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D Guévremont

Publications and source records attributed to D Guévremont.

10 recordsLinked to original sources
PubMed2003

Long-term regulation of N-methyl-D-aspartate receptor subunits and associated synaptic proteins following hippocampal synaptic plasticity.

Synaptic plasticity in the dentate gyrus is dependent on activation of the N-methyl-D-aspartate (NMDA)-subtype of glutamate receptors. In this study, we show that synaptic plasticity in turn regulates NMDA receptors, since subunits of the NMDA receptor complex are bidirectionally and independently regulated in the dentate gyrus following activation of perforant synapses in awake animals. Low-frequency stimulation that produced a mild synaptic depression resulted in a decrease in the NMDA receptor subunits NR1 and NR2B 48 h following stimulation. High-frequency stimulation that produced long-term potentiation resulted in an increase in NR1 and NR2B at the same time point. Further investigations revealed that in contrast to NR2B, NR1 levels increased gradually after long-term potentiation induction, reaching a peak level at 48 h, and were insensitive to the competitive NMDA receptor antagonist 3-3(2-carboxypiperazin-4-yl) propyl-1-phosphate. The increased levels of NR1 and NR2B at 48 h were found associated with synaptic membranes and with increased NMDA receptor-associated proteins, postsynaptic density protein 95, neuronal nitric oxide synthase and Ca(2+)/calmodulin-dependent protein kinase II, alpha subunit. These data suggest that the persistence of long-term potentiation is associated with an increase in the number of NMDA receptor complexes, which may be indicative of an increase in synaptic contact area.

Animals↗
PubMed2001

A dynamic competition between release factor 2 and the tRNA(Sec) decoding UGA at the recoding site of Escherichia coli formate dehydrogenase H.

Factors affecting competition between termination and elongation in vivo during translation of the fdhF selenocysteine recoding site (UGA) were studied with wild-type and modified fdhF sequences. Altering sequences surrounding the recoding site UGA without affecting RNA secondary structure indicated that the kinetics of stop signal decoding have a significant influence on selenocysteine incorporation efficiency. The UGA in the wild-type fdhF sequence remains 'visible' to the factor and forms a site-directed cross-link when mRNA stem-loop secondary structure is absent, but not when it is present. The timing of the secondary structure unfolding during translation may be a critical feature of competition between release factor 2 and tRNA(Sec) for decoding UGA. Increasing the cellular concentration of either of these decoding molecules for termination or selenocysteine incorporation showed that they were able to compete for UGA by a kinetic competition that is dynamic and dependent on the Escherichia coli growth rate. The tRNA(Sec)-mediated decoding can compete more effectively for the UGA recoding site at lower growth rates, consistent with anaerobic induction of fdhF expression.

Base Sequence↗
PubMed2000

Functional characterization of yeast mitochondrial release factor 1.

The yeast Saccharomyces cerevisiae mitochondrial release factor was expressed from the cloned MRF1 gene, purified from inclusion bodies, and refolded to give functional activity. The gene encoded a factor with release activity that recognized cognate stop codons in a termination assay with mitochondrial ribosomes and in an assay with Escherichia coli ribosomes. The noncognate stop codon, UGA, encoding tryptophan in mitochondria, was recognized weakly in the heterologous assay. The mitochondrial release factor 1 protein bound to bacterial ribosomes and formed a cross-link with the stop codon within a mRNA bound in a termination complex. The affinity was strongly dependent on the identity of stop signal. Two alleles of MRF1 that contained point mutations in a release factor 1 specific region of the primary structure and that in vivo compensated for mutations in the decoding site rRNA of mitochondrial ribosomes were cloned, and the expressed proteins were purified and refolded. The variant proteins showed impaired binding to the ribosome compared with mitochondrial release factor 1. This structural region in release factors is likely to be involved in codon-dependent specific ribosomal interactions.

Amino Acid Sequence↗
PubMed2000

The ribosomal binding and peptidyl-tRNA hydrolysis functions of Escherichia coli release factor 2 are linked through residue 246.

Replacing a cassette of 31 residues from Escherichia coli release factor 1 with the equivalent residues in release factor 2 gave a protein active in codon-specific binding to the ribosome but inactive in peptidyl-tRNA hydrolysis. Such a phenotype is also found unexpectedly with release factor 2 when expressed at high concentration in bacteria. Substituting threonine with the release factor 1 equivalent serine at position 246 within the cassette restored the impaired activity of the chimeric protein, and also that of inactive recombinant release factor 2, both in vitro and in vivo. The differences in activity are not due to posttranslational modifications or a lack of it at this residue. Random mutagenesis of codon 246 suggests that this position is pivotal for the function of the release factor, being able to affect differentially both its binding to the ribosome and its peptide release activities. We propose that amino acid 246 is close to a sharp turn (GGQ motif at position 250), and is essential for transmitting the signal from cognate codon recognition by correctly positioning the peptidyl-tRNA hydrolysis domain of the release factor into the peptidyltransferase center.

Amino Acid Sequence↗
PubMed1992

Pharmacology of MK-0591 (3-[1-(4-chlorobenzyl)-3-(t-butylthio)-5-(quinolin-2-yl-methoxy)- indol-2-yl]-2,2-dimethyl propanoic acid), a potent, orally active leukotriene biosynthesis inhibitor.

MK-0591 (3-[1-(4-chlorobenzyl)-3-(t-butylthio)-5-(quinolin-2-yl-methoxy)- indol-2-yl]-2,2-dimethyl propanoic acid, previously L-686,708) is a potent inhibitor of leukotriene (LT) biosynthesis in intact human and elicited rat polymorphonuclear leukocytes (PMNLs) (IC50 values 3.1 and 6.1 nM, respectively) and in human, squirrel monkey, and rat whole blood (IC50 values 510, 69, and 9 nM, respectively). MK-0591 had no effect on rat 5-lipoxygenase. MK-0591 has a high affinity for 5-lipoxygenase activating protein (FLAP) as evidenced by an IC50 value of 1.6 nM in a FLAP binding assay and inhibition of the photoaffinity labelling of FLAP by two different photoaffinity ligands. Inhibition of activation of 5-lipoxygenase was shown through inhibition of the translocation of the enzyme from the cytosol to the membrane in human PMNLs. MK-0591 was a potent inhibitor of LT biosynthesis in vivo, first, following ex vivo challenge of blood obtained from treated rats and squirrel monkeys, second, in a rat pleurisy model, and, third, as monitored by inhibition of the urinary excretion of LTE4 in antigen-challenged allergic sheep. Inhibition of antigen-induced bronchoconstriction by MK-0591 was observed in inbred rats pretreated with methysergide, Ascaris-challenged squirrel monkeys, and Ascaris-challenged sheep (early and late phase response). These results indicate that MK-0591 is a potent inhibitor of LT biosynthesis both in vitro and in vivo indicating that the compound will be suitable for assessing the role of leukotrienes in pathological situations.

5-Lipoxygenase-Activating Proteins↗
PubMed1986

Stability of alpha-1 adrenoceptors in surgically excised human brain.

Alpha-1 adrenoceptor sites were measured in membranes prepared from nonepileptic superficial cortex following temporal lobectomy for lesions in deep medial structures. There was no significant change in receptor density (Bmax) or affinity (Kd) when paired samples were either frozen immediately or kept at room temperature for 24 hours before freezing and storage at -70 degrees C. Regional variability in the Bmax or Kd of alpha-1 adrenoceptor binding was not observed in serial samples from lateral temporal cortex. We previously reported a localized decrease in alpha-1 adrenoceptors in epileptic foci when compared to adjacent nonepileptic tissue obtained from the same patient. As nonepileptic control tissue from an adjacent gyrus is frequently not available in the same specimen, the stability of alpha-1 adrenoceptors justifies the use of postmortem brain for comparative studies.

Adolescent↗
PubMedDate not supplied

Transient changes in cortical alpha 1 adrenoceptors and seizure threshold following electroconvulsive seizures in rats.

Alpha 1 adrenoceptor density (Bmax) is consistently decreased in actively spiking human cortical epileptic foci. Interpretation of these unique human data is limited because all surgical excisions are completed shortly after a period of active seizure discharge. To determine the temporal profile of seizure-induced changes in cortical alpha 1 adrenoceptors we examined rats primed by 15 daily electroconvulsive seizures (ECS). Since the noradrenergic system has an inhibitory effect on epileptic activity, we also measured the postictal rise in minimal ECS seizure threshold. Animals were sacrificed immediately before or at intervals after the last scheduled seizure. Cortical membranes were assayed using [3H]prazosin as specific radioligand. Repeated ECS produced an increase in the number of cortical alpha 1 sites from 4 to 24 h postictally, but following the last seizure there was a transient 'normalization' of alpha 1 receptor density which persisted for 3 h. The postictal ECS seizure threshold also remained elevated for a 2 h period. Both these transient postictal changes may in part result from activation of the central NA system. Decreased alpha 1 adrenoceptors in surgical specimens of spiking cerebral cortex may also be a secondary response to focal seizure activity.

Animals↗
PubMedDate not supplied

A trial of clodronate-liposomes as anti-macrophage treatment in a sheep model of arthritis.

OBJECTIVE: Our previous research has concerned the role of macrophages in joint inflammation in rheumatoid arthritis. We have therefore been interested in liposomes containing clodronate as an antimacrophage treatment for arthritis. We have used the antigen-induced arthritis model in sheep to evaluate the effect of clodronate liposomes. METHODS: Arthritis was induced in the right hock joint (day 0). We were able to demonstrate uptake of liposomes into macrophages within the inflamed joint lining. On day 7, sheep were given a single intra-articular injection of clodronate liposomes (group 1, n = 10) or saline liposomes (group 2, n = 10). A further 6 sheep (group 3) had no arthritis and no treatment. RESULTS: No difference in joint diameter was observed between the sheep in group 1 (clodronate) and group 2 (saline treated). Both groups had joint swelling which persisted until the end of the trial (day 20). Histologic scoring was also similar in group 1 and group 2 animals, and both were worse than group 3. CONCLUSION: In vitro studies have shown that interaction of liposomes with neutrophils and monocytes stimulates a respiratory burst. Despite this possible pro-inflammatory effect we did not observe any increase in joint diameter following liposome injection. Thus we were unable to demonstrate a therapeutic effect of a single dose of clodronate liposomes in this large animal model of antigen-induced arthritis.

Analgesics, Non-Narcotic↗
PubMedDate not supplied

Antigen-induced (Dumonde Glynn) arthritis in the sheep: a large joint animal model of arthritis.

OBJECTIVE: To determine if the Dumonde Glynn model of arthritis can be established in sheep since a larger model would facilitate injection and the measurement of joints. METHODS: Three groups of sheep were immunised with ovalbumin in Freund's adjuvant. Arthritis was induced in group 1 (n = 10, by the injection of 5 mg ovalbumin in 0.5 ml to the right hock joint. Control groups received saline (n = 10) or no treatment (n = 6). RESULTS: Following joint injection the mean AP diameter increased so that there was a 32% difference between the right and left joints at 24 hr (p < 0.001) declining gradually to 12% (p < 0.01) 19 days after the induction of arthritis. The level of haptoglobin in group 1 prior to the induction of arthritis was 0.04 +/- 0.01. Haemoglobin binding capacity (mg/ml) peaked on day 3 at 0.33 +/- 0.13 (p < 0.01), and was 0.110 +/- 0.05 thirteen days after joint injection. Features observed included proliferation of the joint lining, fibrin deposition and early erosion of cartilage. Synovial membrane showed an infiltrate of inflammatory cells identified as monocytes/macrophages and lymphocytes. Synovial histology scores were 1.8 +/- 0.2 for the left joint and 9.3 +/- 0.73 for the arthritic right joint. CONCLUSION: We conclude that this is a model of mono-arthritis particularly useful when a larger joint is required for intra-articular injection or repeated joint measurements such as in a clinical trial.

Animals↗