Neuronal ischemic injury: light microscopy, ultrastructure and biochemistry

Emerging Treatment Strategies for Cerebral Ischemia-Reperfusion Injury

Cerebral ischemia-reperfusion injury (CI/RI) injury is a common feature of ischemic stroke which occurs when the blood supply is restored after a period of ischemia in the brain. Reduced blood-flow to the brain during CI/RI compromises neuronal cell health as a result of mitochondrial dysfunction, oxidative stress, cytokine production, inflammation and tissue damage. Reperfusion therapy during CI/RI can restore the blood flow to ischemic regions of brain which are not yet infarcted. The long-term goal of CI/RI therapy is to reduce stroke-related neuronal cell death, disability and mortality. A range of drug and interventional therapies have emerged that can alleviate CI/RI mediated oxidative stress, inflammation and apoptosis in the brain. Herein, we review recent studies on CI/RI interventions for which a mechanism of action has been described and the potential of these therapeutic modalities for future use in the clinic.

Mitochondrial fission and mitophagy are independent mechanisms regulating ischemia/reperfusion injury in primary neurons

Mitochondrial dynamics and mitophagy are constitutive and complex systems that ensure a healthy mitochondrial network through the segregation and subsequent degradation of damaged mitochondria. Disruption of these systems can lead to mitochondrial dysfunction and has been established as a central mechanism of ischemia/reperfusion (I/R) injury. Emerging evidence suggests that mitochondrial dynamics and mitophagy are integrated systems; however, the role of this relationship in the context of I/R injury remains unclear. To investigate this concept, we utilized primary cortical neurons isolated from the novel dual-reporter mitochondrial quality control knockin mice (C57BL/6-Gt(ROSA)26Sortm1(CAG-mCherry/GFP)Ganl/J) with conditional knockout (KO) of Drp1 to investigate changes in mitochondrial dynamics and mitophagic flux during in vitro I/R injury. Mitochondrial dynamics was quantitatively measured in an unbiased manner using a machine learning mitochondrial morphology classification system, which consisted of four different classifications: network, unbranched, swollen, and punctate. Evaluation of mitochondrial morphology and mitophagic flux in primary neurons exposed to oxygen-glucose deprivation (OGD) and reoxygenation (OGD/R) revealed extensive mitochondrial fragmentation and swelling, together with a significant upregulation in mitophagic flux. Furthermore, the primary morphology of mitochondria undergoing mitophagy was classified as punctate. Colocalization using immunofluorescence as well as western blot analysis revealed that the PINK1/Parkin pathway of mitophagy was activated following OGD/R. Conditional KO of Drp1 prevented mitochondrial fragmentation and swelling following OGD/R but did not alter mitophagic flux. These data provide novel evidence that Drp1 plays a causal role in the progression of I/R injury, but mitophagy does not require Drp1-mediated mitochondrial fission.

Differential Age-Dependent Mitochondrial Dysfunction, Oxidative Stress, and Apoptosis Induced by Neonatal Hypoxia-Ischemia in the Immature Rat Brain

Neonatal hypoxia-ischemia (HI) is among the main causes of mortality and morbidity in newborns. Experimental studies show that the immature rat brain is less susceptible to HI injury, suggesting that changes that occur during the first days of life drastically alter its susceptibility. Among the main developmental changes observed is the mitochondrial function, namely, the tricarboxylic acid (TCA) cycle and respiratory complex (RC) activities. Therefore, in the present study, we investigated the influence of neonatal HI on mitochondrial functions, redox homeostasis, and cell damage at different postnatal ages in the hippocampus of neonate rats. For this purpose, animals were divided into four groups: sham postnatal day 3 (ShP3), HIP3, ShP11, and HIP11. We initially observed increased apoptosis in the HIP11 group only, indicating a higher susceptibility of these animals to brain injury. Mitochondrial damage, as determined by flow cytometry showing mitochondrial swelling and loss of mitochondrial membrane potential, was also demonstrated only in the HIP11 group. This was consistent with the decreased mitochondrial oxygen consumption, reduced TCA cycle enzymes, and RC activities and induction of oxidative stress in this group of animals. Considering that HIP3 and the sham animals showed no alteration of mitochondrial functions, redox homeostasis, and showed no apoptosis, our data suggest an age-dependent vulnerability of the hippocampus to hypoxia-ischemia. The present results highlight age-dependent metabolic differences in the brain of neonate rats submitted to HI indicating that different treatments might be needed for HI newborns with different gestational ages.

A Study of Critical Events That Lead to Spinal Cord Injury and the Importance of Rapid Reversal of Surgical Steps in Improving Neurological Outcomes: A Porcine Model

STUDY DESIGN

Porcine model.

OBJECTIVE

To quantify critical vascular and mechanical events that occur before and during an evolving spinal cord injury.

SUMMARY OF BACKGROUND DATA

Spinal cord injuries are one of the most devastating complications in spine surgery. Intraoperative neuromonitoring changes can occur as a secondary event of spinal cord compression and decrease in spinal cord blood flow (SCBF). Laser Doppler flowmetry has been well validated for measuring blood flow.

METHODS

Seventeen pigs were studied, 14 of which completed the experiment. Multilevel, midthoracic laminectomies were performed. Laser Doppler flowmetry electrodes were placed on the dura to measure SCBF. Spinal cord injury was induced by incremental balloon inflation in the epidural space. The animals were separated into two groups. After motor-evoked potential (MEP) loss, group A underwent medical interventions and then balloon decompression approximately 20 minutes later. Group B underwent immediate balloon decompression followed by medical interventions. After interventions, wake-up test was performed and computed tomography scan measured thoracic spinal canal volume.

RESULTS

Median SCBF changes were seen 15.8 (5.4-25.1) minutes before MEP loss. However, the 20% threshold interval was often reached before. At the 20% threshold, median pressure was 7 psi, balloon volume was 0.5 cm, and 50% of the spinal canal was compromised. In group A, no pigs moved and all had pathology indicating ischemia. In group B, 9 of 10 were found to be moving their hind legs with 7 indicating ischemia.

CONCLUSION

Compression spinal cord injury is the end of a cascade involving increasing intracanal pressure, decreasing canal volume, and hypoperfusion. Rapid relief of compression leads to MEP return. SCBF monitoring can detect ischemia preinjury, giving surgeons an opportunity for early intervention.

LEVEL OF EVIDENCE

4.

Nuclear expansion and pore opening are instant signs of neuronal hypoxia and can identify poorly fixed brains

The initial phase of neuronal death is not well characterized. Here, we show that expansion of the nuclear membrane without losing its integrity along with peripheralization of chromatin are immediate signs of neuronal injury. Importantly, these changes can be identified with commonly used nuclear stains and used as markers of poor perfusion-fixation. Although frozen sections are widely used, no markers are available to ensure that the observed changes were not confounded by perfusion-induced hypoxia/ischemia. Moreover, HMGB1 was immediately released and p53 translocated to mitochondria in hypoxic/ischemic neurons, whereas nuclear pore complex inhibitors prevented the nuclear changes, identifying novel neuroprotection targets.

Histology of Brain Trauma and Hypoxia-Ischemia

Forensic pathologists encounter hypoxic-ischemic (HI) brain damage or traumatic brain injuries (TBI) on an almost daily basis. Evaluation of the findings guides decisions regarding cause and manner of death. When there are gross findings of brain trauma, the cause of death is often obvious. However, microscopic evaluation should be used to augment the macroscopic diagnoses. Histology can be used to seek evidence for TBI in the absence of gross findings, e.g., in the context of reported or suspected TBI. Estimating the survival interval after an insult is often of medicolegal interest; this requires targeted tissue sampling and careful histologic evaluation. Retained tissue blocks serve as forensic evidence and also provide invaluable teaching and research material. In certain contexts, histology can be used to demonstrate nontraumatic causes of seemingly traumatic lesions. Macroscopic and histologic findings of brain trauma can be confounded by concomitant HI brain injury when an individual survives temporarily after TBI. Here we review the histologic approaches for evaluating TBI, hemorrhage, and HI brain injury. Amyloid precursor protein (APP) immunohistochemistry is helpful for identifying damaged axons, but patterns of damage cannot unambiguously distinguish TBI from HI. The evolution of hemorrhagic lesions will be discussed in detail; however, timing of any lesion is at best approximate. It is important to recognize artifactual changes (e.g., dark neurons) that can resemble HI damage. Despite the shortcomings, histology is a critical adjunct to the gross examination of brains.

Ultrastructural Characteristics of Neuronal Death and White Matter Injury in Mouse Brain Tissues After Intracerebral Hemorrhage: Coexistence of Ferroptosis, Autophagy, and Necrosis

Although intracerebral hemorrhage (ICH) is a devastating disease worldwide, the pathologic changes in ultrastructure during the acute and chronic phases of ICH are poorly described. In this study, transmission electron microscopy was used to examine the ultrastructure of ICH-induced pathology. ICH was induced in mice by an intrastriatal injection of collagenase. Pathologic changes were observed in the acute (3 days), subacute (6 days), and chronic (28 days) phases. Compared with sham animals, we observed various types of cell death in the injured striatum during the acute phase of ICH, including necrosis, ferroptosis, and autophagy. Different degrees of axon degeneration in the striatum were seen in the acute phase, and axonal demyelination was observed in the ipsilateral striatum and corpus callosum at late time points. In addition, phagocytes, resident microglia, and infiltrating monocyte-macrophages were present around red blood cells and degenerating neurons and were observed to engulf red blood cells and other debris. Many synapses appeared abnormal or were lost. This systematic analysis of the pathologic changes in ultrastructure after ICH in mice provides information that will be valuable for future ICH pathology studies.

Reversible Disruption of Neuronal Mitochondria by Ischemic and Traumatic Injury Revealed by Quantitative Two-Photon Imaging in the Neocortex of Anesthetized Mice

Mitochondria play a variety of functional roles in cortical neurons, from metabolic support and neuroprotection to the release of cytokines that trigger apoptosis. In dendrites, mitochondrial structure is closely linked to their function, and fragmentation (fission) of the normally elongated mitochondria indicates loss of their function under pathological conditions, such as stroke and brain trauma. Using in vivo two-photon microscopy in mouse brain, we quantified mitochondrial fragmentation in a full spectrum of cortical injuries, ranging from severe to mild. Severe global ischemic injury was induced by bilateral common carotid artery occlusion, whereas severe focal stroke injury was induced by Rose Bengal photosensitization. The moderate and mild traumatic injury was inflicted by focal laser lesion and by mild photo-damage, respectively. Dendritic and mitochondrial structural changes were tracked longitudinally using transgenic mice expressing fluorescent proteins localized either in cytosol or in mitochondrial matrix. In response to severe injury, mitochondrial fragmentation developed in parallel with dendritic damage signified by dendritic beading. Reconstruction from serial section electron microscopy confirmed mitochondrial fragmentation. Unlike dendritic beading, fragmentation spread beyond the injury core in focal stroke and focal laser lesion models. In moderate and mild injury, mitochondrial fragmentation was reversible with full recovery of structural integrity after 1-2 weeks. The transient fragmentation observed in the mild photo-damage model was associated with changes in dendritic spine density without any signs of dendritic damage. Our findings indicate that alterations in neuronal mitochondria structure are very sensitive to the tissue damage and can be reversible in ischemic and traumatic injuries.

SIGNIFICANCE STATEMENT

During ischemic stroke or brain trauma, mitochondria can either protect neurons by supplying ATP and adsorbing excessive Ca²⁺, or kill neurons by releasing proapoptotic factors. Mitochondrial function is tightly linked to their morphology: healthy mitochondria are thin and long; dysfunctional mitochondria are thick (swollen) and short (fragmented). To date, fragmentation of mitochondria was studied either in dissociated cultured neurons or in brain slices, but not in the intact living brain. Using real-time in vivo two-photon microscopy, we quantified mitochondrial fragmentation during acute pathological conditions that mimic severe, moderate, and mild brain injury. We demonstrated that alterations in neuronal mitochondria structural integrity can be reversible in traumatic and ischemic injuries, highlighting mitochondria as a potential target for therapeutic interventions.

The Role of the PI3K Pathway in the Regeneration of the Damaged Brain by Neural Stem Cells after Cerebral Infarction

Neurologic deficits resulting from stroke remain largely intractable, which has prompted thousands of studies aimed at developing methods for treating these neurologic sequelae. Endogenous neurogenesis is also known to occur after brain damage, including that due to cerebral infarction. Focusing on this process may provide a solution for treating neurologic deficits caused by cerebral infarction. The phosphatidylinositol-3-kinase (PI3K) pathway is known to play important roles in cell survival, and many studies have focused on use of the PI3K pathway to treat brain injury after stroke. Furthermore, since the PI3K pathway may also play key roles in the physiology of neural stem cells (NSCs), eliciting the appropriate activation of the PI3K pathway in NSCs may help to improve the sequelae of cerebral infarction. This review describes the PI3K pathway, its roles in the brain and NSCs after cerebral infarction, and the therapeutic possibility of activating the pathway to improve neurologic deficits after cerebral infarction.

Xiao-Xu-Ming decoction preserves mitochondrial integrity and reduces apoptosis after focal cerebral ischemia and reperfusion via the mitochondrial p53 pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Xiao-Xu-Ming decoction (XXMD) has been used to treat stroke and other neurological diseases for more than 1000 years. The purpose of this study was to investigate the effects of XXMD on mitochondrial damage and apoptosis after cerebral ischemia and reperfusion.

MATERIALS AND METHODS

Male Sprague-Dawley rats were randomly divided into 3 groups: sham, cerebral ischemia and reperfusion (I/R), and cerebral ischemia and reperfusion plus XXMD (60 g/kg/day) (XXMD60). Focal cerebral ischemia and reperfusion models were induced by middle cerebral artery occlusion. Cerebral ischemic injury was evaluated by hematoxylin and eosin staining. Ultrastructural features of mitochondria in the penumbra of the ischemic cortex were analyzed by transmission electron microscopy. Apoptosis was evaluated by terminal deoxynucleotidyl transferase-mediated deoxyuridine 5-triphosphate nick end labeling (TUNEL) staining and cleaved caspase 3 immunohistochemistry. Proteins in the mitochondrial p53 pathway were detected by western blot and immunofluorescence.

RESULTS

The results showed that XXMD treatment markedly attenuated ischemic changes, preserved mitochondrial integrity, and significantly reduced apoptosis. In addition, we found that XXMD treatment reduced p53 and Bax levels and increased Bcl-2 levels in mitochondrial fractions. XXMD significantly blocked the release of cytochrome c and Smac/Diablo from mitochondria, and inhibited activation of caspase 9 and caspase 3 in cytoplasmic fractions. Increased expression of c-IAP1 was observed in the XXMD60 group.

CONCLUSIONS

The findings demonstrated that XXMD protected mitochondria from ischemic injury and inhibited apoptosis. The mitochondrial p53 pathway could be partially involved in the protective effects.

The effects of propofol on mitochondrial dysfunction following focal cerebral ischemia-reperfusion in rats

Propofol has been shown to attenuate brain injury in experimental ischemia models, but few studies have focused on the direct effect of propofol on mitochondrial dysfunction. In this study, we observed the effects of propofol on multiple aspects of mitochondrial dysfunction by studying the mitochondria isolated from rat brains subjected to focal cerebral ischemia-reperfusion. The mitochondria of the cortical tissue were isolated by the Percoll density gradient centrifugation. The isolated mitochondria were fixed and examined with electron microscopy. The calcium-induced mitochondrial swelling was quantified by measuring the decrease in light transmission at 540 nm with a spectrometer. Fluorescent probes were used to selectively stain mitochondria. Flow cytometry was used to measure the membrane potential and the production of reactive oxidative species. Propofol improved the signs of injury in the cortical mitochondria that were exposed to reperfusion following 2 h of focal ischemia. Propofol prevented calcium-induced mitochondrial swelling in a concentration-dependent manner. It did not affect the reperfusion-induced reduction in mitochondrial membrane potential. However, it decreased the production of the mitochondrial reactive oxidative species, which are generated during reperfusion. These results demonstrate that propofol may protect against mitochondrial dysfunction by preventing the ultrastructural change to the mitochondria and the calcium-induced mitochondrial swelling. This protective effect may be mediated by inhibiting the mitochondrial membrane permeability transition and reducing the production of reactive oxidative species in mitochondria.

TWEAK/Fn14 pathway modulates properties of a human microvascular endothelial cell model of blood brain barrier

BACKGROUND

The TNF ligand family member TWEAK exists as membrane and soluble forms and is involved in the regulation of various human inflammatory pathologies, through binding to its main receptor, Fn14. We have shown that the soluble form of TWEAK has a pro-neuroinflammatory effect in an animal model of multiple sclerosis and we further demonstrated that blocking TWEAK activity during the recruitment phase of immune cells across the blood brain barrier (BBB) was protective in this model. It is now well established that endothelial cells in the periphery and astrocytes in the central nervous system (CNS) are targets of TWEAK. Moreover, it has been shown by others that, when injected into mice brains, TWEAK disrupts the architecture of the BBB and induces expression of matrix metalloproteinase-9 (MMP-9) in the brain. Nevertheless, the mechanisms involved in such conditions are complex and remain to be explored, especially because there is a lack of data concerning the TWEAK/Fn14 pathway in microvascular cerebral endothelial cells.

METHODS

In this study, we used human cerebral microvascular endothelial cell (HCMEC) cultures as an in vitro model of the BBB to study the effects of soluble TWEAK on the properties and the integrity of the BBB model.

RESULTS

We showed that soluble TWEAK induces an inflammatory profile on HCMECs, especially by promoting secretion of cytokines, by modulating production and activation of MMP-9, and by expression of cell adhesion molecules. We also demonstrated that these effects of TWEAK are associated with increased permeability of the HCMEC monolayer in the in vitro BBB model.

CONCLUSIONS

Taken together, the data suggest a role for soluble TWEAK in BBB inflammation and in the promotion of BBB interactions with immune cells. These results support the contention that the TWEAK/Fn14 pathway could contribute at least to the endothelial steps of neuroinflammation.

Reperfusion promotes mitochondrial dysfunction following focal cerebral ischemia in rats

BACKGROUND AND PURPOSE

Mitochondrial dysfunction has been implicated in the cell death observed after cerebral ischemia, and several mechanisms for this dysfunction have been proposed. Reperfusion after transient cerebral ischemia may cause continued and even more severe damage to the brain. Many lines of evidence have shown that mitochondria suffer severe damage in response to ischemic injury. The purpose of this study was to observe the features of mitochondrial dysfunction in isolated mitochondria during the reperfusion period following focal cerebral ischemia.

METHODS

Male Wistar rats were subjected to focal cerebral ischemia. Mitochondria were isolated using Percoll density gradient centrifugation. The isolated mitochondria were fixed for electron microscopic examination; calcium-induced mitochondrial swelling was quantified using spectrophotometry. Cyclophilin D was detected by Western blotting. Fluorescent probes were used to selectively stain mitochondria to measure their membrane potential and to measure reactive oxidative species production using flow cytometric analysis.

RESULTS

Signs of damage were observed in the mitochondrial morphology after exposure to reperfusion. The mitochondrial swelling induced by Ca(2+) increased gradually with the increasing calcium concentration, and this tendency was exacerbated as the reperfusion time was extended. Cyclophilin D protein expression peaked after 24 hours of reperfusion. The mitochondrial membrane potential was decreased significantly during the reperfusion period, with the greatest decrease observed after 24 hours of reperfusion. The surge in mitochondrial reactive oxidative species occurred after 2 hours of reperfusion and was maintained at a high level during the reperfusion period.

CONCLUSIONS

Reperfusion following focal cerebral ischemia induced significant mitochondrial morphological damage and Ca(2+)-induced mitochondrial swelling. The mechanism of this swelling may be mediated by the upregulation of the Cyclophilin D protein, the destruction of the mitochondrial membrane potential and the generation of excessive reactive oxidative species.

LDL receptor-related protein 1: unique tissue-specific functions revealed by selective gene knockout studies

The LDL receptor-related protein (originally called LRP, but now referred to as LRP1) is a large endocytic receptor that is widely expressed in several tissues. LRP1 is a member of the LDL receptor family that plays diverse roles in various biological processes including lipoprotein metabolism, degradation of proteases, activation of lysosomal enzymes, and cellular entry of bacterial toxins and viruses. Deletion of the LRP1 gene leads to lethality in mice, revealing a critical, but as of yet, undefined role in development. Tissue-specific gene deletion studies reveal an important contribution of LRP1 in the vasculature, central nervous system, macrophages, and adipocytes. Three important properties of LRP1 dictate its diverse role in physiology: 1) its ability to recognize more than 30 distinct ligands, 2) its ability to bind a large number of cytoplasmic adaptor proteins via determinants located on its cytoplasmic domain in a phosphorylation-specific manner, and 3) its ability to associate with and modulate the activity of other transmembrane receptors such as integrins and receptor tyrosine kinases.

TWEAK-Fn14 pathway inhibition protects the integrity of the neurovascular unit during cerebral ischemia

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is a member of the tumor necrosis factor superfamily. TWEAK acts via binding to a cell surface receptor named Fn14. To study the role of this cytokine in the regulation of the permeability of the neurovascular unit (NVU) during cerebral ischemia, TWEAK activity was inhibited in wild-type mice with a soluble Fn14-Fc decoy receptor administered either immediately or 1 h after middle cerebral artery occlusion (MCAO). Administration of Fn14-Fc decoy resulted in faster recovery of motor function and a 66.4%+/-10% decrease in Evans blue dye extravasation when treatment was administered immediately after MCAO and a 46.1%+/-13.1% decrease when animals were treated 1 h later (n=4, P<0.05). Genetic deficiency of Fn14 resulted in a 60%+/-12.8% decrease in the volume of the ischemic lesion (n=6, P<0.05), and a 87%+/-22% inhibition in Evans blue dye extravasation 48 h after the onset of the ischemic insult (n=6, P<0.005). Compared with control animals, treatment with Fn14-Fc decoy or genetic deficiency of Fn14 also resulted in a significant inhibition of nuclear factor-kappaB pathway activation, matrix metalloproteinase-9 activation and basement membrane laminin degradation after MCAO. These findings show that the cytokine TWEAK plays a role in the disruption of the structure of the NVU during cerebral ischemia and that TWEAK antagonism is a potential therapeutic strategy for acute cerebral ischemia.

Tissue-type plasminogen activator-mediated shedding of astrocytic low-density lipoprotein receptor-related protein increases the permeability of the neurovascular unit

The low-density lipoprotein receptor-related protein (LRP) is a member of the LDL receptor gene family that binds several ligands, including tissue-type plasminogen activator (tPA). tPA is found in blood, where its primary function is as a thrombolytic enzyme, and in the central nervous system where it mediates events associated with cell death. Cerebral ischemia induces changes in the neurovascular unit (NVU) that result in brain edema. We investigated whether the interaction between tPA and LRP plays a role in the regulation of the permeability of the NVU during cerebral ischemia. We found that the ischemic insult induces shedding of LRP's ectodomain from perivascular astrocytes into the basement membrane. This event associates with the detachment of astrocytic end-feet processes and the formation of areas of perivascular edema. The shedding of LRP's ectodomain is significantly decreased in tPA deficient (tPA(-/-)) mice, is increased by incubation with tPA, and is inhibited by the receptor-associated protein (RAP). Furthermore, treatment with either RAP or anti-LRP IgG results in a faster recovery of motor activity and protection of the integrity of the NVU following middle cerebral artery occlusion (MCAO). Together, these results implicate tPA/LRP interactions as key regulators of the integrity of the NVU.

Time profile of eosinophilic neurons in the cortical layers and cortical atrophy

Eosinophilic neurons (ENs) appear in the post-ischemic cortex; however, whether there are differences in the time profile for different cortical layers and the fate of the cortex with ENs is largely unknown. We examined the time profile of ENs in different cortical layers and evolution of cortical atrophy after transient cerebral ischemia in Mongolian gerbils. Unilateral forebrain ischemia was induced twice by 10-minute unilateral common carotid artery occlusions. Brains at 24 hours, 4 days, and 2, 4, and 16 weeks post-ischemia were prepared for morphometric analysis. Quantitative analysis of ENs in regions of interest in the rostral and caudal cortex showed the highest number of ENs at 4 days post-ischemia in layers 3 and 6. Reduction in ENs after this peak was slower in layer 6 than in layer 3 in both rostral and caudal cortex, and this difference was significant in layer 6 of the caudal cortex. Infarcts with significant atrophy appeared in the rostral cortex. In the caudal cortex, only selective neuronal death with mild but distinct atrophy was observed. We observed a significant difference between cortical layers in the time profile of ENs in the post-ischemic cortex. Selective neuronal death without infarction was sufficient to induce cortical atrophy after transient cerebral ischemia.

Tumor necrosis factor-like weak inducer of apoptosis increases the permeability of the neurovascular unit through nuclear factor-kappa B pathway activation

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is a member of the tumor necrosis factor superfamily. TWEAK acts on responsive cells via binding to a small cell-surface receptor named fibroblast growth factor-inducible-14 (Fn14). TWEAK can stimulate numerous cellular responses including cell proliferation, migration, and proinflammatory molecule production. The present study investigated whether TWEAK plays a role in the regulation of the permeability of the neurovascular unit (NVU). We found that intracerebral injection of TWEAK in wild-type mice induces activation of the nuclear factor-kappaB (NF-kappaB) pathway and matrix metalloproteinase-9 (MMP-9) expression in the brain with resultant disruption in the structure of the NVU and increase in the permeability of the blood-brain barrier (BBB). TWEAK did not increase MMP-9 activity or BBB permeability when injected into mice genetically deficient in the NF-kappaB family member p50. Furthermore, we report that inhibition of TWEAK activity during cerebral ischemia with an Fn14-Fc decoy receptor results in significant preservation of the integrity of the NVU with attenuation of cerebral ischemia-induced increase in the permeability of the BBB. We conclude that the cytokine TWEAK plays a role in the disruption of the structure and permeability of the NVU during physiological and pathological conditions.

Transition of areas of eosinophilic neurons and reactive astrocytes to delayed cortical infarcts after transient unilateral forebrain ischemia in Mongolian gerbils

The fate of postischemic tissues containing eosinophilic neurons (ENs), whether they remain viable or evolve into infarction, is largely unknown. We analyzed the time profile and distribution of ENs, reactive astrocytes (RAs), and infarction after transient cerebral ischemia. Unilateral forebrain ischemia was induced in Mongolian gerbils by two 10-min unilateral common carotid artery occlusions with a 5-h interval, and the brains at 24 h, 4 days, and 2, 4, and 16 weeks were prepared for morphometric analysis. Intra-ischemic laser Doppler flowmetry revealed significant ischemia, deeper in the anterior cortex, during carotid occlusion. Here, ENs appeared in the middle and deep layers at 24 h postischemia, and EN areas had extended to all cortical layers by 4 days. Large areas of high EN density turned into infarcts between 4 days and 4 weeks. In the posterior cortex, middle and deep cortical layers evolved low EN density areas without subsequent transformation into infarcts. RAs were consistently observed in areas with ENs, and RA areas with high EN density were largely transformed into infarcts between 4 days and 4 weeks postischemia. Areas of high, but not low, EN density were slowly transformed into infarcts after transient cerebral ischemia. Delayed astrocytic death took place in the RA areas with high EN density. In conclusion, density of ENs is an important indicator of delayed astrocytic death and infarction in postischemic tissue.

Beyond endocytosis: LRP function in cell migration, proliferation and vascular permeability

The low-density lipoprotein (LDL) receptor related protein (LRP1 or LRP) is a large endocytic receptor widely expressed in several tissues and known to play roles in areas as diverse as lipoprotein metabolism, degradation of proteases, activation of lysosomal enzymes and cellular entry of bacterial toxins and viruses. This member of the LDL receptor superfamily is constitutively endocytosed from the membrane and recycled back to the cell surface. Its many functions were long thought to involve its ability to bind over 30 different ligands and deliver them to lysosomes for degradation. However, LRP has since been shown to interact with scaffolding and signaling proteins via its intracellular domain in a phosphorylation-dependent manner and to function as a co-receptor partnering with other cell surface or integral membrane proteins. This multi-talented receptor has been implicated in regulation of platelet derived growth factor receptor activity, integrin maturation and recycling, and focal adhesion disassembly. These functions may account for recent studies identifying LRP's role in protection of the vasculature, regulation of cell migration, and modulation of the integrity of the blood-brain barrier.

Anxious and hyperactive phenotype following brief ischemic episodes in mice

BACKGROUND

Poststroke emotional and behavioral abnormalities have an impact on outcome but have scarcely been characterized in animal models. We tested whether brief ischemic episodes induce behavioral changes in mice.

METHODS

129/Sv mice were subjected to 30-min occlusion of left or right middle cerebral artery (MCAo) followed by reperfusion or sham operation (n = 9 or 10 per group). Eight to ten weeks later, mice were tested for spontaneous locomotor activity, anxiety in the elevated plus maze, and depressive behavior in the modified Porsolt forced swim test. Outcome was correlated to monoamine and amino acid levels and compared with histologic damage at 10 weeks.

RESULTS

Ischemia was associated with increased activity (right MCAo) and anxiety (left MCAo), but not poststroke depression. Noradrenaline increased by 30%-45% in the ischemic striatum and correlated with locomotor activity (r = .48); dopamine and homovanillinic acid were decreased compared with sham. The lesion was confined to the striatum, and scattered neuronal death was observed in a number of remote brain regions.

CONCLUSION

Brief ischemic episodes in the mouse induce an anxious, hyperactive but not depressive phenotype that may relate to left versus right hemispheric lesion location, alterations in brain monoamine levels, and selective neurodegeneration.

Motor skill learning depends on protein synthesis in motor cortex after training

The role of protein synthesis in memory consolidation is well established for hippocampus-dependent learning and synaptic plasticity. Whether protein synthesis is required for motor skill learning is unknown. We hypothesized that skill learning is interrupted by protein synthesis inhibition (PSI). We intended to test whether local protein synthesis in motor cortex or cerebellum is required during skill acquisition and consolidation. Anisomycin (ANI; 100 microg/microl in 1 microl of PBS) injected into motor cortex, posterior parietal cortex, or cerebellum produced 84.0 +/- 1.44% (mean +/- SEM), 85.9 +/- 2.31%, and 87.3 +/- 0.17% of PSI 60 min after administration, respectively. In motor cortex, protein synthesis was still reduced at 24 hr (72.0 +/- 4.68% PSI) but normalized at 48 hr after a second injection given 24 hr after the first. To test for the effects of PSI on learning of a skilled reaching task, ANI was injected into motor cortex contralateral to the trained limb or into ipsilateral cerebellum immediately after daily training sessions 1 and 2. Two control groups received motor cortex injections of vehicle or ANI injections into contralateral parietal cortex. Control and cerebellar animals showed a sigmoid learning curve, which plateaued after day 4. PSI in motor cortex significantly reduced learning during days 1-4. Thereafter, when protein synthesis normalized, learning was reinitiated. ANI injections into motor cortex did not induce a motor deficit, because animals injected during the performance plateau did not deteriorate. This demonstrates that motor skill learning depends on de novo synthesis of proteins in motor cortex after training.

New functions for an old enzyme: nonhemostatic roles for tissue-type plasminogen activator in the central nervous system

Tissue-type plasminogen activator (tPA) is a highly specific serine proteinase that activates the zymogen plasminogen to the broad-specificity proteinase plasmin. Tissue-type plasminogen activator is found not only in the blood, where its primary function is as a thrombolytic enzyme, but also in the central nervous system (CNS), where it promotes events associated with synaptic plasticity and acts as a regulator of the permeability of the neurovascular unit. Tissue-type plasminogen activator has also been associated with pathological events in the CNS such as cerebral ischemia and seizures. Neuroserpin is an inhibitory serpin that reacts preferentially with tPA and is located in regions of the brain where either tPA message or tPA protein are also found, indicating that neuroserpin is the selective inhibitor of tPA in the CNS. There is a growing body of evidence demonstrating the participation of tPA in a number of physiological and pathological events in the CNS, as well as the role of neuroserpin as the natural regulator of tPA's activity in these processes. This review will focus on nonhemostatic roles of tPA in the CNS with emphasis on its newly described function as a regulator of permeability of the neurovascular unit and on the regulatory role of neuroserpin in these events.

Temporal profile of ultrastructural changes in cortical neurons after a photochemical lesion

A photochemical lesion was induced in the right sensory motor cortex of rat brains. We examined at various time points the occurrence of different types of neuronal death with respect to a potential therapeutic window. The lesion appearance was documented by magnetic resonance imaging, and functional recovery was evaluated by behavioral tests showing recovery at 48 hr after lesioning. At 0.5, 1, 3, 6, 12, 24, 48, and 72 hr postlesion, cortical layers IV and V were examined by light and electron microscopy. Ultrastructural changes, which corresponded well to light microscopy findings, were found in both hemispheres. In the lesioned area, the neuropil appeared disorganized at 0.5 hr, and apoptotic and necrotic cell death was found at 0.5-3 hr. After 3 hr, the tissue was disintegrated. On the contralateral side, chromatin clumping appeared at 0.5-3 hr. At 3 hr, ruptured membranes were found, a sign of irreversible cell death. At 6-72 hr, the membranes were intact, and the chromatin was not clumped but heterogeneously distributed. The nuclei contained dispersed nucleoli at 48-72 hr. The morphology correlated well with magnetic resonance images and functional behavior. Our study demonstrates that a photochemical lesion is a useful model for studying morphological changes in injured cells. It results in a permanent infarction within 3 hr. In that the morphology on the contralateral side drastically changed between 3 and 6 hr, the cellular alterations at these time points might represent a break point at which cells either progress toward cell death or recover.

Tissue-type plasminogen activator induces opening of the blood-brain barrier via the LDL receptor-related protein

The regulation of cerebrovascular permeability is critical for normal brain homeostasis, and the "breakdown" of the blood-brain barrier (BBB) is associated with the development of vasogenic edema and intracranial hypertension in a number of neurological disorders. In this study we demonstrate that an increase in endogenous tissue-type plasminogen activator (tPA) activity in the perivascular tissue following cerebral ischemia induces opening of the BBB via a mechanism that is independent of both plasminogen (Plg) and MMP-9. We also show that injection of tPA into the cerebrospinal fluid in the absence of ischemia results in a rapid dose-dependent increase in vascular permeability. This activity is not seen with urokinase-type Plg activator (uPA) but is induced in Plg-/- mice, confirming that the effect is Plg-independent. However, the activity is blocked by antibodies to the LDL receptor-related protein (LRP) and by the LRP antagonist, receptor-associated protein (RAP), suggesting a receptor-mediated process. Together these studies demonstrate that tPA is both necessary and sufficient to directly increase vascular permeability in the early stages of BBB opening, and suggest that this occurs through a receptor-mediated cell signaling event and not through generalized degradation of the vascular basement membrane.

Beneficial effects of systemic administration of recombinant human erythropoietin in rabbits subjected to subarachnoid hemorrhage

Cerebral vasospasm and ischemic damage are important causes of mortality and morbidity in patients affected by aneurysmal subarachnoid hemorrhage (SAH). Recently, i.p. administration of recombinant human erythropoietin (r-Hu-EPO) has been shown to exert a neuroprotective effect during experimental SAH. The present study was conducted to evaluate further the effect of r-Hu-EPO administration after SAH in rabbits on neurological outcome, degree of basilar artery spasm, and magnitude of neuronal ischemic damage. Experimental animals were divided into six groups: group 1 (n = 8), control; group 2 (n = 8), control plus placebo; group 3 (n = 8), control plus r-Hu-EPO; group 4 (n = 8), SAH; group 5 (n = 8), SAH plus placebo; group 6 (n = 8), SAH plus r-Hu-EPO. r-Hu-EPO, at a dose of 1,000 units/kg, and placebo were injected i.p. starting 5 min after inducing SAH and followed by clinical and pathological assessment 72 h later. Systemic administration of r-Hu-EPO produced significant increases in cerebrospinal fluid EPO concentrations (P < 0.001), and reduced vasoconstriction of the basilar artery (P < 0.05), ischemic neuronal damage (P < 0.001), and subsequent neurological deterioration (P < 0.05). These observations suggest that r-Hu-EPO may provide an effective treatment to reduce the post-SAH morbidity.

Does administration of recombinant human erythropoietin attenuate the increase of S-100 protein observed in cerebrospinal fluid after experimental subarachnoid hemorrhage?

OBJECT

Results of recent studies indicate that erythropoietin (EPO) produces a neuroprotective effect on experimental subarachnoid hemorrhage (SAH). It has been reported that S-100 protein levels increase in cerebrospinal fluid (CSF) after SAH, providing a highly prognostic indication of unfavorable outcome. This study was conducted to validate further the findings of S-100 protein as an index of brain damage and to assess whether treatment with recombinant human EPO (rhEPO) would limit the increase of S-100 protein level in CSF following experimental SAH.

METHODS

Thirty-two rabbits were each assigned to one of four groups: Group 1, control; Group 2, SAH; Group 3, SAH plus placebo; and Group 4, SAH plus rhEPO (each group consisted of eight rabbits). The rhEPO and placebo were administered to the rabbits after SAH had been induced, and S-100 protein levels in the CSF of these animals were measured at 24, 48, and 72 hours after the experimental procedure. In each group of animals levels of S-100 protein were compared with the mortality rate, neurological outcome, and neuronal ischemic damage. High S-100 protein levels were found in rabbits in Groups 2 and 3, which exhibited poor neurological status and harbored a high number of damaged cortical neurons. Favorable neurological outcome and significant reductions in total numbers of damaged neurons were observed in animals in Group 4 in which there were significantly lower S-100 protein concentrations compared with animals in Groups 2 and 3 (p < 0.001).

CONCLUSIONS

The results of this study support the concept that determination of the S-100 protein level in CSF has prognostic value after SAH. The findings also confirm that rhEPO acts as a neuroprotective agent during experimental SAH.

Ultrastructural changes of neuronal mitochondria after transient and permanent cerebral ischemia

BACKGROUND AND PURPOSE

Mitochondrial swelling is one of the most striking and initial ultrastructural changes after acute brain ischemia. The purpose of the present study was to examine the role of reperfusion of the cerebral cortex after transient focal cerebral ischemia on neuronal mitochondrial damage.

METHODS

Male Sprague-Dawley rats (n=16) were subjected to either temporary or permanent occlusion of the middle cerebral artery and bilateral carotid arteries. Three experimental conditions were compared: group I, permanent ischemia (3, 5, and 24 hours); group II, transient ischemia (2, 24 hours of reperfusion); and sham surgery. Anesthetized rats were killed by cardiac perfusion, and brain tissue was removed ipsilaterally and contralaterally from the ischemic core section of the frontoparietal cortex. Fixed tissue was prepared for electron microscopic examination, and electron microscopic thin sections of random neurons were photographed. Perinuclear neuronal mitochondria were analyzed in a blinded manner for qualitative ultrastructural changes (compared with sham control) by 2 independent investigators using an objective grading system.

RESULTS

Cortical neuronal mitochondria exposed to severe ischemic/reperfusion conditions demonstrated dramatic signs of injury in the form of condensation, increased matrix density, and deposits of electron-dense material followed by disintegration by 24 hours. In contrast, mitochondria exposed to an equivalent time of permanent ischemia demonstrated increasing loss of matrix density with pronounced swelling followed by retention of their shape by 24 hours.

CONCLUSIONS

Neuronal mitochondria undergoing transient versus permanent ischemia exhibit significantly different patterns of injury. Structural damage to neuronal mitochondria of the neocortex occurs more acutely and to a greater extent during the reperfusion phase in comparison to ischemic conditions alone. Further research is in progress to delineate the role of oxygen free radical production in the observed mitochondrial damage during postischemic reoxygenation.

Histopathologic response of the immature rat to diffuse traumatic brain injury

The purpose of this study was to characterize the histopathologic response of rats at postnatal day (PND) 17 following an impact-acceleration diffuse traumatic brain injury (TBI) using a 150-g/2-meter injury as previously described. This injury produces acute neurologic and physiologic derangements as well as enduring motor and Morris water maze (MWM) functional deficits. Histopathologic studies of perfusion-fixed brains were performed by gross examination and light microscopy using hematoxylin and eosin, Bielschowsky silver stain, and glial fibrillary acidic protein (GFAP) immunohistochemistry at 1, 3, 7, 28, and 90 day after injury. Gross pathologic examination revealed diffuse subarachnoid hemorrhage (SAH) at 1-3 days but minimal supratentorial intraparenchymal hemorrhage. Petechial hemorrhages were noted in ventral brainstem segments and in the cerebellum. After 1-3-day survivals, light microscopy revealed diffuse SAH and intraventricular hemorrhage (IVH), mild edema, significant axonal injury, reactive astrogliosis, and localized midline cerebellar hemorrhage. Axonal injury most commonly occurred in the long ascending and descending fiber tracts of the brainstem and occasionally in the forebrain, and was maximal at 3 days, but present until 7 days after injury. Reactive astrocytes were similarly found both in location and timing, but were also significantly identified in the hippocampus, white matter tracts, and corpus callosum. Typically, TBI produced significant diffuse SAH accompanied by cerebral and brainstem astrogliosis and axonal injury without obvious neuronal loss. Since this injury produces some pathologic changes with sustained functional deficits similar to TBI in infants and children, it should be useful for the further study of the pathophysiology and therapy of diffuse TBI and brainstem injury in the immature brain.

Effects of tempol, a membrane-permeable radical scavenger, in a gerbil model of brain injury

There is evidence that the excessive generation of reactive-oxygen radicals contributes to the brain injury associated with transient, cerebral ischemia. This study investigates the effects of tempol, a small, water-soluble molecule, that crosses biological membranes, on the brain injury caused by bilateral occlusion and reperfusion of both common carotid arteries in the gerbil (BCO). Treatment of gerbils with tempol (30 mg/kg i.p. at 30 min prior to reperfusion and at 1 and 6 h after the onset of reperfusion) reduced the formation of post-ischemic brain oedema. Tempol also attenuated the increase in the cerebral levels of malondialdehyde (MDA) and the hippocampal levels of myeloperoxidase (MPO) caused by cerebral ischemia and reperfusion. The immunohistochemical analysis of the hippocampal region of brains subjected to ischemia-reperfusion exhibited positive staining for nitrotyrosine (an indicator of the generation of peroxynitrite) and poly(ADP-ribose) synthetase (PARS) (an indicator of the activation of this nuclear enzyme secondary to single strand breaks in DNA). In gerbils subjected to BCO, which were treated with tempol, the degree of staining for nitrotyrosine and PARS was markedly reduced. Tempol increased survival and reduced the hyperactivity (secondary to the ischemia-induced neurodegeneration) caused by cerebral ischemia and reperfusion. The loss of neurons from the pyramidal layer of the CA1 region caused by ischemia and reperfusion was also attenuated by treatment of gerbils with tempol. This is the first evidence that the membrane-permeable, radical scavenger tempol reduces the cerebral injury caused by transient, cerebral ischemia in vivo.

Improved selective, simple, and contrast staining of acidophilic neurons with vanadium acid fuchsin

Acidophilia is one of the hallmarks of acute neuronal damage and death in brain ischemia, excitotoxic and traumatic lesions and epileptic seizures. We here describe a novel and simple method for visualizing acidophilic neurons on paraffin sections, using vanadium acid fuchsin (VAF) staining and toluidine blue or hematoxylin counterstaining. Paraffin sections of the brain fixed in ethanol-formalin-acetic acid mixture are stained in 0.1% acid fuchsin containing 0.125% of ammonium metavanadate and 1% of glacial acetic acid, differentiated if overstained in 0.01% of borax solution, and counterstained with 0.05-0.025% of toluidine blue in acetate buffer (pH 3.3) or Gill's II hematoxylin. The sections are dehydrated, cleared in xylene and mounted in Canada balsam or any synthetic mounting media for light microscopy. VAF combined with toluidine blue or hematoxylin results in highly selective and reproducible color contrast staining of acidophilic neurons as well as glial nuclei and hyperchromatic neurons. As a progressive method, acid fuchsin staining usually does not require differentiation. The red acidophilic neurons are clearly visible on the background of non-damaged cells, which significantly facilitates the identification, and localization of damaged neurons, even at low magnification under the light microscope.

Spinal cord ischemia. Development of a model in the mouse

BACKGROUND AND PURPOSE

Spinal cord ischemia with resulting paraplegia is a devastating complication of thoracoabdominal aortic surgery. Experimental models of spinal cord ischemia have been developed in primate, dog, pig, rabbit, and rat with variable reproducibility, but none has been developed in mouse. Because genetically engineered mice have become important to examine the impact of specific genes in ischemic pathophysiology, we sought to develop a reproducible mouse model of spinal cord ischemia.

METHODS

C57BL/6NCrlBR mice were subjected to cross-clamping of the aortic arch, left subclavian artery, and internal mammary artery for 9 minutes (group A; n=8) or 11 minutes (group B; n=29) followed by reperfusion for 24 or 48 hours. Mean distal arterial blood pressure (left femoral artery) and lumbar (L1) spinal cord blood flow (laser-Doppler flowmetry) were measured for the duration of the procedure. The arterial blood supply of the spinal cord was visualized by intravascular perfusion of carbon black ink. We evaluated motor function in the hind limbs at 0, 1, 3, 6, and 24 hours after reperfusion using a rating scale of 0 (normal function) to 6 (total absence of movement). Spinal cord histopathology was evaluated after 24 and 48 hours of reperfusion by Luxol fast blue-hematoxylin and eosin.

RESULTS

The vascular anatomy of the mouse and human spinal cord appeared similar in that blood was supplied by 1 anterior and 2 posterior spinal arteries and heterosegmental radicular arteries. During combined occlusion of aortic arch and left subclavian artery, mean distal arterial blood pressure dropped to 10+/-5 mm Hg, and spinal cord blood flow at the L1 level decreased to 27+/-7% of baseline. All animals recovered from anesthesia with acute paraplegia. Animals in the 9-minute group (group A) showed steady recovery of hind limb function over the ensuing 24 hours, whereas the majority (80%) in the 11-minute group (group B) remained paralyzed with maximum deficit throughout the postoperative period. Mortality was 0% and 21% in groups A and B, respectively. Maximal ischemic damage was observed at the lower thoracic and higher lumbar spinal levels in both groups. In group A (9 minutes), tissue damage was mild, affecting predominantly dorsal horns and intermediate gray matter, whereas ventral horns were minimally involved. All mice in group B (11 minutes) showed extensive gray matter lesions particularly involving dorsal horns and intermediate areas; in ventral horns, >50% of motor neurons died. White matter lesions were present in the most severely damaged cords only.

CONCLUSIONS

Spinal cord ischemia caused by aortic arch plus left subclavian artery cross-clamping provides a mouse model useful for the study of spinal cord injury and of potential relevance to the complications following thoracoabdominal aortic surgery in humans.

Neuroprotective effect of hypothermia on neuronal injury in diffuse traumatic brain injury coupled with hypoxia and hypotension

It is well established in mechanical head trauma that posttraumatic secondary insults, such as hypoxia and hypotension exacerbate neuronal injury and lead to worse outcome. In this study, the neuroprotective effect of hypothermia on the reduction of supraventricular subcortical neuronal damage was evaluated using an impact-acceleration model of diffuse traumatic brain injury coupled with both moderate and severe periods of hypoxia and hypotension. A total of 135 adult male Sprague-Dawley rats (340-375 g) were divided into three experimental studies: (I) physiological evaluation (n = 36); (II) quantitative analysis of the effect of trauma coupled with moderate and severe hypotension on neuronal damage assessed at 4 (n = 39) and 24 h (n = 24); and (III) the neuroprotective effect of hypothermia following moderate secondary insult (n = 36). Induction of hypothermia occurred at 15 min postinjury, to a level of 30 degrees C for 60 min. At the designated time points (4 and 24 h), the animals were sacrificed via standard transcardial perfusion techniques for histological processing. Quantitative assessment of neuronal damage using routine H&E staining at 4 hours showed neuronal damage which correlated with the severity of secondary insult. Animals exposed to trauma alone had a mean number of damaged neurons of 7.61 +/- 3.08/high powered field (hpf) compared with a mean of 1.21 +/- 0.30/hpf in the sham operated group (p = 0.015). Animals exposed to trauma with 10 min of hypoxia and hypotension (THH-10) showed a statistically significant number of damaged neurons compared to the sham-operated animals (7.50 +/- 2.15 damaged neurons/hpf, p = 0.013), whereas, neuronal damage in animals undergoing trauma with a 30-min secondary insult of hypoxia and hypotension (THH-30) was markedly increased (100 +/- 30.20/hpf, p = 0.002). Statistical analysis showed no significant difference in neuronal damage in animals subjected to secondary insult alone. At 24 h, the evolution of neuronal damage in the trauma alone group (5.08 +/- 1.63/hpf) was relatively static; however, there was a remarkable increase in the neuronal damage of the THH-10 group (29.88 50 +/- 8.20/hpf). However, hypothermia provided nearly complete protection against secondary insults, and neuronal damage was equal to that of the trauma alone group (p = 0.42). The results of this study confirm that hypothermia provides remarkable protection against the adverse effects of neuronal damage exacerbated by secondary injury. This study also presents a new model of secondary insult, which can be used experimentally to further define the mechanism of increased vulnerability of the injured brain.

An integrated analysis of the progression of cell responses induced by permanent focal middle cerebral artery occlusion in the rat

Defining the chronology and severity of cell damage in an evolving lesion after ischemia is important for understanding the underlying mechanisms in the development of therapeutic intervention. In the present study, we used a combination of histological and immunocytochemical methods to evaluate cell responses from 30 min to 48 h after permanent occlusion of the middle cerebral artery (MCAO) in the rat. Specific immunocytochemical markers clearly revealed acute early responses in neurons (neurofilament protein 200), astrocytes (glial fibrillary acidic protein), and microglia/macrophages (OX-42 and ED-1) such as enlarged, convoluted neuronal processes, and disintegration of glia. Progressive topographic changes in the developing lesion, pinpointed by immunolabeling, indicated the severity and extension of the cell damage. Proliferation and hypertrophy of astrocytes and microglia around the infarct, and contralaterally, occurred 24-48 h after MCAO and coincided with mass necrosis and infiltration of neutrophils and macrophages into the core. These observations corroborate the suggestion that the inflammatory process is involved in the progression of the infarct.

Alterations of local cerebral blood flow, phorbol 12,13-dibutyrate binding activity, and histological damage during acute focal ischaemia in rat brain. A pathophysiology of acute focal ischaemia: Part 1

The alterations of the local cerebral blood flow (LCBF), 3H-phorbol 12,13-dibutyrate (PDBu) binding activity were measured, and histological findings were also examined during the closed time course (0, 1, 3, 5, 7 hour) after middle cerebral artery occlusion (MCAO) in rat brain to assess the complex pathophysiology of acute focal ischaemia. From 1 to 3 hours after the start of MCAO, significant (p < 0.01) hyperreactivity of the second messenger system involving PDBu binding may be present, despite low perfusion of LCBF, and severe damage in the striatum whereas sparing almost completely the cortex on histological examination. At 5 hours, the PDBu binding activity increased slightly but not significantly but is reduced markedly at 7 hours after MCAO compared with the control group. The measurement of PDBu binding activity, additionally to measuring the LCBF and observation of the histological change might be a useful indicator in determining the threshold and duration of ischaemia which cause functionally irreversible cell damage in the brain.

Induction of spreading depression in the ischemic hemisphere following experimental middle cerebral artery occlusion: effect on infarct morphology

This study was undertaken to test whether transient depolarizations occurring in periinfarct regions are important in contributing to infarct spread and maturation. Following middle cerebral artery (MCA) occlusion we stimulated the ischemic penumbra with recurrent waves of spreading depression (SD) and correlated the histopathological changes with the electrophysiological recordings. Halothane-anesthetized, artificially ventilated Sprague-Dawley rats underwent repetitive stimulation of SD in intact brain (Group 1; n = 8) or photothrombotic MCA occlusion coupled with ipsilateral common carotid artery occlusion (Groups 2 and 3, n = 9 each). The electroencephalogram and direct current (DC) potential were recorded for 3 h in the parietal cortex, which represented the periinffarct border zone in ischemic rats. In Group 2, only spontaneously occurring negative DC shifts occurred; in Group 3, the (nonischemic) frontal pole of the ischemic hemisphere was electrically stimulated to increase the frequency of periinfarct DC shifts. Animals underwent perfusion-fixation 24 h later, and volumes of complete infarction and scattered neuronal injury ("incomplete infarction") were assessed on stained coronal sections by quantitative planimetry. Electrical induction of SD in Group 1 did not cause morphological injury. During the initial 3 h following MCA occlusion, the number of spontaneous periinfarct depolarization in Group 2 (7.0 +/- 1.5 DC shifts) was doubled in Group 3 by frontal current application (13.4 +/- 2.7 DC shifts; p < 0.001). The duration as well as the integrated negative amplitude of DC shifts over time were significantly greater in Group 3 than in Group 2 rats (duration, 5.7 +/- 3.8 vs. 4.1 +/- 2.5 min; p < 0.05). Histopathological examination disclosed well-defined areas of pannecrosis surrounded by a cortical rim exhibiting selectively damaged acidophilic neurons and astrocytic swelling in otherwise normal-appearing brain. Induction of SD in the ischemic hemisphere led to a significant increase in the volume of incomplete infarction (19.0 +/- 6.1 mm3 in Group 3 vs. 10.3 +/- 5.1 mm3 in Group 2; p < 0.01) and of total ischemic injury (100.7 +/- 41.0 mm3 in Group 3 vs. 66.5 +/- 24.7 mm3 in Group 2; p < 0.05). The integrated magnitude of DC negativity per experiment correlated significantly with the volume of total ischemic injury (r = 0.780, p < 0.0001). Thus, induction of SD in the ischemic hemisphere accentuated the development of scattered neuronal injury and increased the volume of total ischemic injury. This observation may be explained by the fact that with limited perfusion reserve, periinfarct depolarization are associated with episodic energy failure in the acute ischemic penumbra.

Ultrastructural studies of cerebral vascular spasm after cardiac arrest-related global cerebral ischemia in rats

The present investigation was undertaken to study the ultrastructural morphology of brain blood vessels during vasospasm following total cerebral ischemia. Global cerebral ischemia was produced in rats by compression of the cardiac vessel bundle (i.e., cardiac arrest) using a metal hook that was introduced into the mediastinum. Ischemia lasted for 10 min with blood recirculation for 6, 12 and 24 h. Rat brains were perfusion-fixed and regions from the cerebral cortex and associated leptomeningeal vessels were evaluated by scanning and transmission electron microscopy. We noted three general vasoconstrictive responses in vessels of various sizes including veins and arteries. These alterations related to the smooth muscle cell arrangement associated with each constricted vessel including a circumferential, and longitudinal arrangement, or a combination of both types. Other features in the three types of vasoconstricted vessels included thickening of the vessel basement membranes with increased endothelial microfilaments and vesicular profiles. Our studies present evidence that ischemia of 10-min duration with blood reflow for 6, 12 and 24 h produces profound and variable vasospastic changes in some but not all vessels. These vascular alterations are thought to be caused in part by vasoactive substances released both by endothelial and blood cells and by perivascular cellular elements in response to the ischemic episode.

Changes in N-acetyl-aspartate content during focal and global brain ischemia of the rat

N-Acetyl-aspartate (NAA) is almost exclusively localized in neurons in the mature brain and might be used as a neuronal marker. It has been reported that the NAA content in human brain is decreased in neurodegenerative diseases and in stroke. Since the NAA content can be determined by nuclear magnetic resonance techniques, it has potential as a diagnostic and prognostic marker. The objective of this study was to examine the change of NAA content and related substances following cerebral ischemia and compare the results to the damage of the tissue. We used rats to study the changes of NAA, N-acetyl-aspartyl-glutamate (NAAG), glutamate, and aspartate contents over a time course of 24 h in brain regions affected by either permanent middle cerebral artery occlusion (focal ischemia) or decapitation (global ischemia). The decreases of NAA and NAAG contents following global brain ischemia were linear over time but significant only after 4 and 2 h, respectively. After 24 h, the levels of NAA and NAAG were 24 and 44% of control values, respectively. The concentration of glutamate did not change, whereas the aspartate content increased at a rate comparable with the rate of decrease of NAA content. This is consistent with NAA being preferentially degraded by the enzyme amidohydrolase II in global ischemia. In focal ischemia, there was a rapid decline of NAA within the first 8 h of ischemia followed by a slower rate of reduction. The reductions of NAA and NAAG contents in focal ischemia were significant after 4 and 24 h, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Retrograde cerebral perfusion with hypothermic blood provides efficient protection of the brain: a neuropathological study

Retrograde cerebral perfusion is a method that is recently being used for protection of the brain during operations on the aortic arch. This method is useful but is said to provide a limited time for protecting the brain. We designed an experiment in dogs to investigate neuropathologically the effect of protecting the brain for 120 minutes under: (1) circulatory arrest (CA); (2) retrograde cerebral perfusion with moderately cooled blood (RCPMC); and (3) retrograde cerebral perfusion with deeply cooled blood (RCPDC). We calculated the number of the abnormal cells of 400 hippocampal neurons per dog light microscopically. The number was 199 +/- 23 (mean +/- 1 SD) in the CA group, 149 +/- 50 in the RCPMC group, and 72 +/- 33 in the RCPDC group. The difference between the CA group and the RCPMC group was not statistically significant (p < 0.05), but there was a significant difference between the RCPMC and RCPDC groups (p < 0.05). The degree of cerebral protection provided by retrograde cerebral perfusion for 120 minutes is not sufficient when using moderately cooled blood. If we use deeply cooled blood at a temperature of about 10 degrees C, we should obtain a sufficient degree of protection of the brain.

Mitochondrial hyperoxidation signals residual intracellular dysfunction after global ischemia in rat neocortex

Reperfusion after global ischemia (10-60 min in duration) in rat neocortex most commonly provoked transient hyperoxidation of mitochondrial electron carriers, tissue hyperoxygenation, and CBF hyperemia. These responses were normally accompanied by recovery of K+ homeostasis and EEG spike activity. Goals of this research were to understand putative relationships among these postreperfusion events with special emphasis on determining whether mitochondrial hyperoxidation results from intracellular changes that may modulate residual damage. The amplitude of postischemic mitochondrial hyperoxidation (PIMHo) did not increase when CBF increased above an apparent threshold during reperfusion, and tissue hyperoxygenation was not required for PIMHo to occur or to continue. These findings suggest that PIMHo is not merely a response to increased CBF and tissue hyperoxygenation; rather, PIMHo is modulated, at least in part, by residual intracellular derangements that limit mitochondrial electron transport. This suggestion was supported by observations that NAD became hyperoxidized after reoxygenation in anoxic hippocampal slices. Also, PIMHo occurred and subsequently resolved in many animals, but K+o never was cleared fully to baseline and/or EEG spike activity never was evident. One suggestion is that PIMHo signals or initiates residual intracellular derangements that in turn impair electrical and metabolic recovery of cerebral neurons after ischemia; an alternative suggestion is that PIMHo and tissue hyperoxygenation are not the sole factors modulating the immediate restoration of electrical activity after ischemia. Present data also support the following: Decreased oxygen consumption, despite adequate oxygen delivery, likely contributes to tissue hyperoxygenation after ischemia; and mitochondrial hyperoxidation is modulated by a limitation in the supply of electrons to the mitochondrial respiratory chain.

DNA fragmentation indicative of apoptosis following unilateral cerebral hypoxia-ischemia in the neonatal rat

DNA extracted from regional brain samples of hypoxic/ischemic neonatal rats showed internucleosomal cleavage indicative of apoptosis. Cells containing cleaved DNA were identified by in situ labelling in the cortex, hippocampus, striatum and thalamus of the ipsilateral hemisphere. When the effects of increasing the length of the hypoxia were examined, increases were seen in the amount of internucleosomally cleaved DNA and in the number of labelled cells.

Antagonism of neutrophil adherence in the deteriorating stroke model in rabbits

Adhesion of leukocytes to the endothelium can occur in a few hours after the onset of ischemia, and the actions of leukocytes have been suggested to aggravate reperfusion injury. Adhesion is a prerequisite for the harmful leukocyte actions. Rapid mediation of leukocyte adhesion and aggravation of reperfusion injury can occur through production of platelet-activating factor (PAF). The authors hypothesized that prevention of leukocyte adhesion during ischemia reperfusion would have beneficial effects and that these effects might be enhanced by a PAF antagonist. To test this hypothesis, rabbits were anesthetized with pentobarbital and subjected to severe spinal cord ischemia (25 minutes) followed by 30 minutes of reperfusion, at which time either vehicle, antibody against the CD11/CD18 (anti-CD) leukocyte adhesion molecule (1 mg/kg), or the anti-CD and PAF antagonist, WEB 2086 (3 mg/kg), was administered intravenously and the animals were monitored for 6.5 hours. Using a score from 0 to 5, recovery of motor function was improved at 5.5 hours by the CD antibody (2.0 +/- 0.5 versus 0.4 +/- 0.2 in the six animals in the vehicle group, p < 0.05). No further improvement was induced by WEB 2086 in the six anti-CD treated animals (1.6 +/- 0.7). Spinal cord blood flow (laser Doppler flowmetry) at 6 hours was at the preischemic level in the control animals (-7% +/- 20%), but clearly increased in the anti-CD group (+73% +/- 29%, p < 0.5). The severity of blood-brain barrier damage in the spinal cord gray matter was decreased by the treatments. Extravasation of intravenously injected Evans blue albumin (EBA), measured by detection of EBA fluorescence, was reduced by approximately 50% in both treated groups (p < 0.05). The number of morphologically normal motor neurons in the lumbar anterior horns of the infarcted spinal cord showed protection in the seven animals in the anti-CD treated group at 6.5 hours: 12.7 +/- 1.7 versus 5.3 +/- 1.6 (vehicle), p < 0.05 without an additional effect by PAF antagonist 12.2 +/- 2.6 (anti-CD + WEB 2086). Our results suggest that ultraacute treatment of reperfusion injury based on special inhibition of leukocyte effects may be beneficial. Platelet-activating factor antagonism failed to enhance this therapeutic effect, which may suggest dependency on a common mechanism.

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

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

Temporal profile of ischemic tissue damage, neutrophil response, and vascular plugging following permanent and transient (2H) middle cerebral artery occlusion in the rat

We investigated the temporal profile of ischemic tissue damage, neutrophil response, and vascular occlusion after permanent and transient middle cerebral artery occlusion in the rat. Focal cerebral ischemia was induced by advancing a nylon monofilament to occlude middle cerebral artery (MCA). Two groups of rats were investigated: (1) those with permanent MCA occlusion (n = 29), and (2) and those having the arterial occlusion released after 2 h (n = 34). Experiments were terminated at 6, 12, 24, 48, 72, 96 and 168 h after the onset of ischemia, and brain sections were stained with hematoxylin and eosin for histological evaluation. Initially, the cortical lesion was smaller in rats subjected to transient MCA occlusion than in rats subjected to permanent MCA occlusion (p < 0.02). The surface area of the lesion was identical in both groups at 48 h after the onset of ischemia. Neutrophil infiltration into tissue and the time of peak neutrophil infiltration occurred earlier after transient MCA occlusion than after permanent MCA occlusion (6 h, 48 h in transient; 12 h, 72 h in permanent). Within the lesions, the number of occluded vessels was significantly lower in the transient ischemia group than in the permanent ischemia group during the time interval between 12-48 h (p < 0.01). Our data suggest that the temporal evolution of the lesion, the pattern of neutrophil infiltration and the chronology of microvascular occlusion differs depending on whether the MCA occlusion is transient (2 h) or permanent; however, significant differences in the size of the brain lesion disappeared 48 h after onset of ischemia.

Ultrastructural features of the isolated guinea-pig brain maintained in vitro by arterial perfusion

The morphological features of cerebral tissue in the isolated guinea-pig brain maintained in vitro by arterial perfusion are described. Light and electron microscopic analysis of the thalamus, the somatosensory cortex and the limbic cortices (hippocampus, piriform and entorhinal cortices) was performed after different periods of incubation in vitro (1, 7 and 12 h), in parallel with an electrophysiological study. The morphological analysis showed that neuronal elements retained their normal appearance at both cellular and subcellular level in the examined brain regions up to an incubation period of 12 h. Immunoreactivity for GABA was also preserved for up to 12 h of in vitro perfusion. Vasogenic edema and perivascular extracellular swelling appeared after 7 h, together with signs of progressive astrocytic deterioration. These findings show that normal electrophysiological recordings correlate with good anatomical preservation of the isolated guinea-pig brain preparation after prolonged times of arterial in vitro perfusion.