Biomedical subjects

S H Graham

Publications and source records attributed to S H Graham.

At least 73 records · Page 4Linked to original sources

PubMed1996

A dose-response study of neuroprotection using the AMPA antagonist NBQX in rat focal cerebral ischemia.

AMPA antagonists have been shown to be remarkably neuroprotective in models of global ischemia, but the data in focal ischemia remain controversial. We, therefore, studied the dose-response characteristics and the time window of efficacy of the AMPA antagonist NBQX in a rat model of permanent focal ischemia. NBQX 40, 60 or 100 mg/kg i.v., substantially reduced infarct size. Neuroprotection was maintained when the initiation of drug administration was withheld for 15, 45 or 90 min after permanent middle cerebral artery occlusion. Furthermore, NBQX did not induce heat shock protein in cingulate cortex, as do some N-methyl-D-aspartate antagonists. Thus, the compound is a potent neuroprotectant in focal ischemia and has an unusually long time window of effectiveness.

Animals↗

PubMed1995

HSP70 heat shock protein induction following global ischemia in the rat.

Stress proteins, including the 70 kD heat shock protein (HSP70), are induced in injured cells. The present study was designed to characterize the cells injured by global ischemia in rat brain. Adult rats were subjected to forebrain ischemia using bilateral carotid occlusion and systemic hypotension. HSP70 protein immunostaining of brain sections was performed using the C92 monoclonal antibody one day later. HSP70 immunoreactive cells were found in many brain regions including cortex. HSP70 positive neurons in cortex were found in certain laminae, especially layers 2 and 3. Acid fuchsin positive neurons, cells presumed to be dead, were located only in the layers of cortex where HSP70 immunoreactive neurons were found and were infrequent compared to the large number of HSP70 positive neurons. HSP70 immunoreactive glial cells were detected at the margins of ischemic areas, and were mostly OX42 immunoreactive microglia plus some GFAP immunoreactive astrocytes. In some animals HSP70 stained bipolar cells were detected in the striatum and in white matter which may be type 2 astrocytes. These findings confirm that global ischemia injures microglia and astrocytes, and that cells in a given ischemic region sustain varying degrees of injury--from the HSP70 stained neurons that likely survive the ischemia to acid fuchsin stained cells that die.

Animals↗

PubMed1995

A comparison of the effects of a sodium channel blocker and an NMDA antagonist upon extracellular glutamate in rat focal cerebral ischemia.

Agents such as 619C89 decrease extracellular glutamate concentrations by a primary action at voltage sensitive sodium channels, but NMDA antagonists also have been shown to decrease extracellular glutamate concentration after ischemia. To address the question as to whether 619C89's effect upon extracellular glutamate concentrations is any different than the effect of the NMDA antagonist dextrorphan, 24 rats were given either optimally neuroprotective doses of these drugs or saline prior to middle cerebral artery occlusion. In caudate, the 619C89-treated, but not dextrorphan-treated rats had less microdialysate glutamate than ischemic controls. In cortex, both 619C89- and dextrorphan-treated groups had significantly decreased glutamate compared with ischemic controls. These results support a specific effect of 619C89 upon glutamate release in caudate but not cortex.

Animals↗

PubMed1995

bcl-2 is expressed in neurons that survive focal ischemia in the rat.

Expression of the proto-oncogene bcl-2 prevents programmed cell death in vitro, but it is not known whether bcl-2 plays a role in determining cell survival after cerebral ischemia. Using immunohistochemistry and Western blot analysis, bcl-2 protein expression was studied in the rat brain 24 h following 60 or 120 min of temporary focal ischemia. Sixty minutes of ischemia induced bcl-2 protein in neurons throughout the frontoparietal cortex in non-infarcted regions, whereas 120 min of ischemia induced bcl-2 in neurons only just outside the margin of the infarction. bcl-2 protein was also induced in glial cells, mainly microglia, border zone of the infarction. In the infarcted regions of caudate and cortex, bcl-2 protein was exclusively induced in endothelial cells and the vessel walls. Western blot revealed a characteristic single band at 26 kDa only in ischemic samples. These data show that bcl-2 is induced in sublethally injured cells and suggest that bcl-2 could play a role in determining cell survival in cerebral ischemia.

Animals↗

PubMed1995

Expression of cyclo-oxygenase 2 in rat brain following kainate treatment.

The transcriptional expression of the mitogen-inducible cyclo-oxygenase (COX-2) was investigated by in situ hybridization of kainate-treated rat brains. Kainate treatment rapidly induced COX-2 mRNA in neurons throughout the forebrain which was blocked by pretreatment with MK-801 or NBQX. Transient expression of COX-2 mRNA lasting about 8 h occurred in areas that were resistant to neuronal necrosis, while COX-2 mRNA expression persisted for 24-72 h in regions that were vulnerable. These results show that seizures result in increased COX-2 expression and support the hypothesis that COX-2 could be an important factor in the pathogenesis of delayed neuronal necrosis due to kainate excitotoxicity.

Animals↗

PubMed1995

Correlation of early reduction in the apparent diffusion coefficient of water with blood flow reduction during middle cerebral artery occlusion in rats.

To determine the relationship between reductions in the apparent diffusion coefficient of water (ADC) and in cerebral blood flow (CBF) during focal ischemia, we used diffusion-weighted magnetic resonance (D-MR) imaging and autoradiographic CBF analysis to examine rats subjected to 30 or 90 min of permanent middle cerebral artery (MCA) occlusion. In the 30-min occlusion group (n = 10), the area with substantially reduced ADC (15% or more below the contralateral level [ADC15]) corresponded best to the area with CBF below 25 ml/100 g/min and was significantly smaller than the area with CBF below 50 ml/100 g/min (CBF50), a level associated with reduced protein synthesis and delayed necrosis (40 +/- 13% versus 74 +/- 8% of the ischemic hemisphere; P < 0.0001). In the 90-min occlusion group (n = 6), the ADC15 area corresponded best to the CBF30 to CBF35 area and was again significantly smaller than the CBF50 area (54 +/- 13% versus 73 +/- 20%, P < 0.05). Thus, the area of substantially reduced ADC at 30 and 90 min represents only 53% and 74%, respectively, of the tissue at risk for infarction. These findings indicate a potential limitation in using early D-MR imaging to predict stroke outcome.

Animals↗

PubMed1995

Attenuation of postischemic brain hypoperfusion and reperfusion injury by the cyclooxygenase-lipoxygenase inhibitor BW755C.

Arachidonic acid metabolites are believed to be important mediators of tissue injury during reperfusion after cerebral ischemia. To determine whether inhibiting the oxygen-dependent metabolism of arachidonic acid would reduce reperfusion injury, we administered the mixed cyclooxygenase-lipoxygenase inhibitor BW755C (3-amino-1-[m(trifluoromethyl)phenyl]-2-pyrazoline) near the time of reperfusion in a rat model of temporary focal ischemia. The duration of ischemia + reperfusion was 2 hours + 22 hours, 3 hours + 3 hours, or 3 hours + 21 hours. The effects of drug or saline treatment on infarct volume, blood-brain barrier permeability, and blood flow were determined. Cortical blood flow was monitored with laser Doppler flowmetry and blood-brain barrier permeability was evaluated by the Evans blue dye method. Infarct volume was determined in all groups by computerized image analysis of Nissl-stained sections. We found that BW755C treatment significantly attenuated delayed postischemic hypoperfusion in the 3 + 3 group (p < 0.05) and reduced the volume of Evans blue dye staining in the cortex (p < 0.01) and basal ganglia (p < 0.05). Hemispheric swelling was reduced in all treatment groups (p < 0.01), as was total infarct volume in the ischemic hemisphere (p < 0.05). These results support the hypothesis that arachidonic acid metabolites contribute to acute postischemic reperfusion injury and suggest that using a mixed cyclooxygenase-lipoxygenase inhibitor as an adjunct to thrombolytic or revascularization therapy could lengthen the ischemia time after which reperfusion is beneficial.

4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyraz↗

PubMed1995

Diffusion-weighted magnetic resonance imaging during brief focal cerebral ischemia and early reperfusion: evolution of delayed infarction in rats.

The purpose of this study was to ascertain if the signal intensity ratio and the lesion area determined by diffusion-weighted magnetic resonance imaging during brief focal ischemia and early reperfusion predict outcome determined by diffusion-weighted magnetic resonance imaging and T2-magnetic resonance imaging at 24 h. Seventeen rats were imaged before and during 30 min of endovascular middle cerebral artery occlusion and at 15 min, and 23.5 h after the onset of reperfusion. Both hemisphere and basal ganglia signal intensity ratio increased significantly from baseline during ischemia, decreased significantly from ischemic levels during early reperfusion, and increased again at 24 h. However, signal intensity ratio during ischemia or after 45 min of reperfusion did not correlate statistically with diffusion-weighted-signal intensity ratio at 24 h. Both hemisphere signal intensity ratio and basal ganglia signal intensity ratio at 15 min of reperfusion correlated, but only moderately, with diffusion-weighted-signal intensity ratio at 24 h (r = 0.52, p < or = 0.05). Although lesion areas during ischemia were comparable to those observed at 24 h, lesion areas at both 15 and 45 min of reperfusion were significantly smaller than those observed during ischemia and at 24 hr. Thus, sequential imagining demonstrated partial resolution and delayed recurrence of magnetic resonance-defined ischemic lesions during reperfusion after brief focal ischemia.

Animals↗

PubMed1994

Fluorocitrate and fluoroacetate effects on astrocyte metabolism in vitro.

The Krebs cycle inhibitor fluorocitrate (FC) and its precursor fluoroacetate (FA) are taken up in brain preferentially by glia. These compounds are used experimentally to inhibit glial metabolism in situ. The actions of these agents have been attributed to both the disruption of carbon flux through the Krebs cycle and to impairment of ATP production. We used primary astrocyte cultures to evaluate these two possible modes of action. Astrocyte ATP levels exhibited little or no reduction during incubation with 0.5 mM FC or 25 mM FA. Correspondingly, FC and FA caused less than 30% reductions in glutamate uptake (P > 0.05), an important energy-dependent astrocyte function. Carbon flux through the Krebs cycle was assessed by measuring astrocyte glutamine production in the absence of exogenous glutamate or aspartate. Under these conditions, glutamine production was reduced 65 +/- 5% by 0.5 mM FC and 61 +/- 3% by 25 mM FA (P < 0.01). In contrast, FC and FA had no effect on glutamine production when 50 microM glutamate was provided in the media. These findings suggest that the metabolic effects of FC and FA on astrocytes in vivo result from impairment of carbon flux through the Krebs cycle, and not from impairment of oxidative ATP production.

Animals↗

PubMed1994

BW1003C87 and NBQX but not CGS19755 reduce glutamate release and cerebral ischemic necrosis.

This study examines the relationship between the concentration of extracellular glutamate released during 30 min of forebrain ischemia, and the subsequent development of ischemic neural necrosis, in the presence of three agents which act at distinct sites on the glutamatergic synapse: a presynaptic inhibitor of glutamate release (5-(2,3,5-trichlorophenyl)-2,4-diamino-pyramidine ethane sulphonate (BW1003C87)); a competitive NMDA receptor antagonist (cis-4-phosphonomethyl-2-piperidine carboxylic acid (CGS19755)); and a competitive AMPA receptor antagonist (2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline (NBQX)). Pretreatment with either BW1003C87 or NBQX markedly attenuated the peak concentration of extracellular glutamate and offered protection from post-ischemic neuronal necrosis in the CA1 hippocampus. In contrast, pretreatment with CGS19755 had no effect on extracellular glutamate release and did not protect CA1 hippocampal neurons from ischemic injury.

Analysis of Variance↗

PubMed1994

Mild intraischemic hypothermia suppresses consumption of endogenous antioxidants after temporary focal ischemia in rats.

Oxidative damage by free radicals has been proposed as a mechanism of cerebral injury due to ischemia and reperfusion. Hypothermia protects against ischemic necrosis; however, its effect on oxidative stress has not been investigated. In this study, the effects of hypothermia on oxidative stress were studied by determining consumption of endogenous antioxidants after temporary focal ischemia in rats. Thirty-two Sprague-Dawley rats anesthetized with 1.5% isoflurane underwent 3 h of middle cerebral artery occlusion under hypothermic (33 degrees C) or normothermic (37 degrees C) conditions followed by 3 h of normothermic reperfusion. In the first study (n = 8 per group), intraischemic hypothermia suppressed the reduction of tissue concentrations of endogenous antioxidants, ascorbate (P < or = 0.05), and glutathione (P < or = 0.05) in ischemic cortex but not in caudoputamen. In a parallel study (n = 8 per group), hypothermia reduced tissue damage in ischemic frontoparietal cortex (P < or = 0.05), but not in caudoputamen. Laser-Doppler estimates of cortical blood flow showed that intraischemic hypothermia significantly attenuated early postischemic hyperperfusion (P < or = 0.01) and delayed postischemic hypoperfusion (P < or = 0.01). These results demonstrate that intraischemic mild hypothermia reduces oxidative stress and cell injury after prolonged focal ischemia followed by reperfusion. The reduction of oxidative stress by hypothermia may be related indirectly to attenuation of postischemic blood flow changes.

Animals↗

PubMed1994

Magnetic resonance spectroscopy of N-acetylaspartate in hypoxic-ischemic encephalopathy.

Magnetic resonance imaging and water-suppressed proton magnetic resonance spectroscopic imaging were used to study N-acetylaspartate and other metabolites in a patient with severe hypoxic-ischemic encephalopathy. The N-acetylaspartate signal, a putative marker of neuronal density, was markedly reduced in the forebrain. The relative signal intensity of choline-containing metabolites, which are more abundant in astrocytes than neurons, was increased. These results support the hypothesis that water-suppressed proton magnetic resonance spectroscopic imaging measurements of N-acetylaspartate may be useful for noninvasive detection of selective neuronal loss in a variety of disease states in the human brain.

Adolescent↗

PubMed1994

Glucose can fuel glutamate uptake in ischemic brain.

Astrocytes in culture can maintain glutamate uptake during hypoxia if glucose is available. To determine whether this capacity is shared by brain in situ, extracellular glutamate levels were measured in ischemic brain under conditions of continued glucose delivery. Microdialysis probes were placed bilaterally in caudate nuclei of rats and perfused with artificial cerebrospinal fluid (CSF) containing either 30 or 0 mM glucose. Global cerebral ischemia was induced by cardiac arrest. Dialysate collected from probes not perfused with glucose showed a 50-fold increase in glutamate levels over the 60 min following cardiac arrest. Addition of glucose to the perfusate reduced the glutamate rise to < 20% of the levels attained in the glucose-free probes. The glucose effect was negated by the addition of 0.5 mM of the glutamate uptake blocker threo-beta-hydroxyaspartate to the artificial CSF. These results show that oxygen is not required to maintain efficient uptake of extracellular glutamate in brain and suggest that elevations in extracellular glutamate levels during ischemia result from metabolic perturbations other than hypoxia.

Amino Acids↗

PubMed1994

N-acetylaspartate as an in vivo marker of neuronal viability in kainate-induced status epilepticus: 1H magnetic resonance spectroscopic imaging.

N-acetylaspartate (NAA) has been proposed as a marker of neuronal density. Therefore, regional measurement of NAA by magnetic resonance spectroscopic imaging (MRSI) may provide a sensitive method for detection of selective neuronal loss, in contrast to conventional imaging techniques such as magnetic resonance imaging (MRI). To test this hypothesis, we produced selective neuronal injury by kainate-induced status epilepticus. Three days later three-dimensional 1H-MRSI was obtained and compared with conventional T2-weighted MRI and histological findings in normal and kainate-treated rats. Reduction of NAA determined by MRSI in piriform cortex, amygdala, and hippocampus correlated well with neuronal injury determined from histology. Changes of NAA, without any MRI changes in hippocampus, indicated greater sensitivity of MRSI for detection of neuronal injury. These results are consistent with the hypothesis that reduction of NAA measured by MRSI may be a sensitive marker of neuronal injury in vivo in a variety of disease states.

Animals↗

PubMed1994

Mild intraischemic hypothermia reduces postischemic hyperperfusion, delayed postischemic hypoperfusion, blood-brain barrier disruption, brain edema, and neuronal damage volume after temporary focal cerebral ischemia in rats.

Mild to moderate hypothermia (30-33 degrees C) reduces brain injury after brief (< 2-h) periods of focal ischemia, but its effectiveness in prolonged temporary ischemia is not fully understood. Thirty-two Sprague-Dawley rats anesthetized with 1.5% isoflurane underwent 3 h of middle cerebral artery occlusion under hypothermic (33 degrees C) or normothermic (37 degrees C) conditions followed by 3 or 21 h of reperfusion under normothermic conditions (n = 8/group). Laser-Doppler estimates of cortical blood flow showed that intraischemic hypothermia reduced both postischemic hyperperfusion (p < or = 0.01) and postischemic delayed hypoperfusion (p < or = 0.01). Hypothermia reduced the extent of blood-brain barrier (BBB) disruption as estimated from the extravasation of Evans blue dye at 6 h after the onset of ischemia (p < or = 0.01). Hypothermia also reduced the volume of both brain edema (p < or = 0.01) and neuronal damage (p < or = 0.01) as estimated from Nissl-stained slides at both 6 and 24 h after the onset of ischemia. These results demonstrate that mild intraischemic hypothermia reduces tissue injury after prolonged temporary ischemia, possibly by attenuating postischemic blood flow disturbances and by reducing vasogenic edema resulting from BBB disruption.

Animals↗

PubMed1994

Delayed induction of mild hypothermia to reduce infarct volume after temporary middle cerebral artery occlusion in rats.

Deep to moderate hypothermia (24 degrees to 30 degrees C) during focal cerebral ischemia reduces infarct volume but must be initiated before the onset of ischemia to be effective and has deleterious pulmonary, myocardial and neurological effects. It is not known whether mild hypothermia (32 degrees to 33 degrees C) protects against ischemic neuronal damage, whether hypothermia induced after the onset of ischemia has protective effects, or whether these effects are associated with alterations in cortical blood flow. In this study, mild whole-body hypothermia was induced in rats just before or 10, 30, or 60 minutes after the onset of 2 hours of temporary middle cerebral artery occlusion; rewarming began immediately after reversal of occlusion and normothermia was maintained throughout 22 hours of reperfusion. Infarct volume, measured 24 hours after the end of reperfusion, was significantly smaller in rats made hypothermic within 30 minutes after the onset of ischemia than in normothermic controls; hypothermia induced at 60 minutes of ischemia did not reduce infarct volume. Cortical blood flow, measured by laser Doppler ultrasound flowmetry, was not significantly different between groups during ischemia; however, postischemic cortical blood flow correlated positively with total infarct volume. These results indicate that mild hypothermia initiated during temporary focal ischemia in rats can reduce infarct volume without attenuating the reduction in cortical blood flow.

Animals↗

PubMed1994

Neuroprotective effects of a use-dependent blocker of voltage-dependent sodium channels, BW619C89, in rat middle cerebral artery occlusion.

BW619C89 [4-amino-2-(4-methyl-1-piperazinyl)-5-(2,3,5- trichlorophenyl)pyrimidine is a use-dependent blocker of voltage-dependent sodium channels that blocks veratrine-induced glutamate release in vitro. The aim of this study is to determine if BW619C89 inhibits glutamate release and is neuroprotective in cerebral ischemia produced by proximal middle cerebral artery (MCA) occlusion in rats. Infarct volume was determined at 24 hr after permanent MCA occlusion from 2,3,5-triphenyltetrazolim hydrochloride-stained sections. Pretreatment with BW619C89 (10, 20, 30 and 50 mg/kg i.v. of mesylate salt) decreased infarct volume in a dose-dependent fashion maximal at 30 mg/kg compared to saline controls. Treatment with 30 mg/kg up to 45 min after MCA occlusion also was effective. Microdialysate glutamate in rats treated with 30 mg/kg of drug before MCA occlusion was decreased in both caudate (ischemic core) and rostral cortex (penumbra) compared to controls. BW619C89 did not induce significant arterial hypotension, except when it was administered by rapid bolus administration. In this case, the hypotension was transient and did not reduce efficacy or superficial cortical blood flow. BW619C89 did not induce the 72 kD heat shock protein in cingulate gyrus or retrosplenial cortex as did MK801, suggesting that BW619C89 does not injure neurons in these regions as do N-methyl-D-aspartate antagonists. These results suggest that inhibition of glutamate release by BW619C89 may be an effective and nontoxic treatment for stroke.

Animals↗

PubMed1993

Opioid receptor antagonist nalmefene stereospecifically inhibits glutamate release during global cerebral ischemia.

The opioid receptor antagonist nalmefene improves cellular bioenergetics and attenuates the reduction in tissue glutamate levels after global cerebral ischemia/reperfusion. The latter finding suggests that nalmefene might inhibit glutamate release during ischemia. To test this hypothesis, we used microdialysis techniques to examine the effect of nalmefene pretreatment on extracellular excitatory amino acid levels during global cerebral ischemia in rats. Saline, (-)-nalmefene (20, 100 or 500 micrograms/kg) or the inactive nalmefene enantiomer (+)-nalmefene (100 micrograms/kg) were given 15 min prior to induction of ischemia using a multi-vessel occlusion model. Pretreatment with (-)-nalmefene decreased peak dialysate glutamate in a dose-dependent fashion as compared to saline-treated controls, whereas (+)-nalmefene had no effect. These results suggest that opioid receptors may modulate glutamate release during ischemia and that inhibition of excitatory amino acid release may contribute to the protective actions of opioid receptor antagonists in cerebral ischemia.

Animals↗