bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanisms of Cerebrovascular O2 Sensitivity from Hyperoxia to Moderate Hypoxia in the Rat
Authors: Shinozuka Tadashi , Nemoto Edwin M. , Winter Peter M.
Published: April 2011

Cerebrovascular dilation over PaO2 ranging from hyperoxia to moderate hypoxia is unexplained. We hypothesize that tissue acidosis is the cause. Local cortical cerebral blood flow (LCBF), tissue hydrogen ion concentration [H+]t, and tissue Po2 (Pto2) were measured with microelectrodes in the parietal cortex of 18 rats during a 30-min steady state on 60 to 10% inspired O2 (Pao2, 300 to 40 torr) during 40% N2O analgesia. Five rats kept on 60% O2/40% N2O served as controls. In 18 rats at a Pao2 of 275 ± 7 torr (X̄ ± SEM) and Paco2 of 35 ±1 torr, cerebral values were: LCBF = 129 ± 23 (X̄ ± SEM) ml · 100 g−1 · min−1; [H+], = 62 ± 6 n M; and Pto2 = 25 ± 3 torr. As Pao2 was reduced from about 300 to 40 torr, changes in these variables in percentage of control with respect to Pao2, were described by the following equations, all at P < 0.0001: LCBF = 85.9 + 5,572/Pao2; [H+]t = 97.15 + 1,012/Pao2; and = 108.8 − 3,492/Pao2. Simultaneous solution of the LCBF and [H+]t equations at various Pao2 revealed a slope of 8.82%/n M. Direct correlation between LCBF in ml · 100 g−1 · min−1 and [H+]t in n M revealed a linear relationship defined by the equation Y = − 7.472 + 1.6705 X ( r = 0.6426) for [H+]t between 56 and 160 n M (pH = 7.25 and 6.80) but no correlation at [H+]t values between 56 and 32 n M (pH = 7.25 to 7.50). Cerebrovascular tone is directly correlated with [H+]t during progressive, 30-min steady-state reduction in Pao2 from 350 to 40 torr.
Acetylcholine and Vasoactive Intestinal Peptide in Cerebral Blood Vessels: Effect of Extirpation of the Sphenopalatine Ganglion
Authors: Hara H. , Jansen I. , Ekman R. , Hamel E. , MacKenzie E. T. , Uddman R. , Edvinsson L.
Published: April 2011

The innervation of cerebral blood vessels by nerve fibers containing acetylcholinesterase (AChE) and vasoactive intestinal peptide (VIP) and the vasomotor effects of the two neurotransmitters have been analyzed in the rat following the uni- or bilateral removal of the sphenopalatine ganglion (SPG), which is thought to be the major origin of this innervation. Histochemistry of AChE-positive nerve fibers and the immunoreactivity toward VIP revealed only a 30% reduction in the innervation pattern of the rostral part of the cerebral circulation following the operation. At ∼4 weeks postoperatively, the original nerve network was restored. Quantitative measurements of cholineacetyltransferase activity and VIP revealed similar reductions in the levels of collected large cerebral arteries at the base of the brain and in small pial vessels overlying the cerebral cortex at the various postoperative times following uni- or bilateral removal of the SPG. The two techniques thus complemented each other. Vasomotor reactivity to acetylcholine (ACh) and VIP was examined in proximal segments of the middle cerebral artery at the various postoperative times. Generally, the removal of the SPG had no effect on the responses to ACh or VIP. The evidence indicates that only approximately one-third of the cholinergic/VIP innervation of the rostral part of the cerebral circulation originates in the SPG.
Retrograde Tracing of Nerve Fibers to the Rat Middle Cerebral Artery with True Blue: Colocalization with Different Peptides
Authors: Edvinsson L. , Hara H. , Uddman R.
Published: April 2011

The origin of nerve fibers to the rat middle cerebral artery was studied by retrograde tracing with the fluorescent tracer True Blue (TB) in combination with immunocytochemistry to known perivascular peptides. Application of TB to the middle cerebral artery labeled nerve cell bodies in the ipsilateral superior cervical ganglion, the otic ganglion, the sphenopalatine ganglion, the trigeminal ganglion, and the cervical dorsal root ganglion at level C2. A few labeled nerve cell bodies were seen in contralateral ganglia. Judging from the number and intensity of the labeling, the superior cervical ganglion and the trigeminal ganglion and dorsal root ganglion at level C2 contributed most to the innervation. A moderate number of nerve cell bodies were labeled in the sphenopalatine and otic ganglia. The TB-labeled nerve cell bodies were further examined for the presence of neuropeptides. For that purpose antibodies raised against neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), substance P (SP) and calcitonin gene-related peptide (CGRP) were used. A considerable portion of the TB-labeled nerve cell bodies in the superior cervical ganglion contained NPY. About half of the labeled nerve cell bodies in the sphenopalatine and otic ganglia contained VIP. In the trigeminal ganglion and in the dorsal root ganglion at level C2, one-third of the TB-labeled nerve cell bodies were CGRP-immunoreactive, while only few nerve cell bodies contained SP. The study provides direct evidence for the origin of cerebrovascular peptidergic nerve fibers and demonstrates that not only ipsilateral but also contralateral ganglia contribute to the innervation of the cerebral circulation.
Effect of Hemoglobin on Neurogenic Responses and Cholinergic Parameters in Porcine Cerebral Arteries
Authors: Linnik Matthew D. , Lee Tony Jer-Fu
Published: April 2011

Electrically stimulated neurogenic vasodilation and endothelial-dependent cholinergic vasodilation in cerebral arteries are both blocked by hemoglobin. To determine if neurogenic vasodilation has a cholinergic component, we examined the effect of hemoglobin on neurogenic responses and perivascular cholinergic parameters in isolated porcine cerebral arteries. The perfused circle of Willis has a mixed response to transmural nerve stimulation (TNS) that is predominately vasodilation. Exposure to hemoglobin (5 μM) causes constriction of this preparation while simultaneously blocking TNS-induced vasodilation. At similar concentrations, however, hemoglobin did not alter electrically stimulated, tetrodotoxin-sensitive release of acetylcholine. Hemoglobin also had no effect on neuronal choline uptake or esteratic inactivation of acetylcholine. These results demonstrate the ability of low concentrations of hemoglobin to alter cerebral neurogenic vasodilation. The failure of hemoglobin to affect any aspect of cholinergic transmission, however, provides further evidence against a direct vasodilatory role for acetylcholine as a terminal transmitter in isolated cerebral blood vessels.
The Transport of Leucine and Aminocyclopentanecarboxylate across the Intact, Energy-Depleted Rat Blood—Brain Barrier
Authors: Greenwood J. , Hazell A. S. , Pratt O. E.
Published: April 2011

The transport across the blood-brain barrier of the large neutral amino acid leucine and the nonmetabolised aminocyclopentanecarboxylate (ACPC), of similar molecular size, was studied in the perfused, energy-depleted rat brain. It was found that when both leucine and ACPC were perfused for periods of up to 10 min their accumulation in the brain increased in a linear fashion. The ratio of perfusate radioactivity per milliliter and tissue radioactivity per gram (Rt/Rp) rose to above unity for both leucine and ACPC, indicating continued uptake against a concentration gradient of the radiolabel within the CNS. When the effect of increasing the concentration of the amino acid upon its influx into the brain was studied, it was found that under these conditions the kinetics of transport for both leucine and ACPC were of a similar order of magnitude to those reported previously in vivo. The values for the Michaelis constant for transport ( Km), maximum rate of transport ( Vmax), and the constant for the apparently linear, nonsaturable component ( Kd) for leucine into the cerebrum were 84.5 ± 29.0 μ M, 45.5 ± 1.5 nmole/min/g, and 2.62 ± 0.15 μl/min/g, respectively, and for ACPC 381 ± 64 μ M, 54.0 ± 1.5 nmole/min/g and 0.35 ± 0.10 μl/min/g, respectively. Comparing this data with previously reported values it is suggested that the transport of leucine into the central nervous system from a perfusate or bolus where no other competing amino acids are present, is flow dependent. Furthermore, ACPC enters the brain almost entirely by a carrier-mediated process, with little or no nonsaturable influx despite a similar oil/water partition coefficient as leucine.
Postnatal Changes in Local Cerebral Blood Flow Measured by the Quantitative Autoradiographic [14C]Iodoantipyrine Technique in Freely Moving Rats
Authors: Nehlig Astrid , de Vasconcelos Anne Pereira , Boyet Sylvette
Published: April 2011

The postnatal changes in local cerebral blood flow in freely moving rats were measured by means of the quantitative autoradiographic [14C]iodoantipyrine method. The animals were studied at 10, 14, 17, 21, and 35 days and at the adult stage. At 10 days after birth, rates of blood flow were very low and quite homogeneous in most cerebral structures except in a few posterior areas. From these relatively uniform levels, values of local cerebral blood flow rose notably to reach a peak at 17 days in all brain regions studied. Rates of blood flow decreased between 17 and 21 days after birth and then increased from weaning time to reach the known characteristic distribution of the adult rat. The postnatal evolution of local cerebral blood flow in the rat is in good agreement with previous studies in other species such as dog and humans that also show higher rates of cerebral blood flow and glucose utilization at immature stages. However, in the rat, local cerebral blood flow and local cerebral glucose utilization are not coupled over the whole postnatal period studied, since blood flow rates reach peak values at 17 days whereas glucose utilization remains still quite low at that stage. The high rate of cerebral blood flow in the 17-day-old rat may reflect the energetic and biosynthetic needs of the actively developing brain that are completed by the summation of glucose and ketone body utilization.
Ischemic Flow Threshold for Extracellular Glutamate Increase in Cat Cortex
Authors: Shimada Nobumitsu , Graf Rudolf , Rosner Gerd , Wakayama Akatsuki , George Charles P. , Heiss Wolf-Dieter
Published: April 2011

Extracellular glutamate (Glu), cerebral blood flow (CBF), and auditory-evoked potentials (AEPs) were measured concurrently using microdialysis and hydrogen clearance in the auditory cortex of anesthetized cats during global ischemia of various severities. A threshold-type relationship was observed between extracellular Glu and CBF: Glu increased at CBF levels below about 20 ml/100 g/min. The Glu increase was related to the impairment of AEPs. The results suggest that Glu neurotoxicity is an important factor for ischemic neuronal injury even in penumbra.
Effect of the NMDA Antagonist MK-801 on Local Cerebral Blood Flow in Focal Cerebral Ischaemia in the Rat
Authors: Park C. K. , Nehls D. G. , Teasdale G. M. , McCulloch J.
Published: April 2011

The effects of MK-801 upon local CBF after permanent middle cerebral artery (MCA) occlusion have been examined using [14C]iodoantipyrine autoradiography in halothane-anaesthetised rats. MK-801 (0.5 mg kg-1 i.v.) or saline was administered 30 min before MCA occlusion and CBF measured ∼40 min after occlusion. In the hemisphere contralateral to the occluded MCA, MK-801 significantly reduced local CBF in 19 of the 22 regions examined from the levels in saline-treated rats. In the contralateral hemisphere, after treatment with MK-801, blood flow was reduced by an average of 37% with little variation in the magnitude of the reductions in different regions. In the hemisphere ipsilateral to MCA occlusion, MK-801 reduced CBF in almost every region located outside the territory of the occluded MCA. Within the territory of the occluded MCA, blood flow in the MK-801–treated rat did not significantly differ from values in vehicle-treated rats in any of the five cortical areas examined, although in the caudate nucleus there was a tendency for CBF to be lower in rats pretreated with MK-801. MK-801 had no effect on the amount of hypoperfused cerebral tissue (CBF <30 ml 100 g−1 min−1) in the ipsilateral hemisphere at any coronal plane examined; e.g., at coronal plane anterior 7.2 mm, 51 ± 5% of the hemisphere displayed CBF of <30 ml 100 g−1 min−1 in saline-treated rats with MCA occlusion compared with 52 ± 8% of the hemisphere in rats treated with MK-801 prior to MCA occlusion. Thus, the reported antiischaemic effects of MK-801 in this model cannot be attributed to improvement of blood flow to the hypoperfused cerebral tissue.
NMR Spectroscopic Investigation of the Recovery of Energy and Acid—Base Homeostasis in the Cat Brain after Prolonged Ischemia
Authors: Behar K. L. , Rothman D. L. , Hossmann K.-A.
Published: April 2011

The effects of 1 h of complete global ischemia on the recovery of high-energy phosphates, intracellular pH (pHi), and lactate in the cat brain in vivo was investigated by 31P and 1H NMR spectroscopy. Ischemia led to a decrease in creatine phosphate (CrP), nucleoside triphosphates (NTP), and pHi, while inorganic phosphate and lactate increased. Intracellular pH decreased from a control value of 7.07 ± 0.04 to 6.17 ± 0.12 after 1 h of ischemia ( N = 7). The degree of metabolic recovery after recirculation was variable. In three animals CrP and NTP were detected within 4 min and NTP increased to ≥90% of control within 1 h; these levels were maintained for the 3 h of observation. In four other animals, CrP and NTP reached only 20 to 80% of control; however, high-energy phosphates decreased and lactate increased spontaneously between 1 and 2.5 h. Immediately following recirculation, pHi decreased further by an average of 0.3 units. The rate of recovery of cerebral pHi was slower than that of PCr and NTP for the majority of animals. Recovery of pHi was not detected for an average of 32 min after recirculation—by this time, NTP had attained 80 ± 10% of their preischemic level. Recovery of pHi (and lactate) was not observed in two animals where PCr and NTP recovered transiently to only 30–43% of the preischemic level. Recovery of cerebral pHi was markedly heterogeneous in one animal, since two Pi peaks were detected shortly after recirculation. No correlation was found between the maximum levels of CrP and NTP attained after recirculation and the value of pHi during ischemia.
Changes in Cortical Extracellular Levels of Energy-Related Metabolites and Amino Acids following Concussive Brain Injury in Rats
Authors: Nilsson P. , Hillered L. , Pontén U. , Ungerstedt U.
Published: April 2011

The aim of this study was to measure extracellular chemical changes in the cerebral cortex in response to compression contusion trauma in rats. Energy-related metabolites (i.e., lactate, pyruvate, adenosine, inosine, and hypoxanthine) and amino acids were harvested from the extracellular fluid (ECF) using microdialysis and analyzed by high-performance liquid chromatography. The measurements were performed in cortical tissue, where neuronal injury occurs in this model. The severity of the trauma was varied by using different depths of impact: mild trauma, 1.5 mm; severe trauma, 2.5 mm. The trauma induced a dramatic increase in the ECF levels of energy-related metabolites that was conditioned by the severity of the insult. The ECF level of taurine, glutamate, aspartate, and γ-aminobutyric acid (GABA) also rose markedly, while other amino acids did not change significantly. The results suggest that the trauma induced a transient, profound focal disturbance of energy metabolism in the cortical tissue, probably as a result of mechanically induced disruption of ion homeostasis and reduced blood flow in combination. The data support the potential role of glutamate and aspartate as mediators of traumatic brain injury. However, the concomitantly released adenosine, GABA, and taurine may be protective and ameliorate excitotoxicity. In analogy with the reported cumulative damaging effects of repeated ischemic insults, the observed ECF changes may help explain the vulnerability of traumatized brain tissue to secondary ischemia.
Graphical Analysis of Reversible Radioligand Binding from Time—Activity Measurements Applied to [N-11C-Methyl]-(−)-Cocaine PET Studies in Human Subjects
Authors: Logan Jean , Fowler Joanna S. , Volkow Nora D. , Wolf Alfred P. , Dewey Stephen L. , Schlyer David J. , MacGregor Robert R. , Hitzemann Robert , Bendriem Bernard , Gatley S. John , Christman David R.
Published: April 2011

A graphical method of analysis applicable to ligands that bind reversibly to receptors or enzymes requiring the simultaneous measurement of plasma and tissue radioactivities for multiple times after the injection of a radiolabeled tracer is presented. It is shown that there is a time t† after which a plot of f t0ROI( t') dt'/ROI( t) versus f t0 Cp( t') dt'/ROI( t) (where ROI and Cp are functions of time describing the variation of tissue radioactivity and plasma radioactivity, respectively) is linear with a slope that corresponds to the steady-state space of the ligand plus the plasma volume, Vp. For a two-compartment model, the slope is given by λ + Vp, where λ is the partition coefficient and the intercept is −1/[ k2(1 + Vp/λ)]. For a three-compartment model, the slope is λ(1 + Bmax/ Kd) + Vp and the intercept is −{(1 + Bmax/ Kd)/ k2 + [ koff(1 + Kd/ Bmax)]−1} [1 + Vp/λ(1 + Bmax/ Kd)]−1 (where Bmax represents the concentration of ligand binding sites and Kd the equilibrium dissociation constant of the ligand–binding site complex, koff ( k4) the ligand–binding site dissociation constant, and k2 is the transfer constant from tissue to plasma). This graphical method provides the ratio Bmax/ Kd from the slope for comparison with in vitro measures of the same parameter. It also provides an easy, rapid method for comparison of the reproducibility of repeated measures in a single subject, for longitudinal or drug intervention protocols, or for comparing experimental results between subjects. Although the linearity of this plot holds when ROI/ Cp is constant, it can be shown that, for many systems, linearity is effectively reached some time before this. This analysis has been applied to data from [ N-methyl-11C]-(–)-cocaine ([11C]cocaine) studies in normal human volunteers and the results are compared to the standard nonlinear least-squares analysis. The calculated value of Bmax/ Kd for the high-affinity binding site for cocaine is 0.62 ± 0.20, in agreement with literature values.
Astrocytic Acidosis in Hyperglycemic and Complete Ischemia
Authors: Kraig Richard P. , Chesler Mitchell
Published: April 2011

Nearly complete brain ischemia under normoglycemic conditions results in death of only selectively vulnerable neurons. With prior elevation of brain glucose, such injury is enhanced to include pancellular necrosis (i.e., infarction), perhaps because an associated, severe lactic acidosis preferentially injures astrocytes. However, no direct physiologic measurements exist to support this hypothesis. Therefore, we used microelectrodes to measure intracellular pH and passive electrical properties of cortical astrocytes as a first approach to characterizing the physiologic behavior of these cells during hyperglycemic and complete ischemia, conditions that produce infarction in reperfused brain. Anesthesized rats (n = 26) were made extremely hyperglycemic (blood glucose, 51.4 ± 2.8 m M) so as to create potentially the most extreme acidic conditions possible; then ischemia was induced by cardiac arrest. Two loci more acidic than the interstitial space (6.17–6.20 pH) were found. The more acidic locus [4.30 ± 0.19 (n = 5); range: 3.82–4.89] was occasionally seen at the onset of anoxic depolarization, 3–7 min after cardiac arrest. The less acidic locus [5.30 ± 0.07 (n = 53); range 4.46–5.93)] was seen 5–46 min after cardiac arrest. A small negative change in DC potential [8 ± 1 mV (n = 5); range –3 to –12 mV and 7 ± 2 mV (n = 53); range + 3 to –31 mV, respectively] was always seen upon impalement of acidic loci, suggesting cellular penetration. In a separate group of five animals, electrical characteristics of these cells were specifically measured (n = 17): membrane potential was –12 ± 0.2 mV (range –3 to –24 mV), input resistance was 114 ± 16 MΩ (range 25–250 MΩ), and time constant was 4.4 ± 0.4 ms (range 3.0–7.9 ms). Injection of horseradish peroxidase into cells from either animal group uniformly stained degenerating astrocytes. These findings establish previously unrecognized properties of ischemic astrocytes that may be prerequisites for infarction from nearly complete ischemia: the capacity to develop profound cellular acidosis and a concomitant reduction in cell membrane ion permeability.
Influence of Plasma Glucose Concentration on Lumped Constant of the Deoxyglucose Method: Effects of Hyperglycemia in the Rat
Authors: Schuier Franz , Orzi Francesco , Suda Sumio , Lucignani Giovanni , Kennedy Charles , Sokoloff Louis
Published: April 2011

The lumped constant of the deoxyglucose method was determined by the steady-state, model-independent method in the brain of normal conscious rats with arterial plasma glucose concentrations varying from normoglycemia (i.e., 8 m M) to hyperglycemia (i.e., 31 m M). The lumped constant for brain was found to decrease very gradually with increasing arterial plasma glucose concentration from a value of ∼0.45 in the midnor-moglycemic range (i.e., 7–8 m M) to ∼0.38 at 28–31 m M. 3- O-[14C]Methylglucose was used to assess the distribution of glucose within the brain structures in hyperglycemia; the results indicated that the glucose concentration, and therefore also the values for the lumped constant, remain relatively uniform in hyperglycemia with arterial plasma glucose concentrations as high as 34 m M. The values for the lumped constant for rat brain determined in the present studies were combined with those previously determined in this laboratory for hypoglycemia and normoglycemia by the same method to provide a single source for the values for the lumped constant to be used over the full range of arterial plasma glucose concentrations. In several rats the lumped constant for cephalic extracerebral tissues was also evaluated in parallel with those for the brain. The lumped constant for the cephalic extracerebral tissues was found to be about twice that for brain and to be unaffected by changes in arterial plasma glucose levels.
Nimodipine Pretreatment Improves Cerebral Blood Flow and Reduces Brain Edema in Conscious Rats Subjected to Focal Cerebral Ischemia
Authors: Jacewicz Michael , Brint Steve , Tanabe Jody , Wang Xing-Je , Pulsinelli William A.
Published: April 2011

The effect of nimodipine pretreatment on CBF and brain edema was studied in conscious rats subjected to 2.5 h of focal cortical ischemia. An infusion of nimodipine (2 μg/kg/min i.v.) or its vehicle, polyethylene glycol 400, was begun 2 h before the ischemic interval and was continued throughout the survival period. Under brief halothane anesthesia, the animals' right middle cerebral and common carotid arteries were permanently occluded, and 2.5 h later, they underwent a quantitative CBF study ([14C]iodoantipyrine autoradiography followed by Quantimet 970 image analysis). Nimodipine treatment improved blood flow to the middle cerebral artery territory without evidence of a “vascular steal” and reduced the volume of the ischemic core (cortex with CBF of < 25 ml/100 g/min) and accompanying edema by ∼50% when compared with controls (p = 0.006 and 0.0004, respectively). Mild hypotension induced by nimodipine did not aggravate the ischemic insult. The ischemic core volumes, however, were 50–75% smaller than the 24-h infarct volumes generated in a similar paradigm that demonstrated 20–30% infarct reduction with continuous nimodipine treatment. These results suggest that nimodipine pretreatment attenuates the severity of early focal cerebral ischemia, but that with persistent ischemia, cortex surrounding the ischemic core undergoes progressive infarction and the early benefit of nimodipine treatment is only partly preserved.
The Flux from Glucose to Glutamate in the Rat Brain in vivo as Determined by 1-Observed, 13C-Edited NMR Spectroscopy
Authors: Fitzpatrick Susan M. , Hetherington Hoby P. , Behar Kevin L. , Shulman Robert G.
Published: April 2011

The rate of incorporation of carbon from [1-13C]glucose into the [4-CH2] and [3-CH2] of cerebral glutamate was measured in the rat brain in vivo by 1H-observed, 13C-edited (POCE) nuclear magnetic resonance (NMR) spectroscopy. Spectra were acquired every 98 s during a 60-min infusion of [1-13C]glucose. Complete time courses were obtained from six animals. The measured intensity of the unresolved [4-13CH2] resonances of glutamate and glutamine increased exponentially during the infusion and attained a steady state in ∼20 min with a first-order rate constant of 0.130 ± 0.010 min−1 (t1/2 = 5.3 ± 0.5 min). The appearance of the [3-13CH2] resonance in the POCE difference spectrum lagged behind that of the [4-13CH2] resonance and had not reached steady state at the end of the 60-min infusion (t1/2 = 26.6 ± 4.1 min). The increase observed in 13C-labeled glutamate represented isotopic enrichment and was not due to a change in the total glutamate concentration. The glucose infusion did not affect the levels of high-energy phosphates or intracellular pH as determined by 31P NMR spectroscopy. Since glucose carbon is incorporated into glutamate by rapid exchange with the tricarboxylic acid (TCA) cycle intermediate α-ketoglutarate, the rate of glutamate labeling provided an estimate of TCA cycle flux. We have determined the flux of carbon through the TCA cycle to be ≈1.4 μmol g−1 min−1. These experiments demonstrate the feasibility of measuring metabolic fluxes in vivo using 13C-labeled glucose and the technique of 1H-observed, 13C-decoupled NMR spectroscopy.
The Effects of Dizocilpine Maleate (MK-801), an Antagonist of the N-Methyl-D-Aspartate Receptor, on Neurologic Recovery and Histopathology following Complete Cerebral Ischemia in Primates
Authors: Lanier William L. , Perkins William J. , Karlsson Bente R. , Milde James H. , Scheithauer Bernd W. , Shearman Gary T. , Michenfelder John D.
Published: April 2011

The present study was designed to determine if the noncompetitive excitatory amino acid antagonist, dizocilpine maleate, when administered after a 17 min period of complete cerebral ischemia in primates, would improve postischemic neurologic function and hippocampal histopathologic outcome when compared to placebo-treated animals. Ten pigtail monkeys were anesthetized and subjected to complete cerebral ischemia using an established neck tourniquet model. Five minutes postischemia, five monkeys received dizocilpine 300 μg/kg i.v. over 5 min, followed by an infusion of 150 μg/kg/h for 10 h. This produced plasma levels of the drug in excess of 30 ng/ml for the duration of the infusion. An additional five monkeys were treated with an identical volume of saline placebo. All monkeys received intensive care for the initial 24 to 48 h postischemia. At 96 h postischemia, there was no significant difference in neurologic function between the two groups ( p = 0.53, with the placebo group having the numerically better outcome). There also was no significant difference between hippocampal histopathology scores between dizocilpine and placebo-treated monkeys. The authors conclude that dizocilpine is not an efficacious therapy in the treatment of neurologic injury that occurs following complete cerebral ischemia in this primate model.
A Two-Compartment Description and Kinetic Procedure for Measuring Regional Cerebral [11C]Nomifensine Uptake Using Positron Emission Tomography
Authors: Salmon Eric , Brooks David J. , Leenders Klaus L. , Turton David R. , Hume Sue P. , Cremer Jill E. , Jones Terry , Frackowiak Richard S. J.
Published: April 2011

S-[11C]Nomifensine ( S-[11C]NMF) is a positron-emitting tracer suitable for positron emission tomography, which binds to both dopaminergic and noradrenergic reuptake sites in the striatum and the thalamus. Modelling of the cerebral distribution of this drug has been hampered by the rapid appearance of glucuronide metabolites in the plasma, which do not cross the blood–brain barrier. To date, [11C]NMF uptake has simply been expressed as regional versus nonspecific cerebellar activity ratios. We have calculated a “free” NMF input curve from red cell activity curves, using the fact that the free drug rapidly equilibrates between red cells and plasma, while glucuronides do not enter red cells. With this free [11C]NMF input function, all regional cerebral uptake curves could be fitted to a conventional two-compartment model, defining tracer distribution in terms of [11C]NMF regional volume of distribution. Assuming that the cerebellar volume of distribution of [11C]NMF represents the nonspecific volume of distribution of the tracer in striatum and thalamus, we have calculated an equilibrium partition coefficient for [11C]NMF between freely exchanging specific and nonspecific compartments in these regions, representing its “binding potential” to dopaminergic or noradrenergic uptake sites (or complexes). This partition coefficient was lower in the striatum when the racemate rather than the active S-enantiomer of [11C]NMF was administered. In the striatum of patients suffering from Parkinson's disease and multiple-system atrophy, the specific compartmentation of S-[11C]NMF was significantly decreased compared with that of age-matched volunteers.
Autoregulation of Cerebral Blood Flow in Experimental Focal Brain Ischemia
Authors: Dirnagl Ulrich , Pulsinelli William
Published: April 2011

The relationship between systemic arterial pressure (SAP) and neocortical microcirculatory blood-flow (CBF) in areas of focal cerebral ischemia was studied in 15 spontaneously hypertensive rats (SHRs) anesthetized with halothane (0.5%). Ischemia was induced by ipsilateral middle cerebral artery/common carotid artery occlusion and CBF was monitored continuously in the ischemic territory using laser-Doppler flowmetry during manipulation of SAP with I-norepinephrine (hypertension) or nitroprusside (hypotension). In eight SHRs not subjected to focal ischemia, we demonstrated that 0.5% halothane and the surgical manipulations did not impair autoregulation. Autoregulation was partly preserved in ischemic brain tissue with a CBF of >30% of preocclusion values. In areas where ischemic CBF was <30% of preocclusion values, autoregulation was completely lost. Changes in SAP had a greater influence on CBF in tissue areas where CBF ranged from 15 to 30% of baseline (9% change in CBF with each 10% change in SAP) than in areas where CBF was <15% of baseline (6% change in CBF with each 10% change in SAP). These findings demonstrate that the relationship between CBF and SAP in areas of focal ischemia is highly dependent on the severity of ischemia. Autoregulation is lost in a gradual manner until CBF falls below 30% of normal. In areas without autoregulation, the slope of the CBF/SAP relationship is inversely related to the degree of ischemia.
Dimethylthiourea Reduces Ischemic Brain Edema without Affecting Cerebral Blood Flow
Authors: Martz Dean , Beer Mary , Betz A. Lorris
Published: April 2011

Oxygen free radicals have been implicated as mediators of tissue damage in ischemic brain. We previously demonstrated that the hydroxyl radical scavenger 1,3-dimethyl-2-thiourea (DMTU) reduces infarct size after middle cerebral artery occlusion (MCAO) in rats. The present study was undertaken to determine whether this protection results from a preservation of the CBF. Adult male Sprague-Dawley rats were treated with DMTU (750 mg/kg i.p.) or saline vehicle 1 h before right MCAO. One-half, 4, or 24 h after MCAO, animals were killed and samples were taken from the central, intermediate, and outer zones of the MCA distribution of each cortical mantle. Separate groups of animals were used to analyze these samples for water content (wet and dry weight), CBF ([14C]butanol), or blood–brain barrier permeability ([3H]α-aminoisobutyric acid). CBF was reduced in a graded fashion in the ischemic cortex: 0.169 ± 0.020, 0.261 ± 0.017, and 0.435 ± 0.023 ml/g/min (mean ± SEM, n = 8) after 4 h in the central, intermediate, and outer zones, respectively. Brain edema was present in a similar pattern, while blood–brain barrier permeability remained normal. Treatment with DMTU significantly reduced brain edema in the central and intermediate zones at both 4 and 24 h. However, CBF in the DMTU-treated animals was identical to that of the vehicle-treated animals. These results suggest that hydroxyl radicals play a role in the development of ischemic brain edema, but the mechanism does not appear to involve a direct effect on CBF.
The Lumped Constant of the Deoxyglucose Method in Hypoglycemia: Effects of Moderate Hypoglycemia on Local Cerebral Glucose Utilization in the Rat
Authors: Suda Sumio , Shinohara Mami , Miyaoka Makoto , Lucignani Giovanni , Kennedy Charles , Sokoloff Louis
Published: April 2011

The applicability of the [14C]deoxyglucose method for measuring local cerebral glucose utilization (lCMRglc) has been extended for use in hypoglycemia by determination of the values of the lumped constant to be used in rats with plasma glucose concentrations ranging from approximately 2 to 6 m M. Lumped constant values were higher in hypoglycemia and declined from a value of 1.2 at the lowest arterial plasma glucose level (1.9 m M) to about 0.48 in normoglycemia. The distribution of glucose, and therefore also of the lumped constant, was found to remain relatively uniform throughout the brain at the lowest plasma glucose levels studied. lCMRglc in moderate, insulin-induced hypoglycemia (mean arterial plasma glucose concentration ± SD of 2.4 ± 0.3 m M) was determined with the appropriate lumped constant corresponding to the animal's plasma glucose concentration and compared with the results obtained in six normoglycemic rats. The weighted average rate of glucose utilization for the brain as a whole was significantly depressed by 14% in the hypoglycemic animals, i.e., 61 μmol/100 g/min in hypoglycemia compared to 71 μmol/100 g/min in the normoglycemic controls ( p < 0.05). lCMRglc was lower in 47 of 49 structures examined but statistically significantly below the rate in normoglycemic rats in only six structures ( p < 0.05) by multiple comparison statistics. Regions within the brainstem were most prominently affected. The greatest reductions, statistically significant or not, occurred in structures in which glucose utilization is normally high, suggesting that glucose delivery and transport to the tissue became rate-limiting first in those structures with the greatest metabolic demands for glucose.
Mechanistic Distinctions between Excitotoxic and Acidotic Hippocampal Damage in an in vitro Model of Ischemia
Authors: Tombaugh Geoffrey C. , Sapolsky Robert M.
Published: April 2011

Excitotoxicity is believed to underlie the selective loss of vulnerable neurons after transient ischemia, while lactic acidosis seems to be the principal feature and probable cause of tissue infarcts. Primary hippocampal cultures containing both neurons and astrocytes derived from fetal rats were used to examine the relative contributions of and interactions between excitotoxic and acidotic cell injury. Hypoxia-induced damage was energy dependent and involved the N-methyl-D-aspartate (NMDA) receptor. Glucose above 1 m M could completely protect against hypoxia-induced injury in a pH range of 7.4–6.5, while the NMDA receptor antagonist D,L-2-amino-5-phosphonovaleric acid (500 μ M) during the posthypoxic period provided only partial protection in the absence of glucose. Astrocyte cultures were undamaged by ischemic-like treatment in this pH range, suggesting that hypoxia-induced cell death in mixed cultures was restricted to neurons. Lowering the extracellular pH to 7.0 and 6.5 caused no neuronal damage in normoxic controls, but in each case provided significant protection against hypoxic neuronal injury. In contrast, a second type of neurotoxicity was observed after a 6-h exposure to pH 6.0, while exposure to pH 5.5 was required to kill astrocytes. This acidotic damage appeared to be energy independent and did not involve the NMDA receptor. These results suggest that excitotoxic neuron death has an energetic component and that acidosis may produce both protective and damaging effects in the hippocampus during ischemic insults.
Prevention of Postischemic Hyperthermia Prevents Ischemic Injury of CA1 Neurons in Gerbils
Authors: Kuroiwa Toshihiko , Bonnekoh Petra , Hossmann Konstantin-Alexander
Published: April 2011

Halothane-anesthetized Mongolian gerbils were submitted to 5-min bilateral carotid artery occlusion. After ischemia, halothane anesthesia was continued for various periods of up to 85 min, and the degree of CA1 neuronal injury was estimated 7 days later by counting the number of surviving pyramidal cells. During ischemia and postischemic halothane anesthesia, rectal and cranial temperature was kept at control level (37.7 and 37.0°C, respectively) using a feedback-controlled heating system. When anesthesia was discontinued after ischemia, transient hyperthermia occurred. In animals with 0- and 15-min postischemic halothane anesthesia, both cranial and rectal temperature rose by ∼1.5°C, and the number of surviving CA1 neurons amounted to <25% of control. After 45- or 85-min postischemic anesthesia, hyperthermia was significantly reduced and the number of surviving neurons increased to 65 and 89%, respectively. The protective effect of postischemic anesthesia was lost when anesthetized animals were submitted to the same hyperthermic profile as nonanesthetized ones, using a feedback-controlled heating system (16% surviving neurons in hyperthermia vs. 89% in normothermia, respectively). These observations demonstrate that postischemic anesthesia with 1% halothane protects against delayed neuronal death by preventing postischemic hyperthermia and not by its anesthetic effects.
Kinetic Analysis of the Human Blood-Brain Barrier Transport of Lactate and its Influence by Hypercapnia
Authors: Knudsen Gitte Moos , Paulson Olaf B. , Hertz Marianne M.
Published: April 2011

Blood–brain barrier permeability to L-lactate was studied in 18 patients with the double indicator technique. Venous outflow curves were obtained during normo- and hypercapnia and were analyzed by means of a model that takes tracer backflux and capillary heterogeneity of transit times into account. The average unidirectional extraction of L-lactate was 15%; the transport from the blood to the brain (PS1) was 0.081 ml g−1 min−1 and the transport from the brain to the blood (PS2) was on the same order of magnitude. In hypercapnia, arterial pH decreased from 7.39 to 7.26 and PS1 to L-lactate increased significantly by 110%. PS2 also increased although a statistically significant difference compared to the resting state was not reached. It is concluded that L-lactate is easily taken up by the human brain, and that the mechanism by which it crosses the blood–brain barrier is equilibrative. Furthermore, the brain permeability to lactate is enhanced by hypercapnia and the mechanism is believed to act through the decrease in pH.
Postischemic Hypothermia Fails to Reduce Ischemic Injury in Gerbil Hippocampus
Authors: Welsh Frank A. , Harris Valerie A.
Published: April 2011

The objective of this study was to determine whether postischemic hypothermia diminishes ischemic injury in gerbil hippocampus. Cerebral ischemia was produced by occluding both carotid arteries for 5 min, while maintaining the temperature of the cranium and rectum at 38°C. Upon recirculation, the animals were divided into three groups: Normothermic (38°C), moderately hypothermic (33°C), and deeply hypothermic (23°C). In the normothermic group, cranial and rectal temperatures were maintained at 38°C for 30 min and 2 h, respectively, prior to the removal of the temperature probes. In the moderately hypothermic group, cranial and rectal temperatures were reduced within 10 min to 33°C for 1 h, and then rewarmed to 38°C. In the deeply hypothermic group, rectal temperature was lowered within 10 min to 23°C for 2 h prior to rewarming to 38°C. After recovery for 1 week, the extent of histologic injury in the hippocampus was assessed in stained sections. Maximal injury was present in the CA, subfield in all three groups. These results indicate that hippocampal injury was not diminished by postischemic hypothermia during the first 2 h of reperfusion. Thus, pharmacologic studies of postischemic protection in the gerbil model may not be strongly influenced by transient postischemic hypothermia.
Alterations in Regional Cerebral Blood Flow following Brain Injury in the Rat
Authors: Yamakami Iwao , McIntosh Tracy K.
Published: April 2011

To elucidate the temporal changes in regional cerebral blood flow (rCBF) after experimental traumatic brain injury, serial rCBF measurements were made during a 24-h period following fluid-percussion (F-P) traumatic brain injury in the rat. Brain injury of 2.2 atm was induced over the left parietal cortex and serial measurements of rCBF were performed using the radiolabeled microsphere method. rCBF values were obtained prior to injury and at 15 and 30 min and 1, 2, 4, and 24 h postinjury. At 15 min postinjury, there was a profound, widespread reduction in rCBF in all brain regions studied (p < 0.05). At 30 min and 1 h postinjury, all brain regions except pons-medulla and cerebellum showed significantly reduced rCBF compared to the preinjury values (p < 0.05). By 2 h postinjury, however, a significant focal reduction of rCBF was observed only in the cerebral tissue surrounding the trauma site (p < 0.05); rCBF in the remaining brain regions had recovered to the preinjury levels. By 4 h postinjury, rCBF had returned to normal in all brain regions studied. This recovery of rCBF was still evident at 24 h postinjury. The present study demonstrates that, following the experimental traumatic brain injury in the rat, (a) an initial global suppression of rCBF occurs up to 1 h postinjury; (b) at the trauma site, a more persistent focal reduction of rCBF occurs; and (c) these alterations in rCBF after trauma dissolve by 4 h postinjury. The result was discussed in the context of the neurological, electroencephalographic, magnetic resonance spectroscopic, and pathological findings observed in our lateral F-P brain injury rat model.
Ischemic Thresholds of Cerebral Protein Synthesis and Energy State following Middle Cerebral Artery Occlusion in Rat
Authors: Mies G. , Ishimaru S. , Xie Y. , Seo K. , Hossmann K.-A.
Published: April 2011

The ischemic threshold of protein synthesis and energy state was determined 1, 6, and 12 h after middle cerebral artery (MCA) occlusion in rats. Local blood flow and amino acid incorporation were measured by double tracer autoradiography, and local ATP content by substrate-induced bioluminescence. The various images were evaluated at the striatal level in cerebral cortex by scanning with a microdensitometer with 75 μm resolution. Each 75 × 75 μm digitized image pixel was then converted into the appropriate units of either protein synthesis, ATP content, or blood flow. The ischemic threshold was defined as the flow rate at which 50% of pixels exhibited complete metabolic suppression. One hour after MCA occlusion, the threshold of protein synthesis was 55.3 ± 12.0 ml 100 g−1 min−1 and that of energy failure was 18.5 ± 9.8 ml 100 g−1 min−1. After 6 and 12 h of MCA occlusion, the threshold of protein synthesis did not change (52.0 ± 9.6 and 56.0 ± 6.5 ml 100 g−1 min−1, respectively) but the threshold of energy failure increased significantly at 12 h following MCA occlusion to 31.9 ± 9.7 ml 100 g−1 min−1 ( p < 0.05 compared to 1 h ATP threshold value; all values are mean ± SD). In focal cerebral ischemia, therefore, the threshold of energy failure gradually approached that of protein synthesis. Our results suggest that with increasing duration of ischemia, survival of brain tissue is determined by the high threshold of persisting inhibition of protein synthesis and not by the much lower one of acute energy failure. If the ischemic penumbra is considered to comprise the region in which cerebral protein synthesis is suppressed and energy state is preserved, it follows that the size of the penumbra decreases with the duration of ischemia.
Effects of Dextromethorphan on Regional Cerebral Blood Flow in Focal Cerebral Ischemia
Authors: Lo Eng H. , Steinberg Gary K.
Published: April 2011

Dextromethorphan (DM), a noncompetitive NMDA antagonist, has been demonstrated to reduce ischemic neuronal damage and edema, but DM's influence on cerebral blood flow has not been extensively studied. In this investigation, it is shown that DM has significant effects on regional cerebral blood flow (rCBF) patterns in a rabbit model of focal cerebral ischemia. rCBF was measured using radioactive microspheres following a 1 h permanent occlusion of the left internal carotid, anterior cerebral, and middle cerebral arteries in rabbits. Somatosensory evoked potentials (SEPs) were used to assess the degree of ischemia; only animals where SEPs were completely abolished were used for a frequency distribution analysis of rCBF. It was found that there were significantly more regions with lower flows in animals treated with normal saline (NS) ( n = 7) compared to animals treated with DM ( n = 7) ( p < 0.05, ipsilateral left side; p < 0.001, contralateral right side). The frequency distribution medians were 27.5 ml 100 g−1 min −1 (left) and 70.0 ml 100 g−1 min−1 (right) in the NS group vs. 34.5 ml 100 g−1 min−1 (left) and 80.5 ml 100 g−1 min−1 (right) in the DM group. The left and right hemispheric regional means were 29.4 ± 20 and 74.3 ± 23 ml 100 g−1 min−1, respectively, in the NS group vs. 34.4 ± 16 and 91.0 ± 28 ml 100 g−1 min−1, respectively, in the DM group. However, there were no significant differences in global CBF between the NS group (33.1 ± 18 and 79.2 ± 20 ml 100 g−1 min−1) and the DM group (35.0 ± 10 and 92.0 ± 21 ml 100 g−1 min−1) in both left and right hemispheres, respectively. These results demonstrate that DM has effects on rCBF in focal cerebral ischemia, although it is unclear if these changes represent primary effects of DM on cerebrovascular function, or secondary effects of neuronal protection.
Delayed Neuronal Death is Induced without Postischemic Hyperexcitability: Continuous Multiple-Unit Recording from Ischemic CA1 Neurons
Authors: Imon Hitoshi , Mitani Akira , Andou Yasushi , Arai Tatsuru , Kataoka Kiyoshi
Published: April 2011

It has been proposed that neuronal hyperexcitability during postischemic chronic stage mediates delayed neuronal death in the hippocampal CA1 region. In the present study, multiple-unit spike discharges were continuously recorded from hippocampal CA1 neurons of the awake Mongolian gerbil for 5 days after 5 min of ischemia. Before ischemia, CA1 neurons showed burst-like spike discharges (so-called complex spikes). Spike discharges disappeared 8–40 s after the onset of 5-min ischemia and reappeared 5–30 min after recirculation. The frequency of discharges gradually increased but did not return to the preischemic level. The amplitude of the spike discharges was smaller than that recorded before ischemia and the number of spikes composing the burst-like discharges diminished. CA1 neurons did not show any hyperexcitability for 5 days. However, histological examinations revealed widespread neuronal death in the CA1 region. These results indicate that the delayed neuronal death in the hippocampal CA1 region is induced without postischemic neuronal hyperexcitability.