Cellular mechanisms involved in brain ischemia

Mechanisms Underlying Neuroprotection by the NSAID Mefenamic Acid in an Experimental Model of Stroke

Stroke is a devastating neurological event with limited treatment opportunities. Recent advances in understanding the underlying pathogenesis of cerebral ischemia support the involvement of multiple biochemical pathways in the development of the ischemic damage. Fenamates are classical non-steroidal anti-inflammatory drugs but they are also highly subunit-selective modulators of GABA_A receptors, activators of I_KS potassium channels and antagonists of non-selective cation channels and the NLRP3 inflammosome. In the present study we investigated the effect of mefenamic acid (MFA) in a rodent model of ischemic stroke and then addressed the underlying pharmacological mechanisms in vitro for its actions in vivo. The efficacy of MFA in reducing ischemic damage was evaluated in adult male Wistar rats subjected to a 2-h middle cerebral artery occlusion. Intracerebroventricular (ICV) infusion of MFA (0.5 or 1 mg/kg) for 24 h, significantly reduced the infarct volume and the total ischemic brain damage. In vitro, the fenamates, MFA, meclofenamic acid, niflumic acid, and flufenamic acid each reduced glutamate-evoked excitotoxicity in cultured embryonic rat hippocampal neurons supporting the idea that this is a drug class action. In contrast the non-fenamate NSAIDs, ibuprofen and indomethacin did not reduce excitotoxicity in vitro indicating that neuroprotection by MFA was not dependent upon anti-inflammatory actions. Co-application of MFA (100 μM) with either of the GABA_A antagonists picrotoxin (100 μM) or bicuculline (10 μM) or the potassium channel blocker tetraethylammonium (30 mM) did not prevent neuroprotection with MFA, suggesting that the actions of MFA also do not depend on GABA_A receptor modulation or potassium channel activation. These new findings indicate that fenamates may be valuable in the adjunctive treatment of ischemic stroke.

The dual role of KCNQ/M channels upon OGD or OGD/R insults in cultured cortical neurons of mice: Timing is crucial in targeting M-channels against ischemic injur ies

KCNQ/M potassium channels play a vital role in neuronal excitability; however, it is required to explore their pharmacological modulation on N-Methyl- d-aspartic acid receptors (NMDARs)-mediated glutamatergic transmission of neurons upon ischemic insults. In the current study, both presynaptic glutamatergic release and activities of NMDARs were measured by NMDAR-induced miniature excitatory postsynaptic currents (mEPSCs) in cultured cortical neurons of C57 mice undergoing oxygen and glucose deprivation (OGD) or OGD/reperfusion (OGD/R). The KCNQ/M-channel opener, retigabine (RTG), suppressed the overactivation of postsynaptic NMDARs induced by OGD and then NO transient; RTG also decreased OGD-induced neuronal death measured with MTT assay, suggesting the beneficial role of KCNQ/M-channels for the neurons exposed to ischemic insults. However, when the neurons exposed to the subsequent reperfusion, KCNQ/M-channels played a differential role from its protective effect. OGD/R increased presynaptic glutamatergic release, which was further augmented by RTG or decreased by KCNQ/M-channel blocker, XE991. Reactive oxygen species (ROS) were produced partly in a NO-dependent manner. In addition, XE991 decreased neuronal injuries upon reperfusion measured with DCF and PI staining. Meanwhile, the addition of RTG upon OGD or XE991 upon reperfusion can reverse OGD or OGD/R-reduced mitochondrial membrane potential. Our present study indicates the dual role of KCNQ/M-channels in OGD and OGD/R, which will decide the fate of neurons. Provided that activation of KCNQ/M-channels has differential effects on neuronal injuries during OGD or OGD/R, we propose that therapy targeting KCNQ/M-channels may be effective for ischemic injuries but the proper timing is so crucial for the corresponding treatment.

(S)-Oxiracetam is the Active Ingredient in Oxiracetam that Alleviates the Cognitive Impairment Induced by Chronic Cerebral Hypoperfusion in Rats

Chronic cerebral hypoperfusion is a pathological state that is associated with the cognitive impairments in vascular dementia. Oxiracetam is a nootropic drug that is commonly used to treat cognitive deficits of cerebrovascular origins. However, oxiracetam is currently used as a racemic mixture whose effective ingredient has not been identified to date. In this study, we first identified that (S)-oxiracetam, but not (R)-oxiracetam, was the effective ingredient that alleviated the impairments of spatial learning and memory by ameliorating neuron damage and white matter lesions, increasing the cerebral blood flow, and inhibiting astrocyte activation in chronic cerebral hypoperfused rats. Furthermore, using MALDI-MSI and LC-MS/MS, we demonstrated that (S)-oxiracetam regulated ATP metabolism, glutamine-glutamate and anti-oxidants in the cortex region of hypoperfused rats. Altogether, our results strongly suggest that (S)-oxiracetam alone could be a nootropic drug for the treatment of cognitive impairments caused by cerebral hypoperfusion.

Emergency and critical care management of acute ischaemic stroke

Ischaemic stroke is a devastating condition that is the leading cause of disability in the USA. Over the last 2 decades, the focus of management has shifted from secondary stroke prevention to acute treatment. Coordinated care starts in the field with the emergency medical service providers and continues in the ambulance and the emergency department through to the intensive care unit. After diagnosis and stabilization, a major goal is reperfusion therapy with intravenous fibrinolytics. Neuroimaging research is focused on improving patient selection, expanding treatment windows, and increasing the safety of therapeutic intervention. The role of adjunctive intra-arterial and mechanical thrombectomy remains undefined, and methods to improve reperfusion using sonolysis and new-generation fibrinolytics are currently investigational. Treatment in the intensive care unit targets prevention of secondary brain injury through optimization of blood pressure, cerebral perfusion, glucose, and temperature management, ventilation, and oxygenation. The most feared complications include malignant cerebral edema and symptomatic hemorrhagic transformation. Decompressive craniectomy is life saving, but questions regarding patient selection and timing remain. Hyperosmolar agents are currently used to mitigate cerebral edema, but newer agents to prevent the formation of cerebral edema at the molecular level are being studied. We outline a practical approach to current emergency and intensive care management based on consensus guidelines and the best available evidence.

Mechanisms of acute brain injury after subarachnoid hemorrhage

Brain injury after subarachnoid hemorrhage (SAH) is a biphasic event with an acute ischemic insult at the time of the initial bleed and secondary events such as cerebral vasospasm 3 to 7 days later. Although much has been learned about the delayed effects of SAH, less is known about the mechanisms of acute SAH-induced injury. Distribution of blood in the subarachnoid space, elevation of intracranial pressure, reduced cerebral perfusion and cerebral blood flow (CBF) initiates the acute injury cascade. Together they lead to direct microvascular injury, plugging of vessels and release of vasoactive substances by platelet aggregates, alterations in the nitric oxide (NO)/nitric oxide synthase (NOS) pathways and lipid peroxidation. This review will summarize some of these mechanisms that contribute to acute cerebral injury after SAH.

Malignant hemispheric infarction of the middle cerebral artery. Diagnostic considerations and treatment options

INTRODUCTION

Malignant hemispheric infarction (MHI) is a specific and devastating type of ischemic stroke. It usually affects all or part of the territory of the middle cerebral artery although its effects may extend to other territories as well. Its clinical outcome is frequently catastrophic when only conventional medical treatment is applied.

OBJECTIVE

The purpose of this review is to analyse the available scientific evidence on the treatment of this entity.

DEVELOPMENT

MHI is associated with high morbidity and mortality. Its clinical characteristics are early neurological deterioration and severe hemispheric syndrome. Its hallmark is the development of space-occupying cerebral oedema between day 1 and day 3 after symptom onset. The mass effect causes displacement, distortion, and herniation of brain structures even when intracranial hypertension is initially absent. Until recently, MHI was thought to be fatal and untreatable because mortality rates with conventional medical treatment could exceed 80%. In this unfavourable context, decompressive hemicraniectomy has re-emerged as a therapeutic alternative for selected cases, with reported decreases in mortality ranging between 15% and 40%.

CONCLUSIONS

In recent years, several randomised clinical trials have demonstrated the benefit of decompressive hemicraniectomy in patients with MHI. This treatment reduces mortality in addition to improving functional outcomes.

Effects of SARA on oxygen-glucose deprivation in PC12 cell line

Ischemic stroke is a major composition of cerebrovascular disease, seriously threatening to human health in the world. Activin A (ActA), belonging to transforming growth factor-beta (TGF-β) super family, plays an important role in the hypoxic-ischemic brain injury through ActA/Smads pathway. While as an essential phosphorylation assistor in TGF-β signaling, the functions and mechanisms of smad anchor for receptor activation (SARA) in ischemic brain injury remain poorly understood. To solve this problem and explore the pathological processes of ischemic stroke, we used an Oxygen-Glucose deprivation (OGD) model in nerve growth factor-induced differentiated rattus PC12 pheochromocytoma cells and down regulated the expressions of SARA by RNA interference technology. Our results showed that the repression of SARA before OGD exposure reduced the expressions of Smad2, 3, 4 mRNA and the phosphorylation rate of Smad2 protein, but it did not affect the mRNA expressions of Smad7. After OGD treatment, ActA/Smads pathway was activated and the expression of SARA in the SARA pre-repression group was significantly up-regulated. The pre-repression of SARA increased the sensitivities of nerve-like cells to OGD damage. Moreover, the mRNA expression of Smad7 which was supposed to participate in the negative feedback of ActA/Smads pathway was also elevated due to OGD injury. Taken together, these results suggest a positive role of SARA in assisting the phosphorylation of Smad2 and maintaining the neuron protective effect of ActA/Smads pathway.

Cognitive effects of NSAIDs in cerebral ischemia: a hypothesis exploring mechanical action mediated pharmacotherapy

Cerebral ischemia is associated with altered neuronal mechanics leading to dynamic reshaping of neuronal structures, giving rise to a cascade of biological pathways leading to many deleterious consequences and cognitive deficits. Memory and learning specifically are mediated by neurotransmitter release from vesicles clustered at the synapse. Mechanical tension is an important factor governing the amount of vesicular neurotransmitter release in response to an action potential. Neuroinflammation in cerebral ischemia leads to altered mechanical/physical forces on neurons which gives rise to abnormal mechanical tension along the neuron resulting in neurotransmitter imbalance leading to cognitive dysfunction. We consider the possibility that modulation of mechanical forces on neurons may be a therapeutic strategy to help prevent cognitive deficit in cerebral ischemia. Here we show how NSAIDs may act as candidate pharmacological molecules which have the ability to inhibit neuroinflammation and which can alter neuronal mechanics by their COX-2 inhibiting property.

Pharmacokinetics of125I-radiolabelled PEG-hemoglobin SB1

PEG-hemoglobin SB1 (SB1) is a polyethylene glycol (PEG)-modified hemoglobin-based oxygen carrier, intended for use as resuscitation fluid for brain stroke and as a blood substitute. An intravenous pharmacokinetics (PK) studies with SB1 was investigated in male albino Sprague-Dawley (SD) rats and male beagle dogs at doses of 5 and 12.5 ml/kg for rats and 10 ml/kg for dogs. Total hemoglobin in plasma and whole blood was determined by gamma scintillation counter-detecting 125I-radiolabelled SB1. In the 5 ml/kg rats (n = 9), the Cmax, t1/2, AUCt and Tmax were 9.055 mg equivalents/ml, 9.6 hr, 79.6 mg equivalents.hr/ml and 0.20 hr in the plasma and 4.954 mg equivalents/ml, 9.7 hr, 37.6 mg equivalents.hr/ml and 0.11 hr in the whole blood, respectively. Those parameters in the 12.5 ml/Kg of rats (n = 9) were 19.00 mg equivalents/ml, 10.6 hr, 223.5 mg equivalents.hr/ml and 0.33 hr in the plasma and 10.58 mg equivalents/ml, 16.1 hr, 99.0 mg equivalents.hr/ml and 0.33 hr in the whole blood, respectively. An increase in the dose level from 5 to 12.5 ml/kg resulted in the increase in both Cmax and AUC24, and the increases in these parameters appeared to be in proportion to the dose increment. Thus, following the 2.5-fold increase in administered dose, Cmax was increased by a factor of 2.1 in both plasma and whole blood, while AUC24 was increased by a factor of 2.8 for plasma and 2.6 for whole blood. In the dogs receiving 10 ml/kg (n = 3), the Cmax, t1/2, AUC168 and Tmax were 12.70 mg equivalents/ml, 47.2 hr, 425.7 mg equivalents.hr/ml and 0.083 hr in the plasma and 8.372 mg equivalents/ml, 50.3 hr, 241.3 mg equivalents.hr/ml and 1.003 hr in the whole blood, respectively. The present work provides an insight into the pharmacological behavior of a PEG-modified hemoglobin.

Evidence for neuroprotection by the fenamate NSAID, mefenamic acid

Fenamate NSAIDs are inhibitors of cyclooxygenases, antagonists of non-selective cation channels, subtype-selective modulators of GABA(A) receptors, weak inhibitors of glutamate receptors and activators of some potassium channels. These pharmacological actions are all implicated in the pathogenesis of ischemic stroke. The aim of this study was to investigate the hypothesis that the fenamate, mefenamic acid, is neuroprotective in an in vitro and in vivo model of stroke. Embryonic rat hippocampal neurons were cultured and maintained for up to 14 days in vitro. At 9 or 14 days, cells were exposed to glutamate (5microM) or glutamate (5microM) plus mefenamic acid (10-100microM) or the control agent, MK-801 (10microM) for 10min. 24h later, cell death was determined by measuring lactate dehydrogenase (LDH) levels in the culture media. In vivo, male Wistar rats (300-350g) were subjected to 2h middle cerebral artery occlusion (MCAO) followed by 24h reperfusion. Animals received either a single i.v. dose of MFA (10mg/kg or 30mg/kg), or MK-801 (2mg/kg) or saline prior to MCAO or, four equal doses of MFA (20mg/kg) at 1h intervals beginning 1h prior to MCAO. Ischemic damage was then assessed 24h after MCAO. In vitro, mefenamic acid (10-100microM) and MK-801 (10microM) significantly reduced glutamate-evoked cell death compared with control cultures. In vivo, MFA (20mg/kgx4) significantly reduced infarct volume, total ischemic brain damage and edema by 53% (p< or =0.02), 41% (p< or =0.002) and 45% (p< or =0.002) respectively. Furthermore, mefenamic acid reduced cerebral edema when measured as a function of brain water content. MK-801 was also neuroprotective against MCAO brain injury. This study demonstrates a significant neuroprotective effect by a fenamate NSAID against glutamate-induced cell toxicity, in vitro and against ischemic stroke in vivo. Further experiments are currently addressing the mechanism(s) of this neuroprotection.

Tamoxifen mediated estrogen receptor activation protects against early impairment of hippocampal neuron excitability in an oxygen/glucose deprivation brain slice ischemia model

Pretreatment of ovarectomized rats with estrogen shows long-term protection via activation of the estrogen receptor (ER). However, it remains unknown whether activation of the ER can provide protection against early neuronal damage when given acutely. We simulated ischemic conditions by applying oxygen and glucose deprived (OGD) solution to acute male rat hippocampal slices and examined the neuronal electrophysiological changes. Pyramidal neurons and interneurons showed a time-dependent membrane potential depolarization and reduction in evoked action potential frequency and amplitude over a 10 to 15 min OGD exposure. These changes were largely suppressed by 10 microM TAM. The TAM effect was neuron-specific as the OGD-induced astrocytic membrane potential depolarization was not altered. The TAM effect was mediated through ER activation because it could be simulated by 17beta-estradiol and was completely inhibited by the ER inhibitor ICI 182, 780, and is therefore an example of TAM's selective estrogen receptor modulator (SERM) action. We further show that TAM's effects on OGD-induced impairment of neuronal excitability was largely due to activation of neuroprotective BK channels, as the TAM effect was markedly attenuated by the BK channel inhibitor paxilline at 10 microM. TAM also significantly reduced the frequency and amplitude of AMPA receptor mediated spontaneous excitatory postsynaptic currents (sEPSCs) in pyramidal neurons which is an early consequence of OGD. Altogether, this study demonstrates that both 17beta-estradiol and TAM attenuate neuronal excitability impairment early on in a simulated ischemia model via ER activation mediated potentiation of BK K(+) channels and reduction in enhanced neuronal AMPA/NMDA receptor-mediated excitotoxicity.

Whole isolated neocortical and hippocampal preparations and their use in imaging studies

This study shows that two whole isolated preparations from the young mouse, the neocortical 'slab' and the hippocampal formation, are useful for imaging studies requiring both global monitoring using light transmittance (LT) imaging and high resolution cellular monitoring using 2-photon laser scanning microscopy (2PLSM). These preparations share advantages with brain slices such as maintaining intrinsic neuronal properties and avoiding cardiac or respiratory movement. Important additional advantages include the maintenance of all local input and output pathways, the absence of surfaces injured by slicing and the preservation of three-dimensional tissue structure. Using evoked extracellular field recording, we demonstrate long-term (hours) viability of both whole preparations. We then show that propagating cortical events such as anoxic depolarization (AD) and spreading depression (SD) can be imaged in both preparations, yielding results comparable to those in brain slices but retaining the tissue's three-dimensional structure. Using transgenic mice expressing green fluorescent protein (GFP) in pyramidal and granule cell neurons, 2PLSM confirms that these preparations are free of the surface damage observed in sliced brain tissue. Moreover the neurons undergo swelling with accompanying dendritic beading following AD induced by simulated ischemia, similar to cortical damage described in vivo.

Nitric oxide from neuronal nitric oxide synthase sensitises neurons to hypoxia-induced death via competitive inhibition of cytochrome oxidase

Hypoxia/ischaemia is known to trigger neuronal death, but the role of neuronal nitric oxide synthase (nNOS) in this process is controversial. Nitric oxide (NO) inhibits cytochrome oxidase in competition with oxygen. We tested whether NO derived from nNOS synergises with hypoxia to induce neuronal death by inhibiting mitochondrial cytochrome oxidase. Sixteen hours of hypoxia (2% oxygen) plus deoxyglucose (an inhibitor of glycolysis) caused extensive, excitotoxic death of neurons in rat cerebellar granule cell cultures. Three different nNOS inhibitors (including the selective inhibitor N-4S-4-amino-5-2-aminoethyl-aminopentyl-N'-nitroguanidine) decreased this neuronal death by half, indicating a contribution of nNOS to hypoxic death. The selective nNOS inhibitor did not, however, block neuronal death induced either by added glutamate or by added azide (an uncompetitive inhibitor of cytochrome oxidase), indicating that nNOS does not act downstream of glutamate or cytochrome oxidase. Hypoxia plus deoxyglucose-induced glutamate release and neuronal depolarisation, and the nNOS inhibitor decreased this. Hypoxia inhibited cytochrome oxidase activity in the cultures, but a selective nNOS inhibitor prevented this inhibition, indicating NO from nNOS was inhibiting cytochrome oxidase in competition with oxygen. These data indicate that hypoxia synergises with NO from nNOS to induce neuronal death via cytochrome oxidase inhibition causing neuronal depolarisation. This mechanism might contribute to ischaemia/stroke-induced neuronal death in vivo.

Protective effect of cerebrocrast on rat brain ischaemia induced by occlusion of both common carotid arteries

Diabetes mellitus is accompanied by several cardiovascular complications including atherosclerosis, cerebral ischaemia and stroke. We examined the neuroprotective effect of a 1,4-dihydropyridine derivative cerebrocrast (C, a new antidiabetic agent, synthesized in the Latvian Institute of Organic Synthesis) on the level of ATP in the brain, and on changes of the EEG and ECG, as well as blood pressure parameters in anaesthetized Wistar male rats before and during 10-min occlusion of both common carotid arteries. Cerebrocrast was administered i.v. at doses of 1.0 and 10 microg/kg in the v. femoralis 20 min prior to ischaemia. After 10-min ischaemia animals were decapitated and the brain was immediately frozen in liquid nitrogen and subsequently used for analysis of changes of ATP contention. Cerebrocrast, administered at doses of 1.0 and 10 microg/kg 20 min prior to occlusion of both common carotid arteries, completely prevented a fall in the ATP content of brain compared with the control rats. In control rats the content of ATP in brain during ischaemia decreased from 2.77 +/- 0.22 (basal level) to 1.74 +/- 0.20 micromol/g as a result of ischaemia. By administration of cerebrocrast 20 min before occlusion of the arteries, the content of ATP in the brain remained at the level of preischaemia (1.0 microg/kg C + ischaemia 2.82 +/- 0.36; 10 microg/kg C + ischaemia 2.42 +/- 0.22 micromol/g). Analysis of EEG parameters both before and during 10 min of occlusion showed that at a C dose of 1.0 microg/kg before occlusion produced a regular alpha rhythm during ischaemia and prevented cerebral bioelectric activity from significant changes. The depression of basal rhythm was observed at a C dose of 10 microg/kg during ischaemia in two rats out of six as well as an increase in the ECG ST segment above the isoelectric line. Blood pressure was decreased by about 10-20 mm Hg. We propose that pretreatment of rats with cerebrocrast at doses of 1.0 or 10 microg/kg 20 min prior to ischaemia can prevent ischaemic damage of rat brain, maintain necessary energy consumption, promote ATP production in brain cells, and prevent significant changes in EEG and ECG parameters. These properties are important in diabetes mellitus and its evoked cardiovascular complications as stroke, ischaemia, etc.

Cranberry and blueberry: Evidence for protective effects against cancer and vascular diseases

Growing evidence from tissue culture, animal, and clinical models suggests that the flavonoid-rich fruits of the North American cranberry and blueberry (Vaccinium spp.) have the potential ability to limit the development and severity of certain cancers and vascular diseases including atherosclerosis, ischemic stroke, and neurodegenerative diseases of aging. The fruits contain a variety of phytochemicals that could contribute to these protective effects, including flavonoids such as anthocyanins, flavonols, and proanthocyanidins; substituted cinnamic acids and stilbenes; and triterpenoids such as ursolic acid and its esters. Cranberry and blueberry constituents are likely to act by mechanisms that counteract oxidative stress, decrease inflammation, and modulate macromolecular interactions and expression of genes associated with disease processes. The evidence suggests a potential role for dietary cranberry and blueberry in the prevention of cancer and vascular diseases, justifying further research to determine how the bioavailability and metabolism of berry phytonutrients influence their activity in vivo.

Cytotoxic edema: mechanisms of pathological cell swelling

✓Cerebral edema is caused by a variety of pathological conditions that affect the brain. It is associated with two separate pathophysiological processes with distinct molecular and physiological antecedents: those related to cytotoxic (cellular) edema of neurons and astrocytes, and those related to transcapillary flux of Na+and other ions, water, and serum macromolecules. In this review, the authors focus exclusively on the first of these two processes. Cytotoxic edema results from unchecked or uncompensated influx of cations, mainly Na+, through cation channels. The authors review the different cation channels that have been implicated in the formation of cytotoxic edema of astrocytes and neurons in different pathological states. A better understanding of these molecular mechanisms holds the promise of improved treatments of cerebral edema and of the secondary injury produced by this pathological process.

Brain oedema in focal ischaemia: molecular pathophysiology and theoretical implications

Focal cerebral ischaemia and post-ischaemic reperfusion cause cerebral capillary dysfunction, resulting in oedema formation and haemorrhagic conversion. There are substantial gaps in understanding the pathophysiology, especially regarding early molecular participants. Here, we review physiological and molecular mechanisms involved. We reaffirm the central role of Starling's principle, which states that oedema formation is determined by the driving force and the capillary "permeability pore". We emphasise that the movement of fluids is largely driven without new expenditure of energy by the ischaemic brain. We organise the progressive changes in osmotic and hydrostatic conductivity of abnormal capillaries into three phases: formation of ionic oedema, formation of vasogenic oedema, and catastrophic failure with haemorrhagic conversion. We suggest a new theory suggesting that ischaemia-induced capillary dysfunction can be attributed to de novo synthesis of a specific ensemble of proteins that determine osmotic and hydraulic conductivity in Starling's equation, and whose expression is driven by a distinct transcriptional program.

Novel membrane-localizing TEMPO derivatives for measurement of cellular oxidative stress at the cell membrane

Oxidative stress affecting lipid membranes is considered to be closely related to cardiovascular disease and brain ischemia. In this study, we designed and synthesized membrane-localizing TEMPO derivatives and demonstrated that one of these synthesized probes, compound 1, localized and detected oxidative stress in the cell membrane in an endotoxic model of a mouse macrophage-like cell line. Compound 1 is therefore a potentially useful probe for evaluating oxidative stress at the cell membrane.

Oxidative modification of M-type K(+) channels as a mechanism of cytoprotective neuronal silencing

Voltage-gated K(+) channels of the Kv7 family underlie the neuronal M current that regulates action potential firing. Suppression of M current increases excitability and its enhancement can silence neurons. We here show that three of five Kv7 channels undergo strong enhancement of their activity by oxidative modification induced by physiological concentrations of hydrogen peroxide. A triple cysteine pocket in the channel S2-S3 linker is critical for this effect. Oxidation-induced enhancement of M current produced a hyperpolarization and a dramatic reduction of action potential firing frequency in rat sympathetic neurons. As hydrogen peroxide is robustly produced during hypoxia-induced oxidative stress, we used an oxygen/glucose deprivation neurodegeneration model that showed neuronal death to be severely accelerated by M current blockade. Such blockade had no effect on survival of normoxic neurons. This work describes a novel pathway of M-channel regulation and suggests a role for M channels in protective neuronal silencing during oxidative stress.

Ca2+-Permeable Acid-sensing Ion Channels and Ischemic Brain Injury

Acidosis is a common feature of brain in acute neurological injury, particularly in ischemia where low pH has been assumed to play an important role in the pathological process. However, the cellular and molecular mechanisms underlying acidosis-induced injury remain unclear. Recent studies have demonstrated that activation of Ca(2+)-permeable acid-sensing ion channels (ASIC1a) is largely responsible for acidosis-mediated, glutamate receptor-independent, neuronal injury. In cultured mouse cortical neurons, lowering extracellular pH to the level commonly seen in ischemic brain activates amiloride-sensitive ASIC currents. In the majority of these neurons, ASICs are permeable to Ca(2+), and an activation of these channels induces increases in the concentration of intracellular Ca(2+) ([Ca(2+)](i)). Activation of ASICs with resultant [Ca(2+)](i) loading induces time-dependent neuronal injury occurring in the presence of the blockers for voltage-gated Ca(2+) channels and the glutamate receptors. This acid-induced injury is, however, inhibited by the blockers of ASICs, and by reducing [Ca(2+)](o). In focal ischemia, intracerebroventricular administration of ASIC1a blockers, or knockout of the ASIC1a gene protects brain from injury and does so more potently than glutamate antagonism. Furthermore, pharmacological blockade of ASICs has up to a 5 h therapeutic time window, far beyond that of glutamate antagonists. Thus, targeting the Ca(2+)-permeable acid-sensing ion channels may prove to be a novel neuroprotective strategy for stroke patients.

1α,25-Dihydroxyvitamin D3 treatment does not alter neuronal cyclooxygenase-2 expression in the cerebral cortex after stroke

The inducible prostaglandin synthase, cyclooxygenase-2, is upregulated in response to cerebral ischemia and contributes to potentiation of oxidative injury. Cyclooxygenase-2 expression is regulated by retinoic acid receptors, which form heterodimers with vitamin D receptors and vitamin D. In addition, vitamin D has been reported to have neuroprotective qualities. The aim of this study was to examine whether the biologically active vitamin D3-metabolite 1alpha,25-dihydroxyvitamin D3 (1,25-D3), influences the expression of inducible cyclooxygenase-2 in photothrombotically lesioned brain or is part of an independent neuroprotective mechanism. We compared groups of nonlesioned control rats and infarcted animals, which were treated with either 1,25-D3 or solvent at different times postlesion. In control animals, cyclooxygenase-2 immunoreactivity was readily evident in almost all cortical neurons of layers II/III as well as in a few pyramidal cells in layer V. Following photothrombotic infarction of the right cortical hindlimb area, there was a significant, but transient, increase in cyclooxygenase-2 labeling which was restricted to neurons of the injured hemisphere in both 1,25- D3-treated and solvent-treated rats. Highest levels of cyclooxygenase-2 immunoreactivity were seen at 12 and 24 h postlesion, followed by a gradual decrease at later time points. However, no significant differences were detected between 1,25-D3-treated and solvent-treated lesioned rats, indicating that postischemic neuronal cyclooxygenase-2 upregulation is not influenced by 1,25-D3. It is concluded that the neuroprotective effect of 1,25-D3 does not depend on modulations of neuronal COX-2 expression caused by postlesional hyperexcitation.

Cell-permeant calcium buffer induced neuroprotection after cortical devascularization

An excitotoxic cascade resulting in a significant intracellular calcium load is thought to be a primary mechanism leading to neuronal death after ischemia. One way to protect neurons from injury is through the use of cell-permeant calcium buffers. These molecules have been reported to be neuroprotective via their ability to increase the cell's overall Ca(2+) buffering load as well as by attenuating neurotransmitter release. However, their efficacy when given after injury has yet to be determined. We used diffusion-weighted magnetic resonance imaging (DWI), histological, and immunohistochemical methods to determine the neuroprotective efficacy of 2-aminophenol-N, N, O-triacetic acid acetoxymethyl ester (APTRA-AM) after focal cerebral ischemia. Injured animals were given two injections of APTRA-AM at 1 and 12 h after injury. Animals were imaged prior to injury and then at 12, 24, 48 h and 3 and 7 days after injury. After 7 days the animals were euthanized for correlative cresyl violet histology and immunohistochemistry. Injury resulted in a decrease in the apparent diffusion coefficient (ADC) of the injured area within the first 12 h of injury, which returned to normal by 7 days. In contrast, animals injected with APTRA-AM showed no significant change in the ADC at any time point studied. Tissue analysis showed that APTRA-AM significantly reduced the infarct size by 85% and extent of inflammatory cell infiltration by 94%. The results clearly demonstrate significant neuroprotection by APTRA-AM when given after injury.

Effects of 1α,25 dihydroxyvitamin D3 on the expression of HO-1 and GFAP in glial cells of the photothrombotically lesioned cerebral cortex

In ischemic cerebral injuries a cascade of degenerative mechanisms, all participating in the development of oxidative stress, influence the condition of the tissue. The survival of viable tissue affected by secondary injury largely depends on the balance between endogenous protective mechanisms and the ongoing degenerative processes. The inducible enzyme, heme oxygenase-1 metabolizes and thus detoxifies free heme to the powerful endogenous antioxidants biliverdin and bilirubin therefore enhancing neuroprotection. The secosteroid 1alpha,25-dihydroxyvitamin D3 (1,25-D3) is a modulator of the immune system and also exhibits a strong potential for neuroprotection as recently shown in the MCAO model of cerebral ischemia. We studied the effects of 1,25-D3 treatment on heme oxygenase-1 expression following focal cortical ischemia elicited by photothrombosis. Postlesional treatment with 1,25-D3 (4 microg/kg body weight) resulted in a transient, but significant upregulation of glial heme oxygenase-1 immunoreactivity concomitant with a reduction in glial fibrillary acidic protein immunoreactivity in remote cortical regions affected by a secondary spread of injury, whereas the size of the lesion's core remained unaffected. 1,25-D3 did not produce a temporal shift or extension of injury-related heme oxygenase-1 responses, indicating that 1,25-D3 did not prolong ischemia-related heme oxygenase-1 expression. In contrast to glial heme oxygenase-1 upregulation, glial fibrillary acidic protein, a sensitive marker for reactive gliosis, was significantly reduced. These findings support an additional protective action of 1,25-D3 at the cellular level in regions affected by secondary injury-related responses.

Nitric oxide from inflammatory-activated glia synergizes with hypoxia to induce neuronal death

Inflammatory-activated glia are seen in numerous central nervous system (CNS) pathologies and can kill nearby neurons through the release of cytotoxic mediators. Glia, when activated, can express the inducible isoform of nitric oxide synthase (iNOS) producing high levels of nitric oxide (NO), which can kill neurons in certain conditions. We show, however, that inflammatory activation of glia in a mature culture of cerebellar granule neurons and glia causes little or no neuronal death under normal (21%) oxygen conditions. Similarly, hypoxia (2% oxygen) or low levels of an NO donor (100 microM DETA/NO) caused little or no neuronal death in nonactivated cultures. If inflammatory activation of glia or addition of NO donor was combined with hypoxia, however, extensive neuronal death occurred. Death in both cases was prevented by the N-methyl-D-aspartate (NMDA) receptor blocker MK-801, implying that death was mediated by the glutamate receptor. Low levels of NO were found to increase the apparent K(M) of cellular oxygen consumption for oxygen, probably due to NO-induced inhibition of mitochondrial respiration, in competition with oxygen, at cytochrome oxidase. Necrotic death, induced by hypoxia plus DETA/NO, was increased further by deoxyglucose, an inhibitor of glycolysis, suggesting that necrosis was mediated by energy depletion. Hypoxia was found to be a potent stimulator of microglia proliferation, but this proliferation was not significant in inflammatory-activated cultures. These results suggest that low levels of NO can induce neuronal death under hypoxic conditions, mediated by glutamate after NO inhibition of respiration in competition with oxygen. Brain inflammation can thus sensitize to hypoxia-induced death, which may be important in pathologies such as stroke, neurodegeneration, and brain aging.

The effects of temperature on hypoxic-ischemic brain injury

Over the past 15 years it has been recognized that the temperature of the brain has an important influence on the extent of brain injury that follows intervals of hypoxia-ischemia. Available data in animals and humans show that brain injury is worsened when fever is superimposed on an ischemic event. Furthermore, data in neonates and adults strongly suggest a neuroprotective role for modest hypothermia (temperature reductions of 1 to 6 degrees C) applied during or following ischemia or hypoxia-ischemia. This article provides an overview of the effects of brain temperature, including its role in the development of brain injury, mechanisms of brain injury which may be temperature sensitive, the regulation of brain temperature, thermal characteristics during brain cooling, and current clinical investigations that use temperature as a therapeutic modality.

Effects of global cerebral ischemia and preconditioning on heat shock protein 27 immunocontent and phosphorylation in rat hippocampus

Global cerebral ischemia, with or without preconditioning, leads to an increase in heat shock protein 27 (HSP27) immunocontent and alterations in HSP27 phosphorylation in CA1 and dentate gyrus areas of the hippocampus. We studied different times of reperfusion (1, 4, 7, 14, 21 and 30 days) using 2 min, 10 min or 2+10 min of ischemia. The results showed an increase in HSP27 immunocontent of about 300% after 10 min of ischemia in CA1 and dentate gyrus. CA1, a hippocampal vulnerable area, showed an increase in HSP27 phosphorylation, parallel with immunocontent. In dentate gyrus, a resistant area, the increase in HSP phosphorylation was lower than immunocontent. After preconditioned ischemia (2+10 min), when CA1 neurons are protected to a lethal, 10 min insult, we observed an increase in HSP immunocontent and a decrease in phosphorylation in both regions of the hippocampus, suggesting that, when there is no neuronal death, HSP27 in a vulnerable area responds similarly to the resistant area.When dephosphorylated, HSP27 acts as a chaperone, protecting other proteins from denaturation. As it is markedly expressed in astrocytes, we suggest that HSP27 could be protecting hippocampal astrocytes, which could then be helping neurons to resist to the insult, maintaining tissue normal homeostasis.

Cortical devascularization: quantitative diffusion weighted magnetic resonance imaging and histological findings

This study investigates the development of a small focal cortical lesion produced in a model of brain injury. Two approaches were chosen: diffusion weighted magnetic resonance imaging (DWI) and histology. DW images were collected before devascularization and at 0.5, 1, 2, 3, 5, 7 and 14 days after treatment. Apparent diffusion coefficient (ADC) maps were calculated from the DW images to quantify lesion development. As a second measure of injury, tissue morphology was analyzed using cresyl violet histochemistry. A significant reduction in ADC values within the cortex below the injury site by 0.5 days after surgery was observed. Between 5 and 14 days the ADC values recovered to control levels. ADC changes were also observed in the contralateral cortex at 0.5, 1 and 5 days. The decrease in ADC observed at the early time points suggested cytotoxic edema, whereas the recovery to control levels at later time points suggested infarct formation. This model of brain injury resulted in progressive but relatively slow formation of a pan-necrotic infarct within 14 days. In particular, substantial amounts of cell death were not observed until 2 days after surgery. Overall, the quantitative and histological measures of this lesion are consistent with those observed for an ischemic type of injury, however, the time course of these lesions' development are consistent with other models of traumatic brain injury. Our data demonstrates that DWI is a highly sensitive metric for ischemic-type damage that results from brain injury.

Involvement of GDNF in neuronal protection against 6-OHDA-induced parkinsonism following intracerebral transplantation of fetal kidney tissues in adult rats

Exogenous application of transforming growth factors-beta (TGF beta) family proteins, including glial cell line-derived neurotrophic factor (GDNF), neurturin, activin, and bone morphogenetic proteins, has been shown to protect neurons in many models of neurological disorders. Finding a tissue source containing a variety of these proteins may promote optimal beneficial effects for treatment of neurodegenerative diseases. Because fetal kidneys express many TGF beta trophic factors, we transplanted these tissues directly into the substantia nigra after a unilateral 6-hydroxydopamine lesion. We found that animals that received fetal kidney tissue grafts exhibited (1) significantly reduced hemiparkinsonian asymmetrical behaviors, (2) a near normal tyrosine hydroxylase immunoreactivity in the lesioned nigra and striatum, (3) a preservation of K(+)-induced dopamine release in the lesioned striatum, and (4) high levels of GDNF protein within the grafts. In contrast, lesioned animals that received grafts of adult kidney tissues displayed significant behavioral deficits, dopaminergic depletion, reduced K(+)-mediated striatal dopamine release, and low levels of GDNF protein within the grafts. The present study suggests that fetal kidney tissue grafts can protect the nigrostriatal dopaminergic system against a neurotoxin-induced parkinsonism, possibly through the synergistic release of GDNF and several other neurotrophic factors.

Role of astrocytes in pathogenesis of ischemic brain injury

Astrocytes play an important role in the homeostasis of the CNS both in normal conditions and after ischemic injury. The swelling of astrocytes is observed during and several seconds after brain ischemia. Then ischemia stimulates sequential morphological and biochemical changes in glia and induces its proliferation. Reactive astrocytes demonstrate stellate morphology, increased glial fibrillary acidic protein (GFAP) immunoreactivity, increased number of mitochondria as well as elevated enzymatic and non-enzymatic antioxidant activities. Astrocytes can re-uptake and metabolize glutamate and in this way they control its extracellular concentration. The ability of astrocytes to protect neurons against the toxic action of free radicals depends on their specific energy metabolism, high glutathione level, increased antioxidant enzyme activity (catalase, superoxide dismutase, glutathione peroxidase) and overexpression of antiapoptotic bcl-2 gene. Astrocytes produce cytokines (TNF-alpha, IL-1, IL-6) involved in the initiation and maintaining of immunological response in the CNS. In astrocytes, like in neurones, ischemia induces the expression of immediate early genes: c-fos, c-jun, fos B, jun B, jun D, Krox-24, NGFI-B and others. The protein products of these genes modulate the expression of different proteins, both destructive ones and those involved in the neuroprotective processes.

Calcium imaging in live rat optic nerve myelinated axons in vitro using confocal laser microscopy

Intracellular Ca(2+) plays a major role in the physiological responses of excitable cells, and excessive accumulation of internal Ca(2+) is a key determinant of cell injury and death. Many studies have been carried out on the internal Ca(2+) dynamics in neurons. In constrast, there is virtually no such information for mammalian central myelinated axons, due in large part to technical difficulty with dye loading and imaging such fine myelinated structures. We developed a technique to allow imaging of ionized Ca(2+) in live rat optic nerve axons with simultaneous electrophysiological recording in vitro at 37 degrees C using confocal microscopy. The K(+) salt of the Ca(2+)-sensitive indicator Oregon Green 488 BAPTA-2 and the Ca(2+)-insensitive reference dye Sulforhodamine 101 were loaded together into rat optic nerves using a low-Ca(2+)/low-Na(+) solution. Axonal profiles, confirmed immunohistochemically by double staining with neurofilament-160 antibodies, were clearly visualized by S101 fluorescence up to 800 microm from the cut ends. The Ca(2+) signal was very low at rest, just above the background fluorescence intensity, indicating healthy tissue, and increased significantly after caffeine (20 mM) exposure designed to release internal Ca(2+) stores. The health of imaged regions was further confirmed by a virtual absence of spectrin breakdown, which is induced by calpain activation in damaged CNS tissue. Red and green fluorescence decayed to no less than 70% of control after 60 min of recording at 37 degrees C, with the green:red fluorescence ratio increasing slightly by 21% after 60 min. Electrophysiological responses recorded simultaneously with confocal images remained largely stable as well.

Does fucose or piracetam modify the effect of hypoxia preconditioning against pentylenetetrazol-induced seizures?

To clarify the question whether the duration of hypoxia exposure has an influence on the point in time or the strength of hypoxic preconditioning, hypoxia exposure of rats lasting 1 and 8 h was tested regarding the modification of susceptibility to acute pentylenetetrazol-induced seizures. Following the short-lasting (1 h) hypoxia, the maximum level of preconditioning action was observed 7 days after hypoxia, whereas the longer-lasting hypoxia (8 h) produced the maximum level of protection 14 days after hypoxia. We investigated the influence of fucose and piracetam on the effect of hypoxia preconditioning by the application of the substances 20 min before the beginning of hypoxia exposure. Fucose did not modify the result of hypoxia preconditioning. But after the treatment with piracetam, the preconditioning effect was prevented following hypoxia lasting 1 and 8 h. We suggest that the radical scavenger properties of piracetam are responsible for the absence of protection against pentylenetetrazol-evoked seizures.

Mitochondrial and intrinsic optical signals imaged during hypoxia and spreading depression in rat hippocampal slices

During hypoxia in the CA1 region of the rat hippocampus, spreading-depression-like depolarization (hypoxic spreading depression or HSD) is accompanied by both a negative shift of the extracellular DC potential (DeltaV(o)), and a sharp decrease in light transmittance (intrinsic optical signal or IOS). To investigate alterations in mitochondrial function during HSD and normoxic spreading depression (SD), we simultaneously imaged mitochondrial depolarization, using rhodamine-123 (R123) fluorescence, and IOS while monitoring extracellular voltage. Three major phases of the R123 signal were observed during hypoxia: a gradual, diffuse fluorescence increase, a sharp increase in fluorescence coincident with the HSD-related DeltaV(o), primarily in the CA1 region, and a plateau-like phase if reoxygenation is delayed after HSD onset, persisting until reoxygenation occurs. Two phases occurred following re-oxygenation: an abrupt and then slow decrease in fluorescence to near baseline and a slow secondary increase to slightly above baseline and a late recovery. Parallel phases of the IOS response during hypoxia were also observed though delayed compared with the R123 responses: an initial increase, a large decrease coincident with the HSD-related DeltaV(o), and a trough following HSD. After reoxygenation, there occurred a delayed increase in transmittance and then a slow decrease, returning to near baseline. When Ca(2+) was removed from the external medium, resulting in complete synaptic blockade, the mitochondrial response to hypoxia did not significantly differ from control (normal Ca(2+)) conditions. In slices maintained in low-chloride (2.4 mM) medium, a dramatic reversal in the direction of the IOS signal associated with HSD occurred, and the R123 signal during HSD was severely attenuated. Normoxic SD induced by micro-injection of KCl was also associated with a decrease in light transmittance and a sharp increase in R123 fluorescence but both responses were less pronounced than during HSD. Our results show two mitochondrial responses to hypoxia: an initial depolarization that appears to be caused by depressed electron transport due to lack of oxygen and a later, sudden, sharp depolarization linked to HSD. The depression of the second, sharp depolarization and the inversion of the IOS in low-chloride media suggest a role of Cl(-)-dependent mitochondrial swelling. Lack of effect of Ca(2+)-free medium on the R123 and IOS responses suggests that the protection against hypoxic damage by low Ca(2+) is not due to the prevention of mitochondrial depolarization.

Protective effect of oren-gedoku-to against induction of neuronal death by transient cerebral ischemia in the C57BL/6 mouse

We examined the neuroprotective effects of oren-gedoku-to (TJ15), a herbal medicine, after transient forebrain ischemia. Transient forebrain ischemia was induced by occlusion of both common carotid arteries for 15 min in C57BL/6 mice treated with TJ15. In the control ischemic group without TJ15 treatment, histologic examination of brain tissue collected seven days after reperfusion showed death of pyramidal cells in CA2-3 area of the hippocampus, unilaterally or bilaterally. In mice treated with oral TJ15 (845 mg/kg/day) for five weeks, the frequency of ischemic neuronal death was significantly lower. Immunohistochemistry for Cu/Zn-superoxide dismutase (Cu/Zn-SOD) showed strongly reactive astrocytes in the hippocampus of ischemic mice treated with TJ15. Damage to nerve cells by free radicals plays an important role in the induction of neuronal death by ischemia-reperfusion injury. Our results suggest that TJ15 protects against ischemic neuronal death by increasing the expression of Cu/Zn-SOD and suggest that oren-gedoku-to reduces the exposure of hippocampal neurons to oxidative stress.

Hyperglycemia enhances extracellular glutamate accumulation in rats subjected to forebrain ischemia

BACKGROUND AND PURPOSE

An increase in serum glucose at the time of acute ischemia has been shown to adversely affect prognosis. The mechanisms for the hyperglycemia-exacerbated damage are not fully understood. The objective of this study was to determine whether hyperglycemia leads to enhanced accumulation of extracellular concentrations of excitatory amino acids and whether such increases correlate with the histopathological outcome.

METHODS

Rats fasted overnight were infused with either glucose or saline 45 minutes before the induction of 15 minutes of forebrain ischemia. Extracellular glutamate, glutamine, glycine, taurine, alanine, and serine concentrations were measured before, during, and after ischemia in both the hippocampus and the neocortex in both control and hyperglycemic animals. The histopathological outcome was evaluated by light microscopy.

RESULTS

There was a significant increase in extracellular glutamate levels in the hippocampus and cerebral cortex in normoglycemic ischemic animals. The increase in glutamate levels in the cerebral cortex, but not in the hippocampus, was significantly higher in hyperglycemic animals than in controls. Correspondingly, exaggerated neuronal damage was observed in neocortical regions in hyperglycemic animals.

CONCLUSIONS

The present results demonstrate that, at least in the neocortex, preischemic hyperglycemia enhances the accumulation of extracellular glutamate during ischemia, providing a tentative explanation for why neuronal damage is exaggerated.

Management of oxidative stress in the CNS: the many roles of glutathione

An outline is given of mechanisms that generate oxidative stress and inflammation. Considered are the metabolic mechanisms that give rise to peroxides, the source of strong oxidants; the production of dicarbonyls that interact with macromolecules to form advanced glycation endproducts; and the role that activation of the transcription factor NF(Kappa)B has in the expression of pro-inflammatory genes. Management of oxidative stress is considered by outlining the central role of reduced glutathione (GSH) in peroxide scavenging, dicarbonyl scavenging and activation of NF(Kappa)B. Cellular GSH levels are dictated by the balance between consumption, oxidation of GSH, reduction of oxidized-glutathione, and synthesis. The rate-limiting enzyme in GSH synthesis is L-gamma-glutamyl-L-cysteine synthase, a phase II enzyme. Phase II enzyme inducers are found in many fruits and vegetables. It is suggested that dietary phase II enzyme inducers be investigated for their potential for preventing or retarding the development of degenerative diseases that have an underlying oxidative stress and inflammatory component.

Effects of transient cerebral ischemia on glial fibrillary acidic protein phosphorylation and immunocontent in rat hippocampus

Transient global cerebral ischemia induced in rats by four-vessel occlusion for 20 min produced an increase in the immunocontent of glial fibrillary acidic protein and a protein phosphorylation response that was different in the CA1 and dentate gyrus areas of the hippocampus. We studied different times of reperfusion (one, four, seven, 14 and 30 days) and observed that the immunocontent and in vitro rate of phosphorylation of glial fibrillary acidic protein in the CA1 region was significantly increased at all intervals after the ischemic insult, indicating that the astrocytic response was maintained for at least 30 days. After reperfusion for 14 days a significant increase in the ratio "in vitro phosphorylation rate/immunocontent" in the CA1 region was observed when compared to control values, to other intervals and to the dentate gyrus, suggesting a hyperphosphorylation of this intermediate filament protein at this interval. In the dentate gyrus, an area less vulnerable to the insult, labelling and immunocontent of glial fibrillary acidic protein were equally increased from four days of reperfusion and the increase remained significant until 30 days, confirming that neuronal death is not the only determining factor for gliosis to occur. In control sham-operated animals, neither the CA1 region nor the dentate gyrus showed significant increases in labelling or immunocontent. Changes in the phosphorylation of glial fibrillary acidic protein may be essential for the plastic response of astrocytes to neuronal damage, as neurons and astrocytes can act as functional units involved in homeostasis, plasticity and neurotransmission.

Cytosolic Ca2+ changes during in vitro ischemia in rat hippocampal slices: major roles for glutamate and Na+-dependent Ca2+ release from mitochondria

This work determined Ca2+ transport processes that contribute to the rise in cytosolic Ca2+ during in vitro ischemia (deprivation of oxygen and glucose) in the hippocampus. The CA1 striatum radiatum of rat hippocampal slices was monitored by confocal microscopy of calcium green-1. There was a 50-60% increase in fluorescence during 10 min of ischemia after a 3 min lag period. During the first 5 min of ischemia the major contribution was from Ca2+ entering via NMDA receptors; most of the fluorescence increase was blocked by MK-801. Approximately one-half of the sustained increase in fluorescence during 10 min of ischemia was caused by activation of Ca2+ release from mitochondria via the mitochondrial 2Na+-Ca2+ exchanger. Inhibition of Na+ influx across the plasmalemma using lidocaine, low extracellular Na+, or the AMPA/kainate receptor blocker CNQX reduced the fluorescence increase by 50%. The 2Na+-Ca2+ exchange blocker CGP37157 also blocked the increase, and this effect was not additive with the effects of blocking Na+ influx. When added together, CNQX and lidocaine inhibited the fluorescence increase more than CGP37157 did. Thus, during ischemia, Ca2+ entry via NMDA receptors accounts for the earliest rise in cytosolic Ca2+. Approximately 50% of the sustained rise is attributable to Na+ entry and subsequent Ca2+ release from the mitochondria via the 2Na+-Ca2+ exchanger. Sodium entry is also hypothesized to compromise clearance of cytosolic Ca2+ by routes other than mitochondrial uptake, probably by enhancing ATP depletion, accounting for the large inhibition of the Ca2+ increase by the combination of CNQX and lidocaine.

Role of mitochondrial dysfunction in the Ca2+-induced decline of transmitter release at K+-depolarized motor neuron terminals

The present study tested whether a Ca2+-induced disruption of mitochondrial function was responsible for the decline in miniature endplate current (MEPC) frequency that occurs with nerve-muscle preparations maintained in a 35 mM potassium propionate (35 mM KP) solution containing elevated calcium. When the 35 mM KP contained control Ca2+ (1 mM), the MEPC frequency increased and remained elevated for many hours, and the mitochondria within twitch motor neuron terminals were similar in appearance to those in unstimulated terminals. All nerve terminals accumulated FM1-43 when the dye was present for the final 6 min of a 300-min exposure to 35 mM KP with control Ca2+. In contrast, when Ca2+ was increased to 3.6 mM in the 35 mM KP solution, the MEPC frequency initially reached frequencies >350 s-1 but then gradually fell approaching frequencies <50 s-1. A progressive swelling and eventual distortion of mitochondria within the twitch motor neuron terminals occurred during prolonged exposure to 35 mM KP with elevated Ca2+. After approximately 300 min in 35 mM KP with elevated Ca2+, only 58% of the twitch terminals accumulated FM1-43. The decline in MEPC frequency in 35 mM KP with elevated Ca2+ was less when 15 mM glucose was present or when preparations were pretreated with 10 microM oligomycin and then bathed in the 35 mM KP with glucose. When glucose was present, with or without oligomycin pretreatment, a greater percentage of twitch terminals accumulated FM1-43. However, the mitochondria in these preparations were still greatly swollen and distorted. We propose that prolonged depolarization of twitch motor neuron terminals by 35 mM KP with elevated Ca2+ produced a Ca2+-induced decrease in mitochondrial ATP production. Under these conditions, the cytosolic ATP/ADP ratio was decreased thereby compromising both transmitter release and refilling of recycled synaptic vesicles. The addition of glucose stimulated glycolysis which contributed to the maintenance of required ATP levels.

Redox-mediated gene therapies for environmental injury: approaches and concepts

Cellular redox state has been increasingly recognized as a critical component of stress-induced cellular responses and disease. Inherent in these responses are reactive oxygen species (ROS), which inflict direct cellular damage in addition to acting as intracellular second messengers modulating signal transduction pathways. These intracellular highways of communication are critical in determining cell fates and whole-organ responses following environmental injury. Although gene therapy for inherited and acquired disorders has exploded in the last decade, the application of gene therapeutic approaches for transient pathologic conditions resulting from environmental stress is just beginning to be recognized. This review will summarize the theoretical and practical applications of gene therapy for the treatment of environmental injury by modulating redox-activated cellular responses. Several approaches can be utilized to achieve this goal. These include the application of gene targeting to modulate the cellular redox state directly by expressing recombinant genes capable of degrading ROS at pathophysiologic important subcellular sites. The use of mitochondrial superoxide dismutase (MnSOD), which degrades superoxides arising from ischemia/reperfusion injury, is one example of this approach. MnSOD serves as a "garbage disposal" for potentially toxic ROS prior to cellular injury and the activation of signal transduction cascades important in whole-organ pathology and inflammation. In contrast, some ROS have been suggested to have beneficial effects on cellular responses following environmental injury. Hence, expressing the nitrogen oxygen synthetase gene (NOS) to enhance the levels of nitric oxide (NO.) and augment the beneficial effects of this compound has also been suggested as a useful redox-modulating gene therapy approach. Lastly, indirect intervention in signal transduction pathways following environmental stress by expressing dominant inhibitory proteins of redox-activated signal transduction cascades has also been useful in modulating cellular responses to redox stress. Two such examples have utilized dominant inhibitory forms of the retinoblastoma gene product (Rb) and IkappaBalpha which prevent activation of cyclin-dependent protein kinases and NF-kappaB, respectively. Ultimately, the most efficacious therapeutic approach or combination of approaches that alter the redox responsiveness of cells and organs to environmental injury will be determined through a comprehensive understanding of the relevant pathophysiologic processes.

Electrically evoked [3H]GABA release from cerebral cortical cultures: an in vitro approach for studying glutamate-induced neurotoxicity

In the present study the [3H]GABA release in the rat cerebral cortex primary cultures, kept at rest or electrically stimulated, was measured. In addition, the development of excitotoxic cell damage caused by pretreating the cells for 10 min with increasing glutamate concentrations (10-300 microM) was examined 2 and 24 h after the insult. Cellular injury was quantitatively assessed by measuring the electrically-evoked [3H] GABA release, the [3H] GABA uptake, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide staining. Trains of electrical pulses at different frequencies (2, 5, 10, and 20 Hz) applied to the cultures elicited a [3H]GABA release which was frequency related, Ca++-dependent, and tetrodotoxin sensitive. Either 2 or 24 h after glutamate exposure, the electrically evoked [3H]GABA release was reduced by glutamate in a concentration dependent manner, while [3H]GABA uptake and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide staining appeared less sensitive. The N-methyl-D-aspartate, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and metabotropic receptor antagonists were tested on 100 microM glutamate-exposed cells and a prominent N-methyl-D-aspartate receptor-mediated component was observed. The present findings indicate that the electrically-evoked [3H]GABA release from cerebral cortical cells could represent a useful approach not only to study the spike-triggered neurosecretion but also to the neuronal damage caused by glutamate, as well as to test potential neuroprotective compounds.

Experimental protocol for studying delayed effects of in vitro ischemia on neurotransmitter release from brain slices

The mechanisms by which ischemic injury leads to delayed neuronal death are not completely understood. Notably, no data are so far available on the modifications in neurosecretory responses evoked by a period of ischemia. Superfused brain slices represent a useful preparation in studying the effects of in vitro ischemia on neurotransmitter release. Using this experimental model we describe a protocol which allows to study not only the immediate effects of an ischemic insult, but also, more interestingly, its delayed (1 h) effects on the release of different neurotransmitters. A first pulse (S1) of 50 mM KCl was applied at the 60th min of perfusion and a second one was applied at the 210th min (S2). In vitro ischemia was performed from the 120th to the 150th min, during the inclusive period between the two depolarizing stimuli. The delayed effects of the ischemic treatment on slice response to KCl were calculated as S2/S1 ratio. This protocol allows to study neurotransmitter release mechanisms associated with postischemic neuronal death. Moreover it will be useful in the evaluation of the neuroprotective potential of new drugs.

Upregulation of the enzyme chain hydrolyzing extracellular ATP after transient forebrain ischemia in the rat

A short ischemic period induced by the transient occlusion of major brain arteries induces neuronal damage in selectively vulnerable regions of the hippocampus. Adenosine is considered to be one of the major neuroprotective substances produced in the ischemic brain. It can be released from damaged cells, but it also could be generated extracellularly from released ATP via a surface-located enzyme chain. Using the rat model of global forebrain ischemia, we applied a short (10 min) transient interruption of blood flow and studied the distribution of ectonucleotidase activities in the hippocampus. Northern hybridization of mRNA isolated from hippocampi of sham-operated and ischemic animals revealed an upregulation of ectoapyrase (capable of hydrolyzing nucleoside 5'-tri- and diphosphates) and ecto-5'-nucleotidase (capable of hydrolyzing nucleoside 5'-monophosphates). A histochemical analysis that used ATP, UTP, ADP, or AMP as substrates revealed a strong and selective increase in enzyme activity in the injured areas of the hippocampus. Enhanced staining could be observed first at 2 d. Staining increased within the next days and persisted at 28 d after ischemia. The spatiotemporal development of catalytic activities was identical for all substrates. It was most pronounced in the CA1 subfield and also could be detected in the dentate hilus and to a marginal extent in CA3. The histochemical staining corresponded closely to the development of markers for reactive glia, in particular of microglia. The upregulation of ectonucleotidase activities implies increased nucleotide release from the damaged tissue and could play a role in the postischemic control of nucleotide-mediated cellular responses.

Protective effect of GV150526A on the glutamate-induced changes in basal and electrically-stimulated cytosolic Ca++ in primary cultured cerebral cortical cells

Glutamate-induced changes in intracellular free Ca++ concentration ([Ca++]i) were recorded in resting and electrically-stimulated primary cultures of rat cerebral cortical cells, employing the Ca++ indicator Fura 2. A brief (10 min) exposure to glutamate led to a concentration-dependent basal [Ca++]i increase, measured 30 min after glutamate removal. In order to unmask more subtle modifications in [Ca++]i movements associated with neurosecretion, the glutamate effect was also studied in electrically-stimulated cells. The application of trains (10 s) of electrical pulses (intensity 30 mA, duration 1 ms) induced frequency-related Na+- and Ca++-dependent [Ca++]i transients. A 5 min treatment with 50 microM glutamate reduced to 48% the electrically-evoked [Ca++]i transients, evaluated 30 min after glutamate challenge. The neuroprotective effect of sodium 4,6-dichloro-3-[(E)-3-(N-phenyl)propenamide]indole-2-carboxylate (GV150526A), a new indole derivative with high affinity and selectivity for the glycine site of the NMDA receptor-channel complex, was compared with that of DL-2-amino-5-phosphonopentanoic acid (AP5), ifenprodil, 7-chlorokynurenic acid and 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(f)-quinoxaline (NBQX) on glutamate-induced [Ca++]i changes in resting and electrically-stimulated cells. In both experimental conditions, GV150526A showed to be the most potent compound. Moreover, GV150526A and 7-chlorokynurenic acid were 2-3 times more active in stimulated neurons than in resting neurons, indicating a major involvement of the glycine site in the protection of the cells kept in an active state.