Biomedical subjects

G Unsgård

Publications and source records attributed to G Unsgård.

At least 37 records · Page 2Linked to original sources

PubMed1996

Comparison of MR perfusion imaging and microsphere measurements of regional cerebral blood flow in a rat model of middle cerebral artery occlusion.

The purpose of this investigation was to correlate magnetic resonance (MR) perfusion measurements with absolute regional cerebral blood flow (rCBF) in a rat model of focal ischemia. The MR perfusion measurements were made using dynamic first-pass bolus tracking of a susceptibility contrast agent, whereas rCBF was measured using radioactive microspheres. Two simple MR perfusion parameters, the maximum change in R2* (m delta R2*) and time delay to m delta R2* (t delta R2*), were derived from the signal intensity versus time curves on a pixel-to-pixel basis, without applying curve-fitting procedures or tracer kinetic theory. In each hemisphere, m delta R2* and t delta R2* were compared with the rCBF measurements in four selected regions of interest. Sixteen MR bolus tracking series were performed in 12 rats with occlusion of the middle cerebral artery. In all of the individual series there was a significant correlation (.0001 < or = p < or = .02) between m delta R2* and the microsphere rCBF measurements, with correlation coefficients ranging from .784 to .983. Pooling the m delta R2* data resulted in a correlation coefficient of .809 (p = .0001). There was a nonlinear correlation between the t delta R2* and rCBF. For both parameters there was considerable variation between different measurements regarding both the slope of the regression line and its intercept with the y-axis. Our results justify the use of m delta R2* as a relative measure of perfusion during acute cerebral ischemia. Because of the interindividual variation, calibration of MR perfusion measurements for the estimation of absolute flow values must be considered unreliable. The t delta R2* may have physiological relevance as a marker of collateral flow.

Animals↗

PubMed1995

Effects of aspartame on 45Ca influx and LDH leakage from nerve cells in culture.

Aspartame (ASM), an artificial sweetener, was shown to dose dependently increase 45Ca-influx into and lactate dehydrogenase (LDH) leakage from murine brain cell cultures. Astrocytes were more resistant than neurones to the effects of ASM. In cerebellar granule neurones, a 20% increase in calcium was found after an incubation time of 22 h in the presence of 0.1 mM ASM; at 0.5 mM concentration, calcium influx increased 40% compared with control cultures. At a concentration of 10 mM, influx was increased 13-fold after 5 h. Morphological appearance as judged by phase contrast microscopy was first visibly affected after exposure to 1 mM ASM for 22 h. Citrate, another food additive, was included in the study to demonstrate that cerebellar granule neurones could tolerate 10 mM additions to the medium and citrate did not cause 45Ca influx or morphological changes in neurones after 22 h. LDH leakage, a sign of severe cell damage, was observed at 1 mM concentrations of ASM after 22 h. Cerebral astrocytes on the other hand were more resistant and showed morphological changes, increased calcium influx and LDH leakage first at 5 mM concentrations of ASM.

Animals↗

PubMed1995

[Elevated intracranial pressure following brain infarction--therapeutical possibilities].

Elevated intracranial pressure is a serious complication in the early phase after brain infarction. The most frequent cause of the elevated pressure is oedema following an infarction in the territory of the middle cerebral artery. Non-surgical treatment is inadequate in many of the patients. Although anecdotal, several reports concerning neurosurgical treatment seem to be optimistic. We think that such treatment could be given to selected young patients with large hemispheric infarctions and cerebral oedema.

Brain Edema↗

PubMed1995

Combined perfusion and diffusion-weighted magnetic resonance imaging in a rat model of reversible middle cerebral artery occlusion.

BACKGROUND AND PURPOSE: Diffusion-weighted imaging and dynamic first-pass bolus tracking of susceptibility contrast agents (perfusion imaging) are two new magnetic resonance imaging techniques that offer the possibility of early diagnosis of stroke. The present study was performed to evaluate the diagnostic information derived from these two methods in a rat model of temporary focal ischemia. METHODS: Fifteen male Wistar rats were assigned to 45 (n = 7) or 120 minutes (n = 8) of middle cerebral artery occlusion followed by reperfusion using the intraluminal filament technique. The diffusion-weighted images were collected, and areas of hyperintensity were compared with histologically assessed areas of ischemic injury. The magnetic resonance perfusion image series were postprocessed to produce topographic maps reflecting the maximum reduction in the signal obtained during the first passage of the contrast agent and the time delay between the arrival of the bolus and the point of maximum contrast-agent effect. RESULTS: Hyperintensity in diffusion-weighted images was demonstrated after 30 minutes of middle cerebral artery occlusion and was mainly expressed in the lateral caudoputamen and parts of the lower frontoparietal cortex. Reperfusion after 45 minutes of occlusion reduced the area of hyperintensity from 24.2% to 9.9% of hemispheric area. In the group with 120 minutes of occlusion, the hyperintense area increased from 24.4% to 29.1%. Relative to the nonischemic hemisphere, the changes in the topographic maps of maximum signal reduction occurred in the lateral caudoputamen and adjacent lower neocortical areas. Increased time delay to maximum effect, however, was seen also in the upper frontoparietal cortex. CONCLUSIONS: Hyperintensity in diffusion-weighted images was reversible after 45 minutes but not after 120 minutes of middle cerebral artery occlusion. Analysis of the signal-reduction and time-delay parametric maps demonstrated regions of different perfusion changes in the ischemic hemisphere.

Animals↗

PubMed1995

Perfusion and diffusion-weighted MR imaging for in vivo evaluation of treatment with U74389G in a rat stroke model.

BACKGROUND AND PURPOSE: The present study was performed to examine the potential of diffusion-weighted (DW) imaging and dynamic first-passage bolus tracking of susceptibility contrast agents (perfusion imaging) for early in vivo evaluation of the effects of treatment with the free radical scavenger U74389G in a rat model of temporary focal ischemia. METHODS: After 45 minutes of middle cerebral artery occlusion, the treatment group (n = 9) received an infusion of U74389G, and the control group (n = 9) received the identical volume of the vehicle. Reperfusion was instituted in both groups after 120 minutes of middle cerebral artery occlusion. The DW images were collected during middle cerebral artery occlusion and reperfusion and were compared with histologically assessed areas of tissue injury after 2 hours of reperfusion. The dynamic perfusion series were processed on a pixel-to-pixel basis to produce parametric maps reflecting the maximum reduction in the signal obtained during the first passage of the contrast agent and the time delay between the arrival of the bolus and the point of maximum contrast-agent effect. RESULTS: The area of ischemic injury, as assessed from the DW imaging at 60 minutes of reperfusion, was significantly smaller in the treatment group: 9 +/- 8% of ipsilateral hemisphere compared with 19 +/- 8% in the control group. The histological examination after 2 hours of reperfusion demonstrated an area of ischemic injury of 10 +/- 8% for the treatment group compared to 25 +/- 10% in the control group. In the treatment group, the perfusion imaging showed a reduction in time delay to maximum effect of the contrast agent in the ischemic hemisphere compared with the control group. CONCLUSIONS: The DW imaging during early reperfusion showed a protective effect of postocclusion treatment with the free radical scavenger U74389G. The improvement of time delay to maximum effect of the contrast agent observed in the perfusion imaging of the treatment group may reflect an improvement in the collateral flow to the ischemic tissue.

Animals↗

PubMed1994

13C NMR spectroscopy study of cortical nerve cell cultures exposed to hypoxia.

Primary cultures of cerebral cortical GABA-ergic neurons growing on top of a preformed layer of astrocytes (co-cultures) were incubated with [1-13C]glucose and exposed to a low oxygen atmosphere (2% O2) for 17 hr. 13C, 1H, and 31P nuclear magnetic resonance (NMR) spectroscopy was performed on perchloric acid (PCA) extracts of cells and of media collected from these cultures. In the control groups incorporation of 13C label into glutamine, citrate, and lactate could be demonstrated in both cell extracts and culture media. Labeled GABA and glutamate were only observed in cell extracts. During hypoxia high energy phosphates decreased but lactate production and glucose consumption increased. There was a decreased amount of citrate and glutamine in cell extracts and media of the hypoxic co-cultures. There was a change in distribution of the 13C label within the GABA molecule, with an increase of labeling in the C-2 position. This change in 13C distribution was not found in glutamine present in the media where it is a precursor for GABA in neurons. Instead a decrease in the corresponding C-4 position was observed. These results suggest that energy depletion during hypoxia leads to reduced export from the astrocytic tricarboxylic acid (TCA) cycle as demonstrated by a decreased amount of citrate and changed distribution of 13C in glutamine. The change in the distribution of label in GABA from cell extracts as compared to glutamine in the medium may indicate that neurons are synthesizing GABA using precursors supplied from their own TCA cycle and not from precursors supplied by astrocytes.

Animals↗

PubMed1994

NMR spectroscopic study of cell cultures of astrocytes and neurons exposed to hypoxia: compartmentation of astrocyte metabolism.

Primary cultures of murine cerebral cortical astrocytes or cerebellar granule neurons were exposed to 7 h of hypoxia (3 h in some cases). The culture medium was analyzed at the end of the hypoxic or normoxic period by 1H NMR spectroscopy and intracellular components were analyzed as perchloric acid extracts by 31P and 1H NMR spectroscopy. Lactate production in astrocytes increased only marginally, whereas high energy phosphate concentrations were reduced, during 7 h of hypoxia and after 17 h of reoxygenation. After 3 h of hypoxia full recovery was possible during reoxygenation. Citrate and glutamine secretion was reduced or unchanged, respectively, during 7 h of hypoxia. Succinate secretion was only observed during normoxia, whereas pyruvate was secreted during hypoxia. Cerebellar granule neurons were more efficient in increasing glycolysis and were, therefore, more resistant to the effects of hypoxia than astrocytes. In the neurons lactate production was doubled and no effects on levels of high energy phosphates were seen after 7 h of hypoxia. Astrocytes were reoxygenated for 17 h after hypoxia or normoxia in a medium containing [2-13C]acetate in order to access if astrocytes were still capable of supplying neurons with essential precursors. The media were subsequently analyzed by 13C NMR spectroscopy. After shorter periods of hypoxia (3 h) full recovery was possible. Citrate and glutamine production remained however decreased during reoxygenation after 7 h of hypoxia. 13C incorporation into glutamine was greatly reduced but that into citrate was unchanged. These results suggest that under the present conditions, neurons are more efficient than astrocytes in switching the energy metabolism from aerobic to anaerobic glycolysis and that astrocytes may suffer long term damage to mitochondria from longer periods of hypoxia. Furthermore, evidence is presented for the existence of several TCA cycles within astrocytes based on labeling ratios. During normoxia the labeling ratios in the C-2/C-4 positions in glutamine and in the equivalent positions in citrate were 0.27 and 0.11, respectively.

Adenosine Triphosphate↗

PubMed1994

Cerebrospinal fluid production during proximal aortic cross-clamping.

During cross-clamping (XC) of the thoracic aorta, the cerebrospinal fluid pressure (CSFP) increases. The mechanism of the increased CSFP is unknown but increased cerebrospinal fluid (CSF) production has been suggested as one explanation. The aim of this study was to investigate whether the CSF production rate was influenced by proximal XC of the thoracic aorta in an experimental model. Using the ventriculocisternal perfusion method including [14C] inulin, the rate of CSF production was measured before, during and after XC of the thoracic aorta in seven pigs. The CSFP was measured via a catheter in the lateral ventricle and the thoracic aorta was cross-clamped just distal to the left subclavian artery for 30 minutes. Following cross-clamping the CSFP increased from 5 mmHg to 11 mmHg (p < 0.001) and remained elevated during XC. In contrast the CSF production rate was 0.09 ml/min prior to XC and was not significantly altered following XC. In conclusion this experimental study indicates that increased CSF production is not responsible for the increase in CSFP during XC.

Animals↗

PubMed1994

Uptake, release, and metabolism of citrate in neurons and astrocytes in primary cultures.

Synthesis, uptake, release, and oxidative metabolism of citrate were investigated in neurons and astrocytes cultured from cerebral cortex or cerebellum. In addition, the possible role of citrate as a donor of the carbon skeleton for biosynthesis of neurotransmitter glutamate was studied. All cell types expressed the enzyme citrate synthase at a high activity, the cerebellar granule neurons containing the enzyme at a higher activity than that found in the astrocytes from the two brain regions or the cortical neurons. Saturable citrate uptake could not be detected in any of the cell types, but the astrocytes, and, in particular, those of cerebellar origin, had a very active de novo synthesis and release of citrate (approximately 70 nmol x h-1 x mg of protein-1). The rate of release of citrate from neurons was < 5% of this value. Using [14C]citrate it could be shown that citrate was oxidatively metabolized to 14CO2 at a modest rate (approximately 1 nmol x h-1 x mg-1 of protein) with slightly higher rates in astrocytes compared with neurons. Experiments designed to investigate the ability of exogenously supplied citrate to serve as a precursor for synthesis of transmitter glutamate in cerebellar granule neurons failed to demonstrate this. Rather than citrate serving this purpose it may be suggested that astrocytically released citrate may regulate the extracellular concentration of Ca2+ and Mg2+ by chelation, thereby modulating neuronal excitability.

Animals↗

PubMed1994

NMR spectroscopy of cultured astrocytes: effects of glutamine and the gliotoxin fluorocitrate.

Glial synthesis of glutamine, citrate, and other carbon skeletons, as well as metabolic effects of the gliotoxin fluorocitrate, were studied in cultured astrocytes with 13C and 31P NMR spectroscopy. [2-13C]Acetate and [1-13C]glucose were used as labeled precursors. In some experiments glutamine (2.5 mM) was added to the culture medium. Fluorocitrate (20 microM) inhibited the tricarboxylic acid (TCA) cycle without affecting the level of ATP. The net export of glutamine was reduced significantly, and that of citrate increased similarly, consistent with an inhibition of aconitase. Fluorocitrate (100 microM) inhibited TCA cycle activity even more and (without addition of glutamine) caused a 40% reduction in the level of ATP. In the presence of 2.5 mM glutamine, 100 microM fluorocitrate did not affect ATP levels, although glutamine synthesis was nearly fully blocked. The consumption of the added glutamine increased with increasing concentrations of fluorocitrate, whereas the consumption of glucose decreased. This shows that glutamine fed into the TCA cycle, substituting for glucose as an energy substrate. These findings may explain how fluorocitrate selectively lowers the level of glutamine and inhibits glutamine formation in the brain in vivo, viz., not by depleting glial cells of ATP, but by causing a rerouting of 2-oxoglutarate from glutamine synthesis into the TCA cycle during inhibition of aconitase. Analysis of the 13C labeling of the C-2 versus the C-4 positions in glutamine obtained with [2-13C]acetate revealed that 57% of the TCA cycle intermediates were lost per turn of the cycle.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetates↗

PubMed1994

NBQX (2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline) did not affect recovery of high energy phosphates and pH in early reperfusion in a rat model of transient forebrain ischemia. Or: an in vivo 31P NMR spectroscopy study.

The new non-NMDA (N-methyl-D-aspartate) receptor antagonist NBQX (2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline) has previously been shown to exert a neuroprotective effect in animal models of cerebral ischemia when administered in the post-ischemic phase. In this investigation the effect of NBQX on acidosis and energy recovery in early reperfusion after 10 min of transient forebrain ischemia with the 2-vessel occlusion model in the rat was studied with 31P NMR spectroscopy. In the intervention group the animals received a bolus dose of NBQX 30 mg.kg-1 i.v. at the start of reperfusion. 31P NMR spectroscopy was used to measure intracellular pH, ATP and phosphocreatine continuously in-vivo during, and after, the ischemic event. The recovery of high energy phosphates and pH was followed during 30 min of reperfusion. Pre-ischemic levels of phosphocreatine were reached after approximately 9-10 min in both groups. Although a slight improvement could be seen in the intervention group there was no significant difference in the rate of recovery between the two groups. ATP reached 90% of preischemic levels after about 8 min without significant difference between the two groups. With respect to the recovery of intracellular pH, no difference could be shown. Our results do not contradict previously published results, but suggest that the potential protective effect of NBQX is not mediated through improved recovery of energy metabolism in early reperfusion.

Acidosis↗

PubMed1994

Nuclear magnetic resonance spectroscopy: biochemical evaluation of brain function in vivo and in vitro.

Nuclear magnetic resonance spectroscopy (MRS) offers a unique opportunity to monitor mmolar concentrations of high energy phosphates, glucose, lactate and amino acids. The possibility of obtaining information about chemical constituents noninvasively is of great importance. MRS and chemical shift imaging (CSI) are emerging as tools for tumor grading, monitoring of treatment, ischemia research, in pediatric research for follow-up of children with borderline mental retardation, for defining brain death and to define epileptic foci. It is important to know which cell type (neuronal or glial) shows changes as a result of external manipulations (e.g. excitotoxins) or internal changes (brain pathology). Metabolic studies have been carried out on brain cell cultures. By using 13C labeled glucose and acetate in combination with 13C MRS it was shown that astrocytes release lactate, glutamine, citrate and alanine and that cerebral cortical neurons use glutamine released from astrocytes as a precursor for GABA synthesis. An important feature in MRS is the localization of N-acetyl aspartate in neurons, since this enables monitoring of neuronal reactions, such as survival after neurotoxic insults. Recent advances have yielded high speed functional echo planar imaging (EPI) techniques that are sensitive to changes in cerebral blood volume, blood flow and blood oxygenation (Functional MRI). During cognitive task performance, local alterations in neuronal activity induce local changes in cerebral metabolism and cerebral perfusion, which can now be detected with MRI.

Animals↗

PubMed1993

[Intracranial tumors in children (under 15 years)].

Primary intracranial tumours develop in 30-35 Norwegian children each year. Of these tumours, astrocytomas are the most frequent, followed by medulloblastomas, oligoastrocytomas and ependymomas. In this article we give an overview of tumour classification, epidemiology, diagnosis, treatment and prognosis of intracranial tumours in children.

Adolescent↗

PubMed1993

[Intracranial tumors in adults (over 15 years)].

Primary intracranial tumours develop in 420 adult Norwegians each year. Of these tumours, gliomas are the most frequent, followed by meningiomas, pituitary adenomas and acoustic neurinomas. Glioblastomas represent more than 50% of the gliomas. Less than 10% of the patients with glioblastoma survive for two years, despite aggressive therapy (surgery, radiotherapy and chemotherapy). The prognosis for low grade gliomas is much better. In the case of meningiomas, 95% of the tumours are benign. The primary treatment for meningiomas is surgery. If surgery is impossible, radiosurgery should be considered. Pituitary adenomas are often hormone-secreting (e.g. prolactin, growth hormone, adrenocorticotrophic hormone). Many prolactinomas are treated with bromocriptine alone. The rest of the pituitary adenomas are treated by microsurgery and radiotherapy. The prognosis for patients with pituitary adenomas is good. Acoustic neurinomas, which in most cases are benign, are treated by microsurgery or radiosurgery. Postoperative morbidity due to cochlear nerve and facial nerve dysfunction is a problem. Brain metastases are far more frequent than primary intracranial tumours. Solitary metastases in patients with stable systemic disease should be treated by surgery or radiosurgery.

Adult↗

PubMed1993

Direct demonstration by [13C]NMR spectroscopy that glutamine from astrocytes is a precursor for GABA synthesis in neurons.

Primary cultures of cerebral cortical astrocytes and neurons, as well as neurons growing on top of the astrocytes (sandwich co-cultures), were incubated with 1-[13C]glucose or 2-[13C]acetate and in the presence or absence of the glutamine synthetase inhibitor methionine sulfoximine. [13C]NMR spectroscopy at 125 MHz was performed on perchloric acid extracts of the cells or on media collected from the cultures. In addition, the [13C/12C] ratios of the amino acids glutamine, glutamate and 4-aminobutyrate (GABA) were determined by gas chromatography/mass spectroscopy, showing a larger degree of labeling in GABA than in glutamate and glutamine from glucose. Glutamine and glutamate were predominantly labeled from acetate. A picture of cellular metabolism mainly regarding the tricarboxylic acid cycle and glycolysis was obtained. Due to the fact that acetate is not metabolized by neurons to any significant extent, it could be shown that precursors from astrocytes are incorporated into the GABA pool of neurons grown in co-culture with astrocytes. Spectra of media removed from these cultures revealed that likely precursor candidates for GABA were glutamine and citrate. The importance of glutamine is further substantiated by the finding that inhibition of glutamine synthetase, an enzyme present in astrocytes only, significantly decreased the labeling of GABA in co-cultures incubated with 2-[13C]acetate.

Acetates↗

PubMed1993

Metabolism of [U-13C]glutamate in astrocytes studied by 13C NMR spectroscopy: incorporation of more label into lactate than into glutamine demonstrates the importance of the tricarboxylic acid cycle.

Primary cultures of cerebral cortical astrocytes were incubated with [U-13C]glutamate (0.5 mM) in modified Dulbecco's medium for 2 h. Perchloric acid (PCA) extracts of the cells as well as redissolved lyophilized media were subjected to NMR spectroscopy to identify 13C-labeled metabolites. NMR spectra of the PCA extracts exhibited distinct multiplets for glutamate, aspartate, glutamine, and malate. The culture medium showed peaks for a multitude of compounds released from the astrocytes, among which lactate, glutamine, alanine, and citrate were readily identifiable. For the first time incorporation of label into lactate from glutamate was clearly demonstrated by doublet formation in the C-3 position and two doublets in the C-2 position of lactate. This labeling pattern can only occur by incorporation from glutamate, because natural abundance will only produce singlets in proton-decoupled 13C spectra. Glutamine, released into the medium, was labeled uniformly to a large extent, but the C-3 position not only showed the expected apparent triplet but also a doublet due to 13C incorporation into the C-4 position of glutamine. The doublet accounted for 11% of the total label in the glutamine synthesized and released within the incubation period. The corresponding labeling pattern of [13C]glutamate in the PCA extracts showed that 19% of the glutamate contained 12C. Labeling of lactate, citrate, malate, and aspartate as well as incorporation of 12C into uniformly labeled glutamate and glutamine could only arise via the tricarboxylic acid cycle. The relative amount of glutamate metabolized via this route is at least 70% as calculated from the areas of the C-3 resonances of these compounds.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

NMR spectroscopic studies of 13C acetate and 13C glucose metabolism in neocortical astrocytes: evidence for mitochondrial heterogeneity.

Neocortical astrocytes were incubated with 13C-labeled substrates to determine metabolic pathways. 13C NMR spectroscopy was used to analyze 13C incorporation into glutamine and citrate from the different precursors--[1-13C]glucose or [2-13C]acetate. When glucose was the labeling substrate, incorporation due to pyruvate carboxylation should be observed in the C-2 position in glutamine and the C-4 position in citrate. A large incorporation due to pyruvate carboxylation was observed in glutamine in the C-2 and C-3 positions, but not in citrate. When acetate was the precursor, the labeling ratios in the C-2/C-4 positions in glutamine and in the equivalent positions in citrate were 0.27 and 0.11, respectively. Moreover, acetate labeled lactate in the C-2 position much less than did glucose. Altogether, these observations led to the conclusion that glutamine precursors and citrate are either produced in different types of astrocytes or in different tricarboxylic acid cycles, situated in functionally different mitochondria in the same cell, and that in all likelihood pyruvate carboxylase is expressed differently in these mitochondria.

Acetates↗

PubMed1992

Hyperglycemia in global cerebral ischemia and reperfusion: a 31-phosphorous NMR spectroscopy study in rats.

31-phosphorous magnetic resonance spectroscopy was used in a rat model of 10 min severe incomplete forebrain ischemia (two-vessel occlusion with hypotension) to assess the effect of hyperglycemia on intracellular pH and high energy phosphates during ischemia and early reperfusion. One group (n = 8) with preischemic hyperglycemia (serum glucose 20 mmol.l-1) showed an increased intracellular acidosis (pH 6.35) during ischemia compared to 6.55 in the normoglycemic control group (n = 7, P less than 0.001), but the recovery of phosphocreatine and ATP in early reperfusion was the same in the two groups. Another group (n = 7) was normoglycemic during ischemia, but received an i.v. bolus of glucose during the first minute of reperfusion. In this group the recovery of intracellular pH in early reperfusion was slower than in the control group (0.034 +/- 0.006 pH units per minute compared to 0.052 +/- 0.11 in the controls, +/- s.d. and P less than 0.01).

Acidosis↗