischemic area of the brain. Rats were anesthetized with isoflurane and mechanically ventilated. Fifteen minutes after a permanent middle cerebral artery (MCA) occlusion, one half of the rats were infused with bicuculline 1mg/kg/min iv for 2 min followed by 0.1mg/kg/min iv to the end of the experiment. The other half were infused with normal saline. At one hour after MCA occlusion, rCBF was determined using 1?C-iodoantipyrine and BBB permeability was determined by measuring the transfer coefficient (Ki) of 1?C-α-aminoisobutyric acid. With MCA occlusion, rCBF was decreased in the ischemic cortex (IC) (-70%) in the control rats. In the bicuculline treated rats, the rCBF of the IC was lower (-48%) than the contralateral cortex but higher than the rCBF of the IC of the control rats (+55%). MCA occlusion increased Ki in the IC of the control rats (+72%) and bicuculline administration increased Ki further (+53%) in the IC. Blockade of GABA(A) receptors did not significantly affect rCBF or BBB permeability in the non-ischemic brain regions under isoflurane anesthesia. Our data demonstrated that blockade of GABA(A) receptors increased rCBF and enhanced the BBB disruption in focal cerebral ischemia. Our data suggest that GABA(A) receptors are involved, at least in part, in modulating rCBF and BBB disruption in focal cerebral ischemia.     

Normobaric hyperoxia delays perfusion/diffusion mismatch evolution, reduces infarct volume, and differentially affects neuronal cell death pathways after suture middle cerebral artery occlusion in rats.

Normobaric hyperoxia (NBO) has been shown to extend the reperfusion window after focal cerebral ischemia. Employing diffusion (DWI)- and perfusion (PWI)-weighted magnetic resonance imaging (MRI), the effect of NBO (100% started at 30 mins after middle cerebral artery occlusion (MCAO)) on the spatiotemporal evolution of ischemia during and after permanent (pMCAO) and transient suture middle cerebral artery occlusion (tMCAO) was investigated (experiment 3). In two additional experiments, time window (experiment 1) and cell death pathways (experiment 2) were investigated in the pMCAO model. In experiment 1, NBO treatment reduced infarct volume at 24 h after pMCAO by 10% when administered for 3 h (P>0.05) and by 44% when administered for 6 h (P<0.05). In experiment 2, NBO acutely (390 mins, P<0.05) reduced in situ end labeling (ISEL) positivity in the ipsilesional penumbra but increased contralesional necrotic as well as caspase-3-mediated apoptotic cell death. In experiment 3, CBF characteristics and CBF-derived lesion volumes did not differ between treated and untreated animals, whereas the apparent diffusion coefficient (ADC)-derived lesion volume essentially stopped progressing during NBO treatment, resulting in a persistent PWI/DWI mismatch that could be salvaged by delayed (3 h) reperfusion. In conclusion, NBO (1) acutely preserved the perfusion/diffusion mismatch without altering CBF, (2) significantly extended the time window for reperfusion, (3) induced lasting neuroprotection in permanent ischemia, and (4) although capable of reducing cell death in hypoperfused tissue it also induced cell death in otherwise unaffected areas. Our data suggest that NBO may represent a promising strategy for acute stroke treatment.     

Effects of blockade of ionotropic glutamate receptors on blood–brain barrier disruption in focal cerebral ischemia

To determine whether blockade of ionotropic glutamate receptors such as NMDA or AMPA receptors would attenuate blood–brain barrier (BBB) disruption in focal cerebral ischemia, 15 min before middle cerebral artery (MCA) occlusion, CGS-19755 or NBQX was injected intraperitoneally in rats. At 1 h after MCA occlusion, BBB permeability was determined by measuring the transfer coefficient (K _i ) of ¹⁴C-α-aminoisobutyric acid and the volume of dextran distribution. With MCA occlusion, K _i was increased in the ischemic cortex (IC) (316%). CGS-19755 attenuated the increase in K _i in the IC (−46%), but NBQX did not significantly decrease it. The difference in the volume of dextran distribution between the IC and the contralateral cortex became insignificant with the blockade of NMDA or AMPA receptors. Our data demonstrated that blockade of NMDA or AMPA receptors could attenuate the BBB disruption in focal cerebral ischemia and suggest that ionotropic glutamate receptors are involved in part in BBB disruption.     

The effect of the NMDA receptor antagonist MK-801 on cerebral blood flow and infarct volume in experimental focal stroke

The non-competitive N-methyl-D-aspartate receptor/channel antagonist dizocilipine maleate (MK-801) has been reported to reduce infarct volume in a variety of focal stroke models. We examined the effect of MK-801 on infarct volume and cerebral blood flow in temporary and permanent focal ischemia in rats. In Wistar rats exposed to permanent right common carotid artery and 2 h of transient right middle cerebral and left common carotid artery occlusion followed by 22 h of reperfusion, MK-801 reduced infarct volume by 73% (P less than 0.05) and significantly increased cerebral blood flow to the ischemic core throughout the 2-h period of ischemia. In spontaneously hypertensive rats (SHRs) exposed to permanent right common carotid artery occlusion and 2 h of transient right middle cerebral artery occlusion followed by 22 h of reperfusion, MK-801 decreased infarct volume by 13% (P greater than 0.05) and increased cerebral blood flow to the penumbral region. In SHRs subjected to permanent right common carotid and middle cerebral artery occlusion MK-801 reduced infarct volume by 18% at 3 h (P greater than 0.05), by 25% at 6 h (P less than 0.01) and by 18% at 24 h (P less than 0.05). MK-801-treated SHRs had no difference in cerebral blood flow to the ischemic core, but increased cerebral blood flow to penumbral zones as compared with untreated SHRs. These results suggest that the protective effect of MK-801, at least in part, relates to improved cerebral blood flow.     

Ultrastructural studies of the neurovascular unit reveal enhanced endothelial transcytosis in hyperglycemia-enhanced hemorrhagic transformation after stroke

AimsPre‐existing hyperglycemia (HG) aggravates the breakdown of blood–brain barrier (BBB) and increases the risk of hemorrhagic transformation (HT) after acute ischemic stroke in both animal models and patients. To date, HG‐induced ultrastructural changes of brain microvascular endothelial cells (BMECs) and the mechanisms underlying HG‐enhanced HT after ischemic stroke are poorly understood.MethodsWe used a mouse model of mild brain ischemia/reperfusion to investigate HG‐induced ultrastructural changes of BMECs that contribute to the impairment of BBB integrity after stroke. Adult male mice received systemic glucose administration 15 min before middle cerebral artery occlusion (MCAO) for 20 min. Ultrastructural characteristics of BMECs were evaluated using two‐dimensional and three‐dimensional electron microscopy and quantitatively analyzed.ResultsMice with acute HG had exacerbated BBB disruption and larger brain infarcts compared to mice with normoglycemia (NG) after MCAO and 4 h of reperfusion, as assessed by brain extravasation of the Evans blue dye and microtubule‐associated protein 2 immunostaining. Electron microscopy further revealed that HG mice had more endothelial vesicles in the striatal neurovascular unit than NG mice, which may account for their deterioration of BBB impairment. In contrast with enhanced endothelial transcytosis, paracellular tight junction ultrastructure was not disrupted after this mild ischemia/reperfusion insult or altered upon HG. Consistent with the observed increase of endothelial vesicles, transcytosis‐related proteins caveolin‐1, clathrin, and hypoxia‐inducible factor (HIF)‐1α were upregulated by HG after MCAO and reperfusion.ConclusionOur study provides solid structural evidence to understand the role of endothelial transcytosis in HG‐elicited BBB hyperpermeability. Enhanced transcytosis occurs prior to the physical breakdown of BMECs and is a promising therapeutic target to preserve BBB integrity.     

Ischemic brain edema and the osmotic gradient between blood and brain

The relationship of the osmotic pressure gradient between blood and brain, and the development of ischemic brain edema was studied. Focal cerebral ischemia was produced by left middle cerebral artery occlusion in rats. Brain osmolality was determined with a vapor pressure osmometer, brain water content by wet-dry weight, and tissue sodium and potassium contents by flame photometry. Permeability of the BBB was tested by Evans blue. Measurements were made from the ischemic cortex within 14 days of occlusion. Brain osmolality increased from 311 +/- 2 to 329 +/- 2 mOsm/kg by 6 h after occlusion. Serum osmolality did not change significantly. The osmotic gradient between blood and brain peaked at approximately 26 mOsm/kg. Brain osmolality then decreased to 310 +/- 2 mOsm/kg by 12 h after occlusion and remained at about that same level. Water content increased progressively within 1 day of occlusion, then gradually decreased by 14 days. Brain tissue sodium plus potassium content did not increase within 6 h of occlusion, and Evans blue extravasation was not seen within that time. These findings indicate that an osmotic pressure gradient contributes to the formation of edema only during the early stage of cerebral ischemia. Furthermore, the increase in brain osmolality is not related to tissue electrolyte change or BBB disruption to protein.     

Chinese medicine Tongxinluo capsule protects against blood-brain barrier disruption after ischemic stroke by inhibiting the low-density lipoprotein receptor-related protein 1 pathway in mice

BackgroundChinese medicine Tongxinluo capsule (TXL) has been extensively used to treat ischemic stroke in China, and one of its mechanisms is to protect against blood brain barrier (BBB) disruption after stroke. However, the underlying protective mechanisms are not fully illuminated. It is reported that the low-density lipoprotein receptor-related protein 1 (LRP-1) is involved in BBB disruption after brain ischemia. In this study, we explored whether TXL could downregulate LRP-1 expression and subsequently protect against BBB disruption after stroke using permanent middle cerebral artery occlusion (pMCAO) in mice.MethodsThe animal model of ischemic stroke was induced by pMCAO in male adult C57BL/6J mice. The mice were orally administered TXL (3.0 g/kg) at 1, 3 and 21 h after pMCAO. Meanwhile, the LRP-1 antagonist receptor associated protein (RAP) was intracerebroventricularly injected at 1 and 21 h after stroke. We measured the following parameters at 6 and 24 h: LRP-1 protein level, BBB leakage, and the expression of tight junction (TJ) proteins including occludin, claudin‐5 and zonula occludens‐1 (ZO‐1).ResultsOur results showed that TXL downregulated LRP-1 level, upregulated these TJ proteins level, and reduced BBB leakage in peri-infarct regions after pMCAO. Further study found that the inhibitor RAP played the same role as did TXL in upregulating these TJ proteins level and reducing BBB leakage after stroke.ConclusionOur study demonstrates that TXL protects against BBB disruption after stroke via inhibiting the LRP-1 pathway.     

Experimental focal cerebral ischemia produced by embolization with silicone cylinder in normotensive (NTR) and spontaneously hypertensive rats (SHR): comparison of neurological and pathological findings

A focal cerebral ischemic model was produced by occlusion of the intracranial main cerebral artery with a silicone cylinder in normotensive (NTR) and spontaneously hypertensive rats (SHR). Main cerebral artery could be successfully occluded in approximately 90%. The most frequent embolized site was the distal part of the internal cerebral artery (ICb) and less frequently the horizontal segment of the anterior cerebral artery (Al). Mortality rate of NTR with ICb occlusion (NTR-ICb) was 43% at 72 hours after embolization and that of SHR with ICb occlusion (SHR-ICb) was 67% at 24 hours after embolization. NTR-ICb showed neurological signs (i.e. circling movement, hemiparesis, poor response to pain stimuli) and histologically, showed infarction in the deep cerebral structures (i.e. thalamus, hypothalamus, hippocampus, and internal capsule) accompanied with mild disruption of blood-brain barrier (BBB). SHR-ICb showed more serious neurological signs and more severe cerebral infarction in the deep cerebral structures with severe disruption of BBB. In SHR-ICb, ischemic cerebral edema was more prominent which may deteriorate symptoms and pathological findings compared to NTR-ICb. This embolization model is proposed to be useful for studying the pathophysiology of focal cerebral ischemia, especially, early ischemic edema.     

A hemorrhagic transformation model of mechanical stroke therapy with acute hyperglycemia in mice

Clinical benefit for mechanical thrombectomy (MT) in stroke was recently demonstrated in multiple large prospective studies. Acute hyperglycemia (HG) is an important risk factor of poor outcome in stroke patients, including those that underwent MT. The aim of this therapy is to achieve a complete reperfusion in a short time, given that reperfusion damage is dependent on the duration of ischemia. Here, we investigated the effects of acute HG in a mouse model of ischemic stroke induced by middle cerebral artery occlusion (MCAO). Hyperglycemic (intraperitoneal [ip] injection of glucose) and control (ip saline injection) 10‐week male C57BL6 mice were subjected to MCAO (30, 90, and 180 min) followed by reperfusion obtained by withdrawal of the monofilament. Infarct volume, hemorrhagic transformation (HT), neutrophil infiltration, and neurological scores were assessed at 24 hr by performing vital staining, ELISA immunofluorescence, and behavioral test, respectively. Glucose injection led to transient HG (blood glucose = 250–390 mg/dL) that significantly increased infarct volume, HT, and worsened neurological outcome. In addition, we report that HG promoted blood‐brain barrier disruption as shown by hemoglobin accumulation in the brain parenchyma and tended to increase neutrophil extravasation within the infarcted area. Acute HG increased neurovascular damage for all MCAO durations tested. HTs were observed as early as 90 min after ischemia under hyperglycemic conditions. This model mimics MT ischemia/reperfusion and allows the exploration of brain injury in hyperglycemic conditions.     

Cycloheximide reduces infarct volume when administered up to 6 h after mild focal ischemia in rats

We have previously described a rodent model of brief (30 min) middle cerebral artery occlusion followed by reperfusion, in which infarction develops gradually, reaching completion more than 3 days after ischemia, accompanied by morphological, biochemical, and pharmacological evidence of apoptosis. In the present study, we tested the hypotheses that delayed administration of a protein synthesis inhibitor would be effective in reducing tissue injury in this slowly evolving ischemic infarction, and that efficacy of this treatment would wane with more prolonged ischemia. Focal cerebral ischemia was induced in Long-Evans rats by occlusion of the right middle cerebral artery. Infarction volume was analyzed using triphenyl tetrazolium chloride staining, and morphology was studied using hematoxylin and eosin stained sections. Following 30 min middle cerebral artery occlusion and reperfusion, the core ischemic region exhibited vacuolization in the neuropil by 36 h after ischemia, and infarction reached full size by 7 days after ischemia. Cycloheximide reduced infarct volume when given up to 6 h after ischemia. If the duration of ischemic insult was increased to 90 min, the therapeutic window for delayed cycloheximide was only 30 min. In permanent middle cerebral artery occlusion, cycloheximide was ineffective even when given prior to ischemia onset. After mild, but not severe, ischemic insults, cerebral infarction develops slowly and may be treatable with protein synthesis inhibitors, even when treatment is delayed for up to 6 h after the onset of ischemia.     

Antioxidant CR-6 protects against reperfusion injury after a transient episode of focal brain ischemia in rats

Oxidative and nitrosative stress are targets for intervention after ischemia/reperfusion. The aim of this study was to explore the effect of CR-6, a vitamin-E analogue that is antioxidant and scavenger of nitrogen-reactive species. Sprague–Dawley rats had the middle cerebral artery (MCA) occluded either for 90 mins or permanently. Cortical perfusion was continuously monitored by laser–Doppler flowmetry. CR-6 (100 mg/kg) was administered orally either at 2 and 8 h after MCA occlusion, or at 2 h only. Infarct volume, neurological deficit, and signs of reperfusion injury were evaluated. CR-6 was detected in plasma and brain by HPLC. CR-6 reduced glutathione consumption in the ischemic brain and superoxide generation in the isolated MCA. CR-6 decreased infarct volume and attenuated the neurological deficit at 1 and 7 days after ischemia/reperfusion, but not after permanent ischemia. Immediately after reperfusion, cortical blood flow values returned to their baseline (±20%) in several animals, whereas others showed hyper-perfusion (>20% of baseline). Reactive hyperemia was associated with adverse events such as increased cortical BBB leakage, edema, protein nitrotyrosination, COX-2 expression, and neutrophil accumulation; and with a poorer outcome, and CR-6 attenuated these effects. In conclusion, oral CR-6 administration after transient ischemia protects the brain from reperfusion injury.     

抗肿瘤坏死因子抗体减轻小鼠短暂性脑缺血损伤

脑缺血后肿瘤坏死因子的表达明显增加。本研究将中和性抗肿瘤坏死因子单克隆抗体注入脑室内，以观察阻断内源性肿瘤坏死因子过度表达对小鼠短暂性脑缺血损伤的影响。小鼠随机分为对照组和抗肿瘤坏死因子抗体组，每组８只。脑缺血和再灌流均通过监测脑血流证实。将中和性单克隆Ｈａｍｓｔｅｒ抗小鼠肿瘤坏死因子抗体或对照载体在恢复再灌时立即注入脑室。小鼠大脑中动脉阻塞１ｈ再灌流２３ｈ断头取脑。脑梗塞体积测定用常规ＨＥ染色和计算机图象分析。以血管外内源性白蛋白免疫组化染色检测血脑屏障的损伤。对照组和肿瘤坏死因子抗体治疗组在脑缺血和再灌后脑血流无显著差异（Ｐ＞０．０５）。抗肿瘤坏死因子抗体组脑梗塞体积和血脑屏障损伤体积较对照组明显减小。阻断内源性肿瘤坏死因子能显著减少小鼠暂时性脑缺血脑梗塞体积和血脑屏障损伤体积（Ｐ＜０．０５）。脑梗塞体积的减小和血脑屏障损伤体积的减小相对应。提示内源性肿瘤坏死因子能加重暂时性脑缺血损伤。     

High-dose methylprednisolone treatment in experimental focal cerebral ischemia

Previous studies using steroids for experimental focal stroke have demonstrated conflicting results, possibly related to dose used or ischemic models employed. In this study we examined high-dose methylprednisolone treatment following permanent and temporary focal cerebral ischemia in the rat. Focal stroke was induced in spontaneously hypertensive rats by permanent right common carotid and either permanent or 3 h of temporary middle cerebral artery (MCA) occlusion. Methylprednisolone (105 mg/kg) was administered intra-arterially. Infarct volume was measured at 24 h after permanent and temporary MCA occlusion. Cerebral edema was determined by measuring right and left hemispheric volumes and water content 24 h after permanent MCA occlusion in one experiment. Methylprednisolone, whether administered in divided doses over 12 h (n = 15 in each group) or a single bolus (n = 9 per group), had no effect on infarct volume after permanent MCA occlusion. Methylprednisolone treatment also had no influence on cerebral edema (n = 9 per group). In two different experiments, methylprednisolone given in divided doses over 12 h (n = 11, n = 25) after temporary MCA occlusion decreased infarct volume (P < 0.05) by 20% compared with saline controls (n = 10, n = 25). High dose methylprednisolone decreased infarct volume following temporary, but not permanent, focal ischemia. The benefit suggests that high dose methylprednisolone may prove useful clinically if reperfusion can be established with thrombolytic agents. Furthermore, the differential treatment effect in the setting of comparable ischemic insults implies that different modifiable biochemical processes may be present during temporary but not permanent focal ischemia, thus providing indirect evidence for reperfusion injury.     

VEGF protects brain against focal ischemia without increasing blood--brain permeability when administered intracerebroventricularly.

Delayed administration of vascular endothelial growth factor (VEGF) promotes functional recovery after focal cerebral ischemia. However, early intravenous injection of VEGF increases blood-brain barrier (BBB) leakage, hemorrhagic transformation and infarct volume whereas its application to cortical surface is neuroprotective. We have investigated whether or not early intracerebroventricular administration of VEGF could replicate the neuroprotective effect observed with topical application and the mechanism of action of this protection. Mice were subjected to 90 mins middle cerebral artery (MCA) occlusion and 24 h of reperfusion. Vascular endothelial growth factor (8 ng, intracerebroventricular) was administered 1 or 3 h after reperfusion. Compared with the vehicle-treated (intracerebroventricular) group, VEGF decreased the infarct volume along with BBB leakage in both treatment groups. Neurologic disability scores improved in parallel to the changes in infarct volume. Independently of the decrease in infarct size, VEGF also reduced the number of TUNEL-positive apoptotic neurons. Phospo-Akt levels were significantly higher in ischemic hemispheres of the VEGF-treated mice. Contrary to intracerebroventricular route, intravenous administration of VEGF (15 microg/kg) enhanced the infarct volume as previously reported for the rat. In conclusion, single intracerebroventricular injection of VEGF protects brain against ischemia without adversely affecting BBB permeability, and has a relatively long therapeutic time window. This early neuroprotective action, observed well before recovery-promoting actions such as angiogenesis, possibly involves activation of the PI-3-Akt pathway.     

钙拮抗剂对大鼠脑缺血后血脑屏障通透性的影响

目的 研究钙离子拮抗剂对大鼠脑缺血再灌注后血脑屏障(BBB)通透性和脑梗死灶体积的影响. 方法 插线法制作大鼠脑缺血再灌注模型.缺血2 h后再灌注.将150只大鼠按随机数字表法分尼莫地平组和对照组,每组分再灌注6h、12h、24 h、48h、72 h五个时间段,再灌注后尼莫地平组和对照组立即分别腹腔注射尼莫地平和生理盐水2 mg/kg.每12小时注射一次,用甲酰胺荧光法及透射电镜观察不同时段BBB通透性破坏的情况,TTC染色后计算梗死灶体积百分比.结果 大鼠脑缺血再灌注后BBB通透性和梗死灶体积百分比随时间延长逐渐增加.且BBB通透性的增加呈现两个高峰,第一个高峰在再灌注后12 h,第二个高峰在再灌注后48 h.尼莫地平组BBB通透性及脑梗死灶体积百分比的增加均较对照组明显,差异有统计学意义(P<0.05). 结论 脑缺血再灌注增加BBB的通透性和脑梗死灶体积百分比.再灌注后给予尼莫地平可加重这些病理变化.