bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantification of Muscarinic Cholinergic Receptors with [11C]NMPB and Positron Emission Tomography: Method Development and Differentiation of Tracer Delivery from Receptor Binding
Authors: Zubieta Jon-Kar , Koeppe Robert A. , Mulholland G. Keith , Kuhl David E. , Frey Kirk A.
Published: November 2003

Quantification of human brain muscarinic cholinergic receptors was investigated with the use of [11C]N-methyl-4-piperidyl benzylate (NMPB) and positron emission tomography (PET). Whole-brain uptake of NMPB at 90 to 110 minutes after intravenous injection was approximately 10% of the administered dose. The initial cerebral distribution of NMPB corresponded to the pattern of cerebral perfusion; however, at progressively longer postinjection intervals, regional distinctions consistent with muscarinic receptor binding were evident: activity at 90 to 110 minutes postinjection was highest in the striatum and cerebral cortex, intermediate in the thalamus and pons, and lowest in the cerebellum. After the development of a chromatographic system for isolation of authentic [11C]NMPB in plasma, tracer kinetic modeling was used to estimate receptor binding from the cerebral and arterial plasma tracer time-courses. Ligand transport rate and receptor-binding estimates were obtained with the use of compartmental models and analytical methods of varying complexity, including a two-parameter pixel-by-pixel-weighted integral approach and regional least-squares curve-fitting analyses employing both two-and three-compartment model configurations. In test—retest experiments, precision of the methods and their abilities to distinguish altered ligand delivery from binding in occipital cortex during an audiovisual presentation were evaluated. Visual stimulation increased the occipital blood-to-brain NMPB transport rate by 25% to 46% in estimates arising from the various approaches. Weighted integral analyses resulted in lowest apparent transport changes and in a concomitant trend toward apparent binding increases during visual activation. The regional least-squares procedures were superior to the pixel-by-pixel method in isolating the effects of altered tracer delivery from receptor-binding estimates, indicating larger transport effects and unaltered binding. Precision was best (less than 10% test—retest differences) for the weighted integral analyses and was somewhat lower in the least-squares analyses (10–25% differences). The authors conclude that pixel-by-pixel-weighted integral analyses of NMPB distribution introduce transport biases into receptor-binding estimates. Similar confounding effects also are predicted in noncompartmental analyses of delayed radiotracer distribution. The use of regional nonlinear least-squares fitting to two- and three-compartment models, although more labor intensive, provides accurate distinction of receptor-binding estimates from tracer delivery with acceptable precision in both intra- and intersubject comparisons.
Simultaneous Glutamate and Perfusion fMRI Responses to Regional Brain Stimulation
Authors: Forman Steven D. , Silva Afonso C. , Dedousis Nikolas , Barbier Emmanuel L. , Fernstrom John D. , Koretsky Alan P.
Published: November 2003

Functional magnetic resonance imaging (fMRI) rests on the assumption that regional brain activity is closely coupled to regional cerebral blood flow (rCBF) in vivo. To test the degree of coupling, cortical brain activity was locally stimulated in rats by reversed microdialysis infusion of picrotoxinin, a γ-aminobutyric acid-A antagonist. Before and during the first 30 minutes of infusion, simultaneous fMRI (rCBF) and neurochemical (interstitial glutamate concentration) measures of brain activity were highly correlated (r = 0.83). After 30 minutes of picrotoxinin-induced stimulation, glutamate levels decreased but rCBF remained elevated, suggesting that additional factors modulate the relationship between neuronal neurotransmitters and hemodynamics at these later stages.
High-Resolution Functional Magnetic Resonance Imaging of the Rat Brain: Mapping Changes in Cerebral Blood Volume Using Iron Oxide Contrast Media
Authors: van Bruggen Nicholas , Busch Elmar , Palmer James T. , Williams Simon-Peter , de Crespigny Alexander J.
Published: November 2003

Contrast-enhanced magnetic resonance imaging was used to produce high-resolution activation maps reflecting local changes in cerebral blood volume after a simple sensory stimulus, Activation of the forelimb region of the somatosensory cortex was performed in α-chloralose—anaesthetized rats with an electrical stimulus (5 V, 3 Hz) delivered through needle electrodes placed subcutaneously on the left forelimb, A gradient echo magnetic resonance imaging sequence, sensitive to changes in the relative amount of deoxyhemoglobin within the cerebral vasculature, produced a 4.05% ± 1.69% increase in signal intensity. This effect was enhanced with an injection of an intravascular iron oxide contrast agent (Combidex, Advanced Magnetics), resulting in a 9.11% ± 1.52% decrease in signal intensity.
Effect of Cortical Spreading Depression on the Levels of mRNA Coding for Putative Neuroprotective Proteins in Rat Brain
Authors: Karikó Katalin , Harris Valerie A. , Rangel Yolanda , Monica E , Welsh Frank A.
Published: November 2003

Previous studies have demonstrated that cortical spreading depression (CSD) induces neuronal tolerance to a subsequent episode of ischemia, The objective of the present investigation was to determine whether CSD alters levels of mRNA coding for putative neuroprotective proteins. Unilateral CSD was evoked in male Wistar rats by applying 2 mol/L KCl over the frontal cortex for 2 hours. After recovery for 0, 2, or 24 hours, levels of several mRNA coding for neuroprotective proteins were measured bilaterally in parietal cortex using Northern blot analysis. Levels of c-fos mRNA and brain-derived neurotrophic factor (BDNF) mRNA were markedly elevated at 0 and 2 hours, but not 24 hours after CSD. Tissue plasminogen activator (tPA) mRNA levels were also significantly increased at 0 and 2 hours, but not 24 hours after CSD. Levels of the 72-kDa heat-shock protein (hsp72) mRNA were not significantly increased by CSD, except for a small elevation (20%) at 2 hours recovery. Levels of the 73-kDa heat-shock cognate (hsc73) mRNA were slightly, but significantly, increased at 2 and 24 hours of recovery. Finally, levels of mRNA for protease nexin-1 and glutamine synthetase were not significantly altered by CSD at any time studied. The current results support the hypothesis that neuronal tolerance to ischemia after CSD may be mediated by increased expression of FOS, BDNF, or tPA, but not by increased expression of hsp72, hsc73, nexin-1, or glutamine synthetase.
Outcome in Acute Stroke with Successful Intra-Arterial Thrombolysis and Predictive Value of Initial Single-Photon Emission-Computed Tomography
Authors: Ueda Toshihiro , Sakaki Saburo , Yuh William T. C. , Nochide Ichiro , Ohta Shinsuke
Published: November 2003

This study investigates retrospectively, in selected patients, the ischemic outcome (reversible ischemia, infarction, and hemorrhage) and neurologic outcome of acute stroke treated with intra-arterial thrombolysis and the predictive value of pretreatment single-photon emission-computed tomography (SPECT). Thirty patients with complete recanalization within 12 hours were analyzed. The extent of ischemia was outlined on SPECT, and two CBF parameters were calculated: the ratio of ischemic regional activity to CBF in the cerebellum and the asymmetry index. Reversible ischemia, infarction, and hemorrhage were identified by comparing SPECT and follow-up computed tomography. Nine patients (30%) had no or small infarction, 14 (47%) had medium or large infarction, and seven (23%) had hemorrhage. Forty-two lesions were identified (22 reversible ischemia, 13 infarction, and 7 hemorrhage). Duration of ischemia, urokinase dose, disease type, and occlusion site were nonsignificant factors, whereas neurologic outcome and CBF parameters were significant among the three patient groups and three types of ischemic lesions. Ischemic tissue with CBF greater than 55% of cerebellar flow still may be salvageable, even with treatment initiated 6 hours after onset of symptoms. Ischemic tissue with CBF greater than 35% of cerebellar flow still may be salvageable with early treatment (less than 5 hours). Ischemic tissue with with CBF less than 35% of cerebellar flow may be at risk for hemorrhage within the critical time window. Pretreatment SPECT can provide useful parameters to increase the efficacy of thrombolysis by reducing hemorrhagic complications and improving neurologic outcome.
Transforming Growth Factor-α Acting at the Epidermal Growth Factor Receptor Reduces Infarct Volume after Permanent Middle Cerebral Artery Occlusion in Rats
Authors: Justicia Carles , Planas Anna M.
Published: November 2003

Transforming growth factor-α (TGF-α) is a ligand for the epidermal growth factor (EGF) receptor (EGFR), and is more abundant than EGF in the brain. The authors studied whether administration of exogenous TGF-α into the brain can protect neurons against ischemia in a model of permanent middle cerebral artery (MCA) occlusion in the rat, and whether any effect of TGF-α was mediated by EGFR by administering 4,5-dianilinophthalimide (DAPH), a protein-tyrosine kinase inhibitor with high selectivity for EGFR. Rats received either TGF-α (10 or 25 ng), DAPH (100 ng), DAPH plus TGF-α (25 ng), or vehicle in the ipsilateral first ventricle. Drugs were administered twice: 30 minutes before and 30 minutes after MCA occlusion, and infarct volume was evaluated 24 hours later. Transforming growth factor-α at the dose of 25 ng caused a statistically significant reduction of infarct volume (60%) in relation to ischemic rats administered vehicle. This reduction was no longer seen when TGF-α was administered in combination with DAPH. The present results show that TGF-α can protect neurons from ischemic damage, and that this effect is mediated by EGFR. It is suggested that activation of EGFR-mediated intracellular signalling pathways contributes to the survival of neural cells susceptible to ischemic injury.
Expression of Neuropeptide Y Receptors mRNA and Protein in Human Brain Vessels and Cerebromicrovascular Cells in Culture
Authors: Abounader Roger , Elhusseiny Ahmed , Cohen Zvi , Olivier André , Stanimirovic Danica , Quirion Rémi , Hamel Edith
Published: November 2003

Neuropeptide Y (NPY) has been suggested as an important regulator of CBF. However, except for the presence of Y1 receptors in large cerebral arteries, little is known about its possible sites of action on brain vessels. In this study, we sought to identify the NPY receptors present in the human cerebrovascular bed. Specific Y1 receptor binding sites, localized on the smooth muscle of human pial vessels and potently competed by NPY, polypeptide YY (PYY), and the selective Y1 receptor antagonist BIBP 3226, were identified by quantitative radioautography of the Y1 radioligand [125I]_[Leu31, pro34]-PYY. In contrast, no specific binding of the Y2-([125I]-PYY3-36) and Y4/Y5-(125I-human pancreatic polypeptide [hPP]) radioligands could be detected. By in situ hybridization, expression of Y1 receptor mRNA was restricted to the smooth muscle layer of pial vessels, whereas no specific signals were detected for either Y2, Y4, or Y5 receptors. Similarly, using reverse transcriptase-polymerase chain reaction (RT-PCR), mRNA for Y1 but not Y2, Y4, or Y5 receptors was consistently detected in isolated human pial vessels, intracortical microvessels, and capillaries. In human brain microvascular cells in culture, PCR products for the Y1 receptors were exclusively found in the smooth muscle cells. In cultures of human brain astrocytes, a cell type that associates intimately with brain microvessels, PCR products for Y1, Y2, and Y4 but not Y5 receptors were identified. Finally, NPY significantly inhibited the forskolin-induced cAMP production in smooth muscle but not in endothelial cell cultures. We conclude that smooth muscle Y1 receptors are the primary if not exclusive NPY receptors associated with human brain extraparenchymal and intraparenchymal blood vessels, where they most likely mediate cerebral vasoconstriction.
Indefatigable CA1 Sector Neuroprotection with Mild Hypothermia Induced 6 Hours after Severe Forebrain Ischemia in Rats
Authors: Colbourne Frederick , Li Hui , Buchan Alastair M.
Published: November 2003

Considerable controversy exists about whether postischemic hypothermia can permanently salvage hippocampal CA 1 neurons or just postpone injury. Studies of very brief cooling in rat have found transient benefit, whereas experiments in gerbil using protracted hypothermia report lasting protection. This discrepancy might be because of the greater efficacy of longer cooling or it might, for example, represent an important species difference. In the present study, a 48-hour period of mild hypothermia was induced starting 6 hours after 10 minutes of severe four-vessel occlusion ischemia in rats. Untreated normothermic ischemia resulted in total CA1 cell loss (99%), whereas delayed hypothermia treatment reduced neuronal loss to 14% at a 28-day survival. In unregulated rats, brain temperature spontaneously fell during ischemia, and stayed subnormal for an extended period after ischemia. This mild cooling resulted in more variable and less severe CA1 injury (75%). Finally, vertebral artery cauterization under halothane anesthesia caused an approximately 2°C drop in brain temperature for 1 hour, but prevention of this hypothermia did not significantly affect CA1 damage. In summary, protracted postischemic hypothermia provided robust and long-term CA 1 protection in rat. These results encourage the clinical assessment of prolonged hypothermia and its use as a model to understand ischemic CA1 injury.
Neuroprotective Effects of a Novel Nitrone, NXY-059, after Transient Focal Cerebral Ischemia in the Rat
Authors: Kuroda Satoshi , Tsuchidate Ryoichi , Smith Maj-Lis , Maples Kirk R. , Siesjö Bo K.
Published: November 2003

Recent results have demonstrated that the spin trapping agent α-phenyl- N- tert-butyl nitrone (PBN) reduces infarct volume in rats subjected to 2 hours of middle cerebral artery occlusion, even when given 1 to 3 hours after the start of recirculation. In the current study, the authors assessed the effect of NXY-059, a novel nitrone that is more soluble than PBN. Loading doses were given of 0.30, 3.0, or 30 mg · kg−1 followed by 0.30, 3.0, or 30 mg · kg−1 · h−1 for 24 or 48 hours. Dose–response studies showed that when treatment was begun 1 hour after recirculation, 0.30 mg · kg−1 had a small and 30 mg · kg-i a marked effect on infarct volume. At equimolar doses (3.0 mg · kg−1 for NXY-059 and 1.4 mg · kg−1 for PBN), NXY-059 was more efficacious than PBN. Similar results were obtained when a recovery period of 7 days was allowed. The window of therapeutic opportunity for NXY-059 was 3 to 6 hours after the start of recirculation. Studies of the transfer constant of [14C]NXY-059 showed that, in contrast to PBN, this more soluble nitrone penetrates the blood-brain barrier less extensively. This fact, and the pronounced antiischemic effect of NXY-059, suggest that the delayed events leading to infarction may be influenced by reactions occurring at the blood–endothelial interface.
Butanol is Superior to Water for Performing Positron Emission Tomography Activation Studies
Authors: Votaw John R. , Henry Thomas R. , Shoup Timothy M. , Hoffman John M. , Woodard John L. , Goodman Mark M.
Published: November 2003

[15O]Butanol has been shown to be superior to [15O]water for measuring cerebral blood flow with positron emission tomography. This work demonstrates that it is also superior for performing activation studies. Data were collected under three conditions: a visual confrontation animal-naming task, nonsense figure size discrimination, and a nonvisual darkroom control task. Time–activity curves (TAC) were obtained for regions known to be activated by the confrontation naming task to compare absolute uptake and the different kinetics of the two tracers. Also, t statistic maps were calculated from the data of 10 subjects for both tracers and compared for magnitude of change and size of activated regions. Peak uptake in the whole-brain TAC were similar for the two tracers. For all regions and conditions, the washout rate of [15O]butanol was 41% greater than that of [15O]water. At a threshold of 0, the [15O]water and [15O]butanol percent difference (nonnormalized) and t statistic (global normalization) images are nearly identical, indicating that the same property is being measured with both tracers. The [15O]butanol parametric images displayed at a threshold of |t| = 5 look similar to the [15O]water parametric maps displayed at a threshold of |t| = 4, which is consistent with the observation that t statistic values in [15O]butanol images are generally greater. The t statistic values were equal when the [15O]butanol parametric map was created from any subset of 6 subjects and the [15O]water parametric map was created from all 10 subjects. Fewer subjects need to be studied with [15O]butanol to reach the same statistical power as an [15O]water-based study.
Cerebral Vasodilatation Causing Acute Intracranial Hypertension: A Method for Noninvasive Assessment
Authors: Schmidt Bernhard , Czosnyka Marek , Schwarze Jens Jürgen , Sander Dirk , Gerstner Werner , Lumenta Christianto Benjamin , Pickard John D. , Klingelhöfer Jürgen
Published: November 2003

Deep spontaneous vasodilatatory events are frequently recorded in various cerebral diseases, causing dramatic increases (A-waves) in intracranial pressure (ICP) and subsequently provoking ischemic brain insults, The relationship between fluctuations in CBF, ICP, and arterial blood pressure (ABP) is influenced by properties of cerebrovascular control mechanisms and the cerebrospinal pressure-volume compensation, The goal of this study was to construct a mathematical model of this relationship and to assess its ability to predict the occurrence and time course of A-waves, A group of 17 severely head-injured patients were included in the study, In our model ICP was derived from the ABP waveform using a linear signal transformation. The transformation was modified during the simulation by a relationship between ABP and flow velocity, i.e., by the characterization of the cerebrovascular bed. In this way the ICP could be calculated from the ABP waveform. This model was verified by comparison of simulated and directly measured ICP during A-waves recorded in seven of the patients. In all simulations, plateau elevations of ICP were well replicated. The mean absolute error between real and simulated ICP was 8.3 ± 5.4 mm Hg at the baseline and 7.9 ± 4.3 mm Hg at the top of plateau waves. The correlation coefficient between real and simulated increase in ICP was R = 0.98; P < .001. Similarly, correlation between real and simulated increase in pulse amplitude of ICP was highly significant (R = 0.94; P < .001). The mathematical model of the relationship between ABP, flow velocity, and ICP is of potential clinical use for the noninvasive detection of A-waves in patients in whom invasive ICP assessment is not conducted.
Evidence for Neuroprotective Effects of Endogenous Brain-Derived Neurotrophic Factor after Global Forebrain Ischemia in Rats
Authors: Larsson Elin , Nanobashvili Avtandil , Kokaia Zaal , Lindvall Olle
Published: November 2003

The levels of brain-derived neurotrophic factor (BDNF) vary between different forebrain areas and show region-specific changes after cerebral ischemia. The present study explores the possibility that the levels of endogenous BDNF determine the susceptibility to ischemic neuronal death. To block BDNF activity the authors used the TrkB-Fc fusion protein, which was infused intraventriculary in rats during 1 week before and 1 week after 5 or 30 minutes of global forebrain ischemia. Ischemic damage was quantified in the striatum and hippocampal formation after 1 week of reperfusion using immunocytochemistry and stereological procedures. After the 30-minute insult, there was a significantly lower number of surviving CA4 pyramidal neurons, neuropeptide Y -immunoreactive dentate hilar neurons, and choline acetyltransferase- and TrkA-positive, cholinergic striatal interneurons in the TrkB-Fc-infused rats as compared to controls. In contrast, the TrkB-Fc treatment did not influence survival of CA1 or CA3 pyramidal neurons or striatal projection neurons. Also, after the mild ischemic insult (5 minutes), neuronal death in the CA1 region was similar in the TrkB-Fc-treated and control groups. These results indicate that endogenous BDNF can protect certain neuronal populations against ischemic damage. It is conceivable, though, that efficient neuroprotection after brain insults is dependent not only on this factor but on the concerted action of a large number of neurotrophic molecules.
Hypoxia on Hippocampal Slices from Mice Deficient in Dystrophin (mdx) and Isoforms (mdx3cv)
Authors: Godfraind Jean-Marie , Tekkök Selva Baltan , Krnjević Krešimir
Published: November 2003

Slices from control C57, mdx, and mdx3cv mice were made hypoxic until both field excitatory postsynaptic potential (fEPSP) and presynaptic afferent volley (AV) disappeared (H1). After reoxygenation and recovery of fEPSP, a second and longer hypoxic test (H2) lasted 3 minutes beyond the time required to block AV. When slices were kept in 10 mmol/L glucose, H1 abolished AV 37 and 19% earlier in slices from mdx and mdx3cv mutants than in control slices (where H1 = 12 ± 4.6 minutes, mean ± SD). During H2 or when slices were kept in 4 mmol/L glucose, AV vanished even more quickly, but the times to block did not differ significantly between slices from controls and mutants. After reoxygenation, AV fully recovered in most slices. Rates of blockade of fEPSPs were comparable in all slices, and most fEPSPs recovered fully after H1. But even in the presence of 10 mmol/L glucose, the second hypoxia suppressed fEPSPs irreversibly in some slices: 2 of 10 from control, 3 of 7 from mdx, and 1 of 6 from mdx3cv mice. Most slices in 4 mmol/L glucose showed no recovery at all: six of seven from control, three of five from mdx, and four of five from mdx3cv mice. Thus, slices from mdx mice were more susceptible than other slices to irreversible hypoxic failure when slices were kept in 10 mmol/L glucose, but they were less susceptible than other slices when kept in 4 mmol/L glucose. In conclusion, the lack of full-length dystrophin (427 kDa) predisposes to quicker loss of nerve conduction in slices from mdx and mdx3cv mutants and improved posthypoxic recovery of fEPSPs in 4 mmol/L glucose in slices from mdx but not mdx3cv mutants, perhaps because the 70-kDa and other C-terminal isoforms are still present in mdx mice.
7-Nitroindazole Impedes Erythrocyte Flow Response to Isovolemic Hemodilution in the Cerebral Capillary Circulation
Authors: Hudetz Antal G. , Wood James D. , Kampine John P.
Published: November 2003

The role of nitric oxide (NO) in the mechanism of hemodilution-induced cerebral hyperemia is unclear. Based on findings in hypoxemia, the authors hypothesize that NO of neuronal origin contributes to an increase in velocity of erythrocytes in the cerebral microcirculation during anemia produced by isovolemic hemodilution. The change in erythrocyte velocity in cerebrocortical capillaries was assessed by intravital fluorescence video microscopy. A closed cranial window was implanted over the frontoparietal cortex of barbiturate-anesthetized, ventilated adult rats. Erythrocytes were labeled in vitro with fluorescein isothiocyanate and infused intravenously, and their velocity in subsurface capillaries was measured by frame-to-frame image tracking. Arterial blood was withdrawn in increments of 2 mL and replaced by serum albumin; arterial blood pressure was maintained at control level with an infusion of methoxamine. Erythrocyte velocity increased progressively, reaching 215% of baseline, as arterial hematocrit was reduced from 45% to 17%. Pretreatment of a separate group of rats with 7-nitroindazole (20 mg/kg intraperitoneally), a relatively selective inhibitor of neuronal NO synthase, abolished the increase in velocity at hematocrits greater than 20%, but the maximum velocity attained at the lowest hematocrit was similar to that in the control group. The results suggest that NO from neuronal source may contribute to the increase in capillary erythrocyte flow during moderate isovolemic hemodilution.
Correlation between N-Acetylaspartate Levels and Histopathologic Changes in Cortical Infarcts of Mice after Middle Cerebral Artery Occlusion
Authors: Sager Thomas N. , Hansen Anker J. , Laursen Henning
Published: November 2003

The aim of the present study was to evaluate the use of the endogenous neuronal compound N-acetylaspartate (NAA) as a marker of neuronal damage after focal cerebral ischemia in mice. After occlusion of the middle cerebral artery (MCAO) the ischemic cortex was sampled, guided by 2,3,5-triphenyltetrazolium chloride (TTC) staining, and the NAA concentration was measured by high-pressure liquid chromatography (HPLC). Conventional histology and immunohistological methods using antibodies against neuron-specific enolase (NSE), neurofilaments (NF), synaptophysin, glial fibrillary acidic protein (GFAP), and carbodiamide-linked NAA and N-acetylaspartylglutamate (NAAG). The level of NAA rapidly declined to 50% and 20% of control levels in infarcted tissue after 6 hours and 24 hours, respectively. No further decrease was observed during the observation period of 1 week. Within the first 6 hours the number of normal-appearing neurons in the infarcted cortical tissue decreased to 70% of control, of which the majority were eosinophilic. After 24 hours almost no normal-appearing neurons were seen. The number of eosinophilic neurons decreased steadily to virtually zero after 7 days. The number of immunopositive cells in the NSE, NF, and synaptophysin staining within the infarct was progressively reduced, and after 3 to 7 days the immunoreactions were confined to discrete granulomatous structures in the center of the infarct, which otherwise was infested with macrophages. This granulomatous material also stained positive for NAA. The number of cells with positive GFAP immunoreactions progressively increased in the circumference of the infarct. They also showed increased immunoreaction against NAA and NSE. The study shows that the level of NAA 7 days after ischemia does not decline to zero but remains at 10% to 20% of control values. The fact NAA is trapped in cell debris and NAA immunoreactivity is observed in the peri-infarct areas restricts its use as a marker of neuronal density.
High-Resolution CMRO2 Mapping in Rat Cortex: A Multiparametric Approach to Calibration of BOLD Image Contrast at 7 Tesla
Authors: Kida Ikuhiro , Kennan Richard P. , Rothman Douglas L. , Behar Kevin L. , Hyder Fahmeed
Published: November 2003

The blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) method, which is sensitive to vascular paramagnetic deoxyhemoglobin, is dependent on regional values of cerebral metabolic rate of oxygen utilization (CMRO2), blood flow (CBF), and volume (CBV). Induced changes in deoxyhemoglobin function as an endogenous contrast agent, which in turn affects the transverse relaxation rates of tissue water that can be measured by gradient-echo and spin-echo sequences in BOLD fMRI. The purpose here was to define the quantitative relation between BOLD signal change and underlying physiologic parameters. To this end, magnetic resonance imaging and spectroscopy methods were used to measure CBF, CMRO2, CBV, and relaxation rates (with gradient-echo and spin-echo sequences) at 7 Tesla in rat sensorimotor cortex, where cerebral activity was altered pharmacologically within the autoregulatory range. The changes in tissue transverse relaxation rates were negatively and linearly correlated with changes in CBF, CMRO2, and CBV. The multiparametric measurements revealed that CBF and CMRO2 are the dominant physiologic parameters that modulate the BOLD fMRI signal, where the ratios of (ΔCMRO2/CMRO2)/(ΔCBF/CBF) and (ΔCBV/CBV)/(ΔCBF/CBF) were 0.86 ± 0.02 and 0.03 ± 0.02, respectively. The calibrated BOLD signals (spatial resolution of 48 μL) from gradient-echo and spin-echo sequences were used to predict changes in CMRO2 using measured changes in CBF, CBV, and transverse relaxation rates. The excellent agreement between measured and predicted values for changes in CMRO2 provides experimental support of the current theory of the BOLD phenomenon. In gradient-echo sequences, BOLD contrast is affected by reversible processes such as static inhomogeneities and slow diffusion, whereas in spin-echo sequences these effects are refocused and are mainly altered by extravascular spin diffusion. This study provides steps by which multiparametric MRI measurements can be used to obtain high-spatial resolution CMRO2 maps.
Validation and Reproducibility of Measurement of 5-HT1A Receptor Parameters with [carbonyl-11C]WAY-100635 in Humans: Comparison of Arterial and Reference Tissue Input Functions
Authors: Parsey Ramin V. , Slifstein Mark , Hwang Dah-Ren , Abi-Dargham Anissa , Simpson Norman , Mawlawi Osama , Guo Ning-Ning , Van Heertum Ronald , Mann J. John , Laruelle Marc
Published: November 2003

Serotonin 5-HT1A receptors are implicated in the pathophysiology of neuropsychiatric conditions. The goal of this study was to evaluate methods to derive 5-HT1A receptor parameters in the human brain with positron emission tomography (PET) and [ carbonyl-11C]WAY 100635. Five healthy volunteer subjects were studied twice. Three methods of analysis were used to derive the binding potential (BP), and the specific to nonspecific equilibrium partition coefficient (k3/k4). Two methods, kinetic analysis based on a three compartment model and graphical analysis, used the arterial plasma time-activity curves as the input function to derive BP and k3/k4. A third method, the simplified reference tissue model (SRTM), derived the input function from uptake data of a region of reference, the cerebellum, and provided only k3/k4. All methods provided estimates of regional 5-HT1A receptor parameters that were highly correlated. Results were consistent with the known distribution of 5-HT1A receptors in the human brain. Compared with kinetic BP, graphical analysis slightly underestimated BP, and this phenomenon was mostly apparent in small size-high noise regions. Compared with kinetic k3/k4, the reference tissue method underestimated k3/k4 and the underestimation was apparent primarily in regions with high receptor density. Derivation of BP by both kinetic and graphical analysis was highly reliable, with an intraclass correlation coefficient (ICC) of 0.84 ± 0.14 (mean ± SD of 15 regions) and 0.84 ± 0.19, respectively. In contrast, the reliability of k3/k4 was lower, with ICC of 0.53 ± 0.28, 0.47 ± 0.28, and 0.55 ± 0.29 for kinetic, graphical, and reference tissue methods, respectively. In conclusion, derivation of BP by kinetic analysis using the arterial plasma input function appeared as the method of choice because of its higher test—retest reproducibility, lower vulnerability to experimental noise, and absence of bias.
Cortical Neurogenesis in Adult Rats after Reversible Photothrombotic Stroke
Authors: Gu WeiGang , Brännström Thomas , Wester Per
Published: November 2003

Neurogenesis occurs throughout life in the dentate gyrus of hippocampus and subventricular zone, but this phenomenon has rarely been observed in other brain regions of adult mammals. The aim of the current study was to investigate the cell proliferation process in the ischemically challenged region-at-risk after focal cerebral ischemia in the adult rat brain. A reversible photothrombotic ring stroke model was used, which features sustained hypoperfusion followed by late spontaneous reperfusion and a remarkable morphologic tissue recovery in the anatomically well defined somatosensory cortical region-at-risk. Twelve-week-old male Wistar rats received repeated intraperitoneal injections of the cell proliferation specific marker 5-bromodeoxyuridine (BrdU) after stroke induction. Immunocytochemistry of coronal brain sections revealed that the majority of BrdU-positive cells were of glial, macrophage, and endothelial origin, whereas 3% to 6% of the BrdU-positive cells were double-labeled by BrdU and the neuron-specific marker Map-2 at 7 and 100 days after stroke onset in the region-at-risk. They were distributed randomly in cortical layers II-VI. Three-dimensional confocal analyses of BrdU and the neuronal-specific marker Neu N by double immunofluorescence confirmed their colocalization within the same cells at 72 hours and 30 days after stroke induction. This study suggests that, as a potential pathway for brain repair, new neurons can be generated in the cerebral cortex of adult rats after sublethal focal cerebral ischemia.
Quantitative Measurements of Cerebral Blood Oxygen Saturation Using Magnetic Resonance Imaging
Authors: An Hongyu , Lin Weili
Published: November 2003

A quantitative estimate of cerebral blood oxygen saturation is of critical importance in the investigation of cerebrovascular disease because of the fact that it could potentially provide information on tissue viability in vivo. In the current study, a multi-echo gradient and spin echo magnetic resonance imaging sequence was used to acquire images from eight normal volunteer subjects. All images were acquired on a Siemens 1.5T Symphony whole-body scanner (Siemens, Erlangen, Germany). A theoretical signal model, which describes the signal dephasing phenomena in the presence of deoxyhemoglobin, was used for postprocessing of the acquired images and obtaining a quantitative measurement of cerebral blood oxygen saturation in vivo. With a region-of-interest analysis, a mean cerebral blood oxygen saturation of 58.4% ± 1.8% was obtained in the brain parenchyma from all volunteers. It is in excellent agreement with the known cerebral blood oxygen saturation under normal physiologic conditions in humans. Although further studies are needed to overcome some of the confounding factors affecting the estimates of cerebral blood oxygen saturation, these preliminary results are encouraging and should open a new avenue for the noninvasive investigation of cerebral oxygen metabolism under different pathophysiologic conditions using a magnetic resonance imaging approach.
Human Brain β-Hydroxybutyrate and Lactate Increase in Fasting-Induced Ketosis
Authors: Pan Jullie W. , Rothman Douglas L. , Behar Kevin L. , Stein Daniel T. , Hetherington Hoby P.
Published: November 2003

Ketones are known to constitute an important fraction of fuel for consumption by the brain, with brain ketone content generally thought to be low. However, the recent observation of 1-mmol/L levels of brain β-hydroxybutyrate (BHB) in children on the ketogenic diet suggests otherwise. The authors report the measurement of brain BHB and lactate in the occipital lobe of healthy adults using high field (4-T) magnetic resonance spectroscopy, measured in the nonfasted state and after 2-and 3-day fasting-induced ketosis. A 9-mL voxel located in the calcarine fissure was studied, detecting the BHB and lactate upfield resonances using a 1H homonuclear editing sequence. Plasma BHB levels also were measured. The mean brain BHB concentration increased from a nonfasted level of 0.05 ± 0.05 to 0.60 ± 0.26 mmol/L (after second day of fasting), increasing further to 0.98 ± 0.16 mmol/L (after the third day of fasting). The mean nonfasted brain lactate was 0.69 ± 0.17 mmol/L, increasing to 1.47 ± 0.22 mmol/L after the third day. The plasma and brain BHB levels correlated well ( r = 0.86) with a brain–plasma slope of 0.26. These data show that brain BHB rises significantly with 2-and 3-day fasting-induced ketosis. The lactate increase likely results from ketones displacing lactate oxidation without altering glucose phosphorylation and glycolysis.
Acetylcholinesterase Inhibition Increases in VivoN-(2-[18F]Fluoroethyl)-4-piperidyl Benzilate Binding to Muscarinic Acetylcholine Receptors
Authors: Skaddan Marc B. , Kilbourn Michael R. , Snyder Scott E. , Sherman Phil S.
Published: November 2003

Although the inhibition of acetylcholinesterase remains the primary treatment of Alzheimer's disease, little is known of the results of increased acetylcholine levels on muscarinic receptor occupancy or function. Using N-(2-[18F]fluoroethyl)-4-piperidyl benzilate ([18F]FEPB), a moderate affinity (Ki = 1.7 nmol/L) nonsubtype-selective muscarinic receptor antagonist, the authors examined the sensitivity of equilibrium in vivo radioligand binding in rat brain with changes in endogenous acetylcholine levels produced by treatments with acetylcholinesterase inhibitors. Phenserine administration 30 minutes before resulted in a dose-dependent increase in N-(2-[18F]fluoroethyl)-4-piperidyl benzilate binding to muscarinic cholinergic receptors, reaching a maximum increase of 90% in the striatum at a dose of 5 mg/kg intraperitoneally. Constant infusion of physostigmine at a dosage of 250 μg/kg/min produced an identical increase in radioligand binding. This agonist-induced increase of in vivo mAChR radioligand binding offers a new method for monitoring of the efficacy of acetylcholinesterase inhibitors or other drugs to enhance acetylcholine actions at the muscarinic receptors.
Activation of Akt/Protein Kinase B Contributes to Induction of Ischemic Tolerance in the CA1 Subfield of Gerbil Hippocampus
Authors: Yano Shigetoshi , Morioka Motohiro , Fukunaga Kohji , Kawano Takayuki , Hara Tsuyoshi , Kai Yutaka , Hamada Jun-ichiro , Miyamoto Eishichi , Ushio Yukitaka
Published: November 2003

Apoptosis plays an important role in delayed neuronal cell death after cerebral ischemia. Activation of Akt/protein kinase B has been recently reported to prevent apoptosis in several cell types. In this article the authors examine whether induction of ischemic tolerance resulting from a sublethal ischemic insult requires Akt activation. Sublethal ischemia gradually and persistently stimulated phosphorylation of Akt-Ser-473 in the hippocampal CA1 region after reperfusion. After lethal ischemia, phosphorylation of Akt-Ser-473 showed no obvious decrease in preconditioned gerbils but a marked decrease in nonconditioned gerbils. Changes in Akt-Ser-473 phosphorylation were correlated with changes in Akt activities, as measured by an in vitro kinase assay. Intracerebral ventricular infusion of wortmannin before preconditioning blocked both the increase in Akt-Ser-473 phosphorylation in a dose-dependent manner and the neuroprotective action of preconditioning. These results suggest that Akt activation is induced by a sublethal ischemic insult in gerbil hippocampus and contributes to neuroprotective ischemic tolerance in CA1 pyramidal neurons.
Ionic Mechanisms of Aglycemic Axon Injury in Mammalian Central White Matter
Authors: Brown Angus M. , Wender Regina , Ransom Bruce R.
Published: November 2003

The authors investigated ionic mechanisms underlying aglycemic axon injury in adult rat optic nerve, a central white matter tract. Axon function was assessed using evoked compound action potentials (CAPs). Glucose withdrawal led to delayed CAP failure, an alkaline extracellular pH shift, and an increase in extracellular [K+]. Sixty minutes of glucose withdrawal led to irreversible axon injury. Aglycemic axon injury required extracellular calcium; the extent of injury progressively declined as bath [Ca2+] was decreased. To evaluate Ca2+ movements during aglycemia, the authors recorded extracellular [Ca2+] ([Ca2+]o) using Ca2+-sensitive microelectrodes. Under control conditions, [Ca2+]o fell with a similar time course to CAP failure, indicating extracellular Ca2+ moved to an intracellular position during aglycemia. The authors quantified the magnitude of [Ca2+]o decrease as the area below baseline [Ca2+]o during aglycemia and used this as a qualitative measure of Ca2+ influx. The authors studied the mechanisms of Ca2+ influx. Blockade of Na+ influx reduced Ca2+ influx and improved CAP recovery, suggesting Na+-Ca2+ exchanger involvement. Consistent with this hypothesis, bepridil reduced axon injury. In addition, diltiazem or nifedipine decreased Ca2+ influx and increased CAP recovery. The authors conclude aglycemic central white matter injury is caused by Ca2+ influx into intracellular compartments through reverse Na+-Ca2+ exchange and L-type Ca2+ channels.
Astrocytes as a Predominant Cellular Site of 99mTc-HMPAO Retention
Authors: Zerarka Sabrina , Pellerin Luc , Slosman Daniel , Magistretti Pierre J.
Published: November 2003

Technetium-99m-d,l-hexamethylpropylene amine oxime (99mTc-HMPAO) retention in the brain monitored by single photon emission computed tomography (SPECT) is currently used as a marker of cerebral blood flow. The purported mechanism by which 99mTc-HMPAO accumulates in the brain is through its intracellular conversion from a lipophilic form to more hydrophilic derivatives within the brain parenchyma. The issue of the contribution of different cell types on 99mTc-HMPAO retention was investigated in vitro by studying the accumulation of 99mTc-HMPAO in primary cultures of mouse cortical astrocytes and neurons. Results show that 99mTc-HMPAO retention predominates in astrocytes over neurons by a factor of ∼2.5 (0.26 ± 0.05 vs. 0.095 ± 0.042 fmol/mg protein after 120 minutes, respectively). Diethyl maleate (60 μmol/L), ethacrynic acid (1 mmol/L) and buthionine sulfoximine (1 mmol/L), 3 agents which significantly reduced glutathione levels also decreased 99mTc-HMPAO retention in both astrocytes (29%, 3%, and 46% of control, respectively) and neurons (69%, 11% and 63% of control). Decrease did not always correlate with glutathione levels, however, which suggests that other factors could be involved. The possibility that cell energy status determines 99mTc-HMPAO retention was also assessed. Agents that activate (glutamate, azide) or inhibit (cytochalasin B) glucose utilization in astrocytes, as measured by the 3H-2-deoxyglucose method, were without effect on 99mTc-HMPAO retention. In conclusion, the data presented indicate that astrocytes may constitute a prominent site of 99mTc-HMPAO retention and most likely contribute significantly to the SPECT signal. In addition, the data also suggest that specific alterations in glial cell metabolism could explain flow-independent changes in 99mTc-HMPAO retention in the brain as observed by SPECT in some pathologies.
A Reversible Tracer Analysis Approach to the Study of Effective Dopamine Turnover
Authors: Sossi Vesna , Doudet Doris J. , Holden James E.
Published: November 2003

Changes in dopamine turnover resulting from disease states such as Parkinson's disease may be reflected in corresponding changes in the kinetics of the positron emission tomographic tracer [18F]fluorodopa. The authors had previously refined the conventional irreversible-tracer graphical approach to determine both the uptake rate constant Ki and the rate constant kloss that describes the slow loss of the trapped kinetic component. Because these parameters change in the opposite sense with disease, their ratios may be more powerfully discriminating than either one alone. The ratio kloss/Ki is indicative of effective dopamine turnover. Its inverse, Ki/kloss, can be interpreted as the effective distribution volume (EDV) of the specific uptake compartment referred to the fluorodopa concentration in plasma. Here the authors present a new approach to the estimation of EDV based on reversible-tracer graphical methods. When implemented with a plasma input function, the method evaluates EDV directly. When implemented with a tissue input function, the outcome is proportional to the ratio of the distribution volumes of the specific uptake and precursor compartments. Comparison of the new and previous approaches strongly validates this alternative approach to the study of effective dopamine turnover.
Proteolysis of Oxidized Proteins after Oxygen–Glucose Deprivation in Rat Cortical Neurons is Mediated by the Proteasome
Authors: Weih Markus , Schmitt Marion , Gieche Janette , Harms Christoph , Ruscher Karsten , Dirnagl Ulrich , Grune Tilman
Published: November 2003

Oxidative injury contributes to cellular damage during and after cerebral ischemia. However, the downstream catabolic pathways of damaged cellular components in neurons are largely unknown. In the current study, the authors examined the formation of oxidized proteins and their active degradation by the proteasome. In near-pure rat primary cortical neurons, it was found that protein-bound carbonyls as markers for oxidized proteins are increased after oxygen-glucose deprivation (OGD). During and after OGD, degradation of proteins metabolically radiolabeled before OGD increases two-to threefold compared with the normal protein turnover. Proteolysis after reoxygenation was attenuated by the presence of dimethylthiourea, a radical scavenger, and was blocked by lactacystin, a specific proteasome inhibitor. Lactacystin also increased the amount of protein carbonyls formed. In contrast, the activity of the proteasome complex itself after OGD was not different from sham-washed controls. The authors suggest that oxygen-glucose deprivation increases free radicals, which, in turn, oxidize proteins that are recognized and actively degraded by the proteasome complex. This protease itself is relatively resistant against oxidative injury. The authors conclude that the proteasome may be an active part of the cellular defense system against oxidative stress after cerebral ischemia.
Administration of Transforming Growth Factor-α Reduces Infarct Volume after Transient Focal Cerebral Ischemia in the Rat
Authors: Justicia Carles , Pérez-Asensio Fernando J. , Burguete María C. , Salom Juan B. , Planas Anna M.
Published: November 2003

Growth factors promote cell growth and survival and protect the brain from developing injury after ischemia. In this article, the authors examined whether transforming growth factor-α (TGF-α) was protective in transient focal ischemia and whether alteration of cerebral circulation was involved. Rats received intraventricular TGF-α (50 ng, either split into 2 doses given 30 minutes before and 30 minutes after middle cerebral artery occlusion (MCAO), or 1 dose given 30 minutes after MCAO) or vehicle. Rats were subjected to 1-hour intraluminal MCAO and cerebral blood flow was recorded continuously by laser–Doppler flowmetry. Infarct volume was measured 1 and 4 days later. The effects of TGF-α on arterial tone were assessed in isolated rabbit basilar and common carotid arteries. Transforming growth factor-α before and after ischemia reduced infarct volume by 70% at 1 day and 50% at 4 days. Transforming growth factor-α given only after ischemia also did reduce infarct volume by 70% at 1 day and 80% at 4 days. The protective effect was more marked in cortex than in striatum. Transforming growth factor-α did not change cortical microvascular perfusion and did not modify arterial passive tone nor agonist-induced active tone. It can be concluded that TGF-α reduces infarct volume, even when the factor is exclusively administered at reperfusion, and that this effect is not mediated by changes in microvascular perfusion or cerebral arteries. It is therefore suggested that TGF-α has a protective effect against neuronal cell death after transient focal ischemia.