Showing papers in "Journal of Cerebral Blood Flow and Metabolism in 2002"
TL;DR: Reports suggest that water homeostasis in the brain is maintained by regulatory processes that, by control of aquaporin expression and distribution, induce and organize water movements.
Abstract: Water homeostasis in the brain is of central physiologic and clinical importance. Neuronal activity and ion water homeostasis are inextricably coupled. For example, the clearance of K+ from areas of high neuronal activity is associated with a concomitant water flux. Furthermore, cerebral edema, a final common pathway of numerous neurologic diseases, including stroke, may rapidly become life threatening because of the rigid encasement of the brain. A water channel family, the aquaporins, facilitates water flux through the plasma membrane of many cell types. In rodent brain, several recent studies have demonstrated the presence of different types of aquaporins. Aquaporin 1 (AQP1) was detected on epithelial cells in the choroid plexus whereas AQP4, AQP5 and AQP9 were localized on astrocytes and ependymal cells. In rodent brain, AQP4 is present on astrocytic end-feet in contact with brain vessels, and AQP9 is found on astrocytic processes and cell bodies. In basal physiologic conditions, AQP4 and AQP9 appear to be implicated in brain homeostasis and in central plasma osmolarity regulation. Aquaporin 4 may also play a role in pathophysiologic conditions, as shown by the reduced edema formation observed after water intoxication and focal cerebral ischemia in AQP4-knockout mice. Furthermore, pathophysiologic conditions may modulate AQP4 and AQP9 expression. For example, AQP4 and AQP9 were shown to be upregulated after ischemia or after traumatic injuries. Taken together, these recent reports suggest that water homeostasis in the brain is maintained by regulatory processes that, by control of aquaporin expression and distribution, induce and organize water movements. Facilitation of these movements may contribute to the development of edema formation after acute cerebral insults such as ischemia or traumatic injury.
492 citations
TL;DR: Analysis of the spatial and temporal profiles of blood–brain barrier leakage, angiogenesis, vascular endothelial growth factor (VEGF), associated receptors, and angiopoietins and receptors after embolic stroke in the rat suggests that acute alteration of VEGF and Ang 1 in the ischemic core may mediate BBB leakage, whereas upregulation of V EGF/VEGF receptors and Ang/Tie2 at the boundary zone may regulate neovascularization in ische
Abstract: In an effort to elucidate the molecular mechanisms underlying cerebral vascular alteration after stroke, the authors measured the spatial and temporal profiles of blood–brain barrier (BBB) leakage, angiogenesis, vascular endothelial growth factor (VEGF), associated receptors, and angiopoietins and receptors after embolic stroke in the rat. Two to four hours after onset of ischemia, VEGF mRNA increased, whereas angiopoietin 1 (Ang 1) mRNA decreased. Three-dimensional immunofluorescent analysis revealed spatial coincidence between increases of VEGF immunoreactivity and BBB leakage in the ischemic core. Two to 28 days after the onset of stroke, increased expression of VEGF/VEGF receptors and Ang/Tie2 was detected at the boundary of the ischemic lesion. Concurrently, enlarged and thin-walled vessels were detected at the boundary of the ischemic lesion, and these vessels developed into smaller vessels via sprouting and intussusception. Three-dimensional quantitative analysis of cerebral vessels at the boundary...
398 citations
TL;DR: It is demonstrated that SRTM2 should be a useful method to improve the quality of neuroreceptor functional images thanks to the constrained k′2, which showed somewhat larger biases due to violations of the one-compartment model assumption.
Abstract: The Simplified Reference Tissue Model (SRTM) produces functional images of receptor binding parameters using an input function derived from a reference region and assuming a model with one tissue compartment. Three parameters are estimated: binding potential (BP), relative delivery (R1), and the reference region clearance constant k'2. Since k'2 should not vary across brain pixels, the authors developed a two-step method (SRTM2) using a global value of k'2. Whole-brain simulations were performed using human input functions and rate constants for [18F]FCWAY, [11C]flumazenil, and [11C]raclopride, and parameter SD and bias were determined for SRTM and SRTM2. The global mean of k'2 was slightly biased (2% to 6%), but the median was unbiased (<1%) and was used as the global value. Binding potential noise reductions with SRTM2 were 4% to 14%, 20% to 53%, and 10% to 30% for [18F]FCWAY, [11C]flumazenil, and [11C]raclopride, respectively, with larger reductions for shorter scans. R1 noise reduction was larger than that of BP. Simulations were also performed to assess bias when the reference and/or tissue regions followed a two-tissue compartment model. Owing to the constrained k'2, SRTM2 showed somewhat larger biases due to violations of the one-compartment model assumption. These studies demonstrate that SRTM2 should be a useful method to improve the quality of neuroreceptor functional images.
381 citations
TL;DR: The evidence supporting a role for these kinases in the mechanisms underlying ischemia-induced cell death is discussed, with a growing body of evidence showing that these kinase signaling pathways become activated following a variety of injury stimuli including focal cerebral ischemIA.
Abstract: Protein kinase-mediated signaling cascades constitute the major route by which cells respond to their extracellular environment. Of these, three well-characterized mitogen-activated protein kinase (MAPK) signaling pathways are those that use the extracellular signal-regulated kinase (ERK1/2) or the stress-activated protein kinase (p38/SAPK2 or JNK/SAPK) pathways. Mitogenic stimulation of the MAPK-ERK1/2 pathway modulates the activity of many transcription factors, leading to biological responses such as proliferation and differentiation. In contrast, the p38/SAPK2 and JNK/SAPK (c-Jun amino-terminal kinase/stress-activated protein kinase) pathways are only weakly, if at all, activated by mitogens, but are strongly activated by stress stimuli. There is now a growing body of evidence showing that these kinase signaling pathways become activated following a variety of injury stimuli including focal cerebral ischemia. Whether their activation, however, is merely an epiphenomenon of the process of cell death, or is actually involved in the mechanisms underlying ischemia-induced degeneration, remains to be fully understood. This review provides an overview of the current understanding of kinase pathway activation following cerebral ischemia and discusses the evidence supporting a role for these kinases in the mechanisms underlying ischemia-induced cell death.
367 citations
TL;DR: The results suggest that caution should be exercised when comparing stimulus-induced fMRI responses under different physiologic or pharmacologic states, and significantly affects both the magnitude and dynamics of the BOLD response induced by neural activity.
Abstract: The effect of the basal cerebral blood flow (CBF) on both the magnitude and dynamics of the functional hemodynamic response in humans has not been fully investigated. Thus, the hemodynamic response to visual stimulation was measured using blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) in human subjects in a 7-T magnetic field under different basal conditions: hypocapnia, normocapnia, and hypercapnia. Hypercapnia was induced by inhalation of a 5% carbon dioxide gas mixture and hypocapnia was produced by hyperventilation. As the fMRI baseline signal increased linearly with expired CO2 from hypocapnic to hypercapnic levels, the magnitude of the BOLD response to visual stimulation decreased linearly. Measures of the dynamics of the visually evoked BOLD response (onset time, full-width-at-half-maximum, and time-to-peak) increased linearly with the basal fMRI signal and the end-tidal CO2 level. The basal CBF level, modulated by the arterial partial pressure of CO2, signifi...
362 citations
TL;DR: The authors' findings show that hypoxia elicits a delayed, short-lasting (<72 hours) tolerance to focal permanent ischemia in the adult mouse brain, and this model might be a useful paradigm to further study the mechanisms of ischemic tolerance, to identify new therapeutic targets for stroke.
Abstract: Tolerance to cerebral ischemia is achieved by preconditioning sublethal stresses, such as ischemia or hypoxia, paradigms in which the decrease of O2 availability may constitute an early signal inducing tolerance. In accordance with this concept, this study shows that hypoxia induces tolerance against focal permanent ischemia in adult mice. Normobaric hypoxia (8% O2 of 1-hour, 3-hour, or 6-hour duration), performed 24 hours before ischemia, reduces infarct volume by approximately 30% when compared with controls. To elucidate the mechanisms underlying this neuroprotection, the authors investigated the effects of preconditioning on cerebral expression of hypoxia-inducible factor-1α (HIF-1α) and its target genes, erythropoietin and vascular endothelial growth factor (VEGF). Hypoxia, whatever its duration (1 hour, 3 hours, 6 hours), rapidly increases the nuclear content of HIF-1α as well as the mRNA levels of erythropoietin and VEGF. Furthermore, erythropoietin and VEGF are upregulated at the protein level 24 ...
356 citations
TL;DR: The results support the notion that reallocation of cortical blood resources could overcome a local demand for increased cerebral blood flow induced by increased neural activity and imply that caution should be taken when interpreting the negative BOLD signals as a decrease in neuronal activity.
Abstract: Functional magnetic resonance imaging (fMRI) techniques are based on the assumption that changes in spike activity are accompanied by modulation in the blood oxygenation level-dependent (BOLD) signal. In addition to conventional increases in BOLD signals, sustained negative BOLD signal changes are occasionally observed and are thought to reflect a decrease in neural activity. In this study, the source of the negative BOLD signal was investigated using T2*-weighted BOLD and cerebral blood volume (CBV) techniques in isoflurane-anesthetized cats. A positive BOLD signal change was observed in the primary visual cortex (area 18) during visual stimulation, while a prolonged negative BOLD change was detected in the adjacent suprasylvian gyrus containing higher-order visual areas. However, in both regions neurons are known to increase spike activity during visual stimulation. The positive and negative BOLD amplitudes obtained at six spatial-frequency stimuli were highly correlated, and negative BOLD percent changes were approximately one third of the positive changes. Area 18 with positive BOLD signals experienced an increase in CBV, while regions exhibiting the prolonged negative BOLD signal underwent a decrease in CBV. The CBV changes in area 18 were faster than the BOLD signals from the same corresponding region and the CBV changes in the suprasylvian gyrus. The results support the notion that reallocation of cortical blood resources could overcome a local demand for increased cerebral blood flow induced by increased neural activity. The findings of this study imply that caution should be taken when interpreting the negative BOLD signals as a decrease in neuronal activity.
350 citations
TL;DR: Three alternative linear methods to Logan graphical analysis are evaluated: GA using total least squares (TLS), and two multilinear analyses, MA1 and MA2, based on mathematical rearrangement of GA equation and two-tissue compartments, respectively, using simulated and actual PET data of two receptor tracers.
Abstract: In an attempt to improve neuroreceptor distribution volume (V) estimates, the authors evaluated three alternative linear methods to Logan graphical analysis (GA): GA using total least squares (TLS), and two multilinear analyses, MA1 and MA2, based on mathematical rearrangement of GA equation and two-tissue compartments, respectively, using simulated and actual PET data of two receptor tracers, [(18)F]FCWAY and [(11)C]MDL 100,907. For simulations, all three methods decreased the noise-induced GA bias (up to 30%) at the expense of increased variability. The bias reduction was most pronounced for MA1, moderate to large for MA2, and modest to moderate for TLS. In addition, GA, TLS, and MA1, methods that used only a portion of the data (T > t*, chosen by an automatic process), showed a small underestimation for [(11)C]MDL 100,907 with its slow kinetics, due to selection of t* before the true point of linearity. These noniterative methods are computationally simple, allowing efficient pixelwise parameter estimation. For tracers with kinetics that permit t* to be accurately identified within the study duration, MA1 appears to be the best. For tracers with slow kinetics and low to moderate noise, however, MA2 may provide the lowest bias while maintaining computational ease for pixelwise parameter estimation.
309 citations
TL;DR: It seems likely that drugs currently used in the treatment of stroke, such as aspirin, statins, and modulators of the renin–angiotensin–aldosterone system, act at least partly via antiinflammatory mechanisms.
Abstract: Stroke has enormous clinical, social, and economic implications, and demands a significant effort from both basic and clinical science in the search for successful therapies. Atherosclerosis, the pathologic process underlying most coronary artery disease and the majority of ischemic stroke in humans, is an inflammatory process. Complex interactions occur between the classic risk factors for atherosclerosis and its clinical consequences. These interactions appear to involve inflammatory mechanisms both in the periphery and in the CNS. Central nervous system inflammation is important in the pathophysiologic processes occurring after the onset of cerebral ischemia in ischemic stroke, subarachnoid hemorrhage, and head injury. In addition, inflammation in the CNS or in the periphery may be a risk factor for the initial development of cerebral ischemia. Peripheral infection and inflammatory processes are likely to be important in this respect. Thus, it appears that inflammation may be important both before, in predisposing to a stroke, and afterwards, where it is important in the mechanisms of cerebral injury and repair. Inflammation is mediated by both molecular components, including cytokines, and cellular components, such as leukocytes and microglia, many of which possess pro- and/or antiinflammatory properties, with harmful or beneficial effects. Classic acute-phase reactants and body temperature are also modified in stroke, and may be useful in the prediction of events, outcome, and as therapeutic targets. New imaging techniques are important clinically because they facilitate dynamic evaluation of tissue damage in relation to outcome. Inflammatory conditions such as giant cell arteritis and systemic lupus erythematosus predispose to stroke, as do a range of acute and chronic infections, principally respiratory. Diverse mechanisms have been proposed to account for inflammation and infection-associated stroke, ranging from classic risk factors to disturbances of the immune and coagulation systems. Considerable opportunities therefore exist for the development of novel therapies. It seems likely that drugs currently used in the treatment of stroke, such as aspirin, statins, and modulators of the renin-angiotensin-aldosterone system, act at least partly via antiinflammatory mechanisms. Newer approaches have included antimicrobial and antileukocyte strategies. One of the most promising avenues may be the use of cytokine antagonism, for example, interleukin-1 receptor antagonist.
301 citations
TL;DR: The results of this study indicate that inhibition of MCP-1 signaling could be a new acute treatment approach to limit infarct size after stroke.
Abstract: Inflammatory processes have been implicated in the pathogenesis of brain damage after stroke In rodent stroke models, focal ischemia induces several proinflammatory chemokines, including monocyte chemoattractant protein-1 (MCP-1) The individual contribution to ischemic tissue damage, however, is largely unknown To address this question, the authors subjected MCP-1-deficient mice (MCP-1-/-) to permanent middle cerebral artery occlusion (MCAO) Measurement of basal blood pressure, cerebral blood flow, and blood volume revealed no differences between wild-type (wt) and MCP-1-/- mice MCAO led to similar cerebral perfusion deficits in wt and MCP-1-/- mice, excluding differences in the MCA supply territory and collaterals However, compared with wt mice, the mean infarct volume was 29% smaller in MCP-1-/- mice 24 hours after MCAO (P = 0022) Immunostaining showed a reduction of phagocytic macrophage accumulation within infarcts and the infarct border in MCP-1-/- mice 2 weeks after MCAO At the same time point, the authors found an attenuation of astrocytic hypertrophy in the infarct border and thalamus in MCP-1-/- mice However, these effects on macrophages and astrocytes in MCP-1-/- mice occurred too late to suggest a protective role in acute infarct growth Of note: at 6 hours after MCAO, MCP-1-/- mice produced significantly less interleukin-1beta in ischemic tissue; this might be related to tissue protection The results of this study indicate that inhibition of MCP-1 signaling could be a new acute treatment approach to limit infarct size after stroke
295 citations
TL;DR: Methods have now been developed that make it possible to incorporate sufficient amounts of superparamagnetic iron oxide into cells, enabling their detection in vivo using MR imaging, and it is anticipated that this technique may ultimately become an important tool for monitoring the efficacy of clinical (stem) cell transplantation protocols.
Abstract: During the last few years, the therapeutic use of stem and progenitor cells as a substitute for malfunctioning endogenous cell populations has received considerable attention. Unlike their current use in animal models, the introduction of therapeutic cells in patients will require techniques that can monitor their tissue biodistribution noninvasively. Among the different imaging modalities, magnetic resonance (MR) imaging offers both near-cellular (i.e., 25- to 50-mu) resolution and whole-body imaging capability. In order to be visualized, cells must be labeled with an intracellular tracer molecule that can be detected by MR imaging. Methods have now been developed that make it possible to incorporate sufficient amounts of superparamagnetic iron oxide into cells, enabling their detection in vivo using MR imaging. This is illustrated for (neural stem cell-derived) magnetically labeled oligodendroglial progenitors, transplanted in the central nervous system of dysmyelinated rats. Cells can be followed in vivo for at least 6 weeks after transplantation, with a good histopathologic correlation including the formation of myelin. Now that MR tracking of magnetically labeled cells appears feasible, it is anticipated that this technique may ultimately become an important tool for monitoring the efficacy of clinical (stem) cell transplantation protocols.
TL;DR: It is concluded that housing rats in an enriched environment significantly increases spine density in superficial cortical layers in intact and lesioned brain, but in deeper layers of intact brain.
Abstract: The authors compared the influence of environmental enrichment on intact and lesioned brain, and tested the hypothesis that postischemic exposure to an enriched environment can alter dendritic spine density in pyramidal neurons contralateral to a cortical infarct. The middle cerebral artery was occluded distal to the striatal branches in spontaneously hypertensive rats postoperatively housed either in a standard or in an enriched environment. Intact rats were housed in the same environment. Three weeks later the brains were perfused in situ. The dendritic and spine morphology was studied with three-dimensional confocal laser scanning microscopy after microinjection of Lucifer yellow in pyramidal neurons in layers II/III and V/VI in the somatosensory cortex. In intact rats, the number of dendritic spines was significantly higher in the enriched group than in the standard group in all layers ( P < 0.05). Contralateral to the infarct, pyramidal neurons in layers II/III, which have extensive intracortical connections that may play a role in cortical plasticity, had significantly more spines in the enriched group than in the standard group ( P < 0.05). No difference was observed in layers V/VI. They conclude that housing rats in an enriched environment significantly increases spine density in superficial cortical layers in intact and lesioned brain, but in deeper layers of intact brain.
TL;DR: Although the method is presented in the context of PET neuroreceptor binding studies, it has general applicability to the quantification of PET/SPECT radiotracer studies in neurology, oncology, and cardiology.
Abstract: A kinetic modeling approach for the quantification of in vivo tracer studies with dynamic positron emission tomography (PET) is presented The approach is based on a general compartmental description of the tracer's fate in vivo and determines a parsimonious model consistent with the measured data The technique involves the determination of a sparse selection of kinetic basis functions from an overcomplete dictionary using the method of basis pursuit denoising This enables the characterization of the systems impulse response function from which values of the systems macro parameters can be estimated These parameter estimates can be obtained from a region of interest analysis or as parametric images from a voxel-based analysis In addition, model order estimates are returned that correspond to the number of compartments in the estimated compartmental model Validation studies evaluate the methods performance against two preexisting data led techniques, namely, graphical analysis and spectral analysis Application of this technique to measured PET data is demonstrated using [11C]diprenorphine (opiate receptor) and [11C]WAY-100635 (5-HT1A receptor) Although the method is presented in the context of PET neuroreceptor binding studies, it has general applicability to the quantification of PET/SPECT radiotracer studies in neurology, oncology, and cardiology
TL;DR: Results are consistent with the proinflammatory properties of the induced molecules, which are involved in the initiation of the inflammatory cascade, and may thus contribute to secondary cellular responses that lead to further brain damage.
Abstract: Ischemia-reperfusion brain injury initiates an inflammatory response involving the expression of adhesion molecules and cytokines, some of which are regulated by the nuclear transcription factor NF-kappaB. In this study the authors examined mRNA expression levels for several important genes associated with inflammation at five time points (3, 6, 12, 24, and 72 hours) after transient middle cerebral artery occlusion (MCAO) in Sprague-Dawley rats. A sensitive and quantitative technique (TaqMan real-time QRT-PCR) was used to simultaneously measure mRNA levels for key cell adhesion molecules and inflammatory cytokines. Gene expression increased significantly in the injured hemisphere for interleukin (IL)-1beta (12-fold increase at 24 hours), IL-6 (25-fold increase at 6 hours) and ICAM-1 (4-fold increase at 24 hours), and the interhemispheric differences for these genes were significant for every time point examined (P < 0.05 for all values). Tumor necrosis factor-alpha mRNA was upregulated in the injured versus uninjured hemisphere from 3 to 24 hours (5-fold increase at 6 hours), while E-selectin showed a significant increase in mRNA levels from 6 to 24 hours after MCAO (10-fold increase at 6 hours) (P < 0.05 for all values). VCAM-1 mRNA levels did not respond differentially to injury at any time point between the two brain hemispheres. At all time points examined, activated NF-kappaB immunoreactivity was observed in cells throughout the infarct-damaged tissue. These results are consistent with the proinflammatory properties of the induced molecules, which are involved in the initiation of the inflammatory cascade, and may thus contribute to secondary cellular responses that lead to further brain damage.
TL;DR: The authors report that mice given diazoxide, an activator of mitochondrial ATP-sensitive potassium channels, exhibited a large decrease in cortical infarct size after permanent occlusion of the middle cerebral artery, and identify agents that activate mitochondria-related potassium channels as potential therapeutics for stroke and related neurodegenerative conditions.
Abstract: Neurons express a variety of plasma-membrane potassium channels that play important roles in regulating neuronal excitability and synaptic transmission, but also contain mitochondrial ATP-sensitive potassium channels, the functions of which are unknown. Studies of cardiac cells suggest that similar mitochondrial ATP-sensitive potassium channels are involved in the process of ischemic preconditioning, suggesting a role in regulating cell survival. The authors report that mice given diazoxide, an activator of mitochondrial ATP-sensitive potassium channels, exhibited a large (60% to 70%) decrease in cortical infarct size after permanent occlusion of the middle cerebral artery. Diazoxide decreases neuronal apoptosis and increases astrocyte survival and activation in the penumbral region of the ischemic cortex. The neuroprotective effect of diazoxide is abolished by 5-hydroxydecanoate, a selective antagonist of mitochondrial ATP-sensitive potassium channels. Studies of cultured hippocampal neurons reveal that ...
TL;DR: The current understanding shifts the focus from protein synthesis inhibition to the molecular pathways that underlie this inhibition, and the role that these pathways play in prosurvival and proapoptotic processes that may be differentially expressed in vulnerable and resistant regions of the reperfused brain.
Abstract: Protein synthesis inhibition occurs in neurons immediately on reperfusion after ischemia and involves at least alterations in eukaryotic initiation factors 2 (eIF2) and 4 (eIF4). Phosphorylation of...
TL;DR: In this article, the authors used intracerebral microdialysis in conscious human subjects undergoing electrophysiologic evaluation for medically intractable epilepsy and measured ECF levels of glucose and lactate under basal conditions and during a hyperglycemia-hypoglycemia clamp study.
Abstract: Brain levels of glucose and lactate in the extracellular fluid (ECF), which reflects the environment to which neurons are exposed, have never been studied in humans under conditions of varying glycemia. The authors used intracerebral microdialysis in conscious human subjects undergoing electrophysiologic evaluation for medically intractable epilepsy and measured ECF levels of glucose and lactate under basal conditions and during a hyperglycemia-hypoglycemia clamp study. Only measurements from nonepileptogenic areas were included. Under basal conditions, the authors found the metabolic milieu in the brain to be strikingly different from that in the circulation. In contrast to plasma, lactate levels in brain ECF were threefold higher than glucose. Results from complementary studies in rats were consistent with the human data. During the hyperglycemia-hypoglycemia clamp study the relationship between plasma and brain ECF levels of glucose remained similar, but changes in brain ECF glucose lagged approximately 30 minutes behind changes in plasma. The data demonstrate that the brain is exposed to substantially lower levels of glucose and higher levels of lactate than those in plasma; moreover, the brain appears to be a site of significant anaerobic glycolysis, raising the possibility that glucose-derived lactate is an important fuel for the brain.
TL;DR: Cerebral hypoxia-ischemia near-infrared spectroscopy thresholds for functional impairment are Sco2 33% to 44%, a range that is well below baseline Sco2 of 68%, suggesting a buffer between normal and dysfunction that also exists for CBF and Svo2.
Abstract: Detection of cerebral hypoxia-ischemia remains problematic in neonates. Near-infrared spectroscopy, a noninvasive bedside technology has potential, although thresholds for cerebral hypoxia-ischemia have not been defined. This study determined hypoxic-ischemic thresholds for cerebral oxygen saturation (SCO2) in terms of EEG, brain ATP, and lactate concentrations, and compared these values with CBF and sagittal sinus oxygen saturation (SVO2). Sixty anesthetized piglets were equipped with near-infrared spectroscopy, EEG, laser-Doppler flowmetry, and a sagittal sinus catheter. After baseline, SCO2 levels of less than 20%, 20% to 29%, 30% to 39%, 40% to 49%, 50% to 59%, 60% to 79%, or 80% or greater were recorded for 30 minutes of normoxic normocapnia, hypercapnic hyperoxia, or bilateral carotid occlusion with or without arterial hypoxia. Brain ATP and lactate concentrations were measured biochemically. Logistic and linear regression determined the SCO2, CBF, and SVO2 thresholds for abnormal EEG, ATP, and lactate findings. Baseline SCO2 was 68 + 5%. The SCO2 thresholds for increased lactate, minor and major EEG change, and decreased ATP were 44 +/- 1%, 42 +/- 5%, 37 +/- 1%, and 33 +/- 1%. The SCO2 correlated linearly with SVO2 (r = 0.98) and CBF (r = 0.89), with corresponding SVO2 thresholds of 23%, 20%, 13%, and 8%, and CBF thresholds (% baseline) of 56%, 52%, 42%, and 36%. Thus, cerebral hypoxia-ischemia near-infrared spectroscopy thresholds for functional impairment are SCO2 33% to 44%, a range that is well below baseline SCO2 of 68%, suggesting a buffer between normal and dysfunction that also exists for CBF and SVO2.
TL;DR: Small decreases in temperature inhibit apoptosis very early, possibly at the level of the initiation of apoptosis, as suggested by reduced cJun N-terminal kinase activation and before the translocation of cytochrome c, with subsequent prevention of caspase activation.
Abstract: Recent experimental work has shown that hypothermia with even small decreases in temperature is broadly neuroprotective, but the mechanism of this protection remains unclear. Although reduction of metabolism could explain protection by deep hypothermia, it does not explain the robust protection found with mild hypothermia. Several reports have suggested that ischemic apoptosis is reduced by hypothermia. The authors examined the effects of hypothermia on neuronal apoptosis using serum deprivation, a well-accepted model that induces neuronal apoptosis. Mild hypothermia (33 degrees C) significantly reduced the number of morphologically apoptotic neurons to less than half the number seen in normothermic culture temperatures (37 degrees C) after 48 hours. They examined the effect of hypothermia on several steps in the cascade. Caspase-3, -8, and -9 activity was significantly increased after 24 hours at 37 degrees C, and was significantly lower in cultures deprived of serum at 33 degrees C. Cytochrome c translocation was reduced by hypothermia. Western blot analysis failed to detect significant changes in Bax, bcl -2, or hsp -70 at early time points, whereas hypothermia significantly reduced cJun N-terminal kinase activation. The authors conclude that small decreases in temperature inhibit apoptosis very early, possibly at the level of the initiation of apoptosis, as suggested by reduced cJun N-terminal kinase activation and before the translocation of cytochrome c, with subsequent prevention of caspase activation.
TL;DR: Analysis illustrates that erythropoietin modulates two distinct components of programmed cell death that involve the degradation of DNA and the externalization of cellular membrane phosphatidylserine residues.
Abstract: In addition to promoting the survival, proliferation, and differentiation of immature erythroid cells, erythropoietin and the erythropoietin receptor have recently been shown to modulate cellular signal transduction pathways that extend beyond the erythropoietic function of erythropoietin. In particular, erythropoietin has been linked to the prevention of programmed cell death in neuronal systems. Although this work is intriguing, the underlying molecular mechanisms that serve to mediate neuroprotection by erythropoietin are not well understood. Further analysis illustrates that erythropoietin modulates two distinct components of programmed cell death that involve the degradation of DNA and the externalization of cellular membrane phosphatidylserine residues. Initiation of the cascades that modulate protection by erythropoietin and its receptor may begin with the activation of the Janus tyrosine kinase 2 protein. Subsequent downstream mechanisms appear to lead to the activation of multiple signal transduc...
TL;DR: Results indicate that gap-junctional communication contributes to the propagation of hypoxic injury and that specific gap junctions could be a novel target to reduce brain damage.
Abstract: Ischemic brain injury results in neuronal loss and associated neurologic deficits. Although there is some evidence that intercellular communication via gap junctions can spread oxidative cell injury, the possible role of gap-junctional communication in ischemia-induced cell death is the object of debate. Because gap junctions directly connect the cytoplasms of coupled cells, they offer a way to propagate stress signals from cell to cell. The authors investigated the contribution of gap-junctional communication to cell death using an in vitro ischemia model, which was reproduced by submersion of organotypic hippocampal slices into glucose-free deoxygenated medium. The gap-junctional blocker carbenoxolone significantly decreased the spread of cell death, as measured by propidium iodide staining, over a 48-hour period after the ischemic episode. Carbenoxolone ameliorated the hypoxia-induced impairment of the intrinsic neuronal electrophysiologic characteristics, as measured by whole-cell patch clamp recordin...
TL;DR: The authors provide the first in vitro and in vivo evidence that perturbations in mitogen-activated protein kinase (MAPK) signal-transduction pathways are involved in the pathophysiology of traumatic brain injury and suggest that ERK is a novel therapeutic target in traumatic head injury.
Abstract: The authors provide the first in vitro and in vivo evidence that perturbations in mitogen-activated protein kinase (MAPK) signal-transduction pathways are involved in the pathophysiology of traumatic brain injury. In primary rat cortical cultures, mechanical trauma induced a rapid and selective phosphorylation of the extracellular signal-regulated kinase (ERK) and p38 kinase, whereas there was no detectable change in the c-jun N-terminal kinase (JNK) pathway. Treatment with PD98059, which inhibits MAPK/ERK 1/2, the upstream activator of ERK, significantly increased cell survival in vitro. The p38 kinase and JNK inhibitor SB203580 had no protective effect. Similar results were obtained in vivo using a controlled cortical impact model of traumatic injury in mouse brain. Rapid and selective upregulation occurred in ERK and p38 pathways with no detectable changes in JNK. Confocal immunohistochemistry showed that phospho-ERK colocalized with the neuronal nuclei marker but not the astrocytic marker glial fibrillary acidic protein. Inhibition of the ERK pathway with PD98059 resulted in a significant reduction of cortical lesion volumes 7 days after trauma. The p38 kinase and JNK inhibitor SB203580 had no detectable beneficial effect. These data indicate that critical perturbations in MAPK pathways mediate cerebral damage after acute injury, and further suggest that ERK is a novel therapeutic target in traumatic brain injury.
TL;DR: It is shown that desferrioxamine dose-dependents and time-dependently induces tolerance against focal cerebral ischemia in rats and mice, and against oxygen–glucose deprivation in purified cortical neurons.
Abstract: The widely prescribed drug desferrioxamine is a known activator of the hypoxia-inducible transcription factor 1 (HIF-1) and the subsequent transcription of erythropoietin. In the brain, HIF-1 is a master switch of the transcriptional response to hypoxia, whereas erythropoietin is a potent neuroprotectant. The authors show that desferrioxamine dose-dependently and time-dependently induces tolerance against focal cerebral ischemia in rats and mice, and against oxygen–glucose deprivation in purified cortical neurons. Desferrioxamine induced HIF-1 DNA binding and transcription of erythropoietin in vivo, the temporal kinetics of which were congruent with tolerance induction. Desferrioxamine is a promising drug for the induction of tolerance in humans when ischemia can be anticipated.
TL;DR: Intense MCT2 immunoreactivity was found in cerebellar Purkinje cell bodies and their processes, on mossy fibers in the cerebellum, and on sensory fiber in the brainstem, and it is suggested that mature neurons could use monocarboxylates such as lactate as additional energy substrates.
Abstract: Although previous Northern blot and in situ hybridization studies suggested that neurons express the monocarboxylate transporter MCT2, subsequent immunohistochemical analyzes either failed to confirm the presence of this transporter or revealed only a low density of immunolabeled neuronal processes in vivo. The authors report that appropriate section pretreatment (brief warming episode or proteinase K exposure) leads to extensive labeling of the neuropil, which appears as tiny puncta throughout the whole mouse brain. In addition, intense MCT2 immunoreactivity was found in cerebellar Purkinje cell bodies and their processes, on mossy fibers in the cerebellum, and on sensory fibers in the brainstem. Double immunofluorescent labeling with appropriate markers and observation with epifluorescence and confocal microscopy did not show extensive colocalization of MCT2 immunoreactivity with presynaptic or postsynaptic elements, but colocalization could be observed occasionally in the cortex with the postsynaptic density protein PSD95. Observations made at the electron microscopic level in the cortex corroborated these results and showed that MCT2 immunoreactivity was associated with wide membrane segments of neuronal processes. These data provide convincing evidence that MCT2 represents a major neuronal monocarboxylate transporter in the adult mouse brain, and further suggest that mature neurons could use monocarboxylates such as lactate as additional energy substrates.
TL;DR: The very high glycogen levels in normal rat brain suggest an unrecognized role for astrocytic energy metabolism during brain activation and neurotransmitters are known to stimulate glycogenolysis during experiment, and glycogen lability during tissue sampling and extraction can further reduce glycogen Levels.
Abstract: The concentration of glycogen, the major brain energy reserve localized mainly in astrocytes, is generally reported as about 2 or 3 micromol/g, but sometimes as high as 3.9 to 8 micromol/g, in normal rat brain. The authors found high but very different glycogen levels in two recent studies in which glycogen was determined by the routine amyloglucosidase procedure in 0.03N HCl digests either of frozen powders (4.8 to 6 micromol/g) or of ethanol-insoluble fractions (8 to 12 micromol/g). To evaluate the basis for these discrepant results, glycogen was assayed in parallel extracts of the same samples. Glycogen levels in ethanol extracts were twice those in 0.03N HCl digests, suggesting incomplete enzyme inactivation even with very careful thawing. The very high glycogen levels were biologically active and responsive to physiologic and pharmacological challenge. Glycogen levels fell after brief sensory stimulation, and metabolic labeling indicated its turnover under resting conditions. About 95% of the glycogen was degraded under in vitro ischemic conditions, and its "carbon equivalents" recovered mainly as glc, glc-P, and lactate. Resting glycogen stores were reduced by about 50% by chronic inhibition of nitric oxide synthase. Because neurotransmitters are known to stimulate glycogenolysis, stress or sensory activation due to animal handling and tissue-sampling procedures may stimulate glycogenolysis during an experiment, and glycogen lability during tissue sampling and extraction can further reduce glycogen levels. The very high glycogen levels in normal rat brain suggest an unrecognized role for astrocytic energy metabolism during brain activation.
TL;DR: Results indicate that hyperoxia treatment during focal cerebral ischemia—reperfusion is neuroprotective, and does not increase oxidative stress.
Abstract: Recent studies suggest that normobaric hyperoxia can be beneficial, if administered during transient stroke. However, increased oxygenation theoretically may increase oxygen free-radical injury, particularly during reperfusion. In the present study, the authors assessed the benefit and risks of hyperoxia during focal cerebral ischemia and reperfusion. Rats were subjected to hyperoxia (Fio2 100%) or normoxia (Fio2 30%) during 2-hour filament occlusion and 1-hour reperfusion of the middle cerebral artery. At 24 hours, the hyperoxia group showed 70% (total) and 92% (cortical) reduction in infarct volumes as compared to the normoxia group. Levels of oxidative stress were evaluated using three indirect methods. First, since oxygen free radicals increase blood-brain barrier (BBB) damage, Evan's blue dye extravasation was quantified to assess BBB damage. Second, the expression of heme oxygenase-1 (HO-1), a heat shock protein inducible by oxidative stress, was assessed using Western blot techniques. Third, an immunoblot technique ("OxyBlot") was used to assess levels of protein carbonyl formation as a marker of oxidative stress-induced protein denaturation. At 24 hours, Evan's blue dye extravasation per average lesion volume was similar between groups. There were no significant differences in HO-1 induction and protein carbonyl formation between groups, in the ipsilateral or contralateral hemispheres, at 6 hours and at 24 hours. These results indicate that hyperoxia treatment during focal cerebral ischemia-reperfusion is neuroprotective, and does not increase oxidative stress.
TL;DR: Reports show that a major consequence of afferent activity, in addition to the release of excitatory neurotransmitters from presynaptic terminals and the import of glutamate by astrocytes, is the establishment of rates of blood flow commensurate with increased rates of oxidative energy metabolism associated with efferent activity projecting from the site of activation.
Abstract: There is evidence that the metabolic responses to afferent and efferent nervous activity are dissociated at sites of neuronal excitation in brain. Whether efferent activity follows afferent activity depends on the responsiveness of postsynaptic neurons, which in turn depends on the summation of excitatory and inhibitory postsynaptic potentials. The afferent activity excites the presynaptic terminals and astrocytes, whereas the efferent activity arises from excitation of the dendrites of projection neurons. Measurements in vivo indicate that primary stimulation, elicited by simple stimuli, gives rise to limited increases of energy metabolism associated with afferent activity. Reports show that a major consequence of afferent activity, in addition to the release of excitatory neurotransmitters from presynaptic terminals and the import of glutamate by astrocytes, is the establishment of rates of blood flow commensurate with increased rates of oxidative energy metabolism associated with efferent activity projecting from the site of activation. Increased flow rates overcome the inherent diffusion limitation of oxygen delivery, while increased rates of glycolysis elevate tissue pyruvate contents, to which oxygen consumption rates are matched. In vivo, neurons in the baseline condition sustain no net import of pyruvate or lactate, and the reported changes of metabolism subserving afferent and efferent activity are additive rather than linked by significant additional transfer of pyruvate or lactate from astrocytes. The dissociation of blood flow changes from efferent activity weakens the identification of functional states by changes of blood flow alone. It raises the possibility that uncoupling of flow from oxidative metabolism occurs at sites of low efferent activity, such that dissociations of flow and glycolysis from oxygen consumption signify imbalances of afferent and efferent activity.
TL;DR: In this article, the role of interleukin (IL)-18, a member of the IL-1 family, in brain trauma has not been reported to date, and the authors investigated the posttraumatic release of IL-18 in murine brains following experimental closed head injury (CHI) and in CSF of CHI patients.
Abstract: Proinflammatory cytokines are important mediators of neuroinflammation after traumatic brain injury. The role of interleukin (IL)-18, a new member of the IL-1 family, in brain trauma has not been reported to date. The authors investigated the posttraumatic release of IL-18 in murine brains following experimental closed head injury (CHI) and in CSF of CHI patients. In the mouse model, intracerebral IL-18 was induced within 24 hours by ether anesthesia and sham operation. Significantly elevated levels of IL-18 were detected at 7 days after CHI and in human CSF up to 10 days after trauma. Published data imply that IL-18 may play a pathophysiological role in inflammatory CNS diseases; therefore its inhibition may ameliorate outcome after CHI. To evaluate the functional aspects of IL-18 in the injured brain, mice were injected systemically with IL-18-binding protein (IL-18BP), a specific inhibitor of IL-18, 1 hour after trauma. IL-18BP-treated mice showed a significantly improved neurological recovery by 7 days, accompanied by attenuated intracerebral IL-18 levels. This demonstrates that inhibition of IL-18 is associated with improved recovery. However, brain edema at 24 hours was not influenced by IL-18BP, suggesting that inflammatory mediators other than IL-18 induce the early detrimental effects of intracerebral inflammation.
TL;DR: The authors examined the contribution made by the creatine transporter (CRT) at the blood–brain barrier in supplying creatine to the brain from blood and found that CRT is expressed in TM-BBB cells and isolated mouse brain microvessels.
Abstract: Although creatine plays a pivotal role in the storage of phosphate-bound energy in the brain, the source of cerebral creatine is still unclear. The authors examined the contribution made by the creatine transporter (CRT) at the blood-brain barrier in supplying creatine to the brain from blood. An intravenous administration study suggested that creatine is continuously transported from the blood to the brain against the creatine concentration gradient that exists between brain and blood. Conditionally immortalized mouse brain capillary endothelial cells (TM-BBB) exhibited creatine uptake, which is Na+ and Cl- dependent and inhibited by CRT inhibitors, such as beta-guanidinopropionate and guanidinoacetate. Northern blot and immunoblot analyses demonstrated that CRT is expressed in TM-BBB cells and isolated mouse brain microvessels. Moreover, high expression of CRT was observed in the mouse brain capillaries by confocal immunofluorescent microscopy. These results suggest that CRT plays an important role in supplying creatine to the brain via the blood-brain barrier.
TL;DR: In this paper, a mathematical framework has been developed to accommodate both tissue fraction and spillover effects in positron emission tomography (PET) data and to facilitate the development of new PVC algorithms based on the description of the problem.
Abstract: Partial volume effects in positron emission tomography (PET) lead to quantitative under- and over-estimations of the regional concentrations of radioactivity in reconstructed images and corresponding errors in derived functional or parametric images. The limited resolution of PET leads to "tissue-fraction" effects, reflecting underlying tissue heterogeneity, and "spillover" effects between regions. Addressing the former problem in general requires supplementary data, for example, coregistered high-resolution magnetic resonance images, whereas the latter effect can be corrected for with PET data alone if the point-spread function of the tomograph has been characterized. Analysis of otherwise homogeneous region-of-interest data ideally requires a combination of tissue classification and correction for the point-spread function. The formulation of appropriate algorithms for partial volume correction (PVC) is dependent on both the distribution of the signal and the distribution of the underlying noise. A mathematical framework has therefore been developed to accommodate both of these factors and to facilitate the development of new PVC algorithms based on the description of the problem. Several methodologies and algorithms have been proposed and implemented in the literature in order to address these problems. These methods do not, however, explicitly consider the noise model while differing in their underlying assumptions. The general theory for estimation of regional concentrations, associated error estimation, and inhomogeneity tests are presented in a weighted least squares framework. The analysis has been validated using both simulated and real PET data sets. The relations between the current algorithms and those published previously are formulated and compared. The incorporation of tensors into the formulation of the problem has led to the construction of computationally rapid algorithms taking into account both tissue-fraction and spillover effects. The suitability of their application to dynamic and static images is discussed.