Triple-tracer autoradiography demonstrates effects of hyperglycemia on cerebral blood flow, pH, and glucose utilization in cerebral ischemia of rats

Astrocyte-neuron metabolic crosstalk in ischaemic stroke

Ischemic stroke (IS) is caused by temporary or permanent obstruction of the brain's blood supply. The disruption in glucose and oxygen delivery that results from the drop in blood flow impairs energy metabolism. A significant pathological feature of IS impaired energy metabolism. Astrocytes, as the most prevalent glial cells in the brain, sit in between neurons and the microvasculature. By taking advantage of their special anatomical location, they play a crucial part in regulating cerebral blood flow (CBF) and metabolism. Astrocytes can withstand hypoxic and ischemic conditions better than neurons do. Additionally, astrocytes are essential for maintaining the metabolism and function of neurons. Therefore, the "neurocentric" perspective on neuroenergetics is gradually giving way to a more comprehensive perspective that takes into account metabolic interaction between astrocytes and neurons. Since neurons in the core region of the infarct are unable to undergo oxidative metabolism, the focus of attention in this review is on neurons in the peri-infarct region. We'll go over the metabolic crosstalk of astrocytes and neurons during the acute phase of IS using three different types of metabolites: lactate, fatty acids (FAs), and amino acids, as well as the mitochondria. After IS, astrocytes in the peri-infarct zone can produce lactate, ketone bodies (KBs), glutamine (Gln), and l-serine, shuttling these metabolites, along with mitochondria, to neurons. This process helps maintain the energy requirements of neurons, preserves their redox state, and regulates neurotransmitter receptor activity.

Brain targeted polymeric micelles as drug carriers for ischaemic stroke treatment

Ischaemic stroke is a central nervous system disease with high morbidity, recurrence and mortality rates. Thrombolytic and neuroprotective therapies are the main therapeutic strategies for ischaemic stroke, however, the poor delivery efficiency of thrombolytic and neuroprotective drugs to the brain limits their clinical application. So far, the development of nanomedicine has brought opportunities for the above challenges, which can not only realise the effective accumulation of drugs in the target site, but also improve the pharmacokinetic behaviour of the drugs. Among the most rapidly developing nanoparticles, micelles gradually emerging as an effective strategy for ischaemic stroke treatment due to their own unique advantages. This review provided an overview of targeted and response-release micelles based on the physicochemical properties of the ischaemic stroke microenvironment, summarised the targeting strategies for delivering micellar formulations to the thrombus, blood-brain barrier, and brain parenchyma, and finally described the potentials and challenges of polymeric micelles in the treatment of ischaemic stroke.

A review of stress-induced hyperglycaemia in the context of acute ischaemic stroke: Definition, underlying mechanisms, and the status of insulin therapy

The transient elevation of blood glucose produced following acute ischaemic stroke (AIS) has been described as stress-induced hyperglycaemia (SIH). SIH is common even in patients with AIS who have no previous diagnosis of diabetes mellitus. Elevated blood glucose levels during admission and hospitalization are strongly associated with enlarged infarct size and adverse prognosis in AIS patients. However, insulin-intensive glucose control therapy defined by admission blood glucose for SIH has not achieved the desired results, and new treatment ideas are urgently required. First, we explore the various definitions of SIH in the context of AIS and their predictive value in adverse outcomes. Then, we briefly discuss the mechanisms by which SIH arises, describing the dual effects of elevated glucose levels on the central nervous system. Finally, although preclinical studies support lowering blood glucose levels using insulin, the clinical outcomes of intensive glucose control are not promising. We discuss the reasons for this phenomenon.

Recent trends in bioresponsive linker technologies of Prodrug-Based Self-Assembling nanomaterials

Prodrugs are designed to improve pharmaceutical properties of potent compounds and represent a central approach in drug development. The success of the prodrug strategy relies on incorporation of a reversible linkage facilitating controlled release of the parent drug. While prodrug approaches enhance pharmacokinetic properties over their parent drug, they still face challenges in absorption, distribution, metabolism, elimination, and toxicity (ADMET). Conjugating a drug to a carrier molecule such as a polymer can create an amphiphile that self-assembles into nanoparticles. These nanoparticles display prolonged blood circulation and passive targeting ability. Furthermore, the drug release can be tailored using a variety of linkers between the parent drug and the carrier molecule. In this review, we introduce the concept of self-assembling prodrugs and summarize different approaches for controlling the drug release with a focus on the linker technology. We also summarize recent clinical trials, discuss the emerging challenges, and provide our perspective on the utility and future potential of this technology.

Elevated glucose is associated with hemorrhagic transformation after mechanical thrombectomy in acute ischemic stroke patients with severe pretreatment hypoperfusion

Several pretreatment variables such as elevated glucose and hypoperfusion severity are related to brain hemorrhage after endovascular treatment of acute stroke. We evaluated whether elevated glucose and severe hypoperfusion have synergistic effects in the promotion of parenchymal hemorrhage (PH) after mechanical thrombectomy (MT). We included 258 patients MT-treated who had a pretreatment computed tomography perfusion (CTP) and a post-treatment follow-up MRI. Severe hypoperfusion was defined as regions with cerebral blood volume (CBV) values < 2.5% of normal brain [very-low CBV (VLCBV)-regions]. Median baseline glucose levels were 119 (IQR = 105-141) mg/dL. Thirty-nine (15%) patients had pretreatment VLCBV-regions, and 42 (16%) developed a PH after MT. In adjusted models, pretreatment glucose levels interacted significantly with VLCBV on the prediction of PH (p-interaction = 0.011). In patients with VLCBV-regions, higher glucose was significantly associated with PH (adjusted-OR = 3.15; 95% CI = 1.08-9.19, p = 0.036), whereas this association was not significant in patients without VLCBV-regions. CBV values measured at pretreatment CTP in coregistered regions that developed PH or infarct at follow-up were not correlated with pretreatment glucose levels, thus suggesting the existence of alternative deleterious mechanisms other than direct glucose-driven hemodynamic impairments. Overall, these results suggest that both severe hypoperfusion and glucose levels should be considered in the evaluation of adjunctive neuroprotective strategies.

Hyperglycemia, acute ischemic stroke, and thrombolytic therapy

Ischemic stroke is a leading cause of disability and is considered now the fourth leading cause of death. Many clinical trials have shown that stroke patients with acute elevation in blood glucose at onset of stroke suffer worse functional outcomes, longer in-hospital stay, and higher mortality rates. The only therapeutic hope for these patients is the rapid restoration of blood flow to the ischemic tissue through intravenous administration of the only currently proven effective therapy, tissue plasminogen activator (tPA). However, even this option is associated with the increased risk of intracerebral hemorrhage. Nonetheless, the underlying mechanisms through which hyperglycemia (HG) and tPA worsen the neurovascular injury after stroke are not fully understood. Accordingly, this review summarizes the latest updates and recommendations about the management of HG and coadministration of tPA in a clinical setting while focusing more on the various experimental models studying (1) the effect of HG on stroke outcomes, (2) the potential mechanisms involved in worsening the neurovascular injury, (3) the different therapeutic strategies employed to ameliorate the injury, and finally, (4) the interaction between HG and tPA. Developing therapeutic strategies to reduce the hemorrhage risk with tPA in hyperglycemic setting is of great clinical importance. This can best be achieved by conducting robust preclinical studies evaluating the interaction between tPA and other therapeutics in order to develop potential therapeutic strategies with high translational impact.

Spatiotemporal uptake characteristics of [18]F-2-fluoro-2-deoxy-D-glucose in a rat middle cerebral artery occlusion model

BACKGROUND AND PURPOSE

Alterations of cerebral glucose metabolism are well anticipated during cerebral ischemia. However, detailed spatiotemporal characteristics of disturbed cerebral glucose metabolism during acute ischemia remain largely elusive. This study aims to delineate spatiotemporal distributions of [18]F-2-fluoro-2-deoxy-D-glucose (FDG) uptake using positron emission tomography imaging, particularly at the peri-ischemic zone, and its correlation with tissue outcome.

METHODS

The intraluminal suture middle cerebral artery occlusion model was used to induce focal cerebral ischemia in rats (n=48). All animals underwent sequential MRI and FDG positron emission tomography imaging at different times (30-150 minutes) after middle cerebral artery occlusion. MR and positron emission tomography images were coregistered. FDG uptake in the peri-ischemic zone was assessed in relation to middle cerebral artery occlusion duration, cerebral blood flow, apparent diffusion coefficient, and 24-hour T2 lesions.

RESULTS

Elevated FDG uptake was consistently observed at the peri-ischemic zone surrounding the presumed ischemic core with low FDG uptake. Both the spatial volume and the uptake level of the hyper-uptake region were inversely correlated with the duration of middle cerebral artery occlusion. The hyper-uptake regions exhibited a mild reduction of cerebral blood flow (28.2±3.2%) and apparent diffusion coefficient (9.1±1.4%) when compared with that in the contralateral hemisphere. Colocalization analysis revealed that, with reperfusion, an average of 12.1±1.7% of the hyper-uptake volume was recruited into final infarction.

CONCLUSIONS

Elevated FDG uptake at the peri-ischemic zone is consistently observed during acute cerebral ischemia. The region with elevated FDG uptake likely reflects viable tissues that can be salvaged with reperfusion. Therefore, acute FDG positron emission tomography imaging might hold promise in the management of patients with acute stroke.

The potential roles of 18F-FDG-PET in management of acute stroke patients

Extensive efforts have recently been devoted to developing noninvasive imaging tools capable of delineating brain tissue viability (penumbra) during acute ischemic stroke. These efforts could have profound clinical implications for identifying patients who may benefit from tPA beyond the currently approved therapeutic time window and/or patients undergoing neuroendovascular treatments. To date, the DWI/PWI MRI and perfusion CT have received the most attention for identifying ischemic penumbra. However, their routine use in clinical settings remains limited. Preclinical and clinical PET studies with [¹⁸F]-fluoro-2-deoxy-D-glucose (¹⁸F-FDG) have consistently revealed a decreased ¹⁸F-FDG uptake in regions of presumed ischemic core. More importantly, an elevated ¹⁸F-FDG uptake in the peri-ischemic regions has been reported, potentially reflecting viable tissues. To this end, this paper provides a comprehensive review of the literature on the utilization of ¹⁴C-2-DG and ¹⁸F-FDG-PET in experimental as well as human stroke studies. Possible cellular mechanisms and physiological underpinnings attributed to the reported temporal and spatial uptake patterns of ¹⁸F-FDG are addressed. Given the wide availability of ¹⁸F-FDG in routine clinical settings, ¹⁸F-FDG PET may serve as an alternative, non-invasive tool to MRI and CT for the management of acute stroke patients.

Hyperglycaemia and infarct size in animal models of middle cerebral artery occlusion: systematic review and meta-analysis

Poststroke hyperglycaemia (PSH) is common, has an unclear pathophysiology, and is associated with poor outcomes. Animal studies report conflicting findings. We systematically reviewed the effects of hyperglycaemia on infarct volume in middle cerebral artery occlusion (MCAO) models, generating weighted mean differences between groups using random effects models summarised as effect size (normalised to control group infarct volume as 100%) and 95% confidence interval. Of 72 relevant papers, 23 reported infarct volume. Studies involved 664 animals and 35 distinct comparisons. Hyperglycaemia was induced by either streptozotocin (STZ, 17 comparisons, n=303) or dextrose (18 comparisons, n=356). Hyperglycaemic animals had infarcts that were 94% larger, but STZ was associated with significantly greater increase in infarct volumes than dextrose infusion (140% larger versus 48% larger). In seven studies, insulin did not significantly reduce infarct size and results were heterogeneous. Although hyperglycaemia exacerbates infarct volume in MCAO models, studies are heterogeneous, and do not address the common clinical problem of PSH because they have used either the STZ model of type I diabetes or extremely high glucose loads. Insulin had a nonsignificant and significantly heterogeneous effect. Further studies with relevant models may inform clinical trial design.

Physiologically relevant online electrochemical method for continuous and simultaneous monitoring of striatum glucose and lactate following global cerebral ischemia/reperfusion

This study demonstrates a new electroanalytical method with a high physiological relevance for simultaneous online monitoring of glucose and lactate in the striatum of the rat brain following global cerebral ischemia/reperfusion. The online analytical method is based on the efficient integration of in vivo microdialysis sampling with an online selective electrochemical detection with the electrochemical biosensors with dehydrogenases, i.e., glucose and lactate dehydrogenases, as recognition elements. The dehydrogenase-based electrochemical biosensors are developed onto the dual split-disk plastic carbon film (SPCF) electrodes with methylene green (MG) adsorbed onto single-walled carbon nanotubes (SWNTs) as the electrocatalyst for the oxidation of dihydronicotiamide adenine dinucleotide (NADH) at a low potential of 0.0 V (vs Ag/AgCl). Artificial cerebrospinal fluid (aCSF) containing NAD(+) is externally perfused from a second pump and online mixed with the brain microdialysates to minimize the variation of pH that occurred following the cerebral ischemia/reperfusion and to supply NAD(+) cofactor and O(2) for the enzymatic reactions of dehydrogenases and ascorbate oxidase, respectively. As a result, the developed online electroanalytical method exhibits a high selectivity against the electrochemically active species endogenously existing in the cerebral systems and a high tolerance against the variation of pH and O(2) following cerebral ischemia/reperfusion. This property, along with the good linearity and a high stability toward glucose and lactate as well as little cross-talk between two biosensors, substantially makes this method possible for the continuous, simultaneous, and online monitoring of glucose and lactate in the rat brain following global cerebral ischemia/reperfusion. This study establishes a new and effective platform for the investigation of the energy metabolism in physiological and pathological processes.

Late expression of Na+/H+ exchanger 1 (NHE1) and neuroprotective effects of NHE inhibitor in the gerbil hippocampal CA1 region induced by transient ischemia

Although acidosis may be involved in neuronal death, the participation of Na(+)/H(+) exchanger (NHE) in delayed neuronal death in the hippocampal CA1 region induced by transient forebrain ischemia has not been well established. In the present study, we investigated the chronological alterations of NHE1 in the hippocampal CA1 region using a gerbil model after ischemia/reperfusion. In the sham-operated group, NHE1 immunoreactivity was weakly detected in the CA1 region. Two and 3 days after ischemia/reperfusion, NHE1 immunoreactivity was observed in glial components, not in neurons, in the CA1 region. Four days after ischemia/reperfusion, NHE1 immunoreactivity was markedly increased in CA1 pyramidal neurons as well as glial cells. These glial cells were identified as astrocytes based on double immunofluorescence staining. Western blot analysis also showed that NHE protein level in the CA1 region began to increase 2 days after ischemia/reperfusion. The treatment of 10 mg/kg 5-(N-ethyl-N-isopropyl) amiloride, a NHE inhibitor, significantly reduced the ischemia-induced hyperactivity 1 day after ischemia/reperfusion. In addition, NHE inhibitor potently protected CA1 pyramidal neurons from ischemic damage, and NHE inhibitor attenuated the activation of astrocytes and microglia in the ischemic CA1 region. In addition, NHE inhibitor treatment blocked Na(+)/Ca(2+) exchanger 1 immunoreactivity in the CA1 region after transient forebrain ischemia. These results suggest that NHE1 may play a role in the delayed death, and the treatment with NHE inhibitor protects neurons from ischemic damage.

Reduction of brain injury by antithrombotic agent acutobin after middle cerebral artery ischemia/reperfusion in the hyperglycemic rat

In vivo magnetic resonance imaging (MRI) was used to observe the effect of acutobin, a purified thrombin-like enzyme (TLE), isolated from the snake venom of Deinagkistrodon acutus, on MRI-detected brain lesion volume and tissue perfusion deficit in a hyperglycemic rat right middle cerebral artery occlusion/reperfusion (MCAO/R) model. Acutobin (0.75 U/ml) was intravenously injected with a dosage of 2.5 U/kg body weight 30 min after MCAO (MCAO duration=60 min) and again 24 h after reperfusion. Multislice diffusion weighted imaging (DWI) and single-slice dynamic bolus tracking gradient echo (GE) imaging were sequentially acquired before and after MCAO/R. DWI-detected lesion volume was significantly (p<0.05) reduced by 24-31% from 350+/-45, 369+/-45 and 374+/-36 mm(3) in the saline-treated group to 239+/-17, 282+/-26 and 259+/-32 mm(3) at 3, 4 and 24 h after reperfusion in the acutobin-treated group, respectively. Residual cerebral blood flow (CBF) in the right hemisphere recovered and remained at approximately 80% of normal perfusion over the measurement period in the acutobin-treated group, compared to approximately 40% in the saline-treated group. Mortality at 1 week after MCAO/R in the acutobin-treated group was significantly lower (25% mortality) than the saline control group (85% mortality). Our results indicate that acutobin improves brain tissue perfusion and reduces infarct volume and mortality in the hyperglycemic rat MCAO/R model.

Extra- and Intracellular pH in the Brain During Ischaemia, Related to Tissue Lactate Content in Normo- and Hypercapnic rats

The objective of the present study was to assess the relationship between the amount of lactate accumulated during complete ischaemia and the ensuing changes in extra- and intracellular pH (pHe and pHi, respectively). The preischaemic plasma glucose concentration of anaesthetized rats was varied by administration of glucose or insulin, pHe was determined in neocortex with ion-sensitive microelectrodes, and tissue lactate and CO2 contents were measured, tissue CO2 tension being known from separate experiments. The experiments were carried out in both normocapnic [arterial CO2 tension (PaCO2) approximately 40 mm Hg] and hypercapnic (PaCO2 approximately 80 mm Hg) animals. Irrespective of the preischaemic CO2 tension, DeltapHe was linearly related to tissue lactate content. Depending on the preischaemic glucose concentration, DeltapHe varied from <0.4 to >1.4 units. The results thus fail to confirm previous results that the changes in pHe describe two plateau functions (DeltapHe approximately 0.5 and 1.1, respectively), with a transition zone at tissue lactate contents of 17 - 20 mmol kg-1. Changes in pHi given in this study are based on the assumption of a uniform intracellular space. The pHi changed from a normal value of approximately 7.0 to 6.5, 6.1 and 5.8 at tissue lactate contents of 10, 20 and 30 mmol kg-1. The intrinsic (non-bicarbonate) buffer capacity, derived from these figures, was 23 mmol kg-1 pH-1. Some differences in pH and in HCO3- concentration between extra- and intracellular fluids persisted in the ischaemic tissue. These differences were probably caused by a persisting membrane potential in the ischaemic cells.

Laser Doppler flowmetry mapping of cerebrocortical microflow: characteristics and limitations

The aim of this study was to quantitatively analyze the amount of methodological noise and the spatial and temporal variability of laser Doppler flowmetry (LDF) signals mapping cerebrocortical microflow. In an experimental setup with latex beads, the methodological LDF-signal variability was determined (coefficient of variation or CV(method)). The biological variability of the LDF signals was measured in animal experiments using 10 anesthetized rabbits. One stationary reference probe was used to assess temporal heterogeneity (CV(temp)) and a micromanipulator-driven scanning probe was used to assess spatial heterogeneity (CV(spat)) in a cortical area of 3.5 x 4.5 mm with 252 measurement points. CO(2) tests were used to modulate cerebrovascular resistance. CV(method) was found to be 4.94 +/- 1.7. The CV(temp) for the LDF-velocity signal was assessed to be 13.93 +/- 5.9 during normocapnia. Scanning of the brain surface with the scanning probe revealed a CV(spat) for LDF velocity of 65.0 +/- 16.2 during normocapnia. CO(2) modulation (hypocapnia --> normocapnia --> hypercapnia) of the cerebral resistance did not show a significant change in temporal heterogeneity (10.84 +/- 3.1 --> 13.93 +/- 5.9 --> 14.82 +/- 3.9), whereas spatial heterogeneity decreased significantly (81.31 +/- 12.0 --> 65.0 +/- 16.2 --> 54.04 +/- 21.8). Although the spatial and temporal variability of LDF signals evoked by cerebrocortical microflow is in the same range as with other methods and in other organs, LDF cerebrocortical mapping is restricted by the large temporal and spatial heterogeneity of the cerebrocortical vasculature. The definitions of sample volume, scanning step width, probe to brain surface distance, and average time per scanning point are critical concerning reliable LDF cerebrocortical mapping techniques.

[Focal cerebral ischaemia induced by middle cerebral artery occlusion and the neuroprotective effect of ketoprofen in rats]

Cerebral ischaemia is eventualy observed during neurosurgical procedures and in several clinical entities that may cause severe neurological deficits and even death. Because it is a severe and complex problem, several studies have been done aiming to elucidate the mechanisms of the ischemic phenomenon and aiming to abolish or to diminish its effects, using drugs that protect the neurons from ischaemia-induced damage. Several neurotransmitters play a role in cerebral ischaemia with emphasis to glutamate by its high concentration in the central nervous system. The purpose of this study was to evaluate the effect of focal cerebral ischaemia in the rat through the dosage of the glutamate and morphological findings, and to evaluate a possible protective effect of the ketoprofen to ischemic neurons. Thirty-six rats Wistar were divided into four groups. The first was a control group, the second a sham group and the animals of the third and fourth groups were submitted to induced cerebral ischaemia through selective obstruction of the midlle cerebral artery during 15, 30 and 45 minutes. Animals of the fourth group were previously treated with ketoprofen 15 minutes before the ischaemia. The ischaemia was evaluated through the histopathological examination and through dosage of the extracellular glutamate in vitro. The histopathological examination showed that there was no difference between the animals of the control and of the sham groups. In the animals submitted to ischemia histopathological alterations appeared at 30 minutes and become more intense at 45 minutes of ischaemia. The main findings were interstitial edema, chromatinic disorganization, vacuolization and nuclear desintegration. The animals treated with ketoprofen showed similar alterations, but they were less intense. Decrease in the dosage of glutamate in the parietal cortex of the animals submitted to ischaemia started at 30 minutes and became more intense at 45 minutes of ischaemia and was similar for animals previously treated or not with ketoprofen, indicating that this drug seems not to interfere with the metabolism of the glutamate at the synapses. The morphological findings in the parietal cortex of the animals submitted to ischaemia, previously treated or not with ketoprofen, suggest that this drug has a neuroprotective effect.

Brain tissue PO(2), PCO(2), and pH during cerebral vasospasm

BACKGROUND

The purpose of the present study was to assess brain tissue monitoring for detection of ischemia due to vasospasm in aneurysmal subarachnoid hemorrhage (SAH) patients.

METHODS

After obtaining informed consent, a burr hole was made in 10 patients and a Neurotrend 7 probe was inserted ipsilateral to the region of SAH. In eight patients the probe was inserted during surgery for clipping the aneurysm and in two patients the probe was inserted in the neurosurgery ICU. Brain tissue gases and pH were collected over 6-hour periods for 7 to 10 days until the termination of monitoring. The onset of vasospasm was confirmed by angiography and xenon computed tomography (Xe/CT) cerebral blood flow studies.

RESULTS

Seven patients did not develop vasospasm during monitoring and were considered as controls. In this group, brain tissue oxygen pressure (PO(2)) remained above 20 mmHg, carbon dioxide pressure (PCO(2)) stabilized at 40 mmHg and pH remained between 7.1 and 7.2. In three patients who developed vasospasm during monitoring, PO(2) was not different from the control group. However, PCO(2) increased to 60 mmHg and pH decreased to 6.7 (p < 0.001).

CONCLUSION

In this study, patients with SAH who developed vasospasm had significantly lower brain tissue pH and higher PCO(2) compared to controls. However, there was no significant change in PO(2) levels associated with vasospasm. Brain tissue monitoring can provide an indication of ischemia during vasospasm.

Brain pH monitoring during ischemia

BACKGROUND

Brain tissue acidosis can result from ischemia when cerebral blood flow reduction reaches a critical value. The portable, battery-operated Khuri pH monitor has been used previously in a large number of patients undergoing cardiopulmonary bypass surgery to monitor the intramyocardial pH during aortic clamping. It was found to be easy to use, reliable, and a strong predictor of myocardial preservation. The goal of this study was to evaluate the applicability of this monitor in the measurement of brain pH.

METHODS

Fifteen New Zealand white rabbits underwent general endotracheal anesthesia. A right frontal craniotomy was performed and a pH/temperature glass electrode was inserted in the frontal lobe. Both common carotid arteries were exposed in the neck and prepared for occlusion. Three rabbits were used as control; their brain pH was recorded over 60 minutes. Twelve rabbits underwent bilateral common carotid artery occlusion of varying duration and their brain pH measurements were recorded.

RESULTS

There was no significant difference in pH levels at baseline in the two groups (p = 0.604). There were significant differences in pH over time between the control and occlusion group (p = 0.016). The pH dropped steadily and significantly in the occlusion group (p = 0.008), whereas little change in pH was noted over time in the control group (p = 0.366).

CONCLUSION

The portable Khuri pH monitor has been used by cardiothoracic surgeons to monitor the myocardium during bypass procedures. Our experimental pilot study found it to be reliable in measuring the brain pH and to be relatively simple to use. It is approved by the Food and Drug Administration (FDA). We believe it may be of benefit to neurosurgeons.

Contribution of anion transporters to the acidosis-induced swelling and intracellular acidification of glial cells

This study examines the contribution of anion transporters to the swelling and intracellular acidification of glial cells from an extracellular lactacidosis, a condition well-known to accompany cerebral ischemia and traumatic brain injury. Suspended C6 glioma cells were exposed to lactacidosis in physiological or anion-depleted media, and different anion transport inhibitors were applied. Changes in cell volume and intracellular pH (pH(i)) were simultaneously quantified by flow cytometry. Extracellular lactacidosis (pH 6.2) led to an increase in cell volume to 125.1 +/- 2.5% of baseline within 60 min, whereas the pH(i) dropped from the physiological value of 7.13 +/- 0.05 to 6.32 +/- 0.03. Suspension in Cl(-)-free or HCO(3)(-)/CO(2)-free media or application of anion transport inhibitors [0.1 mM bumetanide or 0.5 mM 4, 4'-diisothio-cyanatostilbene-2,2'-disulfonic acid (DIDS)] did not affect cell volume during baseline conditions but significantly reduced cell swelling from lactacidosis. In addition, the Cl(-)-free or HCO(3)(-)/CO(2)-free media and DIDS attenuated intracellular acidosis on extracellular acidification. From these findings it is concluded that besides the known activation of the Na(+)/H(+) exchanger, activation of the Na(+)-independent Cl(-)/HCO(3)(-) exchanger and the Na(+)-K(+)-Cl(-) cotransporter contributes to acidosis-induced glial swelling and the intracellular acidification. Inhibition of these processes may be of interest for future strategies in the treatment of cytotoxic brain edema from cerebral ischemia or traumatic brain injury.

Role of calcium ions in acidosis-induced glial swelling

Tissue acidosis occurring in cerebral ischemia and traumatic brain injury is a mediator of cytotoxic brain edema. In vitro, extracellular lactacidosis induces swelling of glial cells in a dose dependent manner. pH-regulatory membrane transporters and channels have been identified which are involved in the increase of the glial cell volume. Underlying mechanisms of their activation are poorly understood, however. We have, therefore, addressed the question, whether and how Ca(2+)-ions play a role in acidosis-induced glial swelling and intracellular acidification. For that purpose C6 glioma cells were suspended and the pH in the medium was lowered from 7.4 (baseline) to 6.2 by isotonic lactic acid. Cell volume and intracellular pH (pHi) were assessed by flow cytometry. In the presence of Ca(2+)-ions the cell volume reached a maximum of 125.1% from acidosis. In experiments using a calcium-free suspension medium, cell swelling from acidosis was inhibited by 74%. Additional buffering of intracellular calcium (Ca2+i) had no further inhibitory effect on acidosis-induced cell swelling, while buffering of Ca2+i by BAPTA-AM alone did not affect the glial volume increase secondary to administration of lactic acid. pHi which was decreasing from acidosis was not affected by the experimental modifications of the Ca(2+)-concentration in the medium or cytosol. The present data indicate that lactacidosis-induced glial swelling depends on the presence of extracellular Ca(2+)-ions, while release of Ca(2+)-ions from intracellular stores does not seem to be involved.

Effects of hyperglycemia on cerebral blood flow and edema formation after carotid artery occlusion in Fischer 344 rats

This study examines whether during bilateral carotid artery occlusion in Fischer 344 rats, hyperglycemia induces cerebrovascular changes that enhance brain edema formation. Preischemic hyperglycemia was induced by intraperitoneal administration of D-glucose solution. Laser-Doppler flowmetry, indicated that after the initial decline in blood flow with carotid occlusion (36 +/- 4% of preischemic), hyperglycemic but not control rats showed a further progressive decrease to 19 +/- 2% of preischemic at 120 minutes (p < 0.001). Brain water content was significantly higher in hypercompared to normoglycemic rats after both 2 hours of permanent occlusion (3.86 +/- 0.05 vs. 3.73 +/- 0.03 g/g dry wt.; p < 0.05) and 2 hours of temporary occlusion followed by 1 hour of reperfusion (4.01 +/- 0.08 vs. 3.71 +/- 0.03 g/g dry wt.; p < 0.05). The difference in brain edema formation between normo- and hyperglycemic rats appears to primarily reflect the effects of hyperglycemia on CBF. Cerebral plasma volume (CPV) 2 hours after occlusion was also reduced in hyper-compared to normoglycemic rats (3.9 +/- 0.9 and 7.2 +/- 0.1 microliters/g; p < 0.01). Thus, hyperglycemia in a model of global ischemia induces a reduction in CPV and progressive decline in CBF. In this model, the decline in CBF is of sufficient magnitude to enhance brain injury as evidenced by edema formation.

In vivo uptake of [3H]nimodipine in focal cerebral ischemia: modulation by hyperglycemia

Cell membrane depolarization and tissue acidosis occur rapidly in severely ischemic brain. Preischemic hyperglycemia is recognized to increase ischemic tissue acidosis and the present studies were undertaken to correlate depolarization and tissue acidosis during acute focal cerebral ischemia and hyperglycemia. We used a dual-label autoradiography method to simultaneously measure the in vivo distribution of [3H]nimodipine and [14C]DMO (5,5-dimethyl-2,4-oxazolidinedione) in brain to identify regions of ischemic depolarization and measure regional net tissue pH. Regional cerebral blood flow (CBF) was measured in separate studies. Measurements were made 30 minutes after combined middle cerebral artery and ipsilateral common carotid artery occlusion in normoglycemic and hyperglycemic rats. Tissue pH in the ischemic cortex was depressed to 6.76 +/- 0.11 in normoglycemic rats (n = 12) and 6.57 +/- 0.13 in hyperglycemic rats (n = 12), with significantly greater acidosis in the hyperglycemic group (P < 0.001). In contrast the ratio of [3H]nimodipine uptake in the ischemic cortex relative to the contralateral nonischemic cortex was significantly greater in normoglycemic (1.83 +/- 0.45) than hyperglycemic (1.40 +/- 0.50) rats (P < 0.05). Within this region of ischemic cortex CBF was 31 +/- 22 mL/100 g in normoglycemic rats (n = 8) and 33 +/- 22 mL/100 g/min in hyperglycemic rats (n = 9). Cerebral blood flow did not differ between these two groups in any region. Thus hyperglycemia reduced the extent of ischemic depolarization within the cortex during the first 30 minutes of focal cerebral ischemia. This effect may be related to the increased tissue acidosis or to other factors that may lessen calcium influx and preserve cellular energy stores in the ischemic cortex of the hyperglycemic rats.

Microcirculation after cerebral venous occlusions as assessed by laser Doppler scanning

Research on cerebral venous circulation disturbances (CVCDs) has been limited partly by the paucity of animal models that produce consistent venous infarction. Occlusion of two adjacent cortical veins in rats by means of a photochemical thrombotic technique provides a minimally invasive, clinically relevant, and reproducible model suited to study the pathophysiology of CVCDs. In this study, the effects of venous occlusion on regional cortical blood flow and the brain damage that ensues were evaluated. Cortical vein occlusion was induced by photoactivation of rose bengal via 100-microm fiberoptic illumination. The cerebral venous flow pattern was examined using fluorescence angiography until 90 minutes after venous occlusion, and regional cerebral blood flow (rCBF) was determined at 48 locations by using laser Doppler scanning. Histological damage was assessed 48 hours after vein occlusion. Occlusion of two cortical veins (Group T; seven animals) was compared with single-vein occlusion and its ensuing brain damage (Group S; five animals) and with sham-operated control (five animals). An rCBF reduction occurred 30 minutes after occlusion in Group T and was more extensive than the decrease in Group S after 60 minutes. Observation frequency histograms based on local CBF data obtained in Group T demonstrated that local CBF at some sites decreased to a level below the ischemic threshold within 90 minutes. Six of the seven rats in Group T had a growing venous thrombus with extravasation of fluorescein. The resulting infarction was significantly larger in Group T (9.8 +/- 4.5% of the hemispheric area) than in Group S (only 3 +/- 1.5% of the hemispheric area). In conclusion, microcirculation perturbations occur early after venous occlusion and result in the formation of a venous thrombus accompanied by local ischemia and severe venous infarction. The extent of vein occlusion determines the resulting brain damage. Based on the results of this study, the authors conclude that CVCDs may be attenuated by prevention of venous thrombus progression together with the use of protective measures against the consequences of ischemia.

Perfusion deficit parallels exacerbation of cerebral ischemia/reperfusion injury in hyperglycemic rats

Magnetic resonance imaging (MRI) techniques were used to determine the effect of preexisting hyperglycemia on the extent of cerebral ischemia/reperfusion injury and the level of cerebral perfusion. Middle cerebral artery occlusion (MCAO) was induced by a suture insertion technique. Forty one rats were divided into hyperglycemic and normoglycemic groups with either 4 hours of continuous MCAO or 2 hours of MCAO followed by 2 hours of reperfusion. Diffusion-weighted imaging (DWI) was performed at 4 hours after MCAO to quantify the degree of injury in 6 brain regions. Relative cerebral blood flow (CBF) and cerebral blood volume (CBV) were estimated using gradient echo (GE) bolus tracking and steady-state spin echo (SE) imaging techniques, respectively. Brain injury correlated with the perfusion level measured in both SE CBV and dynamic GE CBF images. In the temporary MCAO model, mean lesion size in DWI was 118% larger and hemispheric CBV was reduced by 37% in hyperglycemic compared with normoglycemic rats. Hyperglycemia did not significantly exacerbate brain injury or CBV deficit in permanent MCAO models. We conclude that preexisting hyperglycemia increases acute postischemic MRI-measurable brain cellular injury in proportion to an associated increased microvascular ischemia.

Local cerebral blood flow in a rat cortical vein occlusion model

The symptoms following sinus and vein occlusion observed in patients and experimental animals display a considerable variability that so far remains largely unexplained. In a rat cortical vein occlusion model using a photochemical thrombotic technique, we examined changes in the cerebral venous flow pattern by fluorescence angiography and regional cerebral blood flow (rCBF) and cerebral blood volume fraction (CBVF) by a modern laser Doppler "scanning" technique. Brain damage was assessed histologically. Fluorescence angiographic findings fell into two groups: group A, rats with an altered venous flow pattern after occlusion (n = 12), and group B, rats with interruption of blood flow and/or a growing venous thrombus (n = 5). In addition, sham-operated animals made up group C (n = 5). Extravasation of fluorescein, a massive decrease in rCBF, a short-lasting increase in CBVF, and regional brain damage were typical for group B. In addition, cortical CBF mapping revealed a transient hyperperfusion zone with hyperemia surrounding a hypoperfused ischemic core in group B. A circulation perturbation following venous occlusion appeared near those occluded cerebral veins without sufficient collateral flow. Furthermore, the venous thrombus continued to grow, accompanied by local critical ischemia and severe brain damage. Conversely, 71% of the animals (12 of 17) tolerated occlusion of a solitary vein without major flow disturbances or histological evidence of damage to the CNS (group A).

Cerebrovascular disorders in patients with diabetes mellitus

Diabetes mellitus is a risk factor for ischemic, but not hemorrhagic stroke. The frequency of transient ischemic attacks is not increased in patients with diabetes compared to the general population. Diabetes mellitus is associated with higher mortality, worse functional outcome, more severe disability after stroke and a higher frequency of recurrent stroke. Diabetes is not associated with an increased size of cerebral infarction. Controversy exists regarding whether hyperglycemia adversely affects stroke outcome or primarily reflects stroke severity. Cerebral blood flow disturbances, impaired cerebrovascular reactivity, and damage to large and small extra- and intracranial cerebral vessels have been found in humans and animals with diabetes. Combinations of some or all of these factors may underlie the high incidence and worse outcome of stroke in patients with diabetes. Knowledge of these pathophysiologic factors will assist in the design of future intervention strategies.

pH-associated Brain Injury in Cerebral Ischemia and Circulatory Arrest

Neuronal injury remains a major limitation in therapies directed toward cardiopulmonary resuscitation and cerebral ischemia. We summarize clinical and experimental information regarding pH-modulated mechanisms of cerebral ischemic injury and the status of antiacidosis therapies relative to the brain. A large body of evidence in animals and humans indicates that cerebral pH can modulate, and perhaps mediate, ischemic brain pathology and influence functional outcome. The importance of low pH and brain bicarbonate levels during reperfusion as a secondary injury remains an open question of therapeutic importance. Under specific conditions, acidosis may be neuroprotective, but this is an area of current controversy. Effective antiacidosis therapy must address the possibility of synergism and competition among multiple injury mechanisms.

AT-877, a Ca2+ antagonist, fails to reduce infarct size following rat middle-cerebral artery occlusion

We investigated the effects of AT-877, a Ca2+ antagonist, on rat middle-cerebral artery occlusion. All rats had 6-h ischemia, and treated animals received either 3 or 10 mg/kg AT-877 s.c. just after the occlusion. Control animals received an equal volume of the vehicle. Prior to sacrifice, significant changes in the decrease of blood pressure and the increase of plasma glucose were observed in the treated rats. Although the infarct size tended to decrease, this decrease was not significant. Only when the blood pressure- or plasma glucose-matched subgroups were compared, the infarct volume decreased significantly in the drug-treated animals. Thus, AT-877 failed to reduce ischemic brain damage unless the blood pressure or plasma glucose were controlled.

Metabolic changes associated with altering blood glucose levels in short duration forebrain ischemia

31P nuclear magnetic resonance spectroscopy was used to follow changes in cerebral pH and high-energy phosphate metabolites during forebrain ischemia in hypo-, normo- and hyperglycemic rats, and during reperfusion in animals in which the blood glucose level was altered post-ischemia. Pre-ischemia, no differences in the levels of inorganic phosphate (Pi) and adenosine triphosphate (ATP) relative to phosphocreatine (PCr) or in tissue pH between blood glucose groups were observed. During ischemia, the decrease in tissue pH was found to be dependent on the pre-ischemic blood glucose concentration, being greatest in hyperglycemic and least in hypoglycemic animals. The increase of Pi, a consequence of the hydrolysis of high-energy phosphate metabolites, also depended on the blood glucose concentration, being greatest in hypoglycemic and least in hyperglycemic animals. ATP and PCr decreased more rapidly in hypoglycemic rats compared to normo- or hyperglycemic animals, which showed no differences in the rates of depletion. Post-ischemic hyperglycemia resulted in delayed recovery of tissue pH in all groups and of PCr and ATP in animals hyperglycemic throughout the experiment. Insulin administration immediately following ischemia increased the rate of recovery of pH, ATP and PCr in hyperglycemic animals. ATP remained significantly below pre-ischemia level in all subgroups at 1 h post-ischemic, while PCr was lower than it was pre-ischemia only in those subgroups hyperglycemic prior to and/or following ischemia. In animals maintained severely hypoglycemic throughout the experiment, erratic blood pressure and cerebral energy failure during the reperfusion interval were observed.

Clinical-radiographic correlations within the first five hours of cerebral infarction

Fifty patients, ages 54-79, with ischemic hemispheric strokes productive of hemiparesis, at a minimum, underwent standardized neurological evaluations, computed tomographic scanning and cerebral angiography (N = 38) or carotid ultrasound (N = 12) within 5 h of onset. A second scan was performed at 5-7 days. Clinical scores were not associated with a history of, or the presence of: hypertension, smoking or cardiac disease, including atrial fibrillation, nor with severe internal carotid artery stenosis or occlusion. Clinical scores were adversely affected by early scan abnormalities (especially mass effect), lesion size, intracranial arterial occlusions, elevated serum glucose levels and the subsequent development of hemorrhagic infarction. Glucose levels correlated with infarct size and the development of hemorrhagic infarction. Delayed intracranial arterial filling and collateral flow were associated with reduced infarct size but did not confer clinical protection. We believe that combining the initial glucose level and scan results has prognostic significance, and early angiography is valuable in characterizing infarct etiology and assessing clinical severity.

Pathophysiology and treatment of focal cerebral ischemia. Part I: Pathophysiology

This article examines the pathophysiology of lesions caused by focal cerebral ischemia. Ischemia due to middle cerebral artery occlusion encompasses a densely ischemic focus and a less densely ischemic penumbral zone. Cells in the focus are usually doomed unless reperfusion is quickly instituted. In contrast, although the penumbra contains cells "at risk," these may remain viable for at least 4 to 8 hours. Cells in the penumbra may be salvaged by reperfusion or by drugs that prevent an extension of the infarction into the penumbral zone. Factors responsible for such an extension probably include acidosis, edema, K+/Ca++ transients, and inhibition of protein synthesis. Central to any discussion of the pathophysiology of ischemic lesions is energy depletion. This is because failure to maintain cellular adenosine triphosphate (ATP) levels leads to degradation of macromolecules of key importance to membrane and cytoskeletal integrity, to loss of ion homeostasis, involving cellular accumulation of Ca++, Na+, and Cl-, with osmotically obligated water, and to production of metabolic acids with a resulting decrease in intra- and extracellular pH. In all probability, loss of cellular calcium homeostasis plays an important role in the pathogenesis of ischemic cell damage. The resulting rise in the free cytosolic intracellular calcium concentration (Ca++) depends on both the loss of calcium pump function (due to ATP depletion), and the rise in membrane permeability to calcium. In ischemia, calcium influx occurs via multiple pathways. Some of the most important routes depend on activation of receptors by glutamate and associated excitatory amino acids released from depolarized presynaptic endings. However, ischemia also interfers with the intracellular sequestration and binding of calcium, thereby contributing to the rise in intracellular Ca++. A second key event in the ischemic tissue is activation of anaerobic glucolysis. The main reason for this activation is inhibition of mitochondrial metabolism by lack of oxygen; however, other factors probably contribute. For example, there is a complex interplay between loss of cellular calcium homeostasis and acidosis. On the one hand, a rise in intracellular Ca++ is apt to cause mitochondrial accumulation of calcium. This must interfere with ATP production and enhance anaerobic glucolysis. On the other hand, acidosis must interfere with calcium binding, thereby contributing to the rise in intracellular Ca++.

The CBF threshold and dynamics for focal cerebral infarction in spontaneously hypertensive rats

Two strategies were used to estimate the blood flow threshold for focal cerebral infarction in spontaneously hypertensive rats (SHRs) subjected to permanent middle cerebral artery and common carotid artery occlusion (MCA/CCAO). The first compared the volume of cortical infarction (24 h after ischemia onset) to the volumes of ischemic cortex (image analysis of [14C]iodoantipyrine CBF autoradiographs) perfused below CBF values less than 50 (VIC50) and less than 25 ml 100 g-1 min-1 (VIC25) at serial intervals during the first 3 h of ischemia. The infarct process becomes irreversible within 3 h in this model. In the second, measurements of CBF at the border separating normal from infarcted cortex at 24 h after ischemia onset were used as an index of the threshold. During the first 3 h of ischemia, VIC50 increased slightly to reach a maximum size at 3 h that closely matched the 24 h infarct volume. VIC25, in contrast, consistently underestimated the infarct volume by a factor of 2-3. CBF at the 24 h infarct border averaged 50 ml 100 g-1 min -1. Taken together, the results indicate that the CBF threshold for infarction in SHRs approaches 50 ml 100 g-1 min-1 when ischemia persists for greater than or equal to 3 h. This threshold value is approximately three times higher than in primates. Since cortical neuronal density is also threefold greater in rats than in primates, the higher injury threshold in the rat may reflect a neuronal primacy in determining the brain's susceptibility to partial ischemia.

Hyperglycemic versus normoglycemic stroke: topography of brain metabolites, intracellular pH, and infarct size

Hyperglycemia aggravates brain pathologic outcome following middle cerebral artery (MCA) occlusion in cats. We presently determined if hyperglycemia during occlusion leads to high lactic acid accumulations in the ischemic MCA territory. We measured brain metabolite concentrations in 14 MCA territory sites at 0.5 and 4 h following occlusion in hyper- (20 mM) and normoglycemic (5 mM) cats and correlated these results with previous brain pathologic findings. Hyper- versus normoglycemia during MCA occlusion resulted in significantly higher lactate concentrations in the ischemic territory and more numerous loci with lactates greater than 17 mumol/g. At 0.5 h of occlusion, ATP levels were lower in normoglycemic cats, while at 4 h, ATP was similarly reduced (40%) in both glycemia groups. At 4 h, PCr was more reduced in hyperglycemics secondary to a greater brain tissue acidosis. Carbohydrate substrates at 0.5 h were more markedly depleted in normoglycemics, likely limiting lactate accumulation (34.3% versus only 5.0% of sites in hyperglycemics with glucose less than 0.5 mumol/g). Although lactate was markedly elevated at both 0.5 and 4 h in hyperglycemic ischemic territories, clip release at 4 versus 0.5 h yields a significantly poorer brain pathologic outcome. Correspondingly, intracellular pH, calculated from the creatine kinase equilibrium, was more markedly depressed at 4 than at 0.5 h of occlusion, demonstrating a time-dependent dissociation between tissue lactate and hydrogen ion accumulations. The present findings show that following MCA occlusion (a) hyperglycemia increases the magnitude and topographic extent of marked tissue lactic acidosis, (b) infarct size following 0.5 h of clip release correlates more closely with tissue acidosis than with lactate concentrations, (c) ischemic tissue ATP concentrations correlate poorly with infarct size, (d) normoglycemia limits lactate accumulation during focal ischemia because tissue glucose is depleted, and (e) early during ischemia, tissue buffering or antiport mechanisms may prevent marked increases in intracellular hydrogen ion activity.

Hemorrhagic infarct conversion in experimental stroke

STUDY OBJECTIVE

This study investigated the relations between hemorrhagic infarction and occlusion, release, levels of glycemia, brain energy state, and lactate content after cerebrovascular occlusion.

DESIGN

Prospective, controlled laboratory investigation.

TYPE OF PARTICIPANTS

One hundred six pentobarbital-anesthetized cats.

INTERVENTIONS

The middle cerebral artery was occluded with a Yasargil clip transorbitally either temporarily (0.5, four, and eight hours) or permanently. Normoglycemic and hyperglycemic animals were closely monitored for eight hours. Brain pathology was assessed after two weeks' survival or at the time of spontaneous animal death. Topographic brain metabolite studies were carried out after four hours of middle cerebral artery occlusion.

MEASUREMENTS AND MAIN RESULTS

Morphometric quantitation of cerebral hemorrhage and infarction and fluorometric determinations of blood and brain tissue, glucose, glycogen, lactate, adenosine triphosphate, and phosphocreatine from 16 topographic brain sites were carried out. Twenty-one of 82 (25.6%) animals evaluated neuropathologically showed hemorrhagic infarcts. Occluding the artery in hyperglycemic animals caused fivefold more frequent and 25-fold more extensive hemorrhage into infarcts than in normoglycemic animals. Temporary occlusion with clip release after four hours in hyperglycemic animals caused the most extensive hemorrhage into infarcts. Most hemorrhages into infarcts (81%) took place in animals that died within a few hours after they experienced ischemia and that showed infarction and marked edema of the entire middle cerebral artery territory. Linear regression analyses demonstrated a close relation between hemorrhage into infarcts and near-total energy depletion (adenosine triphosphate, less than 0.3 microM/g; phosphocreatine, less than 0.5 microM/g) in brain sites that showed extremely high tissue lactate concentrations (more than 30 microM/g). The biochemical changes that correlated with hemorrhage into infarcts were more marked than those with infarcts without hemorrhage.

CONCLUSION

Hyperglycemia and restoration of blood flow to ischemic territories were strong risk factors for hemorrhagic infarct conversion. Concomitant tissue metabolic changes suggest that marked tissue energy depletion accompanied by acidosis damages brain vessels and renders them penetrable for edema fluid and, ultimately, red blood cell extravasation.

Hypertension and hyperglycemia in experimental stroke

Both diabetes mellitus and hypertension are risk factors for stroke and also influence prognosis following stroke. Experimentally, hyperglycemia augments cortical infarct size in stroke models where collateral circulation exists, and infarct size in hypertensive rats is larger than in normotensive strains. Whether the deleterious effect of hyperglycemia is altered in the setting of hypertension has not previously been studied experimentally. The effect of hyperglycemia on infarct size in spontaneously hypertensive rats was examined in this study. Focal neocortical cerebral ischemia was induced by tandem right common carotid and middle cerebral artery occlusion. Preischemic hyperglycemia had no influence on infarct volume whether the duration of postischemic hyperglycemia was transient or prolonged. Although hyperglycemia increases infarct size in cortical stroke models where collateral circulation is available, this study demonstrates the effect can be modified by the presence of underlying hypertension.

Application of simultaneous determination of 3H, 14C, and 22Na by liquid scintillation counting to the measurement of cellular ion-transport

A liquid scintillation counting method for simultaneous determination of three radioactive nuclides (3H, 14C, and 22Na) of biological interest was studied. By comparing the beta spectra of the three nuclides, their counting energy ranges, A, B, and C, were determined. 22NA was set high enough to avoid any spillover counts from lower-energy nuclides. Region A for 3H was set to maximize the counting efficiency. A good correlation between the counting efficiency for 22Na in region C and the counting efficiency of other nuclides in all regions was obtained. Prior to 3H and 14C dpm calculations, the 22Na counts spilled down in regions A and B were subtracted from the total counts in regions A and B. A simple linear equation was then used to compute 3H and 14C dpm. Findings show that the method presented is adaptable for highly quenched samples up to quenching indices of tSIE = 100. The method is useful for studying the biological transport coupled to Na+.

Dynamics of interstitial and intracellular pH in evolving brain infarct

We examined the relationships between intracellular pH (pHi) and interstitial pH (pHe) in a rat model of focal ischemia. Interstitial pH was measured with pH-sensitive microelectrodes, and the average tissue pH was measured with the [14C]dimethadione method in rats subjected to occlusion of the right middle cerebral and common carotid arteries (MCA-CCAO). In normal cortex, pHe and pHi were 7.24 +/- 0.97 and 7.01 +/- 0.13 (means +/- SD, n = 6), respectively. In the ischemic cortex, pHe fell to 6.43 +/- 0.13, whereas pHi decreased only to 6.86 +/- 0.11 (n = 5) 1 h after MCA-CCAO. After 4 h of ischemia, the pHe was 6.61 +/- 0.09 and pHi was 6.62 +/- 0.20 (n = 4). Treatment with glucose before ischemia markedly lowered the pHe (5.88 +/- 0.17) but not pHi (6.83 +/- 0.03, n = 4) measured 1 h after ischemia. In the ischemic cortex of animals made hypoglycemic by pretreatment with insulin, neither pHe (7.25 +/- 0.06) nor pHi (6.99 +/- 0.13, n = 4) decreased. The demonstrated difference in pHi and pHe indicates that some cells remained sufficiently functional to maintain a plasma membrane gradient of protons within the evolving infarct. If the calculated pHi values accurately reflect the true pHi of cells within zones of severe focal ischemia, then cerebral infarction can proceed at pHi levels not greatly altered from normal.

Glucose metabolism and acidosis in the metabolic penumbra of rat brain

The characterization of tissue acid-base status related to the penumbral zone of increased glucose consumption surrounding a focal cerebral ischemic lesion may suggest therapeutic techniques to maximize tissue survivability from stoke. We measured local cerebral metabolic rate for glucose (1 CMRglc) and an index of brain tissue pH (pHt) concurrently and characterized their interaction in a model of focal cerebral ischemia in rats in a double-label autoradiographic study, using [14C]2-deoxyglucose and [14C]dimethyloxazolidinedione. Computer-assisted digitization and analysis permitted the simultaneous quantification of the two variables on a pixel-by-pixel basis in the same brain slices. Hemispheres ipsilateral to intravascular tamponade-induced middle cerebral artery occlusion showed areas of normal, depressed, and elevated glucose metabolic rate (as defined by an interhemispheric asymmetry index) after 2 hr of ischemia. Regions of increased 1 CMRglc showed moderate acidosis (6.87 +/- 0.05), while regions of normal glucose metabolic rate showed normal pHt (pH +/- SD = 6.98 +/- 0.05) and regions of decreased 1 CMRglc showed severe acidosis (6.69 +/- 0.11). A repeated-measures analysis of variance found these values to differ from each other at the P less than 0.0005 significance level. The finding of moderate acidosis coupled with increased 1 CRMglc in the metabolic penumbra suggests that the excess protons may result from the anaerobic dissociation of ATP synthesis and hydrolysis.

Quantitative measurements of regional glucose utilization and rate of valine incorporation into proteins by double-tracer autoradiography in the rat brain tumor model

We examined the rate of glucose utilization and the rate of valine incorporation into proteins using 2-[18F]fluoro-2-deoxyglucose and L-[1-14C]-valine in a rat brain tumor model by quantitative double-tracer autoradiography. We found that in the implanted tumor the rate of valine incorporation into proteins was about 22 times and the rate of glucose utilization was about 1.5 times that in the contralateral cortex. (In the ipsilateral cortex, the tumor had a profound effect on glucose utilization but no effect on the rate of valine incorporation into proteins.) Our findings suggest that it is more useful to measure protein synthesis than glucose utilization to assess the effectiveness of antitumor agents and their toxicity to normal brain tissue. We compared two methods to estimate the rate of valine incorporation: "kinetic" (quantitation done using an operational equation and the average brain rate coefficients) and "washed slices" (unbound labeled valine removed by washing brain slices in 10% trichloroacetic acid). The results were the same using either method. It would seem that the kinetic method can thus be used for quantitative measurement of protein synthesis in brain tumors and normal brain tissue using [11C]-valine with positron emission tomography.

Nimodipine prevents hyperglycemia-induced cerebral acidosis in middle cerebral artery occluded rats

The effects of acute moderate hyperglycemia on local cerebral pH (LCpH) and local cerebral blood flow (LCBF) were studied in rats infused with glucose before middle cerebral artery (MCA) occlusion, and compared with findings in MCA occlusion alone. The effects of nimodipine infusion on LCBF and LCpH in MCA-occluded hyperglycemic rats were also studied. LCpH and LCBF were determined simultaneously by a double-label autoradiographic technique. Hyperglycemia was induced by an intraperitoneal injection of 2 g/kg D-glucose before MCA occlusion. Nimodipine-treated rats received the drug as an intravenous infusion of 0.5 micrograms/kg/min starting 15 min after occlusion, and ending at decapitation 4 h postocclusion. Cortical LCpH of five structures in the MCA territory of hyperglycemic rats varied between 6.64 +/- 0.04 and 6.72 +/- 0.02 (mean +/- SEM). These values were significantly lower than LCpH in the same ischemic structures in the control rats, which varied between 6.76 +/- 0.04 and 6.82 +/- 0.03 (p less than 0.05 for four of five structures). Cortical LCpH of hyperglycemic nimodipine-treated rats ranged between 6.94 +/- 0.02 and 7.05 +/- 0.02, indicating significant elevations in LCpH (p less than 0.001) compared with the untreated ischemic hyperglycemic animals. LCBF in the ischemic structures was not modified by hyperglycemia or nimodipine treatment. This suggests that nimodipine, by mechanisms other than improvement in blood flow, can prevent the enhanced cerebral tissue acidosis produced by hyperglycemia before incomplete focal ischemia.