bluuebunny/crossref_metadata_2025 huggingface dataset:
Microvessels Isolated from Brain: Localization of Muscarinic Sites by Radioligand Binding and Immunofluorescent Techniques
Authors: Moro Véronique , Kacem Kamel , Springhetti Véronique , Seylaz Jacques , Lasbennes François
Published: April 2011

The present investigation was carried out to determine the extent to which muscarinic acetylcholine receptors (mAChRs) in vascular and perivascular structures were colocalized with glial fibrillary acidic protein (GFAP)–positive structures. To this aim, an immunocytochemical approach on free-floating cryosections and isolated microvessels obtained from rat brain was performed to study the possible colocalization of immunostaining with the anti-mAChR protein antibody (M35) and an anti-GFAP antibody. Double-labeling experiments were carried out by fluorescent techniques. Confocal microscopic observations of GFAP and M35 immunoreactivities on free-floating sections showed a high degree of colocalization on astrocyte processes associated with large vessels or capillaries. This pattern suggests that muscarinic receptors are associated with astrocytic endfeet. Confocal microscopic observations of immunoreactivity from isolated cerebral microvessels strengthen this conclusion since double-labeling of M35 and GFAP showed that perivascular astrocytic structures remained attached to the isolated microvessels and were present on vascular segments showing M35 immunoreactivity. In another set of experiments, the specific binding of [3H]quinuclidinylbenzylate ([3H]QNB) to isolated microvessel membrane preparations from cerebral cortex, caudate nucleus, thalamus, and cerebellum showed that a constant binding yield (20% in bovine and 40% in rat) was observed for microvessels compared with the corresponding brain region. According to our immunocytochemical results, the astrocytic membrane remaining attached to microvessels may account for the majority of the muscarinic binding to isolated microvessels. [3H]QNB binding values found in isolated microvessels cannot therefore be considered as artifacts without any link with vascular function. Taken together, the present study strengthens the idea that the muscarinic receptors may be implicated in the functional relationship between glial and vascular structures.
Age Dependency of Changes in Cerebral Hemoglobin Oxygenation during Brain Activation: A Near-Infrared Spectroscopy Study
Authors: Hock Christoph , Müller-Spahn Franz , Schuh-Hofer Sigrid , Hofmann Marc , Dirnagl Ulrich , Villringer Arno
Published: April 2011

We used near-infrared spectroscopy (NIRS) to study noninvasively the influence of aging on changes in the local concentration of oxygenated hemoglobin ([HbO2]), reduced hemoglobin ([HbR]), and total hemoglobin ([HbT] = [HbR] + [HbO2]) during activation of brain function. Young subjects ( n = 12; age, 28 ± 4 years) performing calculation tasks showed an increase in [HbO2] [mean (arbitrary units) ± SD, 2.36 ± 1.07] and [HbT] (2.24 ± 1.13) in the frontal cortex, while [HbR] (−0.11 ± 0.48) decreased. Elderly subjects ( n = 17; age, 52 ± 10 years) showed a significantly lower mean increase ( p < 0.05) in [HbO2] and [HbT] levels (1.21 ± 1.38 and 0.72 ± 1.41, respectively). Regression analysis supports the hypothesis of an age-dependent decline in the activation-induced local increase in [HbO2] ( y = −0.241 x + 20.062; r = −0.431, p < 0.05) as well as [HbT] ( y = −0.346x + 22.496; r = −0.568, p < 0.05). We conclude that NIRS is a promising approach for studying changes in Hb oxygenation during brain activation in physiological aging.
Stimulus Parameters Influence Characteristics of Optical Intrinsic Signal Responses in Somatosensory Cortex
Authors: Blood Anne J. , Narayan Sanjiv M. , Toga Arthur W.
Published: April 2011

Optical imaging of intrinsic signals was performed in the barrel cortex of the rat during whisker deflections of varying frequencies (1 to 20 Hz) and durations (0.1 to 5 s). A dose–response relationship was shown between these stimuli and the characteristics of the optically recorded intrinsic signal response. At constant frequencies, longer stimulus durations increased response magnitude, as defined by mean pixel value in statistically determined regions of interest. At constant durations, higher stimulus frequencies increased response magnitude. Response magnitude was also increased by greater numbers of deflections. When stimulus number was constant, there were no differences in response magnitude, regardless of stimulus frequency and duration. Spatial extent of responses, as defined by number of pixels in regions of interest, did not differ between stimulus frequencies, durations, or numbers. Comparison of the time to reach peak intrinsic signal response after stimulus onset (“time-to-peak”) suggested that higher frequencies were associated with faster time-to-peak. Registration of intrinsic signal responses with cytochrome oxidase-stained whisker barrels demonstrated that responses were located over the barrel corresponding to the stimulated whisker. In summary, we have shown that the absolute number of stimuli delivered to the system is, at least for short stimulus periods (≤5 s), a determining factor for the magnitude of these responses, whereas stimulus frequency appears to influence time-to-peak response.
Increased F1/GAP-43 mRNA Accumulation in Gerbil Hippocampus after Brain Ischemia
Authors: Tagaya Masafumi , Matsuyama Tomohiro , Nakamura Hitoshi , Hata Ryuji , Shimizu Souichiro , Kiyama Hiroshi , Matsumoto Masayasu , Sugita Minoru
Published: April 2011

To assess whether ischemia could induce GAP-43 mRNA expression, we performed in situ hybridization in gerbil brains that had been subjected to 5 min of global ischemia. In control dentate granule cells, little hybridization was detected in contrast to the intense signal generated by pyramidal neurons of the adult hippocampal formation. After ischemia, we detected a robust GAP-43 signal over hippocampal granule cells at 3 h of reperfusion, persisting through 7 days, and disappearing by 14 days. This demonstrated GAP-43 gene induction after ischemia, and suggests that GAP-43 may be involved in reactive events, including fiber sprouting and synaptic reorganization, that follow ischemia.
Adaptive Preservation of ATP and Tolerance to Hypoxia following Carotid Artery Ligation in the Immature Rat
Authors: Hylton Camille M. , Pesenson Michael A. , Welsh Frank A.
Published: April 2011

To investigate the adaptive mechanisms following carotid artery ligation in immature rats, histologic injury and tissue levels of ATP were compared after exposure to identical episodes of hypoxia induced either 3 or 24 h postligation. Histologic injury, assessed in both 9-day- and 23-day-postnatal animals after survival for 1 week, was markedly diminished in animals exposed to hypoxia 24 h postligation compared to that in animals exposed to hypoxia 3 h postligation. In 9-day-postnatal animals, ATP levels in the cerebral cortex ipsilateral to the ligation were depleted during hypoxia to 0.39 ± 0.49 mmol/kg (mean ± SD; N = 15) in animals exposed to hypoxia 3 h postligation but were maintained at 2.04 ± 0.26 mmol/g ( N = 18; p < 0.001) in animals exposed to hypoxia 24 h postligation. Thus, preservation of ATP may account for the diminution of cellular injury that results from delaying the onset of hypoxia from 3 to 24 h after carotid artery ligation in immature rats.
Hypoxia-Induced Electrical Changes in Striatal Neurons
Authors: Calabresi Paolo , Pisani Antonio , Mercuri Nicola B. , Bernardi Giorgio
Published: April 2011

We have studied the effects of hypoxia on the membrane properties of striatal neurons intracellularly recorded from a corticostriatal slice preparation. Brief (2–10 min) periods of hypoxia produced reversible membrane depolarizations. Longer periods of hypoxia (12–20 min) produced irreversible membrane depolarizations. In voltage-clamp experiments, hypoxia caused an inward current coupled with an increased membrane conductance. Tetrodotoxin or low calcium (Ca2+)-high magnesium-containing solutions blocked synaptic transmission, but they did not reduce the hypoxia-induced electrical changes. Antagonists of excitatory amino acid (EAA) receptors failed to affect the electrical effects caused by oxygen (O2) deprivation. In low sodium (Na+)-containing solutions the hypoxia-induced inward current was largely reduced. Blockade of ATP-dependent Na+-potassium (K+) pump by ouabain enhanced hypoxia-induced membrane depolarizations and/or inward currents. Our findings indicate that, at least for in vitro experiments, the release of EAAs is not required for the acute hypoxia-induced electrical changes in striatal neurons.
The Role of Angiotensin II in the Regulation of Blood Flow to Choroid Plexuses and Cerebrospinal Fluid Formation in the Rat
Authors: Chodobski Adam , Szmydynger-Chodobska Joanna , Epstein Mel H. , Johanson Conrad E.
Published: April 2011

The effect of peripherally administered angiotensin II (AII) on blood flow to choroid plexuses was examined in pentobarbital-anesthetized rats. The indicator fractionation method with 123I- or 125I- N-isopropyl- p-iodoamphetamine as the marker was employed to measure blood flow. Basal blood flow to choroid plexus of the lateral cerebral ventricle (LVCP) (3.19 ± 0.23 ml g−1 min−1) was lower than that to choroid plexuses of the third (3VCP) and fourth (4VCP) ventricles (3.90 ± 0.38 and 3.95 ± 0.36 ml g−1 min−1, respectively). The effect of AII on choroidal blood flow varied depending on peptide dose and anatomical location of the choroidal tissue. AII infused intravenously at rates of 30 and 50 ng kg−1 min−1 decreased blood flow to both LVCP and 4VCP by 12–20%. Both lower (10 ng kg−1 min−1) and higher (100 and 300 ng kg−1 min−1) AII doses did not alter blood flow to LVCP and 4VCP. Blood flow to the 3VCP was not affected by any dose of the peptide used. In comparison, blood flow to cerebral cortex increased by 33% during intravenous AII infusion at a rate of 300 ng kg−1 min−1. The choroidal blood flow-lowering effect of moderate AII doses was abolished by both AT1 (losartan) and AT2 (PD 123319) receptor subtype antagonists (3 mg kg−1 i.v.). To determine whether the hemodynamic changes observed in choroid plexuses with moderate AII doses influence CSF formation, the ventriculocisternal perfusion was performed in rats (under the experimental conditions described) with Blue Dextran 2000 as the indicator. CSF production was not altered during intravenous infusion of AII at a rate of 30 ng kg−1 min−1. It is suggested that CSF formation is maintained in pathophysiological situations accompanied by increased plasma AII levels, which implicates a potential role for AII in regulating ion and water balance in the CNS.
Expression of Interleukin-6, c-Fos, and zif268 mRNAs in Rat Ischemic Cortex
Authors: Wang Xinkang , Yue Tian-Li , Young Peter R. , Barone Frank C. , Feuerstein Giora Z.
Published: April 2011

The expression of interleukin-6 (IL-6) mRNA in the focal ischemic rat cortex was studied by means of Northern hybridization. IL-6 mRNA was induced after permanent occlusion of the middle cerebral artery, reached a significant level at 3 h, and peaked at 12 h, i.e., ∼ 10-fold increase in the ischemic zone compared with the nonischemic cortex or sham-operated controls. The increased IL-6 mRNA was elevated for at least 24 h. Low levels of IL-6 mRNA were detected in sham-operated rats or in the contralateral nonischemic cortex. The expression of c- fos and zif268 mRNAs, two early response genes, was rapid (increased by 1 h postischemia) and transient (returned to basal levels by 24 and 12 h, respectively), clearly having different kinetic patterns from that of IL-6 mRNA. The early response kinetic pattern of c- fos and zif268 mRNAs in focal ischemia suggests their transcriptional regulatory roles in response to ischemic insult, while the delayed induction pattern of IL-6 mRNA suggests a role for this pleiotropic cytokine in the inflammatory response to the focal ischemic damage of the brain.
Simultaneous Determination of the Rates of the TCA Cycle, Glucose Utilization, α-Ketoglutarate/Glutamate Exchange, and Glutamine Synthesis in Human Brain by NMR
Authors: Mason Graeme F. , Gruetter Rolf , Rothman Douglas L. , Behar Kevin L. , Shulman Robert G. , Novotny Edward J.
Published: April 2011

13C isotopic tracer data previously obtained by 13C nuclear magnetic resonance in the human brain in vivo were analyzed using a mathematical model to determine metabolic rates in a region of the human neocortex. The tricarboxylic acid (TCA) cycle rate was 0.73 ± 0.19 μmol min−1 g−1 (mean ± SD; n = 4). The standard deviation reflects primarily intersubject variation, since individual uncertainties were low. The rate of α-ketoglutarate/glutamate exchange was 57 ± 26 μmol min−1 g−1 ( n = 3), which is much greater than the TCA cycle rate; the high rate indicates that α-ketoglutarate and glutamate are in rapid exchange and can be treated as a single combined kinetic pool. The rate of synthesis of glutamine from glutamate was 0.47 μmol min−1 g−1 ( n = 4), with 95% confidence limits of 0.139 and 3.094 μmol min−1 g−1; individual uncertainties were biased heavily toward high synthesis rates. From the TCA cycle rate the brain oxygen consumption was estimated to be 2.14 ± 0.48 μmol min−1 g−1 (5.07 ± 1.14 ml 100 g−1 min−1; n = 4), and the rate of brain glucose consumption was calculated to be 0.37 ± 0.08 μmol min−1 g−1 ( n = 4). The sensitivity of the model to the assumptions made was evaluated, and the calculated values were found to be unchanged as long as the assumptions remained near reported physiological values.
Cerebral Blood Flow and Glucose Metabolism of the Ischemic Rim in Spontaneously Hypertensive Stroke-Prone Rats with Occlusion of the Middle Cerebral Artery
Authors: Kita Hideyuki , Shima Katsuji , Tatsumi Miwako , Chigasaki Hiroo
Published: April 2011

To determine acute postischemic metabolic changes of the ischemic rim under conditions of poor collateral circulation, we examined cerebral blood flow and glucose metabolism in the area of the brain around the ischemic tissue in 36 male spontaneously hypertensive stroke-prone rats (SHRSP) in the acute stage of focal ischemia. The right middle cerebral artery (MCA) was occluded dorsal to the rhinal fissure. Four hours after occlusion, local cerebral blood flow (LCBF), glucose content (LCGC), and glucose utilization (LCGU) were measured by quantitative autoradiographic techniques. The lumped constant was determined from the corresponding LCGC. LCBF showed a widespread and marked decrease in the cortex surrounding the ischemic core, in the thalamus, and in the medial portion of the striatum in the MCA-occluded hemisphere, while the lateral segment of the striatum showed an increase of 36%, compared with findings on the contralateral side. LCGC showed little regional variation, but there was an increase of 38% in the zone bordering the ischemic area. LCGU at the cortex surrounding the ischemic core and in the external capsule showed an increase of 55%. The cortex surrounding the ischemic core, the thalamus, and the lateral segment of the striatum in the MCA-occluded hemisphere showed significant decreases in LCGU. It has been speculated that a high accumulation of glucose reflects a demand for glucose for anaerobic glycolysis in the border areas and that such a demand is probably greater in cases of impaired oxygen delivery due to the presence of microcirculatory disturbances in the MCA-occluded SHRSP. The enhancement of glucose consumption may reflect anaerobic glycolysis. Because the hypermetabolic band was present in the cortex and the white matter, hypermetabolism of the white matter may be related to the glial cell.
Mapping of Cerebral Blood Flow Changes during Audiogenic Seizures in Wistar Rats: Effect of Kindling
Authors: Nehlig Astrid , Vergnes Marguerite , Hirsch Edouard , Boyet Sylvette , Koziel Violette , Marescaux Christian
Published: April 2011

The quantitative autoradiographic [14C]iodoantipyrine technique was applied to the measurement of rates of local cerebral blood flow (LCBF) during audiogenic seizures in Wistar AS rats belonging to a genetic strain selected at the Centre de Neurochimie (Strasbourg, France) for their sensitivity to sound. Seizures were elicited in naive rats never exposed to sound (single audiogenic seizures) or in rats previously exposed to 10–40 seizure-inducing sound stimulations until generalization of the seizure to forebrain areas (referred to as “kindled animals”). During single audiogenic seizures, rates of LCBF increased over control values in all areas but the genu of the corpus callosum. The highest increases in LCBF (180–388%) were recorded in the inferior and superior colliculus, reticular formation, monoaminergic cell groupings, especially the substantia nigra, posterior vegetative nuclei, and many thalamic and hypothalamic regions. The lowest increases were seen in forebrain limbic regions and cortical areas. In kindled animals, LCBF rates increased over control levels in 67 areas of the 75 studied. LCBF increases were generally of a lower amplitude in kindled than in naive rats. Differences between the two groups of seizing rats were located mostly in brain-stem regions, mainly the inferior colliculus, reticular formation, substantia nigra, and posterior vegetative nuclei. Conversely, rates of LCBF were similar in forebrain areas of naive and kindled animals. In conclusion, the present data show that there is a good correlation between the structures known to be involved in the expression of audiogenic seizures (inferior colliculus, reticular formation, substantia nigra mainly) and the large increase in LCBF during single audiogenic seizures, while rates of LCBF increase to a lesser extent in forebrain areas not involved in this type of seizures. The circulatory adaptation to kindled seizures is rather a decreased response in brain-stem regions and no change in the forebrain, although the kindling process induces a generalization of the seizure from brain-stem to anterior regions.
Quantification of Benzodiazepine Receptors in Human Brain Using PET, [11C]Flumazenil, and a Single-Experiment Protocol
Authors: Delforge Jacques , Pappata Sabina , Millet Philippe , Samson Yves , Bendriem Bernard , Jobert Antoinette , Crouzel Christian , Syrota André
Published: April 2011

A kinetic method using a multiinjection protocol, positron emission tomography (PET), and [11C]flumazenil as a specific ligand was used to study in vivo the flumazenil-benzodiazepine receptor interactions in the human brain. The model structure is composed of three compartments (plasma, free, and bound ligand) and five parameters (including the benzodiazepine receptor concentration). The arterial plasma concentration, after correction for metabolites, was used as the input function. The experimental protocol, which consisted of three injections of labeled and/or unlabeled ligand, allowed the evaluation of the five model parameters in various brain regions from a single experiment. In particular, the concentration of receptor sites available for binding ( B′max) and the equilibrium dissociation constant ( KD VK, VR being the volume of reaction) were estimated in five brain regions, including the pons, in which these parameters are identified for the first time ( B′max = 4.7 ± 1.7 pmol/ml and KD VR = 4.4 ± 1.3 pmol/ml). Due to the large range of measured receptor concentrations, a linear correlation between B′max and KD VR was pointed out ( r = 0.88, p < 0.0005) and was interpreted as a linear relationship between B′max and VR, the parameter KD being assumed constant. This result and its concordance with the published data are discussed. Simulation of the usual two-experiment Scatchard analysis, using the pons as a reference region, showed that the bias on the receptor concentration estimates introduced by this method is significant (from 20 to 40%) but can be corrected using an estimate of the receptor concentration in the pons. Furthermore, we propose a new experimental protocol, based on a Scatchard analysis of the PET data obtained with a partial-saturation experiment. This single-injection protocol is entirely noninvasive, and thus the estimation of the benzodiazepine receptor concentration and of the flumazenil affinity is now possible in human patients using a single 1-h experiment without blood sampling.
The Neuroprotective Effect of the Novel Noncompetitive NMDA Antagonist, FR115427 in Focal Cerebral Ischemia in Rats
Authors: Katsuta Kiyotaka , Nakanishi Hajime , Shirakawa Kiyoharu , Yoshida Keizo , Takagi Kiyoshi , Tamura Akira
Published: April 2011

The present study was carried out to compare the neuroprotective effect of the novel noncompetitive NMDA antagonist, FR115427, with that of (+)MK-801 in rat focal cerebral ischemia. Focal cerebral ischemia was produced by permanent occlusion of the left middle cerebral artery (MCA). Drugs were administered intraperitoneally immediately after ischemia and once a day for 6 successive days. FR115427 (10 mg/kg, i.p.) significantly improved neurologic deficit at 1 day after ischemia and reduced total infarct volume (54%) at 7 days after ischemia. Although FR115427 (10 mg/kg, s.c.) produced neuronal vacuolization similar to (+)MK-801, FR115427 did not produce adverse effects such as a loss of body weight, mortality, and hypothermia, in contrast to (+)MK-801. These results suggest that FR115427 may be useful in the treatment of stroke.
Marked Induction of Calcium-Independent Nitric Oxide Synthase Activity after Focal Cerebral Ischemia
Authors: Iadecola Costantino , Xu Xiaohong , Zhang Fangyi , El-Fakahany Esam E. , Ross M. Elizabeth
Published: April 2011

We studied the effect of focal cerebral ischemia on inducible (iNOS) and constitutive (cNOS) nitric oxide synthase enzymatic activities in the affected brain. The middle cerebral artery (MCA) was occluded in spontaneously hypertensive rats. Animals were killed 1, 2, 4, and 7 days later. cNOS and iNOS enzymatic activities were determined in the infarcted cortex using the assay of Bredt and Snyder. cNOS was assayed in the presence of calcium, whereas iNOS was assayed in the absence of calcium and in the presence of tetrahydrobiopterin. The validity of the iNOS assay was verified in rats treated with bacterial lipopolysaccharide. In these animals, the magnitude of the induction of iNOS enzymatic activity in lung, spleen, and brain paralleled the expression of iNOS mRNA, assessed by reverse-transcription polymerase chain reaction. After MCA occlusion, calcium-dependent (cNOS) activity was markedly reduced only in lesioned cerebral cortex at days 1–7 ( p < 0.001; analysis of variance and Tukey's test). In contrast to cNOS, calcium-independent (iNOS) activity was induced substantially in the infarct ( p < 0.005) but not in the contralateral intact cortex ( p > 0.05). iNOS activity peaked at day 2 and was not different from baseline at day 7 ( p > 0.05). No NADPH diaphorase-positive neurons were observed in the area of the lesion at days 1–7. Macrophages appeared at day 2 and invaded the infarcted tissue by day 7. At this time, numerous glial fibrillary acidic protein-positive astrocytes were observed within the lesion. The results suggest that the decline in calcium-dependent (cNOS) activity reflects loss of NOS neurons within the lesion. The induction of calcium-independent activity is likely to reflect induction of iNOS in nonneuronal cells. Sustained nitric oxide production by iNOS may contribute to the late phase of tissue damage in focal cerebral ischemia.
Persistent Resetting of the Cerebral Oxygen/Glucose Uptake Ratio by Brain Activation: Evidence Obtained with the Kety—Schmidt Technique
Authors: Madsen Peter Lund , Hasselbalch Steen G. , Hagemann Lars P. , Olsen Karsten Skovgaard , Bülow Jens , Holm Søren , Wildschiødtz Gordon , Paulson Olaf B. , Lassen Niels A.
Published: April 2011

Global cerebral blood flow (CBF), global cerebral metabolic rates for oxygen (CMRO2), and for glucose (CMRglc), and lactate efflux were measured during rest and during cerebral activation induced by the Wisconsin card sorting test. Measurements were performed in healthy volunteers using the Kety–Schmidt technique. Global CMRO2 was unchanged during cerebral activation, whereas global CBF and global CMRglc both increased by 12%, reducing the molar ratio of oxygen to glucose consumption from 6.0 during baseline conditions to 5.4 during activation. Data obtained in the period following cerebral activation showed that the activation-induced resetting of the relation between CMRglc and CMRO2 persisted virtually unaltered for ≥40 min after the mental activation task was terminated. The activation-induced increase in cerebral lactate efflux measured over the same time period accounted for only a small fraction of the activation-induced excess glucose uptake. These data confirm earlier reports that brain activation can induce resetting of the cerebral oxygen/glucose consumption ratio, and indicate that the resetting persists for a long period after cerebral activation has been terminated and physiologic stress indicators returned to baseline values. Activation-induced resetting of the cerebral oxygen/glucose uptake ratio is not necessarily accounted for by increased lactate production from nonoxidative glucose metabolism.
A Simple Method for Evaluation of Superoxide Radical Production in Neural Cells under Various Culture Conditions: Application to Hypoxia
Authors: Daval Jean-Luc , Ghersi-Egea Jean-François , Oillet Jean , Koziel Violette
Published: April 2011

To evaluate the potential deleterious influence of oxygen-derived free radicals following hypoxia in a model of primary culture of neurons obtained from the fetal rat brain, superoxide radicals were measured as a function of time in the extracellular medium. Neuronal cells were grown for 8 days in the presence or absence of serum, then incubated in a buffered Krebs–Ringer solution containing 60 μ M acetyl-cytochrome c. The rate of superoxide radical formation was quantified spectrophotometrically by measuring the specific reduction of acetyl-cytochrome c. Under normoxic conditions (95% air-5% CO2), basal production of superoxide that increased with time was recorded. It was significantly more pronounced in cells grown in serum-free medium. Under both culture conditions, acute hypoxia (95% N2–5% CO2) for 6 h increased superoxide radical amounts in the extracellular medium, and they were still enhanced 3 h after reoxygenation. The addition of superoxide dismutase to the incubating medium abolished the detection of superoxide radicals. The present study describes a new reliable method for superoxide radical measurement in cells in vitro and demonstrates hypoxia/reoxygenation-induced overproduction of superoxide in cultured neurons that may account for cell injury.
Postischemic Cerebral Blood Flow Recovery in the Female: Effect of 17β-Estradiol
Authors: Hurn Patricia D. , Littleton-Kearney Marguerite T. , Kirsch Jeffrey R. , Dharmarajan A. M. , Traystman Richard J.
Published: April 2011

Female reproductive hormones are considered to be protective agents in atherosclerotic vascular disease and stroke. The present study determined if there are unique cerebrovascular responses in female animals to global cerebral ischemia and if 17β-estradiol is important to postischemic outcome in brain. Three groups of anesthetized, sexually mature rabbits were treated with normotensive four-vessel occlusion (6 min) and 3 h of reperfusion: females chronically instrumented with 17β-estradiol implants (EFEM; n = 8, plasma estradiol level = 365 ± 48 pg/ml), untreated females (FEM; n = 8, estradiol = 13 ± 3 pg/ml), and untreated males (M; n = 8, estradiol < limit of radioimmunoassay). CBF (microspheres) and somatosensory evoked potential (SEP) amplitude were measured during ischemia/reperfusion. Baseline hemispheric blood flow and regional flow distribution were not altered by chronic estradiol treatment. Hemispheric blood flow was equivalently reduced during ischemia in FEM and M (6 ± 1 and 9 ± 2 ml min−1 100 g−1 respectively); however postischemic hyperemia was greater in FEM than M (CBF = 257 ± 27 and 183 ± 27 ml min−1 100 g−1. However, EFEM experienced higher CBF during ischemia (e.g., 13 ± 2 ml min−1 100 g−1) and less hyperemia (134 ± 4 ml min−1 100 g−1 in hemispheres) in numerous brain regions than FEM. CBF at 3 h reperfusion was not different among the groups. Recovery of SEPs was incomplete and similar in all groups. We conclude that chronic exogenous 17β-estradiol treatment increases CBF during global incomplete ischemia and ameliorates postischemic hyperemia in the female animal.
Differences in DNA Fragmentation following Transient Cerebral or Decapitation Ischemia in Rats
Authors: MacManus J. P. , Hill I. E. , Preston E. , Rasquinha I. , Walker T. , Buchan A. M.
Published: April 2011

The time course of appearance of cells with DNA damage was studied in rats following transient severe forebrain ischemia. This DNA damage could be detected by in situ end-labeling on brain sections. The breaks in DNA appeared selectively by day 1 in the striatum and later in the CA1 region of the hippocampus. It was possible by double labeling to show that there was no DNA damage in astrocytes. The DNA breaks consisted of laddered DNA fragments indicative of an ordered apoptotic type of internucleosomal cleavage, which persisted without smearing for up to 7 days of reperfusion. In contrast, the DNA breaks following ischemia induced by decapitation were random and, after gel electrophoresis, consisted of smeared fragments of multiple sizes. There was some early regional cellular death, restricted to the dentate of the hippocampus, prior to the pannecrotic degeneration. It is concluded that transient forebrain ischemia leads to a type of neuronal destruction that is not random necrosis but that shares some component of the apoptotic cell death pathway.
Effects of Central Inhibition of Nitric Oxide Synthase on Focal Cerebral Ischemia in Rats
Authors: Hamada Junichi , Greenberg Joel H. , Croul Sid , Dawson Ted M. , Reivich Martin
Published: April 2011

We have investigated whether central inhibition of nitric oxide synthase (NOS) could modify the tissue damage of focal cerebral ischemia produced by occlusion of the middle cerebral artery (MCA) in rats. NG-Nitro-l-arginine methyl ester (l-NAME) was administered intracerebroventricularly at two doses 15 min prior to occlusion of the MCA, as well as 4 and 24 h following occlusion. After the injection of l-NAME, the catalytic activity of the constitutive NOS, considered to be mainly neuronal, was effectively suppressed in the subcortical gray matter bilaterally, but not in the ischemic territory. Seven days after the MCA occlusion, the brains were evaluated for histopathologic damage. High-dose administration of l-NAME (120 μg/kg 15 min prior to MCA occlusion, followed by, 150 μg/kg 4 and 24 h after occlusion) produced an enlargement of the infarct area and increased the volume of ischemic damage. These results indicate that extensive inhibition of NOS by a central route can increase the cerebral infarct size in focal ischemia even if NOS is not inhibited in the ischemic tissue and suggest that NO may also play a potentially beneficial role as well as a neurodestructive role in the pathophysiological mechanisms of focal cerebral ischemia.
Hole mediated magnetism in Mn-doped GaN nanowires
Authors: Zhang Xiu-Wen , Li Jingbo , Chang Kai , Li Shu-Shen , Xia Jian-Bai
Published: April 2011

The hole-mediated magnetism in Mn-doped GaN nanowires is investigated using the k·p method and the mean-field model. The Curie temperature (TC) as a function of the hole density p can be explained based on the calculated band structure of the nanowires. For low Mn concentration, TC vs. p shows many peaks stem from the peaks of the one-dimensional density of states. When the Mn concentration is increased, TC is enhanced, and the peaks of TC versus p are fully merged by the thermal distribution of the holes in the valence band. It is found that the Curie temperature in Mn-doped GaN wire can be higher than room temperature, in agreement with experiment [Song et al., J. Phys.: Condens. Matter 17, 5073 (2005)]. The ferromagnetism in Mn-doped GaN wire is slightly anisotropic due to the small spin-orbit coupling.
Synthesis of Ag–CoFe2O4 dimer colloidal nanoparticles and enhancement of their magnetic response
Authors: Sharma S. K. , Lopes G. , Vargas J. M. , Socolovsky L. M. , Pirota K. R. , Knobel M.
Published: April 2011

This paper reports the structural and magnetic properties of Ag–CoFe2O4 colloidal dimer nanoparticles (NPs) synthesized using a two-step solution-phase route. Ag NPs were used as seeds to grow Ag–CoFe2O4 dimer NPs using thermal decomposition of metallic precursor. By means of temperature and field dependent dc magnetization measurements, it is found that the silver due to its interface with CoFe2O4 particles leads to thermal stabilization of the dimer NPs superior as compared to CoFe2O4 alone. Our results show enhancement of the magnetic anisotropy and a large coercivity at 2 K for dimer NPs, which could be ascribed to interface effect between Ag and CoFe2O4 components and the related structural defects.
Control of the exchange coupling in granular CoPt/Co recording media
Authors: Fan W. J. , Evans R. F. L. , Hancock Y. , Chantrell R. W.
Published: April 2011

In order to control the exchange coupling between the grains in a perpendicular recording media, a simple method is to totally decouple the grains using a thick oxide and apply a continuous magnetic capping layer to improve the uniformity of the coupling. In this paper, a system of CoPt grains coupled with a Co layer is investigated using an atomistic spin model. We show that the exchange coupling between the CoPt grains and the Co layer has an impact on the reversal process of the grains, as well as causing a reduction in the coercivity of the whole system. Further, we have studied the coercivity of the whole system as a function of the exchange coupling parameter between the grains and the exchange layer, and have found a sharp decrease in the coercivity. The coercivity as a function of the exchange layer thickness is also studied for different exchange coupling parameters.
Statistical property of the effect of Au nanoparticle decoration on the carbon nanotube network
Authors: Seo Sung Min , Kang Tae June , Cheon Jun Ho , Lim Jaeheung , Chung In Young , Kim Yong Hyup , Park Young June
Published: April 2011

Statistical analysis of the change in electrical characteristic of single-walled carbon nanotube (swCNT) network after the decoration of Au nanoparticles (NPs) is presented. We have fabricated 100 unitary swCNT network devices on a single chip employing a concentric electrode array by swCNT dip-coating and thermal evaporation of Au. The experimental results show that the decoration of Au-NP on the swCNT network can decrease not only its resistance but also variation in the resistance distribution. Remarkably, we have found that the change in electrical characteristic is correlated with the resistance value of the bare swCNT network.
Collective magnonic modes of pairs of closely spaced magnetic nano-elements
Authors: Dvornik M. , Bondarenko P. V. , Ivanov B. A. , Kruglyak V. V.
Published: April 2011

We report upon a theoretical study of collective magnonic modes in pairs of magnetic nano-elements with quasi-uniform magnetization. The mode spectrum and character are numerically computed for an individual isolated nano-element and then used to analytically calculate the splitting of the modes due to the inter-element magneto-dipole interaction. The results are compared with those obtained using direct simulations for the pairs of elements, yielding a generally good agreement. For the edge mode the interaction between the edges of the neighboring elements can exceed that between the edges of the same element, leading to softening of the mode profile and hence to the violation of the assumptions of the analytical approach. The softening has to be taken into account in the interpretation of dynamical studies of closely packed arrays of magnetic elements (magnonic crystals).
Spin-transfer torque driven ferromagnetic resonance in nano-contact magnetoresistive devices and its characteristics
Authors: Okutomi Yoshihito , Miyake Kousaku , Doi Masaaki , Fuke Hiromi Niu , Iwasaki Hitoshi , Sahashi Masashi
Published: April 2011

We investigated the spin-transfer torque driven ferromagnetic resonance in nano-contact magnetoresistive (NCMR) devices with a current-perpendicular-to-plane spin-valve structure consisting of a FeCo layer, a FeCo-AlOx nano-oxide layer, a FeCo multilayer for the reference, a spacer, and free layers. In contrast with tunneling magnetoresistance devices with an AlOx spacer layer that shows a single resonant frequency, NCMR devices showed multi-resonant frequencies caused by free-layer resonance and other types of resonance appeared in a frequency region higher than that of the free-layer. We discuss these characteristic results in terms of the magnetic structure of the NCMR device, especially the free and reference layers around the nano-contacts.
Structure and magnetic properties of FePd-alloy epitaxial thin films grown on MgO single-crystal substrates with different orientations
Authors: Ohtake Mitsuru , Yabuhara Osamu , Tobari Kousuke , Kirino Fumiyoshi , Futamoto Masaaki
Published: April 2011

FePd-alloy epitaxial films were prepared on MgO substrates of (100)B1, (110)B1, and (111)B1 orientations at a temperature of 600 °C by ultrahigh vacuum rf magnetron sputtering. The structural and the magnetic properties vary depending on the substrate orientation. L10–FePd(001) films are obtained on MgO(100)B1 substrates, whereas L10–FePd(101) films with the c-axis canted from the perpendicular direction are epitaxially grown on MgO(111)B1 substrates with six variants. FePd epitaxial films consisting of L10(100) and L10(112) crystals are formed on MgO(110)B1 substrates. A higher long range ordering parameter is obtained on the order of FePd/MgO(100)B1 > (110)B1 > (111)B1. The films grown on MgO(100)B1 substrates show perpendicular magnetic anisotropy, whereas the films grown on MgO(110)B1 and MgO(111)B1 substrates are easily magnetized in in-plane directions. The magnetization properties reflect the magnetocrystalline anisotropies of bulk L10–FePd crystal.
Crystallization of Nd-Co-B nanocomposite ribbons in high magnetic fields
Authors: Kato Hiroaki , Koyama Keiichi , Takahashi Kohki
Published: April 2011

Effect of high magnetic fields applied during annealing on the structure and magnetic properties were investigated for the melt-spun ribbons of Nd-Co-B system. When the annealing magnetic field is 100 kOe and the annealing temperature is lower than the Curie temperature TC of Nd2Co14B phase, the volume fraction of the Nd2Co14B phase and the coercivity values became much larger than those for the zero-field-annealed sample. A small but significant deviation from random alignment of Nd2Co14B grains was confirmed by the Rietveld analysis of the x-ray diffraction patterns for the sample field-annealed below TC.
Multicomponent gas mixture air bearing modeling via lattice Boltzmann method
Authors: Tae Kim Woo , Kim Dehee , Hari Vemuri Sesha , Kang Soo-Choon , Seung Chung Pil , Jhon Myung S.
Published: April 2011

As the demand for ultrahigh recording density increases, development of an integrated head disk interface (HDI) modeling tool, which considers the air bearing and lubricant film morphology simultaneously is of paramount importance. To overcome the shortcomings of the existing models based on the modified Reynolds equation (MRE), the lattice Boltzmann method (LBM) is a natural choice in modeling high Knudsen number (Kn) flows owing to its advantages over conventional methods. The transient and parallel nature makes this LBM an attractive tool for the next generation air bearing design. Although LBM has been successfully applied to single component systems, a multicomponent system analysis has been thwarted because of the complexity in coupling the terms for each component. Previous studies have shown good results in modeling immiscible component mixtures by use of an interparticle potential. In this paper, we extend our LBM model to predict the flow rate of high Kn pressure-driven flows in multicomponent gas mixture air bearings, such as the air–helium system. For accurate modeling of slip conditions near the wall, we adopt our LBM scheme with spatially dependent relaxation times for air bearings in HDIs. To verify the accuracy of our code, we tested our scheme via simple two-dimensional benchmark flows. In the pressure-driven flow of an air–helium mixture, we found that the simple linear combination of pure helium and pure air flow rates, based on helium and air mole fraction, gives considerable error when compared to our LBM calculation. Hybridization with the existing MRE database can be adopted with the procedure reported here to develop the state-of-the-art slider design software.
Effects of CrRu–SiOx underlayer with MgO intermediate layer on the microstructure and magnetic properties of FePt–C thin film
Authors: Li H. H. , Hu J. F. , Ju G. , Chow G. M. , Chen J. S.
Published: April 2011

The effect of the CrRu–SiOx underlayer with different doping concentrations and the thickness of the CrRu underlayer on the microstructure and magnetic properties of FePt–C films were investigated. FePt films exhibited L10 (001) texture at various SiOx doping concentrations. The coercivities were as large as 28 kOe and the slope of M–H loop at coercivity was approximately equal to 1, suggesting that FePt grains were well exchange decoupled. Grain size was only slightly reduced after introducing the CrRu–SiOx underlayer. But the contact angle between the FePt grains and the MgO intermediate layer around 135° indicated the a MgO intermediate layer was not favored for smaller grains to obtain good L10 (001) texture. X-ray photoelectron spectroscopy in-depth profile showed that Si diffused into a whole FePt–C layer and C diffused to the film surface.
Implication of oxygen vacancies on current conduction mechanisms in TiN/Zr1−xAlxO2/TiN metal-insulator-metal structures
Authors: Paskaleva A. , Lemberger M. , Bauer A. J. , Frey L.
Published: April 2011

The dominating conduction mechanisms through TiN/Zr1−xAlxO2/TiN capacitors have been investigated over a wide temperature range (25 K to 430 K) in order to obtain information about the traps which cause the current transport. Single positive charged oxygen vacancies are the principal transport sites which participate in all mechanisms observed. However, the conduction mostly defined by intrinsic traps could also be strongly influenced by defects originating from undesirable high-k/metal gate interface reactions which could act as real traps or as transport sites.
Influence of oxygen doping and hydration on photostimulated luminescence of CsBr and CsBr:Eu2+
Authors: Appleby G. A. , Kroeber P. , Zimmermann J. , Seggern H. von
Published: April 2011

Powdered samples of CsBr:O2− and CsBr:Eu2+,O2− with oxygen concentrations ranging from 0.01 to 5.00 mol% have been synthesized and are shown to have photostimulated luminescence (PSL) properties which are strongly influenced by the oxygen concentration. In europium free CsBr:O2−, it was found that weak PSL emission at 460 nm arises from oxygen impurities while with oxygen concentrations higher than 0.05 mol% the emission shifts to the 379 nm emission of the CsBr matrix, which is attributed to the nonexcitability of oxygen agglomerates. The F-center concentration in CsBr:O2− is observed to increase with oxygen concentration, due to an increase in Br-vacancies as charge compensation centers for the O2− ions. In all CsBr:Eu2+ samples studied, intense PSL emission arises only following room temperature hydration in an atmosphere of 99% relative humidity, and it is concluded that the presence of water molecules is essential for the PSL in CsBr:Eu2+. In CsBr:Eu2+,O2− this enhancement effect of PSL intensity is reduced as the oxygen concentration increases above 0.05 mol% due to competition between the Eu2+ and O2− luminescence centers. It was found that the effects of hydration can be partially reversed following exposure to a vacuum while the material is rendered completely PSL inactive following thermal annealing up to 600 °C which is caused by agglomeration of the highly mobile Eu2+ ions and subsequent loss of Eu2+ luminescence.
Improved light-emitting diode performance by conformal overgrowth of multiple quantum wells and fully coalesced p-type GaN on GaN nanowires
Authors: Frajtag P. , Hosalli A. M. , Bradshaw G. K. , Nepal N. , El-Masry N. A. , Bedair S. M.
Published: April 2011

We demonstrate a light-emitting diode (LED) structure with multiple quantum wells (MQWs) conformally grown on semipolar and nonpolar plane facets of n-GaN nanowires (NWs), followed by deposition of fully coalesced p-GaN on these nanowires. Overgrowth on the nanowires’ tips results in inclusion of high density voids, about one micron in height, in the GaN film. The light output intensity of NWs LEDs is more than three times higher than corresponding c-plane LEDs grown simultaneously. We believe this results from a reduced defect density, increased effective area of conformally grown MQWs, absence of polar plane orientation, and improved light extraction.
Zeolitic imidazolate framework-8 as a reverse osmosis membrane for water desalination: Insight from molecular simulation
Authors: Hu Zhongqiao , Chen Yifei , Jiang Jianwen
Published: April 2011

A molecular simulation study is reported for water desalination in zeolitic imidazolate framework-8 (ZIF-8) membrane. The simulation demonstrates that water desalination occurs under external pressure, and Na+ and Cl− ions cannot transport across the membrane due to the sieving effect of small apertures in ZIF-8. The flux of water permeating the membrane scales linearly with the external pressure, and exhibits an Arrhenius-type relation with temperature (activation energy of 24.4 kJ/mol). Compared with bulk phase, water molecules in ZIF-8 membrane are less hydrogen-bonded and the lifetime of hydrogen-bonding is considerably longer, as attributed to the surface interactions and geometrical confinement. This simulation study suggests that ZIF-8 might be potentially used as a reverse osmosis membrane for water purification.
Note: Fast, small, and low vibration mechanical laser shutters
Authors: Martínez S. , Hernández L. , Reyes D. , Gomez E. , Ivory M. , Davison C. , Aubin S.
Published: April 2011

We present three novel mechanical laser shutter designs based, respectively, on a stepper motor, a relay, and a piezoelectric actuator. Each shutter type is ideally suited to a specific shuttering application. The stepper motor is well suited for applications requiring low vibrations, the relay is compact and capable of rapid bursts, and the piezoelectric is 2 orders of magnitude faster than other available mechanical shutters.
Go-and-Back method: Effective estimation of the hidden motion of proteins from single-molecule time series
Authors: Miyazaki Makito , Harada Takahiro
Published: April 2011

We present an effective method for estimating the motion of proteins from the motion of attached probe particles in single-molecule experiments. The framework naturally incorporates Langevin dynamics to compute the most probable trajectory of the protein. By using a perturbation expansion technique, we achieve computational costs more than 3 orders of magnitude smaller than the conventional gradient descent method without loss of simplicity in the computation algorithm. We present illustrative applications of the method using simple models of single-molecule experiments and confirm that the proposed method yields reasonable and stable estimates of the hidden motion in a highly efficient manner.