The heterogeneous temporal evolution of focal ischemic neuronal damage in the rat

The neurophysiological effect of mild hypothermia in gyrencephalic brains submitted to ischemic stroke and spreading depolarizations

Objective

Characterize the neurophysiological effects of mild hypothermia on stroke and spreading depolarizations (SDs) in gyrencephalic brains.

Methods

Left middle cerebral arteries (MCAs) of six hypothermic and six normothermic pigs were permanently occluded (MCAo). Hypothermia began 1 h after MCAo and continued throughout the experiment. ECoG signals from both frontoparietal cortices were recorded. Five-minute ECoG epochs were collected 5 min before, at 5 min, 4, 8, 12, and 16 h after MCAo, and before, during, and after SDs. Power spectra were decomposed into fast (alpha, beta, and gamma) and slow (delta and theta) frequency bands.

Results

In the vascular insulted hemisphere under normothermia, electrodes near the ischemic core exhibited power decay across all frequency bands at 5 min and the 4th hour after MCAo. The same pattern was registered in the two furthest electrodes at the 12th and 16th hour. When mild hypothermia was applied in the vascular insulted hemispheres, the power decay was generalized and seen even in electrodes with uncompromised blood flow. During SD analysis, hypothermia maintained increased delta and beta power during the three phases of SDs in the furthest electrode from the ischemic core, followed by the second furthest and third electrode in the beta band during preSD and postSD segments. However, in hypothermic conditions, the third electrode showed lower delta, theta, and alpha power.

Conclusion

Mild hypothermia attenuates all frequency bands in the vascularly compromised hemisphere, irrespective of the cortical location. During SD formation, it preserves power spectra more significantly in electrodes further from the ischemic core.

Infarct Evolution on MR-DWI After Thrombectomy in Acute Stroke Patients Randomized to Nerinetide or Placebo: The REPERFUSE-NA1 Study

BACKGROUND AND OBJECTIVES

The neuroprotectant nerinetide has shown promise in reducing infarct volumes in primate models of ischemia reperfusion. We hypothesized that early secondary infarct growth after endovascular therapy (EVT) (1) may be a suitable surrogate biomarker for testing neuroprotective compounds, (2) is feasible to assess in the acute setting using sequential MRI, and (3) can be modified by treatment with nerinetide.

METHODS

REPERFUSE-NA1 was a prospective, multisite MRI substudy of the randomized controlled trial ESCAPE-NA1 (ClinicalTrials.gov NCT02930018) that involved patients with acute disabling large vessel occlusive stroke undergoing EVT within 12 hours of onset who were randomized to receive intravenous nerinetide or placebo. Patients enrolled in REPERFUSE-NA1 underwent sequential MRI <5 hours post-EVT (day 1) and at 24 hours (day 2). The primary outcome was total diffusion-weighted MRI infarct growth early after EVT, defined as the lesion volume difference between day 2 and day 1. The secondary outcome was region-specific infarct growth in different brain tissue compartments. Statistical analyses were performed using the Mann-Whitney U test and multiple linear regression.

RESULTS

Sixty-seven of 71 patients included had MRI of sufficient quality. The median infarct volume post-EVT was 12.98 mL (IQR, 5.93-28.08) in the nerinetide group and 10.80 mL (IQR, 3.11-24.45) in the control group (p = 0.59). Patients receiving nerinetide showed a median early secondary infarct growth of 5.92 mL (IQR, 1.09-21.30) compared with 10.80 mL (interquartile range [IQR], 2.54-21.81) in patients with placebo (p = 0.30). Intravenous alteplase modified the effect of nerinetide on region-specific infarct growth in white matter and basal ganglia compartments. In patients with no alteplase, the infarct growth rate was reduced by 120% (standard error [SE], 60%) in the white matter (p = 0.03) and by 340% (SE, 140%) in the basal ganglia (p = 0.02) in the nerinetide group compared with placebo after adjusting for confounders.

DISCUSSION

This study highlights the potential of using MR imaging as a biomarker to estimate the effect of a neuroprotective agent in acute stroke treatment. Patients with acute large vessel occlusive stroke exhibited appreciable early infarct growth both in the gray matter and the white matter after undergoing EVT. Acknowledging relatively small overall infarct volumes in this study, treatment with nerinetide was associated with slightly reduced percentage infarct growth in the white matter and basal ganglia compared with placebo in patients not receiving intravenous alteplase and had no effect on the total early secondary infarct growth.

TRIAL REGISTRATION INFORMATION

ClinicalTrials.gov NCT02930018.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that for patients with acute large vessel ischemic stroke undergoing EVT, nerinetide did not significantly decrease early post-EVT infarct growth compared with placebo.

Neutrophil dynamics and inflammaging in acute ischemic stroke: A transcriptomic review

Stroke is among the leading causes of death and disability worldwide. Restoring blood flow through recanalization is currently the only acute treatment for cerebral ischemia. Unfortunately, many patients that achieve a complete recanalization fail to regain functional independence. Recent studies indicate that activation of peripheral immune cells, particularly neutrophils, may contribute to microcirculatory failure and futile recanalization. Stroke primarily affects the elderly population, and mortality after endovascular therapies is associated with advanced age. Previous analyses of differential gene expression across injury status and age identify ischemic stroke as a complex age-related disease. It also suggests robust interactions between stroke injury, aging, and inflammation on a cellular and molecular level. Understanding such interactions is crucial in developing effective protective treatments. The global stroke burden will continue to increase with a rapidly aging human population. Unfortunately, the mechanisms of age-dependent vulnerability are poorly defined. In this review, we will discuss how neutrophil-specific gene expression patterns may contribute to poor treatment responses in stroke patients. We will also discuss age-related transcriptional changes that may contribute to poor clinical outcomes and greater susceptibility to cerebrovascular diseases.

Protective Effect of Beta-Carotene against Myeloperoxidase- Mediated Oxidative Stress and Inflammation in Rat Ischemic Brain Injury

Oxidative stress and inflammatory reaction play critical roles in ischemia/reperfusion (I/R) injury in the brain. β-carotene (βCAR) is a naturally occurring pigment present in fruits and vegetables that expresses antioxidant and anti-inflammatory activities. This study was conducted to investigate the involvement of Bcl2/Bax and NF-κB signaling pathways in the potential protective role of βCAR against brain injury in a middle cerebral artery occlusion (MCAO) rat model. A focal brain ischemia model was created for 2 h, followed by reperfusion. Rats were given 10 and 20 mg/kg of βCAR for 7 days orally before induction of ischemia, at the start of reperfusion, and 3 days after ischemia. Scores of neurological deficit were rated 24 h after induction of ischemia. Motor coordination and spontaneous coordinate activities were assessed using rotarod and activity cage, respectively. After 2 h of the last dose, the animals were killed and their brains were extracted for further examinations. The results of the study show that βCAR diminished the score of neurological deficits and ameliorated motor coordination, balance, and locomotor activity in the I/R control group. Further, βCAR resulted in diminution of malondialdehyde (MDA) and augmentation of reduced glutathione (GSH) contents, as well as the elevation of superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT) enzyme activities in the brain homogenates of I/R rats. βCAR treatment significantly reduced nuclear factor kappa B (NF-κB) brain content and myeloperoxidase (MPO) activity and ameliorated the histological alterations in the brain tissues. βCAR significantly suppressed Bcl-2-associated X protein (Bax) and caspase-3 expression, as well as upregulated B-cell lymphoma-2 (Bcl-2) expression, suggesting a neuroprotective potential via downregulating NF-kB and protecting the rat brain against the I/R-associated apoptotic injury.

Nitric Oxide-Dependent Pathways as Critical Factors in the Consequences and Recovery after Brain Ischemic Hypoxia

Brain ischemia is one of the leading causes of disability and mortality worldwide. Nitric oxide (NO^•), a molecule that is involved in the regulation of proper blood flow, vasodilation, neuronal and glial activity constitutes the crucial factor that contributes to the development of pathological changes after stroke. One of the early consequences of a sudden interruption in the cerebral blood flow is the massive production of reactive oxygen and nitrogen species (ROS/RNS) in neurons due to NO^• synthase uncoupling, which leads to neurotoxicity. Progression of apoptotic or necrotic neuronal damage activates reactive astrocytes and attracts microglia or lymphocytes to migrate to place of inflammation. Those inflammatory cells start to produce large amounts of inflammatory proteins, including pathological, inducible form of NOS (iNOS), which generates nitrosative stress that further contributes to brain tissue damage, forming vicious circle of detrimental processes in the late stage of ischemia. S-nitrosylation, hypoxia-inducible factor 1α (HIF-1α) and HIF-1α-dependent genes activated in reactive astrocytes play essential roles in this process. The review summarizes the roles of NO^•-dependent pathways in the early and late aftermath of stroke and treatments based on the stimulation or inhibition of particular NO^• synthases and the stabilization of HIF-1α activity.

Temporal evolution and spatial distribution of quantitative T2 MRI following acute ischemia reperfusion injury

Background

Determining mechanisms of secondary stroke injury related to cerebral blood flow and the severity of microvascular injury contributing to edema and blood-brain barrier breakdown will be critical for the development of adjuvant therapies for revascularization treatment.

Aim

To characterize the heterogeneity of the ischemic lesion using quantitative T2 imaging along with diffusion-weighted magnetic resonance imaging (DWI) within five hours of treatment.

Methods

Quantitative T2 magnetic resonance imaging was acquired within 5 h (baseline) and at 24 h (follow-up) of stroke treatment in 29 patients. Dynamic contrast enhanced permeability imaging was performed at baseline in a subgroup of patients. Absolute volume change and lesion percent change was determined for the quantitative T2, DWI, and absolute volume change sequences. A Gaussian process with RRELIEFF feature selection algorithm was used for prediction of relative quantitative T2 and DWI lesion growth, baseline and follow-up quantitative T2/DWI lesion ratios, and also NIHSS at 24 h and change in NIHSS from admission to 24 h.

Results

In n = 27 patients, median (interquartile range) lesion percent change was 114.8% (48.9%, 259.1%) for quantitative T2, 48.2% (−12.6%, 179.6%) for absolute volume change, and 62.7% (26.3%, 230.9%) for DWI, respectively. Our model, consisting of baseline NIHSS, CT ASPECTS, and systolic blood pressure, showed a strong correlation with quantitative T2 percent change (cross correlation R2 = 0.80). There was a strong predictive ability for quantitative T2/DWI lesion ratio at 24 h using baseline NIHSS and last seen normal to 24 h magnetic resonance imaging time (cross correlation R2 = 0.93). Baseline dynamic contrast enhanced permeability was moderately correlated to the baseline quantitative T2 values (rho = 0.38).

Conclusion

Quantitative T2 imaging provides critical information for development of therapeutic approaches that could ameliorate microvascular damage during ischemia reperfusion.

The Inflammatory Response After Ischemic Stroke: Targeting β2 and β1 Integrins

Ischemic stroke is a leading cause of death and disability with limited therapeutic options. Resulting inflammatory mechanisms after reperfusion (removal of the thrombus) result in cytokine activation, calcium influx, and leukocytic infiltration to the area of ischemia. In particular, leukocytes migrate toward areas of inflammation by use of integrins, particularly integrins β1 and β2. Integrins have been shown to be necessary for leukocyte adhesion and migration, and thus are of immediate interest in many inflammatory diseases, including ischemic stroke. In this review, we identify the main integrins involved in leukocytic migration following stroke (α L β2, αDβ2, α4β1, and α5β1) and targeted clinical therapeutic interventions.

Diffusion-weighted imaging lesion growth occurs despite recanalization in acute ischemic stroke: Implications for future treatment trials

Background

A proportion of patients presenting with acute small ischemic strokes have poor functional outcomes, even following rapid recanalization treatment.

Aims

Infarct growth may occur even after successful recanalization and could represent an appropriate endpoint for future stroke therapy trials.

Methods

Magnetic resonance diffusion-weighted imaging lesion volumes were obtained at 5 h (initial posttreatment) and 24 h (follow-up) after acute stroke treatment for n = 33 in ischemic stroke patients. Sample sizes per arm (90% power, 30% effect size) for diffusion-weighted imaging lesion growth between initial and 24 h, early change in the National Institutes of Health Stroke Scale between pre- and 24 h, National Institutes of Health Stroke Scale at 24 h, and diffusion-weighted imaging lesion volume at 24 h were estimated to power a placebo-controlled stroke therapy trial.

Results

For patients with poor recanalization (modified thrombolysis in cerebral infarction <2 a; modified arterial occlusion lesion = 0–2) (n = 11), the median diffusion-weighted imaging lesion growth was 8.1 (interquartile range: 4.5, 22.4) ml and with good recanalization (modified thrombolysis in cerebral infarction =2 b or 3; modified arterial occlusion lesion = 3) (n = 22), the median diffusion-weighted imaging lesion growth was 10.0 (interquartile range: 6.0, 28.2) ml ( P = 0.749). When considering a 30% effect size, the sample size required per arm to achieve significance in an acute stroke study would be: (1) N = 49 for the diffusion-weighted imaging lesion growth between initial posttreatment and follow-up time points, (2) N = 65 for the change in the National Institutes of Health Stroke Scale between admission and 24 h, (3) N = 259 for the National Institutes of Health Stroke Scale at 24 h, and (4) N = 256 for diffusion-weighted imaging volume at 24 h.

Conclusion

Despite best efforts to recanalize the ischemic brain, early diffusion-weighted imaging lesion growth still occurs. Treatment trials in stroke should consider early diffusion-weighted imaging lesion growth as a surrogate outcome measure to significantly reduce sample sizes.

Evolution of ischemic damage and behavioural deficit over 6 months after MCAo in the rat: Selecting the optimal outcomes and statistical power for multi-centre preclinical trials

Key disparities between the timing and methods of assessment in animal stroke studies and clinical trial may be part of the reason for the failure to translate promising findings. This study investigates the development of ischemic damage after thread occlusion MCAo in the rat, using histological and behavioural outcomes. Using the adhesive removal test we investigate the longevity of behavioural deficit after ischemic stroke in rats, and examine the practicality of using such measures as the primary outcome for future studies. Ischemic stroke was induced in 132 Spontaneously Hypertensive Rats which were assessed for behavioural and histological deficits at 1, 3, 7, 14, 21, 28 days, 12 and 24 weeks (n>11 per timepoint). The basic behavioural score confirmed induction of stroke, with deficits specific to stroke animals. Within 7 days, these deficits resolved in 50% of animals. The adhesive removal test revealed contralateral neglect for up to 6 months following stroke. Sample size calculations to facilitate the use of this test as the primary experimental outcome resulted in cohort sizes much larger than are the norm for experimental studies. Histological damage progressed from a necrotic infarct to a hypercellular area that cleared to leave a fluid filled cavity. Whilst absolute volume of damage changed over time, when corrected for changes in hemispheric volume, an equivalent area of damage was lost at all timepoints. Using behavioural measures at chronic timepoints presents significant challenges to the basic science community in terms of the large number of animals required and the practicalities associated with this. Multicentre preclinical randomised controlled trials as advocated by the MultiPART consortium may be the only practical way to deal with this issue.

Regulation of brain microglia by female gonadal steroids

Microglial cells are the primary mediators of the CNS immune defense system and crucial for shaping inflammatory responses. They represent a highly dynamic cell population which is constantly moving and surveying their environment. Acute brain damage causes a local attraction and activation of this immune cell type which involves neuron-to-glia and glia-to-glia interactions. The prevailing view attributes microglia a "negative" role such as defense and debris elimination. More topical studies also suggest a protective and "positive" regulatory function. Estrogens and progestins exert anti-inflammatory and neuroprotective effects in the CNS in acute and chronic brain diseases. Recent work revealed that microglial cells express subsets of classical and non-classical estrogen and progesterone receptors in a highly dynamic way. In this review article, we would like to stress the importance of microglia for the spreading of neural damage during hypoxia, their susceptibility to functional modulation by sex steroids, the potency of sex hormones to switch microglia from a pro-inflammatory M1 to neuroprotective M2 phenotype, and the regulation of pro- and anti-inflammatory properties including the inflammasome. We will further discuss the possibility that the neuroprotective action of sex steroids in the brain involves an early and direct modulation of local microglia cell function. This article is part of a Special Issue entitled 'Sex steroids and brain disorders'.

Characterization of a new model of thromboembolic stroke in C57 black/6J mice

This study characterizes a new model of thromboembolic stroke of the middle cerebral artery in C57 black/6J mice, thus offering an opportunity to use the model for studying ischemic stroke in transgenic mice. Thromboembolic stroke was induced by local injection of either 1.5 or 3.0 UI of thrombin directly into the right MCA of C57 black/6J mice. Cerebral blood flow (CBF) velocity was measured continuously by laser Doppler flowmetry, which allowed documentation of both MCA occlusion and of spontaneous recanalization. After 24 h, all animals were euthanized. Cryosections were cut at 400-μm intervals and silver stained with the high-contrast method for volumetric assessment of infarct size. Interleukin (IL)-6, tumor necrosis factor-alpha (TNF-α), caspase-3 and hsp 70 protein levels were investigated by immunofluorescence. Thrombin injection resulted in clot formation in all animals. Cortical infarction occurred in 63% of the mice while 37% had a spontaneous MCA recanalization during the first 20 min following thrombin injection. In cases of successful MCA occlusion with consequent infarction, the clot was stable up to 2 h after formation. Subsequently, 20% recanalized spontaneously. Infarctions were restricted to the cortex with a mean lesion volume of 36 ± 5 for 1.5 UI and 56 ± 8 for 3.0 UI thrombin. Protein levels of IL-6, TNF-α, caspase-3, and hsp 70 were significantly increased after MCAO. The results demonstrate that the mouse thromboembolic stroke model produces cortical infarctions of consistent size in C57 black/6J mice, which is dependent upon the amount of thrombin used for clot formation. Spontaneous MCA recanalization occurs after 2 h of ischemia in 20% of mice. Thus, the thromboembolic model is an applicable stroke model for C57 black/6J mice, which mimics many of the features of human stroke, including spontaneous recanalization. However, strain differences between Swiss and C57 black/6J mice must be taken into account when using the model.

Chronic metformin treatment improves post-stroke angiogenesis and recovery after experimental stroke

Metformin is currently the first-line treatment drug for type 2 diabetes. Metformin is a well-known activator of AMP-activated protein kinase (AMPK). In experimental studies, metformin has been shown to exert direct vascular effects by increasing vascular endothelial growth factor expression and improving microvascular density. As stroke is the leading cause of long-term disability and angiogenesis is implicated as an important mechanism in functional recovery, we hypothesized that chronic metformin treatment would improve post-stroke functional recovery by enhancing functional microvascular density. For this study, C57BL/6N male mice were subjected to a 60-min middle cerebral artery occlusion, and were given 50 mg/kg/day metformin beginning 24 h post-stroke for 3 weeks. Behavioral recovery was assessed using adhesive-tape removal and the apomorphine-induced turning test. The role of angiogenesis was assessed by counting vessel branch points from fluorescein-conjugated lectin-perfused brain sections. Importantly even if metformin treatment was initiated 24 h after injury it enhanced recovery and significantly improved stroke-induced behavioral deficits. This recovery occurred in parallel with enhanced angiogenesis and with restoration of endogenous cerebral dopaminergic tone and revascularization of ischemic tissue. We assessed if the effects on recovery and angiogenesis were mediated by AMPK. When tested in AMPK α-2 knockout mice, we found that metformin treatment did not have the same beneficial effects on recovery and angiogenesis, suggesting that metformin-induced angiogenic effects are mediated by AMPK. The results from this study suggest that metformin mediates post-stroke recovery by enhancing angiogenesis, and these effects are mediated by AMPK signaling.

Epigenetic mechanisms in cerebral ischemia

Treatment efficacy for ischemic stroke represents a major challenge. Despite fundamental advances in the understanding of stroke etiology, therapeutic options to improve functional recovery remain limited. However, growing knowledge in the field of epigenetics has dramatically changed our understanding of gene regulation in the last few decades. According to the knowledge gained from animal models, the manipulation of epigenetic players emerges as a highly promising possibility to target diverse neurologic pathologies, including ischemia. By altering transcriptional regulation, epigenetic modifiers can exert influence on all known pathways involved in the complex course of ischemic disease development. Beneficial transcriptional effects range from attenuation of cell death, suppression of inflammatory processes, and enhanced blood flow, to the stimulation of repair mechanisms and increased plasticity. Most striking are the results obtained from pharmacological inhibition of histone deacetylation in animal models of stroke. Multiple studies suggest high remedial qualities even upon late administration of histone deacetylase inhibitors (HDACi). In this review, the role of epigenetic mechanisms, including histone modifications as well as DNA methylation, is discussed in the context of known ischemic pathways of damage, protection, and regeneration.

Can restoring incomplete microcirculatory reperfusion improve stroke outcome after thrombolysis?

Substantial experimental data and recent clinical evidence suggesting that tissue reperfusion is a better predictor of outcome after thrombolysis than recanalization necessitate that patency of microcirculation after recanalization should be reevaluated. If indeed microcirculatory blood flow cannot be sufficiently reinstituted despite complete recanalization as commonly observed in coronary circulation, it may be one of the factors contributing to low efficacy of thrombolysis in stroke. Although microvascular no-reflow is considered an irreversible process that prevents tissue recovery from injury, emerging evidence suggests that it might be reversed with pharmacological agents administered early during recanalization. Therefore, therapeutic approaches aiming at reducing microvascular obstructions may improve success rate of recanalization therapies. Importantly, promoting oxygen delivery to the tissue, where entrapped erythrocytes cannot circulate in capillaries, with ongoing serum flow may improve survival of the underreperfused tissue. Altogether, these developments bring about the exciting possibility that benefit of reperfusion therapies can be further improved by restoring microcirculatory function because survival in the penumbra critically depends on adequate blood supply. Here, we review the available evidence suggesting presence of an 'incomplete microcirculatory reperfusion' (IMR) after focal cerebral ischemia and discuss potential means that may help investigate IMR in stroke patients after recanalization therapies despite technical limitations.

Loss of Penumbra by Impaired Oxygen Supply? Decreasing Hemoglobin Levels Predict Infarct Growth after Acute Ischemic Stroke: Stroke: Relevant Impact of Hemoglobin, Hematocrit and Transfusion (STRAIGHT) - An Observational Study

Background

The association of mortality and poor outcome with reduced levels of hemoglobin (Hb) and hematocrit (Hct) in patients admitted for ischemic stroke was recently demonstrated. The mechanisms behind this have remained unclear.

Aims

Here, we aimed to investigate a putative association between low Hb and Hct levels and infarct growth.

Methods

All consecutive patients who received intravenous thrombolysis based on multimodal magnetic resonance imaging during the years 1998–2009 were screened. Laboratory data as well as admission magnetic resonance images and follow-up computed tomography scans of 257 patients were assessed. Overall, data of 100 patients were of sufficient quality and further analyzed.

Results

Decrease in Hb and Hct as well as perfusion-weighted imaging volume, mismatch volume, and final infarct size on follow-up computed tomography were associated with infarct growth. A linear regression model revealed Hb decrease (β = 0.23, p = 0.02) to be a predictor of infarct growth, independent of mismatch volume (β = 0.27, p = 0.004) and minimum sodium (β = -0.21, p = 0.03), and adjusted to the non-predicting variables age, National Institute of Health Stroke Scale score, maximum leucocytes and C-reactive protein, blood glucose, and Hct decrease.

Conclusion

Hb levels that decrease after admission independently predict infarct growth in thrombolyzed stroke patients. The clinical implications of this relationship remain to be investigated.

Prevention of hypoglycemia-induced neuronal death by minocycline

Diabetic patients who attempt strict management of blood glucose levels frequently experience hypoglycemia. Severe and prolonged hypoglycemia causes neuronal death and cognitive impairment. There is no effective tool for prevention of these unwanted clinical sequelae. Minocycline, a second-generation tetracycline derivative, has been recognized as an anti-inflammatory and neuroprotective agent in several animal models such as stroke and traumatic brain injury. In the present study, we tested whether minocycline also has protective effects on hypoglycemia-induced neuronal death and cognitive impairment. To test our hypothesis we used an animal model of insulin-induced acute hypoglycemia. Minocycline was injected intraperitoneally at 6 hours after hypoglycemia/glucose reperfusion and injected once per day for the following 1 week. Histological evaluation for neuronal death and microglial activation was performed from 1 day to 1 week after hypoglycemia. Cognitive evaluation was conducted 6 weeks after hypoglycemia. Microglial activation began to be evident in the hippocampal area at 1 day after hypoglycemia and persisted for 1 week. Minocycline injection significantly reduced hypoglycemia-induced microglial activation and myeloperoxidase (MPO) immunoreactivity. Neuronal death was significantly reduced by minocycline treatment when evaluated at 1 week after hypoglycemia. Hypoglycemia-induced cognitive impairment is also significantly prevented by the same minocycline regimen when subjects were evaluated at 6 weeks after hypoglycemia. Therefore, these results suggest that delayed treatment (6 hours post-insult) with minocycline protects against microglial activation, neuronal death and cognitive impairment caused by severe hypoglycemia. The present study suggests that minocycline has therapeutic potential to prevent hypoglycemia-induced brain injury in diabetic patients.

Cerebral tissue repair and atrophy after embolic stroke in rat: a magnetic resonance imaging study of erythropoietin therapy

Using magnetic resonance imaging (MRI) protocols of T(2)-, T(2)*-, diffusion- and susceptibility-weighted imaging (T2WI, T2*WI, DWI, and SWI, respectively) with a 7T system, we tested the hypothesis that treatment of embolic stroke with erythropoietin (EPO) initiated at 24 hr and administered daily for 7 days after stroke onset has benefit in repairing ischemic cerebral tissue. Adult Wistar rats were subjected to embolic stroke by means of middle cerebral artery occlusion (MCAO) and were randomly assigned to a treatment (n = 11) or a control (n = 11) group. The treated group was given EPO intraperitoneally at a dose of 5,000 IU/kg daily for 7 days starting 24 hr after MCAO. Controls were given an equal volume of saline. MRI was performed at 24 hr and then weekly for 6 weeks. MRI and histological measurements were compared between groups. Serial T2WI demonstrated that expansion of the ipsilateral ventricle was significantly reduced in the EPO-treated rats. The volume ratio of ipsilateral parenchymal tissue relative to the contralateral hemisphere was significantly increased after EPO treatment compared with control animals, indicating that EPO significantly reduces atrophy of the ipsilateral hemisphere, although no significant differences in ischemic lesion volume were observed between the two groups. Angiogenesis and white matter remodeling were significantly increased and occurred earlier in EPO-treated animals than in the controls, as evident from T2*WI and diffusion anisotropy maps, respectively. These data indicate that EPO treatment initiated 24 hr poststroke promotes angiogenesis and axonal remodeling in the ischemic boundary, which may potentially reduce atrophy of the ipsilateral hemisphere.

Prostaglandin E2 EP1 receptor inhibition fails to provide neuroprotection in surgically induced brain-injured mice

Recent trials have shown that the prostaglandin E2 EP1 receptor is responsible for NMDA excitotoxicity in the brain after injury. Consequently, in this study, we investigated the use of SC-51089, a selective prostaglandin E2 EP1 receptor antagonist, as a pre-treatment modality to decrease cell death, reduce brain edema, and improve neurobehavioral function after surgically induced brain injury (SBI) in mice. Eleven-week-old C57 black mice (n=82) were randomly assigned to four groups: sham (n=31), SBI (n=27), SBI treated with SC51089 at 10 μg/kg (n=7), and SBI treated with SC51089 at 100 μg/kg (n=17). Treated groups received a single dose of SC51089 intrapertioneally at 12 and 1 h pre-surgery. SBI was performed by resecting the right frontal lobe using a frontal craniotomy. Postoperative assessment occurred at 24 and 72 h, and included neurobehavioral testing and measurement of brain water content and cell death. Results indicated that neither low- nor high-dose EP1 receptor inhibition protected against the SBI-related effects on brain edema formation or cell death. There was however a significant improvement in neurobehavioral function 24 h post-SBI with both dosing regimens. Further studies will be needed to assess the potential therapeutic role of EP1 receptor targeting in SBI.

Dynamics of neuroinflammation in the macrosphere model of arterio-arterial embolic focal ischemia: an approximation to human stroke patterns

Background

Neuroinflammation evolves as a multi-facetted response to focal cerebral ischemia. It involves activation of resident glia cell populations, recruitment of blood-derived leucocytes as well as humoral responses. Among these processes, phagocyte accumulation has been suggested to be a surrogate marker of neuroinflammation. We previously assessed phagocyte accumulation in human stroke by MRI. We hypothesize that phagocyte accumulation in the macrosphere model may resemble the temporal and spatial patterns observed in human stroke.

Methods

In a rat model of permanent focal ischemia by embolisation of TiO₂-spheres we assessed key features of post-ischemic neuroinflammation by the means of histology, immunocytochemistry of glial activation and influx of hematogeneous cells, and quantitative PCR of TNF-α, IL-1, IL-18, and iNOS mRNA.

Results

In the boundary zone of the infarct, a transition of ramified microglia into ameboid phagocytic microglia was accompanied by an up-regulation of MHC class II on the cells after 3 days. By day 7, a hypercellular infiltrate consisting of activated microglia and phagocytic cells formed a thick rim around the ischemic infarct core. Interestingly, in the ischemic core microglia could only be observed at day 7. TNF-α was induced rapidly within hours, IL-1β and iNOS peaked within days, and IL-18 later at around 1 week after ischemia.

Conclusions

The macrosphere model closely resembles the characteristical dynamics of postischemic inflammation previously observed in human stroke. We therefore suggest that the macrosphere model is highly appropriate for studying the pathophysiology of stroke in a translational approach from rodent to human.

Chinese medicine Nao-Shuan-Tong attenuates cerebral ischemic injury by inhibiting apoptosis in a rat model of stroke

ETHNOPHARMACOLOGICAL RELEVANCE

Nao-Shuan-Tong (NST) in capsule form is a compound prescription formulated according to the meridian theory of traditional Chinese medicine (TCM) and is approved by the State Food and Drug Administration of China for the treatment of ischemic stroke.

OBJECTIVES

To test the neuroprotective effects of the Chinese medicine Nao-Shuang-Tong on cerebral ischemia in rats and to explore the underlying mechanisms.

MATERIALS AND METHODS

115 Male Sprague-Dawley rats were randomly divided into 5 groups: sham, ischemia-reperfusion (I/R), and I/R plus NST 0.25, NST 0.5 and NST 1 (n=23 in each group). Cerebral ischemia was induced by 1.5h of middle cerebral artery occlusion. Cerebral infarct area was measured by tetrazolium staining at 24h following reperfusion, and neurological functional deficits were assessed at 1, 3, 7 and 14 d after reperfusion. Neuronal apoptosis was studied by Nissl staining and DNA fragmentation assay at 1 and 3d after reperfusion. The activation of caspase-3, -8, -9 and Bax/Bcl-2 levels were analyzed by western blot 24h after reperfusion.

RESULTS

NST (0.5 and 1g/kg) significantly reduced cerebral infarct area, attenuated neurological functional deficits, and reduced neuronal apoptosis in ischemic cortex and in the CA1 region of hippocampus. NST also suppressed overexpression of Bax and activated caspases-3, -8 and -9, and also inhibited the reduction of Bcl-2 expression and markedly depressed the Bax/Bcl-2 ratio.

CONCLUSIONS

These findings demonstrate that NST is neuroprotective against cerebral ischemia and is likely to act via inhibition of neuronal apoptosis associated with changes in levels of caspases-3 and -8, Bax and Bcl-2.

Exploration of beneficial and deleterious effects of inflammation in stroke: dynamics of inflammation cells

The inflammatory process during stroke consists of activation of resident brain microglia and recruitment of leucocytes, namely neutrophils and monocytes/macrophages. During inflammation, microglial cells, neutrophils and macrophages secrete inflammatory cytokines and chemokines, and phagocytize dead cells. The recruitment of blood cells (neutrophils and macrophages) is mediated by the leucocyte-endothelium interactions and more specifically by cell adhesion molecules. A mathematical model is proposed to represent the dynamics of various brain cells and of immune cells (neutrophils and macrophages). This model is based on a set of six ordinary differential equations and explores the beneficial and deleterious effects of inflammation, respectively phagocytosis by immune cells and the release of pro-inflammatory mediators and nitric oxide (NO). The results of our simulations are qualitatively consistent with those observed in experiments in vivo and would suggest that the increase of phagocytosis could contribute to the increase of the percentage of living cells. The inhibition of the production of cytokines and NO and the blocking of neutrophil and macrophage infiltration into the brain parenchyma led also to the improvement of brain cell survival. This approach may help to explore the respective contributions of the beneficial and deleterious roles of the inflammatory process in stroke, and to study various therapeutic strategies in order to reduce stroke damage.

Inflammation, plasticity and real-time imaging after cerebral ischemia

With an incidence of approximately 350 in 100,000, stroke is the third leading cause of death and a major cause of disability in industrialized countries. At present, although progress has been made in understanding the molecular pathways that lead to ischemic cell death, the current clinical treatments remain poorly effective. There is mounting evidence that inflammation plays an important role in cerebral ischemia. Experimentally and clinically, brain response to ischemic injury is associated with an acute and prolonged inflammatory process characterized by the activation of resident glial cells, production of inflammatory cytokines as well as leukocyte and monocyte infiltration in the brain, events that may contribute to ischemic brain injury and affect brain recovery and plasticity. However, whether the post-ischemic inflammatory response is deleterious or beneficial to brain recovery is presently a matter of debate and controversies. Here, we summarize the current knowledge on the molecular mechanisms underlying post-ischemic neuronal plasticity and the potential role of inflammation in regenerative processes and functional recovery after stroke. Furthermore, because of the dynamic nature of the brain inflammatory response, we highlight the importance of the development of novel experimental approaches such as real-time imaging. Finally, we discuss the novel transgenic reporter mice models that have allowed us to visualize and to analyze the processes such as neuroinflammation and neuronal repair from the ischemic brains of live animals.

Changes in experimental stroke outcome across the life span

Acute ischemic stroke is a leading cause of mortality and disability in the elderly. Age is the most important nonmodifiable risk factor for stroke, yet many preclinical models continue to examine only young male animals. It remains unclear how experimental stroke outcomes change with aging and with biologic sex. If sex differences are present, it is not known whether these reflect an intrinsic differing sensitivity to stroke or are secondary to the loss of estrogen with aging. We subjected both young and aging mice of both sexes to middle cerebral artery occlusion (MCAO). Young female mice had smaller strokes compared with age-matched males, an effect that was reversed by ovariectomy. Stroke damage increased with aging in female mice, whereas male mice had decreased damage after MCAO. Blood-brain barrier (BBB) permeability changes are correlated with infarct size. However, aging mice had significantly less edema formation, an effect that was independent of sex and histologic damage. Differences in the cellular response to stroke occur across the life span in both male and female mice. These differences need to be considered when developing relevant therapies for stroke patients, the majority of whom are elderly.

TTC, fluoro-Jade B and NeuN staining confirm evolving phases of infarction induced by middle cerebral artery occlusion

Considerable debate exists in the literature on how best to measure infarct damage and at what point after middle cerebral artery occlusion (MCAO) infarct is histologically complete. As many researchers are focusing on more chronic endpoints in neuroprotection studies it is important to evaluate histological damage at later time points to ensure that standard methods of tissue injury measurement are accurate. To compare tissue viability at both acute and sub-acute time points, we used 2,3,5-triphenyltetrazolium chloride (TTC), Fluoro-Jade B, and NeuN staining to examine the evolving phases of infarction induced by a 90-min MCAO in mice. Stroke outcomes were examined at 1.5h, 6h, 12h, 24h, 3d, and 7d after MCAO. There was a time-dependent increase in infarct volume from 1.5h to 24h in the cortex, followed by a plateau from 24h to 7d after stroke. Striatal infarcts were complete by 12h. Fluoro-Jade B staining peaked at 24h and was minimal by 7d. Our results indicated that histological damage as measured by TTC and Fluoro-Jade B reaches its peak by 24h after stroke in a reperfusion model of MCAO in mice. TTC staining can be accurately performed as late as 7d after stroke. Neurological deficits do not correlate with the structural lesion but rather transient impairment of function. As the infarct is complete by 24h and even earlier in the striatum, even the most efficacious neuroprotective therapies are unlikely to show any efficacy if given after this point.

Blood-brain barrier tight junction permeability and ischemic stroke

The blood-brain barrier (BBB) is formed by the endothelial cells of cerebral microvessels, providing a dynamic interface between the peripheral circulation and the central nervous system. The tight junctions (TJs) between the endothelial cells serve to restrict blood-borne substances from entering the brain. Under ischemic stroke conditions decreased BBB TJ integrity results in increased paracellular permeability, directly contributing to cerebral vasogenic edema, hemorrhagic transformation, and increased mortality. This loss of TJ integrity occurs in a phasic manner, which is contingent on several interdependent mechanisms (ionic dysregulation, inflammation, oxidative and nitrosative stress, enzymatic activity, and angiogenesis). Understanding the inter-relation of these mechanisms is critical for the development of new therapies. This review focuses on those aspects of ischemic stroke impacting BBB TJ integrity and the principle regulatory pathways, respective to the phases of paracellular permeability.

Delayed administration of a potent cyclin dependent kinase and glycogen synthase kinase 3 beta inhibitor produces long-term neuroprotection in a hypoxia-ischemia model of brain injury

We compared the neuroprotective efficacy of a potent and CNS-penetrant cyclin dependent kinase (CDK) and glycogen synthase kinase 3 beta (GSK3beta) inhibitor (Compound 1) in juvenile (postnatal day 21; P21) and adult C57Bl/6 mice (postnatal day 60; P60) using a model of hypoxic-ischemic brain injury (HI). Neuronal cell counts and density measures from brain sections stained with Cresyl Violet revealed that exposure of P21 mice to 60 min of HI resulted in extensive damage to the ipsilateral cornu ammonis 1 (CA1) region of the hippocampus (40% cell loss) and striatum (30% cell loss) 7 days later. Exposure of P60 mice to 40 min of HI produced a similar pattern of cell loss. Intraperitoneal administration of Compound 1 (3 mg/kg) 1, 5 and 9 h after 60 min of HI did not reduce brain injury in P21 mice relative to vehicle controls. By contrast, in P60 mice, this treatment significantly decreased cell loss in the ipsilateral hippocampus (10% cell loss) and striatum (15% loss) relative to vehicle controls. Terminal uridine deoxynucleotidyl transferase (TUNNEL) positive cell counts and infarct volume were also substantially reduced in P60 mice treated with Compound 1. A motor coordination test performed twice weekly until 5 weeks post-HI confirmed that Compound 1 produced long lasting functional recovery. Our results indicate that Compound 1 produced long lasting neuroprotective effects in adult but not juvenile mice suggesting that inhibition of the CDKs and GSK3beta plays a distinct neuroprotective role in the juvenile and adult brain.

The role of the complement cascade in endotoxin-induced septic encephalopathy

The complement system normally eliminates bacteria and has a protective effect. However, in an inflammatory setting such as sepsis, an exaggerated or insufficient activation of this cascade can have deleterious effect through the activation of glial cells, secretion of proinflammatory cytokines and generation of other toxic products. The aim of the present study was to investigate the role of the complement cascade in septic encephalopathy, through the passive injection of endotoxin/lipopolysaccharide (LPS) into mice overexpressing the potent complement inhibitor, CR1-related y (Crry-tg). Increased gliosis occurred in brains of endotoxemic mice. Concomitant with this, there was a significant rise in mRNA expression of GFAP, CD45 and proinflammatory molecules, TLR4, TNF-alpha and NO, in these brains. Consistent with the capacity of these inflammatory mediators, there was increased apoptosis as determined by DNA fragmentation and TUNEL staining on LPS treatment, which occurred through the Akt pathway. In addition, there was increased water content in brain, similar to cerebral edema observed in sepsis. Relative to wild-type mice, complement-inhibited mice had an attenuated inflammatory response, decreased edema and reduced apoptosis. Therefore, we demonstrate for the first time that the complement cascade appears to be one of the key players that cause brain pathology in an endotoxemic setting and therefore is a viable therapeutic target.

Inflammation in stroke and focal cerebral ischemia

BACKGROUND

A growing number of recent investigations have established a critical role for leukocytes in propagating tissue damage after ischemia and reperfusion in stroke. Experimental data obtained from animal models of middle cerebral artery occlusion implicate inflammatory cell adhesion molecules, chemokines, and cytokines in the pathogenesis of this ischemic damage.

METHODS

Data from recent animal and human studies were reviewed to demonstrate that inflammatory events occurring at the blood-endothelium interface of the cerebral capillaries underlie the resultant ischemic tissue damage.

RESULTS

After arterial occlusion, the up-regulated expression of cytokines including IL-1, and IL-6 act upon the vascular endothelium to increase the expression of intercellular adhesion molecule-1, P-selectin, and E-selectin, which promote leukocyte adherence and accumulation. Integrins then serve to structurally modify the basal lamina and extracellular matrix. These inflammatory signals then promote leukocyte transmigration across the endothelium and mediate inflammatory cascades leading to further cerebral infarction.

CONCLUSIONS

Inflammatory interactions that occur at the blood-endothelium interface, involving cytokines, adhesion molecules, chemokines and leukocytes, are critical to the pathogenesis of tissue damage in cerebral infarction. Exploring these pathophysiological mechanisms underlying ischemic tissue damage may direct rational drug design in the therapeutic treatment of stroke.

Prevention of rat cortical neurons from prostaglandin E2-induced apoptosis by glycogen synthase kinase-3 inhibitors

Cyclooxygenase-2 (COX-2) induction and prostaglandin E(2) (PGE(2)) elevation have been reported to occur after cerebral ischemic insult. PGE(2) induces apoptosis through the PGE(2) EP2 receptor by a cAMP-dependent pathway. Glycogen synthase kinase-3 (GSK-3) affects many fundamental cellular functions. We examined whether GSK-3 is involved in PGE(2)-induced cell death by using GSK-3 inhibitors in rat cultured cortical neurons. Cells treated with 12.5 microM PGE(2) for 2 days shrank. The injured cells underwent chromatin condensation and nuclear fragmentation detected by staining with Hoechst33258, indicating apoptotic cell death. We assayed the effects of selective GSK-3 inhibitors SB216763 and alsteropaullone on PGE(2)-induced apoptosis. These inhibitors completely protected the cells from apoptosis induced by PGE(2). Moreover, dibutyryl cAMP (a cell permeable cAMP)-induced apoptosis was also prevented by alsteropaullone. In addition, GSK-3 inhibitors inhibited caspase-3 activation accompanied by PGE(2)-induced apoptosis. We showed in this report that PGE(2)-induced apoptosis is prevented by GSK-3 inhibitors, suggesting that PGE(2) induces caspase-dependent apoptosis mediated through GSK-3 activation in rat cultured cortical neurons.

Mechanoporation induced by diffuse traumatic brain injury: an irreversible or reversible response to injury?

Diffuse traumatic brain injury (DTBI) is associated with neuronal plasmalemmal disruption, leading to either necrosis or reactive change without cell death. This study examined whether enduring membrane perturbation consistently occurs, leading to cell death, or if there is the potential for transient perturbation followed by resealing/recovery. We also examined the relationship of these events to calpain-mediated spectrin proteolysis (CMSP). To assess plasmalemmal disruption, rats (n = 21) received intracerebroventricular infusion 2 h before DTBI of a normally excluded 10 kDa fluorophore-labeled dextran. To reveal plasmalemmal resealing or enduring disruption, rats were infused with another labeled dextran 2 h (n = 10) or 6 h (n = 11) after injury. Immunohistochemistry for the 150 kDa spectrin breakdown product evaluated the concomitant role of CMSP. Neocortical neurons were followed with confocal and electron microscopy. After DTBI at 4 and 8 h, 55% of all tracer-flooded neurons contained both dextrans, demonstrating enduring plasmalemmal leakage, with many demonstrating necrosis. At 4 h, 12.0% and at 8 h, 15.7% of the dual tracer-flooded neurons showed CMSP, yet, these demonstrated less advanced cellular change. At 4 h, 39.0% and at 8 h, 24.4% of all tracer-flooded neurons revealed only preinjury dextran uptake, consistent with membrane resealing, whereas 7.6 and 11.1%, respectively, showed CMSP. At 4 h, 35% and at 8 h, 33% of neurons demonstrated CMSP without dextran flooding. At 4 h, 5.5% and at 8 h, 20.9% of tracer-flooded neurons revealed only postinjury dextran uptake, consistent with delayed membrane perturbation, with 55.0 and 35.4%, respectively, showing CMSP. These studies illustrate that DTBI evokes evolving plasmalemmal changes that highlight mechanical and potential secondary events in membrane poration.

Prostaglandin E2 deteriorates N-methyl-D-aspartate receptor-mediated cytotoxicity possibly by activating EP2 receptors in cultured cortical neurons

The activation of glutamate receptors, particularly N-methyl-D-aspartate (NMDA) receptors, initiates ischemic cascade in the early stages of cerebral ischemia. Postischemia, cerebral ischemia is also associated with an inflammatory reaction that contributes to tissue damage. The up-regulation of neuronal cyclooxygenase-2 (COX-2) and elevation of prostaglandin E2 (PGE2) have been reported to occur after cerebral ischemic insult. We therefore studied whether the COX-2 reaction product PGE2 affects glutamate receptor-mediated cell death in cultured rat cortical cells. PGE2 was found to augment NMDA-mediated cell death. The transcription of EP1, EP2, EP3 and EP4 PGE2 receptor genes was investigated using reverse transcriptase-polymerase chain reaction (RT-PCR). EP1, EP2 and EP3 receptor genes were found in cortical cells. Butaprost (an EP2 agonist) markedly enhanced NMDA-mediated cell death, whereas 17-phenyl trinor-PGE2 (an EP1 agonist) and sulprostone (an EP3 agonist) had little effect. Both PGE2 and butaprost elevated cAMP intracellular levels in the cortical cells; moreover, forskolin, an activator of adenylate cyclase, enhanced NMDA-mediated cell death. These results suggest that PGE2, acting via EP2 receptors, aggravates excitotoxic neurodegeneration by a cAMP-dependent mechanism.

The broad-spectrum cation channel blocker pinokalant (LOE 908 MS) reduces brain infarct volume in rats: a temperature-controlled histological study

Activation of cation channels conducting Ca2+, Na+ and K+ is involved in the pathogenesis of infarction in experimental focal cerebral ischaemia. Pinokalant (LOE 908 MS) is a novel broad-spectrum inhibitor of several subtypes of such channels and has previously been shown to improve the metabolic and electrophysiologic status of the ischemic penumbra and to reduce lesion size on magnetic resonance images in the acute phase following middle cerebral artery occlusion in rats. The purpose of the present study was to investigate whether these beneficial effects of pinokalant are translated into permanent neuroprotection in terms of a reduction in infarct size one week after middle cerebral artery occlusion in rats. Halothane-anaesthetized male Wistar rats subjected to permanent distal middle cerebral artery occlusion were randomly assigned to one of two treatment groups: 1) Control (vehicle intravenous loading dose followed by infusion); 2) Pinokalant (0.5 mg/kg intravenous loading dose followed by infusion of 1.25 mg/kg/hr). Infusions started 30 min. after middle cerebral artery occlusion and were continued for 24 hr. Body temperature and mean arterial blood pressure were monitored by telemetry during this period and the spontaneous temperature after course in control rats established in other experiments was imitated. Seven days later histological brain sections were prepared and the infarct volumes measured. Body temperature did not differ between the groups. Mean arterial blood pressure was slightly higher in the pinokalant group. Pinokalant treatment significantly reduced cortical infarct volume from 33.8+/-15.8 mm3 to 24.5+/-13.1 mm3 (control group versus pinokalant group, P=0.017, t-test). Taking the effective drug plasma concentration established in other experiments into account revealed that in rats with plasma concentrations within the therapeutic interval, infarct volumes were further reduced to 17.9+/-7.5 mm3 (P<0.005).

Multiple modes of action of tacrolimus (FK506) for neuroprotective action on ischemic damage after transient focal cerebral ischemia in rats

While the immunosuppressant tacrolimus (FK506) is known to be neuroprotective following cerebral ischemia, the mechanisms underlying its neuroprotective properties are not fully understood. To determine the mode of action by which tacrolimus ameliorates neurodegeneration after transient focal ischemia, we therefore evaluated the effect of tacrolimus on DNA damage, release of cytochrome c, activation of microglia and infiltration of neutrophils following a 60-min occlusion of the middle cerebral artery (MCA) in rats. In this model, cortical brain damage gradually expanded until 24 h after reperfusion, whereas brain damage in the caudate putamen was fully developed within 5 h. Tacrolimus (1 mg/kg) administered immediately after MCA occlusion significantly reduced ischemic damage in the cerebral cortex, but not in the caudate putamen. Tacrolimus decreased both apoptotic and necrotic cell death at 24 h and reduced the number of cytochrome c immunoreactive cells at 8 h after reperfusion in the ischemic penumbra in the cerebral cortex. In contrast, tacrolimus did not show significant neuroprotection for necrotic cell death and reduction of cytochrome c immunoreactive cells in the caudate putamen. Tacrolimus also significantly decreased microglial activation at 8 h and inflammatory markers (cytokine-induced neutrophil chemoattractant and myeloperoxidase [MPO] activity) at 24 h after reperfusion in the ischemic cortex but not in the caudate putamen. These results collectively suggest that tacrolimus ameliorates the gradually expanded brain damage by inhibiting both apoptotic and necrotic cell death, as well as suppressing inflammatory reactions.

TGFβ-1 and neurological function after hypoxia-ischemia in adult rats

The present study compared the short-term and long-term neuroprotective and neurobehavioral effects of transforming growth factor beta-1 (TGF beta-1) after hypoxic-ischemic injury in adult rats. TGF beta-1 (10 ng) or vehicle were administered intracerebroventricularly (i.c.v.) 2 h after hypoxia-ischemia. Adhesive removal test was assessed after 10 or 40 days, and the neuronal outcome then determined. TGF beta-1 significantly increased the area of intact cortex compared with vehicle 10 days after the injury, with a significant improvement in neurological function. In contrast, after 40 days recovery TGFbeta-1 neither improved neuronal outcome nor neurological function, suggesting TGFbeta-1 can transiently improve functional and histological recovery from hypoxia-ischemia.

Reduction of mitochondrial electron transport complex activity is restricted to the ischemic focus after transient focal cerebral ischemia in rats: a histochemical volumetric analysis

Using histochemical methods offering high topographical resolution for evaluation of changes in the ischemic focus and the penumbra, the mitochondrial electron transport chain (ETC) complexes I, II, and IV were examined in rats subjected to 2 h of proximal occlusion of the middle cerebral artery (MCAO) followed by no reperfusion, 1 h reperfusion, 4 h reperfusion, or 4 h reperfusion plus treatment with the free radical scavenger alpha-PBN. Serial brain cryosections were histochemically stained to visualize activity of complexes I, II, and IV, and the volumes of tissue with reduced activity in the ipsilateral cortex and caudate putamen were measured by densitometric image analysis. Reductions in complex I, II, and IV activity were restricted to areas in the ischemic foci in cortex and caudate putamen, which microscopically displayed signs of early morphological damage. In cortex, the tissue volume with reduced activity did not change significantly during reperfusion but progressively increased in the caudate putamen, possibly reflecting a faster maturation of morphological damage in this region. Treatment with alpha-PBN did not affect the observed reductions in activities. We deduce that inhibition of mitochondrial ETC complex activity does not play a critical role for recruitment of the penumbra in the infarction process.

The free radical spin-trap α-PBN attenuates periinfarct depolarizations following permanent middle cerebral artery occlusion in rats without reducing infarct volume

The effect of the free radical spin-trap alpha-phenyl-butyl-tert-nitrone (alpha-PBN) in permanent focal cerebral ischemia in rats was examined in two series of experiments. In the first, rats were subjected to permanent occlusion of the middle cerebral artery (MCAO) and treated 1 h after occlusion with a single dose of alpha-PBN (100 mg/kg) or saline. Body temperature was measured and controlled for the first 24 h to obtain identical temperature curves in the two groups. Cortical infarct volumes were determined on histological sections 7 days later. alpha-PBN did not significantly reduce infarct volume (control: 28.3+/-16.3 mm3 vs. alpha-PBN 23.7+/-7.4 mm3). In the second series of experiments, periinfarct depolarizations (PIDs) were recorded with an extracellular DC electrode at two locations in the ischemic penumbra for the initial 3 h following MCAO. alpha-PBN (100 mg/kg, single dose in conjunction with occlusion) significantly reduced the total number (median value of 3 PIDs in the control groups vs. 1 PID in alpha-PBN groups, p<0.001) and total duration of the PIDs (median value 662 s in the control groups vs. 162 s in the alpha-PBN groups, p<0.006). In spite of this, cortical infarct volumes determined 7 days later in the same rats were not smaller in alpha-PBN-treated rats. The study thus demonstrates that attenuation of PIDs does not always lead to smaller infarcts if permanent arterial occlusion is followed by long survival time and does not support the hypothesis that PIDs per se are critical determinants of infarct size in this situation.

Focal cerebral ischemia in rats produced by intracarotid embolization with viscous silicone

Many factors contribute to the severity of neuronal cell death and the functional outcome in stroke. We describe an embolic model of focal cerebral ischemia in the rat that does not require craniotomy and is compatible with continuous measurement of regional CBF using multichannel laser Doppler flow (LDF) technique. Either a 22 microliters (large lesion) or 11 microliters (small lesion) bolus of viscous silicone was injected cephalad into the internal carotid artery. Upon injection, LDF decreased abruptly, most severely in the parietal cortex (-74% +/- 5%) in the large lesion and in the occipital cortex (-69% +/- 10%) in the small lesion model. Over the first hour, post-embolization LDF improved in most areas (e.g. -48% +/- 9% parietal, large lesion) but declined in the small lesion group in the occipital region (-81% +/- 8%). CBF measured by [C]14-IAP autoradiography 1 h post-embolization in the large lesion model demonstrated near-hemispheric ischemia (70% of hemisphere) with sparing of cingulate cortex. Autoradiography demonstrated that ischemia in the small lesion was largely cortical. Light microscopy of brains embolized with 11 microliters of dyed silicone showed filling of pial vessels with no silicone in the Circle of Willis or parenchyma. No animals in the large lesion group survived 24 h. Thirteen of 15 animals in the small lesion group survived for two weeks with resolution of initial hemiplegia, ocular asymmetry and weight loss. Hematoxylin-eosin staining two weeks post-embolization showed signs of severe hypoxia and infarction. In conclusion, the intracarotid silicone embolization technique produces a titrable, reproducible permanent ischemic injury by blocking perfusion in the pial circulation, and is amenable to multisite monitoring with laser Doppler flowmetry. The smaller embolus produces cortical infarction with high rate of survival and neurological recovery.

Insulin-like growth factor-1 improves somatosensory function and reduces the extent of cortical infarction and ongoing neuronal loss after hypoxia-ischemia in rats

Treatment with insulin-like growth factor-1 has been demonstrated to reduce the extent of cortical infarction 5 days after hypoxic-ischemic brain injury. As neuronal death can be progressive and long lasting after initial injury, the present study examined the long-term effects of insulin-like growth factor-1 on late neuronal loss 20 days after hypoxic-ischemic injury, together with evaluating neurobehavioral outcome as assumed by somatosensory function. Unilateral brain injury was induced in adult rats by carotid artery ligation followed by 10 min of hypoxia (6% O2). A single dose of insulin-like growth factor-1 (50 microg) was administered intracerebroventricularly via a stereotaxically pre-fixed cannula 2 h after injury. A bilateral tactile stimulation test was used to examine the degree of somatosensory function at 3, 5, 10 and 20 days after the hypoxia in both insulin-like growth factor-1- (n=12) and its vehicle- (n=12) treated rats, along with sham-operated rats (n=9). Cortical infarction and percentage of selective neuronal loss in the cerebral cortex were examined 20 days after the hypoxic-ischemic injury in both treatment groups. Hypoxic-ischemic injury resulted in a significant delay in the time taken to contact the patch over the period examined (left/right ratio 5.1+/-0.79), particularly at 3 days (7.0+/-2.8) after the hypoxia, compared to sham-operated rats (1.1+/-0.9, P<0.05). The overall effect of insulin-like growth factor-1 in reducing the time taken to contact the patch was significant (P=0.03, 2.6+/-0.79) compared to the vehicle group. There was a trend towards a reduction of cortical infarction after insulin-like growth factor-1 treatment (P=0.058), however insulin-like growth factor-1 significantly reduced the percentage of selective neuronal loss (P=0.027) 20 days following the hypoxia. From these data we suggest that insulin-like growth factor-1 improves somatosensory function by reducing both the extent of cortical infarction and ongoing progressive neuronal death during brain recovery from hypoxic-ischemic injury.

Restoration of function by neural transplantation in the ischemic brain

Stroke remains a major brain disorder that often renders patients severely impaired and permanently disabled. There is no available treatment for reversing these deficits. Hippocampal, striatal and cortical grafting studies demonstrate that fetal cells/tissues, immortalized cells, and engineered cell lines can survive grafting into the ischemic adult brain, correct neurotransmitter release, establish both afferent and efferent connections with the host brain, and restore functional and cognitive deficits in specific models of stroke. The success of neural transplantation depends on several factors: the stroke model (location, extent, and degree of infarction), the donor cell viability and survival at pre- and post-transplantation, and the surgical technique, among others. Further exploitation of knowledge of neural transplantation therapy already available from our experience in treating Parkinson's disease needs to be critically considered for stroke therapy. While the consensus is to create a functional neuronal circuitry in the damaged host brain, there is growing evidence that trophic action of the grafts and host, as well as exogenous application of trophic factors may facilitate functional recovery in stroke. Current treatment modules, specifically that of rehabilitative medicine, should also be explored with neural transplantation therapy. However, validation of neural transplantation and any other treatment for stroke should be critically assessed in laboratory experiments and limited clinical trials. No direct treatment is recognized as safe and effective for reversing the stroke-induced brain damage and functional/cognitive deficits. The first clinical trial of neural transplantation in stroke patients is a mile-stone in stroke therapy, but subsequent large-scale trials should be approached with caution.

Understanding and managing ischemic stroke

Transient or permanent focal brain injury following acute thromboembolic occlusion develops from a complex cascade of pathophysiological events. The processes of excitotoxicity, peri-infarct depolarisation, inflammation, and apoptosis within the ischemic penumbra are proposed. While the translation of therapeutic agents from the animal models to human clinical trials have been disappointing, there remains an atmosphere of optimism as a result of the development of new diagnostic and therapeutic approaches, which include physiological, as opposed to pharmacological, intervention. This article provides an insight into the understanding of cerebral ischemia, together with current and future treatment strategies.Key words: cerebral ischemia, stroke, pathophysiology.

Reduced susceptibility to ischemic brain injury and N-methyl-D-aspartate-mediated neurotoxicity in cyclooxygenase-2-deficient mice

Cyclooxygenase-2 (COX-2), a prostanoid-synthesizing enzyme that contributes to the toxicity associated with inflammation, has recently emerged as a promising therapeutic target for several illnesses, ranging from osteoarthritis to Alzheimer's disease. Although COX-2 has also been linked to ischemic stroke, its role in the mechanisms of ischemic brain injury remains controversial. We demonstrate that COX-2-deficient mice have a significant reduction in the brain injury produced by occlusion of the middle cerebral artery. The protection can be attributed to attenuation of glutamate neurotoxicity, a critical factor in the initiation of ischemic brain injury, and to abrogation of the deleterious effects of postischemic inflammation, a process contributing to the secondary progression of the damage. Thus, COX-2 is involved in pathogenic events occurring in both the early and late stages of cerebral ischemia and may be a valuable therapeutic target for treatment of human stroke.

Correlation between N-acetylaspartate levels and histopathologic changes in cortical infarcts of mice after middle cerebral artery occlusion

The aim of the present study was to evaluate the use of the endogenous neuronal compound N-acetylaspartate (NAA) as a marker of neuronal damage after focal cerebral ischemia in mice. After occlusion of the middle cerebral artery (MCAO) the ischemic cortex was sampled, guided by 2,3,5-triphenyltetrazolium chloride (TTC) staining, and the NAA concentration was measured by high-pressure liquid chromatography (HPLC). Conventional histology and immunohistological methods using antibodies against neuron-specific enolase (NSE), neurofilaments (NF), synaptophysin, glial fibrillary acidic protein (GFAP), and carbodiamide-linked NAA and N-acetylaspartylglutamate (NAAG). The level of NAA rapidly declined to 50% and 20% of control levels in infarcted tissue after 6 hours and 24 hours, respectively. No further decrease was observed during the observation period of 1 week. Within the first 6 hours the number of normal-appearing neurons in the infarcted cortical tissue decreased to 70% of control, of which the majority were eosinophilic. After 24 hours almost no normal-appearing neurons were seen. The number of eosinophilic neurons decreased steadily to virtually zero after 7 days. The number of immunopositive cells in the NSE, NF, and synaptophysin staining within the infarct was progressively reduced, and after 3 to 7 days the immunoreactions were confined to discrete granulomatous structures in the center of the infarct, which otherwise was infested with macrophages. This granulomatous material also stained positive for NAA. The number of cells with positive GFAP immunoreactions progressively increased in the circumference of the infarct. They also showed increased immunoreaction against NAA and NSE. The study shows that the level of NAA 7 days after ischemia does not decline to zero but remains at 10% to 20% of control values. The fact NAA is trapped in cell debris and NAA immunoreactivity is observed in the peri-infarct areas restricts its use as a marker of neuronal density.

Apoptosis and necrosis in cerebrovascular disease

Neuronal death following ischemic insults has been thought to reflect necrosis. However, recent evidence from several labs suggests that programmed cell death, leading to apoptosis, might additionally contribute to this death. We have used both in vitro and in vivo models to study the role of apoptosis in ischemic cell death. Some features of apoptosis (TUNEL staining, internucleosomal DNA fragmentation, sensitivity to cycloheximide) were observed following transient focal ischemia in rats. Brief transient focal ischemia was followed by delayed infarction more than 3 days later; this delayed infarction was sensitive to cycloheximide. A cycloheximide-sensitive component of neuronal cell death was also observed in cultured murine neocortical neurons deprived of oxygen-glucose in the presence of glutamate receptor antagonists. This presumed ischemic apoptosis was attenuated by caspase inhibitors, or by homozygous deletion of the bax gene. Neurons may undergo both apoptosis and necrosis after ischemic insults, and thus it may be therapeutically desirable to block both processes.

Pathobiology of ischaemic stroke: an integrated view

Brain injury following transient or permanent focal cerebral ischaemia (stroke) develops from a complex series of pathophysiological events that evolve in time and space. In this article, the relevance of excitotoxicity, peri-infarct depolarizations, inflammation and apoptosis to delayed mechanisms of damage within the peri-infarct zone or ischaemic penumbra are discussed. While focusing on potentially new avenues of treatment, the issue of why many clinical stroke trials have so far proved disappointing is addressed. This article provides a framework that can be used to generate testable hypotheses and treatment strategies that are linked to the appearance of specific pathophysiological events within the ischaemic brain.

Identification of cerebral ischemic lesions in rat using Eigenimage filtered magnetic resonance imaging

An accurate noninvasive time-independent identification of an ischemic cerebral lesion is an important objective of magnetic resonance imaging (MRI). This study describes a novel application of a multiparameter MRI analysis algorithm, the Eigenimage (EI) filter, to experimental stroke. The EI is a linear filter that maximizes the projection of a desired tissue (ischemic tissue) while it minimizes the projection of undesired tissues (nonischemic tissue) onto a composite image called an eigenimage. Rats (n=26) were subjected to permanent middle cerebral artery occlusion. T2- and T1-weighted coronal MRI were acquired on separate groups of animals. The animals were immediately sacrificed after each imaging session for histopathological analysis of tissue at 4-8 h, 16-24 h, and 48-168 h after stroke onset. Lesion areas from MRI were defined using EI. The EI defined lesion areas were coregistered and warped to the corresponding histopathological sections. The ischemic lesion as defined by EI exhibited ischemic cell damage ranging from scattered acute cell damage to pan necrosis. Ischemic cellular damage was not detected in homologous contralateral hemisphere regions. EI lesion areas overlaid on histopathological sections were significantly correlated (r=0.92, p<0.05) acutely, (r=0.98, p<0.05) subacutely, and (r=0.99, p<0.05) chronically. These data indicate that EI methodology can accurately segment ischemic damage after MCA occlusion from 4-168 h after stroke.

Use of brain slices in the study of pathogenic role of inducible nitric oxide synthase in cerebral ischemia-reperfusion

We have recently demonstrated that inducible nitric oxide synthase (iNOS) is expressed in rat forebrain slices exposed to oxygen and glucose deprivation (OGD). Now, we have found that the expression of iNOS after OGD is time-dependent since 20 min of OGD produces the appearance of iNOS at earlier times than 10 min of OGD. OGD also causes neurotoxicity in this model, as revealed by the increase in excitatory amino acid, neuron specific enolase and lactate dehydrogenase (LDH) efflux to the incubation solution. Finally, the administration of the NMDA receptor antagonist MK-801 (100 nM) inhibits both the expression of iNOS and the release of LDH. Our findings demonstrate that this method may be considered an useful in vitro model of ischemia-reperfusion to determine the therapeutic role of neuroprotective tools.

The transcription factor interferon regulatory factor 1 is expressed after cerebral ischemia and contributes to ischemic brain injury

The transcription factor interferon regulatory factor 1 (IRF-1) is involved in the molecular mechanisms of inflammation and apoptosis, processes that contribute to ischemic brain injury. In this study, the induction of IRF-1 in response to cerebral ischemia and its role in ischemic brain injury were investigated. IRF-1 gene expression was markedly upregulated within 12 h of occlusion of the middle cerebral artery in C57BL/6 mice. The expression reached a peak 4 d after ischemia (6.0 +/- 1.8-fold; P < 0.001) and was restricted to the ischemic regions of the brain. The volume of ischemic injury was reduced by 23 +/- 3% in IRF-1(+/-) and by 46 +/- 9% in IRF-1(-/-) mice (P < 0.05). The reduction in infarct volume was paralleled by a substantial attenuation in neurological deficits. Thus, IRF-1 is the first nuclear transacting factor demonstrated to contribute directly to cerebral ischemic damage and may be a novel therapeutic target in ischemic stroke.