Cerebral blood flow and edema following carotid occlusion in the gerbil

Diffusion-Weighted MRI Stroke Volume Following Recanalization Treatment is Threshold-Dependent

PURPOSE

Infarct lesion segmentation has been problematic as there are a wide range of relative and absolute diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) thresholds that have been used for this purpose. We examined differences of stroke lesion volume and evolution evaluated by magnetic resonance imaging (MRI) during the immediate post-treatment phase (<5 h) and at 24 h.

METHODS

In this study 33 acute ischemic stroke patients were imaged with MRI <5 h and 24 h post-reperfusion treatment. Lesion volumes were segmented on ADC maps and average DWI using literature cited absolute ADC and relative DWI thresholds. The segmented lesion volumes within both time points were compared and the absolute change in lesion volume (infarct growth) between the two time points was calculated and compared using Bland-Altman analysis.

RESULTS

Lesion volumes differed significantly when different relative DWI or absolute ADC thresholds were used (p < 0.05), which held true for baseline as well as follow-up lesions. The median absolute changes in lesion volume from baseline to follow-up for ADC thresholds of 550 × 10^-6 mm²/s, 600 × 10^-6 mm²/s, 630 × 10^-6 mm²/s and 650 × 10^-6 mm²/s were 3.5 ml, 4.2 ml, 4.5 ml, and 6.5 ml, respectively (p < 0.05). Likewise, the median absolute changes in lesion volume from baseline to follow-up for DWI thresholds, k = 0.85, 1.28, 1.64, 1.96, and 2.7 were 10.1 ml, 7.3 ml, 5.7 ml, 5.4 ml and 4.2 ml, respectively (p < 0.05).

CONCLUSION

Absolute lesion volumes and changes in lesion volumes (infarct growth) measured after recanalization treatment were dependent on absolute ADC and relative DWI thresholds, which may have clinical significance. Standardization of techniques for measuring DWI lesion volumes requires immediate attention.

Novel Imaging Markers of Ischemic Cerebral Edema and Its Association with Neurological Outcome

Ischemic cerebral edema (ICE) is a recognized cause of secondary neurological deterioration after large hemispheric stroke, but little is known about the scope of its impact. To study edema in less severe stroke, our group has developed several markers of cerebral edema using brain magnetic resonance imaging (MRI). These tools, which are based on categorical and volumetric measurements in serial diffusion-weighted imaging (DWI), are applicable to a wide variety of stroke volumes. Further, these metrics provide distinct volumetric measurements attributable to ICE, infarct growth, and hemorrhagic transformation. We previously reported that ICE independently predicted neurological outcome after adjustment for known risk factors. We found that an ICE volume of 11 mL or greater was associated with worse neurological outcome.

Glyburide is associated with attenuated vasogenic edema in stroke patients

BACKGROUND

Brain edema is a serious complication of ischemic stroke that can lead to secondary neurological deterioration and death. Glyburide is reported to prevent brain swelling in preclinical rodent models of ischemic stroke through inhibition of a non-selective channel composed of sulfonylurea receptor 1 and transient receptor potential cation channel subfamily M member 4. However, the relevance of this pathway to the development of cerebral edema in stroke patients is not known.

METHODS

Using a case-control design, we retrospectively assessed neuroimaging and blood markers of cytotoxic and vasogenic edema in subjects who were enrolled in the glyburide advantage in malignant edema and stroke-pilot (GAMES-Pilot) trial. We compared serial brain magnetic resonance images (MRIs) to a cohort with similar large volume infarctions. We also compared matrix metalloproteinase-9 (MMP-9) plasma level in large hemispheric stroke.

RESULTS

We report that IV glyburide was associated with T2 fluid-attenuated inversion recovery signal intensity ratio on brain MRI, diminished the lesional water diffusivity between days 1 and 2 (pseudo-normalization), and reduced blood MMP-9 level.

CONCLUSIONS

Several surrogate markers of vasogenic edema appear to be reduced in the setting of IV glyburide treatment in human stroke. Verification of these potential imaging and blood biomarkers is warranted in the context of a randomized, placebo-controlled trial.

Brain edema predicts outcome after nonlacunar ischemic stroke

BACKGROUND AND PURPOSE

In malignant infarction, brain edema leads to secondary neurological deterioration and poor outcome. We sought to determine whether swelling is associated with outcome in smaller volume strokes.

METHODS

Two research cohorts of acute stroke subjects with serial brain MRI were analyzed. The categorical presence of swelling and infarct growth was assessed on diffusion-weighted imaging (DWI) by comparing baseline and follow-up scans. The increase in stroke volume (ΔDWI) was then subdivided into swelling and infarct growth volumes using region-of-interest analysis. The relationship of these imaging markers with outcome was evaluated in univariable and multivariable regression.

RESULTS

The presence of swelling independently predicted worse outcome after adjustment for age, National Institutes of Health Stroke Scale, admission glucose, and baseline DWI volume (odds ratio, 4.55; 95% confidence interval, 1.21-18.9; P<0.02). Volumetric analysis confirmed that ΔDWI was associated with outcome (odds ratio, 4.29; 95% confidence interval, 2.00-11.5; P<0.001). After partitioning ΔDWI into swelling and infarct growth volumetrically, swelling remained an independent predictor of poor outcome (odds ratio, 1.09; 95% confidence interval, 1.03-1.17; P<0.005). Larger infarct growth was also associated with poor outcome (odds ratio, 7.05; 95% confidence interval, 1.04-143; P<0.045), although small infarct growth was not. The severity of cytotoxic injury measured on apparent diffusion coefficient maps was associated with swelling, whereas the perfusion deficit volume was associated with infarct growth.

CONCLUSIONS

Swelling and infarct growth each contribute to total stroke lesion growth in the days after stroke. Swelling is an independent predictor of poor outcome, with a brain swelling volume of ≥11 mL identified as the threshold with greatest sensitivity and specificity for predicting poor outcome.

Neuroprotection of antioxidant enzymes against transient global cerebral ischemia in gerbils

Experimentally transient global cerebral ischemia using animal models have been thoroughly studied and numerous reports suggest the involvement of oxidative stress in the pathogenesis of neuronal death in ischemic lesions. In animal models, during the reperfusion period after ischemia, increased oxygen supply results in the overproduction of reactive oxygen species (ROS), which are involved in the process of cell death. ROS, such as superoxide anions, hydroxyl free radicals, hydrogen peroxide and nitric oxide are produced as a consequence of metabolic reactions and central nervous system activity. These reactive species are directly involved in the oxidative damage of cellular macromolecules such as nucleic acids, lipids and proteins in ischemic tissues, which can lead to cell death. Antioxidant enzymes are believed to be among the major mechanisms by which cells counteract the deleterious effect of ROS after cerebral ischemia. Consequently, antioxidant strategies have been long suggested as a therapy for experimental ischemic stroke; however, clinical trials have not yet been able to promote the translation of this concept into patient treatment regimens. This article focuses on the contribution of oxidative stress or antioxidants to the post-ischemic neuronal death following transient global cerebral ischemia by using a gerbil model.

Trace element, antioxidant activity, and lipid peroxidation levels in brain cortex of gerbils after cerebral ischemic injury

Proper trace element level and antioxidant enzyme activity are crucial for the brain in maintaining normal neurological functions. To our knowledge, alteration of lipid peroxidation status, trace element level, and antioxidant activity in the homogenates of brain cortex after cerebral ischemia in gerbil, however, has not been investigated so far. Male Mongolian gerbils were divided into control and ischemic subjects. Cerebral ischemia was induced by occlusion of the right middle cerebral artery and right common carotid artery for 1 h. Experimental results showed that a significant increase (P < 0.01) of the malondialdehyde level was found in the ischemic brain as compared with the control group. Trace element analysis indicated that a remarkable elevation (P < 0.01) of the level of iron (Fe), chromium (Cr), and a statistical decrease of selenium (Se) and zinc (Zn) (P < 0.05) concentration were observed in the ischemic brain as compared with the control subject. No significant change (P > 0.05) of the copper (Cu) level was found in both experimental groups. Additionally, antioxidant activity of superoxide dismutase (P < 0.01) and catalase (P < 0.05) was significantly decreased in the ischemic brain as compared with the control subject. Taking all results together, it is conceivable to manifest the experimental findings that cerebral ischemia not only may result in an enhanced oxidative stress but also may lead to further oxidative injury. Moreover, disturbance of trace element level combined with declined antioxidant activity seems to play a significant role in responsible for the etiology of cerebral ischemia.

Animal models of neurological disease

The use of animal models to study human pathology has proved valuable in a number of fields. Animal models of neurological disease have successfully and accurately recreated many aspects of human illness allowing for in-depth study ofneuropathophysiology. These models have been the source of a plethora of information, such as the importance of certain molecular mechanisms and genetic contributions in neurological disease. Additionally, animal models have been utilized in the discovery and testing of possible therapeutic treatments. Although most neurological diseases are still not yet completely understood and reliable treatment is lacking, animal models provide a major step in the right direction.

Hypoxic/ischemic conditions induce expression of the putative pro-death gene Clca1 via activation of extrasynaptic N-methyl-D-aspartate receptors

The stimulation of extrasynaptic N-methyl-D-aspartate (NMDA) receptors triggers cell death pathways and has been suggested to play a key role in cell degeneration and neuron loss associated with glutamate-induced excitotoxicity. In contrast, synaptic NMDA receptors promote neuronal survival. One mechanism through which extrasynaptic NMDA receptors damage neurons may involve Clca1, which encodes a putative calcium-activated chloride channel. Here we show that Clca1 expression is induced in cultured rat hippocampal neurons exposed to oxygen/glucose-free media; this induction is mediated by a signaling pathway activated by extrasynaptic NMDA receptors. Clca1 mRNA levels also increased in the gerbil hippocampus following a transient forebrain ischemia caused by bilateral carotid occlusion. Microelectrode array recordings revealed that oxygen-glucose deprivation enhances hippocampal network firing rates, which induces c-fos transcription through a signaling pathway that, in contrast to Clca1, is activated by synaptic but not extrasynaptic NMDA receptors. Thus, conditions of low oxygen/glucose lead to the activation of both extrasynaptic and synaptic NMDA receptors that regulate distinct target genes. Clca1 may be part of the genomic death program triggered by extrasynaptic NMDA receptors; it could be a marker for ischemic brain damage and a possible target for therapeutic interventions.

The determination of brain magnesium and zinc levels by a dual-probe microdialysis and graphite furnace atomic absorption spectrometry

OBJECTIVE

The aim of this study was to develop a microdialysis-graphite furnace atomic absorption spectroscopy (MD-GFAAS) for monitoring dynamic changes of extracellular magnesium (Mg) and zinc (Zn) in the cortex of gerbils subjected to focal cerebral ischemia, that had been produced in anesthetized gerbils by occlusion of the right middle cerebral artery.

METHODS

Two microdialysis probes were inserted into both sides of the cortex to simultaneously collect dialysates during cerebral ischemia. Dynamic changes in these analytes, on ipsilateral and contralateral sides of the brain, were assayed by MD-GFAAS. Optimal conditions and analytical precision of GFAAS were studied in the present assay.

RESULTS

The present study demonstrated significant decreases in Mg (65% of baseline) and zinc (74% of baseline) maintained their levels within 3 h on the ipsilateral side of cortex during cerebral ischemia. Slight changes of Mg and Zn on the contralateral sides were also observed.

CONCLUSION

The derangement of extracellular Mg and Zn could be important in the progression of cell injury and may be associated with cerebral ischemia insult.

On-line microdialysis-graphite furnace atomic absorption spectrometry in the determination of brain magnesium levels in gerbils subjected to cerebral ischemia/reperfusion

OBJECTIVES

Description of use of equipment for on-line microdialysis (MD) coupled with graphite furnace atomic absorption spectrometry (GFAAS) system, for dynamic monitoring of extracellular Mg in gerbils subjected to transient focal cerebral ischemia.

METHODS

Gerbils' right middle cerebral artery (MCA) and common carotid artery (CCA) were occluded for 60 minutes, and then reperfused for 60 minutes with Ringer's solution, after which extracellular fluid samples were collected via a microdialysis probe inserted into the right cortex before, during and after inducing ischemia. Reperfusion was at a rate of 2 microL/min through the microdialysis probe, on-line diluted with measured water injected onto the GFAAS via an autosampler for Mg analysis.

RESULTS

The detection limit of the Mg concentrations has ranged from 0.50 to 3.00 microg/L; our detection limit was 0.03 microg/L. We applied this on-line system to monitor extracellular Mg levels in the cortex during focal cerebral ischemia. Mg concentrations significantly decreased to 41% of baseline during cerebral ischemia and gradually returned to 67% of baseline after 60 minutes of reperfusion.

CONCLUSIONS

We presume that derangement of Mg homeostasis could be important in brain cell injury and is closely associated with cerebral ischemia event. The described analytic system permits autosampling in the brain and allows for continuous determination of Mg and trace minerals in minute sample volumes in a living system.

Acute intraoperative cerebral oedema: are current therapies evidence based?

Acute intraoperative ischaemic cerebral oedema following torrential haemorrhage from the left intracranial internal carotid artery occurred during resection of a recurrent middle cranial fossa meningioma. A series of immediate anaesthetic interventions was effective in reducing brain oedema, allowed for surgical haemostasis, and resulted in no permanent sequelae to patient outcome. A review of the literature indicates that direct evidence for the efficacy of extremely early interventions as described in this case report is lacking and must be extrapolated from other brain injury models.

Animal models of focal and global cerebral ischemia

The use of appropriate animal models is essential to predict the value and effect of therapeutic approaches in human subjects. Focal (stroke) and global (cardiac arrest) cerebral ischemia represents diseases that are common in the human population. Stroke and cardiac arrest, which are major causes of death and disability, affect millions of individuals around the world and are responsible for the leading health care costs of all diseases. Understanding the mechanisms of injury and neuroprotection in these diseases is critical if we are ever to learn new target sites to treat ischemia. There are many animal models available to investigate injury mechanisms and neuroprotective strategies. This review summarizes many (but not all) small and large animal models of focal and global cerebral ischemia and discusses their advantages and disadvantages.

Why do neuroprotective drugs that are so promising in animals fail in the clinic? An industry perspective

1. No neuroprotective drug has yet been shown to be effective in treating acute ischaemic stroke in the clinic, despite evidence of efficacy in animal models. 2. An academic/industry round-table group recently published guidelines to be met if a drug was to be progressed to clinical trial. 3. Major points included obtaining full dose-response evaluation and measurement of the therapeutic time window for efficacy, functional behavioural testing in addition to measurement of infarct volume, measurement of physiological parameters, use of appropriate models (transient and permanent focal ischaemia) and reproducibility of data by external laboratories. 4. The present paper examines both failed compounds and disodium 4-[(tert-butylimino) methyl] benzene-1, 3-disulphonate N-oxide (NXY-059), a nitrone radical-trapping agent currently in clinical development. It aims to determine whether these guidelines were met by compounds that have failed and, thus, determine whether following the guidelines, as is being done with NXY-059, will increase the chances of developing efficacious drugs for treating acute ischaemic stroke. 5. It is concluded that we will only achieve the goal of producing a clinically effective neuroprotective agent if the guidelines have been met by the novel compound under investigation.

Ischaemic brain oedema

Ischaemic brain oedema appears to involve two distinct processes, the relative contribution and time course of which depend on the duration and severity of ischaemia, and the presence of reperfusion. The first process involves an increase in tissue Na+ and water content accompanying increased pinocytosis and Na+, K+ ATPase activity across the endothelium. This is apparent during the early phase of infarction and before any structural damage is evident. This phenomenon is augmented by reperfusion. A second process results from a more indiscriminate and delayed BBB breakdown that is associated with infarction of both the parenchyma and the vasculature itself. Although, tissue Na+ level still seems to be the major osmotic force for oedema formation at this second stage, the extravasation of serum proteases is an additional potentially deleterious factor. The relative importance of protease action is not yet clear, however, degradation of the extracellular matrix conceivably leads to further BBB disruption and softening of the tissue, setting the stage for the most pronounced forms of brain swelling. A number of factors mediate or modulate ischaemic oedema formation, however, most current information comes from experimental models, and clinical data on this microcosmic level is lacking. Clinically significant brain oedema develops in a delayed fashion after large hemispheric strokes and is a cause of substantial mortality. Neurological signs appear to be at least as good as direct ICP measurement and neuroimaging in detecting and gauging the secondary damage produced by stroke oedema. The neuroimaging characteristics of the stroke, specifically the early involvement of greater than half of the MCA territory, are, however, highly predictive of the development of severe oedema over the subsequent hours and days. None of the available medical therapies provide substantial relief from the oedema and raised ICP, or at best, they are temporizing in most cases. Hemicraniectomy appears most promising as a method of avoiding death from brain compression, but the optimum timing and manner of patient selection are currently being investigated. All approaches to massive ischaemic brain swelling are clouded by the potential for survival with poor functional outcome. It is possible to manage blood pressure, serum osmolarity by way of selective fluid administration, and a number of other systemic factors that exaggerate brain oedema. Broad guidelines for treatment of stroke oedema can therefore be given at this time.

Quantitative assessment of the balance between oxygen delivery and consumption in the rat brain after transient ischemia with T2 -BOLD magnetic resonance imaging

The balance between oxygen consumption and delivery in the rat brain after exposure to transient ischemia was quantitatively studied with single-spin echo T2-BOLD (blood oxygenation level-dependent) magnetic resonance imaging at 4.7 T. The rats were exposed to graded common carotid artery occlusions using a modification of the four-vessel model of Pulsinelli. T2, diffusion, and cerebral blood volume were quantified with magnetic resonance imaging, and CBF was measured with the hydrogen clearance method. A transient common carotid artery occlusion below the CBF value of approximately 20 mL x 100 g(-1) x min(-1) was needed to yield a T2 increase of 4.6 +/- 1.2 milliseconds (approximately 9% of cerebral T2) and 6.8 +/- 1.7 milliseconds (approximately 13% of cerebral T2) after 7 and 15 minutes of ischemia, respectively. Increases in CBF of 103 +/- 75% and in cerebral blood volume of 29 +/- 20% were detected in the reperfusion phase. These hemodynamic changes alone could account for only approximately one third of the T2 increase in luxury perfusion, suggesting that a substantial increase in blood oxygen saturation (resulting from reduced oxygen extraction by the brain) is needed to explain the magnetic resonance imaging observation.

Simultaneous monitoring of extracellular glucose, pyruvate, lactate and glutamate in gerbil cortex during focal cerebral ischemia by dual probe microdialysis

The aim of this study was to monitor dynamic changes in energy-related metabolites in the cortex of gerbils subjected to cerebral ischemia by a dual probe microdialysis technique. Focal cerebral ischemia was produced in anesthetized gerbils by occlusion of the right common carotid artery and the right middle cerebral artery for 60 min. Two microdialysis probes were inserted into both sides of the cortex to simultaneously monitor extracellular glucose, lactate, pyruvate and glutamate. Dynamic and comparative changes in these analytes, on the ipsilateral and contralateral sides of the brain, were simultaneously monitored by liquid chromatography and a microdialysis analyzer. The present study demonstrated decreases in glucose and pyruvate, increases in lactate and glutamate on the ipsilateral side whereas all analytes remain constant on the contralateral side of cortex during cerebral ischemia. In vitro recovery of each microdialysis probe was performed to ensure the quality of experiments. The detection limits of pyruvate, glutamate, lactate and glucose were 0.2, 1.0, 2.0 and 20 microM, respectively. The intra- and inter-assay correlations were less than 5% in standard mixtures and pooled brain dialysates.

Use of spin echo T(2) BOLD in assessment of cerebral misery perfusion at 1.5 T

Inadequate blood supply relative to metabolic demand, a haemodynamic condition termed as misery perfusion, often occurs in conjunction with acute ischaemic stroke. Misery perfusion results in adaptive changes in cerebral physiology including increased cerebral blood volume (CBV) and oxygen extraction ratio (OER) to secure substrate supply for the brain. It has been suggested that the presence of misery perfusion may be an indication of reversible ischaemia, thus detection of this condition may have clinical impact in acute stroke imaging. The ability of single spin echo T(2) to detect misery perfusion in the rat brain at 1.5 T owing to its sensitivity to blood oxygenation level dependent (BOLD) contrast was studied both theoretically and experimentally. Based on the known physiology of misery perfusion, tissue morphometry and blood relaxation data, T(2) behaviour in misery perfusion was simulated. The interpretation of these computations was experimentally assessed by quantifying T(2) in a rat model for cerebral misery perfusion. CBF was quantified with the H(2) clearance method. A drop of CBF from 58+/-8 to 17+/-3 ml/100 g/min in the parieto-frontal cortex caused shortening of T(2) from 66.9+/-0.4 to 64.6+/-0.5 ms. Under these conditions, no change in diffusion MRI was detected. In contrast, the cortex with CBF of 42+/-7 ml/100 g/min showed no change in T(2). Computer simulations accurately predicted these T(2) responses. The present study shows that the acute drop of CBF by 70% causes a negative BOLD that is readily detectable by T(2) MRI at 1.5 T. Thus BOLD may serve as an index of misery perfusion thus revealing viable tissue with increased OER.

Early detection of irreversible cerebral ischemia in the rat using dispersion of the magnetic resonance imaging relaxation time, T1rho

The impact of brain imaging on the assessment of tissue status is likely to increase with the advent of treatment methods for acute cerebral ischemia. Multimodal magnetic resonance imaging (MRI) demonstrates potential for selecting stroke therapy patients by identifying the presence of acute ischemia, delineating the perfusion defect, and excluding hemorrhage. Yet, the identification of tissue subject to reversible or irreversible ischemia has proven to be difficult. Here, the authors show that T1 relaxation time in the rotating frame, so-called T1rho, serves as a sensitive MRI indicator of cerebral ischemia in the rat. The T1rho prolongs within minutes after a drop in the CBF of less than 22 mL 100 g(-1) min(-1). Dependence of T1rho on spin-lock amplitude, termed as T1rho dispersion, increases by approximately 20% on middle cerebral artery (MCA) occlusion, comparable with the magnitude of diffusion reduction. The T1rho dispersion change dynamically increases to be 38% +/- 10% by the first 60 minutes of ischemia in the brain region destined to develop infarction. Following reperfusion after 45 minutes of MCA occlusion, the tissue with elevated T1rho dispersion (yet normal diffusion) develops severe histologically verified neuronal damage; thus, the former parameter unveils an irreversible condition earlier than currently available MRI methods. The T1rho dispersion as a novel MRI index of cerebral ischemia may be useful in determination of the therapeutic window for acute ischemic stroke.

A dual-probe microdialysis study in simultaneously monitoring extracellular pyruvate, lactate, and biogenic amines in gerbil striata during unilateral cerebral ischemia

A dual-probe microdialysis technique coupled with liquid chromatographic assays was developed for the simultaneous monitoring of neurochemicals in gerbil striata during cerebral ischemia. Isocratic separation of lactate and pyruvate was achieved within 5 min whereas the separation of biogenic amines was completed within 30 min. An unilateral ligation was produced by occlusion of the right common carotid artery for 30 mins in anesthetized gerbils to perform a typical focal cerebral ischemia. Microdialysis probes were inserted in both sides of the striata to simultaneously monitor biogenic amines, lactate and pyruvate during cerebral ischemia. Dynamic and comparative changes of these analytes in ipsilateral and contralateral sides of the brain can be simultaneously measured by the assay. The present assay can be used as a research tool to explore neurochemical substances and their relationships during cerebral ischemia.

Graded reduction of cerebral blood flow in rat as detected by the nuclear magnetic resonance relaxation time T2: a theoretical and experimental approach

The ability of transverse nuclear magnetic resonance relaxation time, T2, to reveal acutely reduced CBF was assessed using magnetic resonance imaging (MRI). Graded reduction of CBF was produced in rats using a modification of Pulsinelli's four-vessel occlusion model. The CBF in cerebral cortex was quantified using the hydrogen clearance method, and both T2 and the trace of the diffusion tensor (Dav = 1/3TraceD) in the adjacent cortical tissue were determined as a function of reduced CBF at 4.7 T. A previously published theory, interrelating cerebral hemodynamic parameters, hemoglobin, and oxygen metabolism with T2, was used to estimate the effects of reduced CBF on cerebral T2. The MRI data show that T2 reduces in a U-shape manner as a function of CBF, reaching a level that is 2.5 to 2.8 milliseconds (5% to 6%) below the control value at CBF, between 15% and 60% of normal. This reduction could be estimated by the theory using the literature values of cerebral blood volume, oxygen extraction ratio, and precapillary oxygen extraction during compromised CBF. Dav dropped with two apparent flow thresholds, so that a small 11% to 17% reduction occurred between CBF values of 16% to 45% of normal, followed by a precipitous collapse by more than 20% at CBF below 15% of normal. The current data show that T2 can be used as an indicator of acute hypoperfusion because of its ability to indicate blood oxygenation level-dependent phenomena on reduced CBF.

Ischemia-induced inhibition of active calcium transport into gerbil brain microsomes: effect of anesthetics and models of ischemia

The excessive increase in intracellular Ca2+ concentration is associated with events linking cerebral blood flow reduction to neuronal cell damage. We have investigated the possible effect of ischemia and ischemia-reperfusion injury on endoplasmic reticulum (ER) Ca2+ transport. Two different models of ischemia as well as two different anesthetics were used. 5 min and 15 min of global forebrain ischemia caused significant depression of the rate of microsomal Ca2+ accumulation in pentobarbital anesthetised gerbils. The Ca2+ uptake activity recovered partially after 1 hour of reperfusion. Unlike pentobarbital anesthetised gerbils, no significant changes were detected in the active microsomal Ca(2+)-transport after 10 min of global forebrain ischemia in gerbil forebrain and hippocampus under halothane anesthesia. In addition, using the model of decapitation ischemia, we observed significant changes of the Ca2+ uptake in both halothane and pentobarbital anesthetised gerbils. These findings indicate that ischemic insult alters the brain microsomal Ca2+ transport which is not due to inhibition of the Ca(2+)-ATPase activity. However, the effect of ischemia on this transport system is dependent on the model of ischemia and on the type of anesthetics.

Na/K-ATPase under oxidative stress: molecular mechanisms of injury

1. The authors compare oxidative injury to brain and kidney Na/K-ATPase using in vitro and in vivo approaches. The substrate dependence of dog kidney Na/K-ATPase was examined both before and after partial hydrogen peroxide modification. A computer simulation model was used for calculating kinetic parameters. 2. The substrate dependence curve for the unmodified endogenous enzyme displayed a typical curve with an intermediate plateau, adequately described by the sum of hyperbolic and sigmoidal components. 3. The modified enzyme demonstrated a dependent curve that closely approximates normal hyperbola. The estimated ATP K(m) value for the endogenous enzyme was about 85 microM; the Kh was equal to 800 microM. The maximal number of protomers interacting was 8. Following oxidative modification, the enzyme substrate dependence curve did not show a significant change in the maximal protomer rate Vm, while the K(m) was increased slightly and interprotomer interaction was abolished. 4. Na/K-ATPase from an ischemic gerbil brain showed a 22% decrease in specific activity. The maximal rate of ATP hydrolysis by an enzyme protomer changed slightly. but the sigmoidal component, characterizing the enzyme's ability to form oligomers was abolished completely. The K(m) value was almost unchanged, but the Hill coefficient fell to 1. These data show that Na/K-ATPase molecules isolated from the ischemic brain have lost the ability to interact with one another. 5. We suggest that the most important consequence of oxidative modification is Na/K-ATPase oligomeric structure formation and subsequent hydrolysis rate suppression.

A model of perinatal hypoxic-ischemic brain damage

In conclusion, our immature rat model has gained wide acceptance as the animal model of choice to study basic physiologic, biochemical, and molecular mechanisms of perinatal hypoxic-ischemic brain damage. In addition, the model has been used extensively to study those physiologic and therapeutic variables which either are deleterious or beneficial to the perinatal brain undergoing hypoxia-ischemia. As therapeutic interventions are tested in the animal setting, the results will provide important information regarding the effect of these agents in the human setting.

The normal and pathological physiology of brain water

The physicochemical properties of water enable it to act as a solvent for electrolytes, and to influence the molecular configuration and hence the function--enzymatic in particular--of polypeptide chains in biological systems. The association of water with electrolytes determines the osmotic regulation of cell volume and allows the establishment of the transmembrane ion concentration gradients that underlie nerve excitation and impulse conduction. Fluid in the central nervous system is distributed in the intracellular and extracellular spaces (ICS, ECS) of the brain parenchyma, the cerebrospinal fluid, and the vascular compartment--the brain capillaries and small arteries and veins. Regulated exchange of fluid between these various compartments occurs at the blood-brain barrier (BBB), and at the ventricular ependyma and choroid plexus, and, on the brain surface, at the pia mater. The normal BBB is relatively permeable to water, but considerably less so to ions, including the principal electrolytes Brain fluid regulation takes place within the context of systemic fluid volume control, which depends on the mutual interaction of osmo-, volume-, and pressure-receptors in the hypothalamus, heart and kidney, hormones such as vasopressin, renin-angiotensin, aldosterone, atriopeptins, and digitalis-like immunoreactive substance, and their respective sites of action. Evidence for specific transport capabilities of the cerebral capillary endothelium, for example high Na+K(+)-ATPase activity and the presence at the abluminal surface of a Na(+)--H+ antiporter, suggests that cerebral microvessels play a more active part in brain volume regulation and ion homoeostasis than do capillaries in other vascular beds. The normal brain ECS amounts to 12-19% of brain volume, and is markedly reduced in anoxia, ischaemia, metabolic poisoning, spreading depression, and conventional procedures for histological fixation. The asymmetrical distributions of Na+ K+ and Ca2+ between ICS and ECS underlie the roles of these cations in nerve excitation and conduction, and in signal transduction. The relatively large volume of the CSF, and extensive diffusional exchange of many substances between brain ECS and CSF, augment the ion-homeostasing capacity of the ECS. The choroid plexus, in addition to secreting CSF principally by biochemical mechanisms (there is an additional small component from the extracellular fluid), actively transports some substances from the blood (e.g. nucleotides and ascorbic acid), and actively removes others from the CSF. In contrast with CSF secretion, CSF reabsorption is principally a biomechanical process, passively dependent on the CSF-dural sinus pressure gradient. Pathological increases in intracranial water content imply development of an intracranial mass lesion. The additional water may be distributed diffusely within the brain parenchyma as brain oedema, as a cyst, or as increase in ventricular volume due to hydrocephalus. Brain oedema is classified on the basis of pathophysiology into four categories, vasogenic, cytotoxic, osmotic and hydrostatic. The clinical conditions in which brain oedema presents the greatest problems are tumour, ischaemia, and head injury. Peritumoural oedema is predominantly vasogenic and related to BBB dysfunction. Ischaemic oedema is initially cytotoxic, with a shift of Na+ and CI- ions from ECS to ICS, followed by osmotically obliged water, this shift can be detected by diffusion-weighted MRI. Later in the evolution of an ischaemic lesion the oedema becomes vasogenic, with disruption of the BBB. Recent imaging studies in patients with head injury suggest that the development of traumatic brain oedema may follow a biphasic time course similar to that of ischaemic oedema. Hydrocephalus is associated in the great majority of cases with an obstruction to the circulation or drainage of CSF, or, occasionally, with overproduction of CSF by a choroid plexus papilloma. In either case, the consequence is a ris

Synaptosomal Na, K-ATPase during forebrain ischemia in Mongolian gerbils

We studied the activity and kinetic parameters of synaptosomal Na, K-ATPase during 15 min of forebrain ischemia and following 60 min of reperfusion produced by reversible common carotid occlusion in Mongolian gerbils. A synaptosomal fraction was obtained by both differential centrifugation of brain tissue homogenate and centrifugation of crude mitochondrial fraction at a discontinual sucrose density gradient. We found two components of ATP concentration dependence of ATP hydrolysis that represent two types of ATP-binding sites: high affinity and low affinity. Neither ischemia nor reperfusion affected kinetic parameters of a high-affinity site. However, low-affinity site parameters were affected by both ischemia and ischemia followed by reperfusion. Maximal velocity (Vmax) decreased by 43 and 42% after ischemia and after ischemia/reperfusion, respectively. The apparent Km for ATP decreased by 52% after ischemia and by 47% after ischemia/reperfusion. The apparent affinities for K+ and Na+ were determined from the ATP hydrolysis rate as a function of Na+ and K+ concentrations. We found the half-maximal activation constant for K+ (KaK+) increased by 60% after ischemia and by 146% after ischemia/reperfusion. On the other hand, we found that KaNa+ decreased significantly after ischemia/reperfusion (16%). We concluded that it is the dephosphorylation step of the ATPase reaction cycle that is primarily affected by both ischemia and ischemia/reperfusion. This might be caused by alteration of the protein molecule and/or its surroundings subsequent to ischemia.

Resistance to cerebral ischemia in developing gerbils

Two-, three-, four-, five-, and twelve-week-old gerbils were subjected to various periods of bilateral carotid occlusion (BCO). Rectal and cranial temperatures were maintained at 37 degrees C during BCO, and only rectal temperature was monitored for 30 min of reperfusion. Seven days after ischemia, animals were perfusion-fixed and the neuronal densities in the hippocampal CA1 subfields were counted. The extent of cerebral ischemia during BCO was evaluated with [14C]iodoantipyrine autoradiography. The rectal temperature spontaneously fell to 33-34 degrees C during reperfusion in 2-week-old gerbils, although animals over 3 weeks old presented postischemic hyperthermia. Two-week-old animals therefore were divided into three experimental groups: In one group (2-week-old group I) rectal temperature was not regulated during 30 min of reperfusion, while in the other two groups (2-week-old groups II and III) rectal temperature was regulated at 37 and 38 degrees C, respectively, during reperfusion. Five-minute BCO produced almost complete destruction of the CA1 neurons in 12-week-old animals. In contrast, most CA1 neurons survived 30 min of BCO in 2-week-old group I and 15 min of BCO in 2-week-old groups II and III. [14C]Iodoantipyrine autoradiography revealed that BCO produced severe forebrain ischemia in 2-week-old gerbils as well as in 12-week-old gerbils. These findings indicate that developing gerbils have a greater tolerance to cerebral ischemia and that such ischemic tolerance is not due to a collateral network between the vertebrobasilar and the carotid circulations previously reported to develop more abundantly in developing gerbils.

Histamine depletion in brain caused by treatment with (S)alpha-fluoromethylhistidine enhances ischemic damage of gerbil hippocampal CA2 neurons

The effect of (S)alpha-fluoromethylhistidine (FMH), a specific inhibitor of histamine synthesis from histidine, on ischemic damage was examined in gerbil brain after forebrain ischemia. Two h after subcutaneous FMH injection, the histamine content of the brain was significantly reduced. Neuronal loss in the CA2 region of the hippocampus 7 days after 3 min ischemia was enhanced by treatment with FMH. These results indicate that depletion of brain histamine aggravates neuronal death of hippocampal CA2 neurons after 3 min ischemia.

SB 201823-A, a neuronal Ca2+ antagonist is neuroprotective in two models of cerebral ischaemia

We have characterised the Ca2+ channel blocking properties of a new non-peptide Ca2+ channel antagonist, SB 201823-A, in cultures of rat sensory neurones. The IC50 for SB 201823-A against total Ca2+ current in sensory neurones was 4.9 microM. SB 201823-A showed little selectivity for sub-types of neuronal Ca2+ channel but was selective for Ca2+ channels over Na+ and K+ channels. Efficacy against other types of cation channel such as agonist gated channels was not assessed. SB 201823-A was neuroprotective in vivo when administered post-ischaemia in one focal and one global model of neuronal ischaemia. In the rat photothrombotic focal lesion model, SB 201823-A administered i.p. 10 min post-ischaemia resulted in a dramatic reduction in lesion volume. In the gerbil bilateral carotid artery occlusion global model, SB 201823-A dosed i.p. 30 min post-occlusion resulted in both histological and functional improvements when compared to vehicle treated animals. These data suggest that such novel neuronal Ca2+ channel antagonists may have potential in ameliorating both the pathological and functional consequences of stroke in man.

Regional cerebral blood flow following hypothermic circulatory arrest in newborn dogs

A model of hypothermic circulatory arrest has been developed in newborn dogs which simulates the procedure used for the operative repair of congenital cardiac defects in human infants. Hypothermic circulatory arrest for 1.0 h causes no brain damage, whereas cardiac arrest for 1.75 h results in damage of the cerebral cortex, basal ganglia and to a lesser extent the claustrum and amygdaloid nucleus. In the present study, we determined regional cerebral blood flow (rCBF) during 24 h of recovery from hypothermic circulatory arrest. Newborn nitrous oxide anesthetized and artificially ventilated dogs were cooled to 20 degrees C and subjected to cardiac arrest by the i.v. injection of KCl for either 1.0 or 1.75 h. Thereafter, animals were resuscitated, rewarmed to 37 degrees C, and rCBF measured with [14C]iodoantipyrine at either 2 or 18 h of recovery. Control animals were rendered hypothermic to 20 degrees C without cardiac arrest for 1.0 or 1.75 h prior to rewarming. No alterations in CBF at either 2 or 18 h of recovery were present in any of 16 analyzed structures in animals previously subjected to hypothermic circulatory arrest compared to controls rendered hypothermic alone. A direct linear correlation existed between mean arterial blood pressure and blood flow within frontal, parietal and occipital cortex, occipital white matter, hypothalamus and cerebellar vermis in puppies arrested for 1.75 h and recovered for 2 h, suggesting a loss of CBF autoregulation at this interval. No such association between blood pressure and CBF was apparent at 18 h of recovery.(ABSTRACT TRUNCATED AT 250 WORDS)

Mouse strain differences in susceptibility to cerebral ischemia are related to cerebral vascular anatomy

The consequences of cerebral ischemia were studied in three different strains (BDF, CFW, and BALB/C) of mice. The different strains exhibited significant differences in susceptibility to 24-h focal ischemia. Following middle cerebral artery occlusion (MCAO), infarct volumes (mm3) were 5 +/- 3 in BDF, 15 +/- 5 in CFW, and 23 +/- 3 in BALB/C mice (p < 0.05). MCAO plus ipsilateral common carotid artery occlusion (CCAO) resulted in infarct volumes of 15 +/- 9 in BDF, 38 +/- 10 in CFW, and 72 +/- 12 in BALB/C mice (p < 0.05). In addition, MCAO plus CCAO produced death by 24 h in 42% of CFW and 67% of BALB/C mice, but not in any BDF mice (p < 0.05). CCAO alone produced multifocal hemispheric infarctions in 36% of BALB/C mice but not in the other two strains. Brains of all mouse strains subjected to sham surgery were free of any ischemic injury. Arterial blood pressures, blood gases, and blood cell profiles were relatively similar for the three mouse strains. However, carbon black studies of the cerebrovascular anatomy revealed an incomplete circle of Willis (i.e., a significant decrease in the frequency of patent posterior communicating arteries) for BALB/C compared with BDF mice (p < 0.05), with CFW mice being intermediary. Based on these anatomical data, BALB/C mice also were evaluated following transient global brain ischemia produced by bilateral CCAO. BALB/C mice exhibited a > 85% reduction in cortical microvascular perfusion and EEG power within 1 min of bilateral CCAO. Also, hippocampal neuronal CA1 damage and mortality over 7 days were related to the duration of global brain ischemia (p < 0.05). These data demonstrate a significant difference between mouse strains in their sensitivity to cerebral ischemia that appears to be related, at least in part, to the functional vascular anatomy at the level of the posterior communicating arteries. In particular, we point out the potential usefulness of BALB/C mice as a sensitive and reproducible model of focal and global ischemia.

Relationship between blood flow and blood-brain barrier permeability of sodium and albumin in focal ischaemia of rats: a triple tracer autoradiographic study

Local cerebral blood flow, the permeability of the blood-brain barrier to sodium and serum albumin, and the content of electrolytes were investigated in rats before and at 4 h and 24 h following permanent occlusion of the middle cerebral artery (MCA). Measurements were carried out by triple tracer autoradiography, using 131I-iodoantipyrin, 22NaCl and 125I-iodinated bovine serum albumin, respectively. Regional sodium and albumin transfer coefficients were calculated by multiple time point analysis, and correlated with the corresponding flow and tissue electrolyte values. In sham operated controls regional sodium and albumin transfer coefficients ranged between 2.16-2.30 x 10(-3) and 0.22-0.48 x 10(-3) ml/min per g, respectively. Four hours after MCA occlusion sodium and albumin transfer coefficients were unchanged although tissue sodium content was already increased. After 24 h the sodium-but not albumin-transfer coefficient increased 2-3 fold but the rise in tissue sodium content was slower than after 4 h. At both ischaemia times the unidirectional sodium influx was substantially higher than the actual changes of tissue sodium content. The development of stroke oedema is, therefore, not limited by the alterations of barrier permeability.

Effect of systemic hypotension on cerebral energy metabolism during chronic cerebral vasospasm in primates

The influence of systemic hypotension on cerebral blood flow (CBF) and energy metabolism during chronic cerebral vasospasm after subarachnoid hemorrhage was studied in 15 monkeys. Changes in the phosphorus spectrum, as demonstrated by in vivo phosphorus-31 (31P) magnetic resonance (MR) spectroscopy, or in regional CBF were measured in the parietal cortex during graded hypotension. Sequential changes in the phosphorus spectrum were observed during moderate hypotension in the animals 7 days after the introduction of an autologous blood clot around the right middle cerebral artery (MCA). Angiograms revealed a reduction in vessel caliber by approximately 50% in the right MCA. The mean CBF in the spasm side decreased in parallel with a decrease in the mean arterial blood pressure (MABP) from 120 to 40 mm Hg, indicating the abolition of autoregulation. There were no significant differences in the mean percentage totals of inorganic phosphate (Pi), phosphocreatine (PCr), adenosine triphosphate (ATP), and pH between the hemispheres at baseline MABP before hypotension. The values of PCr, ATP, and pH decreased significantly (p < 0.05) and Pi increased significantly (p < 0.05) at an MABP of less than 60 mm Hg in the involved hemisphere. The ratio of PCr:Pi decreased in parallel with a decrease in MABP. The ATP showed a stepwise decrease during moderate hypotension (MABP 60 mm Hg) and was reduced significantly 20 minutes after the beginning of hypotension (p < 0.05). The results indicate that, during chronic vasospasm, changes in cerebral energy metabolism are coupled with changes in CBF in the state of impaired autoregulation. There exists a critical level for ischemia below which high-energy phosphorus metabolites become markedly depleted. It is suggested that 31P MR spectroscopy may be useful to evaluate the ischemic vulnerability of brain tissue in order to prevent delayed neurological deficit during cerebral vasospasm.

Nature, time-course, and extent of cerebral edema in perinatal hypoxic-ischemic brain damage

To ascertain the nature, time-course, and extent of the cerebral edema that accompanies perinatal hypoxic-ischemic brain damage, 7-day postnatal rats were subjected to unilateral right common carotid artery ligation followed by exposure to hypoxia with 8% oxygen for up to 3 hours. Some rat pups were sacrificed during hypoxia-ischemia or recovery for determination of cerebral hemispheric water content and percentage of brain swelling. Other animals were sacrificed and their brains processed either for determination of cerebral cortical edema and infarct volume or for horseradish peroxidase staining. The results indicated that cerebral edema occurs even during the course of hypoxia-ischemia and that the extent and duration of edema formation during the recovery period is dependent upon the severity of tissue injury. The data also disclosed a direct, linear correlation between infarct volume and the extent of cerebral edema. Accordingly, the greater the severity of cerebral edema, the proportionately greater the extent of infarction. Horseradish peroxidase staining, a reflection of vasogenic edema, occurred in 17 of 19 brains in a distribution which corresponded closely to the distribution of neuropathologic alterations observed histologically. The findings indicate that cerebral edema can occur in the absence of consequent infarction and that when infarction does occur, the associated edema contributes little or nothing to the severity of the ultimate brain damage.

Long-term changes in gerbil brain neurotransmitter receptors following transient cerebral ischaemia

1. Receptor autoradiographic and histological techniques were used to investigate long-term changes in the gerbil brain following transient cerebral ischaemia. 2. Transient ischaemia was induced for 3 min and 10 min, and the animals were allowed to survive for 8 months. 3. Histological examination revealed that 3 min ischaemia caused neuronal damage and mild shrinkage only in the hippocampal CA1 sector. Ten minutes of ischaemia produced severe neuronal damage in the striatum and the hippocampal CA1 and CA3 sectors. Considerable shrinkage was seen in the hippocampus; the dentate gyrus, however, was not damaged. 4. Three minutes of ischaemia produced changes in the binding of [3H]-quinuclidinylbenzilate ([3H]-QNB), [3H]-muscimol, and [3H]-MK-801 in various brain regions, as determined autoradiographically. In contrast, [3H]-cyclohexladenosine ([3H]-CHA) and [3H]-PN200-110 ([3H]-isradipine) binding in the brain was unaltered. 5. Ten minutes of ischaemia resulted in a major loss of neurotransmitter receptors, especially in the hippocampus. The substantia nigra showed a significant reduction in [3H]-CHA binding, whereas the striatum, which was morphologically damaged, showed no significant changes in any of the neurotransmitter receptors examined. 6. The results demonstrated that long-term survival after transient cerebral ischaemia produced alterations in neurotransmitter receptors, especially in the hippocampal formation, where considerable shrinkage was noted. These results also suggest that the hippocampal damage was not static, but progressive.

The effect of immunosuppression on the development of cerebral oedema in an experimental model of intracerebral haemorrhage: whole body and regional irradiation

The oedema which forms around an intracerebral haemorrhage has a complex aetiology. The immune response may have a role in its formation. There is clinical and experimental evidence that circulating leucocytes and platelets may mediate oedema formation. Global depletion of circulating leucocytes and platelets by whole body irradiation in a rodent model of intracerebral haemorrhage was found to confer protection against both ischaemia and oedema formation. This was not a direct effect of irradiation of the brain. The possible mechanisms for this protection are discussed.

Development of prolonged focal cerebral edema and regional cation changes following experimental brain injury in the rat

The present study examined the formation of regional cerebral edema in adult rats subjected to lateral (parasagittal) experimental fluid-percussion brain injury. Animals receiving fluid-percussion brain injury of moderate severity over the left parietal cortex were assayed for brain water content at 6 h, 24 h, and 2, 3, 5, and 7 days post injury. Regional sodium and potassium concentrations were measured in a separate group of animals at 10 min, 1 h, 6 h, and 24 h following fluid-percussion injury. Injured parietal cortex demonstrated significant edema, beginning at 6 h post injury (p less than 0.05) and persisting up to 5 days post injury. In the hippocampus ipsilateral to the site of cortical injury, significant edema occurred as early as 1 h post injury (p less than 0.05), with resolution of water accumulation beginning at 3 days. Sodium concentrations significantly increased in both injured cortex (1 h post injury, p less than 0.05) and injured hippocampus (10 min post injury, p less than 0.05). Potassium concentrations fell significantly 1 h post injury within the injured cortex (p less than 0.05), whereas significant decreases were not observed until 24 h post injury within the injured hippocampus. Cation alterations persisted throughout the 24-h post injury period. These results demonstrate that regional brain edema and cation deregulation occur in rats subjected to lateral fluid-percussion brain injury and that these changes may persist for a prolonged period after brain injury.

Neuroprotective activity of chlormethiazole following transient forebrain ischaemia in the gerbil

1. The effect of chlormethiazole, and other drugs which potentiate gamma-aminobutyric acid (GABA) function on delayed neuronal death in the hippocampus has been examined in the gerbil. 2. Chlormethiazole (100 mg kg-1, i.p.) and two other drugs previously reported to be neuroprotective (dizocilpine, 3 mg kg-1, i.p. and ifenprodil, 4 mg kg-1, i.p.) were all found to prevent neurodegeneration of CA1/CA2 neurones in the hippocampus when given 30 min before a 5 min episode of bilateral carotid artery occlusion. 3. Chlormethiazole (100 mg kg-1) was neuroprotective when given up to 3 h, after the ischaemic episode. 4. Given 1 h after the cartoid artery occlusion, chlormethiazole produced significant protection against hippocampal neurodegeneration at a dose of 50 mg kg-1, but not at 25 mg kg-1. 5. Phenobarbitone (100 mg kg-1, i.p.) and Saffan (alphaxalone, 45 mg kg-1 plus alphadalone, 15 mg kg-1, i.p.) were not protective when given 1 h after the ischaemic episode while pentobarbitone (30 mg kg-1, i.p.) had a modest protective effect. 6. Evidence is presented to show that neither the operating procedure nor the chlormethiazole administration lowered rectal or cerebral temperature. 7. The data suggest that chlormethiazole may be a useful treatment in the prevention of neurodegeneration following stroke or cardiac arrest.

A new model of global postischemic reperfusion in rabbit

An ideal model of global ischemia in rabbits has not yet been developed. The present study describes a new model of global postischemic reperfusion (GPIR) in the rabbit, characterized by lack of systemic hypotension. The experimental procedure involves reversible occlusion of the bilateral internal carotid arteries (ICA) and bilateral external carotid arteries (ECA) for 60 min combined with permanent ligation of bilateral vertebral arteries (VA). This grouping is called 6-artery occlusion (6AO). Sixty minutes after the occlusion, bilateral ICA and bilateral ECA were released for 120 min at which time the experiment was terminated. The results revealed severely depressed EEG activity; Water content of brain tissue increased to 80.33 +/- 1.20% (control 78.28 +/- 0.59%, p less than 0.01); K, Mg, and Zn decreased (p less than 0.05 or p less than 0.01), and were negatively correlated with tissue water content. Na increased (p less than 0.05) and correlated with water content of brain. No significant changes were observed in lipid peroxide (LPO) levels, but the activity of superoxide dismutase (SOD) of brain tissue decreased (p less than 0.01), and was negatively correlated with water content (r = -0.5808, p less than 0.05). These results were compared with those obtained with the model of 4-artery (bilateral common carotid arteries (CCA) and VA) occlusion (4AO) and suggested that the brain damage be more severe with 6AO than with 4AO.

A new model of brainstem ischemia by embolization technique in cats

An experimental model of brainstem ischemia was developed by embolization technique with cylindrical silicone rubber emboli in cats. The embolus reached the basilar artery in 55 cats (58.5%) and stopped in the upper basilar artery (UB) in 32, the middle basilar artery (MB) in 22 and the lower basilar artery (LB) in one animal. When the basilar artery distal to the embolus was not visualized (type 1) by postoperative vertebral angiogram, Evans blue extravasation was observed in the brainstem caudal to the embolus. When only a filling defect of the basilar artery at the site of the embolus was noted (type 2), dye extravasation was observed in the brainstem around the site of the embolus. In UB type 1, the regional cerebral blood flow of pons and medulla oblongata decreased immediately after embolization, and six hours after embolization it was 11.4 +/- 5.7 (pons) and 11.7 +/- 4.6 ml/100 g/min (medulla oblongata). In UB type 1 and MB type 1 animals, coma, apnea, tetraplegia, and disturbance of swallowing were noted. These animals died within 50 hours after embolization. Animals of UB type 2 and MB type 2 showed neurological deficits, but survived for three days. This paper discusses this method of producing experimental brainstem ischemia, the sites of ischemic lesions, and clinicopathological findings.

Sequential cerebral blood flow changes in short-term cerebral ischemia in gerbils

Using quantitative autoradiography, we studied sequential changes in regional cerebral blood flow during and after 2 minutes of bilateral common carotid artery occlusions in 18 gerbils. Occlusion (n = 4) led to severe ischemia in the forebrain (regional cerebral blood flow less than 5% of control [n = 4]) and midbrain (regional cerebral blood flow less than 10% of control), but was morphologically nonlethal. Reperfusion of the brain was complete, and regional cerebral blood flow was not different from control 1 minute after ischemia (n = 4), but hypoperfusion (regional cerebral blood flow 30-50% of control) occurred at 5 minutes (n = 3) and was pronounced at 1 hour (n = 4); at this stage blood flow was inhomogeneous. Hypoperfusion had disappeared at 4 hours (n = 3). Our results indicate that the well-documented sequence of cerebral blood flow changes (i.e., ischemia, initial recovery of blood flow, and delayed hypoperfusion) takes place even after nonlethal cerebral ischemia.

Mannitol therapy in perinatal hypoxic-ischemic brain damage in rats

To study the efficacy of mannitol in reducing cerebral edema and improving the ultimate neuropathologic outcome in perinatal cerebral hypoxia-ischemia, 67 7-day postnatal rats were subjected to unilateral common carotid artery ligation followed by exposure to 8% oxygen at 37 degrees C for 3 hours. Twenty-seven rat pups received a subcutaneous injection of 0.1 ml mannitol in a dosage of 4 mg/kg body wt immediately following cerebral hypoxia-ischemia and every 12 hours thereafter for a total of four doses. Control animals received either no therapy (n = 16) or an equivalent volume of normal saline (n = 24). Mannitol injections in six rat pups not subjected to hypoxia-ischemia produced no mortality but significantly increased serum osmolality from 287 to 361 mos/l (p less than 0.01). Preliminary studies indicated that substantial mortality occurred when greater doses of mannitol were administered to rats. After 48 hours of recovery from hypoxia-ischemia, the animals were killed and their brains were examined for either tissue water content (33 rat pups) or the presence of neuropathologic alterations (34 rat pups). Mannitol significantly reduced (p less than 0.001) brain water content, as a reflection of cerebral edema, in both the ipsilateral (88.5% compared with 90.6% in controls) and the contralateral (85.0% compared with 87.2% in controls) cerebral hemispheres. Mannitol therapy did not ameliorate the incidence, distribution, or severity of tissue injury in the cerebral cortex, subcortical white matter, hippocampus, striatum, or thalamus of the ipsilateral cerebral hemisphere compared with the controls. Thus, while mannitol substantially reduces the extent of cerebral edema following hypoxia-ischemia, no beneficial affect on ultimate brain damage occurs.(ABSTRACT TRUNCATED AT 250 WORDS)

Local cerebral blood flow during and after bilateral carotid artery occlusion in unanesthetized gerbils

Using [14C]iodoantipyrine autoradiography, we measured regional cerebral blood flow in unanesthetized gerbils subjected to 2 (n = 5) or 30 (n = 6) minutes of bilateral carotid artery occlusion or 5 (n = 6), 30 (n = 6), or 120 (n = 5) minutes of reflow after 30 minutes of occlusion. Blood pressure, respiratory rate, and blood gases were recorded, and these and other gerbils were evaluated with periodic neurologic examinations. Blood flow to structures above the level of the diencephalon ceased almost totally during occlusion. The lateral thalamus, the rostral three quarters of the hypothalamus, and the superior colliculi were also markedly ischemic. Blood flow to the brainstem and cerebellum was only slightly affected. After release of the occlusion, blood flow was restored in some of the affected areas but to levels somewhat below that in eight sham-operated gerbils. In several areas, principally column-shaped areas in the cortex as well as patchy areas in other structures, blood flow did not recover. This inhomogeneous blood flow distribution lasted at least 30 minutes after release of the occlusion. Thereafter, the inhomogeneity slowly disappeared in such a manner that blood flow to originally well reperfused areas appeared to decrease while that to poorly reperfused areas increased. During reflow, blood flow in the brainstem and cerebellum slowly and continuously decreased. We show that there is an early no-reflow phenomenon that is inhomogeneous and appears to be of vascular origin and lasts approximately 30 minutes after release of the occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Eicosanoids in rat brain during ischemia and reperfusion--correlation to DC depolarization

The effects of complete ischemia on cerebral arachidonic acid (AA) metabolism were investigated in the isolated perfused rat brain. During 12.5 min of ischemia, AA, 5-hydroxy-6,8,11,14-eicosatetraenoic acid, and 15-hydroxy-5,8,11,13-eicosatetraenoic acid increased 129-, 4-, and 10-fold, respectively, while subsequent reperfusion for 30 min resulted in normalized levels independently of the duration of preceding ischemia. Prostaglandin (PG) F2 alpha, PGE2, PGD2, 6-keto-PGF1 alpha, and thromboxane (Tx) B2 remained at preischemic levels during 12.5 min of complete ischemia. However, at the end of subsequent reperfusion for 30 min, the levels of the prostanoids PGF2 alpha, PGE2, PGD2, 6-keto-PGF1 alpha, and TxB2 increased according to the preceding ischemic time. The levels reached a maximum after 7.5 min of ischemia and were elevated by 7-, 14-, 48-, 3-, and 30-fold, respectively. A prolongation of ischemia of up to 12.5 min was not associated with further increases of prostanoids at the end of reperfusion. The mechanisms underlying the metabolism of eicosanoids are discussed in relation to the changes of cortical direct current potential.

A new enzymatic cycling technique for glutamate determination in brain microdialysates

A quantitative analysis of glutamate in brain dialysate was made by using an enzymatic cycling technique. This method made it possible to measure the concentration of glutamate in dialysate collected at 30-s intervals. Dialysates were collected from Mongolian gerbil hippocampus before, during, and after two 90-s ischemic insults at an interval of 5 min. An extracellular increase in levels of glutamate was already observed in samples collected during a 30-60 s period after the onset of each ischemia, and the levels of glutamate were maximal at the end of each period of ischemia (approximately a fourfold increase). The increased levels of glutamate rapidly returned almost to preischemic levels by 30 s of recirculation. This method will provide more precise information about temporal changes in the extracellular glutamate concentration in the brain during ischemia.