bluuebunny/crossref_metadata_2025 huggingface dataset:
In Vivo Measurements of Brain Glucose Transport Using the Reversible Michaelis–Menten Model and Simultaneous Measurements of Cerebral Blood Flow Changes during Hypoglycemia
Authors: Choi In-Young , Lee Sang-Pil , Kim Seong-Gi , Gruetter Rolf
Published: November 2003

Glucose is the major substrate that sustains normal brain function. When the brain glucose concentration approaches zero, glucose transport across the blood–brain barrier becomes rate limiting for metabolism during, for example, increased metabolic activity and hypoglycemia. Steady-state brain glucose concentrations in α-chloralose anesthetized rats were measured noninvasively as a function of plasma glucose. The relation between brain and plasma glucose was linear at 4.5 to 30 mmol/L plasma glucose, which is consistent with the reversible Michaelis–Menten model. When the model was fitted to the brain glucose measurements, the apparent Michaelis-Menten constant, Kt, was 3.3 ± 1.0 mmol/L, and the ratio of the maximal transport rate relative to CMRglc, Tmax/CMRglc, was 2.7 ± 0.1. This Kt is comparable to the authors' previous human data, suggesting that glucose transport kinetics in humans and rats are similar. Cerebral blood flow (CBF) was simultaneously assessed and constant above 2 mmol/L plasma glucose at 73 ± 6 mL 100 g−1 min−1. Extrapolation of the reversible Michaelis–Menten model to hypoglycemia correctly predicted the plasma glucose concentration (2.1 ± 0.6 mmol/L) at which brain glucose concentrations approached zero. At this point, CBF increased sharply by 57% ± 22%, suggesting that brain glucose concentration is the signal that triggers defense mechanisms aimed at improving glucose delivery to the brain during hypoglycemia.
The Intraparietal Cortex: Subregions Involved in Fixation, Saccades, and in the Visual and Somatosensory Guidance of Reaching
Authors: Gregoriou Georgia G. , Savaki Helen E.
Published: November 2003

The functional activity of the intraparietal cortex was mapped with the [14C]deoxyglucose method in monkeys performing fixation of a central visual target, saccades to visual targets, reaching in the light during fixation of a central visual target, and acoustically triggered reaching in the dark while the eyes maintained a straight ahead direction. Different subregions of the intraparietal cortical area 7 were activated by fixation, saccades to visual targets, and acoustically triggered reaching in the dark. Subregions in the ventral part of the intraparietal cortex (around the fundus of the intraparietal sulcus) were activated only during reaching in the light, in which case visual information was available to guide the moving forelimb. In contrast, subregions in the dorsal part of the intraparietal cortical area 5 were activated during both reaching in the light and the dark, in which cases somatosensory information was the only one available in common. Thus, visual guidance of reaching is associated with the ventral intraparietal cortex, whereas somatosensory guidance, based on proprioceptive information about the current forelimb position, is associated with dorsal intraparietal area 5.
Neuroprotection in Ischemia–Reperfusion Injury: An Antiinflammatory Approach Using a Novel Broad-Spectrum Chemokine Inhibitor
Authors: Beech John S. , Reckless Jill , Mosedale David E. , Grainger David J. , Williams Steve C. R. , Menon David K.
Published: November 2003

Cerebral ischemia–reperfusion injury is associated with a developing inflammatory response with pathologic contributions from vascular leukocytes and endogenous microglia. Signaling chemokines orchestrate the communication between the different inflammatory cell types and the damaged tissue leading to cellular chemotaxis and lesion occupation. Several therapies aimed at preventing this inflammatory response have demonstrated neuroprotective efficacy in experimental models of stroke, but to date, few investigators have used the chemokines as potential therapeutic targets. In the current study, the authors investigate the neuroprotective action of NR58–3.14.3, a novel broad-spectrum inhibitor of chemokine function (both CXC and CC types), in a rat model of cerebral ischemia–reperfusion injury. Rats were subjected to 90 minutes of focal ischemia by the filament method followed by 72 hours of reperfusion. Both the lesion volume, measured by serial magnetic resonance imaging, and the neurologic function were assessed daily. Intravenous NR58–3.14.3 was administered, 2 mg/kg bolus followed by 0.5 mg/kg · hour constant infusion for the entire 72-hour period. At 72 hours, the cerebral leukocytic infiltrate, tumor necrosis factor-α (TNF-α), and interleukin-8 (IL-8)-like cytokines were analyzed by quantitative immunofluorescence. NR58–3.14.3 significantly reduced the lesion volume by up to 50% at 24, 48, and 72 hours post–middle cerebral artery occlusion, which was associated with a marked functional improvement to 48 hours. In NR58–3.14.3-treated rats, the number of infiltrating granulocytes and macrophages within perilesional regions were reduced, but there were no detectable differences in inflammatory cell numbers within core ischemic areas. The authors reported increased expression of the cytokines, TNF-α, and IL-8–like cytokines within the ischemic lesion, but no differences between the NR58–3.14.3-treated rats and controls were reported. Although chemokines can have pro-or antiinflammatory action, these data suggest the overall effect of chemokine up-regulation and expression in ischemia–reperfusion injury is detrimental to outcome.
Induction of Tie-1 and Tie-2 Receptor Protein Expression after Cerebral Ischemia—Reperfusion
Authors: Lin Teng-Nan , Nian Gau-Ming , Chen Shu-Fen , Cheung Wai-Mui , Chang Chen , Lin Wen-Chang , Hsu Chung Y.
Published: November 2003

Tie-1 and Tie-2 are receptor tyrosine kinases (RTKs) that are exclusively expressed in endothelial cells and play important roles in endothelial cell biology. The authors have reported previously the temporal profiles of Tie-1 and Tie-2 mRNA expression after focal cerebral ischemia–reperfusion. In the current study, the localization of Tie-1/Tie-2 mRNA and proteins were further investigated in the same focal ischemia model. In situ hybridization showed that, after 60-minute ischemia and 72-hour reperfusion, both Tie-1 and Tie-2 mRNA appeared as capillary-like structures in the ischemic middle cerebral artery (MCA) cortex. Western blot analysis showed a biphasic expression of Tie-1 protein in the same region. The first peak, spanning the ischemic and early reperfusion period, was of low intensity and short-lived. The second peak was of greater intensity and spanning the period from 72 to 168 hours after reperfusion. Similarly, Tie-2 expression at the protein level also exhibited a biphasic pattern. Immunohistochemical studies, after 72 hours of reperfusion, showed that although Tie-1 and Tie-2 were detected within the ischemic cortex, they actually were expressed in different populations of endothelial cells in different regions. In agreement with the in situ hybridization study, Tie-1 immunoreactivity appeared as capillary-like structures in cortical layers 2 to 4. Similar capillary-like appearance of Tie-2 immunoreactivity was noted in the outer cortical layers. In addition, Tie-2 immunoreactivity also was observed in cortical layer 6b, where de novo large vessel formation was noted. Cellular colocalization experiments revealed that Tie-2 is expressed in proximity to its antagonist, Angpo-2, as well as basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) in cortical layer 1, where active vessel remodeling was noted. Interestingly, bFGF only partially colocalized with VEGF, suggesting differential roles for these angiogenic factors during vessel remodeling. Tie-1 protein, to a lesser degree, also colocalized with Angpo-2, bFGF, and VEGF in cortical layer 1. Magnetic resonance imaging (MRI) showed increased regional cerebral blood flow (CBF) corresponding to the expression of these angiogenesis gene products. Together, these findings suggest that the evolving expression of angiogenesis genes underlie the robust vascular remodeling after ischemia and reperfusion.
Attenuation of Ischemia-Induced Mouse Brain Injury by SAG, a Redox-Inducible Antioxidant Protein
Authors: Yang Guo-Yuan , Pang Li , Ge Hai-Liang , Tan Mingjia , Ye Wen , Liu Xiao-Hong , Huang Feng-Ping , Wu Du-Chu , Che Xiao-Ming , Song Ying , Wen Rong , Sun Yi
Published: November 2003

Cerebral ischemia resulting from a disruption of blood flow to the brain initiates a cascade of events that causes neuron death and leads to neurologic dysfunction. Reactive oxygen species are thought, at least in part, to mediate this disease process. The authors recently cloned and characterized an antioxidant protein, SAG (sensitive to apoptosis gene), that is redox inducible and protects cells from apoptosis induced by redox agents in a number of in vitro cell model systems. This study reports a neuroprotective role of SAG in ischemia/reperfusion-induced brain injury in an in vivo mouse model. SAG was expressed at a low level in brain tissue and was inducible after middle cerebral artery occlusion with peak expression at 6 to 12 hours. At the cellular level, SAG was mainly expressed in the cytoplasm of neurons and astrocytes, revealed by double immunofluorescence. An injection of recombinant adenoviral vector carrying human SAG into mouse brain produced an overexpression of SAG protein in the injected areas. Transduction of AdCMVSAG (wild-type), but not AdCMVmSAG (mutant), nor the AdCMVlacZ control, protected brain cells from ischemic brain injury, as evidenced by significant reduction of the infarct areas where SAG was highly expressed. The result suggests a rather specific protective role of SAG in the current in vivo model. Mechanistically, SAG overexpression decreased reactive oxygen species production and reduced the number of apoptotic cells in the ischemic areas. Thus, antioxidant SAG appears to protect against reactive oxygen species–induced brain damage in mice. Identification of SAG as a neuroprotective molecule could lead to potential stroke therapies.
Fractal Branching Pattern in the Pial Vasculature in the Cat
Authors: Hermán Peter , Kocsis László , Eke Andras
Published: November 2003

Arborization pattern was studied in pial vascular networks by treating them as fractals. Rather than applying elaborate taxonomy assembled from measures from individual vessel segments and bifurcations arranged in their branching order, the authors' approach captured the structural details at once in high-resolution digital images processed for the skeleton of the networks. The pial networks appear random and at the same time having structural elements similar to each other when viewed at different scales—a property known as self-similarity revealed by the geometry of fractals. Fractal (capacity) dimension, Dcap, was calculated to evaluate the network's spatial complexity by the box counting method (BCM) and its variant, the extended counting method (XCM). Box counting method and XCM were subject to numerical testing on ideal fractals of known D. The authors found that precision of these fractal methods depends on the fractal character (branching, nonbranching) of the structure they evaluate. Dcap s (group mean ± SD) for the arterial and venous pial networks in the cat (n = 6) are 1.37 ± 0.04, 1.37 ± 0.02 by XCM, and 1.30 ± 0.04, 1.31 ± 0.03 by BCM, respectively. The arterial and venous systems thus appear to be developed according to the same fractal generation rule in the cat.
Uncoupling of Cerebral Blood Flow and Metabolism after Cerebral Contusion in the Rat
Authors: Richards Hugh K. , Simac Sretan , Piechnik Stefan , Pickard John D.
Published: November 2003

Positron emission tomography scans of patients with head injuries often show discrete areas of increased 18F-fluorodeoxyglucose uptake (“hot spots”) when performed hours to days after the initial ictus. Using quantitative autoradiographic methods, the authors have investigated whether cerebral blood flow and glucose metabolism are uncoupled 2 hours after controlled head injury in an animal model, and whether any “hot spots” are accompanied by changes in cerebral glucose concentration. Experiments were performed on 18 anesthetized, ventilated (1.5% halothane in 2:1 nitrous oxide:oxygen) Sprague-Dawley rats weighing 300 to 330 g. A burr hole was made over the left parietal cortex, and all animals received a piston impact on the intact dura (2 mm in diameter, 2.0 m/sec, 2 mm in depth). All animals remained anesthetized and ventilated for a further 2 hours, after which quantitative autoradiography was used to determine either (1) local cerebral blood flow (LCBF) using 14C-iodoantipyrine, (2) local cerebral glucose utilization (LCGU) using 14C-deoxyglucose, or (3) local cerebral glucose content (LCGC) using 14C-methylglucose. Local CBF, LCGU, and LCGC were measured in five regions adjacent to the contusion, and values then were normalized on the contralateral cortex. Normalized LCBF, LCGU, or LCGC varied in parallel in ipsilateral cortex (no change) and in the ischemic core of the contusion (reduced). However, there were marked changes in the patterns observed in the boundary zone (within 1 mm of the contusion). In all six rats used for LCGU measurement, there were discrete areas of high metabolism, whereas in all six rats used for LCBF measurement, flow was universally depressed in the boundary zone. Of the six rats used for LCGC determination, there was a discrete area of high signal in only one. The authors conclude that there are discrete areas of uncoupling of cerebral blood flow and metabolism after head injury within 2 hours of cerebral contusion in the rat that cannot be explained by changes in cerebral glucose content in the majority of animals.
Chronic Cerebral Hypoperfusion Induces MMP-2 but Not MMP-9 Expression in the Microglia and Vascular Endothelium of White Matter
Authors: Ihara Masafumi , Tomimoto Hidekazu , Kinoshita Makoto , Oh Junseo , Noda Makoto , Wakita Hideaki , Akiguchi Ichiro , Shibasaki Hiroshi
Published: November 2003

White matter lesions are closely associated with cognitive impairment and motor dysfunction in the aged. To explore the pathophysiology of these lesions, the authors examined the expression of matrix metalloproteinase-2 (MMP-2) and MMP-9 in the white matter in a rat model of chronic cerebral hypoperfusion. After bilateral clipping of the common carotid arteries, myelin staining revealed demyelinating changes in the optic tract and the corpus callosum on day 7. Zymographic analyses indicated an increase in the level of MMP-2, but not MMP-9, after the hypoperfusion. Immunohistochemical analyses revealed the presence (most abundantly on day 3) of MMP-2–expressing activated microglia in the optic tract and corpus callosum. In contrast, the capillary endothelial cells expressed MMP-2 later. IgM-immunoreactive glial cells were absent in the sham-operated animals, but were present in the hypoperfused animals by day 3, reflecting the disrupted blood–brain barrier. These findings suggest that the main sources of the elevated MMP-2 were the microglia and the endothelium, and that these cells may contribute to the remodeling of the white matter myelin and microvascular beds in chronic cerebral hypoperfusion.
Cloned Blood–Brain Barrier Adenosine Transporter is Identical to the Rat Concentrative Na+ Nucleoside Cotransporter CNT2
Authors: Li Jian Yi , Boado Ruben J. , Pardridge William M.
Published: November 2003

Adenosine transport into brain is regulated by the activity of the adenosine transporter located at the brain capillary endothelial wall, which forms the blood–brain barrier (BBB) in vivo. To facilitate cloning of BBB adenosine transporters, poly A+ RNA was purified from isolated rat brain capillaries for production of a rat BBB cDNA library in the pSPORT vector. The cloned RNA (cRNA) generated from in vitro transcription of this library was injected into frog oocytes followed by measurement of [3H]-adenosine uptake. After dilutional cloning, a full-length, 2905-nucleotide adenosine transporter cDNA, designated clone A-11, was isolated. The A-11 clone yielded [3H]-adenosine flux ratios of 400 to 500 after injection of cRNA in oocytes. The adenosine uptake was sodium-dependent and insensitive to inhibition by S-(4-nitrobenzyl)-6-thioinosine (NBTI). The Km and Vmax of adenosine transport in the cRNA-injected oocytes were 23.1 ± 3.7 μmol/L and 10.8 ± 0.9 pmol/oocyte · min. The K0.5 for sodium was 2.4 ± 0.1 mmol/L, with a Hill coefficient (n) of 1.06 ± 0.07. DNA sequence analysis indicated the rat BBB A-11 adenosine cDNA was identical to rat concentrative nucleoside transporter type 2 (CNT2). The adenosine transporter activity of the rat BBB A-11 CNT2 clone is 50-fold more active than previously reported rat CNT2 clones. In summary, these studies describe the expression cloning of CNT2 from a rat BBB library and show that the pattern of sodium dependency and NBTI insensitivity of the cloned CNT2 are identical to patterns of adenosine transport across the BBB in vivo. These results suggest that BBB adenosine transport in vivo is mediated by CNT2, which would make CNT2 one of the few known sodium-dependent cotransporters that mediate substrate transport across the BBB in the blood to brain direction.
Transient Cerebral Ischemia Increases Tyrosine Phosphorylation of the Synaptic RAS-GTPase Activating Protein, SynGAP
Authors: Pei Lin , Teves R. Lucy , Wallace M. Christopher , Gurd James W.
Published: November 2003

Cerebral ischemia results in activation of the mitogen-activated protein kinase pathway and increased tyrosine phosphorylation of proteins associated with postsynaptic densities (PSDs). The authors investigated the possible relation between these events by determining the effect of ischemia on tyrosine phosphorylation of the brain-specific, PSD-enriched, Ras-GTPase activating protein, SynGAP. Transient (15 minutes) global ischemia was produced in rats by 4-vessel occlusion and PSDs prepared from forebrains immediately after ischemia or at 20 minutes, 1 hour, or 24 hours of reperfusion. Tyrosine phosphorylation of SynGAP was elevated relative to sham-operated controls by 20 minutes of reperfusion and remained elevated for at least 24 hours. Tyrosine phosphorylation of SynGAP also increased in CA1 and CA3/DG subfields of the hippocampus. Enhanced tyrosine phosphorylation of SynGAP was not accompanied by a change in PSD RasGAP activity. SynGAP bound to the SH2 domains of Src and Fyn in a tyrosine phosphorylation-dependent fashion, and this interaction increased after ischemia. SynGAP binds to the PDZ domains of PSD-95/SAP90 and coimmunoprecipitated with PSD-95. The coimmunoprecipitation of SynGAP with PSD-95 decreased after ischemia. The results indicate that changes in the properties and interactions of SynGAP may be involved in the neuropathology of ischemia.
Delayed rt-PA Treatment in a Rat Embolic Stroke Model: Diagnosis and Prognosis of Ischemic Injury and Hemorrhagic Transformation with Magnetic Resonance Imaging
Authors: Dijkhuizen Rick M. , Asahi Minoru , Wu Ona , Rosen Bruce R. , Lo Eng H.
Published: November 2003

The authors characterized effects of late recombinant tissue plasminogen activator (rt-PA) administration in a rat embolic stroke model with magnetic resonance imaging (MRI), to assess potential MRI correlates, or predictors, or both, of rt-PA–induced hemorrhage. Diffusion-, perfusion-, and postcontrast T1 -weighted MRI were performed between 4 and 9 hours and at 24 hours after embolic stroke in spontaneously hypertensive rats. Treatment with either rt-PA or saline was started 6 hours after stroke. A spectrophotometric hemoglobin assay quantified hemorrhage severity. Before treatment, relative cerebral blood flow index (rCBFi) and apparent diffusion coefficient (ADC) in the ischemic territory were 30% ± 23% and 60% ± 5% (of contralateral), respectively, which increased to 45% ± 39% and 68% ± 4% 2 hours after rt-PA. After 24 hours, rCBFi and ADC were 27% ± 27% and 59 ± 5%. Hemorrhage volume after 24 hours was significantly greater in rt-PA–treated animals than in controls (8.7 ± 3.7 μL vs. 5.1 ± 2.4 μL, P < 0.05). Before rt-PA administration, clear postcontrast T1 -weighted signal intensity enhancement was evident in areas of subsequent bleeding. These areas had lower rCBFi levels than regions without hemorrhage (23% ± 22% vs. 36% ± 29%, P < 0.05). In conclusion, late thrombolytic therapy does not necessarily lead to successful reperfusion. Hemorrhage emerged in areas with relatively low perfusion levels and early blood–brain barrier damage. Magnetic resonance imaging may be useful for quantifying effects of thrombolytic therapy and predicting risks of hemorrhagic transformation.
Postural Effects on Brain Hemodynamics in Unilateral Cerebral Artery Occlusive Disease: A Positron Emission Tomography Study
Authors: Ouchi Yasuomi , Nobezawa Shuji , Yoshikawa Etsuji , Futatsubashi Masami , Kanno Toshihiko , Okada Hiroyuki , Torizuka Tatsuo , Nakayama Teiji , Tanaka Keisei
Published: November 2003

To investigate effect of assuming of upright posture on brain hemodynamics in patients with unilateral internal carotid or middle cerebral artery occlusion (MCAO), local tissue oxygen extraction fraction (OEF), and postural changes in regional cerebral blood flow (rCBF) during supine and sitting conditions were examined using positron emission tomography (PET) with 15O-gas steady-state method and H215O autoradiographic method. A total of 22 minor stroke patients at relatively early stages participated. The regions of interest method was used for analyzing levels of perfusion and oxygen metabolic parameters, and postural rCBF change within MCAO group was investigated using statistical parametric mapping. Region of interest analyses showed significant rCBF reduction in the cortical and subcortical regions distal to the artery occlusion in CAO patients during sitting. Regression analyses showed that magnitudes of rCBF reduction in those areas were correlated positively with OEF values and inversely with metabolic rates of oxygen ( P < 0.05). Statistical parametric mapping for MCAO patients demonstrated further rCBF reduction by sitting in the occlusion-side MCA territory. The current study suggested that assumption of upright posture could exert an adverse effect on local perfusion in hemodynamically compromised patients with major cerebral vessel occlusion, possibly caused by impairment of local autoregulation.
Measurement of Cortical Dopamine D1 Receptor Binding with [11C]SCH 23390: A Test–Retest Analysis
Authors: Hirvonen Jussi , Någren Kjell , Kajander Jaana , Hietala Jarmo
Published: November 2003

[11C]SCH 23390 is a standard ligand for positron emission tomography (PET) studies on striatal dopamine D1 receptors. Its usefulness for cortical D1 receptor quantification in human PET studies has been questioned but has not been addressed previously. The authors tested the reproducibility of [11C]SCH 23390 binding potential (BP) in cortical areas in five healthy volunteers using three-dimensional PET. Measurement of D1 receptor BP was reproducible in basal ganglia, as well as in all cortical areas studied (intraclass correlation coefficients between 0.81 and 0.92). The absolute variability in cortical areas was 9.21% ± 0.07%. The reproducibility of cortical D1 receptor BP measurement with [11C]SCH 23390 is equal to that observed with a more recent D1 -ligand, [11C]NNC 112. [11C]NNC 112 produces slightly higher specific-to-nonspecific binding ratios but has markedly slower kinetics resulting in a need for a longer scan time. These aspects should be considered when designing studies on the cortical D1 -like receptors.
Apomorphine-Induced Changes in Synaptic Dopamine Levels: Positron Emission Tomography Evidence for Presynaptic Inhibition
Authors: de la Fuente-Fernández Raúl , Lim Andrew S. , Sossi Vesna , Holden James E. , Calne Donald B. , Ruth Thomas J. , Stoessl A. Jon
Published: November 2003

The authors developed a novel positron emission tomography method to estimate changes in the synaptic level of dopamine ([DA]) induced by direct dopamine agonists (for example, apomorphine) in patients with Parkinson disease. The method is based on the typical asymmetry of the nigrostriatal lesion that often occurs in Parkinson disease. Using the between-side difference (ipsilateral (I) and contralateral (C) putamen to the more affected body side) of the inverse of the putamen [11C]raclopride binding potential (BP), the authors obtained

[Formula: see text]

at baseline (that is, before apomorphine administration) and

[Formula: see text]

after apomorphine administration (assuming the concentration of apomorphine is equal in both putamina). The between-side difference in the estimated synaptic concentration of dopamine (diff[DA]) should remain constant unless apomorphine affects dopamine release differently between the two sides. The authors found that apomorphine given subcutaneously at doses of 0.03 and 0.06 mg/kg induced significant changes in their estimate of diff[DA] (P < 0.05). Such changes were more pronounced when only patients with a stable response to levodopa were considered ( P < 0.01). These findings provide in vivo evidence that direct dopamine agonists can inhibit the release of endogenous dopamine. The authors propose that this effect is mainly mediated by the activation of presynaptic D2 /D3 dopamine receptors.
Cerebral Glucose Transport Implies Individualized Glial Cell Function
Authors: Feinendegen Ludwig E. , Herzog Hans , Thompson Keith H.
Published: November 2003

Previous positron emission tomography (PET) measurements of cerebral glucose transport using [11C]-3-O-methylglucose (CMG) suggested an interindividual variation in the values of the rate constant of tracer outflow (k2) larger than that for the clearance rate of inflow (K1). These two parameters were examined in healthy cerebral cortex by dynamic PET in 4 men and 2 women (aged 24 to 73 years) without neurologic disease, and in 1 man (42 years) with a recent left hemispheric cerebral infarction under normoglycemia (average blood plasma d-glucose concentration, 5.44 ± 1.94 μmol/mL) and again under hyperglycemia (average, 10.24 ± 1.44 μmol/mL). Time-radioactivity curves were obtained from healthy cortex (grey matter) and plasma and analyzed for the values of K1 and k2 by two graphical approaches and two fitting procedures. Both K1 and k2 significantly declined with increasing plasma glucose levels. A highly significant interindividual but not intraindividual variability for k2 was found at normoglycemia and hyperglycemia. The interindividual variability of K1, although borderline significant, was less than that of k2. Accordingly variable were the distribution volumes K1 /k2. These data suggest individualized glial cell function and may be relevant to pathogenesis of neuropsychiatric disease.
Magnetic Resonance Angiography in Facial and other Pain: Neurovascular Mechanisms of Trigeminal Sensation
Authors: May Arne , Büchel Christian , Turner Robert , Goadsby Peter J.
Published: November 2003

For much of the twentieth century migraine and cluster headache have been considered as vascular headaches whose pathophysiology was determined by changes in cranial vascular diameter. To examine nociceptive neural influences on the cranial circulation, the authors studied healthy volunteers' responses to injection of the pain-producing compound capsaicin in terms of the caliber of the internal carotid artery. The study was conducted using magnetic resonance angiographic techniques. Injection of capsaicin into the skin innervated by the ophthalmic (first) division of the trigeminal nerve elicited 40% ± 27% (mean ± SD) increase in vascular cross-sectional area in the right (ipsilateral) internal carotid artery when compared with the mean baseline ( P < 0.001). Injection of capsaicin into the skin of the chin to stimulate the mandibular (third) division of the trigeminal nerve and into the leg led to a similar pain perception and failed to produce any significant change in vessel caliber. The data suggest that there is a highly functionally organized, somatotopically congruent trigeminal innervation of the cranial vessels, with a potent vasodilator effect of the ophthalmic division on the large intracranial vessels. The data are consistent with the notion that pain drives changes in vessel caliber in migraine and cluster headache, not vice versa. These conditions therefore should be regarded as primary neurovascular headaches not as vascular headaches.
Phosphorylation of Cyclic Adenosine Monophosphate Response Element Binding Protein in Oligodendrocytes in the Corpus Callosum after Focal Cerebral Ischemia in the Rat
Authors: Tanaka Kortaro , Nogawa Shigeru , Ito Daisuke , Suzuki Shigeaki , Dembo Tomohisa , Kosakai Arifumi , Fukuuchi Yasuo
Published: November 2003

Phosphorylation of cyclic adenosine monophosphate (AMP) response element binding protein (CREB) was examined immunohistochemically in the corpus callosum of the rat brain at various time points after 90-minute focal cerebral ischemia. Focal ischemia was induced by occlusion of the middle cerebral artery (MCA) using the intraluminal suture method. Sham animals showed that numerous oligodendrocytes (OLGs) constitutively express unphosphorylated CREB. Local cerebral blood flow (lCBF) measured by the14 C-iodoantipyrine method was reduced from 44.2 ± 15.4 (mL 100 g−1 min−1) to 18.4 ± 3.8 and from 53.9 ± 14.4 to 4.8 ± 4.5 in the medial and the lateral regions of the corpus callosum, respectively, during MCA occlusion (MCAO). After release of the MCAO, lCBF recovered to the control level in each region. The medial region of the corpus callosum showed a marked increase in phosphorylated CREB-positive OLGs at 3.5 hours of recirculation, and it remained increased until 2 weeks of recirculation as it gradually declined. The activation of CREB phosphorylation in the OLGs was accompanied by expression of antiapoptotic protein bcl-2, normal staining with cresyl violet, and negative TUNEL (terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling) staining. Myelination detected by immunostaining with anti-myelin basic protein (MBP) antibody and anti-myelin associated glycoprotein (MAG) antibody remained normal in the medial region of the corpus callosum. The lateral region of the corpus callosum showed a significant but only transient increase in phosphorylated CREB-positive OLGs at 3.5 hours of recirculation, which was followed by a rapid decrease during the subsequent recirculation period. Expression of bcl-2 was suppressed in this region, and demyelination became apparent. These findings suggest that signal transduction through CREB phosphorylation may be closely associated with survival of OLGs and maintenance of myelination in the corpus callosum after cerebral ischemia.
GAT2/BGT-1 as a System Responsible for the Transport of γ-Aminobutyric Acid at the Mouse Blood–Brain Barrier
Authors: Takanaga Hitomi , Ohtsuki Sumio , Hosoya Ken-Ichi , Terasaki Tetsuya
Published: November 2003

In this study, the γ-aminobutyric acid (GABA) transporter at the blood–brain barrier (BBB) was identified by reverse transcription–polymerase chain reaction (RT-PCR), Western blot, and immunostaining analysis, and the transport mechanism was characterized using a conditionally immortalized mouse brain capillary endothelial cell line (TM-BBB) as an in vitro model of the BBB. γ-Aminobutyric acid transport was studied by the cellular uptake of [3H]GABA. [3H]GABA uptake by TM-BBB cells was Na+−, Cl−-, and concentration-dependent. The corresponding Michaelis–Menten constant was 679 ± 80 μmol/L and the maximal uptake rate was 4,790 ± 494 pmol/(mg protein · 5 minutes). [3 H]GABA uptake by TM-BBB cells was significantly inhibited by betaine, β-alanine, nipecotic acid, taurine, and quinidine, whereas probenecid, L-proline, creatine, and glycine had no effect. This type of inhibition is consistent with the predominant involvement of the GAT2/BGT-1 transporter in TM-BBB cells. RT-PCR analysis showed that GAT2/BGT-1 mRNA was expressed in TM-BBB cells, whereas Western blot analysis showed that TM-BBB cells and mouse brain capillaries express GAT2/BGT-1 protein. Moreover, confocal immunofluorescent microscopy of dual-labeled mouse brain sections demonstrated the colocalization of GAT2/BGT-1 and P-glycoprotein, a BBB-specific marker, on brain capillaries labeled with anti–GAT2/BGT-1 antibody and anti–P-glycoprotein antibody, respectively. These results are evidence that GAT2/BGT-1 is expressed at the BBB and is involved in GABA transport across the BBB.
Concurrent Assessment of Calpain and Caspase-3 Activation after Oxygen–Glucose Deprivation in Primary Septo-Hippocampal Cultures
Authors: Newcomb-Fernandez Jennifer K. , Zhao Xiurong , Pike Brian R. , Wang Kevin K. W. , Kampfl Andreas , Beer Ronald , DeFord S. Michelle , Hayes Ronald L.
Published: November 2003

The contributions of calpain and caspase-3 to apoptosis and necrosis after central nervous system (CNS) trauma are relatively unexplored. No study has examined concurrent activation of calpain and caspase-3 in necrotic or apoptotic cell death after any CNS insult. Experiments used a model of oxygen–glucose deprivation (OGD) in primary septo-hippocampal cultures and assessed cell viability, occurrence of apoptotic and necrotic cell death phenotypes, and protease activation. Immunoblots using an antibody detecting calpain and caspase-3 proteolysis of α-spectrin showed greater accumulation of calpain-mediated breakdown products (BDPs) compared with caspase-3–mediated BDPs. Administration of calpain and caspase-3 inhibitors confirmed that activation of these proteases contributed to cell death, as inferred by lactate dehydrogenase release. Oxygen–glucose deprivation resulted in expression of apoptotic and necrotic cell death phenotypes, especially in neurons. Immunocytochemical studies of calpain and caspase-3 activation in apoptotic cells indicated that these proteases are almost always concurrently activated during apoptosis. These data demonstrate that calpain and caspase-3 activation is associated with expression of apoptotic cell death phenotypes after OGD, and that calpain activation, in combination with caspase-3 activation, could contribute to the expression of apoptotic cell death by assisting in the degradation of important cellular proteins.
Regional Dependence of Cerebral Reperfusion after Circulatory Arrest in Rats
Authors: Liachenko Serguei , Tang Pei , Hamilton Ronald L. , Xu Yan
Published: November 2003

The severity of neurologic dysfunction after circulatory arrest depends on cerebral reperfusion during and after resuscitation. The objective of current study was to investigate the temporal and spatial patterns of the cerebral perfusion immediately after resuscitation. Precise control of circulatory arrest was achieved in rats by combination of asphyxia and transient blockage of cardiac-specific β-adrenergic receptors with esmolol, an ultra-short-acting β-blocker. Animals were randomized into 3 groups with resuscitation starting 0.5 (sham group, no asphyxia, n = 5), 4 (Group 2, n = 5), or 12 minutes (Group 3, n = 8) later by retrograde intraarterial infusion of donor blood along with a resuscitation mixture. Cerebral perfusion was measured by magnetic resonance imaging (MRI) using arterial spin labeling. The average perfusion before arrest was 163 ± 27 mL 100 g−1 min−1 under isoflurane anesthesia. Resuscitation led to transient perfusion increase, which started from thalamus and hypothalamus and later shifted to the cortex. Severe hypoperfusion to as low as 6% to 20% of the normal level developed in the first 10 to 20 minutes of reperfusion and lasted for at least 2 hours. On the fifth day after circulatory arrest, all animals showed a normal level of perfusion (159 ± 57 mL 100 g−1 min−1) and minimal neurologic deficit. Nevertheless, histologic examination revealed extensive changes in the CA1 region of the hippocampus consistent with global ischemia and reperfusion damage. The combination of an improved circulatory arrest model and noninvasive MRI cerebral perfusion measurements provides a powerful tool for investigations of circulatory arrest and resuscitation, allowing for evaluation of therapies aimed at modulating cerebral reperfusion.
Event-Related Functional Magnetic Resonance Imaging Study of the Extrastriate Cortex Response to a Categorically Ambiguous Stimulus Primed by Letters and Familiar Geometric Figures
Authors: Gros Hélène , Boulanouar Kader , Viallard Gérard , Cassol Emmanuelle , Celsis Pierre
Published: November 2003

Functional neuroimaging studies have suggested a specific role of the extrastriate cortex in letter string and visual word form processing. However, this region has been shown to be involved in object recognition and its specificity for the processing of linguistic stimuli may be questioned. The authors used an event-related functional magnetic resonance imaging design with category priming to record the response elicited by the passive viewing of single letters, geometric figures, and of the categorically ambiguous stimulus “O” that pertains to both sets of familiar symbols. Bilateral activations in the extrastriate cortex were found, with a left predominance particularly pronounced for the ambiguous stimulus. Individual analysis of spatial extent and signal intensity showed a priming × stimulus × hemisphere interaction. When primed by the congruous categoric set, a bilateral decrease in activation was observed for letters and geometric figures. The ambiguous stimulus behaved as a letter for the left hemisphere, with decreased activation when primed by letters, whereas in the right hemisphere, an adaptation effect occurred when primed by geometric figures. These priming effects suggest that, for the ambiguous stimulus, letter processing was systematically involved in the left extrastriate cortex. The current results support the existence of a neural substrate for the abstract category of letters.
Glycolysis in Neurons, Not Astrocytes, Delays Oxidative Metabolism of Human Visual Cortex during Sustained Checkerboard Stimulation in vivo
Authors: Gjedde Albert , Marrett Sean
Published: November 2003

The regulation of brain energy metabolism during neuronal activation is poorly understood. Specifically, the extent to which oxidative metabolism rather than glycolysis supplies the additional ATP necessary to sustain neuronal activation is in doubt. A recent hypothesis claims that astrocytes generate lactate with the muscle-type lactate dehydrogenase (LDH) isozyme LD5. Lactate from astrocytes then undergoes oxidation in neurons after reconversion to pyruvate by the LDH subtype LD1. On the basis of this hypothesis, the authors predicted that the time course of an excitatory increase of the oxidative metabolism of brain tissue must depend on the degree to which astrocytes provide neurons with pyruvate in the form of lactate. From the known properties of the LDH subtypes, the authors predicted two time courses for the changes of oxygen consumption in response to neuronal stimulation: one reflecting the properties of the neuronal LDH subtype LD1, and the other reflecting the astrocytic LDH subtype LD5. Measuring oxygen consumption (CMR o2) with positron emission tomography, the authors demonstrated increased CMR o2 during sustained stimulation of visual cortex with a complex stimulus. The CMR o2 increased 20.5% after 3 minutes and 27.5% after 8 minutes of stimulation, consistent with a steady-state oxygen–glucose metabolism ratio of 5.3, which is closest to the index predicted for the LD1 subtype. The index is equal to the oxygen–glucose metabolism ratio of 5.5 calculated at baseline, indicating that pyruvate is converted to lactate in a cellular compartment with an LDH reaction closest to that of LD1, whether at rest or during stimulation of the visual cortex with the current stimulus. The findings are consistent with a claim that neurons increase their oxidative metabolism in parallel with an increase of pyruvate, the latter generated by neuronal rather than astrocytic glycolysis.
Ischemic Preconditioning Preserves Mitochondrial Function after Global Cerebral Ischemia in Rat Hippocampus
Authors: Dave Kunjan R. , Saul Isabel , Busto Raul , Ginsberg Myron D. , Sick Thomas J. , Pérez-Pinzón Miguel A.
Published: November 2003

Ischemic tolerance in brain develops when sublethal ischemic insults occur before “lethal” cerebral ischemia. Two windows for the induction of tolerance by ischemic preconditioning (IPC) have been proposed: one that occurs within 1 hour after IPC, and another that occurs 1 or 2 days after IPC. The authors tested the hypotheses that IPC would reduce or prevent ischemia-induced mitochondrial dysfunction. IPC and ischemia were produced by bilateral carotid occlusions and systemic hypotension (50 mm Hg) for 2 and 10 minutes, respectively. Nonsynaptosomal mitochondria were harvested 24 hours after the 10-minute “test” ischemic insult. No significant changes were observed in the oxygen consumption rates and activities for hippocampal mitochondrial complexes I to IV between the IPC and sham groups. Twenty-four hours of reperfusion after 10 minutes of global ischemia (without IPC) promoted significant decreases in the oxygen consumption rates in presence of substrates for complexes I and II compared with the IPC and sham groups. These data suggest that IPC protects the integrity of mitochondrial oxidative phosphorylation after cerebral ischemia.
Chemokine Receptor Antagonist Peptide, Viral MIP-II, Protects the Brain against Focal Cerebral Ischemia in Mice
Authors: Takami Shinya , Minami Masabumi , Nagata Izumi , Namura Shobu , Satoh Masamichi
Published: November 2003

The authors previously reported that mRNA for macrophage inflammatory protein-1α (MIP-1 α), a member of the CC chemokines, was expressed in glial cells after focal cerebral ischemia in rats. However, the function of chemokines in the ischemic brain remains unclear. Recently, viral macrophage inflammatory protein-II (vMIP-II), a chemokine analogue encoded by human herpesvirus-8 DNA, has been demonstrated to have antagonistic activity at several chemokine receptors. In the present study, the effects of vMIP-II and MIP-1α on ischemic brain injury were examined in mice to elucidate the roles of chemokines endogenously produced in the ischemic brain. Intracerebroventricular injection of vMIP-II (0.01–1 μg) reduced infarct volume in a dose-dependent manner when examined 48 hours after 1-hour middle cerebral artery occlusion followed by reperfusion. However, 1 μg MIP-1α increased infarct volume in the cortical region. These results supported the possibility that chemokines endogenously produced in the brain are involved in ischemic injury, and that chemokine receptors are potential targets for therapeutic intervention of stroke.
Effects of Acetazolamide on Cerebral Blood Flow, Blood Volume, and Oxygen Metabolism: A Positron Emission Tomography Study with Healthy Volunteers
Authors: Okazawa Hidehiko , Yamauchi Hiroshi , Sugimoto Kanji , Toyoda Hiroshi , Kishibe Yoshihiko , Takahashi Masaaki
Published: November 2003

To evaluate changes in cerebral hemodynamics and metabolism induced by acetazolamide in healthy subjects, positron emission tomography studies for measurement of cerebral perfusion and oxygen consumption were performed. Sixteen healthy volunteers underwent positron emission tomography studies with15O-gas and water before and after intravenous administration of acetazolamide. Dynamic positron emission tomography data were acquired after bolus injection of H215O and bolus inhalation of15O2. Cerebral blood flow, metabolic rate of oxygen, and arterial-to-capillary blood volume images were calculated using the three-weighted integral method. The images of cerebral blood volume were calculated using the bolus inhalation technique of C15O. The scans for cerebral blood flow and volume and metabolic rate of oxygen after acetazolamide challenge were performed at 10, 20, and 30 minutes after drug injection. The parametric images obtained under the two conditions at baseline and after acetazolamide administration were compared. The global and regional values for cerebral blood flow and volume and arterial-to-capillary blood volume increased significantly after acetazolamide administration compared with the baseline condition, whereas no difference in metabolic rate of oxygen was observed. Acetazolamide-induced increases in both blood flow and volume in the normal brain occurred as a vasodilatory reaction of functioning vessels. The increase in arterial-to-capillary blood volume made the major contribution to the cerebral blood volume increase, indicating that the raise in cerebral blood flow during the acetazolamide challenge is closely related to arterial-to-capillary vasomotor responsiveness.
Dual-[11C]Tracer Single-Acquisition Positron Emission Tomography Studies
Authors: Koeppe Robert A. , Raffel David M. , Snyder Scott E. , Ficaro Edward P. , Kilbourn Michael R. , Kuhl David E.
Published: November 2003

The ability to study multiple physiologic processes of the brain simultaneously within the same subject would provide a new means to explore the interactions between neurotransmitter systems in vivo. Currently, examination of two distinct neuropharmacologic measures with positron emission tomography (PET) necessitates performing two separate scans spaced in time to allow for radionuclide decay. The authors present results from a dual-tracer PET study protocol using a single dynamic-scan acquisition where the injections of two tracers are offset by several minutes. Kinetic analysis is used to estimate neuropharmacologic parameters for both tracers simultaneously using a combined compartmental model configuration. This approach results in a large reduction in total study time of nearly 2 hours for carbon-11–labeled tracers. As multiple neuropharmacologic measures are obtained at nearly the same time, interventional protocols involving a pair of dual-tracer scans become feasible in a single PET session. Both computer simulations and actual human PET studies were performed using combinations of three different tracers: [11C]flumazenil, N-[11C]methylpiperidinyl propionate, and [11C]dihydrotetrabenazine. Computer simulations of tracer-injection separations of 10 to 30 minutes showed the feasibility of the approach for separations down to 15 to 20 minutes or less. Dual-tracer PET studies were performed in 32 healthy volunteers using injection separations of 10, 15, or 20 minutes. Model parameter estimates for each tracer were similar to those obtained from previously performed single-injection studies. Voxel-by-voxel parametric images were of good quality for injections spaced by 20 minutes and were nearly as good for 15-minute separations, but were degraded noticeably for some model parameters when injections were spaced by only 10 minutes. The authors conclude that dual-tracer single-scan PET is feasible, yields accurate estimates of multiple neuropharmacologic measures, and can be implemented with a number of different radiotracer pairs.