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Oliver Meissner

Publications and source records attributed to Oliver Meissner.

8 recordsLinked to original sources
PubMed2006

Influence of xanthohumol on the binding behavior of GABAA receptors and their lateral mobility at hippocampal neurons.

The influence of the xanthohumol from Humulus lupulus L. on the binding of muscimol-Alexa Fluor 532 (Mu-Alexa), a fluorescently labeled GABAA receptor agonist, was studied by fluorescence correlation spectroscopy. An incubation of hippocampal neurons with 75 nM of xanthohumol increased the specific Mu-Alexa binding by approximately 17%, which was selectively found in GABAA receptor Mu-Alexa complexes with hindered lateral mobility [D(bound2) = (0.11 +/- 0.03) microm2/s] as described with midazolam.

Animals↗
PubMed2006

Diagnostic accuracy of optical coherence tomography and intravascular ultrasound for the detection and characterization of atherosclerotic plaque composition in ex-vivo coronary specimens: a comparison with histology.

BACKGROUND: Both intravascular ultrasound and optical coherence tomography have been purported to accurately detect and characterize coronary atherosclerotic plaque composition. The aim of our study was to directly compare the reproducibility and diagnostic accuracy of optical coherence tomography and intravascular ultrasound for the detection and characterization of coronary plaque composition ex vivo as compared with histology. METHODS AND RESULTS: Intravascular ultrasound (20 MHz) and optical coherence tomography imaging was performed in eight heart specimens using motorized pullback. Standard histology using hematoxylin-eosin and van Gieson staining was performed on 4 mum thick slices. Each slice was divided into quadrants and accurately matched cross-sections were analyzed for the presence of fibrous, lipid-rich, and calcified coronary plaque using standard definitions for both intravascular ultrasound and optical coherence tomography and correlated with histology. After exclusion of 145/468 quadrants, we analyzed the remaining 323 quadrants with excellent image quality in each procedure. Optical coherence tomography demonstrated a sensitivity and specificity of 91/88% for normal wall, 64/88% for fibrous plaque, 77/94% for lipid-rich plaque, and 67/97% for calcified plaque as compared with histology. Intravascular ultrasound demonstrated a sensitivity and specificity of 55/79% for normal wall, 63/59% for fibrous plaque, 10/96% for lipid-rich plaque, and 76/98% for calcified plaque. Both intravascular ultrasound and optical coherence tomography demonstrated excellent intraobserver and interobserver agreement (optical coherence tomography: kappa=0.90, kappa=0.82; intravascular ultrasound: kappa=0.87, kappa=0.86). CONCLUSION: Optical coherence tomography is superior to intravascular ultrasound for the detection and characterization of coronary atherosclerotic plaque composition, specifically for the differentiation of noncalcified, lipid-rich, or fibrous plaque.

Aged↗
PubMed2005

HPLC analysis of flavokavins and kavapyrones from Piper methysticum Forst.

A simultaneous HPLC separation of the six major kavapyrones and the flavokavins A-C in an ethanolic extract of Piper methysticum was carried out on a Symmetry C18 column. For quantitative determinations of the flavokavins, calibration curves with correlation coefficients between 0.9986 and 0.9998 were established. Detection limit for each flavokavin of 0.5 ng per injection was measured at 355 nm. The precision of the HPLC analysis was verified by six determinations of the content of flavokavins in the kava extract. Flavokavins A-C contents of 0.62+/-0.01 mg/100 mg, 0.34+/-0.01 mg/100 mg and 0.14+/-0.003 mg/100 mg ethanolic kava extract was found, respectively. From the corresponding relative standard deviation of 1.53, 1.99 and 2.30% the confidential interval (P=95) of the mean value was calculated for each flavokavin. The accuracy of the method was proven by recoveries between 99.2+/-0.3% and 101.1+/-0.4% for the flavokavins A-C.

Chalcone↗
PubMed2003

Lateral mobility and specific binding to GABA(A) receptors on hippocampal neurons monitored by fluorescence correlation spectroscopy.

The binding behavior of a fluorescently labeled muscimol derivative to the GABA(A) receptor was analyzed at rat hippocampal neurons by fluorescence correlation spectroscopy. After muscimol had been labeled with the fluorophore Alexa Fluor 532, specific binding constants for binding of the dye-labeled ligand (Mu-Alexa) to the GABA(A) receptor were determined. We found a high specific binding affinity of Mu-Alexa with a K(D) value of 3.4 +/- 0.5 nM and a rate constant of ligand-receptor dissociation (k(diss)) of (5.37 +/- 0.95) x 10(-2) s(-1). A rate constant of ligand-receptor association (k(ass)) of (1.57 +/- 0.28) x 10(7) L mol(-1) s(-1) was calculated. The following diffusion coefficients were observed: D(free) = 233 +/- 20 microm(2)/s (n = 66) for free diffusing Mu-Alexa, D(bound1) = 2.8 +/- 0.9 microm(2)/s (n = 64) for the lateral mobility, and D(bound2) = 0.14 +/- 0.05 microm(2)/s (n = 56) for the hindered mobility of the GABA(A) receptor-ligand complex in the cell membrane. Saturation of Mu-Alexa binding was observed at a concentration of 50 nM. A maximum number of binding sites [B(max) = 18.4 +/- -0.4 nM (n = 5)] was found. Similar K(i) values of 4.5 +/- 1.0 nM for nonlabeled muscimol and 8.8 +/- 1.8 nM for Mu-Alexa were found by RRAs using [(3)H]muscimol as a radioligand. A concentration-dependent increase in the level of specific Mu-Alexa binding was demonstrated by the positive cooperative activity of co-incubated midazolam, which was selectively found in GABA(A) receptor-ligand complexes with hindered mobility.

Allosteric Site↗
PubMed2003

Positive cooperation of protoberberine type 2 alkaloids from Corydalis cava on the GABA(A) binding site.

Protoberberine alkaloids from the rhizomes of Corydalis cava were investigated with regard to their influence on the GABA A receptor using radioreceptor assays. Whereas the protoberberine type 2 alkaloids, isoapocavidine, corydaline, tetrahydropalmatine, scoulerine and isocorypalmine, increased the specific [(3)H]BMC-binding in a range of 21 - 49 %, the protoberberine type 1 alkaloids, palmatine, coptisine, dehydroapocavidine, and dehydrocorydaline, had no influence on the binding behaviour of the GABA A receptor. To confirm the modulatory activity of the protoberberine type 2 alkaloids on living cells, GABA A receptor binding studies were performed by fluorescence correlation spectroscopy (FCS) using hippocampal neurons and the fluorescently labelled ligand, muscimol-Alexa (Mu-Alexa). The incubation of hippocampal neurons with 7.5 nM Mu-Alexa showed a specific binding of 5.25 nM (70 %). The evaluation of the autocorrelation curve revealed two different mobilities of receptor ligand complexes, D bound1 = (2.8 +/- 0.91) microm 2/s for the free lateral mobility and D bound2 = (0.14 +/- 0.05) microm 2/s for the hindered mobility. An incubation of hippocampal neurons with 7.5 nM Mu-Alexa and 7.5 nM scoulerine showed a maximal increase of the specific Mu-Alexa binding of approximately 27 % by selectively modulating the amount of receptor-ligand complexes with a hindered mobility (9 % to 27 %).

Alkaloids↗
PubMed2003

Primary endovascular stent placement for focal infrarenal aortic stenosis: initial and midterm results.

The objectives of this retrospective study were to determine the technical success, safety, and midterm results of primary stent placement of infrarenal aortic stenosis. Eight stenoses and one occlusion were treated with stent placement after balloon pre-dilation. Primary technical success was achieved in all patients. Five patients showed reperfusion or restored normal direction of flow of the inferior mesenteric artery. No complications occurred. There was a mean follow-up of 12 months (range, 3-20 months). Primary clinical and hemodynamic patency rates were 100% on follow-up examinations. Stent placement after balloon pre-dilation in properly selected patients with isolated infrarenal aortic stenosis is a promising durable treatment.

Aged↗
PubMed2002

MR imaging of the brain in pediatric patients: diagnostic value of HASTE sequences.

OBJECTIVE: The objective of this study was to determine the diagnostic value of half-Fourier single-shot turbo spin-echo (HASTE) sequences in MR imaging of the brain in pediatric patients. SUBJECTS AND METHODS: HASTE sequences were performed in 80 infants and children. Two radiologists who were unaware of the patients' medical histories independently reviewed the images for the presence of nine findings: defects of the parenchyma, hypoplasia or agenesis of the corpus callosum, edema, signs of increased intracranial pressure, myelination disorders, migration disorders, malformations, tumors, and widening of spaces of the cerebrospinal fluid. A conventional MR imaging examination that served as the reference examination was evaluated by the same two radiologists in a final consensus interpretation. The findings detected on the HASTE images were compared with the findings seen on the conventional MR images. The sensitivity and specificity of HASTE sequences were calculated, and Cohen's kappa statistic was used to determine interobserver agreement. RESULTS: Both radiologists correctly diagnosed all 20 defects of the parenchyma that were present in the patients. Radiologist 1 correctly identified 20 and radiologist 2 correctly identified 21 of the 22 patients with hypoplasia or agenesis of the corpus callosum. Both radiologists correctly diagnosed edema in eight of the nine patients in whom edema was present, and both correctly identified signs of increased intracranial pressure in eight of the nine children who had this condition. Radiologist 1 correctly diagnosed seven and radiologist 2 correctly identified nine of the 11 cases of myelination disorders. Both radiologists correctly diagnosed six of the 14 cases with migration disorders. All 13 brain malformations present in the patients were correctly identified by both reviewers. Both radiologists correctly identified all 11 patients with tumors, and both correctly identified all 35 patients with widening of spaces of the cerebrospinal fluid. CONCLUSION: HASTE images are highly sensitive for excluding the presence of brain tumor, hydrocephalus, or malformations of the brain. HASTE images are not reliable for evaluating patients with suspected myelination disorders or migration disorders.

Adolescent↗