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Query: UMLS:C0432222 (SEM)
 47,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Previous studies have shown that complete blockade of metabolism in embryonic chick retina causes a time-dependent increase in the release of glutamate into the extracellular space. The present study examined the cellular source of this glutamate, i.e., neuronal and/or glial. Pure cultures of retinal neurons or glia were labeled for 10 min at 37 degrees C with [3H]acetate. Retinal glia, but not retinal neurons, were found to selectively and preferentially metabolize acetate, thus producing 3H-labeled amino acids in the glial compartment. This finding provides direct evidence to substantiate findings from several other laboratories that have indirectly determined the preferential metabolism of acetate by glia by using mixed neuronal/glial populations. To study the cellular source of glutamate released during total metabolic blockade, whole retina were prelabeled with [3H]acetate plus [U-14C]glucose (to label the neuronal compartment). Total metabolic blockade was instituted with a combination of iodoacetate (IOA) plus KCN, and the release of glutamate into the medium was followed at 5, 15, and 30 min. During total energy blockade, net extracellular glutamate was not elevated at 5 min [0.17 +/- 0.02 vs. 0.12 +/- 0.01 microM for treated vs. control retina (means +/- SEM), respectively], but was increased significantly at 15 (1.2 +/- 0.26 microM) and 30 min (2.6 +/- 0.22 microM). Total [3H]glutamate in the medium during IOA/KCN treatment was unchanged at 5 min, but was increased 1.5- and threefold above basal levels at 15 and 30 min, respectively. During the time when extracellular glutamate increased, the specific activity of [3H]glutamate remained fairly constant, 731 +/- 134 and 517 +/- 82 dpm/nmol (means +/- SEM) at 15 and 30 min, respectively. In contrast, 14C-labeled glutamate in the medium did not increase during IOA/KCN treatment and paralleled basal levels. Thus, the specific activity of 14C-labeled extracellular glutamate decreased from 309 +/- 87 dpm/nmol at 15 min to 42 +/- 8 dpm/nmol at 30 min. Prior loading of the tissue with 0.5 mM trans-pyrrolidine-2,4-dicarboxylate (t-PDC), a glutamate transport inhibitor, blocked 57% of the glutamate released at 30 min of IOA/KCN exposure, suggesting that reversal of an Na+-dependent glutamate transporter was a key contributor to the appearance of extracellular glutamate during energy deprivation. The increase in extracellular [3H]glutamate, constancy of the specific activity of extracellular [3H]glutamate, decrease in the specific activity of extracellular [14C]glutamate, and attenuation of release by prior loading with t-PDC indicate that glial pools of glutamate released via reversal of the transporter contribute significantly to the rise in extracellular glutamate after metabolic inhibition in this preparation.
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PMID:Origins of the extracellular glutamate released during total metabolic blockade in the immature retina. 983 35

The anticholinergic drug orphenadrine is used in the treatment of Parkinson's disease. In this study we evaluate the neuroprotective effects of orphenadrine on excitotoxicity in vivo and in vitro. Orphenadrine prevented the mitochondrial and the cytoplasmic membrane potential decrease evoked by NMDA (100 microM) in rat dissociated cerebellar granule cells showing an IC50 value of 11.6 +/- 4.7 microM (mean +/- SEM, n = 5) and 13.5 +/- 2.3 microM (n = 3), respectively. Orphenadrine was able to protect cerebellar granule cell cultures from glutamate-induced neurotoxicity. Kainic acid (KA, 10 mg/kg)-induced excitotoxicity was evaluated in vivo using the microglial marker peripheral-type benzodiazepine receptor (PBR) and heat shock protein 72 (HSP72) expression in the hippocampus. The Bmax of PBR for control tissues was 589.1 +/- 40.0 fmol/mg protein (n = 4), increasing to 1692.5 +/- 51.6 fmol/mg protein (n = 5) after the KA treatment. Pretreatment with orphenadrine (10 mg/kg) blocked the KA-induced increase in PBR density. As expected, KA-administration induced the expression of HSP72 that was blocked in the orphenadrine + KA-treated rats. We demonstrate that orphenadrine, interacting at the NMDA receptor, is able to prevent the neurotoxicity mediated by activation at glutamate ionotropic receptors.
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PMID:In vitro and in vivo protective effect of orphenadrine on glutamate neurotoxicity. 1034 Mar 4

The effect of mild to moderate hypothermia (32/27 degrees C) was analyzed on the cell volume of C6 glioma cells and primary cultured astrocytes at normal pH, during lactacidosis (pH6.2) and during exposure to glutamate or arachidonic acid in vitro. The cells were suspended in an incubation chamber under continuous control of pH, pO2 and temperature. Cell swelling was quantified by an advanced Coulter-system. Following a control period at 37 degrees C, the ambient temperature was decreased to 27 and 32 degrees C for 30 min. Hypothermia alone led to an immediate and significant cell volume increase of 107.3 +/- 0.4% (mean +/- SEM) of control after 30 min at 32 degrees C. Yet, hypothermia (27 degrees C) afforded partial protection against the acidosis-induced cell swelling at pH 6.2, attaining 120.4 +/- 0.9% in the normothermic control group after 60 min, while only 111.3 +/- 0.9% at 27 degrees C. Hypothermia, however, was not associated with a reduction of the glutamate- or arachidonic acid-induced cell swelling. The results demonstrate that mild hypothermia per se induces glial cell swelling, but simultaneously inhibits cell swelling from acidosis, while not from glutamate- or arachidonic acid.
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PMID:Glial cell swelling--effect of hypothermia. 1049 43

Previous efforts to utilize mammalian spinal cord neurons as biosensor elements have relied on neuronal: glial co-cultures maintained in serum-containing media. We have examined the feasibility of culturing primary spinal cord neurons in serum-free medium, modified for neuronal longevity, on fabricated microelectrode arrays. Embryonic day 15 rat spinal cord cells were plated on trimethoxysilyl-propyldiethylenetriamine coated microelectrode arrays comprised of gold recording sites passivated with silicon nitride. Immunocytochemistry was performed to verify the presence of neurons and quantitatively assess astrocytes using antibodies against glial fibrillary acidic protein on the silicon nitride substrates. Modifications to culture media enabled viable neuronal culture to extend from approximately 14 days in vitro (DIV) to 40 DIV on the arrays containing only 1.1 +/- 0.5% (mean +/- SEM) astrocytes. Extracellular recording revealed tetrodotoxin-sensitive spontaneous electrical activity from the enriched neuronal culture. Threshold detection of extracellular potentials showed an increase in spike rate as a function of glutamate concentration with neurotoxicity at elevated levels. This approach suggests that functional measures related to biosensor applications, pharmacological screening, or the evaluation of neurological disease models can be implemented in a defined culture system.
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PMID:Characterization of rat spinal cord neurons cultured in defined media on microelectrode arrays. 1050 98

Trimethylolpropane phosphate (TMPP) is a neuroactive organophosphate generated during partial pyrolysis of a synthetic ester turbine engine lubricant. While TMPP had been shown to have little affinity for acetylcholinesterase, previous binding studies and 6Cl- flux measurements have implicated TMPP as an antagonist of GABA, receptor/Cl- channels. Using the whole-cell patch clamp method, spontaneous inhibitory postsynaptic currents (sIPSCs) mediated by bicuculline-sensitive GABA(A) receptors were measured in neurons cultured from the rat embryonic hippocampus for 13-21 days. Experiments were conducted in the presence of tetrodotoxin and 6-cyano-7-nitroquinoxaline to inhibit spontaneous presynaptic action potentials and glutamate transmission, respectively, thus isolating GABAergic sIPSCs for study. TMPP induced a concentration-dependent inhibition of sIPSC amplitude and frequency suggesting both postsynaptic and presynaptic actions. Administration of 5 microM TMPP reversibly diminished sIPSC amplitude by 23 +/- 8% (mean SEM, n=5 cells) while markedly decreasing the mean sIPSC frequency by 40 +/- 2% (n=5). The mean time constant of sIPSC decay was reversibly decreased by 20 +/- 4% (n=3) in the presence of 20 microM TMPP, suggesting an increase in the rate of inactivation. To directly verify the blockade of ionotropic GABA receptors by TMPP, the effects of TMPP were examined on whole-cell Cl- current responses activated by exogenous GABA. Administration of TMPP (5 microM) depressed peak whole-cell GABA-induced currents to 73 1% (n=4) of control levels, consistent with the results on sIPSC amplitude. Our data directly demonstrate that TMPP directly inhibits GABA(A) receptor function, as indicated by the blockade of whole-cell GABA-mediated Cl- current and the reduction in sIPSC amplitude. Furthermore, TMPP exerts a presynaptic effect on GABAergic transmission, as evidenced by the reduction in sIPSC frequency, which may be independent of a GABA(A) receptor. The molecular basis for the presynaptic action of TMPP remains to be elucidated.
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PMID:Inhibition of spontaneous GABAergic transmission by trimethylolpropane phosphate. 1059 20

The key role players of brain swelling seen after severe human head injury have only been partly determined. We used our human head injury data base to determine relationships between potassium, glutamate, lactate and cerebral blood flow (CBF). A total of 70 severely head injured patients (GCS < or = 8) were studied using intracerebral microdialysis to measure extracellular glutamate, potassium and lactate. Xenon CT was used to determine regional cerebral blood flow (rCBF). The mean +/- SEM of the r value of all patients, between potassium and glutamate, and potassium and lactate was 0.25 +/- 0.04 (p < 0.0001) and 0.17 +/- 0.06 (p = 0.006), respectively, demonstrating in both cases a positive relationship. rCBF was negatively correlated with potassium with marginal significance (r = -0.35, p = 0.08). When separated into two groups, patients with contusion had higher potassium levels than patients without contusion (1.55 +/- 0.03 mmol/l versus 1.26 +/- 0.02 mmol/l, respectively). These results in severely head injured patients confirm previous in vitro and animal studies in which relationships between potassium, glutamate, lactate and CBF were found. Potassium efflux is a major determinant of cell swelling leading to clinically significant cytotoxic edema due to increased glutamate release during reduced cerebral blood flow.
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PMID:Determinants of cerebral extracellular potassium after severe human head injury. 1063 73

Free amino acids in plasma and total protein, albumin, transferrin and retinol-binding protein (RBP) in serum were determined in two groups of healthy adults consisting of 10 female nonusers and 10 female users of monosodium glutamate (MSG). Users or nonusers of MSG were those consuming or not consuming MSG regularly at their homes for at least 1 y. On the bases of body mass index and serum protein concentrations, each of the two groups appeared to have an adequate protein-energy status. Fasting plasma glutamate concentrations in female nonusers and users of MSG were 22.4 +/- 3.2 and 21.8 +/- 2.0 nmol/mL (means +/- SEM), respectively; these values were not significantly different. These findings indicate that there is no glutamate accumulation in the plasma of MSG users and imply the safety of long-term MSG intake.
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PMID:Plasma amino acid patterns and visceral protein status in users and nonusers of monosodium glutamate. 1073 71

To examine the involvement of different ionotropic glutamate receptors in the mediation of responses evoked by noxious cutaneous stimulation, single unit recordings were made from 31 neurons in the primary somatosensory (SI) cortex of rats anesthetized with urethane. To compare synaptic receptor pharmacology across somatosensory submodalities, 13 of the neurons were also tested with an innocuous, cutaneous air jet stimulus. Mechanical (HT) responses, evoked by a 5-s noxious pinch, decayed gradually upon termination of the stimulus and lasted on average for 15.1+/-1.9 s (+/-SEM; n=10). An increase in baseline activity was also observed during noxious stimulus trials of 5-min stimulus intervals. A correlation between increase in mechanical or thermal HT responses and baseline activity was found for some neurons. However, the normalized ratios of the mechanical or thermal HT response to baseline activity during iontophoretic application of (RS)-3-(2-carboxypiperazine-4-yl)-propyl-l-phosphonic acid (CPP), an N-methyl-D-aspartic acid (NMDA) receptor antagonist (0.6+/-0.1; n=11, or 6-nitro-7-sulfamoylbenz[f]quinoxaline-2,3-dione (NBQX), an (RS)-alpha-amino-3-hydroxy5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptor antagonist (0.8+/-0.1; n=11), suggest that the reductions in baseline activity did not account for the reductions of the mechanical or thermal HT responses observed, which were reduced proportionally more than the baseline activity. A 10-ms air jet evoked a biphasic increase in action potentials above an average background activity of 7+/-2 spikes/s (n=13). The early phase of this low-threshold (LT) response was within two or three 10-ms bins and had an average firing rate of 74+/-11 spikes/s evoked in the first 10-ms bin (n=13). In eight neurons, the early LT response was followed by a lower frequency excitatory component lasting an average of 415+/-92 ms. Iontophoretic application of CPP reduced responses evoked by a noxious pinch (21+/-10% of control responses; n=19) and a noxious thermal stimulus (24+/-18%; n=5). The fast component of the LT responses was only reduced to 85+/-4% (n=12). A slower component of the LT responses, when present, was also reduced by CPP (15+/-19%; n=4). Iontophoretic application of NBQX reduced responses evoked by a noxious pinch (42+/-12%; n=19) and a noxious thermal stimulus (63+/-16%; n=8). The fast component of the LT responses was reduced to 43+/-6% (n=12) and the slower component to 32+/-20% (n=6). These data show that both NMDA and AMPA/kainate receptors are involved in the mediation of SI high-threshold responses. This same combination of glutamate receptors also mediates low-threshold synaptic responses.
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PMID:Ionotropic glutamate receptor-mediated responses in the rat primary somatosensory cortex evoked by noxious and innocuous cutaneous stimulation in vivo. 1078 44

Although serine proteases and their receptors are best known for their role in blood coagulation and fibrinolysis, the CNS expresses many components of an extracellular protease signaling system including the protease-activated receptor-1 (PAR1), for which thrombin is the most effective activator. In this report we show that activation of PAR1 potentiates hippocampal NMDA receptor responses in CA1 pyramidal cells by 2.07 +/- 0.27-fold (mean +/- SEM). Potentiation of neuronal NMDA receptor responses by thrombin can be blocked by thrombin and a protein kinase inhibitor, and the effects of thrombin can be mimicked by a peptide agonist (SFLLRN) that activates PAR1. Potentiation of the NMDA receptor by thrombin in hippocampal neurons is significantly attenuated in mice lacking PAR1. Although high concentrations of thrombin can directly cleave both native and recombinant NR1 subunits, the thrombin-induced potentiation we observe is independent of NMDA receptor cleavage. Activation of recombinant PAR1 also potentiates recombinant NR1/NR2A (1.7 +/- 0.06-fold) and NR1/NR2B (1.41 +/- 0.11-fold) receptor function but not NR1/NR2C or NR1/NR2D receptor responses. PAR1-mediated potentiation of recombinant NR1/NR2A receptors occurred after activation with as little as 300 pm thrombin. These data raise the intriguing possibility that potentiation of neuronal NMDA receptor function after entry of thrombin or other serine proteases into brain parenchyma during intracerebral hemorrhage or extravasation of plasma proteins during blood-brain barrier breakdown may exacerbate glutamate-mediated cell death and possibly participate in post-traumatic seizure. Furthermore, the ability of neuronal protease signaling to control NMDA receptor function may also have roles in normal brain development.
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PMID:Potentiation of NMDA receptor function by the serine protease thrombin. 1084 28

Inhibition of kynurenine 3-hydroxylase suppresses quinolinic acid synthesis and, therefore, shunts all kynurenine metabolism toward kynurenic acid (KYNA) formation. This may be a pertinent antiexcitotoxic strategy because quinolinic acid is an agonist of NMDA receptors, whereas kynurenic acid antagonises all ionotropic glutamate receptors with preferential affinity for the NMDA receptor glycine site. We have examined whether the kynurenine 3-hydroxylase inhibitor Ro 61-8048 increases extracellular (KYNA) sufficiently to control excessive NMDA receptor function. Microdialysis probes incorporating an electrode were implanted into the striatum of anaesthetised rats, repeated NMDA stimuli were applied through the probe, and the resulting depolarisation was recorded. Changes in extracellular KYNA were assessed by HPLC analysis of consecutive dialysate samples. Ro 61-8048 (42 or 100 mg/kg) markedly increased the dialysate levels of KYNA. The maximum increase (from 3.0 +/- 1.0 to 31.0 +/- 6.0 nM; means +/- SEM, n = 6) was observed 4 h after administration of 100 mg/kg Ro 61-8048, but the magnitude of the NMDA-induced depolarisations was not reduced. A separate study suggested that extracellular KYNA would need to be increased further by two orders of magnitude to become effective in this preparation. These results challenge the notion that kynurenine 3-hydroxylase inhibition may be neuroprotective, primarily through accumulation of KYNA and subsequent attenuation of NMDA receptor function.
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PMID:Kynurenine 3-hydroxylase inhibition in rats: effects on extracellular kynurenic acid concentration and N-methyl-D-aspartate-induced depolarisation in the striatum. 1108 Jan 94


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