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Biomedical subjects

M Nielsen

Publications and source records attributed to M Nielsen.

At least 127 records · Page 7Linked to original sources
PubMed1995

Antisense oligonucleotide to GABAA receptor gamma 2 subunit induces loss of neurones in rat hippocampus.

The binding site for 1,4-benzodiazepines in the brain is part of the hetero-oligomeric gamma-aminobutyric acid (GABA)A receptor complex which regulates a chloride ion channel. The presence of the gamma 2 subunit in the complex is necessary for the binding of benzodiazepines to their binding site. This study demonstrates a reduction of benzodiazepine receptor radioligand binding by 43% compared to control following infusion of phosphorothioate antisense oligodeoxynucleotide to gamma 2 subunit into rat hippocampus. Reduction of benzodiazepine binding sites was paralleled by a decrease in [35S]tert-butyl-bicyclo-phosphorothionate ([35S]TBPS) binding (51%) and [3H]muscimol binding (37%), indicating a reduction in the number of GABAA receptors. Changed macroscopic appearance, reduced protein content and severe loss of neurones in antisense-treated hippocampi suggests that the reduced formation of GABAA receptors leads to neuronal cell death.

Animals↗
PubMed1995

Modest reduction of benzodiazepine binding in rat brain in vivo induced by antisense oligonucleotide to GABAA receptor gamma 2 subunit subtype.

The GABAA (gamma-aminobutyric acid-A) receptor gamma 2 subunit subtype is probably a functionally integral part of the benzodiazepine binding site of the GABAA receptor complex, important for benzodiazepine pharmacology. We have evaluated the possibility of specifically reducing benzodiazepine receptor binding properties in vivo using phosphorothioate antisense oligodeoxynucleotides to inhibit the expression of GABAA receptor gamma 2 subunit subtype. Intracerebroventricular infusions of an antisense oligonucleotide reduced benzodiazepine receptor radioligand binding by 9-15% in specific rat brain regions.

Animals↗
PubMed1995

Staphylococcal enterotoxins modulate interleukin 2 receptor expression and ligand-induced tyrosine phosphorylation of the Janus protein-tyrosine kinase 3 (Jak3) and signal transducers and activators of transcription (Stat proteins).

Staphylococcal enterotoxins (SE) stimulate T cells expressing the appropriate variable region beta chain of (V beta) T-cell receptors and have been implicated in the pathogenesis of several autoimmune diseases. Depending on costimulatory signals, SE induce either proliferation or anergy in T cells. In addition, SE can induce an interleukin-2 (IL-2) nonresponsive state and apoptosis. Here, we show that SE induce dynamic changes in the expression of and signal transduction through the IL-2 receptor (IL-2R) beta and gamma chains (IL-2R beta and IL-2R gamma) in human antigen-specific CD4+ T-cell lines. Thus, after 4 hr of exposure to SEA and SEB, the expression of IL-2R beta was down-regulated, IL-2R gamma was slightly up-regulated, while IL-2R alpha remained largely unaffected. The changes in the composition of IL-2Rs were accompanied by inhibition of IL-2-induced tyrosine phosphorylation of the Janus protein-tyrosine kinase 3 (Jak3) and signal transducers and activators of transcription called Stat3 and Stat5. In parallel experiments, IL-2-driven proliferation was inhibited significantly. After 16 hr of exposure to SE, the expression of IL-2R beta remained low, while that of IL2R alpha and IL2R gamma was further up-regulated, and ligand-induced tyrosine phosphorylation of Jak3 and Stat proteins was partly normalized. Yet, IL-2-driven proliferation remained profoundly inhibited, suggesting that signaling events other than Jak3/Stat activation had also been changed following SE stimulation. In conclusion, our data suggest that SE can modulate IL-2R expression and signal transduction involving the Jak/Stat pathway in CD4+ T-cell lines.

Apoptosis↗
PubMed1995

Alpha 2-macroglobulin receptor mediates binding and cytotoxicity of plant ribosome-inactivating proteins.

It has been proposed that unconjugated type I ribosome-inactivating proteins (RIP) enter cells through passive mechanisms such as fluid-phase pinocytosis. However, some observations, such as the difference in sensitivity to type I RIP among different cell types, and the organ-specific toxicity of type I RIP, indicate a specific mechanism for the entry of these proteins into target cells. The alpha 2-macroglobulin receptor (alpha 2MR) is responsible for the binding and endocytosis of several ligands, including alpha 2-macroglobulin/proteinase complexes, plasminogen-activator-inhibitor complexes, apoE-enriched beta-very low density lipoproteins, and lipoprotein lipase. Here we demonstrate that saporin, a potent type I RIP, binds specifically to purified alpha 2MR and the binding is prevented by some alpha 2MR ligands. Moreover, the occupancy of specific ligand-binding sites on cell surface alpha 2MR decreases the cytotoxicity of saporin. The A chain of ricin, a type II RIP, also interacts with alpha 2MR. This, and the fact that saporin and ricin A chain both interact also with alpha 2-macroglobulin, indicates a general mechanism of complex interactions between RIP and cellular membranes that is mediated by alpha 2-macroglobulin and the alpha 2MR system.

Cell Death↗
PubMed1995

Thiomuscimol, a new photoaffinity label for the GABAA receptor.

Thiomuscimol inhibits [3H]muscimol binding to brain GABAA receptors. Exposure of Ag(+)-treated membrane preparations to UV radiation at 254 nm for 40 min in the presence of thiomuscimol (10(-5) M) produced a 20-30% irreversible decrease in high-affinity [3H]muscimol binding sites. The photoaffinity labeling of thiomuscimol was inhibited by GABA (10(-4) M) added prior to exposure to UV light. The data show that thiomuscimol can label the GABAA receptor site and that the ligand can be used as a photoaffinity label for purification and identification of GABA binding sites within the GABAA receptor complex.

Affinity Labels↗
PubMed1995

Inhibition of kainic acid binding to glutamate receptors by extracts of Gastrodia.

S-(4-hydroxybenzyl)glutathione was isolated as the major principle responsible for the inhibition of the in vitro binding of kainic acid to brain glutamate receptors by water extracts of the plant Gastrodia elata. The affinity (IC50 value) of the compound is slightly lower compared to glutamate and glutathione.

Drugs, Chinese Herbal↗
PubMed1995

Managing the medical device directive. A practical case study.

Through a case study of a fictional company, this article provides a guide on how to implement CE-marking procedures, as detailed in the Medical Device Directive. The overlap in transitional periods between the Medical Device and Electromagnetic Compatibility Directives is discussed, together with issues such as selection of conformity assessment routes.

Electroencephalography↗
PubMed1994

Effects of plant diterpenes on the neuronal GABAA receptor-operated chloride current.

The effects of plant diterpenes, horminone (HMN) and taxodione (TXN), on the GABAA receptor-operated Cl-current (IGABA) were investigated in voltage-clamped and internally perfused neurones dissociated from frog dorsal root ganglia. Both diterpenes depressed IGABA in a concentration-dependent manner similar to that of picrotoxin. Concentrations required to elicit 50% depression of the IGABA were 10(-6) M for picrotoxin, 10(-5) M for HMN and 10(-4) M for TXN. Blocking and restoration kinetics of the IGABA with HMN were also similar to those of picrotoxin. Time constants for both the blockade and restoration of the IGABA with TXN were more than five times greater than those with HMN.

Abietanes↗
PubMed1994

A carboxyl-terminal fragment of lipoprotein lipase binds to the low density lipoprotein receptor-related protein and inhibits lipase-mediated uptake of lipoprotein in cells.

It has previously been shown that lipoprotein lipase can mediate uptake of remnant lipoprotein particles via binding to the low density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor (LRP). Binding of lipoprotein lipase, and of triglyceride-rich lipoproteins associated with the lipase, to LRP depends on an intact carboxyl-terminal folding domain of the lipase (Nykjaer, A., Bengtsson-Olivecrona, G., Lookene, A., Moestrup, S. K., Petersen, C. M., Weber, W., Beisiegel, W., and Gliemann, J. (1993) J. Biol. Chem. 268, 15048-15055). Here we show that the site for binding to the receptor is within residues 380-425 of the bovine and residues 378-423 of the human lipoprotein lipase. We demonstrate that a carboxyl-terminal fragment of human lipoprotein lipase (residues 378-448), expressed as fusion protein in Escherichia coli, binds to purified and cellular LRP but not to lipoproteins. Binding of the fragment to purified LRP was blocked by heparin. In addition, the fragment inhibited the binding of lipase and the lipase-mediated binding of lipoproteins to the purified receptor. The fragment exhibited reduced binding to proteoglycan-deficient cells. Moreover, the fragment inhibited the uptake of lipoproteins in cells mediated by the lipase via binding to heparan sulfate proteoglycans and LRP. We conclude that the fragment contains the site for binding to LRP and a candidate site for interaction with heparan sulfate proteoglycans, whereas binding to lipoproteins is inefficient. The fragment can therefore inhibit the lipase-mediated lipoprotein uptake, a process that may promote the development of atherosclerosis when occurring in cells of the arterial wall.

Amino Acid Sequence↗
PubMed1994

Complex correlation between excitatory amino acid-induced increase in the intracellular Ca2+ concentration and subsequent loss of neuronal function in individual neocortical neurons in culture.

Primary cultures of cerebral cortical neurons and single-cell imaging of intracellular free Ca2+ concentration ([Ca2+]i) with the ratiometric dye fura-2 were used to assess excitatory amino acid (EAA)-induced neurotoxicity; the loss of neuronal function as defined by the ability of the cells to respond to K(+)-induced depolarization by a transient increase in Ca2+ influx was measured. The responsiveness of individual neurons was measured quantitatively as the [Ca2+]i values of the second KCl (2.KCl) stimulation divided by those of the first KCl (1.KCl) stimulation, giving the value of the ratio (2.KCl/1.KCl). Exposure to EAAs led to an increase in [Ca2+]i, but no simple correlation between the increase in [Ca2+]i and neuronal responsiveness could be demonstrated. Rather, below a threshold level of [Ca2+]i (ca. 1 microM), the neuronal responsiveness was largely independent of the glutamate receptor-agonist-induced increase in [Ca2+]i. However, when [Ca2+]i increased above this threshold level, the neurons almost invariably lost the ability to respond to a K(+)-induced depolarization, particularly after exposure to glutamate. Therefore, the cortical neurons were found to be exceptionally vulnerable to the glutamate-induced loss of function when compared with the effect induced by the glutamate receptor subtype-specific agonists, N-methyl-D-aspartate, quisqualate, and 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl) propionate. The findings suggest that the loss of neuronal membrane polarization precedes plasma membrane disruption and is a sensitive marker of EAA-induced neurodegeneration observed at the single-cell level.

Animals↗