Aminoguanidine inhibits caspase-3 and calpain activation without affecting microglial activation following neonatal transient cerebral ischemia

Brain Maturation as a Fundamental Factor in Immune-Neurovascular Interactions in Stroke

Injuries in the developing brain cause significant long-term neurological deficits. Emerging clinical and preclinical data have demonstrated that the pathophysiology of neonatal and childhood stroke share similar mechanisms that regulate brain damage, but also have distinct molecular signatures and cellular pathways. The focus of this review is on two different diseases-neonatal and childhood stroke-with emphasis on similarities and distinctions identified thus far in rodent models of these diseases. This includes the susceptibility of distinct cell types to brain injury with particular emphasis on the role of resident and peripheral immune populations in modulating stroke outcome. Furthermore, we discuss some of the most recent and relevant findings in relation to the immune-neurovascular crosstalk and how the influence of inflammatory mediators is dependent on specific brain maturation stages. Finally, we comment on the current state of treatments geared toward inducing neuroprotection and promoting brain repair after injury and highlight that future prophylactic and therapeutic strategies for stroke should be age-specific and consider gender differences in order to achieve optimal translational success.

Cerebral ischemia in the developing brain

Brain ischemia affects all ages, from neonates to the elderly population, and is a leading cause of mortality and morbidity. Multiple preclinical rodent models involving different ages have been developed to investigate the effect of ischemia during different times of key brain maturation events. Traditional models of developmental brain ischemia have focused on rodents at postnatal day 7-10, though emerging models in juvenile rodents (postnatal days 17-25) indicate that there may be fundamental differences in neuronal injury and functional outcomes following focal or global cerebral ischemia at different developmental ages, as well as in adults. Here, we consider the timing of injury in terms of excitation/inhibition balance, oxidative stress, inflammatory responses, blood brain barrier integrity, and white matter injury. Finally, we review translational strategies to improve function after ischemic brain injury, including new ideas regarding neurorestoration, or neural repair strategies that restore plasticity, at delayed time points after ischemia.

SMAlow/undetectable pericytes differentiate into microglia- and macrophage-like cells in ischemic brain

Pericytes are multipotent perivascular cells that play important roles in CNS injury. However, controversial findings exist on how pericytes change and whether they differentiated into microglia-like cells after ischemic stroke. This discrepancy is mainly due to the lack of pericyte-specific markers: the "pericyte" population identified in previous studies contained vascular smooth muscle cells (vSMCs) and/or fibroblasts. Therefore, it remains unclear which cell type differentiates into microglia-like cells after stroke. In this study, lineage-tracing technique was used to mark α-smooth muscle actin (SMA)low/undetectable pericytes, vSMCs, and fibroblasts, and their fates were analyzed after ischemic stroke. We found that SMAlow/undetectable pericytes and fibroblasts but not vSMCs substantially proliferated at the subacute phase after injury, and that SMAlow/undetectable pericyte but not vSMCs or fibroblasts differentiated into Iba1+ cells after ischemic stroke. Further imaging flow cytometry analysis revealed that SMAlow/undetectable pericytes differentiated into both microglia and macrophages at day 7 after stroke. These results demonstrate that SMAlow/undetectable pericytes rather than vSMCs or fibroblasts differentiate into both microglia-like and macrophage-like cells after stroke, suggesting that these pericytes may be targeted in the treatment of ischemic stroke.

Metabolic Syndrome Exacerbates the Recognition Memory Impairment and Oxidative-Inflammatory Response in Rats with an Intrahippocampal Injection of Amyloid Beta 1-42

An important worldwide health problem as the result of current lifestyle is metabolic syndrome (MS). It has been shown that MS induced by a high-calorie diet (HCD) in rats produces cognitive deterioration in the novel object recognition test (NORt) and decreases synaptic connections and dendritic order in the hippocampus and temporal cortex. However, it is unknown whether MS induced by an HCD participates in the cognitive process observed with the injection of Aβ_1–42 into the hippocampus of rats as a model of Alzheimer disease (AD). The induction of MS in rats produces a deterioration in NORt; however, rats with MS injected with Aβ_1–42 show a major deterioration in the cognitive process. This event could be explained by the increment in the oxidative stress in both cases studied (MS and Aβ_1–42): together, the hippocampus and temporal cortex produce an enhancer effect. In the same way, we observed an increment in interleukin-1β, TNF-α, and GFAP, indicative of exacerbated inflammatory processes by the combination of MS and Aβ_1–42. We can conclude that MS might play a key role in the apparition and development of cognitive disorders, including AD. We propose that metabolic theory is important to explain the apparition of cognitive diseases.

Effects of the inducible nitric oxide synthase inhibitor aminoguanidine in two different rat models of schizophrenia

Several lines evidence indicate that the non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist ketamine and the mixed dopamine (DA) D1/D2 receptor agonist apomorphine induce schizophrenia-like symptoms in rodents, including memory impairments and social withdrawal. Nitric oxide (NO) has been proposed to act as an intracellular messenger in the brain and its overproduction is associated with schizophrenia. The current study was designed to investigate the ability of the inducible NO synthase (iNOS) inhibitor aminoguanidine (AG) to counteract schizophrenia-like behavioural deficits produced by ketamine and apomorphine in rats. The efficacy of AG to antagonize extinction of recognition memory, ketamine and apomorphine-induced recognition memory impairments was tested utilizing the novel object recognition task (NORT). Further, the efficacy of AG to attenuate ketamine-induced social withdrawal was examined in the social interaction test. AG (25 and 50mg/kg) antagonized extinction of recognition memory and reversed ketamine (3mg/kg) and apomorphine (1mg/kg)-induced recognition memory deficits. In contrast, AG (50 and 100mg/kg) did not counteract the ketamine (8mg/kg)-induced social isolation. The present data show that the iNOS inhibitor AG counteracted extinction of recognition memory and reversed recognition memory deficits produced by dysfunction of the glutamatergic and the dopaminergic (DAergic) system in rats. Therefore, AG may be efficacious in attenuating memory impairments often observed in schizophrenia patients.

Aminoguanidine treatment ameliorates inflammatory responses and memory impairment induced by amyloid-beta 25-35 injection in rats

Alzheimer disease (AD) is a neurodegenerative disorder caused by accumulation of the amyloid-beta peptide (Aβ) in neuritic plaques. Its neurotoxic mechanisms are associated with inflammatory responses and nitrosative stress generation that promote expression of inducible nitric oxide synthase (iNOS) and increased nitric oxide causing neuronal death and memory impairment. Studies suggest that treatment with anti-inflammatory and anti-oxidant agents decreases the risk of developing AD. Aminoguanidine (AG) is an iNOS inhibitor with anti-inflammatory and anti-oxidant effects. In this study, we evaluated the effects of systemic administration of AG (100 mg/kg/day for 4 days) on spatial memory and inflammatory responses induced by an injection of Aβ(25-35) [100 μM] into the temporal cortex (TCx) of rats. A significant improvement of spatial memory was evident in the Aβ(25-35)-treated group at day 30 post-injection subjected to AG treatment; this effect was correlated with decreases in reactive gliosis, IL-1β, TNF-α, and nitrite levels, as well as a reduction in neurodegeneration in the TCx and hippocampus (Hp). These results suggest that AG treatment inhibited glia activation and cytokine release, which may help to counteract neurodegenerative events induced by the toxicity of Aβ.

Mechanisms of perinatal arterial ischemic stroke

The incidence of perinatal stroke is high, similar to that in the elderly, and produces a significant morbidity and severe long-term neurologic and cognitive deficits, including cerebral palsy, epilepsy, neuropsychological impairments, and behavioral disorders. Emerging clinical data and data from experimental models of cerebral ischemia in neonatal rodents have shown that the pathophysiology of perinatal brain damage is multifactorial. These studies have revealed that, far from just being a smaller version of the adult brain, the neonatal brain is unique with a very particular and age-dependent responsiveness to hypoxia-ischemia and focal arterial stroke. In this review, we discuss fundamental clinical aspects of perinatal stroke as well as some of the most recent and relevant findings regarding the susceptibility of specific brain cell populations to injury, the dynamics and the mechanisms of neuronal cell death in injured neonates, the responses of neonatal blood-brain barrier to stroke in relation to systemic and local inflammation, and the long-term effects of stroke on angiogenesis and neurogenesis. Finally, we address translational strategies currently being considered for neonatal stroke as well as treatments that might effectively enhance repair later after injury.

Early changes in the synapses of the neostriatum induced by perinatal asphyxia

Perinatal asphyxia (PA) is a medical condition associated with a high short-term morbimortality and different long-term neurological diseases. In previous work we have observed at 6 months post-synaptic densities (PSDs) alterations compatible with neurodegeneration highly correlated with the increment in the ubiquitination. Although alterations in the synaptic organization and function have been related with neuronal death after hypoxia, little is known about the synaptic changes in young animals exposed to PA. The main aim of this work is to study the PSDs changes in striatum of 30-day-old rats subjected to PA. Using two-dimensional electron microscopic analyses of synapses staining with ethanolic phosphotungstic acid we observed an increment of PSD thickness in severe hypoxic rats. These data are consistent with the western blot analysis that showed an increment in ubiquitination levels in the synapses of severe hypoxic rat. We did observe any alterations neither in synaptic structure nor in ubiquitinization in mild asphyctic rats. These data suggest that hypoxia might cause early misfolding and aggregation of synaptic proteins in severe anoxic animas that could induce long-term neurodegeneration.

Effects of heat shock protein 72 (Hsp72) on evolution of astrocyte activation following stroke in the mouse

Astrocyte activation is a hallmark of the response to brain ischemia consisting of changes in gene expression and morphology. Heat shock protein 72 (Hsp72) protects from cerebral ischemia, and although several protective mechanisms have been investigated, effects on astrocyte activation have not been studied. To identify potential mechanisms of protection, microarray analysis was used to assess gene expression in the ischemic hemispheres of wild-type (WT) and Hsp72-overexpressing (Hsp72Tg) mice 24 h after middle cerebral artery occlusion or sham surgery. After stroke both genotypes exhibited changes in genes related to apoptosis, inflammation, and stress, with more downregulated genes in Hsp72Tg and more inflammation-related genes increased in WT mice. Genes indicative of astrocyte activation were also upregulated in both genotypes. To measure the extent and time course of astrocyte activation after stroke, detailed histological and morphological analyses were performed in the cortical penumbra. We observed a marked and persistent increase in glial fibrillary acidic protein (GFAP) and a transient increase in vimentin. No change in overall astrocyte number was observed based on glutamine synthetase immunoreactivity. Hsp72Tg and WT mice were compared for density of astrocytes expressing activation markers and astrocytic morphology. In animals with comparable infarct size, overexpression of Hsp72 reduced the density of GFAP- and vimentin-expressing cells, and decreased astrocyte morphological complexity 72 h following stroke. However, by 30 days astrocyte activation was similar between genotypes. These data indicate that early modulation of astrocyte activation provides an additional novel mechanism associated with Hsp72 overexpression in the setting of ischemia.

Hippocampal dendritic spines modifications induced by perinatal asphyxia

Perinatal asphyxia (PA) affects the synaptic function and morphological organization. In previous works, we have shown neuronal and synaptic changes in rat neostriatum subjected to hypoxia leading to long-term ubi-protein accumulation. Since F-actin is highly concentrated in dendritic spines, modifications in its organization could be related with alterations induced by hypoxia in the central nervous system (CNS). In the present study, we investigate the effects of PA on the actin cytoskeleton of hippocampal postsynaptic densities (PSD) in 4-month-old rats. PSD showed an increment in their thickness and in the level of ubiquitination. Correlative fluorescence-electron microscopy photooxidation showed a decrease in the number of F-actin-stained spines in hippocampal excitatory synapses subjected to PA. Although Western Blot analysis also showed a slight decrease in β-actin in PSD in PA animals, the difference was not significant. Taken together, this data suggests that long-term actin cytoskeleton might have role in PSD alterations which would be a spread phenomenon induced by PA.

Long-lasting paracrine effects of human cord blood cells on damaged neocortex in an animal model of cerebral palsy

Neonatal asphyxia is an important contributor to cerebral palsy (CP), for which there is no effective treatment to date. The administration of human cord blood cells (hUCBCs) is emerging as a therapeutic strategy for the treatment of neurological disorders. However, there are few studies on the application of hUCBCs to the treatment of neonatal ischemia as a model of CP. Experiments and behavioral tests (mainly motor tests) performed on neonatal hypoxia/ischemia have been limited to short-term effects of hUCBCs, but mechanisms of action have not been investigated. We performed a study on the use of hUCBCs in a rat model of neonatal hypoxia/ischemia and investigated the underlying mechanism for therapeutic benefits of hUCBC treatment. hUCBCs were intravenously transplanted into a rat model of neonatal hypoxia ischemia. hUCBCs increased microglia temporarily in the periventricular striatum in the early phase of disease, protected mature neurons in the neocortex from injury, paved the way for the near-normalization of brain damage in the subventricular zone (SVZ), and, in consequence, significantly improved performance in a battery of behavioral tests compared to the vehicle-treated group. Although the transplanted cells were rarely observed in the brain 3 weeks after transplantation, the effects of the improved behavioral functions persisted. Our preclinical findings suggest that the long-lasting positive influence of hUCBCs is derived from paracrine effects of hUCBCs that stimulate recovery in the injured brain and protect against further brain damage.

Astrocyte proliferation following stroke in the mouse depends on distance from the infarct

Reactive gliosis is a hallmark of brain pathology and the injury response, yet the extent to which astrocytes proliferate, and whether this is central to astrogliosis is still controversial. We determined the fraction of mature astrocytes that proliferate in a mouse stroke model using unbiased stereology as a function of distance from the infarct edge. Cumulatively 11.1±1.2% of Aldh1l1⁺ astrocytes within 400 µm in the cortical penumbra incorporate BrdU in the first week following stroke, while the overall number of astrocytes does not change. The number of astrocytes proliferating fell sharply with distance with more than half of all proliferating astrocytes found within 100 µm of the edge of the infarct. Despite extensive cell proliferation primarily of microglia and neutrophils/monocytes in the week following stroke, few mature astrocytes re-enter cell cycle, and these are concentrated close to the infarct boundary.

Microglial cells contribute to endogenous brain defenses after acute neonatal focal stroke

Macrophages are viewed as amplifiers of ischemic brain injury, but the origin of injury-producing macrophages is poorly defined. The role of resident brain macrophages-microglial cells-in stroke remains controversial. To determine whether microglial cells exert injurious effects after neonatal focal stroke, we selectively depleted these cells with intracerebral injection of liposome-encapsulated clodronate before transient middle cerebral artery occlusion in postnatal day 7 rats. Phagocytosis of apoptotic neurons by activated microglia was poor in animals with unmanipulated microglia, and depletion of these cells did not increase the number of apoptotic neurons. Lack of microglia increased the brain levels of several cytokines and chemokines already elevated by ischemia-reperfusion, and also increased the severity and volume of injury, suggesting that microglial cells contribute to endogenous protection during the subacute injury phase. Then, to determine whether accumulation of reactive oxygen species in microglia adversely affects phagocytosis of dying neurons and contributes to injury, we delivered reduced glutathione (GSH) into microglia, again using liposomes. Remarkably, pharmacologically increased intracellular GSH concentrations in microglia induced superoxide accumulation in lipid rafts in these cells, further increased the brain levels of macrophage chemoattractants, and exacerbated injury. Together, these data show that microglia are part of the endogenous defense mechanisms and that, while antioxidants can protect the injured neonatal brain, high levels of reducing equivalents in activated microglia, GSH, trigger superoxide production, favor the reorganization of lipids, amplify local inflammation and exacerbate injury.

Microglial cells contribute to endogenous brain defenses after acute neonatal focal stroke

Macrophages are viewed as amplifiers of ischemic brain injury, but the origin of injury-producing macrophages is poorly defined. The role of resident brain macrophages-microglial cells-in stroke remains controversial. To determine whether microglial cells exert injurious effects after neonatal focal stroke, we selectively depleted these cells with intracerebral injection of liposome-encapsulated clodronate before transient middle cerebral artery occlusion in postnatal day 7 rats. Phagocytosis of apoptotic neurons by activated microglia was poor in animals with unmanipulated microglia, and depletion of these cells did not increase the number of apoptotic neurons. Lack of microglia increased the brain levels of several cytokines and chemokines already elevated by ischemia-reperfusion, and also increased the severity and volume of injury, suggesting that microglial cells contribute to endogenous protection during the subacute injury phase. Then, to determine whether accumulation of reactive oxygen species in microglia adversely affects phagocytosis of dying neurons and contributes to injury, we delivered reduced glutathione (GSH) into microglia, again using liposomes. Remarkably, pharmacologically increased intracellular GSH concentrations in microglia induced superoxide accumulation in lipid rafts in these cells, further increased the brain levels of macrophage chemoattractants, and exacerbated injury. Together, these data show that microglia are part of the endogenous defense mechanisms and that, while antioxidants can protect the injured neonatal brain, high levels of reducing equivalents in activated microglia, GSH, trigger superoxide production, favor the reorganization of lipids, amplify local inflammation and exacerbate injury.

The yin and yang of microglia

Microglia, the resident immune cells of the mammalian central nervous system (CNS), play a pivotal role in both physiological and pathological conditions such as the restoration of CNS integrity and the progression of neurodegenerative disorders. Extensive data have been published that describe neuroinflammation by microglial activation to have detrimental consequences on the developing and mature brain. On the other hand, a properly directed and limited inflammatory response is known to be a natural healing process after an insult in several other tissues. Thus, it is not surprising that research results illustrating benefits of neuroinflammation have been emerging over the past decade. Inflammation-mediated benefits for CNS outcomes include mechanisms such as neuroprotection, mobilization of neural precursors for repair, remyelination and axonal regeneration. Here, we review data that highlight the dual aspects of microglia with a focus on the developing brain, i.e. as aggressors potentiating damage and as helpers in the recovery process following CNS damage.

Aminoguanidine administration ameliorates hippocampal damage after middle cerebral artery occlusion in rat

The effects of a selective inducible nitric oxide synthase inhibitor aminoguanidine (AG) on neuronal cells survival in hippocampal CA1 region after middle cerebral artery occlusion (MCAO) were examined. Transient focal cerebral ischemia was induced in rats by 60 or 90 min of MCAO, followed by 7 days of reperfusion. AG treatment (150 mg/kg i.p.) significantly reduced total infarct volumes: by 70% after 90 min MCAO and by 95% after 60 min MCAO, compared with saline-treated ischemic group. The number of degenerating neurons in hippocampal CA1 region was also markedly lower in aminoguanidine-treated ischemic groups compared to ischemic groups without AG-treatment. The number of iNOS-positive cells significantly increased in the hippocampal CA1 region of ischemic animals, whereas it was reduced in AG-treated rats. Our findings demonstrate that aminoguanidine decreases ischemic brain damage and improves neurological recovery after transient focal ischemia induced by MCAO.

Cerebellar abnormalities following hypoxia alone compared to hypoxic-ischemic forebrain injury in the developing rat brain

Two-day-old (P2) rat pups were subjected to either a global hypoxia or to electrocoagulation of the right carotid artery followed by 2.5 h hypoxia. Cellular and regional injury in the cerebellum (CB) was studied at 1, 2 and 19 days using immunohistology. Following hypoxia and hypoxia-ischemia, all neuronal populations of the CB were damaged in a subset of Purkinje cells. The decrease in the number of interneurons, as well as the thickness of molecular and granular layers was significant following hypoxia. Diffuse white matter damage, with loss of preoligodendrocytes was more severe following hypoxia than hypoxia-ischemia. Global hypoxia in the rat at P2 produces extensive damage to many cell types in different areas of the CB. The addition of unilateral forebrain ischemia does not increase the severity of these changes. Our data provide insight into the mechanisms of the changes observed in the CB of premature newborns.

Calpeptin attenuated inflammation, cell death, and axonal damage in animal model of multiple sclerosis

Experimental autoimmune encephalomyelitis (EAE) is an animal model for studying multiple sclerosis (MS). Calpain has been implicated in many inflammatory and neurodegenerative events that lead to disability in EAE and MS. Thus, treating EAE animals with calpain inhibitors may block these events and ameliorate disability. To test this hypothesis, acute EAE Lewis rats were treated dose dependently with the calpain inhibitor calpeptin (50-250 microg/kg). Calpain activity, gliosis, loss of myelin, and axonal damage were attenuated by calpeptin therapy, leading to improved clinical scores. Neuronal and oligodendrocyte death were also decreased, with down-regulation of proapoptotic proteins, suggesting that decreases in cell death were due to decreases in the expression or activity of proapoptotic proteins. These results indicate that calpain inhibition may offer a novel therapeutic avenue for treating EAE and MS.

Inflammation processes in perinatal brain damage

Once viewed as an isolated, immune-privileged organ, the central nervous system has undergone a conceptual change. Neuroinflammation has moved into the focus of research work regarding pathomechanisms underlying perinatal brain damage. In this review, we provide an overview of current concepts regarding perinatal brain damage and the role of inflammation in the disease pathomechanism.

Does inflammation after stroke affect the developing brain differently than adult brain?

The immature brain is prone to hypoxic-ischemic encephalopathy and stroke. The incidence of arterial stroke in newborns is similar to that in the elderly. However, the pathogenesis of ischemic brain injury is profoundly affected by age at the time of the insult. Necrosis is a dominant type of neuronal cell death in adult brain, whereas widespread neuronal apoptosis is unique for the early postnatal synaptogenesis period. The inflammatory response, in conjunction with excitotoxic and oxidative responses, is the major contributor to ischemic injury in both the immature and adult brain, but there are several areas where these responses diverge. We discuss the contribution of various inflammatory mechanisms to injury and repair after cerebral ischemia in the context of CNS immaturity. In particular, we discuss the role of lower expression of selectins, a more limited leukocyte transmigration, undeveloped complement pathways, a more rapid microglial activation, differences in cytokine and chemokine interplay, and a different threshold to oxidative stress in the immature brain. We also discuss differences in activation of intracellular pathways, especially nuclear factor kappaB and mitogen-activated protein kinases. Finally, we discuss emerging data on both the supportive and adverse roles of inflammation in plasticity and repair after stroke.

Protein ubiquitination in postsynaptic densities after hypoxia in rat neostriatum is blocked by hypothermia

Synaptic dysfunction has been associated with neuronal cell death following hypoxia. The lack of knowledge on the mechanisms underlying this dysfunction prompted us to investigate the morphological changes in the postsynaptic densities (PSDs) induced by hypoxia. The results presented here demonstrate that PSDs of the rat neostriatum are highly modified and ubiquitinated 6 months after induction of hypoxia in a model of perinatal asphyxia. Using both two dimensional (2D) and three dimensional (3D) electron microscopic analyses of synapses stained with ethanolic phosphotungstic acid (E-PTA), we observed an increment of PSD thickness dependent on the duration and severity of the hypoxic insult. The PSDs showed clear signs of damage and intense staining for ubiquitin. These morphological and molecular changes were effectively blocked by hypothermia treatment, one of the most effective strategies for hypoxia-induced brain injury available today. Our data suggest that synaptic dysfunction following hypoxia may be caused by long-term misfolding and aggregation of proteins in the PSD.

Overexpression of mitochondrial Hsp70/Hsp75 in rat brain protects mitochondria, reduces oxidative stress, and protects from focal ischemia

Mitochondria are known to be central to the cell's response to ischemia, because of their role in energy generation, in free radical generation, and in the regulation of apoptosis. Heat shock protein 75 (Hsp75/Grp75/mortalin/TRAP1) is a member of the HSP70 chaperone family, which is targeted to mitochondria. Overexpression of Hsp75 was achieved in rat brain by DNA transfection, and expression was observed in both astrocytes and neurons. Rats were subjected to 100 mins middle cerebral artery occlusion followed by assessment of infarct volume, neurological score, mitochondrial function, and levels of oxidative stress at 24 h reperfusion. Overexpression of Hsp75 reduced infarct area from 44.6%+/-21.1% to 25.7%+/-12.1% and improved neurological outcome significantly. This was associated with improved mitochondrial function as shown by protection of complex IV activity, marked reduction of free radical generation detected by hydroethidine fluorescence, reduction of lipid peroxidation detected by 4-hydroxy-2-nonenol immunoreactivity, and increased preservation of ATP levels. This suggests that targeting mitochondria for protection may be a useful strategy to reduce ischemic brain injury.

Early diffusion-weighted MRI as a predictor of caspase-3 activation after hypoxic-ischemic insult in neonatal rodents

BACKGROUND AND PURPOSE

Neonatal encephalopathy in human babies is a serious condition associated with permanent neurological deficits. Diffusion-weighted MRI (DWI) is increasingly used for early diagnosis of brain injury in human babies. The relationship between the presence of DWI abnormalities and cellular injury, including apoptosis, during the neonatal period are not well understood. We asked whether the extent of injury depicted on DWI can predict the presence of caspase-3 activation, a quantitative marker of apoptotic injury, after hypoxia-ischemia (H-I) in postnatal day 7 rats.

METHODS

Injury volume was determined by DWI at 2 hours, 24 hours, and 7 days after H-I and compared with histology. Caspase-3 activation and microgliosis were determined at 24 hours post-H-I.

RESULTS

DWI-defined lesions (eg, decreased apparent diffusion coefficient) at 24 hours post-H-I correlated with a major increase in caspase-3 activity in the injured hemisphere and predicted injury. A modest but significant increase in caspase-3 activity occurred in the cortex of rats that had no apparent diffusion coefficient decrease in the injured hemisphere but had unilaterally enlarged regions of high apparent diffusion coefficient at the ipsilateral ventricle/white matter interface. Caspase-3 activity was similar in both hemispheres in pups with unchanged DWI.

CONCLUSIONS

Abnormal DWI signal at 24 hours post-H-I is predictive of caspase-3 activation and can be used as an indicator that injury involving an apoptotic-like mechanism is present. Our data also suggest that the presence of an enlarged unilateral region with high apparent diffusion coefficient at the ventricle/white matter interface without significant apparent diffusion coefficient decrease in the cortex is a sign of modest caspase-3 activation after H-I.

Macrophages are comprised of resident brain microglia not infiltrating peripheral monocytes acutely after neonatal stroke

Macrophages can be both beneficial and detrimental after CNS injury. We previously showed rapid accumulation of macrophages in injured immature brain acutely after ischemia-reperfusion. To determine whether these macrophages are microglia or invading monocytes, we subjected post-natal day 7 (P7) rats to transient 3 h middle cerebral artery (MCA) occlusion and used flow cytometry at 24 and 48 h post-reperfusion to distinguish invading monocytes (CD45high/CD11b+) from microglia (CD45low/medium/CD11b+). Inflammatory cytokines and chemokines were determined in plasma, injured and contralateral tissue 1-24 h post-reperfusion using ELISA-based cytokine multiplex assays. At 24 h, the number of CD45+/CD11b+ cells increased 3-fold in injured compared to uninjured brain tissue and CD45 expression shifted from low to medium with less than 10% of the population expressing CD45high. MCA occlusion induced rapid and transient asynchronous increases in the pro-inflammatory cytokine IL-beta and chemokines cytokine-induced neutrophil chemoattractant protein 1 (CINC-1) and monocyte-chemoattractant protein 1 (MCP-1), first in systemic circulation and then in injured brain. Double immunofluorescence with cell-type specific markers showed that multiple cell types in the injured brain produce MCP-1. Our findings show that despite profound increases in MCP-1 in injured regions, monocyte infiltration is low and the majority of macrophages in acutely injured regions are microglia.

Inflammation in adult and neonatal stroke

This chapter will discuss the current knowledge of the contribution of systemic and local inflammation in acute and sub-chronic stages of experimental stroke in both the adult and neonate. It will review the role of specific cell types and interactions among blood cells, endothelium, glia, microglia, the extracellular matrix and neurons - cumulatively called "neurovascular unit" - in stroke induction and evolution. Intracellular inflammatory signaling pathways such as nuclear factor kappa beta and mitogen-activated protein kinases, and mediators produced by inflammatory cells such as cytokines, chemokines, reactive oxygen species and arachidonic acid metabolites, as well as the modifying role of age on these mechanisms, will be reviewed as well as the potential for therapy in stroke and hypoxic-ischemic injury.

Limited Role of Inducible Nitric Oxide Synthase in Blood–Brain Barrier Function after Experimental Subarachnoid Hemorrhage

Excessive nitric oxide (NO) produced by inducible nitric oxide synthase (iNOS) may play a pivotal role in blood-brain barrier (BBB) breakdown following subarachnoid hemorrhage (SAH). We investigated if the inhibition of iNOS could reduce BBB breakdown and cerebral edema, thereby leading to improved outcome 24 h after SAH. Forty male rats were assigned to three groups: control, SAH, and treatment groups. SAH was induced by perforating the bifurcation of the internal carotid artery. The neurological score and the mortality were evaluated 24 h after the surgery. The expression of iNOS, the concentration of NO metabolites, morphological changes in neuronal cells, water content, and IgG leakage were also evaluated. The expression of iNOS, as well as the concentration of NO metabolites, was elevated after SAH. Treatment with p-Toluenesulfonate decreased both the expression of iNOS and the concentration of NO metabolites. However, there was no significant change in water content, BBB disruption, or morphological findings between the SAH group and the treatment group. Furthermore no significant differences in neurological score or mortality were observed. The iNOS inhibitor failed to reduce BBB breakdown, brain edema, and neuronal cell death and failed to improve the neurological score and the mortality 24 h after SAH.