Temporal impairment of microcirculatory perfusion following focal cerebral ischemia in the spontaneously hypertensive rat

Progressive microvascular failure in acute ischemic stroke: A systematic review, meta-analysis, and time-course analysis

This systematic review, meta-analysis, and novel time course analysis examines microvascular failure in the treatment of acute ischemic stroke (AIS) patients undergoing endovascular therapy (EVT) and/or thrombolytic administration for stroke management. A systematic review and meta-analysis following PRIMSA-2020 guidelines was conducted along with a novel curve-of-best fit analysis to elucidate the time-course of microvascular failure. Scopus and PubMed were searched using relevant keywords to identify studies that examine recanalization and reperfusion assessment of AIS patients following large vessel occlusion. Meta-analysis was conducted using a random-effects model. Curve-of-best-fit analysis of microvascular failure rate was performed with a negative exponential model. Twenty-seven studies with 1151 patients were included. Fourteen studies evaluated patients within a standard stroke onset-to-treatment time window (≤6 hours after last known normal) and thirteen studies had an extended time window (>6 hours). Our analysis yields a 22% event rate of microvascular failure following successful recanalization (95% CI: 16-30%). A negative exponential curve modeled a microvascular failure rate asymptote of 28.5% for standard time window studies, with no convergence of the model for extended time window studies. Progressive microvascular failure is a phenomenon that is increasingly identified in clinical studies of AIS patients undergoing revascularization treatment.

Rapamycin in ischemic stroke: Old drug, new tricks?

The significant morbidity that accompanies stroke makes it one of the world's most devastating neurological disorders. Currently, proven effective therapies have been limited to thrombolysis and thrombectomy. The window for the administration of these therapies is narrow, hampered by the necessity of rapidly imaging patients. A therapy that could extend this window by protecting neurons may improve outcome. Endogenous neuroprotection has been shown to be, in part, due to changes in mTOR signalling pathways and the instigation of productive autophagy. Inducing this effect pharmacologically could improve clinical outcomes. One such therapy already in use in transplant medicine is the mTOR inhibitor rapamycin. Recent evidence suggests that rapamycin is neuroprotective, not only via neuronal autophagy but also through its broader effects on other cells of the neurovascular unit. This review highlights the potential use of rapamycin as a multimodal therapy, acting on the blood-brain barrier, cerebral blood flow and inflammation, as well as directly on neurons. There is significant potential in applying this old drug in new ways to improve functional outcomes for patients after stroke.

The importance of comorbidities in ischemic stroke: Impact of hypertension on the cerebral circulation

Comorbidities are a hallmark of stroke that both increase the incidence of stroke and worsen outcome. Hypertension is prevalent in the stroke population and the most important modifiable risk factor for stroke. Hypertensive disorders promote stroke through increased shear stress, endothelial dysfunction, and large artery stiffness that transmits pulsatile flow to the cerebral microcirculation. Hypertension also promotes cerebral small vessel disease through several mechanisms, including hypoperfusion, diminished autoregulatory capacity and localized increase in blood-brain barrier permeability. Preeclampsia, a hypertensive disorder of pregnancy, also increases the risk of stroke 4-5-fold compared to normal pregnancy that predisposes women to early-onset cognitive impairment. In this review, we highlight how comorbidities and concomitant disorders are not only risk factors for ischemic stroke, but alter the response to acute ischemia. We focus on hypertension as a comorbidity and its effects on the cerebral circulation that alters the pathophysiology of ischemic stroke and should be considered in guiding future therapeutic strategies.

Transit time homogenization in ischemic stroke - A novel biomarker of penumbral microvascular failure?

Cerebral ischemia causes widespread capillary no-flow in animal studies. The extent of microvascular impairment in human stroke, however, is unclear. We examined how acute intra-voxel transit time characteristics and subsequent recanalization affect tissue outcome on follow-up MRI in a historic cohort of 126 acute ischemic stroke patients. Based on perfusion-weighted MRI data, we characterized voxel-wise transit times in terms of their mean transit time (MTT), standard deviation (capillary transit time heterogeneity - CTH), and the CTH:MTT ratio (relative transit time heterogeneity), which is expected to remain constant during changes in perfusion pressure in a microvasculature consisting of passive, compliant vessels. To aid data interpretation, we also developed a computational model that relates graded microvascular failure to changes in these parameters. In perfusion-diffusion mismatch tissue, prolonged mean transit time (>5 seconds) and very low cerebral blood flow (≤6 mL/100 mL/min) was associated with high risk of infarction, largely independent of recanalization status. In the remaining mismatch region, low relative transit time heterogeneity predicted subsequent infarction if recanalization was not achieved. Our model suggested that transit time homogenization represents capillary no-flow. Consistent with this notion, low relative transit time heterogeneity values were associated with lower cerebral blood volume. We speculate that low RTH may represent a novel biomarker of penumbral microvascular failure.

Contrast-enhanced sonothrombolysis in acute ischemic stroke patients without intracranial large-vessel occlusion

BACKGROUND

Contrast-enhanced sonothrombolysis (CEST) leads to a more rapid recanalization in acute ischemic stroke caused by intracranial large-vessel occlusion (LVO). Animal studies have shown that CEST also may be safe and efficient in treating the ischemic microcirculation in the absence of LVO. The exact mechanism behind this treatment effect is not known. We aimed to assess safety and efficacy of CEST in acute ischemic stroke patients included in the Norwegian Sonothrombolysis in Acute Stroke Study (NOR-SASS) without LVO on admission CT angiography (CTA).

METHODS

NOR-SASS was a randomized controlled trial of CEST in ischemic stroke patients treated with intravenous thrombolysis within 4.5 hours after stroke onset. Patients were randomized to either CEST or sham CEST. In this study, patients were excluded if they had partial or total occlusion on admission CTA, ultrasound-resistant bone window, had received CEST with incorrect insonation as compared to stroke location on Magnetic resonance imaging (MRI), or were stroke mimics.

RESULTS

Of the 183 patients included in NOR-SASS, a total of 83 (45.4%) patients matched the inclusion criteria, of which 40 received CEST and 43 sham CEST. There were no patients with symptomatic intracranial hemorrhage (sICH) in the CEST group. Rates of asymptomatic ICH, microbleeds, and mortality were not increased in the CEST group. Neurological improvement at 24 hours and functional outcome at 90 days were similar in both groups.

CONCLUSION

CEST is safe in ischemic stroke patients without intracranial LVO. There were no differences in clinical outcomes between the treatment groups.

Sonothrombolysis with BR38 Microbubbles Improves Microvascular Patency in a Rat Model of Stroke

Background

Early recanalization of large cerebral vessels in ischemic stroke is associated with improved clinical outcome, however persisting hypoperfusion leads to poor clinical recovery despite large vessel recanalization. Limited experimental sonothrombolysis studies have shown that addition of microbubbles during treatment can improve microvascular patency. We aimed to determine the effect of two different microbubble formulations on microvascular patency in a rat stroke model.

Methods

We tested BR38 and SonoVue® microbubble-enhanced sonothrombolysis in Wistar rats submitted to 90-minute filament occlusion of the middle cerebral artery. Rats were randomized to treatment (n = 6/group): control, rt-PA, or rt-PA+3-MHz ultrasound insonation with BR38 or SonoVue® at full or 1/3 dose. Treatment duration was 60 minutes, beginning after withdrawal of the filament, and sacrifice was immediately after treatment. Vascular volumes were evaluated with microcomputed tomography.

Results

Total vascular volume of the ipsilateral hemisphere was reduced in control and rt-PA groups (p<0.05), but was not significantly different from the contralateral hemisphere in all microbubble-treated groups (p>0.1).

Conclusions

Microbubble-enhanced sonothrombolysis improves microvascular patency. This effect is not dose- or microbubble formulation-dependent suggesting a class effect of microbubbles promoting microvascular reopening. This study demonstrates that microbubble-enhanced sonothrombolysis may be a therapeutic strategy for patients with persistent hypoperfusion of the ischemic territory.

Drowning stars: reassessing the role of astrocytes in brain edema

Edema formation frequently complicates brain infarction, tumors, and trauma. Despite the significant mortality of this condition, current treatment options are often ineffective or incompletely understood. Recent studies have revealed the existence of a brain-wide paravascular pathway for cerebrospinal (CSF) and interstitial fluid (ISF) exchange. The current review critically examines the contribution of this 'glymphatic' system to the main types of brain edema. We propose that in cytotoxic edema, energy depletion enhances glymphatic CSF influx, whilst suppressing ISF efflux. We also argue that paravascular inflammation or 'paravasculitis' plays a critical role in vasogenic edema. Finally, recent advances in diagnostic imaging of glymphatic function may hold the key to defining the edema profile of individual patients, and thus enable more targeted therapy.

Pro-inflammatory mediators and apoptosis correlate to rt-PA response in a novel mouse model of thromboembolic stroke

BACKGROUND

A recent study suggests that patients with persistent occlusion of the middle cerebral artery (MCA) following treatment with recombinant tissue plasminogen activator (rt-PA) have better outcomes than patients with MCA occlusion not receiving rt-PA. We performed a study to elucidate possible mechanisms of this finding in a new model of thromboembolic stroke closely mimicking human pathophysiology.

METHODS

Thromboembolic stroke was induced by local injection of thrombin directly into the right MCA of C57 black/6J mice. Rt-PA was administered 20 and 40 min after clot formation. The efficiency of rt-PA to induce thrombolysis was measured by laser Doppler. After 24 h, all animals were euthanized and interleukin (IL)-6, tumor necrosis factor-alpha (TNF-α), matrix metalloproteinase (MMP)-9, Caspase-3, hsp 32 and hsp 70 protein levels were investigated by immunofluorescence. Presence of hemorrhage was verified and infarct volume was measured using histology.

RESULTS

Thrombin injection resulted in clot formation giving rise to cortical brain infarction. Early rt-PA treatment starting at 20 min after the clot formation resulted in 100% recanalization. However, rt-PA-induced thrombolysis dissolved the clot in only 38% of the animals when administered 40 min after clot formation. Protein levels of IL-6, TNF-α, MMP-9, Caspase-3, hsp 32 and hsp 70 were increased after MCAO, whereas treatment with rt-PA attenuated the expressions of inflammatory markers in those animals where the thrombolysis was successful. In addition, the infarct size was significantly reduced with rt-PA treatment compared to non-treated MCAO, regardless of whether MCA thrombolysis was successful.

CONCLUSIONS

The present study demonstrates a clear correlation of the protein expression of inflammatory mediators, apoptosis and stress genes with the recanalization data after rt-PA treatment. In this model rt-PA treatment decreases the infarct size regardless of whether vessel recanalization is successful.

Blood-brain barrier permeability is positively correlated with cerebral microvascular perfusion in the early fluid percussion-injured brain of the rat

The blood-brain barrier (BBB) opening following traumatic brain injury (TBI) provides a chance for therapeutic agents to cross the barrier, yet the reduction of the cerebral microvascular perfusion after TBI may limit the intervention. Meanwhile, optimizing the cerebral capillary perfusion by the strategies such as fluid administration may cause brain edema due to the BBB opening post trauma. To guide the TBI therapy, we characterized the relationship between the changes in the cerebral capillary perfusion and BBB permeability after TBI. First, we observed the changes of the cerebral capillary perfusion by the intracardiac perfusion of Evans Blue and the BBB disruption with magnetic resonance imaging (MRI) in the rat subjected to lateral fluid percussion (FP) brain injury. The correlation between two variables was next evaluated with the correlation analysis. Since related to BBB breakdown, matrix metalloproteinase-9 (MMP-9) activity was finally detected by gelatin zymography. We found that the ratios of the perfused microvessel numbers in the lesioned cortices were significantly reduced at 0 and 1 h post trauma compared with that in the normal cortex, which then dramatically recovered at 4 and 24 h after injury, and that the BBB permeability was greatly augmented in the ipsilateral parts at 4, 12, and 24 h, and in the contralateral area at 24 h after injury compared with that in the uninjured brain. The correlation analysis showed that the BBB permeability increase was related to the restoration of the cerebral capillary perfusion over a 24-h period post trauma. Moreover, the gelatin zymography analysis indicated that the MMP-9 activity in the injured brain increased at 4 h and significantly elevated at 12 and 24 h as compared to that at 0 or 1 h after TBI. Our findings demonstrate that the 4 h post trauma is a critical turning point during the development of TBI, and, importantly, the correlation analysis may guide us how to treat TBI.

Vascular and neuronal ischemic damage in cryonics patients

Cryonics technology seeks to cryopreserve the anatomical basis of the mind so that future medicine can restore legally dead cryonics patients to life, youth, and health. Most cryonics patients experience varying degrees of ischemia and reperfusion injury. Neurons can survive ischemia and reperfusion injury more than is generally believed, but blood vessels are more vulnerable, and such injury can impair perfusion of vitrifying cryoprotectant solution intended to eliminate ice formation in the brain. Forms of vascular and neuronal damage are reviewed, along with means of mitigating that damage. Recommendations are also made for preventing such damage.

The inhibitor of 20-HETE synthesis, TS-011, improves cerebral microcirculatory autoregulation impaired by middle cerebral artery occlusion in mice

BACKGROUND AND PURPOSE

20-Hydroxyeicosatetraenoic acid is a potent vasoconstrictor that contributes to cerebral ischaemia. An inhibitor of 20-Hydroxyeicosatetraenoic acid synthesis, TS-011, reduces infarct volume and improves neurological deficits in animal stroke models. However, little is known about how TS-011 affects the microvessels in ischaemic brain. Here, we investigated the effect of TS-011 on microvessels after cerebral ischaemia.

EXPERIMENTAL APPROACH

TS-011 (0.3 mg·kg(-1) ) or a vehicle was infused intravenously for 1 h every 6 h in a mouse model of stroke, induced by transient occlusion of the middle cerebral artery occlusion following photothrombosis. The cerebral blood flow velocity and the vascular perfusion area of the peri-infarct microvessels were measured using in vivo two-photon imaging.

KEY RESULTS

The cerebral blood flow velocities in the peri-infarct microvessels decreased at 1 and 7 h after reperfusion, followed by an increase at 24 h after reperfusion in the vehicle-treated mice. We found that TS-011 significantly inhibited both the decrease and the increase in the blood flow velocities in the peri-infarct microvessels seen in the vehicle-treated mice after reperfusion. In addition, TS-011 significantly inhibited the reduction in the microvascular perfusion area after reperfusion, compared with the vehicle-treated group. Moreover, TS-011 significantly reduced the infarct volume by 40% at 72 h after middle cerebral artery occlusion.

CONCLUSIONS AND IMPLICATIONS

These findings demonstrated that infusion of TS-011 improved defects in the autoregulation of peri-infarct microcirculation and reduced the infarct volume. Our results could be relevant to the treatment of cerebral ischaemia.

Combined contrast-enhanced ultrasound and rt-PA treatment is safe and improves impaired microcirculation after reperfusion of middle cerebral artery occlusion

In monitoring of recanalization and in sonothrombolysis, contrast-enhanced ultrasound (CEUS) is applied in extended time protocols. As extended use may increase the probability of unwanted effects, careful safety evaluation is required. We investigated the safety profile and beneficial effects of CEUS in a reperfusion model. Wistar rats were subjected to filament occlusion of the right middle cerebral artery (MCA). Reperfusion was established after 90 minutes, followed by recombinant tissue-type plasminogen activator (rt-PA) treatment and randomization to additional CEUS (contrast agent: SonoVue; 60 minutes). Blinded outcome evaluation consisted of magnetic resonance imaging (MRI), neurologic assessment, and histology and, in separate experiments, quantitative 3D nano-computed tomography (CT) angiography (900 nm(3) voxel size). Nano-CT revealed severely compromised microcirculation in untreated animals after MCA reperfusion. The rt-PA partially improved hemispheric perfusion. Impairment was completely reversed in animals receiving rt-PA and CEUS. This combination was more effective than treatment with either CEUS without rt-PA or rt-PA and ultrasound or ultrasound alone. In MRI experiments, CEUS and rt-PA treatment resulted in a significantly reduced ischemic lesion volume and edema formation. No unwanted effects were detected on MRI, histology, and intracranial temperature assessment. This study shows that CEUS and rt-PA is safe in the situation of reperfusion and displays beneficial effects on the level of the microvasculature.

Severe blood-brain barrier disruption and surrounding tissue injury

BACKGROUND AND PURPOSE

Blood-brain barrier opening during ischemia follows a biphasic time course, may be partially reversible, and allows plasma constituents to enter brain and possibly damage cells. In contrast, severe vascular disruption after ischemia is unlikely to be reversible and allows even further extravasation of potentially harmful plasma constituents. We sought to use simple fluorescent tracers to allow wide-scale visualization of severely damaged vessels and determine whether such vascular disruption colocalized with regions of severe parenchymal injury.

METHODS

Severe vascular disruption and ischemic injury was produced in adult Sprague Dawley rats by transient occlusion of the middle cerebral artery for 1, 2, 4, or 8 hours, followed by 30 minutes of reperfusion. Fluorescein isothiocyanate-dextran (2 MDa) was injected intravenously before occlusion. After perfusion-fixation, brain sections were processed for ultrastructure or fluorescence imaging. We identified early evidence of tissue damage with Fluoro-Jade staining of dying cells.

RESULTS

With increasing ischemia duration, greater quantities of high molecular weight dextran-fluorescein isothiocyanate invaded and marked ischemic regions in a characteristic pattern, appearing first in the medial striatum, spreading to the lateral striatum, and finally involving cortex; maximal injury was seen in the mid-parietal areas, consistent with the known ischemic zone in this model. The regional distribution of the severe vascular disruption correlated with the distribution of 24-hour 2,3,5-triphenyltetrazolium chloride pallor (r=0.75; P<0.05) and the cell death marker Fluoro-Jade (r=0.86; P<0.05). Ultrastructural examination showed significantly increased areas of swollen astrocytic foot process and swollen mitochondria in regions of high compared to low leakage, and compared to contralateral homologous regions (ANOVA P<0.01). Dextran extravasation into the basement membrane and surrounding tissue increased significantly from 2 to 8 hours of occlusion duration (Independent samples t test, P<0.05).

CONCLUSIONS

Severe vascular disruption, as labeled with high-molecular-weight dextran-fluorescein isothiocyanate leakage, is associated with severe tissue injury. This marker of severe vascular disruption may be useful in further studies of the pathoanatomic mechanisms of vascular disruption-mediated tissue injury.

Cryopreservation of composite tissue transplants

Composite tissue allotransplantation holds great promise for upper extremity reconstruction but is limited by donor part availability. Cryopreservation may increase the availability of donor parts and even reduce antigenicity. The purpose of the study was to evaluate the viability of cryopreserved composite tissues and to demonstrate the feasibility of microvascular isotransplantation of cryopreserved composite flaps. Twenty epigastric flaps were harvested from Lewis rats. Ten flaps were analyzed fresh. Ten flaps were perfused with dimethyl sulfoxide (DMSO)/trehelose cryoprotectant agent (CPA), frozen by controlled cooling to -140 degrees C, and stored for 2 weeks. Flaps were evaluated by factor VIII endothelial staining and MTT tetrazolium salt assay. For the in vivo phase, 30 flaps were harvested. Ten were transplanted fresh to isogenetic recipient animals, ten were perfused with CPA and transplanted, and ten were cryopreserved for 2 weeks, thawed, and transplanted. All cryopreserved samples displayed intact vascular endothelia on factor VIII staining. On MTT analysis, the epithelial viability index for the cryopreserved samples was not significantly different from fresh controls (p = 0.12). All freshly transplanted flaps (10/10) were viable at 60 days. Nine of ten flaps in the perfused/transplanted group were viable at 60 days. Survival of cryopreserved/transplanted flaps ranged from 5 to 60 days. The skin and vascular endothelial components of composite tissue flaps appear to retain their viability after cryopreservation. The in vivo studies demonstrate that the long-term survival of cryopreserved composite tissue transplants is feasible and support an indirect injury, rather than direct injury from freezing or cryoprotectant agents, as the mechanism of flap loss.

Mucosal tolerization to E-selectin protects against memory dysfunction and white matter damage in a vascular cognitive impairment model

Vascular cognitive impairment (VCI) is the second most prevalent type of dementia in the world. The white matter damage that characterizes the common subcortical ischemic form of VCI can be modeled by ligating both common carotid arteries in the Wistar rat to induce protracted cerebral hypoperfusion. In this model, we find that repetitive intranasal administration of recombinant E-selectin to induce mucosal tolerance and to target immunomodulation to activating blood vessels potently suppresses both white matter (and possibly gray matter) damage and markers of vessel activation (tumor necrosis factor and E-selectin); it also preserves behavioral function in T-maze spontaneous alternation, T-maze spatial discrimination memory retention, and object recognition tests. Immunomodulation may be an effective novel strategy to prevent progression of VCI.

dl-3n-butylphthalide prevents stroke via improvement of cerebral microvessels in RHRSP

The purpose of the study is to establish a model of cold-induced stroke in hypertensive rats, and to study the preventive effect of dl-3n-butylphthalide ( NBP ) on stroke. Stroke-prone renovascular hypertension(RHRSP) was created in Sprague-Dawley rats. The animals were assigned randomly to NBP, aspirin treated and vehicle control group, with administration of the medications for 7 days, and then subjected to cold treatment in an environmentally controlled chamber for 3 days to induce the occurrence of stroke. The incidence of stroke, the volume of the brain lesion, patency of the microvessels by FITC-dextran perfusion and the number of microvessels by immunohisochemical detection of vwF were investigated. Cold induced different types of stroke in RHRSP. The incidence of ischemic stroke and the volume of the infarct were decreased, and the perfused microvessels were increased with NBP pretreatment. Our data suggest that NBP prevents cold-induced ischemic stroke via improvement of cerebral microvessels.

Role of endoglin and transforming growth factor-beta in progressive white matter damage after an ischemic stroke

We morphologically examined human brains several years after a territorial ischemic stroke to assess the development of progressing white matter damage and its pathomechanisms. Our investigations focused on the role of TGF-beta, one of the factors whose expression increases after tissue damage, and its receptor endoglin in the propagation of postischemic injury. Examination of the white matter adjacent to the postapoplectic cavity revealed structural changes in the capillary vessels, disturbed microcirculation, and deep endothelial cell damage with DNA fragmentation in the TUNEL reaction. Many oligodendrocytes also revealed DNA damage and an increased expression of caspase-3. In the rarefied white matter, the microvessel immune reaction to TGF-beta was diminished while the expression of endoglin was heterogeneous: absent in some capillaries but increased in others in comparison to the vessels located more peripherally from the cavity and in the control material. We conclude that endoglin and TGF-beta can be involved in the development of the microangiopathy responsible for the propagation of postischemic white matter injury in humans. We suggest that disturbances in endoglin expression can influence TGF-beta signaling and, consequently, vessel structure and function. Pronounced endoglin expression can lead to decreased vessel wall integrity while a lack of the constitutively expressed protein is probably a mirror of deep vessel damage.

Imaging the development of an ischemic core following photochemically induced cortical infarction in rats using Laser Speckle Contrast Analysis (LASCA)

Laser Speckle Contrast Analysis (LASCA) has been used to image the development of an ischemic core following photochemically induced infarction in rats up to 1 h post-lesion. Using LASCA, we have been able to image a central ischemic core which had little or no perfusion surrounded by a penumbral region with reduced perfusion. In addition, we have shown the existence of a surrounding region of hyperemic tissue. A potential feature of this imaging approach is its capability to track cerebral blood flow (CBF) changes in the region within and outside the ischemic core besides demonstrating the real-time progression of the ischemic core into the penumbral region. We have demonstrated the continuous disruption of CBF to the ischemic core that eventually affected the blood supply to the surrounding regions. The penumbral flow is shown to exhibit a sudden increase post-ischemic induction followed by a slow decline to the final baseline level. Interestingly, we observed an interaction (P < 0.03) between penumbral flow peak and the time effects of increase in pixel area from the infarct region to the surrounding penumbral region. Using a paired-sample t test, we observed that the mean pixel area was larger for the infarct region than for the penumbral region (P < 0.004) during the time interval between the induction of ischemia and the time point of peak flow in the penumbral region.

Apoptosis is not an invariable component of in vitro models of cortical cerebral ischaemia

Characterising the mechanisms of cell death following focal cerebral ischaemia has been hampered by a lack of an in vitro assay emulating both the apoptotic and necrotic features observed in vivo. The present study systematically characterised oxygen-glucose-deprivation (OGD) in primary rat cortical neurones to establish a reproducible model with components of both cell-death endpoints. OGD induced a time-dependent reduction in cell viability, with 80% cell death occurring 24 h after 3 h exposure to 0% O2 and 0.5 mM glucose. Indicative of a necrotic component to OGD-induced cell death, N-methyl-D-aspartate (NMDA) receptor inhibition with MK-801 attenuated neuronal loss by 60%. The lack of protection by the caspase inhibitors DEVD-CHO and z-VAD-fmk suggested that under these conditions neurones did not die by an apoptotic mechanism. Moderating the severity of the insult by decreasing OGD exposure to 60 min did not reduce the amount of necrosis, but did induce a small degree of apoptosis (a slight reduction in cell death was observed in the presence of 10 uM DEVD-CHO). In separate experiments purported to enhance the apoptotic component, cells were gradually deprived of O2, exposed to 4% O2 (as opposed to 0%) during the OGD period, or maintained in serum-containing media throughout. While NMDA receptor antagonism significantly reduced cortical cell death under all conditions, a caspase-inhibitor sensitive component of cell death was not uncovered. These studies suggest that OGD of cultured cortical cells models the excitotoxic, but not the apoptotic component of cell death observed in vivo.

Lacunar stroke is the major cause of progressive motor deficits

BACKGROUND AND PURPOSE

Severe motor deficits are the predominant cause of long-term disability in stroke patients. In particular, progressive hemiparesis in the initial stage after stroke onset is frequently devastating. Therefore, we attempted to define the population at risk with respect to the presumed pathogenesis.

METHODS

Among 941 stroke patients hospitalized during a 3-year period, 92 patients (41 men, 51 women; mean age, 68 years) had a severe motor deficit (<25 of 42 points on the 7 motor items of the European Stroke Scale) resulting from brain infarcts. Risk factors, neurological examinations, comprehensive diagnostic tests, and therapy were documented. The study population was separated into patients with (group A) and without (group B) progressive motor deficits. Progression was defined as a further decrease of at least 5 points on the initial European Stroke Scale motor score during the first 5 days after stroke onset.

RESULTS

Of the 92 patients, 23.9% had significant worsening of motor function with a decrease in the mean European Stroke Scale motor score from 20.3 to 12.9 points (P<0.01). Infarcts in group A patients were subcortical in 59.1%, whereas most infarcts were cortical in group B (61.4%, P<0.05). Progressive hemiparesis was also significantly associated with lacunar stroke (group A:, 59.1%; group B, 24.3%; P<0.01). With regard to risk factors, diagnostic studies, and neuroimaging, small-vessel disease was the predominant presumed cause of stroke in group A (63.6%, P<0.01), whereas infarcts in group B patients were frequently caused by embolism from cardiac or undetermined sources (61.4%, P<0.01). Prevalence of high-grade carotid stenosis was not significantly different between groups A and B; however, subtotal stenoses and complete internal carotid artery occlusions were found only among patients without progressive motor deficits.

CONCLUSIONS

Lacunar stroke caused by small-vessel disease is the major cause of progressive motor deficits, probably because of stepwise occlusion of the branches of small penetrating arteries.

Delayed treatment with nicotinamide (vitamin B3) reduces the infarct volume following focal cerebral ischemia in spontaneously hypertensive rats, diabetic and non-diabetic Fischer 344 rats

Since hypertension and/or hyperglycemia are risk factors for stroke, we examined whether the putative neuroprotectant, nicotinamide (NAm), could protect spontaneously hypertensive rats (SHR) or diabetic Fischer 344 rats against focal cerebral ischemia using a model of permanent middle cerebral artery occlusion (MCAo). Intravenous NAm given 2 h after MCAo significantly reduced the infarct volume of SHR (750 mg/kg, 31%, P<0.01) and diabetic (500 mg/kg, 56%, P<0.01) as well as non-diabetic (500 mg/kg, 73%, P<0.01) Fischer 344 rats when compared with saline-injected controls. Thus delayed treatment with NAm protected hypertensive and hyperglycemic rats against a robust model of stroke.

Neuroprotective adaptations in hibernation: therapeutic implications for ischemia-reperfusion, traumatic brain injury and neurodegenerative diseases

Brains of hibernating mammals are protected against a variety of insults that are detrimental to humans and other nonhibernating species. Such protection is associated with a number of physiological adaptations including hypothermia, increased antioxidant defense, metabolic arrest, leukocytopenia, immunosuppression, and hypocoagulation. It is intriguing that similar manipulations provide considerable protection as experimental treatments for central nervous system injury. This review focuses on neuroprotective mechanisms employed during hibernation that may offer novel approaches in the treatment of stroke, traumatic brain injury, and neurodegenerative diseases in humans.

High susceptibility to cerebral ischemia in GFAP-null mice

Astrocytes perform a variety of functions in the adult central nervous system (CNS) that contribute to the survival of neurons. Thus, it is likely that the activities of astrocytes affect the extent of brain damage after ischemic stroke. The authors tested this hypothesis by using a mouse ischemia model to compare the infarct volume produced in wild-type mice with that produced in mice lacking glial fibrillary acidic protein (GFAP), an astrocyte specific intermediate filament component. Astrocytes lacking GFAP have been shown to have defects in process formation, induction of the blood-brain barrier. and volume regulation; therefore, they might be compromised in their ability to protect the CNS after injury. The authors reported here that 48 hours after combined permanent middle cerebral artery occlusion (MCAO) and 15 minutes transient carotid artery occlusion (CAO) GFAP-null mice had a significantly (P < 0.001) larger cortical infarct volume (16.7 +/- 2.2 mm3) than their wild-type littermates (10.1 +/- 3.9 mm3). Laser-Doppler flowmetry revealed that the GFAP-null mice had a more extensive and profound decrease in cortical cerebral blood flow within 2 minutes after MCAO with CAO. These results indicated a high susceptibility to cerebral ischemia in GFAP-null mice and suggested an important role for astrocytes and GFAP in the progress of ischemic brain damage after focal cerebral ischemia with partial reperfusion.

Cerebral microvascular obstruction by fibrin is associated with upregulation of PAI-1 acutely after onset of focal embolic ischemia in rats

The mechanisms underlying cerebral microvascular perfusion deficit resulting from occlusion of the middle cerebral artery (MCA) require elucidation. We, therefore, tested the hypothesis that intravascular fibrin deposition in situ directly obstructs cerebral microcirculation and that local changes in type 1 plasminogen activator inhibitor (PAI-1) gene expression contribute to intravascular fibrin deposition after embolic MCA occlusion. Using laser-scanning confocal microscopy (LSCM) in combination with immunofluorescent staining, we simultaneously measured in three dimensions the distribution of microvascular plasma perfusion deficit and fibrin(ogen) immunoreactivity in a rat model of focal cerebral embolic ischemia (n = 12). In addition, using in situ hybridization and immunostaining, we analyzed expression of PAI-1 in ischemic brain (n = 13). A significant (p < 0.05) reduction of cerebral microvascular plasma perfusion accompanied a significant (p < 0.05) increase of intravascular and extravascular fibrin deposition in the ischemic lesion. Microvascular plasma perfusion deficit and fibrin deposition expanded concomitantly from the subcortex to the cortex during 1 and 4 hr of embolic MCA occlusion. Three-dimensional analysis revealed that intravascular fibrin deposition directly blocks microvascular plasma perfusion. Vascular plugs contained erythrocytes, polymorphonuclear leukocytes, and platelets enmeshed in fibrin. In situ hybridization demonstrated induction of PAI-1 mRNA in vascular endothelial cells in the ischemic region at 1 hr of ischemia. PAI-1 mRNA significantly increased at 4 hr of ischemia. Immunohistochemical staining showed the same pattern of increased PAI-1 antigen in the endothelial cells. These data demonstrate, for the first time, that progressive intravascular fibrin deposition directly blocks cerebral microvascular plasma perfusion in the ischemic region during acute focal cerebral embolic ischemia, and upregulation of the PAI-1 gene in the ischemic lesion may foster fibrin deposition through suppression of fibrinolysis.

Endothelin receptor antagonist preserves microvascular perfusion and reduces ischemic brain damage following permanent focal ischemia

Synthesis and release of the potent vasoconstrictor peptide endothelin-1 (ET-1) increases following cerebral ischemia and has previously been shown to mediate the delayed hypoperfusion associated with transient global ischemia. In this study we assessed the impact of ET-1 on perfusion and infarct volume in a focal model of cerebral ischemia by use of the selective ET(A) receptor antagonist Ro 61-1790 (affinity for ET(A) receptor 1000 fold greater than ETB receptor). Control rats subjected to permanent middle cerebral artery occlusion (MCAO) showed extensive reductions in microvascular perfusion 4 h post-MCAO that were significantly attenuated by Ro 61-1790 pretreatment (10 mg/kg, i.v.). Ro 61-1790 concomitantly and significantly reduced the ischemic lesion volume in the same animals. This effect was maintained 24 h post-MCAO providing that the animals received additional i.v. injections of 5 mg/kg Ro 61-1790 at 5 h and 8 h after MCAO. These findings demonstrate that ET(A) receptor antagonism partially preserves tissue perfusion following focal ischemia and that this effect is associated with significant neuroprotection. The results also support the hypothesis that vasoactive mediators, and ET-1 in particular, are important contributors to the pathogenesis of cerebral ischemic injury.

Three-dimensional measurement of cerebral microvascular plasma perfusion, glial fibrillary acidic protein and microtubule associated protein-2 immunoreactivity after embolic stroke in rats: a double fluorescent labeled laser-scanning confocal microscopic study

Early astroglial response to post-ischemic microvascular hypoperfusion may contribute to progressive cerebral microcirculatory impairment and ischemic neuronal injury. Using laser-scanning confocal microscopy and three fluorescent probes, we measured in three-dimensions cerebral microvascular plasma perfusion, astrocytic reactivity, and neuronal injury assessed by fluorescein isothiocyanate (FITC)-dextran, GFAP immunoreactivity, and microtubule associated protein-2 (MAP2) immunoreactivity, respectively, in rats subjected to 2 h of middle cerebral artery occlusion. Three-dimensional quantitative analysis revealed that 2 h of embolic ischemia resulted in a significant (P<0.05) reduction of cerebral microvascular plasma perfusion in the ipsilateral cortex and subcortex. Tissue within the ipsilateral cortex and subcortex with low plasma perfusion exhibited a significant (P<0.05) increase in GFAP immunoreactivity compared with the homologous contralateral tissue. Three-dimensional re-constructed images showed that prominent GFAP immunoreactive astrocytes surrounded large vessels with decreased plasma perfusion in downstream capillaries in the ipsilateral MCA territory when compared to the vessels in the contralateral homologous tissue. Triple fluorescence probe-stained sections showed that tissue with decreased plasma perfusion and with increased GFAP immunoreactivity was accompanied by a reduction of MAP2 immunoreactivity. The present study demonstrates that an impairment of microvascular perfusion induces an early increase in GFAP immunoreactivity, and reactive astrocytes may contribute to a further reduction of cerebral microvascular plasma perfusion. The three-dimensional quantitative imaging analysis used in the present study provides a means to investigate parenchymal cellular responses to changes of cerebral microvascular plasma perfusion after MCA occlusion.

Cerebrovascular hemodynamics and ischemic tolerance: lipopolysaccharide-induced resistance to focal cerebral ischemia is not due to changes in severity of the initial ischemic insult, but is associated with preservation of microvascular perfusion

Lipopolysaccharide (LPS), administered 72 hours before middle cerebral artery (MCA) occlusion, confers significant protection against ischemic injury. For example, in the present study, LPS (0.9 mg/kg intravenously) induced a 31% reduction in infarct volume (compared with saline control) assessed 24 hours after permanent MCA occlusion. To determine whether LPS induces true tolerance to ischemia, or merely attenuates initial ischemic severity by augmenting collateral blood flow, local CBF was measured autoradiographically 15 minutes after MCA occlusion. Local CBF did not differ significantly between LPS- and saline-pretreated rats (e.g., 34 +/- 10 and 29 +/- 15 mL x 100 g(-1) x min(-1) for saline and LPS pretreatment in a representative region of ischemic cortex), indicating that the neuroprotective action of LPS is not attributable to an immediate reduction in the degree of ischemia induced by MCA occlusion, and that LPS does indeed induce a state of ischemic tolerance. In contrast to the similarity of the initial ischemic insult between tolerant (LPS-pretreated) and nontolerant (saline-pretreated) rats, microvascular perfusion assessed either 4 hours or 24 hours after MCA occlusion was preserved at significantly higher levels in the LPS-pretreated rats than in controls. Furthermore, the regions of preserved perfusion in tolerant animals were associated with regions of tissue sparing. These results suggest that LPS-induced tolerance to focal ischemia is at least partly dependent on the active maintenance of microvascular patency and hence the prevention of secondary ischemic injury.