bluuebunny/crossref_metadata_2025 huggingface dataset:
Periendothelial Acetylcholine Synthesis and Release in Bovine Cerebral Cortex Capillaries
Authors: Galea Elena , Estrada Carmen
Published: April 2011

Choline acetyltransferase (ChAT) activity is present in isolated cerebral capillaries, where it has been considered to be a marker for perivascular cholinergic nerve terminals. However, ChAT-like immunoreactivity has been visualized in endothelial cells. This finding raised the possibility that at least part of the biochemically detected ChAT has a nonneuronal origin. To evaluate the relative contribution of endothelial cells and nerve fibers to the total acetylcholine (ACh)-synthesizing capacity of cerebral capillaries, ChAT activity and ACh release were measured in capillaries and in purified endothelial cells isolated from bovine cerebral cortex. Isolated capillaries showed ChAT activity, which was inhibited by 2-benzoylethyl trimethylammonium to the same extent as cerebral ChAT. When preincubated with [3H]choline, these capillaries presented a calcium-dependent enhancement in tritium release upon electrical field stimulation. Purified endothelial cells had minor ChAT activity and lacked the ability to release tritium in response to electrical stimulation, although the endothelial markers alkaline phosphatase, γ-glutamyltranspeptidase, and 1,1'-dioctadecyl-1,3,3',3'-tetramethyl-iodo-carbocyanide perchlorate-labeled acetylated low-density lipoprotein uptake were fully preserved. These data indicate that, within isolated cerebral capillaries, ACh is synthesized and released by a periendothelial structure. The fact that ACh release is provoked by electrical stimulation and by a calcium-dependent mechanism strongly suggests that cerebrovascular ACh has a neuronal origin.
Phorbol 12,13-Diacetate-Induced Contraction of the Canine Basilar Artery: Role of Protein Kinase C
Authors: Sugawa Makoto , Koide Tohru , Naitoh Shigetaka , Takato Michiaki , Matsui Tohru , Asano Takao
Published: April 2011

The pharmacological and biochemical mechanisms of contractile responses to the protein kinase C (PKC) activator phorbol-12, 13-diacetate (PDA) were investigated in canine basilar arteries, In the normal medium, PDA elicited a strong, dose-related, and slow-developing sustained contraction, Among the constrictors examined, including serotonin, prostaglandin F2α and endothelin, only PDA yielded contractions in a 2 Ca2+ -free medium, In both media, the PDA-induced contractions were virtually inhibited by either staurosporine, H-7, or quinacrine, while neither neurotransmitter blockades nor R24571 (calmidazolium) exerted significant effects, In addition, it was shown that 8-bromocyclic GMP, but not 8-bromocyclic AMP, markedly curtailed the PDA-induced contractions, Biochemical analysis, furthermore, showed that PDA induced increased phosphorylations of 27- and 96-kDa and proteins other than the myosin light chain (MLC) 20-kDa protein, Thus, the present results open up a novel mechanism of sustained cerebral artery contractions, where PKC activation rather than Ca2+/calmodulin/MLC system plays a key role that is regulated both by phospholipase A 2 and by cyclic GMP.
Protection after Transient Focal Cerebral Ischemia by the N-Methyl-d-Aspartate Antagonist Dextrorphan is Dependent upon Plasma and Brain Levels
Authors: Steinberg Gary K. , Kunis David , Saleh Jamshid , DeLaPaz Robert
Published: April 2011

Dextrorphan is a dextrorotatory morphinan and a noncompetitive N-methyl-d-aspartate (NMDA) receptor antagonist. We studied the dose response characteristics of dextrorphan's neuroprotective efficacy and side effects, correlating these beneficial and adverse responses with plasma and brain levels in a rabbit model of transient focal cerebral ischemia. Thirty-three rabbits, anesthetized with halothane, underwent occlusion of the left internal carotid and anterior cerebral arteries for 1 h, followed by 4.5 h of reperfusion. One hour after the onset of ischemia, they were treated with an i.v. infusion of varying dextrorphan doses or normal saline. After killing, the brains were analyzed for ischemic high signal intensity using magnetic resonance imaging (MRI) and for ischemic neuronal damage with histopathology. A separate group of 12 anesthetized ischemic rabbits received similar doses of dextrorphan, correlating plasma with brain dextrorphan levels. Twenty-six additional dextrorphan unanesthetized, nonischemic rabbits received infusions of dextrorphan to correlate behavioral side effects with dextrorphan dose and levels. Compared with controls, the dextrorphan 15 mg/kg group had significantly less cortical ischemic neuronal damage (5.3 versus 33.2%, p = 0.01) and a reduction in cortical MRI high signal area (9.1 versus 41.2%, p = 0.02). The dextrorphan 10 mg/kg rabbits showed less cortical ischemic neuronal damage (27.2%) and less MRI high signal (34.8%) but this was not statistically significant (p = 0.6). Dextrorphan 5 mg/kg had no benefit on either neocortical ischemic neuronal damage (35.8%) or MRI high signal (42.9%). The protective effect of dextrorphan was correlated with plasma free dextrorphan levels (r = −0.50, p < 0.02 for ischemic neuronal damage; r = −0.66, p < 0.001 for ischemic MRI high signal). All the rabbits with plasma levels > 2,000 ng/ml had < 12% cortical ischemic neuronal damage and < 34% MRI high signal. All rabbits with plasma levels > 3,000 ng/ml showed < 7% ischemic neuronal damage and < 11% MRI high signal. Plasma levels of ∼2,500 ng/ml correlated with brain dextrorphan levels of ∼6,000 ng/g. Unanesthetized rabbits with plasma levels of ∼2,500 ng/ml demonstrated loss of the righting reflex. These results demonstrate that systemic treatment with dextrorphan after 1 h focal ischemia can significantly protect against cerebral damage if adequate plasma and brain levels of dextrorphan are achieved. The brain levels necessary to obtain in vivo protection are similar to concentrations that prevent glutamate or NMDA-induced injury in neuronal culture.
The Effects of Collimation on PET Image Noise Due to Scatter, Random Counts, and Deadtime
Authors: Thompson C. J.
Published: April 2011

The rates for true coincident events, scattered events, and singles in a Positron Emission Tomograph (PET) depend on the collimator size and shape. Monte Carlo techniques were used to compare efficiencies for wanted and unwanted events in multislice PET (MS-PET) and open collimator positron volumetric imaging (PVI) configurations. All systems used cylindrical arrays of bismuth germanate (BGO) or NaI crystals 51 cm in diameter and 10 cm deep suitable for whole brain imaging. The PVI systems detect about five times more true coincident events at low activity concentrations, but their scatter fraction is about three times higher. They are also much more sensitive to activity outside the scan field. As well as causing random counts when they fall within the energy acceptance window, single events are the main cause of deadtime. When the detectors are made from light-encoded blocks deadtime is the major limitation at high count rates. When discrete crystals are used, the efficiency is lower and the random count rates are a more significant source of noise. Noise-effective count rates are used to compare the relative cost in system performance among different systems and sources of noise.
Effects of Percent Thresholding on the Extraction of [18F]Fluorodeoxyglucose Positron Emission Tomographic Region-of-Interest Data
Authors: Rottenberg D. A. , Moeller J. R. , Strother S. C. , Dhawan V. , Sergi M. L.
Published: April 2011

Although we and others have employed a thresholding strategy to extract “peak” values from positron emission tomographic (PET) regions of interest (ROIs), the effects of peak picking on fitted fluorodeoxyglucose rate constants, regional metabolic rate for glucose (rCMRglc) profiles, patterns of regional metabolic covariation, and PET-neurobehavioral correlations have not been systematically investigated. Our results suggest that under some commonly encountered imaging conditions percent thresholding may increase sensitivity to regional activation; however, the effect of thresholding is determined by a number of factors, including the relative magnitude of regional activation, ROI size, and the specific threshold selected. The difference-annulus concept is proposed as a means to study the effects of different region drawing and thresholding strategies, and to determine if a given ROI contains one and only one source of covarying metabolic activity.
The FDG/PET Methodology for Early Detection of Disease Onset: A Statistical Model
Authors: Clark C. M. , Ammann W. , Martin W. R. W. , Ty P. , Hayden M. R.
Published: April 2011

The development of appropriate statistical methodologies for neuroimaging studies is dependent upon the research question of interest. Often studies are analyzed with techniques that may not be appropriate for the research question but are accepted owing to convention, familiarity, or apparent statistical sophistication. Neuroimaging data are particularly complex owing to (a) the high number of potential dependent variables (i.e., regions of interest) coupled with the practical limitations on sample size; (b) the known physical properties of scanners (e.g., resolution) interacting with the intricate and variable structure of the human brain; and (c) mathematical properties introduced into the data by the physiological model for quantification. In this article, a statistical model will be discussed for addressing a particular problem in clinical studies. Given that there is a characteristic abnormality in regional glucose metabolism in a specific disease, can a probabilistic statement be made with confidence regarding the likelihood of an individual scan being similar to those from the disease group or normal subjects? The model capitalizes on known statistical aspects of normal regional glucose metabolism. To illustrate the model, data will be presented on normal subjects, patients with confirmed Huntington's disease, and subjects at risk for the disease. Reliability and clinical validity of the model will be discussed.
Functional Interactions in the Brain: Use of Correlations between Regional Metabolic Rates
Authors: Horwitz Barry
Published: April 2011

Correlation coefficients between pairs of regional metabolic rates have been used to study patterns of functional associations among brain regions in humans and animals. An overview is provided concerning the additional information about brain functioning this type of analysis yields. A computer simulation model is presented for the purpose of giving a partial validation for correlational analysis. The model generates a set of simulated metabolic data upon which correlational analysis is performed. Because the underlying pattern of functional couplings in the model is known, these simulations demonstrate that the correlation coefficient between normalized metabolic rates is proportional to the strength of the functional coupling constant and that correlational analysis yields information on regional involvement in neural systems not evident in the pattern of absolute metabolic values.
Statistical Analysis of Functional Neuroimaging Data: Exploratory versus Inferential Methods
Authors: Pawlik G.
Published: April 2011

In the following, various image processing and analytical techniques, whose efficiency has been demonstrated empirically by comparison with expert readings of hundreds of positron emission tomography (PET) studies, will be outlined briefly.
Discussion of PET Workshop Reports, Including Recommendations of PET Data Analysis Working Group
Authors: Rapoport Stanley I.
Published: April 2011

On May 1–2, 1989, a PET Data Analysis Working Group convened to consider positron emission tomography (PET) methodology and data analysis. The papers presented and the recommendations of the Group are reviewed. The Group recommended that a standard phantom of the human brain be used by different institutions to examine machine and data reconstruction PET variables. Interinstitutional comparisons could be aided by using a standard three-dimensional coordinate system. Deformations within individual diseased or atypical brains would require nonlinear as well as linear transformations to the standard space, using magnetic resonance images in register with the PET images. Methods for intersubject averaging of pixel-by-pixel or region-of-interest data, as well as appropriate statistical methods, need to be developed. PET data may first be exploratory and hypothesis-generating (with less stringent statistical theory), then later used to test hypotheses (with more stringent statistical criteria). Common databases, obtained by computer simulation models with known inherent structure, or directly by PET measurements on different groups, could be used to compare analytical and statistical methods among institutions.
Modeling the Dependence of Hexose Distribution Volumes in Brain on Plasma Glucose Concentration: Implications for Estimation of the Local 2-Deoxyglucose Lumped Constant
Authors: Holden James E. , Mori Kentaro , Dienel Gerald A. , Cruz Nancy F. , Nelson Thomas , Sokoloff Louis
Published: April 2011

The steady-state distribution volumes of glucose, 3- O-methylglucose, and 2-deoxyglucose (2DG) are known to change as the concentration of glucose in plasma ranges from hypo- to hyperglycemic values. Model estimates of the three distribution volumes were compared with distribution volume values experimentally measured in the brains of conscious rats as the concentration of glucose in plasma was varied from 2 to 28 m M. The dependence on plasma glucose concentration of the 2DG lumped constant, the factor that relates the phosphorylation rate of 2DG to the net rate of glucose utilization at unit specific radioactivity in the plasma, had been determined previously in separate series of experiments. The model was extended to incorporate this dependence of the lumped constant. In the model both the transport and the phosphorylation barriers were assumed to be single and saturable. The values of their respective half-saturation concentrations and the ratio of the two maximum velocities for glucose were assumed to be invariant over the entire range of plasma glucose concentration. Good agreement between measured and estimated values for the distribution volumes and the lumped constant was attained over the full range of plasma glucose concentration. The model estimates reflected the progressive transport limitation of the brain glucose content as plasma glucose levels were reduced to hypoglycemic values. The results also indicated that these changes should be evident in the time course of 2DG in brain following administration by bolus or continuous infusion, and thus that indexes of local lumped constant change could be derived from the time course data.
Quantification of Human Opiate Receptor Concentration and Affinity Using High and Low Specific Activity [11C]Diprenorphine and Positron Emission Tomography
Authors: Sadzot Bernard , Price Julie C. , Mayberg Helen S. , Douglass Kenneth H. , Dannals Robert F. , Lever John R. , Ravert Hayden T. , Wilson Alan A. , Wagner Henry N. , Feldman Marc A. , Frost J. James
Published: April 2011

[11C]Diprenorphine, a weak partial opiate agonist, and positron emission tomography were used to obtain noninvasive regional estimates of opiate receptor concentration ( Bmax) and affinity ( Kd) in human brain. Different compartmental models and fitting strategies were compared statistically to establish the most reliable method of parameter estimation. Paired studies were performed in six normal subjects using high (769–5,920 Ci/mmol) and low (27–80 Ci/mmol) specific activity (SA) [11C]diprenorphine. Two subjects were studied a third time using high SA [11C]diprenorphine after a pretreatment with 1–1.5 mg/kg of the opiate antagonist naloxone. After the plasma radioactivity was corrected for metabolites, the brain data were analyzed using a three-compartment model and nonlinear least-squares curve fitting. Linear differential equations were used to describe the high SA (low receptor occupancy) kinetics. The k3/ k4 ratio varied from 1.0 ± 0.2 (occipital cortex) to 8.6 ± 1.6 (thalamus). Nonlinear differential equations were used to describe the low SA (high receptor occupancy) kinetics and the curve fits provided the kon f2 product. The measured free fraction of [11C]diprenorphine in plasma ( f1) was 0.30 ± 0.03, the average K1/ k2 ratio from the two naloxone studies was 1.1 ± 0.2, and the calculated free fraction of [11C]diprenorphine in the brain ( f2) was 0.3. Using the paired SA studies, the estimated kinetic parameters, and f2, separate estimates of Bmax and Kd were obtained. Bmax varied from 2.3 ± 0.5 (occipital cortex) to 20.6 ± 7.3 (cingulate cortex) n M. The average Kd (eight brain regions) was 0.85 ± 0.17 n M.
Formation of Free Choline in Brain Tissue during in vitro Energy Deprivation
Authors: Djuricic Bogdan , Olson Steven R. , Assaf Hussein M. , Whittingham Tim S. , Lust W. David , Drewes Lester R.
Published: April 2011

Free choline and ATP contents were measured in Mongolian gerbil hippocampal slices (tissue) and incubation media (media) during exposure to 30 min of aglycemia, high potassium, anoxia, or ischemia. Changes in choline levels reflected the degree of energy reduction, lower ATP levels being associated with high choline (4-fold increase during exposure to high potassium and anoxia, and 11-fold increase during ischemia). Media (extracellular) choline was particularly affected and increased about twofold during relatively mild energy depletion (e.g., aglycemia), but tissue choline content was less sensitive to energy reduction. A plot of choline vs. ATP levels indicated a nonlinear correlation, and the sharp increase in choline occurred when ATP values fell to about 2.5 nmol/mg of protein. Inhibition of acetylcholine sterase by 10 μ M physostigmine during ischemia did not prevent an increase in choline contents but rather enhanced them, indicating that acetylcholine hydrolysis was not the source of free choline. Formation of free choline was Ca2+ independent. These findings suggest the involvement of phospholipase D and phosphatidylcholine hydrolysis in free choline formation during energy stress. The extent of choline formation may be an indicator of the degree of membranal damage, which in turn reflects damage to the metabolic machinery of the cell.
Cerebral Ammonia Metabolism in Patients with Severe Liver Disease and Minimal Hepatic Encephalopathy
Authors: Lockwood Alan H. , Yap Eddy W. H. , Wong Wai-Hoi
Published: April 2011

Cerebral ammonia metabolism was studied in five control subjects and five patients with severe liver disease exhibiting minimal hepatic encephalopathy. The arterial ammonia concentration in the control subjects was 30 ± 7 μmol/L (mean ± SD) and 55 ± 13 μmol/L in the patients (p < 0.01). In the normal subjects, the whole-brain values for cerebral blood flow, cerebral metabolic rate for ammonia, and the permeability-surface area product for ammonia were 0.58 ± 0.12 ml g−1 min−1, 0.35 ± 0.15 μmol 100 g−1 min−1, and 0.13 ± 0.03 ml g−1 min−1, respectively. In the patients, the respective values were 0.46 ± 0.16 ml g−1 min−1 (not different from control), 0.91 ± 0.36 μmol 100 g−1 min−1 (p < 0.025), and 0.22 ± 0.07 ml g−1 min−1 (p < 0.05). The increased permeability-surface area product of the blood-brain barrier permits ammonia to diffuse across the blood-brain barrier into the brain more freely than normal. This may cause ammonia-induced encephalopathy even though arterial ammonia levels are normal or near normal and explain the emergence of toxin hypersensitivity as liver disease progresses. Greater emphasis on early detection of encephalopathy and aggressive treatment of minimal hyperammonemia may retard the development of ammonia-induced complications of severe liver disease.
Fetal Cerebral Blood Flow and Metabolism during Oligemia and Early Postoligemic Reperfusion
Authors: Chao Conrad R. , Hohimer A. Roger , Bissonnette John M.
Published: April 2011

The early time period following ischemia may be of pathogenetic importance in hypoxic-ischemic brain injury. Global cerebral oligemia was induced in ten late gestation fetal sheep by inflation of a balloon occluder around the brachiocephalic artery. Cerebral blood flow, oxygen, glucose, and lactate net flux, and oxygen delivery were measured by the Fick principle following 1 h of oligemia and at 5, 30, and 60 min of postoligemic reperfusion. During oligemia, cerebral blood flow decreased by 74 ± 10% (mean ± SD) and oxygen consumption decreased by 34 ± 24%. The glucose:oxygen quotient was elevated throughout the oligemic period. In the early (5 min) reperfusion period, blood flow and oxygen delivery were not different from control but oxygen consumption was persistently depressed by 27 ± 32%; fractional extraction of oxygen was 0.38 ± 0.10 during control and 0.24 ± 0.09 during early reperfusion. The venous oxygen tension increased modestly from 15.2 ± 2.4 to 18.0 ± 1.7 mm Hg; the postoligemic venous pO2 was limited by the lack of reactive hyperemia combined with the low arterial pO2 of the intrauterine environment. Postoligemic carbohydrate fluxes could not be differentiated from control, possibly due to blood–brain barrier limitations. These factors may be related to the relative resistance of the fetal brain to hypoxic–ischemic injury.
The Role of Adenosine in the Vascular Adaptation of Neonatal Cerebral Blood Flow during Hypotension
Authors: Laudignon Nicole , Beharry Kay , Farri Evangelia , Aranda Jacob V.
Published: April 2011

This study investigated the potential role of adenosine in cerebral blood flow (CBF) regulation in the neonate during moderate and severe hypotension. Experiments were done in anesthetized, 1- to 3-day-old piglets. Regional CBF (determined by radiolabeled microsphere technique) and cerebral metabolic rate for O2 (CMRO2) were measured (a) during normotension and (b) during a 3-min period of moderate (58 ± 9 mm Hg) or severe (36 ± 7 mm Hg) hypotension produced by the inflation of a balloon catheter placed in the aortic root. Measurements of CBF and CMRO2 were performed successively after intracerebroventricular (i.c.v.) injections of vehicle (n = 17), the adenosine receptor blocker 8-phenyltheophylline (8–PT, 10 μg, n = 14), and the A2-receptor agonist 5′- N-(ethylcarboxamide)adenosine(NECA, 2 ng, n = 8). After i.c.v. administration of vehicle, none of the parameters studied was significantly altered by moderate hypotension, but severe hypotension decreased the total CBF (mean ± SD) from 86 ± 24 to 40 ± 15 ml min−1 100 g−1 and CMRO2 from 3.2 ± 0.8 to 1.8 ± 1.0 ml min−1 100 g−1 (p < 0.05). Administration of 8-PT did not alter these parameters during normotension, but significantly decreased CBF during moderate hypotension compared to postvehicle values (53 ± 11 versus 81 ± 12 ml min−1 100 g−1, p < 0.05). This loss of autoregulation was completely reversed by NECA. During severe hypotension, 8-PT altered the CBF redistribution towards the brainstem. Mean normotensive CSF concentrations of adenosine (0.76 ± 0.26 μ M) increased during moderate (1.40 ± 1.78 μM) and severe (2.60 ± 2.56 μ M, p < 0.05) hypotension. These data suggest that, in the newborn, adenosine is an important mediator of the cerebral adaptive response to hypotension, even within the range of autoregulation.
Metabolic Effects of R-Phenylisopropyladenosine during Reversible Forebrain Ischemia Studied by in vivo 31P Nuclear Magnetic Resonance Spectroscopy
Authors: Roucher P. , Méric P. , Corrèze J. L. , Mispelter J. , Tiffon B. , Lhoste J. M. , Seylaz J.
Published: April 2011

The metabolic effects of R-phenylisopropyladenosine ( R-PIA), an agonist of adenosine A, receptors, were studied by in vivo 31P NMR spectroscopy before, during, and after 30 min of reversible forebrain ischemia in the rat. R-PIA had no effect on cerebral metabolism before ischemia. During a 30-min ischemia, R-PIA reduced the decrease in phosphocreatine (43 ± 11% of the control level at the end of ischemia vs. 27 ± 9% in the reference group) and ATP (58 ± 12% vs. 40 ± 23%) and the increase in inorganic phosphate (672 ± 210% vs. 905 ± 229%). The intracellular acidosis elicited by ischemia was also less in the treated group (pH of 6.40 ± 0.10 vs. 6.30 ± 0.10). Recirculation was associated with a faster recovery of PCr, ATP, Pi, and pHi to control levels in the treated group than in the reference group. It is concluded that adenosine protects against ischemic injury by mechanisms that include metabolic protection.
Blood to Brain Sodium Transport and Interstitial Fluid Potassium Concentration during Early Focal Ischemia in the Rat
Authors: Schielke Gerald P. , Moises Hylan C. , Betz A. Lorris
Published: April 2011

During partial ischemia, sodium and potassium ions exchange across the blood–brain barrier, resulting in a net increase in cations and brain edema. Since this exchange is likely mediated by specific transporters such as Na,K–ATPase in the capillary endothelium and because brain capillary Na,K–ATPase activity is stimulated by increased extracellular potassium in vitro, this study was designed to determine if the rate of blood to brain sodium transport is increased in ischemic tissue having an elevated interstitial fluid potassium concentration ([K]ISF) in vivo. Sprague-Dawley rats were studied between 2–3 h after occlusion of the right middle cerebral artery. To identify where cortical tissue with an elevated [K]ISF could be sampled for transport studies, the regional pattern of cerebral blood flow and [K]ISF was obtained in a group of 17 rats using hydrogen clearance and potassium-selective microelectrode techniques. We observed severely elevated [K]ISF (> 10 m M) when CBF was less than 20 ml 100 g−1 min−1 and mildly elevated levels at CBF between 20–45 ml 100 g−1 min−1. In a second group of seven rats, permeability-surface area products (PS products) for 22Na and [3H]α-aminoisobutyric acid ([3H]AIB) were determined in ischemic cortex with elevated [K]ISF and in nonischemic cortex. The PS products for AIB were similar in both tissues (2.2 ± 0.7 and 2.1 ± 0.4 μl/g/min) while the PS products for sodium was significantly increased in the ischemic tissue (1.5 ± 0.2 and 2.4 ± 1.1 μl/g/min). This study demonstrates that blood to brain sodium transport is increased in ischemic tissue at early times before the BBB is disrupted. Stimulation of the Na,K pumps in the capillary endothelium by elevated [K]ISF may mediate this effect.
A Three-Dimensional Statistical Analysis for CBF Activation Studies in Human Brain
Authors: Worsley K. J. , Evans A. C. , Marrett S. , Neelin P.
Published: April 2011

Many studies of brain function with positron emission tomography (PET) involve the interpretation of a subtracted PET image, usually the difference between two images under baseline and stimulation conditions. The purpose of these studies is to see which areas of the brain are activated by the stimulation condition. In many cognitive studies, the activation is so slight that the experiment must be repeated on several subjects and the subtracted images are averaged to improve the signal-to-noise ratio. The averaged image is then standardized to have unit variance and then searched for local maxima. The main problem facing investigators is which of these local maxima are statistically significant. We describe a simple method for determining an approximate p value for the global maximum based on the theory of Gaussian random fields. The p value is proportional to the volume searched divided by the product of the full widths at half-maximum of the image reconstruction process or number of resolution elements. Rather than working with local maxima, our method focuses on the Euler characteristic of the set of voxels with a value larger than a given threshold. The Euler characteristic depends only on the topology of the regions of high activation, irrespective of their shape. For large threshold values this is approximately the same as the number of isolated regions of activation above the threshold. We can thus not only determine if any activation has taken place, but we can also estimate how many isolated regions of activation are present.
Development and Remodeling of Cerebral Blood Vessels and Their Flow in Postnatal Mice Observed with in vivo Videomicroscopy
Authors: Wang Dan-Bing , Blocher Nissa C. , Spence Mary Ellen , Rovainen Carl M. , Woolsey Thomas A.
Published: April 2011

Changes of blood vessels in the mouse somatosensory (barrel) cortex were assessed from birth (P0) to adulthood. Surface vessel anatomy and flow were observed directly with videomicroscopy through closed cranial windows and with intravascular fluorescent tracers. Histology was used to determine the internal capillary density. At birth, arterioles had numerous anastomoses with each other, pial capillaries formed a dense surface plexus, and pial venules and veins were relatively small and irregular. Morphological changes over the next 2 weeks included (a) fewer arteriolar anastomoses, (b) formation and growth of venules, (c) more uniform diameters of all types of vascular segments, (d) increase in intraparenchymal capillary length density ( Lv), and (e) decreases in superficial capillary density and diameters. A simple morphological test showed that wall shear rates at arteriolar branch points were matched on average in neonates and adults. Flow characteristics in single vessels were evaluated. In arterioles of like diameters, (a) Vmax, (b) peak wall shear rates, and (c) peak flows were similar at all ages; (d) velocity was very high in occasional arteriovenous (AV) shunts in newborns; and (e) flow in arteriolar anastomoses was slow and variable. Although flow was heterogeneous in all types of vessel, the marked similarities in newborn and adult mice of average peak velocities and calculated wall shear rates in arterioles of the same size suggest that blood flow regulates in part the remodeling of blood vessels during development (Rovainen et al., 1992). The rodent barrel cortex undergoes major neuronal and vascular development, functional differentiation, and remodeling during the first weeks after birth. It provides special opportunities for testing how blood vessels grow and adapt to supply the local metabolic requirements of neural modules in the brain.
Effect of Nitric Oxide Blockade by NG-Nitro-l-Arginine on Cerebral Blood Flow Response to Changes in Carbon Dioxide Tension
Authors: Wang Qiong , Paulson Olaf B. , Lassen Niels A.
Published: April 2011

The importance of nitric oxide (NO) for CBF variations associated with arterial carbon dioxide changes was investigated in halothane-anesthetized rats by using an inhibitor of nitric oxide synthase, NG-nitro-l-arginine (NOLAG). CBF was measured by intracarotid injection of 133Xe. In normocapnia, intracarotid infusion of 1.5, or 7.5, or 30 mg/kg NOLAG induced a dose-dependent increase of arterial blood pressure and a decrease of normocapnic CBF from 85 ± 10 to 78 ± 6, 64 ± 5, and 52 ± 5 ml 100g−1 min−1, respectively. This effect lasted for at least 2 h. Raising Paco2 from a control level of 40 to 68 mm Hg increased CBF to 230 ± 27 ml 100g−1 min−1, corresponding to a percentage CBF response (CO2 reactivity) of 3.7 ± 0.6%/mm Hg Paco2 in saline-treated rats. NOLAG attenuated this reactivity by 32, 49, and 51% at the three-dose levels. Hypercapnia combined with angiotensin to raise blood pressure to the same level as the highest dose of NOLAG did not affect the CBF response to hypercapnia. l-Arginine significantly prevented the effect of NOLAG on normocapnic CBF as well as blood pressure and also abolished its inhibitory effect on hypercapnic CBF. d-Arginine had no such effect. Decreasing Paco2 to 20 mm Hg reduced control CBF to 46 ± 3 ml 100g−1 min−1 with no further reduction after NOLAG. Furthermore, NOLAG did not change the percentage CBF response to an extracellular acidosis induced by acetazolamide (50 mg/kg). The results suggest that NO or a closely related compound is involved in the regulation of CBF in normocapnia and even more so in hypercapnia.
Blood Flow in Portal Systems with Special Reference to the Rat Pituitary Gland
Authors: Lees P. D. , Lynch D. T. , Richards H. K. , Lovick A. H. J. , Perry S. , Pickard J. D.
Published: April 2011

Regional pituitary blood flow has been studied in adult female Fischer 344 rats by [14C]iodoantipyrine autoradiography. A general mathematical solution has been derived to allow the calculation of blood flow in the second compartment of a portal system and the proportion of blood “shunted” through the first compartment without exposure to tissue uptake from a knowledge of (a) the volume ratios of the two compartments, (b) the tissue tracer uptakes of the two compartments, and (c) the arterial tracer concentration with respect to time of a freely diffusible tracer. Significant diffusion limitation and/or arteriovenous shunting has been demonstrated in the neurohypophysis, suggesting that the majority of incoming blood is “shunted” unchanged to the adenohypophysis. The mean value of the shunt is 89% (range of 84–93%) for the median eminence and lies between 72% (range of 52–82%) and 73% (range of 59–81%) for the posterior pituitary. Neurohypophysial flow rates of 1.20 (range of 0.99–1.55) ml g−1 min−1 for the median eminence and 1.68 (range of 0.83–3.53) ml g−1 min−1 for the posterior pituitary were measured. These values represent “tissue-available” (nonshunted) flow; estimated mean total (shunted plus nonshunted) neurohypophysial flow rates were 11.7 (range of 9.5–17.5) ml g−1 min−1 for the median eminence and 6.1 (range of 3.1–8.9) ml g−1 min−1 (minimum) for the posterior pituitary. Adenohypophysial blood flow is heterogeneous. In the long portal territory, the flow rate was 1.18 (range of 0.95–1.75) ml g−1 min−1 but short portal territory flow calculation is complicated by an unquantifiable nonportal venous drainage; using the natural limits of zero and 100% gives a minimum adenohypophysial flow rate of 1.42 (range of 0.76–2.07) ml g−1 min−1 and a maximum value of 1.97 (range of 1.03–2.82) ml g−1 min−1.
Regional Expression of Heat Shock Protein-70 mRNA and c-Fos mRNA following Focal Ischemia in Rat Brain
Authors: Welsh Frank A. , Moyer Donald J. , Harris Valerie A.
Published: April 2011

In situ hybridization was used to estimate regional levels of heat shock protein-70 (HSP-70) mRNA and c-fos mRNA in two related models of focal cerebral ischemia. In the first model, permanent occlusion of the distal middle cerebral artery (MCA) alone caused a patchy increase in HSP-70 mRNA by 1 h in the central zone of the MCA territory of the ipsilateral neocortex. Tissue levels of HSP-70 mRNA continued to increase for several hours and remained elevated at 24 h. In contrast to the focal expression of HSP-70, c-fos mRNA was increased throughout the ipsilateral cerebral cortex by 15 min and remained elevated for least 3 h. The wide distribution of c-fos expression suggests it may have been caused by spreading depression. In the second model, severe focal ischemia was produced with a combination of transient (1-h) bilateral carotid artery occlusion and permanent MCA occlusion. Combined occlusion for 1 h without reperfusion caused expression of HSP-70 mRNA only in regions adjacent to the central zone of the MCA territory of the neocortex. However, reperfusion of the carotids for 2 h generated intense expression of HSP-70 mRNA throughout most of the ipsilateral cerebral cortex, white matter, striatum, and hippocampus. The widespread increase in HSP-70 mRNA suggests that reperfusion triggered expression in all previously ischemic regions. However, at 24 h of reperfusion, increased levels of HSP-70 mRNA were restricted primarily to the ischemic core of the neocortex. These results suggest that expression of HSP-70 mRNA is prolonged in regions undergoing injury, but is transient in surrounding regions that recover.
Effects of Propentofylline on Hypoxia—Hypoglycemia-Induced Calcium Accumulation in Gerbil Hippocampal Slices
Authors: Kadoya Fumito , Mitani Akira , Arai Tatsuru , Kataoka Kiyoshi
Published: April 2011

The xanthine derivative propentofylline (HWA 285) has been reported to show protective effects against neuronal damage induced by cerebral ischemia. In the present study, microfluorometry was used to investigate the effect of propentofylline on the hypoxia–hypoglycemia-induced intracellular calcium accumulation in gerbil hippocampal slices. When slices were superfused with hypoxic–hypoglycemic medium that did not contain propentofylline, an acute increase in calcium accumulation was detected 75–200 s (mean latency of 123 s) after the beginning of hypoxia–hypoglycemia. When slices were superfused with hypoxic–hypoglycemic mediums that contained 10 μ M, 100 μ M, and 1 m M propentofylline, the latency of the acute increase in calcium accumulation was prolonged in all subregions of the hippocampus in a dose-dependent manner: mean latencies in field CA1 were 146, 168, and 197 s after hypoxia–hypoglycemia, respectively. This retardation in calcium accumulation may be involved in the mechanisms by which propentofylline diminishes ischemic injury.
Metabolic Impairment in Human Amnesia: A PET Study of Memory Networks
Authors: Fazio Ferruccio , Perani Daniela , Gilardi Maria Carla , Colombo Fabio , Cappa Stefano F. , Vallar Giuseppe , Bettinardi Valentino , Paulesu Eraldo , Alberoni Margherita , Bressi Sergio , Franceschi Massimo , Lenzi Gian Luigi
Published: April 2011

Human amnesia is a clinical syndrome exhibiting the failure to recall past events and to learn new information. Its “pure” form, characterized by a selective impairment of long-term memory without any disorder of general intelligence or other cognitive functions, has been associated with lesions localized within Papez's circuit and some connected areas. Thus, amnesia could be due to a functional disconnection between components of this or other neural structures involved in long-term learning and retention. To test this hypothesis, we measured regional cerebral metabolism with 2-[18F]fluoro-2-deoxy-d-glucose ([18F]FDG) and positron emission tomography (PET) in 11 patients with “pure” amnesia. A significant bilateral reduction in metabolism in a number of interconnected cerebral regions (hippocampal formation, thalamus, cingulate gyrus, and frontal basal cortex) was found in the amnesic patients in comparison with normal controls. The metabolic impairment did not correspond to alterations in structural anatomy as assessed by magnetic resonance imaging (MRI). These results are the first in vivo evidence for the role of a functional network as a basis of human memory.
Neuronal Damage after Repeated 5 Minutes of Ischemia in the Gerbil is Preceded by Prolonged Impairment of Protein Metabolism
Authors: Widmann R. , Weber C. , Bonnekoh P. , Schlenker M. , Hossmann K.-A.
Published: April 2011

The effect of single or repeated episodes of cerebral ischemia on protein biosynthesis and neuronal injury was studied in halothane-anesthetized gerbils by autoradiography of [14C]leucine incorporation into brain proteins and light microscopy. For quantification of the protein synthesis rate, the steady-state precursor pool distribution space for labeled and unlabeled free leucine was determined by clamping the specific activity of [14C]leucine in plasma, and by measuring free tissue leucine in samples taken from various parts of the brain. Control values of protein synthesis were 14.6 ± 2.2, 5.8 ± 2.3, 14.2 ± 3.1, and 10.0 ± 3.8 nmol g−1 min−1 (means ± SD) in the frontal cortex, striatum, CA1 sector, and thalamus, respectively. Following a single episode of 5 or 15 min of ischemia, protein synthesis recovered to normal in all brain regions except the CA1 sector, where it returned to only 50% of control after 6 h and to less than 20% after 3 days of recirculation. After three episodes of 5 min of ischemia spaced at 1 h intervals, protein synthesis remained severely suppressed in all brain regions after both 6 h and 3 days of recirculation. Inhibition of protein synthesis after 6 h predicted histological injury after 3 days of recirculation. In animals submitted to a single episode of 5 or 15 min of ischemia, histological damage was restricted to the CA1 sector but injury occurred throughout the brain after three episodes of 5 min of ischemia. These observations demonstrate that persisting inhibition of protein synthesis following cerebral ischemia is an early manifestation of neuronal injury. Prevention of neuronal injury requires restoration of a normal protein synthesis rate.
NMR Determination of the TCA Cycle Rate and α-Ketoglutarate/Glutamate Exchange Rate in Rat Brain
Authors: Mason Graeme F. , Rothman Douglas L. , Behar Kevin L. , Shulman Robert G.
Published: April 2011

A mathematical model of cerebral glucose metabolism was developed to analyze the isotopic labeling of carbon atoms C4 and C3 of glutamate following an intravenous infusion of [1-13C]glucose. The model consists of a series of coupled metabolic pools representing glucose, glycolytic intermediates, tricarboxylic acid (TCA) cycle intermediates, glutamate, aspartate, and glutamine. Based on the rate of 13C isotopic labeling of glutamate C4 measured in a previous study, the TCA cycle rate in rat brain was determined to be 1.58 ± 0.41 μmol min−1 g−1 (mean ± SD, n = 5). Analysis of the difference between the rates of isotopic enrichment of glutamate C4 and C3 permitted the rate of exchange between α-ketoglutarate (α-KG) and glutamate to be assessed in vivo. In rat brain, the exchange rate between α-KG and glutamate is between 89 ± 35 and 126 ± 22 times faster than the TCA cycle rate (mean ± SD, n = 4). The sensitivity of the calculated value of the TCA cycle rate to other metabolic fluxes and to concentrations of glycolytic and TCA cycle intermediates was tested and found to be small.
A Rat Model of Reproducible Cerebral Infarction Using Thrombotic Blood Clot Emboli
Authors: Overgaard Karsten , Sereghy Tomas , Boysen Gudrun , Pedersen Hans , Høyer Søren , Diemer Nils H.
Published: April 2011

The purpose of this study was the development of a model of embolic stroke with high reproducibility concerning infarct volume. In 37 male Sprague–Dawley rats, the internal carotid artery was embolized with in vitro preformed suspensions of autologous microemboli resembling arterial thrombi. With a method of continuous flow through the carotid arterial catheter, reflux of blood with uncontrolled clotting and embolization was avoided, thereby providing control animals free of ischemic damage. The embolized animals had arterial occlusions on angiograms immediately after embolization and no spontaneous recanalization on angiograms 2 h later. The cerebral blood flow measured by the intraarterial 133Xe injection method decreased to 21–37% of baseline values. All embolized animals developed hemiparesis with spontaneous circling behavior, embolization with more than 150 μl clot suspension resulted in hemispherical infarcts. There was a strong statistically significant correlation between amount of emboli, rate of vascular occlusion, and volume of infarcted tissue. This is the first model presented utilizing autologous in vitro microemboli imitating “white” arterial thrombi. The animals developed infarction, resembling human stroke.
Decreases in Frontal and Parietal Lobe Regional Cerebral Blood Flow Related to Habituation
Authors: Warach Steven , Gur Ruben C. , Gur Raquel E. , Skolnick Brett E. , Obrist Walter D. , Reivich Martin
Published: April 2011

We previously reported decreased mean CBF between consecutive resting conditions, ascribed to habituation. Here we address the regional specificity of habituation over three consecutive flow studies. Regional CBF (rCBF) was measured in 55 adults (12 right-handed men, 12 right-handed women, 14 left-handed men, 17 left-handed women), with the 133Xe inhalation technique, during three conditions: Resting, verbal tasks (analogies), and spatial tasks (line orientation). Changes in rCBF attributable to the cognitive tasks were eliminated by correcting these values to a resting equivalent. There was a progressive decrease in mean rCBF over time, reflecting habituation. This effect differed by region, with specificity at frontal (prefrontal, inferior frontal, midfrontal, superior frontal) and inferior parietal regions. In the inferior parietal region, habituation was more marked in the left than the right hemisphere. Right-handers showed greater habituation than did left-handers. There was no sex difference in global habituation, but males showed greater left whereas females showed greater right hemispheric habituation. The results suggest that habituation to the experimental setting has measurable effects on rCBF, which are differently lateralized for men and women. These effects are superimposed on task activation and are most pronounced in regions that have been implicated in attentional processes. Thus, regional decrement in brain activity related to habituation seems to complement attentional effects, suggesting a neural network for habituation reciprocating that for attention.
Evoked Neuronal Activity Accompanied by Transmitter Release Increases Oxygen Concentration in Rat Striatum in vivo but Not in vitro
Authors: Zimmerman Jayne B. , Kennedy Robert T. , Wightman R. Mark
Published: April 2011

Dopamine and oxygen (O2) were measured in the caudate nucleus of anesthetized rats and in striatal slices during electrical stimulation. Simultaneous electrochemical detection of dopamine and O2 was accomplished with fast-scan cyclic voltammetry at a Nafion-coated carbon-fiber microelectrode. Stimulation of the medial forebrain bundle resulted in synaptic overflow of dopamine in the caudate nucleus. At the same time, O2 concentration increased in the extracellular fluid with two separate phases. The amplitude of the initial increase directly correlated with the frequency of the stimulus, with the time of maximum concentration reproducible across a range of frequencies. The second increase occurred at later times with a more random amplitude and with a broad, variable shape. Agents which blocked vasodilation affected both phases: Atropine attenuated the initial increase, while the second feature was nearly absent after theophylline. Yohimbine and α-methyl- p-tyrosine did not affect the O2 responses. Local electrical stimulation of the slice preparation also resulted in dopamine overflow, but a prolonged decrease in O2 concentration accompanied this event. Striatal field stimulation in vivo produced changes in O2 concentration dependent on the relative position of the stimulating and working electrodes, but none of the responses resembled that seen in the caudate slice. Thus, while measurements in brain slices show O2 consumption as a result of stimulated neuronal activity, an apparent elevation of local cerebral blood flow during and after stimulation dominate the in vivo response.
Ubiquinone Protects Cultured Neurons against Spontaneous and Excitotoxin-Induced Degeneration
Authors: Favit Antonella , Nicoletti Ferdinando , Scapagnini Umberto , Canonico Pier Luigi
Published: April 2011

Ubiquinone is an endogenous quinone with pharmacological actions mainly related to its antioxidant properties. Here we report that ubiquinone protects cultured cerebellar granule cells against glutamate-induced neurotoxicity. In control cultures at 9 days of maturation in vitro (DIV), a 30-min exposure to 100 μ M glutamate induced neuronal degeneration, as reflected by the great percentage (>90%) of cells labeled with propidium iodide 24 h after the exposure. Glutamate-induced neuronal death was dramatically reduced in cultures treated daily with ubiquinone since the second DIV. In these cultures, glutamate failed to induce a “delayed” increase in the influx of 45Ca2+, an established parameter of excitotoxicity. Similarly, repeated addition of ubiquinone attenuated in a concentration-dependent manner the age-dependent degeneration of granule cells that is due to the toxic action of the endogenous glutamate progressively released into the medium. These results suggest that ubiquinone may be a useful drug in the therapy of acute and chronic neurodegenerative diseases related to hyperactivity of excitatory amino acid neurotransmission.