Selective vulnerability in the gerbil hippocampus following transient ischemia

Tumor necrosis factor receptor 2 is required for ischemic preconditioning-mediated neuroprotection in the hippocampus following a subsequent longer transient cerebral ischemia

Tumor Necrosis Factor-α (TNF-α) is a proinflammatory cytokine implicated in neuronal damage in response to cerebral ischemia. Ischemic preconditioning (IPC) provides neuroprotection against a subsequent severer or longer transient ischemia by ischemic tolerance. Here, we focused on the role of TNF-α in IPC-mediated neuroprotection against neuronal death following a subsequent longer transient cerebral ischemia (TCI). Gerbils used in this study were randomly assigned to eight groups; sham group, TCI operated group, IPC plus (+) sham group, IPC + TCI operated group, sham + etanercept (an inhibitor of TNF-a) group, TCI + etanercept group, IPC + sham + etanercept group, and IPC + TCI + etanercept group. IPC was induced by a 2-min sublethal transient ischemia, which was operated 1 day prior to a longer (5-min) TCI. A significant death of neurons was found in the stratum pyramidale (SP) in the CA1 area (CA1) of the hippocampus 5 days after TCI; however, IPC protected SP neurons from TCI. We found that TNF-α immunoreactivity was significantly increased in CA1 pyramidal neurons in the TCI and IPC + TCI groups compared to the sham group. TNF-R1 expression in CA1 pyramidal neurons of the TCI group was also increased 1 and 2 days after TCI; however, in the IPC + TCI group, TNF-R1 expression was significantly lower than that in the TCI group. On the other hand, we did not detect TNF-R2 immunoreactivity in CA1 pyramidal neurons 1 and 2 days after TCI; meanwhile, in the IPC + TCI group, TNF-R2 expression was significantly increased compared to TNF-R2 expression at 1 and 2 days after TCI. In addition, in this group, TNF-R2 was newly expressed in pericytes, which are important cells in the blood brain barrier, from 1 day after TCI. When we treated etanercept to the IPC + TCI group, IPC-induced neuroprotection was significantly weakened. In brief, this study indicates that IPC confers neuroprotection against TCI by TNF-α signaling through TNF-R2 and suggests that the enhancement of TNF-R2 expression by IPC may be a legitimate strategy for a therapeutic intervention of TCI.

Diazoxide inhibits of ER stress‑mediated apoptosis during oxygen‑glucose deprivation in vitro and cerebral ischemia‑reperfusion in vivo

Neuroprotective strategies using diazoxide (DZX) have been demonstrated to limit ischemia/reperfusion (I/R)-induced injury and cell apoptosis. In type 2 diabetes mellitus, DZX has been reported to improve β-cell function and reduce their apoptosis, through suppressing endoplasmic reticulum (ER) stress. However, the effects of DZX on ER stress during I/R-induced neuronal apoptosis in the hippocampus remains to be elucidated. In the present study, pretreatment of hippocampal neurons with DZX was revealed to inhibit oxygen-glucose deprivation (OGD)-stimulated apoptosis in vitro and to alleviate I/R-induced hippocampal injury and behavioral deficits in rats in vivo. Furthermore, OGD and I/R were demonstrated to induce ER stress via upregulating the expression of ER stress-associated proteins, including C/EBP homologous protein, 78 kDa glucose-regulated protein and caspase-12, whereas the exogenous administration of DZX effectively downregulated ER stress-associated protein expression following OGD and I/R. In addition, DZX was revealed to significantly increase the protein expression of B-cell lymphoma (Bcl)-2 and suppress the expression of caspase-3 and Bcl-2-associated X protein. These findings suggested that DZX may protect cells against apoptosis via regulating the expression of ER stress-associated proteins in vitro and in vivo, thus enhancing the survival of hippocampal cells. The present results suggested a novel mechanism that may underlie the protective effect of DZX administration in the central nervous system.

Acidosis mediates recurrent hypoglycemia-induced increase in ischemic brain injury in treated diabetic rats

OBJECTIVES

Cerebral ischemia is a serious possible manifestation of diabetic vascular disease. Recurrent hypoglycemia (RH) enhances ischemic brain injury in insulin-treated diabetic (ITD) rats. In the present study, we determined the role of ischemic acidosis in enhanced ischemic brain damage in RH-exposed ITD rats.

METHODS

Diabetic rats were treated with insulin and mild/moderate RH was induced for 5 days. Three sets of experiments were performed. The first set evaluated the effects of RH exposure on global cerebral ischemia-induced acidosis in ITD rats. The second set evaluated the effect of an alkalizing agent (Tris-(hydroxymethyl)-aminomethane: THAM) on ischemic acidosis-induced brain injury in RH-exposed ITD rats. The third experiment evaluated the effect of the glucose transporter (GLUT) inhibitor on ischemic acidosis-induced brain injury in RH-exposed ITD rats. Hippocampal pH and lactate were measured during ischemia and early reperfusion for all three experiments. Neuronal survival in Cornu Ammonis 1 (CA1) hippocampus served as a measure of ischemic brain injury.

FINDINGS

Prior RH exposure increases lactate concentration and decreases pH during ischemia and early reperfusion when compared to controls. THAM and GLUT inhibitor treatments attenuated RH-induced increase in ischemic acidosis. GLUT inhibitor treatment reduced the RH-induced increase in lactate levels. Both THAM and GLUT inhibitor treatments significantly decreased ischemic damage in RH-exposed ITD rats.

CONCLUSIONS

Ischemia causes increased acidosis in RH-exposed ITD rats via a GLUT-sensitive mechanism. Exploring downstream pathways may help understand mechanisms by which prior exposure to RH increases cerebral ischemic damage.

Stress primes microglial polarization after global ischemia: Therapeutic potential of progesterone

Despite the fact that stress is associated with increased risk of stroke and worsened outcome, most preclinical studies have ignored this comorbid factor, especially in the context of testing neuroprotective treatments. Preclinical research suggests that stress primes microglia, resulting in an enhanced reactivity to a subsequent insult and potentially increasing vulnerability to stroke. Ischemia-induced activated microglia can be polarized into a harmful phenotype, M1, which produces pro-inflammatory cytokines, or a protective phenotype, M2, which releases anti-inflammatory cytokines and neurotrophic factors. Selective modulation of microglial polarization by inhibiting M1 or stimulating M2 may be a potential therapeutic strategy for treating cerebral ischemia. Our laboratory and others have shown progesterone to be neuroprotective against ischemic stroke in rodents, but it is not known whether it will be as effective under a comorbid condition of chronic stress. Here we evaluated the neuroprotective effect of progesterone on the inflammatory response in the hippocampus after exposure to stress followed by global ischemia. We focused on the effects of microglial M1/M2 polarization and pro- and anti-inflammatory mediators in stressed ischemic animals. Male Sprague-Dawley rats were exposed to 8 consecutive days of social defeat stress and then subjected to global ischemia or sham surgery. The rats received intraperitoneal injections of progesterone (8mg/kg) or vehicle at 2h post-ischemia followed by subcutaneous injections at 6h and once every 24h post-injury for 7days. The animals were killed at 7 and 14days post-ischemia, and brains were removed and processed to assess outcome measures using histological, immunohistochemical and molecular biology techniques. Pre-ischemic stress (1) exacerbated neuronal loss and neurodegeneration as well as microglial activation in the selectively vulnerable CA1 hippocampal region, (2) dysregulated microglial polarization, leading to upregulation of both M1 and M2 phenotype markers, (3) increased pro-inflammatory cytokine expression, and (4) reduced anti-inflammatory cytokine and neurotrophic factor expression in the ischemic hippocampus. Treatment with progesterone significantly attenuated stress-induced microglia priming by modulating polarized microglia and the inflammatory environment in the hippocampus, the area most vulnerable to ischemic injury. Our findings can be taken to suggest that progesterone holds potential as a candidate for clinical testing in ischemic stroke where high stress may be a contributing factor.

Cerebral gray matter volume reduction in subcortical vascular mild cognitive impairment patients and subcortical vascular dementia patients, and its relation with cognitive deficits

INTRODUCTION

Subcortical vascular mild cognitive impairment (svMCI) is the predementia stage of subcortical vascular dementia (SVaD). The aim of this research is to explore and compare cerebral gray matter (GM) volume reduction in svMCI patients and SVaD patients, and to investigate the relationship between cerebral GM volume reduction and cognitive deficits.

METHODS

Thirty one svMCI patients, 29 SVaD patients, and 31 healthy controls were recruited in our research. They conducted neuropsychological tests and brain structural magnetic resonance imaging (MRI) examination. To detect cerebral GM volume reduction in svMCI patients and SVaD patients, we used statistical parametric mapping 8-voxel-based morphometry 8 (SPM8-VBM8) method to analyze MRI data. To detect the relationship between cerebral GM volume reduction and cognitive deficits, multiple linear regression analysis was used.

RESULTS

Compared with healthy controls, svMCI patients showed cerebral GM volume reduction in hippocampus and parahippocampal gyrus, insula and superior temporal gyrus. Compared with healthy controls, SVaD patients exhibited more atrophy which encompasses all of these areas plus anterior and middle cingulate, inferior temporal gyrus, orbitofrontal cortex, and superior frontal gyrus. In svMCI patients, cerebral GM volume reduction correlated with memory loss, attention dysfunction, and language dysfunction; in SVaD patients, besides those cognitive deficits, cerebral GM volume reduction correlated with more cognitive impairments, including executive dysfunction, neuropsychiatric symptom, and depression.

CONCLUSIONS

Our findings prove that both svMCI patients and SVaD patients exhibit cerebral GM volume reduction and there may exist a hierarchy between svMCI and SVaD, and cerebral GM volume reduction in both svMCI patients and SVaD patients correlates with cognitive deficits, which can help us understand the mechanism of cognitive impairments in svMCI patients and SVaD patients, and diagnose SVaD at its early stage.

In-Depth Proteomic Analysis of the Hippocampus in a Rat Model after Cerebral Ischaemic Injury and Repair by Danhong Injection (DHI)

Stroke is the second most common cause of death worldwide. A systematic description and characterization of the strokes and the effects induced in the hippocampus have not been performed so far. Here, we analysed the protein expression in the hippocampus 24 h after cerebral ischaemic injury and repair. Drug intervention using Danhong injection (DHI), which has been reported to have good therapeutic effects in a clinical setting, was selected for our study of cerebral ischaemia repair in rat models. A larger proteome dataset and total 4091 unique proteins were confidently identified in three biological replicates by combining tissue extraction for rat hippocampus and LC-MS/MS analysis. A label-free approach was then used to quantify the differences among the four experimental groups (Naive, Sham, middle cerebral artery occlusion (MCAO) and MCAO + DHI groups) and showed that about 2500 proteins on average were quantified in each of the experiment group. Bioinformatics analysis revealed that in total 280 unique proteins identified above were differentially expressed (P < 0.05). By combining the subcellular localization, hierarchical clustering and pathway information with the results from injury and repair phase, 12 significant expressed proteins were chosen and verified with respect to their potential as candidates for cerebral ischaemic injury by Western blot. The primary three signalling pathways of the candidates related may be involved in molecular mechanisms related to cerebral ischaemic injury. In addition, a glycogen synthase kinase-3β (Gsk-3β) inhibitor of the candidates with the best corresponding expression trends between western blotting (WB) and label-free quantitative results were chosen for further validation. The results of Western blot analysis of protein expression and 2,3,5- chloride three phenyl tetrazole (TTC) staining of rat brains showed that DHI treatment and Gsk-3β inhibitor are both able to confer protection against ischaemic injury in rat MCAO model. The observations of the present study provide a novel understanding regarding the regulatory mechanism of cerebral ischaemic injury.

Transient cerebral ischemia induces albumin expression in microglia only in the CA1 region of the gerbil hippocampus

Albumin, the most abundant plasma protein, is known to exhibit a neuroprotective effect in animal models of focal and global cerebral ischemia. In the present study, the expression and immunoreactivity of albumin was examined in the hippocampus following 5 min of transient cerebral ischemia in gerbils. Albumin immunoreactivity was observed in microglia of the CA1 hippocampal region 2 days post-ischemic insult, and it was significantly increased at 4 days following ischemia-reperfusion. In addition, at 4 days post-ischemic insult, albumin-immunoreactive microglia were abundant in the stratum pyramidale of the CA1 region. The present results demonstrated that albumin was newly expressed post-injury in microglia in the CA1 region, suggesting ischemia-induced neuronal loss. Albumin expression may therefore be associated with ischemia-induced delayed neuronal death in the CA1 region following transient cerebral ischemia.

Autophagy-regulated AMPAR subunit upregulation in in vitro oxygen glucose deprivation/reoxygenation-induced hippocampal injury

Autophagy has been implicated to mediate experimental cerebral ischemia/reperfusion-induced neuronal death; the underlying molecular mechanisms, though, are poorly understood. In this study, we investigated the role of autophagy in regulating the expression of AMPAR subunits (GluR1, GluR2, and GluR3) in oxygen glucose deprivation/reperfusion (OGD/R)-mediated injury of hippocampal neurons. Our results showed that, OGD/R-induced hippocampal neuron injury was accompanied by accumulation of autophagosomes and autolysosomes in cytoplasm alongside a dramatic increase in expression of autophagy-related genes, LC3 and Beclin 1 and increased intracellular Ca²⁺ levels. Pre-treatment with autophagy inhibitor 3-methyladenine (3-MA) significantly reduced this effect. Moreover, the OGD/R-induced upregulation of mRNA and protein expressions of GluR1, GluR2, and GluR3 were also effectively reversed in cells pretreated with 3-MA. Our findings indicate that OGD/R induced the expression of GluRs by activating autophagy in in vitro cultured hippocampal neurons, which could be effectively reversed by the administration of 3-MA.

Physiology Of Drowning: A Review

Drowning physiology relates to two different events: immersion (upper airway above water) and submersion (upper airway under water). Immersion involves integrated cardiorespiratory responses to skin and deep body temperature, including cold shock, physical incapacitation, and hypovolemia, as precursors of collapse and submersion. The physiology of submersion includes fear of drowning, diving response, autonomic conflict, upper airway reflexes, water aspiration and swallowing, emesis, and electrolyte disorders. Submersion outcome is determined by cardiac, pulmonary, and neurological injury. Knowledge of drowning physiology is scarce. Better understanding may identify methods to improve survival, particularly related to hot-water immersion, cold shock, cold-induced physical incapacitation, and fear of drowning.

White matter hyperintensities are associated with disproportionate progressive hippocampal atrophy

This study investigates relationships between white matter hyperintensity (WMH) volume, cerebrospinal fluid (CSF) Alzheimer's disease (AD) pathology markers, and brain and hippocampal volume loss. Subjects included 198 controls, 345 mild cognitive impairment (MCI), and 154 AD subjects with serial volumetric 1.5‐T MRI. CSF Aβ₄₂ and total tau were measured (n = 353). Brain and hippocampal loss were quantified from serial MRI using the boundary shift integral (BSI). Multiple linear regression models assessed the relationships between WMHs and hippocampal and brain atrophy rates. Models were refitted adjusting for (a) concurrent brain/hippocampal atrophy rates and (b) CSF Aβ₄₂ and tau in subjects with CSF data. WMH burden was positively associated with hippocampal atrophy rate in controls (P = 0.002) and MCI subjects (P = 0.03), and with brain atrophy rate in controls (P = 0.03). The associations with hippocampal atrophy rate remained following adjustment for concurrent brain atrophy rate in controls and MCIs, and for CSF biomarkers in controls (P = 0.007). These novel results suggest that vascular damage alongside AD pathology is associated with disproportionately greater hippocampal atrophy in nondemented older adults. © 2016 The Authors Hippocampus Published by Wiley Periodicals, Inc.

Neuroprotective effects of ischemic preconditioning on hippocampal CA1 pyramidal neurons through maintaining calbindin D28k immunoreactivity following subsequent transient cerebral ischemia

Ischemic preconditioning elicited by a non-fatal brief occlusion of blood flow has been applied for an experimental therapeutic strategy against a subsequent fatal ischemic insult. In this study, we investigated the neuroprotective effects of ischemic preconditioning (2-minute transient cerebral ischemia) on calbindin D28k immunoreactivity in the gerbil hippocampal CA1 area following a subsequent fatal transient ischemic insult (5-minute transient cerebral ischemia). A large number of pyramidal neurons in the hippocampal CA1 area died 4 days after 5-minute transient cerebral ischemia. Ischemic preconditioning reduced the death of pyramidal neurons in the hippocampal CA1 area. Calbindin D28k immunoreactivity was greatly attenuated at 2 days after 5-minute transient cerebral ischemia and it was hardly detected at 5 days post-ischemia. Ischemic preconditioning maintained calbindin D28k immunoreactivity after transient cerebral ischemia. These findings suggest that ischemic preconditioning can attenuate transient cerebral ischemia-caused damage to the pyramidal neurons in the hippocampal CA1 area through maintaining calbindin D28k immunoreactivity.

Differential spread of anoxic depolarization contributes to the pattern of neuronal injury after oxygen and glucose deprivation (OGD) in the Substantia Nigra in rat brain slices

Anoxic depolarization (AD) is an acute event evoked by brain ischemia, involving a profound loss of cell membrane potential and swelling that spreads over susceptible parts of the gray matter. Its occurrence is a strong predictor of the severity of neuronal injury. Little is known about this event in the Substantia Nigra, a midbrain nucleus critical for motor control. We tested the effects of oxygen and glucose deprivation (OGD), an in vitro model of brain ischemia, in rat midbrain slices. AD developed within 4min from OGD onset and spread in the Substantia Nigra pars reticulata (SNr), but not through the Substantia Nigra pars compacta (SNc). This differential effect involved a contrasting pattern of changes in membrane potential between dopamine-producing SNc and non-dopaminergic SNr neurons. A fast depolarization in SNr neurons was not followed by repolarization after the end of OGD, and was associated with swollen somata and beaded dendrites. In contrast, slowly developing depolarization of SNc neurons led to repolarization after OGD ended, and no changes in neuronal morphology were observed. The AD-resistance of the SNc involved smaller dysregulations of K⁺ and Ca²⁺ ions, and a slower loss of energy metabolites. Our results show that acute ischemia profoundly impairs the function and morphology of SNr neurons but not adjacent SNc neurons, and that the surprising higher tolerance of SNc neurons correlates with the resistance of the SNc region to AD. This differential response may affect the pattern of early neuronal injury that develops in the brainstem after acute ischemic insults.

Repeated Glucose Deprivation/Reperfusion Induced PC-12 Cell Death through the Involvement of FOXO Transcription Factor

BACKGROUND

Cognitive impairment and brain damage in diabetes is suggested to be associated with hypoglycemia. The mechanisms of hypoglycemia-induced neural death and apoptosis are not clear and reperfusion injury may be involved. Recent studies show that glucose deprivation/reperfusion induced more neuronal cell death than glucose deprivation itself. The forkhead box O (FOXO) transcription factors are implicated in the regulation of cell apoptosis and survival, but their role in neuronal cells remains unclear. We examined the role of FOXO transcription factors and the involvement of the phosphatidylinositol 3-kinase (PI3K)/Akt and apoptosis-related signaling pathways in PC-12 cells exposed to repeated glucose deprivation/reperfusion.

METHODS

PC-12 cells were exposed to control (Dulbecco's Modified Eagle Medium [DMEM] containing 25 mM glucose) or glucose deprivation/reperfusion (DMEM with 0 mM glucose for 6 hours and then DMEM with 25 mM glucose for 18 hours) for 5 days. MTT assay and Western blot analysis were performed for cell viability, apoptosis, and the expression of survival signaling pathways. FOXO3/4',6-diamidino-2-phenylindole staining was done to ascertain the involvement of FOXO transcription factors in glucose deprivation/reperfusion conditions.

RESULTS

Compared to PC-12 cells not exposed to hypoglycemia, cells exposed to glucose deprivation/reperfusion showed a reduction of cell viability, decreased expression of phosphorylated Akt and Bcl-2, and an increase of cleaved caspase-3 expression. Of note, FOXO3 protein was localized in the nuclei of glucose deprivation/reperfusion cells but not in the control cells.

CONCLUSION

Repeated glucose deprivation/reperfusion caused the neuronal cell death. Activated FOXO3 via the PI3K/Akt pathway in repeated glucose deprivation/reperfusion was involved in genes related to apoptosis.

Effect of ischemic preconditioning on antioxidant status in the gerbil hippocampal CA1 region after transient forebrain ischemia

Ischemic preconditioning (IPC) is a condition of sublethal transient global ischemia and exhibits neuroprotective effects against subsequent lethal ischemic insult. We, in this study, examined the neuroprotective effects of IPC and its effects on immunoreactive changes of antioxidant enzymes including superoxide dismutase (SOD) 1 and SOD2, catalase (CAT) and glutathione peroxidase (GPX) in the gerbil hippocampal CA1 region after transient forebrain ischemia. Pyramidal neurons of the stratum pyramidale (SP) in the hippocampal CA1 region of animals died 5 days after lethal transient ischemia without IPC (8.6% (ratio of remanent neurons) of the sham-operated group); however, IPC prevented the pyramidal neurons from subsequent lethal ischemic injury (92.3% (ratio of remanent neurons) of the sham-operated group). SOD1, SOD2, CAT and GPX immunoreactivities in the sham-operated animals were easily detected in pyramidal neurons in the stratum pyramidale (SP) of the hippocampal CA1 region, while all of these immunoreactivities were rarely detected in the stratum pyramidale at 5 days after lethal transient ischemia without IPC. Meanwhile, their immunoreactivities in the sham-operated animals with IPC were similar to (SOD1, SOD2 and CAT) or higher (GPX) than those in the sham-operated animals without IPC. Furthermore, their immunoreactivities in the stratum pyramidale of the ischemia-operated animals with IPC were steadily maintained after lethal ischemia/reperfusion. Results of western blot analysis for SOD1, SOD2, CAT and GPX were similar to immunohistochemical data. In conclusion, IPC maintained or increased the expression of antioxidant enzymes in the stratum pyramidale of the hippocampal CA1 region after subsequent lethal transient forebrain ischemia and IPC exhibited neuroprotective effects in the hippocampal CA1 region against transient forebrain ischemia.

Forced treadmill exercise can induce stress and increase neuronal damage in a mouse model of global cerebral ischemia

Physical exercise is known to be a beneficial factor by increasing the cellular stress tolerance. In ischemic stroke, physical exercise is suggested to both limit the brain injury and facilitate behavioral recovery. In this study we investigated the effect of physical exercise on brain damage following global cerebral ischemia in mice. We aimed to study the effects of 4.5 weeks of forced treadmill running prior to ischemia on neuronal damage, neuroinflammation and its effect on general stress by measuring corticosterone in feces. We subjected C57bl/6 mice (n = 63) to either treadmill running or a sedentary program prior to induction of global ischemia. Anxious, depressive, and cognitive behaviors were analyzed. Stress levels were analyzed using a corticosterone ELISA. Inflammatory and neurological outcomes were analyzed using immunohistochemistry, multiplex electrochemoluminescence ELISA and Western blot. To our surprise, we found that forced treadmill running induced a stress response, with increased anxiety in the Open Field test and increased levels of corticosterone. In accordance, mice subjected to forced exercise prior to ischemia developed larger neuronal damage in the hippocampus and showed higher cytokine levels in the brain and blood compared to non-exercised mice. The extent of neuronal damage correlated with increased corticosterone levels. To compare forced treadmill with voluntary wheel running, we used a different set of mice that exercised freely on running wheels. These mice did not show any anxiety or increased corticosterone levels. Altogether, our results indicate that exercise pre-conditioning may not be beneficial if the animals are forced to run as it can induce a detrimental stress response.

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Enforcement to run results in anxious behavior.

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Mice that are forced to run have elevated levels of corticosterone.

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Enforcement to run results in more neuronal death in hippocampus.

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Corticosterone levels correlates with the neuronal damage in hippocampus.

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Increased corticosterone and anxiety is not seen in mice that run voluntarily.

Ischemia-Induced Changes of PRAS40 and p-PRAS40 Immunoreactivities in the Gerbil Hippocampal CA1 Region After Transient Cerebral Ischemia

Proline-rich Akt substrate of 40-kDa (PRAS40) is one of the important interactive linkers between Akt and mTOR signaling pathways. The increase of PRAS40 is related with the reduction of brain damage induced by cerebral ischemia. In the present study, we investigated time-dependent changes in PRAS40 and phospho-PRAS40 (p-PRAS40) immunoreactivities in the hippocampal CA1 region of the gerbil after 5 min of transient cerebral ischemia. PRAS40 immunoreactivity in the CA1 region was decreased in pyramidal neurons from 12 h after ischemic insult in a time-dependent manner, and, at 5 days post-ischemia, PRAS40 immunoreactivity was newly expressed in astrocytes. p-PRAS40 immunoreactivity in the CA1 pyramidal neurons was hardly found 12 h and apparently detected again 1 and 2 days after ischemic insult. At 5 days post-ischemia, p-PRAS40 immunoreactivity in the CA1 pyramidal neurons was not found. These results indicate that ischemia-induced changes in PRAS40 and p-PRAS40 immunoreactivities in CA1 pyramidal neurons and astrocytes may be closely associated with delayed neuronal death in the hippocampal CA1 region following transient cerebral ischemia.

Neuroprotection of ischemic preconditioning is mediated by thioredoxin 2 in the hippocampal CA1 region following a subsequent transient cerebral ischemia

Preconditioning by brief ischemic episode induces tolerance to a subsequent lethal ischemic insult, and it has been suggested that reactive oxygen species are involved in this phenomenon. Thioredoxin 2 (Trx2), a small protein with redox-regulating function, shows cytoprotective roles against oxidative stress. Here, we had focused on the role of Trx2 in ischemic preconditioning (IPC)-mediated neuroprotection against oxidative stress followed by a subsequent lethal transient cerebral ischemia. Animals used in this study were randomly assigned to six groups; sham-operated group, ischemia-operated group, IPC plus (+) sham-operated group, IPC + ischemia-operated group, IPC + auranofin (a TrxR2 inhibitor) + sham-operated group and IPC + auranofin + ischemia-operated group. IPC was subjected to a 2 minutes of sublethal transient ischemia 1 day prior to a 5 minutes of lethal transient ischemia. A significant loss of neurons was found in the stratum pyramidale (SP) of the hippocampal CA1 region (CA1) in the ischemia-operated-group 5 days after ischemia-reperfusion; in the IPC + ischemia-operated-group, pyramidal neurons in the SP were well protected. In the IPC + ischemia-operated-group, Trx2 and TrxR2 immunoreactivities in the SP and its protein level in the CA1 were not significantly changed compared with those in the sham-operated-group after ischemia-reperfusion. In addition, superoxide dismutase 2 (SOD2) expression, superoxide anion radical ( O2-) production, denatured cytochrome c expression and TUNEL-positive cells in the IPC + ischemia-operated-group were similar to those in the sham-operated-group. Conversely, the treatment of auranofin to the IPC + ischemia-operated-group significantly increased cell damage/death and abolished the IPC-induced effect on Trx2 and TrxR2 expressions. Furthermore, the inhibition of Trx2R nearly cancelled the beneficial effects of IPC on SOD2 expression, O2- production, denatured cytochrome c expression and TUNEL-positive cells. In brief, this study shows that IPC conferred neuroprotection against ischemic injury by maintaining Trx2 and suggests that the maintenance or enhancement of Trx2 expression by IPC may be a legitimate strategy for therapeutic intervention of cerebral ischemia.

Comparison of catalase immunoreactivity in the hippocampus between young, adult and aged mice and rats

Catalase (CAT) is an important antioxidant enzyme and is crucial in modulating synaptic plasticity in the brain. In this study, CAT expression as well as neuronal distribution was compared in the hippocampus among young, adult and aged mice and rats. Male ICR mice and Sprague Dawley rats were used at postnatal month (PM) 1, PM 6 and PM 24 as the young, adult and aged groups, respectively (n=14/group). CAT expression was examined by immunohistochemistry and western blot analysis. In addition, neuronal distribution was examined by NeuN immunohistochemistry. In the present study, the mean number of NeuN-immunoreactive neurons was marginally decreased in mouse and rat hippocampi during aging, although this change was not identified to be significantly different. However, CAT immunoreactivity was significantly increased in pyramidal and granule neurons in the adult mouse and rat hippocampi and was significantly decreased in the aged mouse and rat hippocampi compared with that in the young animals. CAT protein levels in the hippocampus were also lowest in the aged mouse and rat hippocampus. These results indicate that CAT expression is significantly decreased in the hippocampi of aged animals and decreased CAT expression may be closely associated with aging.

Raised Intracellular Calcium Contributes to Ischemia-Induced Depression of Evoked Synaptic Transmission

Oxygen-glucose deprivation (OGD) leads to depression of evoked synaptic transmission, for which the mechanisms remain unclear. We hypothesized that increased presynaptic [Ca²⁺]_i during transient OGD contributes to the depression of evoked field excitatory postsynaptic potentials (fEPSPs). Additionally, we hypothesized that increased buffering of intracellular calcium would shorten electrophysiological recovery after transient ischemia. Mouse hippocampal slices were exposed to 2 to 8 min of OGD. fEPSPs evoked by Schaffer collateral stimulation were recorded in the stratum radiatum, and whole cell current or voltage clamp recordings were performed in CA1 neurons. Transient ischemia led to increased presynaptic [Ca²⁺]_i, (shown by calcium imaging), increased spontaneous miniature EPSP/Cs, and depressed evoked fEPSPs, partially mediated by adenosine. Buffering of intracellular Ca²⁺ during OGD by membrane-permeant chelators (BAPTA-AM or EGTA-AM) partially prevented fEPSP depression and promoted faster electrophysiological recovery when the OGD challenge was stopped. The blocker of BK channels, charybdotoxin (ChTX), also prevented fEPSP depression, but did not accelerate post-ischemic recovery. These results suggest that OGD leads to elevated presynaptic [Ca²⁺]_i, which reduces evoked transmitter release; this effect can be reversed by increased intracellular Ca²⁺ buffering which also speeds recovery.

Hippocampal subfield volumetry in patients with subcortical vascular mild cognitive impairment

Memory impairment is a typical characteristic of patients with subcortical vascular mild cognitive impairment (svMCI) or with amnestic mild cognitive impairment (aMCI). The hippocampus, which plays an important role in the consolidation of information from short-term memory to long-term memory, is a heterogeneous structure that consists of several anatomically and functionally distinct subfields. However, whether distinct hippocampal subfields are differentially and selectively affected by svMCI pathology and whether these abnormal changes in hippocampal subfields are different between svMCI and aMCI patients are largely unknown. A total of 26 svMCI patients, 26 aMCI patients and 26 healthy controls matched according to age, gender and years of education were enrolled in this study. We utilized an automated hippocampal subfield segmentation method provided by FreeSurfer to estimate the volume of several hippocampal subfields, including the cornu ammonis (CA) areas, the dentate gyrus (DG), the subiculum and the presubiculum. Compared with controls, the left subiculum and presubiculum and the right CA4/DG displayed significant atrophy in patients with svMCI. Interestingly, we also found significant differences in the volume of the right CA1 between the svMCI and aMCI groups. Taken together, our results reveal region-specific vulnerability of hippocampal subfields to svMCI pathology and identify distinct hippocampal subfield atrophy patterns between svMCI and aMCI patients.

Cell-Permeable Peptide Targeting the Nrf2-Keap1 Interaction: A Potential Novel Therapy for Global Cerebral Ischemia

The current study examined efficacy of a small Tat (trans-activator of transcription)-conjugated peptide activator of the Nrf2 (nuclear factor-E2-related factor-2) antioxidant/cell-defense pathway as a potential injury-specific, novel neuroprotectant against global cerebral ischemia (GCI). A competitive peptide, DEETGE-CAL-Tat, was designed to facilitate Nrf2 activation by disrupting interaction of Nrf2 with Keap1 (kelch-like ECH-associated protein 1), a protein that sequesters Nrf2 in the cytoplasm and thereby inactivates it. The DEETGE-CAL-Tat peptide contained the critical sequence DEETGE for the Nrf2-Keap1 interaction, the cell transduction domain of the HIV-Tat protein, and the cleavage sequence of calpain, which is sensitive to Ca(2+) increase and allows injury-specific activation of Nrf2. Using an animal model of GCI, we demonstrated that pretreatment with the DEETGE-CAL-Tat peptide markedly decreased Nrf2 interaction with Keap1 in the rat hippocampal CA1 region after GCI, and enhanced Nrf2 nuclear translocation and DNA binding. The DEETGE-CAL-Tat peptide also induced Nrf2 antioxidant/cytoprotective target genes, reduced oxidative stress, and induced strong neuroprotection and marked preservation of hippocampal-dependent cognitive function after GCI. These effects were specific as control peptides lacked neuroprotective ability. Intriguingly, the DEETGE-CAL-Tat peptide effects were also injury specific, as it had no effect upon neuronal survival or cognitive performance in sham nonischemic animals. Of significant interest, peripheral, postischemia administration of the DEETGE-CAL-Tat peptide from days 1-9 after GCI also induced robust neuroprotection and strongly preserved hippocampal-dependent cognitive function. Based on its robust neuroprotective and cognitive-preserving effects, and its unique injury-specific activation properties, the DEETGE-CAL-Tat peptide represents a novel, and potentially promising new therapeutic modality for the treatment of GCI.

SIGNIFICANCE STATEMENT

The current study demonstrates that DEETGE-CAL-Tat, a novel peptide activator of a key antioxidant gene transcription pathway in the hippocampus after global cerebral ischemia, can exert robust neuroprotection and preservation of cognitive function. A unique feature of the peptide is that its beneficial effects are injury specific. This feature is attractive as it targets drug activation specifically in the site of injury, and likely would lead to a reduction of undesirable side effects if translatable to the clinic. Due to its injury-specific activation, robust neuroprotection, and cognitive-preserving effects, this novel peptide may represent a much-needed therapeutic advance that could have efficacy in the treatment of global cerebral ischemia.

Monocarboxylate transporter 4 plays a significant role in the neuroprotective mechanism of ischemic preconditioning in transient cerebral ischemia

Monocarboxylate transporters (MCTs), which carry monocarboxylates such as lactate across biological membranes, have been associated with cerebral ischemia/reperfusion process. In this study, we studied the effect of ischemic preconditioning (IPC) on MCT4 immunoreactivity after 5 minutes of transient cerebral ischemia in the gerbil. Animals were randomly designated to four groups (sham-operated group, ischemia only group, IPC + sham-operated group and IPC + ischemia group). A serious loss of neuron was found in the stratum pyramidale of the hippocampal CA1 region (CA1), not CA2/3, of the ischemia-only group at 5 days post-ischemia; however, in the IPC + ischemia groups, neurons in the stratum pyramidale of the CA1 were well protected. Weak MCT4 immunoreactivity was found in the stratum pyramidale of the CA1 in the sham-operated group. MCT4 immunoreactivity in the stratum pyramidale began to decrease at 2 days post-ischemia and was hardly detected at 5 days post-ischemia; at this time point, MCT4 immunoreactivity was newly expressed in astrocytes. In the IPC + sham-operated group, MCT4 immunoreactivity in the stratum pyramidale of the CA1 was increased compared with the sham-operated group, and, in the IPC + ischemia group, MCT4 immunoreactivity was also increased in the stratum pyramidale compared with the ischemia only group. Briefly, present findings show that IPC apparently protected CA1 pyramidal neurons and increased or maintained MCT4 expression in the stratum pyramidale of the CA1 after transient cerebral ischemia. Our findings suggest that MCT4 appears to play a significant role in the neuroprotective mechanism of IPC in the gerbil with transient cerebral ischemia.

Neuroprotective Effects of Thymoquinone on the Hippocampus in a Rat Model of Traumatic Brain Injury

BACKGROUND

Traumatic brain injury is a leading cause of morbidity and mortality worldwide. We evaluated the neuroprotective effects of thymoquinone (TQ) in a rat model of traumatic brain injury by using biochemical and histopathologic methods for the first time.

MATERIALS AND METHODS

Twenty-four rats were divided into sham (n = 8), trauma (n = 8), and TQ-treated (n = 8) groups. A moderate degree of head trauma was induced with the use of Feeney's falling weight technique, and TQ (5 mg/kg/day) was administered to the TQ-treated group for 7 days. All animals were killed after cardiac perfusion. Brain tissues were extracted immediately after perfusion without damaging the tissues. Biochemical procedures were performed with the serum, and a histopathologic evaluation was performed on the brain tissues. Biochemical experiments included malondialdehyde (MDA), reduced and oxidized coenzyme Q10 analysis, DNA isolation and hydroylazation, and glutathione peroxidase, and superoxide dismutase analyses.

RESULTS

Neuron density in contralateral hippocampal regions (CA1, CA2-3, and CA4) 7 days after the trauma decreased significantly in the trauma and TQ-treated groups, compared with that in the control group. Neuron densities in contralateral hippocampal regions (CA1, CA2-3, and CA4) were greater in the TQ-treated group than in the trauma group. TQ did not increase superoxide dismutase or glutathione peroxidase antioxidant levels. However, TQ decreased the MDA levels.

CONCLUSIONS

These results indicate that TQ has a healing effect on neural cells after head injury and this effect is mediated by decreasing MDA levels in the nuclei and mitochondrial membrane of neurons.

Neuroprotection of Ischemic Preconditioning is Mediated by Anti-inflammatory, Not Pro-inflammatory, Cytokines in the Gerbil Hippocampus Induced by a Subsequent Lethal Transient Cerebral Ischemia

Ischemic preconditioning (IPC) induced by sublethal transient cerebral ischemia could reduce neuronal damage/death following a subsequent lethal transient cerebral ischemia. We, in this study, compared expressions of interleukin (IL)-2 and tumor necrosis factor (TNF)-α as pro-inflammatory cytokines, and IL-4 and IL-13 as anti-inflammatory cytokines in the gerbil hippocampal CA1 region between animals with lethal ischemia and ones with IPC followed by lethal ischemia. In the animals with lethal ischemia, pyramidal neurons in the stratum pyramidale (SP) of the hippocampal CA1 region were dead at 5 days post-ischemia; however, IPC protected the CA1 pyramidal neurons from lethal ischemic injury. Expressions of all cytokines were significantly decreased in the SP after lethal ischemia and hardly detected in the SP at 5 days post-ischemia because the CA1 pyramidal neurons were dead. IPC increased expressions of anti-inflammatory cytokines (IL-4 and IL-13) in the stratum pyramidale of the CA1 region following no lethal ischemia (sham-operation), and the increased expressions of IL-4 and IL-13 by IPC were continuously maintained is the SP of the CA1 region after lethal ischemia. However, pro-inflammatory cytokines (IL-2 and TNF-α) in the SP of the CA1 region were similar those in the sham-operated animals with IPC, and the IL-4 and IL-13 expressions in the SP were maintained after lethal ischemia. In conclusion, this study shows that anti-inflammatory cytokines significantly increased and longer maintained by IPC and this might be closely associated with neuroprotection after lethal transient cerebral ischemia.

Delayed hippocampal neuronal death in young gerbil following transient global cerebral ischemia is related to higher and longer-term expression of p63 in the ischemic hippocampus

The tumor suppressor p63 is one of p53 family members and plays a vital role as a regulator of neuronal apoptosis in the development of the nervous system. However, the role of p63 in mature neuronal death has not been addressed yet. In this study, we first compared ischemia-induced effects on p63 expression in the hippocampal regions (CA1–3) between the young and adult gerbils subjected to 5 minutes of transient global cerebral ischemia. Neuronal death in the hippocampal CA1 region of young gerbils was significantly slow compared with that in the adult gerbils after transient global cerebral ischemia. p63 immunoreactivity in the hippocampal CA1 pyramidal neurons in the sham-operated young group was significantly low compared with that in the sham-operated adult group. p63 immunoreactivity was apparently changed in ischemic hippocampal CA1 pyramidal neurons in both ischemia-operated young and adult groups. In the ischemia-operated adult groups, p63 immunoreactivity in the hippocampal CA1 pyramidal neurons was significantly decreased at 4 days post-ischemia; however, p63 immunoreactivity in the ischemia-operated young group was significantly higher than that in the ischemia-operated adult group. At 7 days post-ischemia, p63 immunoreactivity was decreased in the hippocampal CA1 pyramidal neurons in both ischemia-operated young and adult groups. Change patterns of p63 level in the hippocampal CA1 region of adult and young gerbils after ischemic damage were similar to those observed in the immunohistochemical results. These findings indicate that higher and longer-term expression of p63 in the hippocampal CA1 region of the young gerbils after ischemia/reperfusion may be related to more delayed neuronal death compared to that in the adults.

Ischemic preconditioning maintains the immunoreactivities of glucokinase and glucokinase regulatory protein in neurons of the gerbil hippocampal CA1 region following transient cerebral ischemia

Glucokinase (GK) is involved in the control of blood glucose homeostasis. In the present study, the effect of ischemic preconditioning (IPC) on the immunoreactivities of GK and its regulatory protein (GKRP) following 5 min of transient cerebral ischemia was investigated in gerbils. The gerbils were randomly assigned to four groups (sham-operated group, ischemia-operated group, IPC + sham-operated group and IPC + ischemia-operated group). IPC was induced by subjecting the gerbils to 2 min of ischemia, followed by 1 day of recovery. In the ischemia-operated group, a significant loss of neurons was observed in the stratum pyramidale (SP) of the hippocampal CA1 region (CA1) at 5 days post-ischemia; however, in the IPC+ischemia-operated group, the neurons in the SP were well protected. Following immunohistochemical investigation, the immunoreactivities of GK and GKRP in the neurons of the SP were markedly decreased in the CA1, but not the CA2/3, from 2 days post-ischemia, and were almost undetectable in the SP 5 days post-ischemia. In the IPC + ischemia-operated group, the immunoreactivities of GK and GKRP in the SP of the CA1 were similar to those in the sham-group. In brief, the findings of the present study demonstrated that IPC notably maintained the immunoreactivities of GK and GKRP in the neurons of the SP of CA1 following ischemia-reperfusion. This indicated that GK and GKRP may be necessary for neuron survival against transient cerebral ischemia.

Differences in the protein expression levels of Trx2 and Prx3 in the hippocampal CA1 region between adult and aged gerbils following transient global cerebral ischemia

The thioredoxin (Trx) and peroxiredoxin (Prx) redox system is associated with neuronal damage and neuroprotective effects via the regulation of oxidative stress in brain ischemia. In the present study, ischemia-induced changes in the protein expression levels of Trx2 and Prx3 in the stratum pyramidale (SP) of the hippocampal CA1 region were investigated in adult and aged gerbils, subjected to 5 min of transient global cerebral ischemia, using immunohistochemistry and western blot analysis. In the adult ischemia-group, minimal Trx2 immunoreactivity was detected in the SP 2 days after ischemia-reperfusion. In the aged animals, the Trx2 immunoreactivity in the sham-group was marginally lower compared with that in the adult sham-group. In the aged ischemia-group, Trx2 immunoreactivity in the SP was significantly higher 1, 2 and 4 days post-ischemia, compared with that in the adult ischemia-group and, in the 5 days post-ischemia group, Trx2 immunoreactivity was significantly decreased in the SP. Prx3 immunoreactivity in the SP of the adult ischemia-group was significantly decreased from 4 days after ischemia-reperfusion. In the aged animals, Prx3 immunoreactivity in the sham-group was also marginally lower compared with that in the adult sham-group. Prx3 immunoreactivity in the aged ischemia-group was also significantly higher 1, 2 and 4 days post-ischemia, compared with the adult ischemia-group; however, the Prx3 immunoreactivity was significantly decreased 5 days post-ischemia. The western blot analyses revealed that the pattern of changes in the protein levels of Trx2 and Prx3 in the adult and aged hippocampal CA1 region following ischemic damage were similar to the results obtained in the immunohistochemical data. These findings indicated that cerebral ischemia lead to different protein expression levels of Trx2 and Prx3 in the hippocampal CA1 region between adult and aged gerbils, and these differences may be associated with more delayed neuronal death in the aged gerbil hippocampus following transient global cerebral ischemia.

p63 Expression in the Gerbil Hippocampus Following Transient Ischemia and Effect of Ischemic Preconditioning on p63 Expression in the Ischemic Hippocampus

p63 is a transcription factor of p53 gene family, which are involved in development, differentiation and cell response to stress; however, its roles in ischemic preconditioning (IPC) in the brain are not clear. In the present study, we investigated the effect of IPC on p63 immunoreactivity caused by 5 min of transient cerebral ischemia in gerbils. IPC was induced by subjecting the gerbils to 2 min of transie ischemia 1 day prior to 5 min of transient ischemia. The animals were randomly assigned to four groups (sham-operated-group, ischemia-operated-group, IPC plus (+)-sham-operated-group and IPC + ischemia-operated-group). The number of viable neurons in the stratum pyramidale of the hippocampal CA1 region (CA1) was significantly increased by IPC + ischemia-operated-group compared with that in the ischemia-operated-group 5 days after ischemic insult. We found that strong p63 immunoreactivity was detected in the CA1 pyramidal neurons in the sham-operated-group, and the immunoreactivity was decreased with time after ischemia-reperfusion. In addition, strong p63 immunoreactivity was newly expressed in microglial cells of the CA1 region from 2 days after ischemia-reperfusion. In all the IPC + sham-operated-groups, p63 immunoreactivity in the CA1 pyramidal neurons was similar to that in the sham-operated-group, and the immunoreactivity was well maintained in the IPC + ischemia-operated-groups after cerebral ischemia. In brief, our present findings show that IPC dramatically protected the reduction of p63 immunoreactivity in the pyramidal neurons of the CA1 region after ischemia-reperfusion, and this result suggests that the expression of p63 may be necessary for neurons to survive after transient cerebral ischemia.

Comparison of different quantification methods to determine hippocampal damage after cerebral ischemia

BACKGROUND

Experimental stroke studies use multiple techniques to evaluate histopathological damage. Unfortunately, sensitivity and reproducibility of these techniques are poorly characterized despite pivotal influence on results.

METHOD

The present study compared several quantification methods to differentiate between two severities of global cerebral ischemia and reperfusion. Male Sprague-Dawley rats were randomized to moderate (10min) or severe (14min) ischemia by bilateral carotid occlusion (BCAO) with hemorrhagic hypotension. Neuronal cell count was determined in hippocampus at bregma -3.14mm and -3.8mm on day 3 and 28 post insult by counting neurons in the whole CA1 or in one to three defined regions of interest (ROI) placed in NeuN and Fluoro-Jade B stained sections.

RESULTS

In healthy rats hippocampal neurons were arranged uniformly, while distribution became inhomogeneous after ischemia. The number of NeuN and Fluoro-Jade B positive cells was dependent on localization. Differences between ischemia severities became more prominent at 28 days compared to 3 days. Fluoro-Jade B positive cell count increased at 28 days, staining rather injured not dying neurons.

COMPARISON WITH EXISTING METHODS

Placement of counting windows has a major influence on extent of differences between degree of neuronal injury and variations within groups.

CONCLUSIONS

The investigated quantification methods result in inconsistent information on the degree of damage. To obtain consistent and reliable results observation period should be extended beyond 3 days. Due to inhomogeneous distribution of viable neurons in CA1 after ischemia neuronal counting should not be performed in a single ROI window, but should be performed in multiple ROIs or the whole CA1 band.

Prosurvival NMDA 2A receptor signaling mediates postconditioning neuroprotection in the hippocampus

Ischemic postconditioning (Post C), which involves administration of a brief ischemia after the initial ischemic event, has been demonstrated to be strongly neuroprotective against global cerebral ischemia (GCI) and to improve cognitive outcome. To enhance understanding of the underlying mechanisms, the current study examined the role of NMDA receptors in mediating the beneficial effects of Post C (3 min ischemia) administered 2 days after GCI in adult male rats. The results revealed that Post C was strongly neuroprotective against GCI, and that this effect was blocked by administration of the NMDA receptor antagonist MK-801. Further work revealed that the NR2A-type NMDA receptors mediate the Post C beneficial effects as administration of a NR2A-preferring antagonist (NVP-A) blocked Post C neuroprotection and cognitive enhancement, while administration of a NR2B-preferring antagonist (Ro25) was without effect. Post C significantly up-regulated NR2A levels and phosphorylation of NR2A in the hippocampal CA1 region after Post C. Post C also increased Ca(2+) influx and activation/phosphorylation of CamKIIα at Thr(286), effects that were NR2A mediated as they were blocked by NVP-A. Phosphorylation of ERK and CREB was also increased by Post C, as were two downstream CREB-dependent prosurvival factors, brain derived neurotropic factor (BDNF) and Bcl2, effects that were blocked by the NR2A antagonist, NVP-A. Taken as a whole, the current study provides evidence that NR2A-activation and downstream prosurvival signaling is a critical mediator of Post C-induced neuroprotection and cognitive enhancement following GCI.

Effects of high-fat diet on neuronal damage, gliosis, inflammatory process and oxidative stress in the hippocampus induced by transient cerebral ischemia

In this study, we investigated the effects of a normal diet (ND) and high-fat diet (HFD) on delayed neuronal death in the gerbil hippocampal CA1 region after transient cerebral ischemia. In the HFD-fed gerbils, ischemia-induced hyperactivity was significantly increased and neuronal damage was represented more severely compared to the ND-fed gerbils. Ischemia-induced glial activation was accelerated in the HFD-fed gerbils. Cytokines including interleukin-2 and -4 were more sensitive in the hippocampal CA1 region of the HFD-fed gerbils after ischemia-reperfusion. Additionally, we found that decreased 4-HNE and SODs immunoreactivity and protein levels in the hippocampal CA1 region of the HFD-fed gerbils after ischemia-reperfusion. These results indicate that HFD may lead to the exacerbated effects on ischemia-induced neuronal death in the hippocampal CA1 region after ischemia-reperfusion. These effects of HFD may be associated with more accelerated activations of glial cells and imbalance of pro- and anti-inflammatory cytokines and/or antioxidants after transient cerebral ischemia.

Effects of ischemic preconditioning on VEGF and pFlk-1 immunoreactivities in the gerbil ischemic hippocampus after transient cerebral ischemia

Ischemia preconditioning (IPC) displays an important adaptation of the CNS to sub-lethal ischemia. In the present study, we examined the effect of IPC on immunoreactivities of VEGF-, and phospho-Flk-1 (pFlk-1) following transient cerebral ischemia in gerbils. The animals were randomly assigned to four groups (sham-operated-group, ischemia-operated-group, IPC plus (+) sham-operated-group, and IPC+ischemia-operated-group). IPC was induced by subjecting gerbils to 2 min of ischemia followed by 1 day of recovery. In the ischemia-operated-group, a significant loss of neurons was observed in the stratum pyramidale (SP) of the hippocampal CA1 region (CA1) alone 5 days after ischemia-reperfusion, however, in all the IPC+ischemia-operated-groups, pyramidal neurons in the SP were well protected. In immunohistochemical study, VEGF immunoreactivity in the ischemia-operated-group was increased in the SP at 1 day post-ischemia and decreased with time. Five days after ischemia-reperfusion, strong VEGF immunoreactivity was found in non-pyramidal cells, which were identified as pericytes, in the stratum oriens (SO) and radiatum (SR). In the IPC+sham-operated- and IPC+ischemia-operated-groups, VEGF immunoreactivity was significantly increased in the SP. pFlk-1 immunoreactivity in the sham-operated- and ischemia-operated-groups was hardly found in the SP, and, from 2 days post-ischemia, pFlk-1 immunoreactivity was strongly increased in non-pyramidal cells, which were identified as pericytes. In the IPC+sham-operated-group, pFlk-1 immunoreactivity was significantly increased in both pyramidal and non-pyramidal cells; in the IPC+ischemia-operated-groups, the similar pattern of VEGF immunoreactivity was found in the ischemic CA1, although the VEGF immunoreactivity was strong in non-pyramidal cells at 5 days post-ischemia. In brief, our findings show that IPC dramatically augmented the induction of VEGF and pFlk-1 immunoreactivity in the pyramidal cells of the CA1 after ischemia-reperfusion, and these findings suggest that the increases of VEGF and Flk-1 expressions may be necessary for neurons to survive from transient ischemic damage.

Postconditioning mitigates cell death following oxygen and glucose deprivation in PC12 cells and forebrain reperfusion injury in rats

Postconditioning mitigates ischemia-induced cellular damage via a modified reperfusion procedure. Mitochondrial permeability transition (MPT) is an important pathophysiological change in reperfusion injury. This study explores the role of MPT modulation underlying hypoxic postconditioning (HPoC) in PC12 cells and studies the neuroprotective effects of ischemic postconditioning (IPoC) on rats. Oxygen-glucose deprivation (OGD) was performed for 10 hr on PC12 cells. HPoC was induced by three cycles of 10-min reoxygenation/10-min rehypoxia after OGD. The MPT inhibitor N-methyl-4-isoleucine cyclosporine (NIM811) and the MPT inducer carboxyatractyloside (CATR) were administered to selective groups before OGD. Cellular death was evaluated by flow cytometry and Western blot analysis. JC-1 fluorescence signal was used to estimate the mitochondrial membrane potential (△Ψm ). Transient global cerebral ischemia (tGCI) was induced via the two-vessel occlusion and hypotension method in male Sprague Dawley rats. IPoC was induced by three cycles of 10-sec reperfusion/10-sec reocclusion after index ischemia. HPoC and NIM811 administration attenuated cell death, cytochrome c release, and caspase-3 activity and maintained △Ψm of PC12 cells after OGD. The addition of CATR negated the protection conferred by HPoC. IPoC reduced neuronal degeneration and cytochrome c release and cleaved caspase-9 expression of hippocampal CA1 neurons in rats after tGCI. HPoC protected PC12 cells against OGD by modulating the MPT. IPoC attenuated degeneration of hippocampal neurons after cerebral ischemia.

Amyloid burden, cerebrovascular disease, brain atrophy, and cognition in cognitively impaired patients

BACKGROUND

We investigated the independent effects of Alzheimer's disease (AD) and cerebrovascular disease (CVD) pathologies on brain structural changes and cognition.

METHODS

Amyloid burden (Pittsburgh compound B [PiB] retention ratio), CVD markers (volume of white matter hyperintensities [WMH] and number of lacunae), and structural changes (cortical thickness and hippocampal shape) were measured in 251 cognitively impaired patients. Path analyses were utilized to assess the effects of these markers on cognition.

RESULTS

PiB retention ratio was associated with hippocampal atrophy, which was associated with memory impairment. WMH were associated with frontal thinning, which was associated with executive and memory dysfunctions. PiB retention ratio and lacunae were also associated with memory and executive dysfunction without the mediation of hippocampal or frontal atrophy.

CONCLUSIONS

Our results suggest that the impacts of AD and CVD pathologies on cognition are mediated by specific brain regions.

Change of peroxisome proliferator-activated receptor γ expression pattern in the gerbil dentate gyrus after transient global cerebral ischemia

Peroxisome proliferator-activated receptor γ (PPARγ) has various actions including the regulation of adipocyte differentiation, lipid metabolism and glucose homeostasis. In the present study, we examined the changes of PPARγ immunoreactivity and protein levels in the gerbil dentate gyrus (DG) after transient global cerebral ischemia using immunohistochemistry and western blot analysis. PPARγ immunoreactivity was gradually increased from 1 day after ischemia-reperfusion. PPARγ immunoreactivity, in accordance with protein level, was highest at 2 days after ischemia-reperfusion and was detected in microglia at this time. Thereafter, both PPARγ immunoreactivity and protein level were decreased with time in the ischemic DG. These results indicate that PPARγ may be related to the ischemia-induced microglial activation and neuronal damage/death in the DG after transient global cerebral ischemia.

Changes and expressions of Redd1 in neurons and glial cells in the gerbil hippocampus proper following transient global cerebral ischemia

Redd1 (known as RTP801/Dig2/DDIT4) is a stress-induced protein, and it is known to be regulated in response to some stresses including hypoxia and oxidative stress. In the present study, we investigated the time-dependent changes in Redd1 immunoreactivity and its protein levels in the gerbil hippocampus proper (CA1-3 regions) after 5 min of transient global cerebral ischemia using immunohistochemistry and Western blot analysis. Redd1 immunoreactivity was apparently changed in the pyramidal neurons of the ischemic CA1 region, not in the pyramidal neurons of the ischemic CA2/3 region. Redd1 immunoreactivity in the CA1 pyramidal neurons was significantly increased at 6 h post-ischemia, decreased until 1 day post-ischemia, increased again at 2 days post-ischemia and weakly observed at 5 days post-ischemia. Especially, at 5 days after ischemic damage, Redd1 immunoreactivity was newly expressed in astrocytes and GABAergic interneurons in the CA1 region. Redd1 protein levels in the ischemic CA1 region were changed like the pattern of the Redd1 immunoreactivity. These results indicate that Redd1 immunoreactivity and protein levels are increased in the ischemic CA1 region at an early time after ischemic damage and that the increased Redd1 expression may be closely related to the delayed neuronal death of the CA1 pyramidal neurons following 5 min of transient global cerebral ischemia.

Comparison of neuroprotective effects of extract and fractions from Agarum clathratum against experimentally induced transient cerebral ischemic damage

CONTEXTS: Agarum clathratum (Laminariaceae), a typical brown algae, has been identified by National Plant Quarantine Service in Korea. The extract of A. clathratum has antioxidant activities.

OBJECTIVE

We investigated the neuroprotective effects of crude-extract, ethyl acetate (EA)-, n-butanol (BU)-, dichloromethane (DCM)- and n-hexane (Hx)-fractions from A. clathratum on ischemic damage in the gerbil hippocampal CA1 region (CA1) after 5 min of transient cerebral ischemia.

MATERIALS AND METHODS

Agarum clathratum was collected in Kangwon province (South Korea) and treated with 95% ethanol. The ethanol extract was suspended in distilled water and subjected to a series of partitions with EA, BU, DCM and Hx. Each of extract and fraction was orally administered with 50 mg/kg once a day for one week before ischemia--reperfusion (I-R).

RESULT

In the crude-extract-, EA- and BU-fraction-treated ischemia groups, we found strong neuroprotection in the CA1--about 80-89% of CA1 pyramidal neurons survived. However, in the DCM- and Hx-fraction-treated ischemia groups, we did not find any significant neuroprotection. In addition, we observed changes in astrocytes and microglia in the ischemic CA1. In the crude-extract, EA- and BU-fraction-treated ischemia groups, the distribution pattern and activity of the glial cells were similar to that found in the sham group.

DISCUSSION

Repeated supplements of crude-extract, EA- and BU-fractions of A. clathratum could protect neurons from I-R injury in the hippocampal CA1 induced by transient cerebral ischemia via decrease of glial activation.

GABA(A) receptor dephosphorylation followed by internalization is coupled to neuronal death in in vitro ischemia

Cerebral ischemia is characterized by an early disruption of GABAergic neurotransmission contributing to an imbalance of the excitatory/inhibitory equilibrium and neuronal death, but the molecular mechanisms involved are not fully understood. Here we report a downregulation of GABA(A) receptor (GABA(A)R) expression, affecting both mRNA and protein levels of GABA(A)R subunits, in hippocampal neurons subjected to oxygen-glucose deprivation (OGD), an in vitro model of ischemia. Similar alterations in the abundance of GABA(A)R subunits were observed in in vivo brain ischemia. OGD reduced the interaction of surface GABA(A)R with the scaffold protein gephyrin, followed by clathrin-dependent receptor internalization. Internalization of GABA(A)R was dependent on glutamate receptor activation and mediated by dephosphorylation of the β3 subunit at serine 408/409. Expression of phospho-mimetic mutant GABA(A)R β3 subunits prevented receptor internalization and protected hippocampal neurons from ischemic cell death. The results show a key role for β3 GABA(A)R subunit dephosphorylation in the downregulation of GABAergic synaptic transmission in brain ischemia, contributing to neuronal death. GABA(A)R phosphorylation might be a therapeutic target to preserve synaptic inhibition in brain ischemia.

Cortical thickness and hippocampal shape in pure vascular mild cognitive impairment and dementia of subcortical type

BACKGROUND AND PURPOSE

The progression pattern of brain structural changes in patients with isolated cerebrovascular disease (CVD) remains unclear. To investigate the role of isolated CVD in cognitive impairment patients, patterns of cortical thinning and hippocampal atrophy in pure subcortical vascular mild cognitive impairment (svMCI) and pure subcortical vascular dementia (SVaD) patients were characterized.

METHODS

Forty-five patients with svMCI and 46 patients with SVaD who were negative on Pittsburgh compound B (PiB) positron emission tomography imaging and 75 individuals with normal cognition (NC) were recruited.

RESULTS

Compared with NC, patients with PiB(-) svMCI exhibited frontal, language and retrieval type memory dysfunctions, which in patients with PiB(-) SVaD were further impaired and accompanied by visuospatial and recognition memory dysfunctions. Compared with NC, patients with PiB(-) svMCI exhibited cortical thinning in the frontal, perisylvian, basal temporal and posterior cingulate regions. This atrophy was more prominent and extended further toward the lateral parietal and medial temporal regions in patients with PiB(-) SVaD. Compared with NC subjects, patients with PiB(-) svMCI exhibited hippocampal shape deformities in the lateral body, whilst patients with PiB(-) SVaD exhibited additional deformities within the lateral head and inferior body.

CONCLUSIONS

Our findings suggest that patients with CVD in the absence of Alzheimer's disease pathology can be demented, showing cognitive impairment in multiple domains, which is consistent with the topography of cortical thinning and hippocampal shape deformity.