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  • 1
    ISSN: 1432-1106
    Keywords: Ischaemia ; Hippocampal damage ; Microdialysis ; Glutamate ; Immunocytochemistry ; Amino acid neurotransmitters ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The redistribution of neurotransmitter amino acids resulting from 20 min of ischaemia was studied in the rat hippocampus by quantitative, electron microscopic immunocytochemistry and by in vivo microdialysis. Changes in the distribution of glutamate, glutamine, aspartate and GABA in various cell compartments of CA1 were analysed immediately after ischaemia or after 60 min of reperfusion, by incubating ultrathin sections with antisera raised against protein glutaraldehyde conjugates of the respective amino acids and subsequently with a secondary antibody coupled to colloidal gold particles. Transverse microdialysis probes coupled with HPLC and implanted in the same animals were used to determine the extracellular concentration of amino acids in the left hippocampus and to apply a drug (BW 1003C87) believed to modify the extracellular release of amino acids induced by ischaemia. Forebrain ischaemia was induced by temporary occlusion of the common carotid arteries in rats with permanently occluded vertebral arteries. The extracellular concentrations of glutamate, aspartate and GABA increased markedly during ischaemia, but returned rapidly to normal during reperfusion. BW 1003C87 (250 μM, in the dialysis fluid) did not modify the increase in extracellular concentration of amino acids during ischaemia. Glutamate-like immunoreactivity was reduced in pyramidal cell somata both immediately after ischaemia and after 60 min of reperfusion. This reduction appeared to be somewhat less pronounced for cells in the left hemisphere (perfused with BW 1003C87) than in the contralateral hemisphere. Ischaemia caused no consistent changes in terminals. The ratio between the intracellular levels of glutamate and glutamine was assessed by double-labelling immunocytochemistry, using two different gold particle sizes. The glutamate-glutamine ratio in glial cells was greatly increased after ischaemia, but recovered to a normal level within 1 h of reperfusion. Aspartate-like immunoreactivity was substantially reduced in pyramidal cell somata both immediately and 60 min after ischaemia, while profiles that were immunopositive for GABA in control brains showed increased GABA immunolabelling. These results suggest that postsynaptic neuronal elements as well as glial cells contribute to the extracellular overflow of excitatory amino acids during an ischaemic event: post-synaptic elements by leaking or releasing glutamate and aspartate, and glial cells by losing their ability to convert glutamate to glutamine effectively. The temporal association between the changes in the glial contents of glutamate and glutamine, and the extracellular amino acid fluctuations recorded by microdialysis in the same animals, underline the strategic role of glia in regulating the extracellular level of glutamate.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1106
    Keywords: Hippocampus ; Ischemia ; Glial glutamate transporter ; In situ hybridization ; Immunoblotting
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Perturbations of the synaptic handling of glutamate have been implicated in the pathogenesis of brain damage after transient ischemia. Notably, the ischemic episode is associated with an increased extracellular level of glutamate and an impaired metabolism of this amino acid in glial cells. Glutamate uptake is reduced during ischemia due to breakdown of the electrochemical ion gradients across neuronal and glial membranes. We have investigated, in the rat hippocampus, whether an ischemic event additionally causes a reduced expression of the glial glutamate transporter GLT1 (Pines et al. 1992) in the postischemic phase. Quantitative immunoblotting, using antibodies recognizing GLT1, revealed a 20% decrease in the hippocampal contents of the transporter protein, 6 h after an ischemic period lasting 20 min induced by four vessel occlusion. In situ hybridization histochemistry with 35S labelled oligonucleotide probes or digoxigenin labelled riboprobes directed to GLT1 mRNA showed a decreased signal in the hippocampus, particularly in CA1. This reduction was more pronounced at 3 h than at 24 h after the ischemic event. We conclude that the levels of GLT1 mRNA and protein show a modest decrease in the postischemic phase. This could contribute to the delayed neuronal death typically seen in the hippocampal formation after transient ischemia.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-1106
    Keywords: Taurine ; Immunocytochemistry ; Hippocampus ; Baboon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary An antiserum raised against taurine conjugated to bovine serum albumin by glutaraldehyde produced intense staining of hippocampal pyramidal neurons at the CA1/CA3 transition (including CA2) and of a small proportion of the granule cells. Strongly immunoreactive neurons were also found in a zone overlapping the second reflected blade in the hilus. Most glial cells were unlabeled.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 55 (1990), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Intracellular free [Ca2+]j was measured using fura-2 in synaptosomes prepared from cerebral cortices of adult male rats (12 weeks). L-(+)-Glutamate, d-(-)-glutamate, and quisqualate produced similar dose-dependent increases in [Ca2+]i, with EC50 values of 0.38 μM, 0.74 μM, and 0.1 μM, respectively, and maximum increases of approximately 40%. Ibotenate showed less affinity (EC50 4.4 μM) but had a greater maximum effect (57%). N-methyl-d-aspartate (NMDA) and α- amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) did not increase [Ca2+]i- The increases in [Ca2+]i induced by quisqualate and ibotenate were not diminished in the absence of extrasynaptosomal Ca2+. l-2-Amino-4-phosphonobutyrate (L-AP4) (1 μM) completely blocked the changes in [Ca2+]i induced by l-(+)-glutamate, d-(-)-glutamate, quisqualate, or ibotenate. The effects of quisqualate and ibotenate on [Ca2+]i were also blocked by coincubation of synaptosomes with l-(+)-serine-O-phosphate (L-SP) (1 mM) (which, like L-AP4, blocks the effects of quisqualate and ibotenate on inositol phospholipid metabolism). 6-Cyano-7-nitroquinoxaline-2,3-dione (CNQX) had no effect on agonist-mediated increases in [Ca2+]i when coincubated with either quisqualate or ibotenate. These data are consistent with the existence of presynaptic glutamate receptors (of the excitatory amino acid metabotropic type) which activate phospholipase C leading to the elevation of inositol 1,4,5-trisphosphate and release of Ca2+ from intracellular stores.
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  • 5
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Microdialysis experiments performed in the dorsal hippocampus of freely moving rats showed that L-(E)- 4-(3-phosphono-2-propenyl) piperazine-2-carboxylic acid (L-CPPene) is 10 times as potent as D-CPPene in inhibiting potassium-induced increases in extracellular levels of aspartate and glutamate. In control experiments, two 100 mM KCI stimuli (S1 and S2) applied for 10 min each (separated by a 40-min recovery period) produced substantial (300–500%) increases in the extracellular levels of aspartate, glutamate, taurine, and GABA and a 50% decrease in the glutamine level. S2/S1 ratios in the control groups were 0.67 (aspartate), 0.78 (glutamate), 0.83 (GABA), and 0.85 (taurine). In the experimental groups, D- or L-CPPene was applied via the probe during the second potassium stimulus (S2). L-CPPene (25 or 250 μM) produced selective suppression of potassium-induced increases of extracellular glutamate (S2/S1 ratio: 0.25) and aspartate (S2/S1 ratio: 0.20) levels, whereas 250 μM D-CPPene was required to inhibit the extracellular aspartate and glutamate increases. Neither enantiomer of CPPene affected the potassium-induced increases of GABA and taurine or the decrease in extracellular glutamine concentration. An addtional study comparing the anticonvulsant potencies of D- and L-CPPene was performed using audiogenic DBA/2 mice. The anticonvulsant potency of D-CPPene, as assessed against sound-induced seizures in DBA/2 mice, was an order of magnitude higher than that of L-CPPene [ED50 clonic phase (intraperitoneal, 45 min): 1.64 μmol/kg and 16.8 μmol/kg, respectively]. We attribute the anticonvulsant action of D-CPPene to its antagonist action at the NMDA receptor. The selective inhibition by L-CPPene of potassium-induced increases in extracellular aspartate and glutamate levels is presumably due to an action on presynaptic glutamate receptors.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 49 (1987), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Pretreatment of rats with the excitatory amino acid antagonist 2-amino-7-phosphonoheptanoic acid (2-APH; 0.5 mmol/kg, i.p.) protected against insulin-induced clonic seizures. Complete protection was observed in 38% of the rats and partial protection in an additional 50%. Le-sioning of the corticostriatal pathway by frontal cortical ablation caused decreases in the striatal levels of aspartate (-28%) and glutamate (-18%), an increase in striatal glutamine level (45%), and decreased high-affinity uptake of D-[3H]aspartate (-27%) in the lesioned dorsal neostriatum. Insulin-induced hypoglycemia caused a predicted sharp increase in aspartate level (165%) and decreased glutamate (-20%) and glutamine (-38%) levels in the intact striatum. Pretreatment of rats with 2-APH significantly reversed the insulin-induced changes in striatal aspartate, glutamate, and glutamine levels, especially in the intact hemisphere. In normoglycemic control rats, the “metabolic”, i.e., concentration in the lesioned hemisphere, aspartate pool constituted 72% and the “synaptic”, i.e., the concentration difference between the intact and lesioned hemispheres, 28% of the total striatal aspartate pool. 2-APH had no effect on the level of “metabolic” aspartate in the striata of normoglycemic rats but caused an almost complete suppression of “synaptic” aspartate. Following insulin-induced hypoglycemia, the “metabolic” aspartate pool doubled, whereas the “synaptic” aspartate pool increased 3.5-fold in the absence of 2-APH. The insulin-induced rise in “synaptic” aspartate level was almost completely blocked by 2-APH (a 5% rise instead of a 3.5-fold rise). The turnover of “metabolic” aspartate was also affected by 2-APH, but to a lesser extent (a 25% rise in the presence vs. a 94% rise in the absence of 2-APH). The striatal changes in levels of dicarboxylic acids after systemic 2-APH administration can be most simply explained in terms of an action of 2-APH in the cortex blocking excitatory inputs to the corticostriatal pathway.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 39 (1982), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The properties of γ-aminobutyric acid recognition sites, benzodiazepine binding sites and the effect of exogeneous γ-aminobutyric acid on benzodiazepine binding were determined in crude membrane fractions prepared from the brains of DBN/2 mice at ages before (8-9 and 17-18 days), during (22-23 and 28-29 days) and after (40-43 days) the age of high susceptibility to audiogenic seizures. These have been compared with data from age- matched mice of a strain (TO) with lower audiogenic seizure susceptibility. The number of high-affinity [3H]γ-aminobutyric acid binding sites was lower at all ages in DBN/2 mice compared with TO mice, but the affinity was higher in DBN/2 mice. The number of low-affinity [3H]y-aminobutyric acid binding sites was lower at 8-9 days and 40-43 days in DBN/2 mice, but was not significantly different from TO mice at other ages. For [3H]flunitrazepam binding, the only difference found was a slight reduction in the number of binding sites at 28-29 days of age in DBN/2 mice. γ-Aminobutyric acid stimulation of [3H]-flunitrazepam binding was not significantly different up to 22-23 days of age, but was higher in DBN/2 mice at 28-29 days and lower at 40-43 days. Impairment of γ-aminobutyric acid function is a possible permissive factor in the age-dependent audiogenic seizure susceptibility in DBN/2 mice.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The effect of the non-N-methyl-D-aspartate (non-NMDA) receptor antagonist 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine hydrochloride (GYKI 52466) on ischaemia-induced changes in the microdialysate and tissue concentrations of glutamate, aspartate, and γ-aminobutyric acid (GABA) was studied in rats. Twenty minutes of four-vessel occlusion resulted in a transient increase in microdialysate levels of glutamate, aspartate, and GABA in striatum, cortex, and hippocampus. Administration of GYKI 52466 (10 mg/kg bolus + 10 mg/kg/60 min intravenously starting 20 min before onset of ischaemia) inhibited ischaemia-induced increases in microdialysate glutamate and GABA in striatum without affecting the increases in hippocampus or cortex. Twenty minutes of four-vessel occlusion resulted in immediate small decreases and larger delayed (72 h) decreases in tissue levels of glutamate and aspartate. Transient increases in tissue levels of GABA were shown in all three structures at the end of the ischaemic period. At 72 h, after the ischaemic period, significantly reduced GABA levels were observed in striatum and hippocampus. GYKI 52466, given under identical conditions as above, augmented the ischaemia-induced decrease in striatal tissue levels of glutamate and aspartate, without significantly affecting the decreases in hippocampus and cortex. Twenty minutes of ischaemia resulted in a large increase in microdialysate dopamine in striatum. GYKI 52466 failed to inhibit this increase. Kainic acid (500 μM infused through the probe for 20 min) caused increases in microdialysate glutamate and aspartate in the striatum. GYKI 52466 (10 mg/ kg bolus + 10 mg/kg/60 min) completely inhibited the kainic acid-induced glutamate release. In conclusion, the action of the non-NMDA antagonist, GYKI 52466, in the striatum is different from that in the cortex and hippocampus. The inhibition by GYKI 52466 of ischaemia-induced and kainate-induced increases in microdialysate glutamate concentration in the striatum may be related to the neuroprotection provided by GYKI 52466 in this region.
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 24 (1975), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: —The convulsant action of methyldithiocarbazinate (MDTC), thiocarbohydrazide (TCH) and thiosemicarbazide (TSC) has been studied in mice. The relationship between dose and time to convulsions indicated that MDTC has a dual action and is more potent than TSC. Pretreatment of mice with pyridoxal phosphate (0.25 mmol/kg) protected against convulsions and death produced by low doses of MDTC or TCH, and low or high doses of TSC. Pretreatment with pyridoxine hydrochloride (0.25 mmol/kg) protected mice against TSC but not against TCH. It protected against low doses of MDTC (0.12 mmol/kg), but shortened the latency to convulsions after intermediate doses of MDTC (0.37 mmol/kg).Glutamate decarboxylase activity (GAD, EC 4.1.1.15) in whole brain homogenates from mice killed at the onset of seizures, was significantly reduced by all 3 drugs at all doses. This inhibition did not exceed 30% after any dose of TSC or TCH, but was 64% in mice killed 4 min after the injection of MDTC (0.98 mmol/kg). The addition of pyridoxal phosphate to brain homogenates abolished GAD inhibition after MDTC but not after TCH. In vitro brain GAD was 50% inhibited by 10−4m-MDTC, 18% by 10−4m-TSC and 8% by 10 −4m-TCH. Kinetic studies suggested that at low concentrations MDTC inhibits by competing with pyridoxal phosphate. At the onset of convulsions the cerebral content of pyridoxal phosphate was reduced after low or high doses of TSC (0.27 and 2.2 mmol/kg) and after high doses of MDTC (0.98 mmol/kg). All three drugs (at 10−5−10−4m) inhibited pyridoxal phosphokinase (EC 2.7.1.35) in vitro. Short latency convulsions after MDTC (0.37–0.98 mmol/kg) very probably arise from inhibition of cerebral GAD, due to competition for coenzymic sites and/or unavailability of coenzyme. Long-latency convulsions after MDTC (0.12–0.37 mmol/kg) are comparable to those seen after TSC (0.27–2.2 mmol/kg) and may depend on a mechanism additional to inhibition of GAD.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 21 (1973), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: —The time course of effects of 2-deoxy-d-glucose on cerebral glucose metabolism has been studied in vivo and the inhibitory actions of 2-deoxy-d-glucose and 2-deoxy-d-glucose-6-phosphate on cerebral glycolytic enzymes in vitro. Mice were given 2-deoxy-d-glucose 3 g/kg intraperitoneally. Blood 2-deoxy-d-glucose/glucose ratio was 2–3 from 5 to 30 min after injection, the hyperglycaemic response to 2-deoxy-d-glucose having been suppressed with propranolol. Maximal cerebral 2-deoxy-d-glucose uptake observed was 1μ11 μmol/g/min between 5 and 10 min after injection. At 10 min brain concentrations of 2-deoxy-d-glucose and 2-deoxy-d-glucose-6-phosphate were 5·82 and 3·12 μmol/g. Analysis of the fate of d-[U-14C] glucose given subcutaneously 5 min before death showed that glucose uptake was reduced to 40–60 per cent of control from 5 to 30 min after 2-deoxy-d-glucose. However brain glucose concentration rose three to five-fold 20–30 min after 2-deoxy-d-glucose. The majority of glucose entering the brain after 10 min of 2-deoxy-d-glucose treatment was recovered as glucose. Conversion of brain glucose to other acid soluble components was reduced to 1/3 at 10 min and 1/5 at 20–30 min. Glucose-6-phosphate concentration rose from 5 min onwards and was maintained at twice control concentration from 10–30 min. However, because of the rapid entry of 2-deoxy-d-glucose and its conversion to 2-deoxy-d-glucose-6-phosphate, the 2-deoxy-d-glucose 6-P/glucose 6-P ratio was between 19 and 32. Brain adenosine triphosphate concentration did not change, creatine phosphate concentration fell after 25 min.Measurement of enzyme activities in cerebral homogenates (using 1 mivs substrate concentration) showed that hexokinase (EC 2.7.1.1) was 40 per cent inhibited by 5 mm-deoxy-d-glucose (but not by 2-deoxy-d-glucose 6-P). Glucose 6-P dehydrogenase (EC 1.1.1.49), 6-phosphogluconate dehydrogenase (EC 1.1.1.43) and phosphoglucomutase (EC 2.7.5.1) were not affected by either 2-deoxy-d-glucose (5 mm) or 2-deoxy-d-glucose 6-P (5 or 20 mm). Hexose-phosphate isomerase (EC 5.3.1.9) was 70 per cent inhibited by 20 mm-d-deoxy-d-glucose 6-P. Phosphofructokinase (EC 2.7.1.11) was inhibited by 17 per cent by 2-deoxy-d-glucose 6-P (20 mm). During the initial impairment of cerebral function by 2-deoxy-d-glucose there is competitive inhibition of glucose transport into the brain; later, glycolysis is more powerfully depressed by the inhibition of isomerase produced by the high intracerebral concentration of 2-deoxyglucose-6-phosphate.
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