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T Michel

Publications and source records attributed to T Michel.

At least 19 recordsLinked to original sources
PubMed2006

Raman active phonons of identified semiconducting single-walled carbon nanotubes.

The resonant Raman spectra of (n, m) semiconducting single-walled carbon nanotubes, unambiguously identified from their electron diffraction patterns, have been measured. The diameter dependence of the frequency of the tangential modes with A symmetry has been obtained in the diameter range from 1.4 to 2.5 nm. The comparison between the excitation energies and the calculated transition energies allowed us to determine precisely the values of the Es33 and Es44 transition energies. Finally, in the debate concerning the dominant process at the origin of the first-order Raman scattering in single-walled carbon nanotubes (single resonance process or double resonance process), our results are well understood in the framework of a single resonance process.

Journal Article↗
PubMed2005

Measurement of helicity-dependent photoabsorption cross sections on the neutron from 815 to 1825 MeV.

Helicity-dependent total photoabsorption cross sections on the deuteron have been measured for the first time at ELSA (Bonn) in the photon energy range from 815 to 1825 MeV. Circularly polarized tagged photons impinging on a longitudinally polarized LiD target have been used together with a highly efficient 4pi detector system. The data around 1 GeV are not compatible with predictions from existing multipole analyses. From the measured energy range an experimental contribution to the GDH integral on the neutron of [33.9 +/- 5.5(stat) +/- 4.5(syst)] microb is extracted.

Journal Article↗
PubMed2005

Epoxide adducts at the guanine residue within single-stranded DNA chains: reactivity and stability studies.

Emphasis was placed in this work on the assessment of structural and biological features of nucleobase adducts that result from the reaction of DNA with epoxide derivatives. Thus we have prepared and characterized a set of site-specifically modified oligonucleotides at N7-position of a guanine residue, upon reaction with diepoxibutane, with the purpose of further investigating some of their biochemical features. The stability of the lesion-containing DNA fragments has also been investigated and clearly shows that the latter modified oligomers may be used as substrates for in vitro enzymatic assays, aimed at determining the biological effects within cell of these chemically induced DNA damage.

Butanes↗
PubMed2004

Experimental check of the Gerasimov-Drell-Hearn sum rule for 1H.

For the first time we checked the fundamental Gerasimov-Drell-Hearn (GDH) sum rule for the proton experimentally in the photon energy range from 0.2-2.9 GeV with the tagged photon facilities at MAMI (Mainz) and ELSA (Bonn). New data of the doubly polarized total cross section difference are presented in the energy range from 1.6 to 2.9 GeV. The contribution to the GDH integral from 0.2-2.9 GeV yields [254+/-5(stat)+/-12(syst)] microb with negative contributions in the Regge regime at photon energies above 2.1 GeV. This trend supports the validity of the GDH sum rule.

Journal Article↗
PubMed2004

[Near-infrared spectroscopy in psychiatry].

Near-infrared spectroscopy (NIRS) is a noninvasive optical method for in vivo measurement of regional brain tissue oxygenation. Light from the near-infrared spectrum can penetrate the skull and is mainly absorbed by oxyhaemoglobin (O(2)Hb) and desoxyhaemoglobin (HHb). From the amount of reflected near-infrared light in relation to the amount absorbed by brain tissue, regional changes in O(2)Hb and HHb concentrations can be calculated spectrophotometrically. It has been shown that NIRS is not only able to measure massive disturbances in cerebral blood circulation due to serious neurological diseases, but that it also is sensitive enough to assess task-specific patterns of activation in healthy subjects during circumscribed cognitive processes. Preliminary investigations indicate altered regional brain tissue oxygenation in psychiatric patients during cognitive activation tasks. The NIRS outmatches other functional imaging methods in that it has no side effects and is well tolerated by psychiatric patients. Furthermore, it can be applied quickly and easily. Thus, NIRS is a potential screening method in psychiatric settings, provided that robust parameters of reliable diagnostic and/or prognostic value can be developed for individual psychiatric illnesses. However, this will depend on broader application of the method combined with established neurophysiological procedures and functional imaging techniques in psychiatric research.

Arousal↗
PubMed2003

First Measurement of the Gerasimov-Drell-Hearn Sum Rule for 1H from 0.7 to 1.8 GeV at ELSA.

To verify the fundamental Gerasimov-Drell-Hearn (GDH) sum rule for the first time experimentally, we measured the helicity dependent total photoabsorption cross section with circularly polarized real photons and longitudinally polarized nucleons in the photon energy range 0.68-1.82 GeV with the tagged photon facility at ELSA. The experiment was carried out with a 4pi detection system, a circularly polarized tagged photon beam, and a frozen spin polarized proton target. The contribution to the GDH sum rule in this photon energy range is [49.9+/-2.4(stat)+/-2.2(syst)] microb.

Journal Article↗
PubMed2003

Gender and personality in alcoholism.

The topic gender and personality in alcoholism is discussed on the background of a research project on clinical aspects of alcoholism at the University of Würzburg, Germany. The data of this study are presented in the context of two questions: Which personality differences are there between women and men dependent on alcohol, and is there a connection between these personality differences and features of the alcohol dependence? Additionally, we take a look at gender-related differences in the development of alcoholism. In a first step, gender differences in the development and the course of alcoholism are investigated. The data revealed only weak differences between female and male alcoholics when important confounding variables like age and education are taken into consideration. Secondly, the female and male alcoholics are matched according to age and education and their personality structures are compared by using several well-established and standardized self-report questionnaires. No serious gender differences concerning the main characteristics of alcohol dependence could be discovered. However, some remarkable personality differences between female and male alcoholics are found: women scored significantly higher on Neuroticism and Harm-Avoidance while men reached significantly higher scores on Venturesomeness and Sensation-Seeking. In order to detect a possible connection between alcoholism and gender-related personality differences, both males and females are subdivided into two groups using the scores of Neuroticism, Harm-Avoidance, Venturesomeness and Sensation-Seeking, respectively. We have found no indication for a gender-specific relevance of personality differences between female and male alcoholics with regard to Harm-Avoidance, Venturesomeness or Sensation-Seeking. However, differences in Neuroticism have revealed a greater relevance in alcohol-dependent women than in men.

Adolescent↗
PubMed2002

Helicity amplitudes A1/2 and A3/2 for the D13(1520) resonance obtained from the gamma-->p-->-->ppi(0) Reaction.

The helicity dependence of the gamma-->p-->-->ppi(0) reaction has been measured for the first time in the photon-energy range from 550 to 790 MeV. The experiment, performed at the Mainz microtron MAMI, used a 4pi-detector system, a circularly polarized, tagged photon beam, and a longitudinally polarized frozen-spin target. These data are predominantly sensitive to the D13(1520) resonance and are used to determine its helicity amplitudes.

Journal Article↗
PubMed2002

Potency and sterility of anesthetic drugs in obstetric anesthesia.

In order to estimate how long a medication can remain prepared before the integrity or concentration of the drug is compromised, we assessed the sterility and potency of medications commonly used in our obstetric anesthesia practice. Our goal was to evaluate the following drugs over a 30-day period: epinephrine, atropine, lidocaine, succinylcholine, and ephedrine. The medications were prepared by various medical staff, drawn into sterile plastic syringes and left at room temperature unprotected from light for the duration of the study. The syringes were collected daily, stored and randomly sampled after 7, 14, 21 and 30 days by research personnel. Potency and sterility of atropine, ephedrine and lidocaine were maintained over the study period. Succinylcholine and epinephrine could not be assayed but the solutions remained sterile for 30 and 14 days respectively. Data were incomplete for epinephrine. These findings suggest that some drugs that are commonly used in obstetric anesthesia are stable for long periods of time. Modification of current standards of practice could result in a significant reduction in drug waste and therefore cost.

Journal Article↗
PubMed2001

Drosophila Toll is activated by Gram-positive bacteria through a circulating peptidoglycan recognition protein.

Microbial infection activates two distinct intracellular signalling cascades in the immune-responsive fat body of Drosophila. Gram-positive bacteria and fungi predominantly induce the Toll signalling pathway, whereas Gram-negative bacteria activate the Imd pathway. Loss-of-function mutants in either pathway reduce the resistance to corresponding infections. Genetic screens have identified a range of genes involved in these intracellular signalling cascades, but how they are activated by microbial infection is largely unknown. Activation of the transmembrane receptor Toll requires a proteolytically cleaved form of an extracellular cytokine-like polypeptide, Spätzle, suggesting that Toll does not itself function as a bona fide recognition receptor of microbial patterns. This is in apparent contrast with the mammalian Toll-like receptors and raises the question of which host molecules actually recognize microbial patterns to activate Toll through Spätzle. Here we present a mutation that blocks Toll activation by Gram-positive bacteria and significantly decreases resistance to this type of infection. The mutation semmelweis (seml) inactivates the gene encoding a peptidoglycan recognition protein (PGRP-SA). Interestingly, seml does not affect Toll activation by fungal infection, indicating the existence of a distinct recognition system for fungi to activate the Toll pathway.

Amino Acid Sequence↗
PubMed2001

Brain-derived neurotrophic factor and neurotrophin 3 in schizophrenic psychoses.

Disturbed neural development has been postulated as a crucial factor in the pathophysiology of schizophrenic psychoses. The neurobiochemical basis for such changes of cytoarchitecture and changed neural plasticity could involve an alteration in the regulation of neurotrophic factors. In order to test this hypothesis, BDNF and NT-3 levels in post-mortem brain tissue from schizophrenic patients were determined by ELISA. There was a significant increase in BDNF concentrations in cortical areas and a significant decrease of this neurotrophin in hippocampus of patients when compared with controls. NT-3 concentrations of frontal and parietal cortical areas were significantly lower in patients than in controls. These findings lend further evidence to the neurotrophin hypothesis of schizophrenic psychoses which proposes that alterations in expression of neurotrophic factors could be responsible for neural maldevelopment and disturbed neural plasticity, thus being an important event in the etiopathogenesis of schizophrenic psychoses.

Aged↗
PubMed2001

Sphingosine 1-phosphate and isoform-specific activation of phosphoinositide 3-kinase beta. Evidence for divergence and convergence of receptor-regulated endothelial nitric-oxide synthase signaling pathways.

Sphingosine 1-phosphate (S1P) is a platelet-derived sphingolipid that elicits diverse biological responses, including angiogenesis, via the activation of G protein-coupled EDG receptors. S1P activates the endothelial isoform of nitric-oxide synthase (eNOS), associated with eNOS phosphorylation at Ser-1179, a site phosphorylated by protein kinase Akt. We explored the proximal signaling pathways that mediate Akt activation and eNOS regulation by S1P/EDG receptors. Akt is regulated by the lipid kinase phosphoinositide 3-kinase (PI3-K). We found that bovine aortic endothelial cells (BAEC) express both alpha and beta isoforms of PI3-K, while lacking the gamma isoform. S1P treatment led to the rapid and isoform-specific activation of PI3-Kbeta in BAEC. PI3-Kbeta can be regulated by G protein betagamma subunits (Gbetagamma). The overexpression of a peptide inhibitor of Gbetagamma attenuated S1P-induced eNOS enzyme activation, as well as S1P-induced phosphorylation of eNOS and Akt. In contrast, bradykinin, a classical eNOS agonist, neither activated any PI3-K isoform nor induced eNOS phosphorylation at Ser-1179, despite activating eNOS in BAEC. Vascular endothelial growth factor activated both PI3-Kalpha and PI3-Kbeta via tyrosine kinase pathways and promoted eNOS phosphorylation that was unaffected by Gbetagamma inhibition. These findings indicate that PI3-Kbeta (regulated by Gbetagamma) may represent a novel molecular locus for eNOS activation by EDG receptors in vascular endothelial cells. These studies also indicate that different eNOS agonists activate distinct signaling pathways that diverge proximally following receptor activation but converge distally to activate eNOS.

Animals↗
PubMed2001

Nitric oxide and the control of firefly flashing.

Bioluminescent flashing is essential for firefly reproduction, yet the specific molecular mechanisms that control light production are not well understood. We report that light production by fireflies can be stimulated by nitric oxide (NO) gas in the presence of oxygen and that NO scavengers block bioluminescence induced by the neurotransmitter octopamine. NO synthase is robustly expressed in the firefly lantern in cells interposed between nerve endings and the light-producing photocytes. These results suggest that NO synthesis is a key determinant of flash control in fireflies.

Animals↗
PubMed2001

Sphingosine 1-phosphate and activation of endothelial nitric-oxide synthase. differential regulation of Akt and MAP kinase pathways by EDG and bradykinin receptors in vascular endothelial cells.

Sphingosine 1-phosphate (S1P) is a platelet-derived sphingolipid that elicits numerous biological responses in endothelial cells mediated by a family of G protein-coupled EDG receptors. Stimulation of EDG receptors by S1P has been shown to activate the endothelial isoform of nitric-oxide synthase (eNOS) in heterologous expression systems (Igarashi, J., and Michel, T. (2000) J. Biol. Chem. 275, 32363-32370). However, the signaling pathways that modulate eNOS regulation by S1P/EDG in vascular endothelial cells remain less well understood. We now report that S1P treatment of bovine aortic endothelial cells (BAEC) acutely increases eNOS enzyme activity; the EC(50) for S1P activation of eNOS is approximately 10 nm. The magnitude of eNOS activation by S1P in BAEC is equivalent to that elicited by the agonist bradykinin. S1P treatment activates Akt, a protein kinase implicated in phosphorylation of eNOS. S1P treatment of BAEC leads to eNOS phosphorylation at Ser(1179), a residue phosphorylated by Akt; an eNOS mutant in which this Akt phosphorylation site is inactivated shows attenuated S1P-induced eNOS activation. S1P-induced activation both of Akt and of eNOS is inhibited by pertussis toxin, by the phosphoinositide 3-kinase inhibitor wortmannin, and by the intracellular calcium chelator BAPTA (1,2-bis(aminophenoxy)ethane-N,N,N',N'-tetraacetic acid). By contrast to S1P, activation of G protein-coupled bradykinin B2 receptors neither activates kinase Akt nor promotes Ser(1179) eNOS phosphorylation despite robustly activating eNOS enzyme activity. Understanding the differential regulation of protein kinase pathways by S1P and bradykinin may lead to the identification of new points for eNOS regulation in vascular endothelial cells.

Animals↗
PubMed2001

In memorium.

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History, 20th Century↗
PubMed2001

Multi-photon microscopy in the evaluation of human saphenous vein.

BACKGROUND: The use of conventional fluorescence microscopy to image biological systems at the cellular level is limited by its inability to spatially resolve thick tissues. We have applied the technique of multi-photon fluorescence microscopy to study the structure and function of endothelial cells in living human saphenous vein taken from patients undergoing coronary artery bypass surgery. MATERIALS AND METHODS: Vein segments were preserved for 1-4 h to determine the temporal effects of storage. The effect of pH on endothelial and smooth muscle cell viability was examined by storing segments at pH 6.0, 7.4, and 8.0. Calcein-mediated green fluorescence and ethidium homodimer-mediated red fluorescence were used to differentiate cell viability. Increases in diaminofluorescein fluorescence were used to measure bradykinin activation of endothelial nitric oxide synthase (eNOS) with or without N-nitro-l-arginine (L-NNA). Multi-photon imaging was performed with the BioRad MRC1024ES system. RESULTS: Successful imaging of endothelial and smooth muscle cells of vein segments was achieved. Cell viability was well preserved up to 3 h of storage but dramatically decreased after 4 h. Cell viability was maintained at pH 7.4, diminished at pH 8.0, and was completely lost at pH 6.0. A two- to threefold increase in eNOS activity was observed upon activation by bradykinin which was completely inhibited in L-NNA-treated samples. CONCLUSIONS: We have demonstrated the successful application of multi-photon microscopy in imaging and quantifying nitric oxide production and cell viability under various storage conditions in human saphenous veins. This imaging technique allows for the functional imaging of cellular processes and may have diagnostic potential in cardiovascular surgery for patients undergoing bypass operations.

Cell Survival↗
PubMed2001

In vivo electrophysiologic studies in endothelial nitric oxide synthase (eNOS)-deficient mice.

INTRODUCTION: Endothelial nitric oxide synthase (eNOS) mediates attenuation of the L-type calcium channel and modulates myocyte contractility. Arrhythmogenic afterdepolarizations are seen in vitro in ouabain-treated isolated myocytes from eNOS-deficient mice. The aim of these studies was to characterize the baseline electrophysiologic (EP) phenotype of eNOS-deficient mice and their potential susceptibility to cardiac conduction abnormalities and inducible arrhythmias. METHODS AND RESULTS: Surface ECG and in vivo intracardiac EP studies were performed in 27 mice lacking the eNOS gene and 21 wild-type littermate control mice. Baseline studies were performed in 10 eNOS-deficient mice and 10 wild-type controls. Subsequently, 17 eNOS-deficient mice and 11 wild-type controls were pretreated with digoxin, and ECG and EP testing were repeated. Data analysis revealed no significant differences in ECG intervals or cardiac conduction parameters, except sinus cycle length was higher in eNOS-deficient mice than wild-type mice (P < 0.01). After digoxin pretreatment, 7 of 17 eNOS-deficient mice had inducible ventricular tachycardia and 2 others had frequent ventricular premature beats, compared with only 3 of 11 wild-type mice with inducible ventricular tachycardia. In addition, 2 digoxin-treated eNOS-deficient mice and 1 wild-type mouse had inducible nonsustained atrial fibrillation. CONCLUSION: Mice with a homozygous targeted disruption of the eNOS gene have slower heart rates but no other distinguishable EP characteristics under basal sedated conditions. Partial inhibition of the Na+/K+ ATPase pump with digoxin administration increases ventricular ectopic activity in eNOS-/- mice, a phenotype analogous to afterdepolarizations seen in vitro in this eNOS-deficient mouse model.

Animals↗