Peri-infarct Depolarizations Research Articles

Multimodal, live imaging of peri-infarct depolarisation (PID) during global forebrain ischemia in the rat cerebral cortex

Event Abstract Back to Event Multimodal, live imaging of peri-infarct depolarisation (PID) during global forebrain ischemia in the rat cerebral cortex Z. Bere1*, A. Kulmány1, 2, T. P. Obrenovitch3, F. Bari4 and E. Farkas1, 2 1 University of Szeged, Department of Medical Physics and Informatics, Hungary 2 University of Szeged, Department of Physiology, Hungary 3 University of Bradford, Division of Pharmacology, School of Life Sciences, United Kingdom 4 University of Szeged, Department of Medical Physics and Informatics, Hungary PID and associated changes in cerebral blood flow (CBF) spontaneously occur in the cortex during cerebral ischemia and may contribute to the extension of brain infarcts. We have set out to characterize PID-related changes in membrane potential and hemodynamic variables in rat cerebral cortex. In anesthetized, male Sprague-Dawley rats (n=13) a closed cranial window was mounted over the parietal bone and loaded with voltage sensitive (VS) dye. The left femoral artery and vein were cannulated for the monitoring of mean arterial pressure (MAP) and for blood withdrawal. Global forebrain ischemia was induced by bilateral common carotid artery occlusion combined with subsequent hypovolemic hypotension (MAP<40 mmHg). Using selected illuminations we acquired synchronous changes in membrane potential (VS dye method); cerebral blood volume with green (540–550 nm); hemoglobin saturation with red (620–640 nm) illumination, and CBF by laser speckle contrast imaging. PID occurred at a MAP value of 41.2±3.7 mmHg and at a CBF value of 43.4±4.9%. In most cases the depolarization was not followed by the recovery of membrane potential, and these events were associated with CBF reduction (19±3.6%). In conclusion, PID appears to generate at the lower limit of the autoregulatory range of CBF, originates at a focus with high vulnerability to ischemia, and propagates similar to that known for cortical spreading depression. PID associated CBF responses most often display inverse neurovascular coupling. Acknowledgements (NFM, NNF 78902) (OTKA, K81266) Keywords: disorders, Neuroscience Conference: 13th Conference of the Hungarian Neuroscience Society (MITT), Budapest, Hungary, 20 Jan - 22 Jan, 2011. Presentation Type: Abstract Topic: Disorders Citation: Bere Z, Kulmány A, Obrenovitch TP, Bari F and Farkas E (2011). Multimodal, live imaging of peri-infarct depolarisation (PID) during global forebrain ischemia in the rat cerebral cortex. Front. Neurosci. Conference Abstract: 13th Conference of the Hungarian Neuroscience Society (MITT). doi: 10.3389/conf.fnins.2011.84.00095 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 03 Mar 2011; Published Online: 23 Mar 2011. * Correspondence: Dr. Z. Bere, University of Szeged, Department of Medical Physics and Informatics, Szeged, Hungary, berezsofia@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Z. Bere A. Kulmány T. P Obrenovitch F. Bari E. Farkas Google Z. Bere A. Kulmány T. P Obrenovitch F. Bari E. Farkas Google Scholar Z. Bere A. Kulmány T. P Obrenovitch F. Bari E. Farkas PubMed Z. Bere A. Kulmány T. P Obrenovitch F. Bari E. Farkas Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Effects of AMPA and clomethiazole on spreading depression cycles in the rat neocortex in vivo

In hippocampal slices, inhibition of AMPA receptors unmasks synaptic transmission via NMDA receptors, suggesting that AMPA receptor activation normally inhibits synaptic transmission via NMDA receptors. Activation of NMDA receptors is involved in the pathogenesis of cortical spreading depression (CSD) which has been implicated in the pathogenesis of migraine aura and neuronal damage from peri-infarct depolarizations. In this study we examined whether NMDA receptor transmission could be unmasked in the neocortex in vivo by AMPA receptor blockage and whether AMPA receptors could affect CSD induced by 200mM KCl. We further compared the effects of AMPA to those of the NMDA receptor antagonist, 2-amino-5-phosphono-pentanoic acid (2AP5), and the GABA-mimetic drug clomethiazole. The NMDA receptor antagonist MK-801 did not affect the baseline somatosensory evoked potentials (SEPs). In a medium with no Mg2+, the AMPA receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX) caused marked reduction in the SEP size which subsequently recovered partially; MK-801 blocked these partially recovered SEPs. AMPA (50μM but not at 5μM or 250μM) and 2AP5 (10μM) significantly reduced the number of CSD cycles. The effect of AMPA was not changed by co-applying it with cyclothiazide, which blocks AMPA receptor desensitization. Clomethiazole (100mg/kgi.p.) did not significantly affect the number of CSD cycles. Only 2AP5 significantly reduced the potentiation that follows CSD. We conclude that activation of AMPA receptors can suppress the actions of NMDA receptors in the neocortex; this could be an intrinsic protective mechanism against CSD and also provide a possible therapeutic strategy against CSD-related neurological conditions.

Recurrent spontaneous spreading depolarizations facilitate acute dendritic injury in the ischemic penumbra.

Spontaneous spreading depolarizations (SDs) occur in the penumbra surrounding ischemic core. These SDs, often referred to as peri-infarct depolarizations, cause vasoconstriction and recruitment of the penumbra into the ischemic core in the critical first hours after focal ischemic stroke; however, the real-time spatiotemporal dynamics of SD-induced injury to synaptic circuitry in the penumbra remain unknown. A modified cortical photothrombosis model was used to produce a square-shaped lesion surrounding a penumbra-like "area at risk" in middle cerebral artery territory of mouse somatosensory cortex. Lesioning resulted in recurrent spontaneous SDs. In vivo two-photon microscopy of green fluorescent protein-expressing neurons in this penumbra-like area at risk revealed that SDs were temporally correlated with rapid (<6 s) dendritic beading. Dendrites quickly (<3 min) recovered between SDs to near-control morphology until the occurrence of SD-induced terminal dendritic injury, signifying acute synaptic damage. SDs are characterized by a breakdown of ion homeostasis that can be recovered by ion pumps if the energy supply is adequate. Indeed, the likelihood of rapid dendritic recovery between SDs was correlated with the presence of nearby flowing blood vessels, but the presence of such vessels was not always sufficient for rapid dendritic recovery, suggesting that energy needs for recovery exceeded energy supply of compromised blood flow. We propose that metabolic stress resulting from recurring SDs facilitates acute injury at the level of dendrites and dendritic spines in metabolically compromised tissue, expediting penumbral recruitment into the ischemic core.

Functional and structural correlates of magnetic resonance patterns in a new in vitro model of cerebral ischemia by transient occlusion of the medial cerebral artery

Magnetic resonance imaging (MRI) during the acute phase of a stroke contributes to recognize ischemic regions and is potentially useful to predict clinical outcome. Yet, the functional significance of early MRI alterations during brain ischemia is not clearly understood. We achieved an experimental study to interpret MRI signals in a novel model of focal ischemia in the in vitro isolated guinea pig brain. By combining neurophysiological and morphological analysis with MR-imaging, we evaluated the suitability of MR to identify ischemic and peri-ischemic regions. Extracellular recordings demonstrated depolarizations in the ischemic core, but not in adjacent areas, where evoked activity was preserved and brief peri-infarct depolarizations occurred. Diffusion-weighted MRI and immunostaining performed after neurophysiological characterization showed changes restricted to the core region. Diffusion-weighted MR alterations did not include the penumbra region characterized by peri-infarct depolarizations. Therefore, by comparing neurophysiological, imaging and anatomical data, we can conclude that DW-MRI underestimates the extension of the tissue damage involved in brain ischemia.

New concepts regarding cerebral vasospasm: glial-centric mechanisms

Poor outcome in patients with cerebral vasospasm following subarachnoid hemorrhage remains a serious clinical problem. The current management with focus on the cerebrovascular constriction accounts for the use of "triple-H" therapy (hypertension, hypervolemia, and hemodilution) to enhance cerebral blood flow through constricted vessels. Recent work suggests that spreading depression (a stereotypical response of cerebral cortical tissue to noxious stimuli with subsequent oligemic blood flow) occurs in patients with cerebral vasospasm. A narrative review was conducted to examine the relationship between spreading depression and subarachnoid hemorrhage and to identify the anesthetic effects on the propagation of spreading depression. Following review of the literature, an underlying mechanism is advanced that cerebral vasospasm is not primarily a problem of the cerebral vasculature but a consequence of glial cell dysfunction following spreading depression - a glial-centric cause for vasospasm. Such a mechanism for vasospasm becomes manifest when spreading depression waves transition to peri-infarct depolarization waves - with protracted ischemic blood flow in compromised tissue. The extracellular microenvironment with high potassium and low nitric oxide tension can account for conducting vessel narrowing. The implication for clinical management is discussed supposing glial cell dysfunction is an underlying mechanism responsible for the vascular spasm.

Spreading Depolarizations and Late Secondary Insults after Traumatic Brain Injury

Here we investigated the incidence of cortical spreading depolarizations (spreading depression and peri-infarct depolarization) after traumatic brain injury (TBI) and their relationship to systemic physiologic values during neurointensive care. Subdural electrode strips were placed on peri-contusional cortex in 32 patients who underwent surgical treatment for TBI. Prospective electrocorticography was performed during neurointensive care with retrospective analysis of hourly nursing chart data. Recordings were 84 hr (median) per patient and 2,503 hr in total. In 17 patients (53%), 280 spreading depolarizations (spreading depressions and peri-infarct depolarizations) were observed. Depolarizations occurred in a bimodal pattern with peak incidence on days 1 and 7. The probability of a depolarization occurring increased significantly as a function of declining mean arterial pressure (MAP; R(2) = 0.78; p < 0.001) and cerebral perfusion pressure (R(2) = 0.85; p < 0.01), and increasing core temperature (R(2) = 0.44; p < 0.05). Depolarization probability was 7% for MAP values of >100 mm Hg but 33% for MAP of < or =70 mm Hg. Temperatures of < or =38.4 degrees C were associated with a 21% depolarization risk, compared to 63% for >38.4 degrees C. Intracranial pressures were higher in patients with depolarizations (18.3 +/- 9.3 vs. 13.5 +/- 6.7 mm Hg; p < 0.001). We conclude that depolarization phenomena are a common cortical pathology in TBI. Their association with lower perfusion levels and higher temperatures suggests that the labile balance of energy supply and demand is an important determinant of their occurrence. Monitoring of depolarizations might serve as a functional measure to guide therapeutic efforts and their blockade may provide an additional line of defense against the effects of secondary insults.

Recovery of Slow Potentials in AC-Coupled Electrocorticography: Application to Spreading Depolarizations in Rat and Human Cerebral Cortex

Cortical spreading depolarizations (spreading depressions and peri-infarct depolarizations) are a pathology intrinsic to acute brain injury, generating large negative extracellular slow potential changes (SPCs) that, lasting on the order of minutes, are studied with DC-coupled recordings in animals. The spreading SPCs of depolarization waves are observed in human cortex with AC-coupled electrocorticography (ECoG), although SPC morphology is distorted by the high-pass filter stage of the amplifiers. Here, we present a signal processing method to reverse these distortions and recover approximate full-band waveforms from AC-coupled recordings. We constructed digital filters that reproduced the phase and amplitude distortions introduced by specific AC-coupled amplifiers and, based on this characterization, derived digital inverse filters to remove these distortions from ECoG recordings. Performance of the inverse filter was validated by its ability to recover both simulated and real low-frequency input test signals. The inverse filter was then applied to AC-coupled ECoG recordings from five patients who underwent invasive monitoring after aneurysmal subarachnoid hemorrhage. For 117 SPCs, the inverse filter recovered full-band waveforms with morphologic characteristics typical of the negative DC shifts recorded in animals. Compared with those recorded in the rat cortex with the same analog and digital methods, the negative DC shifts of human depolarizations had significantly greater durations (1:47 vs. 0:45 min:sec) and peak-to-peak amplitudes (10.1 vs. 4.2 mV). The inverse filter thus permits the study of spreading depolarizations in humans, using the same assessment of full-band DC potentials as that in animals, and suggests a particular solution for recovery of biosignals recorded with frequency-limited amplifiers.

PATHOPHYSIOLOGY OF ACUTE ISCHEMIC STROKE

ABSTRACT In acute ischemic stroke, abrupt vessel occlusion results in a drop in regional CBF, leading to time-dependent compartmentalization of the ischemic brain into tissue that is irreversibly damaged (ischemic core), tissue that is functionally impaired but structurally intact and thus potentially salvageable (penumbra), and tissue that is hypoperfused but not threatened under normal circumstances (oligemic brain). At a cellular level, neuronal damage occurs through a complex interaction of mechanisms (necrosis, apoptosis, excitotoxicity, inflammation, peri-infarct depolarization, acidosis, and free radical formation) that are characteristic for each compartment. All these mechanisms are potential targets for neuroprotective therapy, which, combined with flow restoration strategies, is likely to improve outcome significantly in human stroke.

Characterization of periinfarct flow transients with laser speckle and Doppler after middle cerebral artery occlusion in the rat

Little information exists on the role and the characteristics of perfusion changes related to periinfarct depolarization. Our aim was to visualize and monitor periinfarct flow transients (PIFTs) in Sprague-Dawley rats (n = 10) with two different laser methods in a closed-skull model of filament middle cerebral artery occlusion. A laser Doppler probe was placed over the ischemic cortex 5 mm lateral to Bregma, and a 5 x 5 mm area centered 5 mm posterior and 4 mm lateral to Bregma was thinned for laser speckle imaging. Both neurological and histological evaluations were performed at 72 hr postinjury. Mean flow during 90-min ischemia was 29% of baseline measured by laser Doppler and 36-54% by laser speckle. Flow transients occurred in all rats, the number of PIFTs being 4.6 +/- 1.8/90 min. By both methods, 95.6% of them occurred with temporal correlation. The average duration of PIFTs was also identical (162 +/- 24 and 162 +/- 34 sec, respectively). Five different morphologies of flow transients ranging from hypoperfusive to hyperemic were identified by laser speckle. The PIFTs changed their morphology dynamically over certain regions. All of the animals showed an infarct (178.5 +/- 26 mm(3)) in the middle cerebral artery territory. Laser Doppler in itself can be a reliable method for counting/detecting PIFTs, but laser speckle is capable of monitoring the dynamic changes in PIFT morphology over the penumbral and periischemic cortex.

Dynamic changes in cortical NADH fluorescence in rat focal ischemia: Evaluation of the effects of hypothermia on propagation of peri-infarct depolarization by temporal and spatial analysis

Suppression of peri-infarct depolarizations (PIDs) is one of the major mechanisms of hypothermic protection against transient focal cerebral ischemia. Previous studies have shown the lack of hypothermic protection against permanent focal ischemia. We hypothesized the lack of hypothermic protection was due to the poor efficacy in suppression of PIDs. To examine the hypothesis, we elucidated the effects of hypothermia on the manner of propagation of PIDs with temporal and spatial resolutions using NADH (reduced nicotinamide adenine dinucleotide) fluorescence images by illuminating the parietal–temporal cortex with ultraviolet light. Spontaneously hypertensive rats ( n = 14) were subjected to permanent focal ischemia by occlusion of the middle cerebral and left common carotid arteries. 2-h hypothermia (30 °C) was initiated before ischemia. Although hypothermia delayed the appearance of PIDs, it did not suppress their appearance. Furthermore, 54% of the PIDs enlarged the high-intensity area of NADH fluorescence in the hypothermia group, similar to the normothermia group (53%). The high-intensity area of NADH fluorescence widened by each PID was larger in the hypothermia group than in the normothermia group. These findings suggest that PIDs even in hypothermia are one of the major factors causing growth of infarction, emphasizing the importance of therapy that targets suppression of PIDs even during hypothermia.

Persisting Depletion of Brain Glucose following Cortical Spreading Depression, despite Apparent Hyperaemia: Evidence for Risk of an Adverse Effect of Leão's Spreading Depression

Rapid sampling microdialysis (rsMD) directed towards the cerebral cortex has allowed identification of a combined time-series signature for glucose and lactate that characterizes peri-infarct depolarization in experimental focal ischaemia, but no comparable data exist for 'classical' cortical spreading depression (CSD) associated with hyperaemia in the normally perfused brain. Here, we examined the rsMD responses of dialysate glucose and lactate to five hyperaemic spreading depressions induced with intracortical microinjections, typically of 1 mol/L KCl, in open-skull preparations in five cats under chloralose anaesthesia. Depolarization was verified with microelectrodes, and laser speckle flowmetry was used to examine propagation of the events and perfusion responses near the MD probe. Ten minutes after depolarization, dialysate glucose fell and lactate rose by 28% and 58% respectively. There was no recovery of dialysate glucose 30 mins after depolarization. Mean baseline indicative cerebral blood flow was 25.5+/-4.1 mL/100 g/min and mean maximum hyperaemic increase was by 29.6+/-6 mL/100 g/min; hyperaemia remained present 30 mins after CSD. As CSD events are repetitive, frequent, and often clustered temporally in human acute brain injury, these results indicate a high risk of depletion of extracellular glucose in association with depolarization events of a pattern previously thought to be largely benign.

Cortical spreading depression and peri-infarct depolarisation in stroke – a mechanism for secondary deterioration

Cortical spreading depression and peri-infarct depolarisation in stroke – a mechanism for secondary deterioration

Extraluminal Cooling of Bilateral Common Carotid Arteries as a Method to Achieve Selective Brain Cooling for Neuroprotection

Systemic cooling to achieve brain hypothermia has been investigated as a neuroprotective therapy but can present serious adverse effects. Here we describe a novel method to selectively cool the rat brain and investigate its neuroprotective effects following transient middle cerebral artery occlusion (MCAo). The novelty of our method of selective brain cooling (SBC) was that the extraluminal cooling of the carotid arterial blood was achieved by using a cooling cuff wrapped around each common carotid artery (CCA). Within 20 min of CCA cooling, brain temperature could be lowered by 2-5 degrees C below the baseline and maintained stable for approximately 2 h while maintaining body temperature at 37 degrees C. No adverse effects of SBC were observed on systemic physiology, regional cerebral blood flow (rCBF), bleeding time, or tissue histology in normal animals. In rats having sustained 2-h MCAo, intra-ischemic SBC for 90 min, initiated 30 min following the onset of ischemia, significantly reduced infarction measured at 24 h post-injury (normothermic rats=312+/-51 mm3, SBC rats=139+/-83 mm3). In subgroup experiments, the incidence of peri-infarct depolarization (PID) was assessed during the MCAo and cooling period. Compared to normothermic but ischemic rats, SBC significantly reduced the number of PID events from 6.2+/-2.5 to 2.0+/-2.5, and reduced infarct volumes from 323+/-79 to 139+/-102 mm3. In conclusion, this extralumimal cooling method of SBC provides a safe and efficient approach to rapidly and safely achieve hypothermic neuroprotection.

Hypoxia and Hypotension Transform the Blood Flow Response to Cortical Spreading Depression from Hyperemia into Hypoperfusion in the Rat

Cortical spreading depression (CSD) evokes a large cerebral blood flow (CBF) increase in normal rat brain. In contrast, in focal ischemic penumbra, CSD-like periinfarct depolarizations (PID) are mainly associated with hypoperfusion. Because PIDs electrophysiologically closely resemble CSD, we tested whether conditions present in ischemic penumbra, such as tissue hypoxia or reduced perfusion pressure, transform the CSD-induced CBF response in nonischemic rat cortex. Cerebral blood flow changes were recorded using laser Doppler flowmetry in rats subjected to hypoxia, hypotension, or both. Under normoxic normotensive conditions, CSD caused a characteristic transient CBF increase (74+/-7%) occasionally preceded by a small hypoperfusion (-4+/-2%). Both hypoxia (pO(2) 45+/-3 mm Hg) and hypotension (blood pressure 42+/-2 mm Hg) independently augmented this initial hypoperfusion (-14+/-2% normoxic hypotension; -16+/-6% hypoxic normotension; -21+/-5% hypoxic hypotension) and diminished the magnitude of hyperemia (44+/-10% normoxic hypotension; 43+/-9% hypoxic normotension; 27+/-6% hypoxic hypotension). Hypotension and, to a much lesser extent, hypoxia increased the duration of hypoperfusion and the DC shift, whereas CSD amplitude remained unchanged. These results suggest that hypoxia and/or hypotension unmask a vasoconstrictive response during CSD in the rat such that, under nonphysiologic conditions (i.e., mimicking ischemic penumbra), the hyperemic response to CSD becomes attenuated resembling the blood flow response during PIDs.

Mild Induced Hypertension Improves Blood Flow and Oxygen Metabolism in Transient Focal Cerebral Ischemia

In focal ischemic cortex, cerebral blood flow autoregulation is impaired, and perfusion passively follows blood pressure variations. Although it is generally agreed that profound hypotension is harmful in acute stroke, the hemodynamic and metabolic impact of increased blood pressure on the ischemic core and penumbra are less well understood. We, therefore, tested whether pharmacologically induced hypertension improves cerebral blood flow and metabolism and tissue outcome in acute stroke using optical imaging with high spatiotemporal resolution. Cerebral blood flow, oxyhemoglobin, and cerebral metabolic rate of oxygen were measured noninvasively using simultaneous multispectral reflectance imaging and laser speckle flowmetry during distal middle cerebral artery occlusion in mice. Hypertension was induced by phenylephrine infusion starting 10 or 60 minutes after ischemia to raise blood pressure by 30% for the duration of ischemia; control groups received saline infusion. Mild induced hypertension rapidly increased cerebral blood flow, oxyhemoglobin, and cerebral metabolic rate of oxygen in both the core and penumbra and prevented the expansion of cerebral blood flow deficit during 1 hour distal middle cerebral artery occlusion. Induced hypertension also diminished the deleterious effects of periinfarct depolarizations on cerebral blood flow, oxyhemoglobin, and cerebral metabolic rate of oxygen without altering their frequency. Consistent with this, mild induced hypertension reduced infarct volume by 48% without exacerbating tissue swelling when measured 2 days after 1 hour transient distal middle cerebral artery occlusion. Our data suggest that mild induced hypertension increases collateral cerebral blood flow and oxygenation and improves cerebral metabolic rate of oxygen in the core and penumbra, supporting its use as bridging therapy in acute ischemic stroke until arterial recanalization is achieved.

Mechanisms of ischemic brain damage

In the United States stroke is the third leading cause of death and the leading cause of disability. Brain injury following stroke results from the complex interplay of multiple pathways including excitotoxicity, acidotoxicity, ionic imbalance, peri-infarct depolarization, oxidative and nitrative stress, inflammation and apoptosis. There are very few treatments for stroke and the development of new treatments requires a comprehensive understanding of the diverse mechanisms of ischemic brain damage that are responsible for neuronal death. Here, we discuss the underlying pathophysiology of this devastating disease and reveal the intertwined pathways that are the target of therapeutic intervention.

Combined MEG and EEG methodology for non-invasive recording of infraslow activity in the human cortex

Objective Periinfarct depolarisation and spreading depression represent key mechanisms of neuronal injury after stroke. Changes in cortical electrical potentials and magnetic fields in the very low frequency range are relevant parameters to characterize these events, which up to now have only been recorded invasively. In this study, we proved whether a non-invasive combined MEG/EEG recording technique is able to quantitatively monitor cortical infraslow activity in humans. Methods We used repetitive very slow and slow right finger movements as a physiological motor activation paradigm to induce cortical infraslow activity. Infraslow fields were recorded over the left hemisphere using a modulation-based MEG technique. EEG was performed using 16 standard Ag-Cl electrodes that covered the left motor cortex. Results We recorded stable focal motor-related infraslow magnetic field changes in seven out of seven subjects. We also found correlating infraslow electrical potential changes in three out of seven subjects. Slow finger movements generated significantly stronger field and potential changes than very slow movements. Conclusions This study demonstrates the technical feasibility of combined non-invasive electrical potential and magnetic field measurements to localize and quantitatively monitor physiological, low amplitude, infraslow cortical activity in humans. This specific combination of simultaneous recording techniques allows to benefit from the specific physical advantages of each method. Significance This combined non-invasive MEG–EEG methodology is able to provide important information on infraslow neuronal activity originating from tangentially and radially oriented sources. Moreover, this dual approach has the potential to separate neuronal from non-neuronal DC-sources, e.g., radially to the head orientated DC-currents across the skin/scalp/skull/dura occurring during cerebral hypercapnia or hypoxia.

Normobaric hyperoxia improves cerebral blood flow and oxygenation, and inhibits peri-infarct depolarizations in experimental focal ischaemia

Normobaric hyperoxia is under investigation as a treatment for acute ischaemic stroke. In experimental models, normobaric hyperoxia reduces cerebral ischaemic injury and improves functional outcome. The mechanisms of neuroprotection are still debated because, (i) inhalation of 100% O2 does not significantly increase total blood O2 content; (ii) it is not known whether normobaric hyperoxia increases O2 delivery to the severely ischaemic cortex because of its short diffusion distance; and (iii) hyperoxia may reduce collateral cerebral blood flow (CBF) to ischaemic penumbra because it can cause vasoconstriction. We addressed these issues using real-time two-dimensional multispectral reflectance imaging and laser speckle flowmetry to simultaneously and non-invasively determine the impact of normobaric hyperoxia on CBF and oxygenation in ischaemic cortex. Ischaemia was induced by distal middle cerebral artery occlusion (dMCAO) in normoxic (30% inhaled O2, arterial pO2 134 +/- 9 mmHg), or hyperoxic mice (100% inhaled O2 starting 15 min after dMCAO, arterial pO2 312 +/- 10 mmHg). Post-ischaemic normobaric hyperoxia caused an immediate and progressive increase in oxyhaemoglobin (oxyHb) concentration, nearly doubling it in ischaemic core within 60 min. In addition, hyperoxia improved CBF so that the area of cortex with < or =20% residual CBF was decreased by 45% 60 min after dMCAO. Furthermore, hyperoxia reduced the frequency of peri-infarct depolarizations (PIDs) by more than 60%, and diminished their deleterious effects on CBF and metabolic load. Consistent with these findings, infarct size was reduced by 45% in the hyperoxia group 2 days after 75 min transient dMCAO. Our data show that normobaric hyperoxia increases tissue O2 delivery, and that novel mechanisms such as CBF augmentation, and suppression of PIDs may afford neuroprotection during hyperoxia.

NCX and NCKX Operation in Ischemic Neurons

Within the first 2 min of global brain ischemia, extracellular [K+] ([K+]o) increases above 60 mM and [Na+](o) drops to about 50 mM, indicating a massive K+ efflux and Na+ influx, a phenomenon known as anoxic depolarization (AD). Similar ionic shifts take place during repetitive peri-infarct depolarizations (PID) in the area penumbra in focal brain ischemia. The size of ischemic infarct is determined by the duration of AD and PID. However, the mechanism of cytosolic [Ca2+] ([Ca2+]c) elevation during AD or PID is poorly understood. Our data show that the exposure of cultured rat hippocampal CA1 neurons to AD-like conditions promptly elevates [Ca2+]c to about 30 microM. These high [Ca2+]c elevations depend on external Ca2+ and can be prevented by removing Na+ or by simultaneously inhibiting NMDA and AMPA/kainate receptors. These data indicate that [Ca2+]c elevations during AD result from Na+ influx via either NMDA or AMPA/kainate channels. The mechanism of the Na-dependent [Ca2+]c elevations may involve a reversal of plasmalemmal Na+/Ca2+ (NCX) and/or Na+/Ca2+ + K+ (NCKX) exchangers. KB-R7943, an NCX inhibitor, suppresses a fraction of the Na-dependent Ca2+ influx during AD. Therefore, Ca2+ influx via NCX and a KB-R7943-resistant pathway (possibly NCKX) is involved. Inhibition of the Na-dependent Ca2+ influx is likely to decrease ischemic brain damage. No drugs are known that are able to inhibit the KB-R7943-resistant component of Na-dependent Ca2+ influx during AD. The present data encourage development of such agents as potential therapeutic means to limit ischemic brain damage after stroke or heart attack.

Glutamate-Independent Calcium Toxicity

It is widely accepted that a critical factor in determining neuronal death during cerebral ischemia is the progressive accumulation of intracellular Na+ ([Na+]i) and Ca2+ ([Ca2+]i) ions, which can precipitate necrosis and apoptosis of vulnerable neurons. Whereas the detrimental action of [Na+]i increase is attributable to both cell swelling and microtubular disorganization—2 phenomena that lead to cell necrosis1—a change in [Ca2+]i has been shown to be a key factor in ischemic brain damage, for it modulates several death pathways, including oxidative and nitrosative stress, mitochondrial dysfunction, and protease activation. Since Olney’s seminal work firstly suggested that excitatory aminoacids could elicit neurotoxicity,2 a large amount of work has been accumulated showing that glutamate extracellular concentrations briskly rise during acute brain injury, thus triggering an influx of Ca2+ and Na+ ions into neurons through ionotropic glutamate receptor subtypes. This evidence has led to the elaboration of the paradigm of glutamate excitotoxicity that explained ischemic neuronal cell death as a mere consequence of Na+ and Ca2+ influx through glutamate receptors.3 Although this theory has been guiding basic research in the field of neurodegeneration for almost 3 decades, more recently it has become the object of serious criticism and reassessment. What has aroused such skepticism among researchers has been the fact that although first, second, and third generation glutamate receptor antagonists have long yielded promising results in animal models of brain ischemia, they have failed to elicit a neuroprotective action in stroke and traumatic brain injury in humans.4 Therefore, the theory of excitotoxicity, though a fascinating paradigm, can only explain some of the events occurring in the acute phase of anoxic insult but cannot be seen as a major target for …