Showing papers in "Journal of Cerebral Blood Flow and Metabolism in 1998"

Attenuation of delayed neuronal death after mild focal ischemia in mice by inhibition of the caspase family.

Abstract: Inhibitors of apoptosis and of excitotoxic cell death reduce brain damage after transient and permanent middle cerebral artery occlusion We compared the neuroprotective effects of two caspase family inhibitors with the N-methyl-D-aspartate receptor antagonist (+)-MK-801 hydrogen maleate (MK-801) in a newly characterized cycloheximide-sensitive murine model of transient middle cerebral artery occlusion (30 minutes) in which apoptotic cell death is prominent Ischemic infarction, undetected by 2,3,5-triphenyltetrazolium chloride staining at 24-hour reperfusion, featured prominently in the striatum at 72 hours and 7 days on hematoxylin-eosin-stained sections Markers of apoptosis, such as oligonucleosomal DNA damage (laddering) and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL)-positive cells first appeared at 24 hours and increased significantly at 72 hours and 7 days after reperfusion The TUNEL-labeled cells were mostly neurons and stained negative for glial (GFAP, glial fibrillary acid protein) and leukocyte specific markers (CD-45) The caspase inhibitors, N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (z-VADFMK; 120 ng intracerebroventricularly) or N-benzyloxycarbonyl-Asp-Glu-Val-Asp-fluoromethyl ketone (z-DEVDFMK; 480 ng intracerebroventricularly) decreased infarct size and neurologic deficits when administered 6 hours after reperfusion The extent of protection was greater than in models of more prolonged ischemia or after permanent occlusion, and the therapeutic window was extended from 0 to 1 hours after 2-hour middle cerebral artery occlusion to at least 6 hours after brief ischemia Also, z-VADFMK and z-DEVDFMK treatment decreased oligonucleosomal DNA damage (DNA laddering) as assessed by quantitative autoradiography after gel electrophoresis By contrast, MK-801 protected brain tissue only when given before ischemia (3 mg/kg intraperitoneally), but not at 3 or 6 hours after reperfusion Despite a decrease in infarct size after MK-801 pretreatment, the amount of DNA laddering did not decrease 72 hours after reperfusion, thereby suggesting a mechanism distinct from inhibition of apoptosis Hence, 30 minutes of reversible ischemia augments apoptotic cell death, which can be attenuated by delayed z-VADFMK and z-DEVDFMK administration with preservation of neurologic function By contrast, the therapeutic window for MK-801 does not extend beyond the time of occlusion, probably because its primary mechanism of action does not block the development of apoptotic cell death

Magnetic Resonance Imaging of Acute Stroke

Abstract: In the investigation of ischemic stroke, conventional structural magnetic resonance (MR) techniques (eg, T1-weighted imaging, T2-weighted imaging, and proton density-weighted imaging) are valuable for the assessment of infarct extent and location beyond the first 12 to 24 hours after onset, and can be combined with MR angiography to noninvasively assess the intracranial and extracranial vasculature However, during the critical first 6 to 12 hours, the probable period of greatest therapeutic opportunity, these methods do not adequately assess the extent and severity of ischemia Recent developments in functional MR imaging are showing great promise for the detection of developing focal cerebral ischemic lesions within the first hours These include (1) diffusion-weighted imaging, which provides physiologic information about the self-diffusion of water, thereby detecting one of the first elements in the pathophysiologic cascade leading to ischemic injury; and (2) perfusion imaging The detection of acute intraparenchymal hemorrhagic stroke by susceptibility weighted MR has also been reported In combination with MR angiography, these methods may allow the detection of the site, extent, mechanism, and tissue viability of acute stroke lesions in one imaging study Imaging of cerebral metabolites with MR spectroscopy along with diffusion-weighted imaging and perfusion imaging may also provide new insights into ischemic stroke pathophysiology In light of these advances in structural and functional MR, their potential uses in the study of the cerebral ischemic pathophysiology and in clinical practice are described, along with their advantages and limitations

Estradiol Protects Against Ischemic Injury

Abstract: Clinical studies demonstrate that estrogen replacement therapy in postmenopausal women may enhance cognitive function and reduce neurodegeneration associated with Alzheimer's disease and stroke. This study assesses whether physiologic levels of estradiol prevent brain injury in an in vivo model of permanent focal ischemia. Sprague-Dawley rats were ovariectomized; they then were implanted, immediately or at the onset of ischemia, with capsules that produced physiologically low or physiologically high 17beta-estradiol levels in serum (10 or 60 pg/mL, respectively). One week after ovariectomy, ischemia was induced. Estradiol pretreatment significantly reduced overall infarct volume compared with oil-pretreated controls (mean+/-SD: oil = 241+/-88; low = 139+/-91; high = 132+/-88 mm3); this protective effect was regionally specific to the cortex, since no protection was observed in the striatum. Baseline and ischemic regional CBF did not differ between oil and estradiol pretreated rats, as measured by laser Doppler flowmetry. Acute estradiol treatment did not protect against ischemic injury. Our finding that estradiol pretreatment reduces injury demonstrates that physiologic levels of estradiol can protect against neurodegeneration.

An adiabatic approximation to the tissue homogeneity model for water exchange in the brain: I. Theoretical derivation.

Abstract: Using the adiabatic approximation, which assumes that the tracer concentration in parenchymal tissue changes slowly relative to that in capillaries, we derived a time-domain, closed-form solution of the tissue homogeneity model. This solution, which is called the adiabatic solution, is similar in form to those of two-compartment models. Owing to its simplicity, the adiabatic solution can be used in CBF experiments in which kinetic data with only limited time resolution or signal-to-noise ratio, or both, are obtained. Using computer simulations, we investigated the accuracy and the precision of the parameters in the adiabatic solution for values that reflect 2H-labeled water (D2O) clearance from the brain (see Part II). It was determined that of the three model parameters, (1) the vascular volume (Vi), (2) the product of extraction fraction and blood flow (EF), and (3) the clearance rate constant (kadb), only the last one could be determined accurately, and therefore CBF must be determined from this parameter only. From the error analysis of the adiabatic solution, it was concluded that for the D2O clearance experiments described in Part II, the coefficient of variation of CBF was approximately 7% in gray matter and 22% in white matter.

Cerebral Interleukin-6 Is Neuroprotective During Permanent Focal Cerebral Ischemia in the Rat

Abstract: Interleukin-6 (IL-6) is a neurotrophic cytokine expressed in both neurons and glia. The present study shows that cerebral ischemia produced by permanent occlusion of the middle cerebral artery (MCAO) produces a dramatic increase in IL-6 bioactivity in the ischemic hemisphere within 2 hours of MCAO (167 +/- 55 IU versus sham: 50 +/- 35 IU), with further increases at 8 hours (3,456 +/- 1,162 IU) and 24 hours (6,088 +/- 1,772 IU). In a separate series of experiments, intracerebroventricular injection of recombinant IL-6 (3,100 or 31,000 IU) significantly reduced ischemic brain damage after MCAO (to 52% and 65% of controls, respectively). The large increase in endogenous IL-6 bioactivity in response to ischemia, together with the marked neuroprotection produced by exogenous IL-6 suggest that this cytokine is an important endogenous inhibitor of neuronal death during cerebral ischemia.

Matrix metalloproteinases in cerebrovascular disease.

Abstract: Cerebral ischemia and intracerebral hemorrhage cause extensive damage to neurons, disrupt the extracellular matrix, and increase capillary permeability. Multiple substrates participate in the cellular damage, including free radicals and proteases. Matrix metalloproteinases and serine proteases are two classes of proteases that are normally present in brain in latent forms, but once activated, contribute to the injury process. These enzymes have a unique role in the remodeling of the extracellular matrix and in the modulation of the capillary permeability. Intracerebral injection of the matrix metalloproteinase, type IV collagenase, attacks the basal lamina around the capillary and opens the blood-brain barrier. Extracellular matrix-degrading proteases are induced by immediate early genes and cytokines, and regulated by growth factors. Activity of the matrix metalloproteinases is tightly controlled by activation mechanisms and tissue inhibitors of metalloproteinases. During ischemia and hemorrhage, multiple matrix metalloproteinases and serine proteases are produced along with their inhibitors. These proteolytic enzymes are involved in the delayed injury that accompanies the neuroinflammatory response. Synthetic inhibitors to metalloproteinases reduce proteolytic tissue damage, and may limit secondary neuroinflammation.

Cytosolic redistribution of cytochrome c after transient focal cerebral ischemia in rats.

Abstract: Recent in vitro cell-free studies have shown that cytochrome c release from mitochondria is a critical step in the apoptotic process. The present study examined the expression of cytochrome c protein after transient focal cerebral ischemia in rats, in which apoptosis was assumed to contribute to the expansion of the ischemic lesion. In situ labeling of DNA breaks in frozen sections after 90 minutes of middle cerebral artery (MCA) occlusion showed a significant number of striatal and cortical neurons, which were maximized at 24 hours after ischemia, exhibiting chromatin condensation, nuclear segmentation, and apoptotic bodies. Cytosolic localization of cytochrome c was detected immunohistochemically in the ischemic area as early as 4 hours after 90 minutes of MCA occlusion. Western blot analysis of the cytosolic fraction revealed a strong single 15-kDa band, characteristic of cytochrome c, only in the samples from the ischemic hemisphere. Western blot analysis of the mitochondrial fraction showed a significant amount of mitochondrial cytochrome c in nonischemic brain, which was decreased in ischemic brain 24 hours after ischemia. These results provide the first evidence that cytochrome c is being released from mitochondria to the cytosol after transient focal ischemia. Although further evaluation is necessary to elucidate its correlation with DNA fragmentation, our results suggest the possibility that cytochrome c release may play a role in DNA-damaged neuronal cell death after transient focal cerebral ischemia in rats.

Reduced Ischemic Brain Injury in Interleukin-1β Converting Enzyme—Deficient Mice:

Abstract: A variety of recent studies suggest a role for both inflammatory cytokines such as interleukin-1 beta (IL-1 beta), and apoptosis in ischemic brain injury. Because IL-1 beta converting enzyme (ICE) is required for the conversion of proIL-1 beta to its biologically active form, and has homology with proteins that regulate apoptosis in invertebrates, we studied the effect of cerebral ischemia on brain injury in mutant mice deficient in the ICE gene (ICE knockout [KO] mice). Focal cerebral ischemia, produced by occlusion of the middle cerebral artery, resulted in brain edema (increased water and sodium content) at 4 hours and a histologically defined brain lesion at 24 hours. Both of these markers of brain injury were significantly reduced in the ICE KO mice as compared to wild-type C57BL/6 mice. Regional cerebral blood flow, determined using the flow tracer, N-isopropyl [methyl 1,3-(14)C] p-iodoamphetamine (14C-IMP), was similar in the two strains of mice, indicating that the reduced brain injury in the KO mice was not a result of a lesser degree of ischemia. These data show that ICE contributes to the development of ischemic brain damage, and that it plays a role at an early time in the pathologic process. Although the mechanism of this effect is uncertain, our results suggest that pharmacologic inhibition of ICE may be a useful treatment for stroke.

Anoxic and ischemic injury of myelinated axons in CNS white matter: from mechanistic concepts to therapeutics.

Abstract: White matter of the brain and spinal cord is susceptible to anoxia and ischemia. Irreversible injury to this tissue can have serious consequences for the overall function of the CNS through disrupt...

Reduction of ischemic damage by application of vascular endothelial growth factor in rat brain after transient ischemia

Abstract: Vascular endothelial growth factor (VEGF) is a secreted polypeptide and plays a pivotal role in angiogenesis in vivo. However, it also increases vascular permeability, and might exacerbate ischemic brain edema. The effect of this factor on the brain after transient ischemia was investigated in terms of infarct volume and edema formation, as well as cellular injury. After 90 minutes of transient middle cerebral artery occlusion, VEGF (1.0 ng/microL, 9 microL) was topically applied on the surface of the reperfused rat brain. A significant reduction of infarct volume was found in animals with VEGF application (P < 0.001) at 24 hours of reperfusion as compared with cases with vehicle treatment. Brain edema was significantly reduced in VEGF-treated animals (P = 0.01), and furthermore, extravasation of Evans blue was also decreased in those animals (P < 0.01). Terminal deoxynucleotidyl transferase-mediated dUTP-biotin in situ nick end labeling and immunohistochemical analysis for 70-kDa heat shock protein showed an amelioration of the stainings at 24 and 48 hours after reperfusion with VEGF treatment, which indicated reduction of neuronal damage. These results indicate that treatment with topical VEGF application significantly reduces ischemic brain damage, such as infarct volume, edema formation, and extravasation of Evans blue, and that the reductions were associated with that of neuronal injury.

Increased formation of reactive oxygen species after permanent and reversible middle cerebral artery occlusion in the rat

Abstract: In barbiturate-anesthetized rats, we induced 3 hours of permanent middle cerebral artery occlusion (MCAO) by an intraluminal thread (n = 6), or 1 hour MCAO followed by 2 hours of reperfusion (n = 6). Through a closed cranial window over the parietal cortex, the production of reactive oxygen species (ROS) was measured in the infarct border using online in vivo chemiluminescence (CL) while monitoring the appearance of peri-infarct depolarizations (PID). The borderzone localization of the ROS and direct current (DC) potential measurements was confirmed in additional experiments using laser-Doppler scanning, mapping regional CBF changes through the cranial window after permanent (n = 5) or reversible (n = 5) MCAO. CL measurements revealed a short period (10 to 30 minutes) of reduced ROS formation after vessel occlusion, followed by a significant increase (to 162 +/- 51%; baseline = 100%; P < .05) from 100 minutes of permanent MCAO onward. Reperfusion after a 1-hour period of MCAO led to a burst-like pattern of ROS production (peak: 489 +/- 330%; P < .05). When the experiments were terminated 3 hours after induction of MCAO, CL was still significantly increased above baseline after permanent and reversible MCAO (to 190 +/- 67% and 211 +/- 64%, respectively; P < .05). Simultaneous DC potential recordings detected 6.4 +/- 2.7 PID in the first, 4.7 +/- 2.3 in the second, and 2.8 +/- 2.0 in the third hour after permanent MCAO. In animals with reversible MCAO, PID were abolished from 15-minutes recirculation onward. There was no temporal relationship between ROS production and peri-infarct DC potential shifts. In conclusion, using a high temporal resolution ROS detection technique (CL), we found that permanent MCAO (after an initial decrease) was accompanied by a steady increase of ROS production during the 3-hour observation period, while reperfusion after 1 hour of MCAO produced a burst in ROS formation. Both patterns of ROS production were not related to the occurrence of PID.

A reproducible model of middle cerebral artery occlusion in mice : Hemodynamic, biochemical, and magnetic resonance imaging

Abstract: A reproducible model of thread occlusion of the middle cerebral artery (MCA) was established in C57 Black/6J mice by matching the diameter of the thread to the weight of the animals. For this purpose, threads of different diameter (80 to 260 microns) were inserted into the MCA of animals of different weights (18 to 33 g), and the success of vascular occlusion was evaluated by imaging the ischemic territory on serial brain sections with carbon black. Successful occlusion of the MCA resulted in a linear relationship between body weight and thread diameter (r = 0.46, P < 0.01), allowing precise selection of the appropriate thread size. Laser-Doppler measurements of CBF, neurological scoring, and 2,3,5-triphenyltetrazolium chloride staining confirmed that matching of animal weight and suture diameter produced consistent cerebral infarction. Three hours after MCA occlusion, imaging of ATP, tissue pH, and cerebral protein synthesis allowed differentiation between the central infarct core, in which ATP was depleted, and a peripheral penumbra with reduced protein synthesis and tissue acidosis but preserved ATP content. Perfusion deficits and ischemic tissue alterations could also be detected by perfusion- and diffusion-weighted magnetic resonance imaging, demonstrating the feasibility of dynamic evaluations of infarct evolution. The use of multiparametric imaging techniques in this improved MCA occlusion model opens the way for advanced pathophysiological studies of stroke in gene-manipulated animals.

Nitric oxide scavenging by hemoglobin or nitric oxide synthase inhibition by N-nitro-L-arginine induces cortical spreading ischemia when K+ is increased in the subarachnoid space.

Abstract: We investigated the combined effect of increased brain topical K+ concentration and reduction of the nitric oxide (NO.) level caused by nitric oxide scavenging or nitric oxide synthase (NOS) inhibition on regional cerebral blood flow and subarachnoid direct current (DC) potential. Using thiopental-anesthetized male Wistar rats with a closed cranial window preparation, brain topical superfusion of a combination of the NO. scavenger hemoglobin (Hb; 2 mmol/L) and increased K+ concentration in the artificial cerebrospinal fluid ([K+]ACSF) at 35 mmol/L led to sudden spontaneous transient ischemic events with a decrease of CBF to 14+/-7% (n=4) compared with the baseline (100%). The ischemic events lasted for 53+/-17 minutes and were associated with a negative subarachnoid DC shift of -7.3+/-0.6 mV of 49+/-12 minutes' duration. The combination of the NOS inhibitor N-nitro-L-arginine (L-NA, 1 mmol/L) with [K+]ACSF at 35 mmol/L caused similar spontaneous transient ischemic events in 13 rats. When cortical spreading depression was induced by KCl at a 5-mm distance, a typical cortical spreading hyperemia (CSH) and negative DC shift were measured at the closed cranial window during brain topical superfusion with either physiologic artificial CSF (n=5), or artificial CSF containing increased [K+]ACSF at 20 mmol/L (n=4), [K+]ACSF at 3 mmol/L combined with L-NA (n=10), [K+]ACSF at 10 mmol/L combined with L-NA (five of six animals) or [K+]ACSF at 3 mmol/L combined with Hb (three of four animals). Cortical spreading depression induced longlasting transient ischemia instead of CSH, when brain was superfused with either [K+]ACSF at 20 mmol/L combined with Hb (CBF decrease to 20+/-20% duration 25+/-21 minutes, n=4), or [K+]ACSF at 20 mmol/L combined with L-NA (n=19). Transient ischemia induced by NOS inhibition and [K],ACSF at 20 mmol/L propagated at a speed of 3.4+/-0.6 mm/min, indicating cortical spreading ischemia (CSI). Although CSH did not change oxygen free radical production, as measured on-line by in vivo lucigenin-enhanced chemiluminescence, CSI resulted in the typical radical production pattern of ischemia and reperfusion suggestive of brain damage (n=4). Nimodipine (2 microg/kg body weight/min intravenously) transformed CSI back to CSH (n=4). Vehicle had no effect on CSI (n=4). Our data suggest that the combination of decreased NO. levels and increased subarachnoid K+ levels induces spreading depression with acute ischemic CBF response. Thus, a disturbed coupling of metabolism and CBF can cause ischemia. We speculate that CSI may be related to delayed ischemic deficits after subarachnoid hemorrhage, a clinical condition in which the release of Hb and K+ from erythrocytes creates a microenvironment similar to the one investigated here.

Noninvasive Quantification of the Cerebral Metabolic Rate for Glucose Using Positron Emission Tomography, 18F-Fluoro-2-Deoxyglucose, the Patlak Method, and an Image-Derived Input Function

Abstract: The authors developed and tested a method for the noninvasive quantification of the cerebral metabolic rate for glucose (CMRglc) using positron emission tomography (PET), 18F-fluoro-2-deoxyglucose, the Patlak method, and an image-derived input function. Dynamic PET data acquired 12 to 48 seconds after rapid tracer injection were summed to identify carotid artery regions of interest (ROIs). The input function then was generated from the carotid artery ROIs. To correct spillover, the early summed image was superimposed over the last PET frame, a tissue ROI was drawn around the carotid arteries, and a tissue time activity curve (TAC) was generated. Three venous samples were drawn from the tracer injection site at a later time and used for the spillover and partial volume correction by non-negative least squares method. Twenty-six patient data sets were studied. It was found that the image-derived input function was comparable in shape and magnitude to the one obtained by arterial blood sampling. Moreover, no...

Ischemic and Excitotoxic Brain Injury is Enhanced in Mice Lacking the p55 Tumor Necrosis Factor Receptor

Abstract: Ischemic and excitotoxic insults to the brain induce rapid production of tumor necrosis factor-α (TNF), but the role of TNF in neuronal responses to brain injury are unclear. Two different TNF rece...

Cerebral Ischemia after Bilateral Carotid Artery Occlusion and Intraluminal Suture Occlusion in Mice: Evaluation of the Patency of the Posterior Communicating Artery:

Abstract: Cerebral ischemia models using mice have drawn increasing attention, particularly because of the availability of transgenic animals. However, the variability of intracranial vasculature at the circle of Willis in mice can influence the degree of ischemia in both the bilateral common carotid artery (CCA) occlusion and intraluminal suture occlusion models. We have developed a method to predict the extent of the anastomosis between carotid and vertebrobasilar circulation in three mouse strains (C57BL/6, CBA, and DBA/2) by measuring cortical microperfusion with laser Doppler flowmetry during a 1-minute occlusion of both CCA. When animals showed residual cortical microperfusion of less than 12% during bilateral CCA occlusion, the mice showed absence of functional anastomosis, developed ATP depletion in the frontal cortex during occlusion, and had ischemic neuronal death in the hippocampus and caudoputamen after occlusion for 15 minutes and recirculation for 7 days. Furthermore, those mice exhibited decreased local cerebral blood flow and associated ischemic neuronal death in the hippocampus, within the territory supplied by the posterior cerebral artery, with the intraluminal suture occlusion model. The current study demonstrates the need for assessment of intracranial vasculature in each animal by measuring cortical microperfusion during temporary occlusion of both CCA, no matter whether cerebral ischemia is produced by bilateral CCA occlusion or intraluminal suture occlusion in transgenic mice.

Prolonged therapeutic window for ischemic brain damage caused by delayed caspase activation.

Abstract: Apoptotic cell death is prominent in neurodegenerative disorders, such as Alzheimer's disease and Huntington's disease, and is found in cerebral ischemia Using a murine model of delayed cell death, we determined that cleavage of zDEVD-amino-4-trifluoromethyl coumarin (zDEVD-afc) in brain homogenate, a measure of caspase activation, increased initially 9 hours after brief (30 minutes) middle cerebral artery occlusion along with caspase-3p20 immunoreactive cleavage product as determined by immunoblotting zDEVD-afc cleavage activity was blocked by pretreatment or posttreatment with the caspase-inhibitor N-benzyloxycarbonyl-Asp(OMe)-Glu(OMe)-Val-Asp(OMe)-fluoromethyl-ketone (zDEVD-fmk), and ischemic damage was reduced when the drug was injected up to 9 hours after reperfusion The protection was long lasting (21 days) Hence, the period before caspase activation defined the therapeutic opportunity for this neuroprotective agent after mild ischemic brain injury Prolonged protection after caspase inhibition plus the extended treatment window may be especially relevant to the treatment of neurodegenerative disorders

Apolipoprotein E and the CNS response to injury

Abstract: Apolipoprotein E (apoE) is a multifunctional protein with an expanding role in the neurobiology of disease. Although originally described in the context of cholesterol metabolism, interest in the neurobiology of apoE has intensified following the association between apoE genotype and risk of developing Alzheimer's disease. Recent clinical observations also suggest that apoE genotype may influence recovery after a variety of neurological insults. Thus, in addition to the study of disease-specific mechanisms by which apoE may modulate susceptibility of developing Alzheimer's disease, there has been an increasing focus on its role in modulating the CNS response to acute injury. Although the neurobiology of apoE in the injured brain remains incompletely defined, there is evidence to suggest neurotrophic, immunomodulatory, and antioxidant effects.

Cerebral Blood Flow Measurements by Magnetic Resonance Imaging Bolus Tracking: Comparison with [15O]H2O Positron Emission Tomography in Humans:

Abstract: In six young, healthy volunteers, a novel method to determine cerebral blood flow (CBF) using magnetic resonance (MR) bolus tracking was compared with [15O]H2O positron emission tomography (PET) The method yielded parametric CBF images with tissue contrast in good agreement with parametric PET CBF images Introducing a common conversion factor, MR CBF values could be converted into absolute flow rates, allowing comparison of CBF values among normal subjects

Noninvasive measurement of regional cerebral blood flow by near-infrared spectroscopy and indocyanine green.

Abstract: Clinicians lack a practical method for measuring CBF rapidly, repeatedly, and noninvasively at the bedside. A new noninvasive technique for estimation of cerebral hemodynamics by use of near-infrared spectroscopy (NIRS) and an intravenously infused tracer dye is proposed. Kinetics of the infrared tracer indocyanine green were monitored on the intact skull in pigs. According to an algorithm derived from fluorescein flowmetry, a relative blood flow index (BFI) was calculated. Data obtained were compared with cerebral and galeal blood flow values assessed by radioactive microspheres under baseline conditions and during hemorrhagic shock and resuscitation. Blood flow index correlated significantly (rs = 0.814, P < 0.001) with cortical blood flow but not with galeal blood flow (rs = 0.258). However, limits of agreement between BFI and CBF are rather wide (+/- 38.2 +/- 6.4 mL 100 g-1 min-1) and require further studies. Data presented demonstrate that detection of tracer kinetics in the cerebrovasculature by NIRS may serve as valuable tool for the noninvasive estimation of regional CBF. Indocyanine green dilution curves monitored noninvasively on the intact skull by NIRS reflect dye passage through the cerebral, not extracerebral, circulation.

Tissue at Risk of Infarction Rescued by Early Reperfusion: A Positron Emission Tomography Study in Systemic Recombinant Tissue Plasminogen Activator Thrombolysis of Acute Stroke

Abstract: Thrombolytic therapy of acute ischemic stroke can be successful only as long as there is penumbral tissue perfused at rates between the thresholds of normal function and irreversible structural damage, respectively. To determine the proportion of tissue at risk of infarction, cerebral perfusion was studied in 12 patients with acute ischemic stroke who underwent treatment with systemic recombinant tissue plasminogen activator (0.9 mg/kg body weight according to National Institute of Neurological Disorders and Stroke protocol) within 3 hours of onset of symptoms, using [15O]-H2O positron emission tomography (PET) before or during, and repeatedly after thrombolysis. The size of the regions of critically hypoperfused gray matter were identified on the initial PET scans, and changes of perfusion in those areas were related to the clinical course (followed by the National Institutes of Health stroke scale) and to the volume of infarcted gray matter demarcated on magnetic resonance imaging 3 weeks after the stroke. Whereas the initial clinical score was unrelated to the size of the ischemic area, after 3 weeks there was a strong correlation between clinical deficit and volume size of infarcted gray matter (Spearman's rho, 0.96; P < 0.001). All patients with a severely hypoperfused (< 12 mL/100 g/min) gray matter region measuring less than 15 mL on first PET showed full morphologic and clinical recovery (n = 5), whereas those with ischemic areas larger than 20 mL developed infarction and experienced persistent neurologic deficits of varying degree. Infarct sizes, however, were smaller than expected from previous correlative PET and morphologic studies of patients with acute stroke: only 22.7% of the gray matter initially perfused at rates below the conventional threshold of critical ischemia became necrotic. Actually, the percentage of initially ischemic voxels that became reperfused at almost normal levels clearly predicted the degree of clinical improvement achieved within 3 weeks. These sequential blood flow PET studies demonstrate that critically hypoperfused tissue can be preserved by early reperfusion, perhaps related to thrombolytic therapy. The results correspond with experimental findings demonstrating the prevention of large infarcts by early reperfusion to misery perfused but viable tissue.

Absolute cerebral blood flow and blood volume measured by magnetic resonance imaging bolus tracking : Comparison with positron emission tomography values

Abstract: The authors determined cerebral blood flow (CBF) with magnetic resonance imaging (MRI) of contrast agent bolus passage and compared the results with those obtained by O-15 labeled water (H215O) and positron emission tomography (PET). Six pigs were examined by MRI and PET under normo- and hypercapnic conditions. After dose normalization and introduction of an empirical constant phi Gd, absolute regional CBF was calculated from MRI. The spatial resolution and the signal-to-noise ratio of CBF measurements by MRI were better than by the H215O-PET protocol. Magnetic resonance imaging cerebral blood volume (CBV) estimates obtained using this normalization constant correlated well with values obtained by O-15 labeled carbonmonooxide (C15O) PET. However, PET CBV values were approximately 2.5 times larger than absolute MRI CBV values, supporting the hypothesized sensitivity of MRI to small vessels.

Autoregulatory Vasodilation of Parenchymal Vessels is Impaired during Cerebral Vasospasm

Abstract: Impaired CBF autoregulation during vasospasm after aneurysmal subarachnoid hemorrhage (SAH) could reflect impaired capacity of distal vessels to dilate in response to reduced local perfusion pressure or simply indicate that the perfusion pressure distal to large arteries in spasm is so low that vessels are already maximally dilated. Autoregulatory vasodilation can be detected in vivo as an increase in the parenchymal cerebral blood volume (CBV). Regional CBV, CBF, and oxygen extraction fraction in regions with and without angiographic vasospasm obtained from 29 positron emission tomography studies performed after intracranial aneurysm rupture were compared with data from 19 normal volunteers and five patients with carotid artery occlusion. Regional CBF was reduced compared to normal in regions from SAH patients with and without vasospasm as well as with ipsilateral carotid occlusion (P < .0001). Regional oxygen extraction fraction was higher during vasospasm and distal to carotid occlusion than both normal and SAH without vasospasm (P < .0001). Regional CBV was reduced compared to normal in regions with and without spasm, whereas it was increased ipsilateral to carotid occlusion (P < .0001). These findings of reduced parenchymal CBV during vasospasm under similar conditions of tissue hypoxia that produce increased CBV in patients with carotid occlusion provide evidence that parenchymal vessels distal to arteries with angiographic spasm after SAH do not show normal autoregulatory vasodilation.

Circulating Antibody against Tumor Necrosis Factor–Alpha Protects Rat Brain from Reperfusion Injury:

Abstract: The role of tumor necrosis factor-alpha (TNF-α) in brain injury is controversial. We studied the effect of anti-TNF-α antibody in a rat model of reversible middle cerebral artery occlusion. During focal ischemia and early reperfusion, TNF-α was rapidly and transiently released into circulation. Pretreatment with intravenous anti-TNF-α antibody reduced cortical (71%, P < 0.015) and subcortical (58%, P < 0.007) injury, enhanced the cerebral blood flow during reperfusion, and improved the neurologic outcome. This further supports the contention that TNF-α is a deleterious cytokine in stroke, whereas circulating antibody against TNF-α may protect brain from reperfusion injury.

Transient Global Forebrain Ischemia Induces a Prolonged Expression of the Caspase-3 mRNA in Rat Hippocampal CA1 Pyramidal Neurons:

Abstract: The authors recently cloned a cDNA for an ICE/CED3-related cysteine protease from rat brain, which is closely related to human CPP32 (now designated caspase-3). In situ hybridization histochemistry revealed a profound developmental regulation of the caspase-3 transcript in rat brain, with relatively high levels of caspase-3 mRNA observed in neurons of the fetal and neonatal brain and low levels of mRNA in neurons of the adult brain. The authors report that transient forebrain ischemia, which results in a delayed apoptotic death of CA1 pyramidal neurons, results in prolonged expression of caspase-3 mRNA in these same pyramidal neurons. Up-regulation of caspase-3 mRNA in CA1 pyramidal neurons is prominent 24 hours after transient global ischemia, and expression is maintained at higher levels for at least 72 hours after ischemia. However, by 96 hours after ischemia, a marked decrease in caspase-3 mRNA expression is observed in CA1 pyramidal neurons, showing severe degenerative changes (e.g., nuclear condensation). By contrast, there is no change in the expression of a closely related member of caspase family, caspase-2, in CA1 pyramidal neurons after global ischemia. Instead, caspase-2 mRNA is induced in lamina layers of cerebral cortex 24 hours after the ischemia. A selective and prolonged induction of the caspase-3 gene in committed CA1 pyramidal neurons suggests that transcriptional activation of this caspase-3 gene may be involved in the apoptotic cell death cascade of CA1 neurons after transient global ischemia.

Comparison of the transient equilibrium and continuous infusion method for quantitative pet analysis of [11C]raclopride binding

Abstract: Several approaches have been applied for quantification of D2 dopamine receptors in positron emission tomography studies using [11C]raclopride. Initial approaches were based on analyses of data obtained after rapid bolus injection of [11C]raclopride. A continuous infusion paradigm has more recently been applied. The current study compares these approaches in healthy men. Two positron emission tomography measurements were performed in each of six healthy men, the first with rapid bolus injection and the second with continuous infusion of [11C]raclopride. In rapid bolus injection, the binding potential was calculated by the following methods. One approach is the kinetic analysis using the standard three-compartment model. Another is to define a transient equilibrium at the moment when the specific binding reaches its maximum. In continuous infusion, binding potential was calculated by using time-activity data at equilibrium condition. All methods gave almost identical binding potential, representing cross-v...

Exacerbation of ischemic brain damage by localized striatal injection of interleukin-1beta in the rat.

Abstract: Interleukin-1beta (IL-1beta) has been implicated in ischemic brain damage. The site of action of IL-1beta in such damage is not known, but we have demonstrated previously that injection of the interleukin-1 receptor antagonist (IL-1ra) in the striatum but not the cortex of rats inhibits damage caused by permanent middle cerebral artery occlusion. The present study investigated the site of action of IL-1beta on ischemic damage by examining the effects of intracerebroventricular, striatal, or cortical injection of recombinant IL-1beta at the onset of permanent middle cerebral artery occlusion in the rat. Intracerebroventricular injection of IL-1beta (2.5 ng) significantly increased infarct volume in the striatum (35%, P < 0.0001) and in the cortex (44%, P < 0.0001) compared with vehicle treatment. Direct injection of IL-1beta into the striatum also increased infarct volume in both the striatum (36%, P < 0.0001) and the cortex (38%, P < 0.0001), whereas injection of IL-1beta into the cortex failed to affect infarct volume in either the striatum or the cortex. Cortical injection of a higher dose of IL-1beta (20 ng) also failed to affect ischemic damage in either the striatum or the cortex. Injection of IL-1beta into the striatum contralateral to the infarction had no effect on striatal damage in the ischemic hemisphere, but did increase cortical damage by 18% (P < 0.0001). In separate groups of animals, IL-1beta (2.5 ng) was injected into either the striatum or the cortex, and body temperature was recorded continuously in conscious free-moving animals by remote telemetry. Injection of IL-1beta at either site failed to influence body temperature, suggesting that exacerbation of brain damage by striatal injection of IL-1beta is not caused by effects on body temperature. These results imply that IL-1beta exacerbates ischemic damage by specific actions in the striatum where it can influence damage at distant sites in the cortex.

Hibernation in Ground Squirrels Induces State and Species-Specific Tolerance to Hypoxia and Aglycemia: An In Vitro Study in Hippocampal Slices

Abstract: Hibernation in mammals is associated with a regulated depression of global cellular functions accompanied by reductions of cerebral blood flow that would render the brain profoundly ischemic under normal conditions. Homeostatic control is preserved, however, and brain damage does not occur. We investigated the possibility that hibernation not only confers tolerance to profound hypothermia, but also to hypoxia and aglycemia independent of temperature. Hippocampal slices from ground squirrels Citellus tridecemlineatus in both the active and hibernating states and from rats were subjected to in vitro hypoxia and aglycemia at incubation temperatures of 36 degrees C, 20 degrees C, and 7 degrees C and evaluated histologically. A binary bioassay was used to determine the duration of hypoxia/aglycemia tolerated in each group. At all temperatures, slices from hibernating animals were most tolerant compared with both active squirrels and rats. Slices from active ground squirrels were more tolerant than rat at 20 degrees C and 7 degrees C but not at 36 degrees C indicating a species-specific difference that becomes manifest at lower temperatures. These results indicate that hibernation is associated not only with tolerance to profound hypothermia but also to deprivation of oxygen and glucose. Because tolerance was already demonstrable at the shortest duration of hibernation studied, rapid therapeutic induction of a similar state may be possible. Therefore, identification of the regulatory mechanisms underlying this tolerance may lead to novel neuroprotective strategies.

Role of Potassium Channels in Regulation of Cerebral Vascular Tone

Abstract: Several types of potassium (K+) channels are present in cerebral blood vessels. Opening or closure of these ion channels may have significant effects on membrane po­ tential, which is a major determinant of entry of extra­ cellular calcium and thus vascular tone, Because of the ionic properties of the cell membrane at rest, the change in activity of only a few K+ channels is sufficient to change membrane potential significantly and alter vas­ cular tone (Nelson and Quayle, 1995; Quayle et aI., 1997). This review will focus on recent findings regard­ ing the characteristics and functional importance of K+ channels in the cerebral circulation.

Deficiency of intercellular adhesion molecule 1 attenuates microcirculatory disturbance and infarction size in focal cerebral ischemia.

Abstract: Recent evidence has shown crucial roles for cell-adhesion molecules in inflammation-induced rolling, adhesion, and accumulation of neutrophils in tissue. Intercellular adhesion molecule-1 (ICAM-1) is one of these adhesion molecules. Previous studies have shown marked reduction in the size of infarction after focal cerebral ischemia by depletion of granulocytes and administration of the antibody against ICAM-1. In the present study we investigated the role of ICAM-1 in the size of ischemic lesions, accumulation of granulocytes, and microcirculatory compromise in focal cerebral ischemia by using ICAM-1-knockout mice. Ischemic lesions were significantly mitigated in knockout mice after permanent and transient focal ischemia, even though the number of granulocytes in the infarcted tissue was almost the same between knockout and wild-type mice. Depletion of granulocytes further decreased the size of ischemic lesions after transient focal ischemia in ICAM-1-knockout mice. Microcirculation was reduced after focal ischemia, but it was better preserved in the cerebral cortex of knockout mice than that of wild-type mice. The present study demonstrated that ICAM-1 played a role in microcirculatory failure and subsequent development and expansion of infarction after focal cerebral ischemia. However, it is highly unlikely that ICAM-1 played a key role in accumulation of granulocytes after focal cerebral ischemia.