Photothrombotic infarction triggers multiple episodes of cortical spreading depression in distant brain regions

Pathophysiology of Delayed Cerebral Ischemia After Subarachnoid Hemorrhage: A Review

Delayed cerebral ischemia is a major predictor of poor outcomes in patients who suffer subarachnoid hemorrhage. Treatment options are limited and often ineffective despite many years of investigation and clinical trials. Modern advances in basic science have produced a much more complex, multifactorial framework in which delayed cerebral ischemia is better understood and novel treatments can be developed. Leveraging this knowledge to improve outcomes, however, depends on a holistic understanding of the disease process. We conducted a review of the literature to analyze the current state of investigation into delayed cerebral ischemia with emphasis on the major themes that have emerged over the past decades. Specifically, we discuss microcirculatory dysfunction, glymphatic impairment, inflammation, and neuroelectric disruption as pathological factors in addition to the canonical focus on cerebral vasospasm. This review intends to give clinicians and researchers a summary of the foundations of delayed cerebral ischemia pathophysiology while also underscoring the interactions and interdependencies between pathological factors. Through this overview, we also highlight the advances in translational studies and potential future therapeutic opportunities.

The role of spreading depolarizations and electrographic seizures in early injury progression of the rat photothrombosis stroke model

Spreading depolarization (SD) and seizures are pathophysiological events associated with cerebral ischemia. Here, we investigated their role for injury progression in the cerebral cortex. Cerebral ischemia was induced in anesthetized male Wistar rats using the photothrombosis (PT) stroke model. SD and spontaneous neuronal activity were recorded in the presence of either urethane or ketamine/xylazine anesthesia. Blood-brain barrier (BBB) permeability, cerebral perfusion, and cellular damage were assessed through a cranial window and repeated intravenous injection of fluorescein sodium salt and propidium iodide until 4 h after PT. Neuronal injury and early lesion volume were quantified by stereological cell counting and manual and automated assessment of ex vivo T2-weighted magnetic resonance imaging. Onset SDs originated at the thrombotic core and invaded neighboring cortex, whereas delayed SDs often showed opposite propagation patterns. Seizure induction by 4-aminopyridine caused no increase in lesion volume or neuronal injury in urethane-anesthetized animals. Ketamine/xylazine anesthesia was associated with a lower number of onset SDs, reduced lesion volume, and neuronal injury despite a longer duration of seizures. BBB permeability increase inversely correlated with the number of SDs at 3 and 4 h after PT. Our results provide further evidence that ketamine may counteract the early progression of ischemic injury.

Adrenergic receptor antagonism induces neuroprotection and facilitates recovery from acute ischemic stroke

Spontaneous waves of cortical spreading depolarization (CSD) are induced in the setting of acute focal ischemia. CSD is linked to a sharp increase of extracellular K⁺ that induces a long-lasting suppression of neural activity. Furthermore, CSD induces secondary irreversible damage in the ischemic brain, suggesting that K⁺ homeostasis might constitute a therapeutic strategy in ischemic stroke. Here we report that adrenergic receptor (AdR) antagonism accelerates normalization of extracellular K⁺, resulting in faster recovery of neural activity after photothrombotic stroke. Remarkably, systemic adrenergic blockade before or after stroke facilitated functional motor recovery and reduced infarct volume, paralleling the preservation of the water channel aquaporin-4 in astrocytes. Our observations suggest that AdR blockers promote cerebrospinal fluid exchange and rapid extracellular K⁺ clearance, representing a potent potential intervention for acute stroke.

Comparison of Spreading Depolarizations in the Motor Cortex and Nucleus Accumbens: Similar Patterns of Oxygen Responses and the Role of Dopamine

Spreading depolarizations (SD) are pathophysiological phenomena that spontaneously arise in traumatized neural tissue and can promote cellular death. Most investigations of SD are performed in the cortex, a brain region that is susceptible to these depolarizing waves and accessible via a variety of monitoring techniques. Here, we describe SD responses in the cortex and the deep brain region of the nucleus accumbens (NAc) of the anesthetized rat with a minimally invasive, implantable sensor. With high temporal resolution, we characterize the time course of oxygen responses to SD in relation to the electrophysiological depolarization signal. The predominant oxygen pattern consists of four phases: (1) a small initial decrease, (2) a large increase during the SD, (3) a delayed increase, and (4) a persistent decrease from baseline after the SD. Oxygen decreases during SD were also recorded. The latter response occurred more often in the NAc than the cortex (56% vs 20% of locations, respectively), which correlates to denser cortical vascularization. We also find that SDs travel more quickly in the cortex than NAc, likely affected by regional differences in cell type populations. Finally, we investigate the previously uncharacterized effects of dopamine release during SD in the NAc with dopamine receptor blockade. Our results support an inhibitory role of the D2 receptor on SD. As such, the data presented here expands the current understanding of within- and between-region variance in responses to SD.

Anatomical Variants of the Circle of Willis and Brain Lesions in Migraineurs

Background:

Some reports demonstrated vascular alterations in brain magnetic resonance imaging (MRI) in migraineurs and a relationship between circle of Willis (Circle) variants and lacunar brain infarcts. We examined anomalies of the whole circle of Willis and their relationship with vascular brain lesions in migraineurs, to identify any possible vascular mechanism in migraine.

Methods:

We studied, with a cohort controlled study, the circle of Willis in migraineurs seen consecutively in our Headache Center, and in non-headache controls, using angio-MRI of the brain. Statistical analysis used ANOVA, Scheffè's criterion, t-student test.

Results:

We recruited 270 migraineurs (204 without aura (MWOA), 66 with aura (MWA) and 159 controls. Migraineurs presented an anatomical variant in 108 (40%) cases with 34 controls (21.4%) presenting a variant. We found a significant association between MWOA and variants (OR=2.4 CI95% [1.5 to 3.9]) and between MWA and variants (OR=3.2 CI95% [1.6 to 4.1]). Unilateral posterior variants with basilar hypoplasia are statistically associated only with MWA compared to controls (OR=9.2, CI95% [2.3 to 37.2]). Thirty-three percent of MWOA and 24% of MWA sufferers present some kind of brain lesion, included 2% of infra-tentorial lesions. We did not find any statistical association between the presence of Circle variants and ischemic lesions on MRI (OR=1.5 CI95% [0.68; 1.94]), or with infratentorial lacunar lesions (OR=1.58 CI95% [0.48 to 5.24]).

Conclusions:

Anatomical variants of the Circle of Willis are significantly more frequent in migraineurs; posterior anomalies are more frequent in MWA, suggesting a vascular mechanism provoking changes in cerebral blood flow, thereby stimulating cortical spreading depression.

Progress in Clinical Neurosciences: Therapeutic Hypothermia in Severe Traumatic Brain Injury

Severe traumatic brain injury (sTBI) is a relatively common problem with few therapies proven effective. Despite its use for over 50 years, therapeutic hypothermia has not gained widespread acceptance in the treatment of sTBI due to conflicting results from clinical trials. This review will summarize the current evidence from animal, mechanistic and clinical studies supporting the use of therapeutic hypothermia. In addition, issues of rewarming and optimal temperature will be discussed. Finally, the future of hypothermia in sTBI will be addressed.

Dynamic perfusion and diffusion MRI of cortical spreading depolarization in photothrombotic ischemia

Cortical spreading depolarization (CSD) is known to exacerbate ischemic damage, as the number of CSDs correlates with the final infarct volumes and suppressing CSDs improves functional outcomes. To investigate the role of CSD in ischemic damage, we developed a novel rat model of photothrombotic ischemia using a miniature implantable optic fiber that allows lesion induction inside the magnetic resonance imaging (MRI) scanner. We were able to precisely control the location and the size of the ischemic lesion, and continuously monitor dynamic perfusion and diffusion MRI signal changes at high temporal resolution before, during and after the onset of focal ischemia. Our model showed that apparent diffusion coefficient (ADC) and cerebral blood flow (CBF) in the ischemic core dropped immediately after lesion onset by 20±6 and 41±23%, respectively, and continually declined over the next 5h. Meanwhile, CSDs were observed in all animals (n=36) and displayed either a transient decrease of ADC by 17±3% or an increase of CBF by 104±15%. All CSDs were initiated from the rim of the ischemic core, propagated outward, and confined to the ipsilesional cortex. Additionally, we demonstrated that by controlling the size of perfusion-diffusion mismatch (which approximates the penumbra) in our model, the number of CSDs correlated with the mismatch area rather than the final infarct volume. This study introduces a novel platform to study CSDs in real-time with high reproducibility using MRI.

Migraine with aura is associated with an incomplete circle of willis: results of a prospective observational study

Objective

To compare the prevalence of an incomplete circle of Willis in patients with migraine with aura, migraine without aura, and control subjects, and correlate circle of Willis variations with alterations in cerebral perfusion.

Methods

Migraine with aura, migraine without aura, and control subjects were prospectively enrolled in a 1∶1∶1 ratio. Magnetic resonance angiography was performed to examine circle of Willis anatomy and arterial spin labeled perfusion magnetic resonance imaging to measure cerebral blood flow. A standardized template rating system was used to categorize circle of Willis variants. The primary pre-specified outcome measure was the frequency of an incomplete circle of Willis. The association between circle of Willis variations and cerebral blood flow was also analyzed.

Results

170 subjects were enrolled (56 migraine with aura, 61 migraine without aura, 53 controls). An incomplete circle of Willis was significantly more common in the migraine with aura compared to control group (73% vs. 51%, p = 0.02), with a similar trend for the migraine without aura group (67% vs. 51%, p = 0.08). Using a quantitative score of the burden of circle of Willis variants, migraine with aura subjects had a higher burden of variants than controls (p = 0.02). Compared to those with a complete circle, subjects with an incomplete circle had greater asymmetry in hemispheric cerebral blood flow (p = 0.05). Specific posterior cerebral artery variants were associated with greater asymmetries of blood flow in the posterior cerebral artery territory.

Conclusions

An incomplete circle of Willis is more common in migraine with aura subjects than controls, and is associated with alterations in cerebral blood flow.

Simultaneous detection of hemodynamics, mitochondrial metabolism and light scattering changes during cortical spreading depression in rats based on multi-spectral optical imaging

Cortical spreading depression (CSD) is a self-propagating wave of cellular depolarization that plays an important role in the development of cerebral pathology following ischemia or trauma. Optical intrinsic signal (OIS) imaging has been widely used to investigate CSD. Sources of OIS are complex and related to the changes in brain tissue absorption and scattering. The absorbing chromophores may include oxy-hemoglobin, deoxy-hemoglobin, cytochromes, flavin adenine dinucleotide (FAD) and nicotinamide adenine dinucleotide (NADH). Considering only one or part of these elements in studies involving OIS may cause inaccurate results. Thus, we simultaneously calculated changes in HbO, HbR, FAD, cytochrome c, cytochrome aa3 and light scattering during CSD by applying multi-spectral OIS imaging at 450, 470, 500, 530, 550, 570, 600, 630, and 650 nm in the rat brain. We also showed that the hemodynamic changes during CSD may not be correctly estimated if the scattering and other chromophores such as FAD, cytochrome c and cytochrome aa3, are not included in the fitting model of multi-wavelength data analysis. As shown in our results, if considering the changes in scattering and other chromophores in data fitting model, deoxy-hemoglobin (HbR) showed a triphasic change while only a monophasic decrease in HbR will be resolved without considering changes in scattering and other chromophores as reported in previous studies. Moreover, our results showed that changes in cytochrome c was tightly related to OIS at 550 nm, cytochrome aa3 was closely related to OIS at 450, 600 and 650 nm, and FAD was closely related to OIS at 450 and 470 nm during CSD. It indicates that if the contribution by these related chromophores is not considered, using OIS at these wavelengths to determine the hemoglobin changes during CSD may lead to inaccurate results.

Peri-infarct blood-brain barrier dysfunction facilitates induction of spreading depolarization associated with epileptiform discharges

Recent studies showed that spreading depolarizations (SDs) occurs abundantly in patients following ischemic stroke and experimental evidence suggests that SDs recruit tissue at risk into necrosis. We hypothesized that BBB opening with consequent alterations of the extracellular electrolyte composition and extravasation of albumin facilitates generation of SDs since albumin mediates an astrocyte transcriptional response with consequent disturbance of potassium and glutamate homeostasis. Here we show extravasation of Evans blue-albumin complex into the hippocampus following cortical photothrombotic stroke in the neighboring neocortex. Using extracellular field potential recordings and exposure to serum electrolytes we observed spontaneous SDs in 80% of hippocampal slices obtained from rats 24 h after cortical photothrombosis. Hippocampal exposure to albumin for 24 h through intraventricular application together with serum electrolytes lowered the threshold for the induction of SDs in most slices irrespective of the pathway of stimulation. Exposing acute slices from naive animals to albumin led also to a reduced SD threshold. In albumin-exposed slices the onset of SDs was usually associated with larger stimulus-induced accumulation of extracellular potassium, and preceded by epileptiform activity, which was also observed during the recovery phase of SDs. Application of ifenprodil (3 μM), an NMDA-receptor type 2 B antagonist, blocked stimulus dependent epileptiform discharges and generation of SDs in slices from animals treated with albumin in-vivo. We suggest that BBB opening facilitates the induction of peri-infarct SDs through impaired homeostasis of K+.

Experience-dependent brain plasticity after stroke: effect of ibuprofen and poststroke delay

Despite indications that brain plasticity may be enhanced after stroke, we have described impairment of experience-dependent plasticity in rat cerebral cortex neighboring the stroke-induced lesion. Photothrombotic stroke was centered behind the barrel cortex in one cerebral hemisphere of rats. Plasticity of cortical representation of one row of vibrissae was induced by sensory deprivation of all surrounding whiskers for 1 month, and visualized with [(14)C]-2-deoxyglucose autoradiography. In control rats deprivation resulted in an enlargement of functional cortical representation of the spared row of vibrissae. After a focal stroke neighbouring the barrel cortex, no plasticity of the spared row representation was found. Investigation of plastic changes with deprivation initiated 1 week and 1 month after stroke have shown that later poststroke onset of deprivation resulted in a partial recovery of cortical plasticity in the barrel field. Western blot analysis of proinflammatory enzyme cyclooxygenase-2 (COX-2) expression revealed its strong upregulation in the barrel cortex 24 h after stroke. When chronic treatment with the anti-inflammatory drug ibuprofen (10 mg/kg or 20 mg/kg) accompanied deprivation, plasticity was restored. Ibuprofen applied before the ischemia also prevented the poststroke upregulation of COX-2. The results strongly suggest that poststroke impairment of experience-dependent cortical plasticity is caused by stroke-induced inflammatory reactions that subside with poststroke delay and can be at least partially ameliorated by pharmacological treatment.

An experimental model of intraoperative venous injury in the rat

Intraoperative obliteration of cerebral veins occasionally causes unexpected severe complications, especially in elderly patients. However, very title information is available on the pathophysiology of cerebral venous circulation disturbance. Occlusion of cortical veins in rats by a photochemical thrombotic technique is a less invasive, clinically relevant and reproducible model that is suitable for the study of venous circulation disturbance. In the present study, 54 male Wistar rats were used. We examined changes of the cerebral venous flow pattern by fluorescence anglography and brain damage histologically in a one- or two-(cortical) vein occlusion model using a photochemical thrombotic technique. Approximately 30% (9 of 27) of animals in the single-vein occlusion group and 90% (15 of 17) of those in the two-vein occlusion group had microcirculation perturbation, which results very soon in the formation of venous thrombus accompanied by severe venous infarction. In addition, infarction size in the two-vein occlusion group (9.7 +/- 3.2%) was significantly larger than in the single-vein group (2.9 +/- 1.3%) (unpaired T-test, P < 0.01).In conclusion, the photochemical dye technique of attaining cerebral venous occlusion is a worth while addition to the study of circulation perturbations of the brain.

Transient widespread blood-brain barrier alterations after cerebral photothrombosis as revealed by gadofluorine M-enhanced magnetic resonance imaging

Magnetic resonance imaging (MRI) is a powerful tool to assess brain lesions, but currently available contrast agents are limited in the assessment of cellular and functional alterations. By use of the novel MRI contrast agent gadofluorine M (Gf) we report on imaging of transient and widespread changes of blood-brain barrier (BBB) properties as a consequence of focal photothrombotic brain lesions in rats. After i.v. application, Gf led to bright contrast in the lesions, but also the entire ipsilateral cortex on T1-weighted MRI. In contrast, enhancement after application of gadolinium diethylenetriamine-pentaacetic acid (Gd-DTPA), a common clinical indicator of BBB leakage was restricted to the lesions. Remote Gf enhancement was restricted in time to the first 24 h after photothrombosis and corresponded to a transient breakdown of the BBB as revealed by extravasation of the dye Evans blue. In conclusion, our study shows that Gf can visualize subtle disturbances of the BBB in three dimensions not detectable by Gd-DTPA. Upon entry into the central nervous system Gf most likely is locally trapped by interactions with extracellular matrix proteins. The unique properties of Gf hold promise as a more sensitive contrast agent for monitoring BBB disturbances in neurologic disorders, which appear more widespread than anticipated previously.

Microthrombosis after aneurysmal subarachnoid hemorrhage: an additional explanation for delayed cerebral ischemia

Patients with aneurysmal subarachnoid hemorrhage (SAH) who experience delayed cerebral ischemia (DCI) have an increased risk of poor outcome. Delayed cerebral ischemia is considered to be caused by vasospasm. However, not all patients with DCI have vasospasm. Inversely, not all patients with vasospasm develop clinical symptoms and signs of DCI. In the past, treatments aiming at vasospasm were not successful in preventing ischemia. The purpose of this review is to give an overview of clinical data showing that DCI cannot always be attributed to vasospasm, and to present an in-depth analysis of clinical and autopsy studies on the role of microthrombosis in the pathogenesis of DCI. Clinical studies show that DCI is associated with an activation of the coagulation cascade within a few days after SAH, preceding the time window during which vasospasm occurs. Furthermore, impaired fibrinolytic activity, and inflammatory and endothelium-related processes, lead to the formation of microthrombi, which ultimately result in DCI. The presence of microthrombi is confirmed by autopsy studies. Insight in the pathophysiology of DCI is crucial for the development of effective therapies against this complication. Because multiple pathways are involved, future research should focus on drugs with pleiotropic effects.

ATP release by way of connexin 36 hemichannels mediates ischemic tolerance in vitro

Spreading depression (SD) is a self-propagating wave of neuronal and glial depolarization that may occur in virtually any gray matter region in the brain. One consequence of SD is an increased tolerance to ischemia. It has been shown that during cortical SD ATP is released into the extracellular space and activation of purinergic receptors leads to the induction of ischemic tolerance. In the present study we show that depolarization of cultured neurons induces ischemic tolerance which is mediated by purinergic receptor activation. Depolarization causes the release of ATP into the extracellular medium, which may be prevented by treatment with the connexin hemichannel blockers flufenamic acid and quinine, but not the pannexin hemichannel blocker carbenoxolone. Knockdown of connexin 36 expression by siRNA greatly reduces the amount of ATP released during depolarization and the subsequent degree of ischemic tolerance. We conclude that during depolarization neurons release ATP by way of connexin 36 hemichannels.

Rapid morphologic plasticity of peri-infarct dendritic spines after focal ischemic stroke

BACKGROUND AND PURPOSE

Focal stroke is associated with cell death, abnormal synaptic activity, and neurologic impairments. Given that many of these neuropathologic processes can be attributed to events that occur shortly after injury, it is necessary to understand how stroke affects the structure of neurons in surviving peri-infarct regions, particularly at the level of the dendritic spines, which transmit normal and potentially abnormal and injurious synaptic signaling. Recently, we described ischemia-induced changes in the structure of layer 1 dendritic tufts of transgenic mice expressing YFP in layer 5 cortical neurons. However, these in vivo imaging experiments could not address ischemia-related phenomena that occur in deeper cortical structures/layers, other cortical regions, or submicron changes in dendritic spine structure.

METHODS

Focal stroke was induced in the forelimb sensorimotor cortex by the photothrombotic method. Two, 6, and 24 hours after stroke, brains were processed for Golgi-Cox staining to permit a detailed analysis of primary apical dendritic spine structure from layer 2/3 and 5 cortical pyramidal neurons.

RESULTS

Photothrombotic stroke caused a rapid deterioration of neurons, as revealed by Golgi-Cox labeling, in the infarct core that could be readily distinguished from surviving peri-infarct regions. Analysis of >15,000 dendritic spines revealed that although many spines were lost in the peri-infarct cortex during the first 24 hours after stroke (approximately 38% lost), spines that remained were significantly longer (approximately 25% at 6 hours). Furthermore, these effects were found in both layer 2/3 and 5 neurons and were restricted primarily to peri-infarct regions (<200 mum from the infarct border).

CONCLUSIONS

These rapid changes in dendritic spine number and length may reflect an early adaptive response of potentially vulnerable peri-infarct neurons coping with postischemic spreading depression-like depolarizations and the loss of presynaptic contacts.

Modified labeling technique for in vivo visualization of platelets in the cerebral microcirculation of Mongolian gerbils

Activation of platelets induces interactions with platelets, endothelial cells, and leukocytes. In vivo observation of these interactions in the cerebral microcirculation is rare. The purpose of the present study was to develop a model enabling the in vivo observation of platelet kinetics in the cerebral microcirculation. Intravital fluorescence microscopy was performed in the Mongolian gerbil. Platelets of a donor were labeled ex vivo with carboxyfluorescein diacetat-succinimidylester (CFDA-SE), providing long-term fluorescence. Platelet function was tested ex vivo by flow cytometric analysis and in vivo by analyzing platelet-endothelium interactions. Labeled platelets stimulated with adenosine diphosphate ADP (200 micromol/L) or thrombin (1000 U/L) showed aggregation in flow cytrometric analysis, whereas unstimulated platelets were not aggregated. Irradiation of the brain surface after intravenous injection of the photosensitizing dye Photosan first induced rolling and firm adherence of platelets on arteriolar and venular endothelium, followed by the formation of a thrombus obstructing the vessel. Quantitative analysis (n x 100 microm(-1) min(-1)) before and after 6 mins of irradiation showed 2.6+/-3.2 versus 29.0+/-28.9 rolling, and 0.0+/-0.0 versus 1.7+/-2.3 firm adherent platelets in arterioles, and 3.9+/-3.3 versus 36.6+/-20.9 rolling and 0.0+/-0.0 versus 13.6+/-8.9 firm adherent platelets in venules. Thus, we conclude that ex vivo labeling of platelets with CFDA-SE does not activate platelets. Platelet aggregation and adhesion was achieved by platelet-specific stimulation such as ADP, thrombin or irradiation. In vivo assessment of physiologic and pathophysiologic mechanisms of platelets in the cerebral microcirculation can be achieved in this model.

Transient expression of Nxf, a bHLH-PAS transactivator induced by neuronal preconditioning, confers neuroprotection in cultured cells

Cortical spreading depression (CSD) induces waves of neuronal depolarization that confer neuroprotection to subsequent ischemic events in the rat brain. To gain insights into the molecular mechanisms elicited by CSD, we used representational difference analysis (RDA) to identify mRNAs induced by potassium depolarization in vivo. Using this approach, we have isolated a cDNA encoding the SIM2-related bHLH-PAS protein Nxf. Our results confirm that Nxf mRNA and protein are rapidly and transiently expressed in cortical neurons following CSD. Reporter assays show that Nxf is a transcriptional activator that associates with the bHLH-PAS sub-class co-factor ARNT2. Adenovirus-mediated expression of epitope-tagged Nxf results in cell death and the direct activation of the Bax gene in cultured cells. However, RNA interference studies show that endogenous Nxf is required for optimal neuroprotection by preconditioning in cultured F-11 cells. Together, our data indicate that Nxf is a novel bHLH-PAS transactivator transiently induced by preconditioning and that its sustained expression is detrimental. The identification of Nxf may represent an important step in our understanding of the molecular mechanisms of brain preconditioning and injury.

Métabolisme énergétique et agression cérébrale

Brain energy metabolism and signal transduction are intimely intricated. At the cellular level this is reflected by the interdependent metabolism of glutamate and glucose and the energetic compartmentalization between astrocytic glycolysis and neuronal metabolism. Astrocytes appear to have a particular importance in brain metabolism by regulating microcirculation and the repartition of energetic substrates in function of synaptic activity. The high level of O(2) consumption compared to the mass of tissue confers a particular vulnerability of brain to oxidative stress. The synthesis of glutathione, the main anti-oxidant of brain, appears to be dependent of the regulation of synaptic glutamate concentration by astrocytes. Deficiencies of astrocytes functions appear to play a key role in the physiopathology of brain injury.

Induction of granulocyte colony-stimulating factor mRNA by focal cerebral ischemia and cortical spreading depression

Granulocyte colony-stimulating factor (G-CSF) is a hematopoietic growth factor with neuroprotective and antiinflammatory properties. By real-time polymerase chain reaction we show that G-CSF transcripts are induced 485-fold at 4 h and 65-fold at 16 h in ischemic lesions after middle cerebral artery occlusion compared to control brains. Further analysis in photochemically induced focal ischemia revealed that G-CSF induction involved both the infarct area and remote nonischemic brain regions. Remote responses could be blocked by the noncompetitive NMDA receptor antagonist MK-801, suggesting periinfarct depolarizations as a trigger. To further confirm this notion, cortical spreading depression (CSD) was induced by focal application of KCl to the brain surface. CSD led to a 90-fold increase in G-CSF mRNA. Contrastingly, the induction of granulocyte-monocyte (GM)-CSF, another member of the hematopoietic growth factor family, was only moderate (sixfold) and restricted to ischemic brain lesions. In conclusion, G-CSF induction in the brain may be part of an intrinsic stress response aimed at limitation of neuronal damage.

Nuclear magnetic resonance (NMR) measurement of the apparent diffusion coefficient (ADC) of tissue water and its relationship to cell volume changes in pathological states

Diffusion-weighted nuclear magnetic resonance (NMR) imaging (DWI) is sensitive to the random translational motion of water molecules due to Brownian motion. Although the mechanism is still not completely understood, the cellular swelling that accompanies cell membrane depolarization results in a reduction in the net displacement of diffusing water molecules and thus a concomitant reduction in the apparent diffusion coefficient (ADC) of tissue water. Cerebral regions of reduced ADC appear hyperintense in a DWI and this technique has been used extensively to study acute stroke. In addition to cerebral ischemia, reductions in the ADC of cerebral water have been observed following cortical spreading depression, ischemic depolarizations (IDs), transient ischemic attack (TIA), status epilepticus, and hypoglycemia. Although the mechanism responsible for initiating membrane depolarization varies in each case, the ensuing cell volume changes follow a similar pattern. Water ADC values are also affected by the presence and orientation of barriers to translational motion (such as cell membranes and myelin fibers) and thus NMR measures of anisotropic diffusion are sensitive to more chronic pathological states where the integrity of these structures is modified by disease. Both theoretical prediction and experimental evidence suggest that the ADC of tissue water is related to the volume fraction of the interstitial space via the electrical conductivity of the tissue. The implication is that acute neurological disorders that exhibit electrical conductivity changes should also exhibit ADC changes that are detectable by DWI. A qualitative correlation between electrical conductivity and the ADC of water has been demonstrated in a number of animal model studies and the results indicate that reduced ADC values are associated with reductions in the extracellular volume fraction and increased extracellular tortuosity. The close relationship between ADC changes and cell volume changes in various pathological states suggests that NMR measurements are also sensitive to chemical communication between cells through the extracellular space (i.e., extrasynaptic or volume transmission, VT).

Cortical spreading depression activates and upregulates MMP-9

Cortical spreading depression (CSD) is a propagating wave of neuronal and glial depolarization and has been implicated in disorders of neurovascular regulation such as stroke, head trauma, and migraine. In this study, we found that CSD alters blood-brain barrier (BBB) permeability by activating brain MMPs. Beginning at 3-6 hours, MMP-9 levels increased within cortex ipsilateral to the CSD, reaching a maximum at 24 hours and persisting for at least 48 hours. Gelatinolytic activity was detected earliest within the matrix of cortical blood vessels and later within neurons and pia arachnoid (> or =3 hours), particularly within piriform cortex; this activity was suppressed by injection of the metalloprotease inhibitor GM6001 or in vitro by the addition of a zinc chelator (1,10-phenanthroline). At 3-24 hours, immunoreactive laminin, endothelial barrier antigen, and zona occludens-1 diminished in the ipsilateral cortex, suggesting that CSD altered proteins critical to the integrity of the BBB. At 3 hours after CSD, plasma protein leakage and brain edema developed contemporaneously. Albumin leakage was suppressed by the administration of GM6001. Protein leakage was not detected in MMP-9-null mice, implicating the MMP-9 isoform in barrier disruption. We conclude that intense neuronal and glial depolarization initiates a cascade that disrupts the BBB via an MMP-9-dependent mechanism.

Cortical spreading depression activates and upregulates MMP-9

Cortical spreading depression (CSD) is a propagating wave of neuronal and glial depolarization and has been implicated in disorders of neurovascular regulation such as stroke, head trauma, and migraine. In this study, we found that CSD alters blood-brain barrier (BBB) permeability by activating brain MMPs. Beginning at 3-6 hours, MMP-9 levels increased within cortex ipsilateral to the CSD, reaching a maximum at 24 hours and persisting for at least 48 hours. Gelatinolytic activity was detected earliest within the matrix of cortical blood vessels and later within neurons and pia arachnoid (> or =3 hours), particularly within piriform cortex; this activity was suppressed by injection of the metalloprotease inhibitor GM6001 or in vitro by the addition of a zinc chelator (1,10-phenanthroline). At 3-24 hours, immunoreactive laminin, endothelial barrier antigen, and zona occludens-1 diminished in the ipsilateral cortex, suggesting that CSD altered proteins critical to the integrity of the BBB. At 3 hours after CSD, plasma protein leakage and brain edema developed contemporaneously. Albumin leakage was suppressed by the administration of GM6001. Protein leakage was not detected in MMP-9-null mice, implicating the MMP-9 isoform in barrier disruption. We conclude that intense neuronal and glial depolarization initiates a cascade that disrupts the BBB via an MMP-9-dependent mechanism.

Transcriptional response to circumscribed cortical brain ischemia: spatiotemporal patterns in ischemic vs. remote non-ischemic cortex

Focal brain infarcts are surrounded by extended perilesional zones that comprise the partially ischemic penumbra but also completely non-ischemic cortex of the remote ipsilateral hemisphere. To delineate the impact of lesion-associated vs. remote processes on transcriptional programming after focal ischemia, we used cDNA array analysis, quantitative real-time polymerase chain reaction and immunohistochemistry in the photothrombosis model of circumscribed cortical ischemia in rats. At an early stage of 4 h after ischemia, gene induction occurred to a similar extent in the ischemic infarct and remote non-ischemic cortex of the ipsilateral hemisphere. Among the genes induced in non-ischemic cortex we found the NGF-inducible genes PC3, VGF and Arc, the transcriptional regulators I kappa B-alpha and Stat3, and the beta-chemokine MIP-1 alpha (CCL3). At 3 days, the spatial pattern of gene expression had changed dramatically with brain fatty acid-binding protein as the only gene significantly induced in non-ischemic ipsilateral cortex. In contrast, numerous genes were exclusively regulated at the lesion site, comprising genes involved in cell cycle regulation, proteolysis, apoptosis, lipid homeostasis and anti-inflammatory counter-regulation. Cortical spreading depression was identified as the main mechanism underlying gene induction in remote non-ischemic cortex. Our data demonstrate a dynamic spatiotemporal pattern of gene induction, which may contribute to delayed progression of damage or, alternatively, mediate neuroprotection, tissue remodeling and functional compensation.

Pathophysiology of cerebral ischemia and brain trauma: similarities and differences

Current knowledge regarding the pathophysiology of cerebral ischemia and brain trauma indicates that similar mechanisms contribute to loss of cellular integrity and tissue destruction. Mechanisms of cell damage include excitotoxicity, oxidative stress, free radical production, apoptosis and inflammation. Genetic and gender factors have also been shown to be important mediators of pathomechanisms present in both injury settings. However, the fact that these injuries arise from different types of primary insults leads to diverse cellular vulnerability patterns as well as a spectrum of injury processes. Blunt head trauma produces shear forces that result in primary membrane damage to neuronal cell bodies, white matter structures and vascular beds as well as secondary injury mechanisms. Severe cerebral ischemic insults lead to metabolic stress, ionic perturbations, and a complex cascade of biochemical and molecular events ultimately causing neuronal death. Similarities in the pathogenesis of these cerebral injuries may indicate that therapeutic strategies protective following ischemia may also be beneficial after trauma. This review summarizes and contrasts injury mechanisms after ischemia and trauma and discusses neuroprotective strategies that target both types of injuries.

Delayed secondary phase of peri-infarct depolarizations after focal cerebral ischemia: relation to infarct growth and neuroprotection

In focal cerebral ischemia, peri-infarct depolarizations (PIDs) cause an expansion of core-infarcted tissue into adjacent penumbral regions of reversible injury and have been shown to occur through 6 hr after injury. However, infarct maturation proceeds through 24 hr. Therefore, we studied PID occurrence through 72 hr after both transient and permanent middle cerebral artery occlusion (MCAo) via continuous DC recordings in nonanesthetized rats. PIDs occurred an average 13 times before reperfusion at 2 hr and then ceased for an average approximately 8 hr. After this quiescent period, PID activity re-emerged in a secondary phase, which reached peak incidence at 13 hr and consisted of a mean 52 PIDs over 2-24 hr. This phase corresponded to the period of infarct maturation; rates of infarct growth through 24 hr coincided with changes in PID frequency and peaked at 13 hr. In permanent MCAo, PIDs also occurred in a biphasic pattern with a mean of 78 events over 2-24 hr. Parameters of secondary phase PID incidence correlated with infarct volumes in transient and permanent ischemia models. The role of secondary phase PIDs in infarct development was further investigated in transient MCAo by treating rats with a high-affinity NMDA receptor antagonist at 8 hr after injury, which reduced post-treatment PID incidence by 57% and provided 37% neuroprotection. Topographic mapping with multielectrode recordings revealed multiple sources of PID initiation and patterns of propagation. These results suggest that PIDs contribute to the recruitment of penumbral tissue into the infarct core even after the restoration of blood flow and throughout the period of infarct maturation.

Relationship between Intracranial Pressure and Cortical Spreading Depression following Fluid Percussion Brain Injury in Rats

Traumatic brain injury (TBI) is known to be accompanied by an increase in intracranial pressure (ICP) and in some cases, by spontaneous generation of cortical spreading depression (CSD) cycles. However, the role of CSD in the pathophysiology of cerebral contusion is still unknown. A multiparametric monitoring assembly was placed on the right hemisphere of the rat brain to evaluate ICP, DC potential, extracellular K(+), cerebral blood flow (CBF), and electrocorticogram in 27 rats during 5 h. Fluid percussion brain injury (FPBI) with the magnitude of the impact 2.9, 3.3, 4.1, and 5.0 atmospheres was induced to the left parietal cortex in animal groups A, B, C, and D, respectively. A slow increase in ICP was evident, and was pronounced in group C and especially in group D, where four of nine animals died during the monitoring. At the end of the 5 h experiment, the mean ICP levels were 6.75 +/- 2.87, 8.40 +/- 2.70, 12.75 +/- 4.03, 29.56 +/- 9.25, and the mean total number of CSD cycles was 2.00 +/- 1.41, 4.29 +/- 4.23, 11.71 +/- 13.29, and 20.11 +/- 19.26 in groups A, B, C, and D, respectively. The maximal level of intensity of CSD cycle generation after FPBI was obtained in group D, where almost constant activity was maintained until the end of the experiment. A significant coefficient of correlation between ICP level and total number of CSD cycles was found for all ICP measurements (r = 0.47-0.63, p < 0.05, n = 27), however more significant (p < 0.001) was the coefficient during the period of monitoring between 2 and 4 h after FPBI. Our results suggest that numerous repeating CSD cycles are typical phenomena in moderate and especially severe forms of FPBI. The rising number of CSD cycles under condition of an ICP level >/=20 mm Hg may demonstrate, with high probability, the unfavorable development of TBI, caused by growing secondary hypoxic insult.

Mefenamate, an agent that fails to attenuate experimental cerebral infarction

BACKGROUND

Blockade of nonselective cation channels is a potential therapeutic approach that has not been attempted in cerebral ischemia, in spite of the ability of these channels to allow cellular calcium influx into neurons. Fenamates are a class of molecules that block these channels, and many congeners are also anti-inflammatory and free radical scavenging. These three mechanisms may contribute to brain damage in ischemia.

METHODS

Pretreatment or posttreatment with mefenamate (30 mg/kg) was evaluated in a temperature-controlled rat transient focal ischemia model. Quantitative histopathology on 26 coronal sections allowed determination of tissue necrosis and tissue atrophy at one week survival.

RESULTS

Neither pre- nor postischemic administration of a dose previously shown effective in preventing epileptic neuronal necrosis was found to reduce necrosis in cortex, nor in any subcortical structures.

CONCLUSIONS

We conclude that nonselective cation channel blockade with mefenamate affords no neuroprotection in this model. Publication bias against negative studies exists in the literature, but we here report negative findings due to the multiple potentially positive actions of the drug. Closer examination of the effects of the molecule, however, reveals several potentially negative effects as well. We conclude there may be inherent weakness in pharmacologic monotherapy, even with molecules having protean potentially beneficial effects. This conclusion seems to have been borne out by the results of recent clinical trials.

Detrimental and beneficial effects of injury-induced inflammation and cytokine expression in the nervous system

Lesions in the nervous system induce rapid activation of glial cells and under certain conditions additional recruitment of granulocytes, T-cells and monocytes/macrophages from the blood stream triggered by upregulation of cell adhesion molecules, chemokines and cytokines. Hematogenous cell infiltration is not restricted to infectious or autoimmune disorders of the nervous system, but also occurs in response to cerebral ischemia and traumatic lesions. Neuroinflammation can cause neuronal damage, but also confers neuroprotection. Granulocytes occlude vessels during reperfusion after transient focal ischemia, while the functional role of T-cells and macrophages in stroke development awaits further clarification. After focal cerebral ischemia neurotoxic mediators released by microglia such as the inducible nitric oxide synthase (leading to NO synthesis) and the cytokines interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) are upregulated prior to cellular inflammation in the evolving lesion and functionally contribute to secondary infarct growth as revealed by numerous pharmacological experiments and by use of transgenic animals. On the other hand, cytokine induction remote from ischemic lesions involves NMDA-mediated signalling pathways and confers neuroprotection. After nerve injury T cells can rescue CNS neurons. In the peripheral nervous system neuroinflammation is a prerequisite for successful regeneration that is impeded in the CNS. In conclusion, there is increasing evidence that neuroinflammation represents a double edged sword. The opposing neurotoxic and neuroprotective properties of neuroinflammation during CNS injury provide arich and currently unexplored set of research problems.

Widespread and long-lasting alterations in GABA(A)-receptor subtypes after focal cortical infarcts in rats: mediation by NMDA-dependent processes

Impairment of inhibitory neurotransmission has been reported to occur in widespread, structurally intact brain regions after focal ischemic stroke. These long-lasting alterations contribute to the functional deficit and influence long-term recovery. Inhibitory neurotransmission is primarily mediated by gamma-aminobutyric acid (GABA)A receptors assembled of five subunits that allow a variety of adaptive changes. In this study, the regional distribution of five major GABA(A)-receptor subunits (alpha1, alpha2, alpha3, alpha5, and gamma2) was analyzed immunohistochemically 1, 7, and 30 days after photochemically induced cortical infarcts. When compared with sham-operated controls, a general and regionally differential reduction in immunostaining was found within the cortex, hippocampus, and thalamus of both hemispheres for almost all subunits. Within ipsilateral and contralateral neocortical areas, a specific pattern of changes with a differential decrease of subunits alpha1, alpha2, alpha5, and gamma2 and a significant upregulation of subunit alpha3 was observed in the contralateral cortex homotopic to the infarct. This dysregulation was most prominent at day 7 and still present at day 30. Interestingly, a single application of the noncompetitive N-methyl-D-aspartate-receptor antagonist MK-801 during lesion induction completely blocked these bihemispheric alterations. Cortical spreading depressions induced by topical application of KCl do not change GABA(A)-receptor subunit expression. As alterations in subtype distribution crucially influence inhibitory function, ischemia-induced modifications in GABA(A)-receptor subtype expression may be of relevance for functional recovery after stroke.

Prereperfusion saline infusion into ischemic territory reduces inflammatory injury after transient middle cerebral artery occlusion in rats

BACKGROUND AND PURPOSE

In ischemic stroke, the ischemic crisis activates a cascade of events that are potentiated by reperfusion, eventually leading to cell death. The chief aim in this study was to investigate whether our new experimental model for stroke therapy, flushing the ischemic territory with saline before reperfusion, could minimize this damage by (1) reducing the inflammatory reaction and (2) improving regional microcirculation.

METHODS

Stroke in Sprague-Dawley rats (n=39) was induced by a 2-hour middle cerebral artery occlusion with the use of a novel intraluminal hollow filament. Before 48-hour reperfusion, 20 of the ischemic rats received 7 mL isotonic saline at 23 degrees C or 37 degrees C infused into the ischemic area through the filament. Regional cerebral blood flow in cortex supplied by the right middle cerebral artery was measured by laser-Doppler flowmetry during ischemia and reperfusion. Leukocyte infiltration, microvascular plugging, and infarct volume were compared with the use of hematoxylin and eosin staining. Expression of intercellular adhesion molecule 1 (ICAM-1) was determined by immunocytochemistry. Neurological deficits were evaluated.

RESULTS

After the prereperfusion infusion of saline, significantly (P<0.001) improved cerebral blood flow (105+/-12% of baseline) was obtained up to 48 hours after reperfusion, compared with 45+/-7% at 24 hours and 25+/-3% at 48 hours after reperfusion without local saline infusion. Significant (P<0.001) reductions in leukocyte infiltration (61%), vascular plugging (45%), infarct volume (approximately 65%), and neurological deficits were also produced. ICAM-1 expression in the infarct region was significantly (P<0.05) minimized by 37%.

CONCLUSIONS

The reduced brain infarct and neurological deficits may be attributed to adequate reperfusion and ameliorated inflammation induced by local prereperfusion infusion.

Photothrombotic brain infarction results in seizure activity in aging Fischer 344 and Sprague Dawley rats

This study was designed to determine whether photothrombotic brain infarction could result in epileptic seizures in adult animals. Male Fischer 344 (F344) rats at 2, 6, 12, 24, and 30 months of age and male Sprague Dawley (SD) rats at 2 and 6 months of age underwent photothrombotic brain infarction with the photosensitive dye rose bengal by focusing a wide (6 mm) or narrow (3 mm) diameter white light beam on the skull overlying left hemisphere anterior frontal, midfrontal, frontoparietal, or parietal areas. Animals were monitored with video and EEG recordings. Morphological analysis of infarct size was performed with a computer-assisted image analysis system. The primary finding of this study was that epileptic seizures were recorded in post-mature rats 2 months after lesioning the frontoparietal cortex with large photothrombotic infarcts that extended to the cortical-subcortical interface. These seizures were characterized behaviorally by motor arrest, appeared to originate in the periinfarct area, and could be distinguished from inherited spontaneous bilateral cortical discharges by the morphology, frequency, duration, and laterality of the ictal discharges. Small cortical lesions were ineffective in producing seizures except for one animal that demonstrated recurrent prolonged focal discharges unaccompanied by behavioral change. Stage 3 seizures were observed in a small number of mid-aged and aged animals lesioned with large infarcts in anterior frontal and frontoparietal areas. These results suggest that the technique of photothrombosis can be used to produce neocortical infarction as a means to study mechanisms of secondary epileptogenesis.

Preconditioning with cortical spreading depression does not upregulate Cu/Zn-SOD or Mn-SOD in the cerebral cortex of rats

Previous studies have demonstrated that preconditioning the brain with cortical spreading depression (CSD) induces tolerance to a subsequent episode of ischemia. In other models of preconditioning, induction of ischemic tolerance has been associated with increased expression of the antioxidant enzyme, superoxide dismutase (SOD). The objective of the present study was to determine whether CSD upregulates Cu/Zn-SOD or Mn-SOD. CSD was induced in one hemisphere by applying 2 M KCl to the frontal cortex in Wistar rats. After 2 or 24 h of recovery, Cu/Zn-SOD and Mn-SOD mRNA levels were determined in both hemispheres using Northern blot analysis. In separate rats, Cu/Zn-SOD and Mn-SOD protein levels were determined 24 and 72 h after CSD using Western blot analysis. In addition, total SOD, Cu/Zn-SOD and Mn-SOD enzymatic activities were measured 24 and 72 h after CSD using spectrophotometric and zymographic assays. At the times investigated, no significant differences in mRNA or protein levels for Cu/Zn-SOD or Mn-SOD were observed between the ipsilateral and contralateral cortex. Further, there were no significant differences in Cu/Zn-SOD or Mn-SOD enzymatic activities between the two hemispheres at 24 or 72 h after CSD. In addition, CSD did not alter the activities of Cu/Zn-SOD or Mn-SOD in either hemisphere, relative to those in unoperated animals. Taken together, these results fail to support the hypothesis that CSD-induced tolerance is mediated through the upregulation of Cu/Zn-SOD or Mn-SOD.

Calcium ion transients in peri-infarct depolarizations may deteriorate ion homeostasis and expand infarction in focal cerebral ischemia in cats

BACKGROUND AND PURPOSE

Harmful effects of peri-infarct depolarizations (PIDs) may depend on recurrent Ca(2+) influx. Thus far, few studies have documented the relevance of PIDs in gyrencephalic animals, and the progressive nature of this process has not been investigated over extended periods. We therefore studied in prolonged focal ischemia in cats spatial and temporal profiles of extracellular calcium ([Ca(2+)](o)) shifts in relation to direct current (DC) potential, nitric oxide (NO) concentration and regional cerebral blood flow alterations, and final pathological outcome.

METHODS

In halothane-anesthetized cats receiving either vehicle (n=12) or MK-801 treatment (5 mg/kg IV; n=10), the left middle cerebral artery was permanently occluded. Laser-Doppler probes, ion-selective microelectrodes, and NO electrodes measured simultaneously regional cerebral blood flow, DC potential, electrocorticogram, [Ca(2+)](o), and NO concentrations in ectosylvian and suprasylvian gyri of the left cerebral cortex.

RESULTS

Persistent depolarization immediately after middle cerebral artery occlusion occurred in 10 ectosylvian and 4 suprasylvian gyri of vehicle-treated animals and in 9 ectosylvian and 3 suprasylvian gyri of MK-801-treated animals. PIDs associated with transient decreases of [Ca(2+)](o) were detected in suprasylvian gyri of only 4 vehicle-treated animals, of which 3 developed recurrent PIDs. Electrocorticogram was suppressed during PIDs, and electrocorticogram recovery worsened in a stepwise manner with consecutive depolarizations. PID duration increased slightly with ongoing ischemia and evolved to persistent depolarization at a final stage. NO transients were not detected during PID, and regional cerebral blood flow transients were not pronounced. Infarction was larger with initial persistent depolarization than with PID and was smallest in MK-801-treated animals.

CONCLUSIONS

PID is not a common finding in peri-infarct zones in cats, and it is suppressed by the N:-methyl-D-aspartate antagonist MK-801. However, if repeated PIDs are generated, they result in a stepwise, progressive breakdown of neuronal function and ion homeostasis, probably contributing to the growth of infarction in focal cerebral ischemia. Recurrent Ca(2+) influx is a mechanism that presumably contributes to this process.

Imaging anoxic depolarization during ischemia-like conditions in the mouse hemi-brain slice

Focal ischemia evokes a sudden loss of membrane potential in neurons and glia of the ischemic core termed the anoxic depolarization (AD). In metabolically compromised regions with partial blood flow, peri-infarct depolarizations (PIDs) further drain energy reserves, promoting acute and delayed neuronal damage. Visualizing and quantifying the AD and PIDs and their acute deleterious effects are difficult in the intact animal. In the present study, we imaged intrinsic optical signals to measure changes in light transmittance in the mouse coronal hemi-brain slice during AD generation. The AD was induced by oxygen/glucose deprivation (OGD) or by ouabain exposure. Potential neuroprotective strategies using glutamate receptor antagonists or reduced temperature were tested. Eight minutes of OGD (n = 18 slices) or 4 min of 100 microM ouabain (n = 14) induced a focal increase of increased light transmittance (LT) in neocortical layers II/III that expanded concentrically to form a wave front coursing through neocortex and independently through striatum. The front was coincident with a negative voltage shift in extracellular potential. Wherever the LT front (denoting cell swelling) propagated, a decrease in LT (denoting dendritic beading) followed in its wake. In addition the evoked field potential was permanently lost, indicating neuronal damage. Glutamate receptor antagonists did not block the onset and propagation of AD or the extent of irreversible damage post-AD. Lowering temperature to 25-30 degrees C protected the tissue from OGD damage by inhibiting AD onset. This study shows that anoxic depolarization evoked by global ischemia-like conditions is a spreading process that is focally initiated at multiple sites in cortical and subcortical gray. The combined energy demands of O(2)/glucose deprivation and the AD greatly exacerbate neuronal damage. Glutamate receptor antagonists neither block the AD in the ischemic core nor, we propose, block recurrent PID arising close to the core.

High speed diffusion magnetic resonance imaging of ischemia and spontaneous periinfarct spreading depression after thromboembolic stroke in the rat

Spontaneous episodes of transient cell membrane depolarization (spreading depression [SD]) occur in the surroundings of experimental stroke lesions and are believed to contribute to infarct growth. Diffusion-weighted imaging (DWI) is capable of detecting the water shifts from extracellular to intracellular space associated with SD waves and ischemia, and can make in vivo measurements of these two features on a pixel-by-pixel basis with good temporal resolution. Using continuous high speed DWI with a temporal resolution of 12 seconds over a period of 3 hours, the in vivo contribution of spontaneous SDs to the development of ischemic tissue injury was examined in 8 rats using a thromboembolic stroke model. During the observation period, the initial lesion volume increased in 4 animals, remained unchanged in 1 animal, and decreased in 3 animals (most likely because of spontaneous clot lysis). Irrespective of the lesion evolution patterns, animals demonstrated 6.5 +/- 2.1 spontaneous SDs outside of the ischemic core. A time-to-peak analysis of apparent diffusion coefficient (ADC) changes for each SD wave demonstrated multidirectional propagation patterns from variable initiation sites. Maps of the time constants of ADC recovery, reflecting the local energy supply and cerebral blood flow, revealed prolonged recovery times in areas close to the ischemic core. However, repetitive SD episodes in the periinfarct tissue did not eventually lead to permanent ADC reductions. These results suggest that spontaneous SD waves do not necessarily contribute to the expansion of the ischemic lesion volume in this model.

Role of NMDA receptor signaling in the regulation of inflammatory gene expression after focal brain ischemia

Inflammatory mediators are involved in the pathogenesis of focal ischemic brain damage. In this study we used quantitative reverse transcriptase-polymerase chain reaction to analyze the spatiotemporal pattern of tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), and inducible nitric oxide synthase (iNOS) expression in focal ischemia of the rat brain. Focal ischemia of the rat parietal cortex was induced noninvasively by photothrombosis of cortical microvessels. In a proportion of the animals NMDA receptor signaling was blocked by the noncompetitive receptor antagonist MK-801. Within 4 h after ischemia we found induction of TNF-alpha and IL-1beta mRNA not only in the infarcts but also in all representative tissue samples removed from noninfarcted frontal, lateral, and occipital cortex of the ipsilateral, but not contralateral hemisphere. Contrastingly, the expression of iNOS mRNA remained restricted to the evolving infarcts. Pretreatment with MK-801 strongly inhibited remote cytokine expression (mean reduction by 80% relative to vehicle treated animals at 4 h; P<0.001) whereas in the lesions only partial reductions in the expression of IL-1beta and iNOS mRNA were found. Our data for the first time demonstrate remote cytokine induction following focal brain ischemia and suggest that NMDA receptor-mediated signaling can activate inflammatory gene expression independently from the occurrence of neuronal cell death.

Hyperbaric oxygen reduces infarct volume in rats by increasing oxygen supply to the ischemic periphery

OBJECTIVE

Hyperbaric oxygen (HBO) increases oxygen supply to anoxic areas. To examine the therapeutic effect of HBO on ischemic stroke, we measured infarct volume as well as cerebral blood flow (CBF), oxygen supply, and lipid peroxidation in the ischemic periphery.

DESIGN

Prospective experimental study in rats.

SETTING

Experimental laboratory in a university teaching hospital.

SUBJECTS

Thirty-eight adult rats.

INTERVENTION

The rats were anesthetized (1% halothane) and intubated. Focal ischemia was induced by ligating the right middle cerebral and right common carotid arteries. Nineteen animals were exposed to 2 hrs of HBO (100% oxygen, 3 atmospheres absolute), initiated 10 mins after the onset of ischemia. The remaining animals were kept at ambient pressure and used as controls.

MEASUREMENTS AND MAIN RESULTS

At the initiation of ischemia, CBF measured by a laser-Doppler flow probe placed in the ischemic periphery was reduced to 47%+/-11% and 51%+/-15% of normal levels in animals exposed or not to HBO, respectively. These altered values were not affected further by administration of HBO and remained stable throughout a 2-hr observation period. Arterial oxygen pressure and content were significantly increased to 1571+/-130 torr (209.41+/-17.32 kPa; p < .0001) and 1.03+/-0.04 mmol/dL (p < 0.0001), respectively, in HBO-treated animals compared with nontreated animals (139+/-14 torr [18.53+/-1.87 kPa] and 0.86+/-0.04 mmol/dL, respectively). The calculated increase in the oxygen supply to the ischemic periphery was 20%. The infarct volume of HBO-treated animals measured 24 hrs after the onset of focal cerebral ischemia was significantly reduced by 18% (HBO-treated, 132+/-13 mm3 vs. nontreated, 161+/-29 mm3; p = .02). Lipid peroxidation was unchanged after 120 mins of HBO administration in the cerebral cortex where the laser-Doppler flow probe was placed.

CONCLUSIONS

HBO at 3 atmospheres absolute reduced infarct volume by increasing oxygen supply to the ischemic periphery without aggravating lipid peroxidation, suggesting that HBO can be useful in treating stroke victims.

Effects of single and repetitive spreading depression on cerebral blood flow and glucose metabolism in cats: a PET study

To clarify the effects of spreading depression (SD) on cerebral circulation and metabolism, we elicited a single or repetitive episode of SD and evaluated CBF and CMRglc three-dimensionally in normal cats (n=4, in each group) using a high-resolution positron emission tomography (PET) scanner. SD was evoked by applying KCl to the left occipital cortex. We then monitored DC potential changes with tungsten electrodes inserted into the left temporal cortex. CBF was measured twice before and three times (immediately, 30-60 min, and 60-120 min) following KCl application using [15O]H(2)O, and CMRglc was determined using 2-[18F]fluoro-2-deoxy-D-glucose immediately following the last CBF measurement. The following results were obtained: (1) a single episode of SD produced a temporary CBF increase, followed by a long-lasting hypoperfusion in the cortex, with no significant changes to CBF observed in the subcortex; (2) no significant CMRglc changes were observed in either cortical or subcortical regions following a single episode of SD; (3) a flow-metabolism uncoupling was observed in the cortical regions concurrently with persistent hypoperfusion; (4) repetitive SD produced significant CBF changes in the cortex; and (5) the cortical CMRglc increased as a result of repeated episodes of SD, with no significant changes observed in the subcortex. Thus, we succeeded in determining three-dimensionally the effects of single and repetitive SD on CBF and CMRglc in cats using a high-resolution PET scanner. The present study provides the first direct evidence of CBF-CMRglc uncoupling occurring concurrently with persistent hypoperfusion following SD.

Thromboembolic events lead to cortical spreading depression and expression of c-fos, brain-derived neurotrophic factor, glial fibrillary acidic protein, and heat shock protein 70 mRNA in rats

The hypotheses that cerebral embolic events lead to repetitive episodes of cortical spreading depression (CSD) and that these propagating waves trigger the expression of c-fos, brain-derived neurotrophic factor (BDNF), glial fibrillary acidic protein (GFAP), and heat shock protein 70 (HSP70) mRNA were tested. Wistar rats underwent photochemically induced right common carotid artery thrombosis (CCAT) (n = 18) or sham (n = 8) procedures. In a subgroup of rats (n = 5), laser-Doppler flowmetry probes were placed overlying the right parietal cortex to record CSD-like changes in cortical blood flow during the initial 2-hour postinjury period. Rats were killed by decapitation at 2 or 24 hours after CCAT, and brains were processed for in situ localization of the gene expression. Two to five intermittent transient hyperemic episodes lasting 1 to 2 minutes were recorded ipsilaterally after CCAT. At 2 hours after CCAT, the widespread expression of c-fos and BDNF mRNAs was observed throughout the ipsilateral cerebral cortex. Pretreatment with the N-methyl-D-aspartate receptor blocker MK-801 (2 mg/kg) 1 hour before CCAT reduced the expression of BDNF mRNA expression at 2 hours. At 24 hours after CCAT, increased expression of GFAP mRNA was present in cortical and subcortical regions. In contrast, multifocal regions of HSP70 expression scattered throughout the thrombosed hemisphere were apparent at both 2 and 24 hours after injury. These data indicate that thromboembolic events lead to episodes of CSD and time-dependent alterations in gene expression. The ability of embolic processes to induce widespread molecular responses in neurons and glia may be important in the pathogenesis of transient ischemic attacks and may influence the susceptibility of the postembolic brain to subsequent insults including stroke.

Prolonged induction of neuronal NOS expression and activity following cortical spreading depression (SD): implications for SD- and NO-mediated neuroprotection

Cortical spreading depression (CSD) is associated with various short- and long-term physiological and neurochemical changes and has been shown to confer an increased susceptibility to accompanying ischemic injury or provide protection against a subsequent experimental ischemia. Nitric oxide is involved in the processes of ischemic injury and under certain conditions mediates cellular protection. To investigate the possibility that CSD-induced alterations in nitric oxide synthase (NOS) expression and activity occur and might be associated with the time-dependent enhancement or prevention by CSD of ischemic damage, this study examined the spatiotemporal changes in nNOS expression and activity in cerebral cortex following CSD. Anesthetized rats had unilateral CSD induced by a 10-min topical application of KCl and were killed at various times thereafter. CSD increased both nNOS mRNA and protein levels throughout layers II-III of cortex. nNOS mRNA in the affected neocortex was significantly increased by 30-90% at 2, 7, and 14 days (P < or = 0.05) compared with contralateral levels, but was not significantly above control values at 1-6 h, 1 day, and 28 days after CSD induction. Levels of [3H]-L-N(G)-nitroarginine binding to NOS were increased by 40-170% 7, 14, and 28 days (P < or = 0.01) after CSD in a similar, but delayed, profile to nNOS mRNA. Levels of nNOS-immunoreactivity were also increased in both neurons and astrocytes of ipsilateral cortex 7 and 14 days after CSD--confirmed by double-immunofluorescence localization. Ex vivo NOS activity in layers I-III of ipsilateral cortex was also increased by 30-50% (P < or = 0.01) at 7 and 14 days after CSD, times coincident with reported maximal ischemic protection. These results demonstrate that nNOS is up-regulated by cellular depolarization/depression occurring during CSD, or by resultant stimuli and suggest that "CSD-conditioned" cortex may be capable of producing appropriate levels of NO to mediate or contribute to protective/adaptive responses to subsequent physical ischemic injury.

Mild hypothermia improves recovery of cortical extracellular potassium ion activity and excitability after middle cerebral artery occlusion in the rat

BACKGROUND AND PURPOSE

Mild brain hypothermia significantly alleviates damage after focal ischemia, although the mechanism of this protection remains poorly defined. In the present study, we tested the hypothesis that mild hypothermia would protect cortex from early deterioration of ion homeostasis and loss of excitability associated with reperfusion after focal ischemia.

METHODS

Cortical extracellular potassium ion activity ([K+]o) and the response of [K+]o to direct cortical stimulation was measured both in the ischemic core and in the ischemic penumbra of normothermic and mildly hypothermic (31.5 degrees C to 32 degrees C) rats after distal middle cerebral artery occlusion (MCAO) and reperfusion.

RESULTS

The response of [K+]o during MCAO was similar in normothermic and hypothermic animals. However, within 1 hour of reperfusion, [K+]o in the ischemic core region of normothermic animals showed incomplete recovery and was refractory to direct cortical stimulation. [K+]o in hypothermic animals returned to preischemic levels on reperfusion and continued to respond to direct cortical stimulation. Mild hypothermia prevented extensive infarction 24 hours after transient MCAO.

CONCLUSIONS

The data suggest that transient focal ischemia is accompanied by early disturbances of potassium ion homeostasis during reperfusion, which are accompanied by loss of excitability and which may contribute ultimately to cortical infarction.

Widespread up-regulation of N-methyl-D-aspartate receptors after focal photothrombotic lesion in rat brain

Following focal brain lesions, complex adaptive processes take place in remote intact areas. The present study examines changes in NMDA (N-methyl-D-aspartate), AMPA ((+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid) and kainate receptors following focal photothrombotic ischemic lesions using quantitative receptor autoradiography. Increases in binding density of NMDA receptors were seen in both hemispheres for up to 30 days. In the contralateral hemisphere, this increase of NMDA receptors occurred as early as 4 h after lesion whereas it appeared with a delay for 14 days on the lesioned side. Binding density of [3H]AMPA and [3H]kainate was unchanged. We suggest that the translational process is differentially regulated by spreading depressions. The delayed up-regulation of NMDA receptor binding on the lesioned side may be due to a translation block similar to that previously described for GABA(A) receptor subunits.

Experimental therapy of a platelet-activating factor antagonist (ginkgolide B) on photochemically induced thrombotic cerebral ischaemia in tree shrews

1. The aim of the present study was to investigate the effects of a platelet-activating factor (PAF) antagonist (ginkgolide B; GB) on brain oedema, ion homeostasis, monoamine neurotransmitter disturbances in ischaemic penumbra and the neuroprotective mechanisms of the PAF antagonist. 2. Photochemically induced thrombotic cerebral ischaemia in tree shrews was used as the experimental model and changes in histopathology and the content of monoamine neurotransmitters (measured by a spectrofluorometer), water content (measured by a specific gravimetric method), sodium and calcium (measured by an atomic absorption spectrophotometer) in the penumbra were observed. 3. Results show that content of noradrenaline (NA), dopamine (DA) and 5-hydroxytryptamine (5-HT) decreased in the penumbra, while 5-HT metabolite 5-hydroxyindole-3-acetic acid, sodium, calcium and water contents increased markedly (P < 0.01) after photochemical reaction. 4. In tree shrews treated with GB (5 mg/kg, i.v.) 6 h after photochemical reaction, cortical NA, DA and 5-HT contents recovered to control levels and water and calcium contents decreased significantly (P < 0.01). 5. The results suggest that PAF may play an important role in inducing calcium overload, brain oedema and secondary brain damage in penumbra and that GB produces its neuroprotective effects by inhibiting the pathological manifestation of PAF.