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Biomedical subjects

H Fischer

Publications and source records attributed to H Fischer.

At least 109 records · Page 6Linked to original sources
PubMed2000

Fear conditioning and brain activity: a positron emission tomography study in humans.

Regional cerebral blood flow (rCBF) was measured with H2 (15)O positron emission tomography in 8 healthy women before and after fear conditioning (i.e., paired shocks) and unpaired shocks to videotape cues. Conditioning was supported by enhanced peripheral nervous system recordings and subjective ratings. Fear conditioning increased rCBF in the central gray of the midbrain; bilaterally in the hypothalamus, the thalamus, and the left striatum; and in the right and left anterior cingulate and right prefrontal cortices. Regional CBF was attenuated bilaterally in the right and left prefrontal, temporal (including the amygdala), parietal, and occipital cortices, and in the left orbitofrontal cortex. When compared with unpaired shock presentations, fear conditioning resulted in elevated rCBF in the left cerebellum. Hence, in the present paradigm, only neural activity in the left cerebellum solely reflected processes associated with true Pavlovian conditioning.

Adult↗
PubMed2000

Congenital sodium diarrhea is an autosomal recessive disorder of sodium/proton exchange but unrelated to known candidate genes.

BACKGROUND & AIMS: Congenital sodium diarrhea (CSD) is caused by defective sodium/proton exchange with only 6 sporadic cases reported. The genetics of the disease have not been established. We studied 5 infants with secretory diarrhea, identified in a circumscribed rural area in Austria, to define the mode of transmission and the involvement of candidate genes known to encode for sodium/proton exchangers (NHEs). METHODS: We collected clinical and laboratory data from 5 affected patients, analyzed the pedigrees of their families, and performed homozygosity mapping and multipoint linkage analysis studies in 4 candidate regions known to contain NHE genes. RESULTS: The diagnosis of CSD in 4 of 5 patients was based on daily fecal sodium excretion between 98 and 190 mmol/L, hyponatremia, metabolic acidosis, and low-to-normal urinary sodium concentrations. Pedigree analysis of the affected 2 CSD families revealed parental consanguinity and a common single ancestor 5 generations ago. Homozygosity mapping and/or multipoint linkage analysis excluded the NHE1 locus on chromosome 1, NHE2 locus on chromosome 2, NHE3 locus on chromosome 5, and NHE5 locus on chromosome 16 as potential candidate genes for CSD in this pedigree. Results on NHE4 were inconclusive because the precise chromosomal location of this NHE gene in humans is currently unknown. CONCLUSIONS: Our data indicate that CSD is an autosomal recessive disorder but is not related to mutations in the NHE1, NHE2, NHE3, and NHE5 genes encoding for currently known sodium/proton exchangers.

Chromosome Mapping↗
PubMed2000

[Tissue harmonic imaging sonography. Is the image quality in routine abdominal ulstrasound improved?].

PURPOSE: Evaluation and statistical analysis of the influence of THI with pulse-inversion technology on image quality in abdominal ultrasound in comparison to conventional sonography. MATERIAL AND METHODS: In 25 patients 398 ultrasound images of the abdomen were evaluated in a prospective, double blind study. 49% of the images were obtained with THI sonography, 51% with conventional sonography, respectively. Image parameter, anatomical region and image plane were kept constant by using a switchable ultrasound probe. Image contrast, delineation of organs, detection of vessels and artifacts in cystic structures were evaluated by four radiologists using a 3-grade scale. The interobserver variability was determined. RESULTS: The results of all groups showed statistically significant improvement compared to conventional sonography. High agreement of the evaluaters was achieved for image contrast and delineation of organs, less agreement in detection of vessels and artifacts in cystic structures, respectively. CONCLUSION: Image contrast and delineation of organs to neighboring structures as well as reduction of artifacts in cystic structures and vessels are statistically significantly improved with THI sonography using pulse-inversion technology in comparison to conventional sonography.

Abdomen↗
PubMed2000

The role of psychosocial factors in fibromyalgia syndrome.

OBJECTIVE: The main objective of this review was to evaluate the role of psychosocial factors in the development of fibromyalgia syndrome. METHOD: Review of the literature concerning the influence of psychosocial factors. RESULTS: In fibromyalgia syndrome psychosocial factors are relevant at different etiological levels. They can be classified into predisposing, triggering and stabilising/"chronifying" factors. CONCLUSION: Due to the increasing knowledge about the influence of psychosocial factors for the development of fibromyalgia, the biomedical model has to be expanded to a biopsychosocial model. The biopsychosocial concept has an impact on the therapeutic approach. Strong evidence for the model is provided by the good results of interdisciplinary treatment studies.

Disease Susceptibility↗
PubMed2000

Robotic system for biopsy and therapy of breast lesions in a high-field whole-body magnetic resonance tomography unit.

RATIONALE AND OBJECTIVES: With magnetic resonance mammography, significant progress has been achieved in the diagnosis of small breast cancers. However, biopsy and therapy of suspicious lesions must take place at a later time. Diagnosis and simultaneous biopsy and therapy in one single examination would considerably reduce costs, strain on the patient, and side effects. METHODS: ROBITOM (Robotic system for biopsy and interventional therapy of mammary lesions) is used to approach a lesion found in the breast in an image-controlled manner under a high magnetic field (eg, 1.5 T). The robotic system works in the direct vicinity of the isocenter of a magnet and consists of a trocar, coaxial sleeve, biopsy needle, laser applicator, and a control and driving unit. It contains a rack, a driving unit along the three coaxes of space, and a gripping unit for instruments or biopsy sample removal. The system has six degrees of freedom. RESULTS: In vitro experiments in pig liver including eight targets (vitamin E capsules, 4 mm in diameter) were performed. All eight capsules were hit precisely by the robotic biopsy system. The procedure was performed directly in the isocenter of a 1.5-T whole-body scanner. CONCLUSIONS: The system allows the coordinates of a lesion in the breast to be approached in a high magnetic field without shifting the patient. A combination of imaging with biopsy and subsequent therapy (eg, laser therapy or cryotherapy) seems to be feasible in the future.

Animals↗
PubMed2000

Structural determinants for activation and block of CFTR-mediated chloride currents by apigenin.

Apigenin (4',5,7-trihydroxyflavone) is an activator of cystic fibrosis transmembrane conductance regulator (CFTR)-mediated Cl(-) currents across epithelia at low concentrations and a blocker at high concentrations. We determined the roles of structural components of apigenin for both stimulation and block of Cl(-) currents across Calu-3 epithelia. The half-maximal binding affinity of apigenin for current stimulation (K(s)) was 9.1 +/- 1.3 microM, and the rank-order of molecular structures was 7-hydroxyl > pyrone = 4'-hydroxyl > 5-hydroxyl. Both the 7-hydroxyl and the 4'-hydroxyl served as H-bond acceptors, whereas the 5-hydroxyl was an H-bond donor. The half-maximal binding affinity of apigenin during current block was 74 +/- 11 microM. Blocked Cl(-) currents were structurally determined by 7-hydroxyl = 4'-hydroxyl > pyrone > 5-hydroxyl. Prestimulation of tissues with forskolin significantly affected activation kinetics and binding characteristics. After forskolin stimulation, K(s) was 4.1 +/- 0.9 microM, which was structurally determined by pyrone > all hydroxyls > single hydroxyls. In contrast, block of Cl(-) current by apigenin was not affected by forskolin stimulation. We conclude that apigenin binds to a stimulatory and an inhibitory binding site, which are distinguished by their affinities and the molecular interactions during binding.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed2000

Relationships between body mass, motor output and flight variables during free flight of juvenile and mature adult locusts, Schistocerca gregaria.

Little information is available about how the adult locust flight system manages to match the aerodynamic demands that result from an increase in body mass during postmoult maturation. In Schistocerca gregaria of both sexes, flight variables, including flight speed, ascent angle and body angle, were investigated under closed-loop conditions (i.e. during free flight) as a function of adult maturation. Motor patterns were examined by telemetric electromyography in juvenile and adult mature animals of both sexes. Functional relationships between particular flight variables were investigated by additional loading of the animals and by reductions in wing area. The results indicate that an increase in flight speed as the flight system matures enables it to match the aerodynamic demands resulting from increases in body mass. Furthermore, the data suggest that this postmoult increase in flight speed is not simply a consequence of the increase in wingbeat frequency observed during maturation. The instantaneous body angle during flight is controlled mainly by aerodynamic output from the wings. In addition, the mean body angle decreases during maturation in both sexes, and this may play an important part in the directional control of the resultant flight force vector.

Animals↗
PubMed2000

Evaluation of the ADVIA Centaur TSH-3 assay.

An analytical evaluation of the thyroid stimulating hormone (TSH-3) assay on the Bayer ADVIA Centaur immunoassay system was performed. General analytical requirements (linearity, resistance to typical interferences, absence of a carry-over effect) were fulfilled and reproducibility was satisfactory. Inter-assay coefficient of variation (CV) of a human serum pool with a concentration of 0.014 mU/l was 22.3%; at concentrations between 0.26 and 83 mU/l CV was below 6%. Method comparison study demonstrated close agreement of TSH results compared to those obtained with the Roche Elecsys 2010 TSH assay (ADVIA Centaur = 1.08 x Elecsys - 0.18 mU/l; r=0.987; n=324). Handling and practicability of the ADVIA Centaur system proved to be convenient with a very high sample throughput. We conclude that the ADVIA Centaur TSH-3 assay meets requirements for clinical use.

Humans↗
PubMed2000

CT of the head by use of reduced current and kilovoltage: relationship between image quality and dose reduction.

BACKGROUND AND PURPOSE: CT is a frequent examination that is performed using ionizing radiation. We sought to assess image-quality changes on CT scans of the head when the radiation dose is reduced by changing tube current and kilovoltage. METHODS: A formalin-fixed cadaver was examined in conventional and helical mode by use of two CT-scanners. Surface dose was measured with standard scanning parameters, and after reduction of tube current and kilovoltage. Five experienced examiners independently evaluated subjective image quality. RESULTS: In the conventional mode, the highest surface dose was 83.2 mGy (scanner 1: helical mode, 55.6 mGy), and 66.0 mGy (scanner 2: helical mode, 55.9 mGy). By changing kVp and mAs, a dose reduction of up to 75% (scanner 1), and 60% (scanner 2) was achieved. No observable differences in image quality between scans obtained with doses from 100% to 60% of standard settings were noted. Ten of 20 images obtained with the highest dose and 13 of 20 images obtained with lowest dose (19-29.4 mGy) were reliably identified by subjective quality assessment. Scans produced with a surface dose of less than 30 mGy were judged uninterpretable. CONCLUSION: Standard parameters used in cranial CT are oriented toward best image quality. A dose reduction up to 40% may be possible without loss of diagnostic image quality.

Cadaver↗
PubMed1999

Dual modes of the carbon cycle since the Last Glacial Maximum.

The most conspicuous feature of the record of past climate contained in polar ice is the rapid warming which occurs after long intervals of gradual cooling. During the last four transitions from glacial to interglacial conditions, over which such abrupt warmings occur, ice records indicate that the CO2 concentration of the atmosphere increased by roughly 80 to 100 parts per million by volume. But the causes of the atmospheric CO2 concentration increases are unclear. Here we present the stable-carbon-isotope composition (delta 13 CO2) of CO2 extracted from air trapped in ice at Taylor Dome, Antarctica, from the Last Glacial Maximum to the onset of Holocene times. The global carbon cycle is shown to have operated in two distinct primary modes on the timescale of thousands of years, one when climate was changing relatively slowly and another when warming was rapid, each with a characteristic average stable-carbon-isotope composition of the net CO2 exchanged by the atmosphere with the land and oceans. delta 13 CO2 increased between 16.5 and 9 thousand years ago by slightly more than would be estimated to be caused by the physical effects of a 5 degrees C rise in global average sea surface temperature driving a CO2 efflux from the ocean, but our data do not allow specific causes to be constrained.

Antarctic Regions↗
PubMed1999

Expression of constitutive nitric oxide synthase in rat and human gastrointestinal tract.

The aim of this study was to determine the expression of constitutive NO synthases (ecNOS and bNOS) at the protein level in rat and human gastrointestinal tract. We established a quantitative Western blotting method for detection and quantification of ecNOS and bNOS in both species. Human gastric fundus was further analyzed by immunohistochemistry. EcNOS expression at the protein level could be quantified in different organs of the rat gastrointestinal tract and in human gastric mucosal biopsies. Immunohistochemistry of gastric fundus revealed that immunoreactivity for ecNOS was localized mainly in the endothelium of small vessels. In rats, expression of bNOS at the protein level was highest in esophagus. By means of immunohistochemistry of human gastric fundus, immunoreactivity was detected mainly in the plexus of Auerbach. We conclude that isoforms of constitutive nitric oxide synthase can be identified and quantified at the protein level both in rat and human gastrointestinal tract. The presence of bNOS in nerve tissue supports previous observations that NO serves as a transmitter in non-adrenergic, non-cholinergic nerves in human esophagus and stomach. The observation that ecNOS has been found mainly in endothelial cells suggests the involvement of NO in the regulation of mucosal blood flow.

Aged↗
PubMed1999

Arctic ozone loss due to denitrification

Measurements from the winter of 1994-95 indicating removal of total reactive nitrogen from the Arctic stratosphere by particle sedimentation were used to constrain a microphysical model. The model suggests that denitrification is caused predominantly by nitric acid trihydrate particles in small number densities. The denitrification is shown to increase Arctic ozone loss substantially. Sensitivity studies indicate that the Arctic stratosphere is currently at a threshold of denitrification. This implies that future stratospheric cooling, induced by an increase in the anthropogenic carbon dioxide burden, is likely to enhance denitrification and to delay until late in the next century the return of Arctic stratospheric ozone to preindustrial values.

Journal Article↗
PubMed1999

Ice core records of atmospheric CO2 around the last three glacial terminations

Air trapped in bubbles in polar ice cores constitutes an archive for the reconstruction of the global carbon cycle and the relation between greenhouse gases and climate in the past. High-resolution records from Antarctic ice cores show that carbon dioxide concentrations increased by 80 to 100 parts per million by volume 600 +/- 400 years after the warming of the last three deglaciations. Despite strongly decreasing temperatures, high carbon dioxide concentrations can be sustained for thousands of years during glaciations; the size of this phase lag is probably connected to the duration of the preceding warm period, which controls the change in land ice coverage and the buildup of the terrestrial biosphere.

Journal Article↗
PubMed1999

New drugs for the Na+/H+ exchanger. Influence of Na+ concentration and determination of inhibition constants with a microphysiometer.

The NHE-1 isoform of the Na+/H+ exchanger is excessively activated in cardiac cells during ischemia. Hence NHE-1 specific inhibitors are being developed since they could be of beneficial influence under conditions of cardiac ischemia and reperfusion. In this study, the Cytosensortrade mark microphysiometer was used to measure the potency of four new drug molecules, i.e., EMD 84021, EMD 94309, EMD 96785 and HOE 642 which are inhibitors of the isoform 1 of the Na+/H+ exchanger. The experiments were performed with Chinese hamster ovary cells (CHO K1) which are enriched in the NHE-1 isoform of the Na+/H+ antiporter. The Na+/H+ exchanger was stimulated with NaCl and the rate of extracellular acidification was quantified with the Cytosensor. The proton exchange rate was measured as a function of the NaCl concentration in the range of 10-138 mm NaCl stimulation. The proton exchange rate followed Michaelis-Menten kinetics with a KM = 30 +/- 4 mm for Na+. Addition of either one of the four inhibitors decreased the acidification rate. The IC50 values of the four compounds could be determined as 23 +/- 7 nm for EMD 84021, 5 +/- 1 nm for EMD 94309, 9 +/- 2 nm for EMD 96785 and 8 +/- 2 nm for HOE 642 at 138 mm NaCl, in good agreement with more elaborate biological assays. The IC50 values increased with the NaCl concentration indicating competitive binding of the inhibitor. The microphysiometer approach is a fast and simple method to measure the activity of the Na+/H+ antiporter and allows a quantitative kinetic analysis of the proton excretion rate.

Animals↗
PubMed1999

Substrate specificity of catechol oxidase from Lycopus europaeus and characterization of the bioproducts of enzymic caffeic acid oxidation.

The substrate specificity of catechol oxidase from Lycopus europaeus towards phenols is examined. The enzyme catalyzes the oxidation of o-diphenols to o-quinones without hydroxylating monophenols, the additional activity of tyrosinase. Substrates containing a -COOH group are inhibitors for catechol oxidase. The products of enzymic oxidation of caffeic acid were analyzed and isolated by HPLC with diode array detection. The neolignans of the 2,3-dihydro-1,4-benzodioxin type (3, 6-8), 6,7-dihydroxy-1-(3,4-dihydroxyphenyl)-2,3-dicarboxy-1,2-dihydro naphthaline (1) 6,7-dihydroxy-1-(3,4-dihydroxyphenyl)-3-carboxynaphthaline (5) and 2,6-bis-(3',4'-dihydroxyphenyl)-1-carboxy-3-oxacyclo-(3,0)-pent an-2-on-1-ene (4) were formed. A reaction mechanism for the formation of (1, 4 and 5) is discussed.

Caffeic Acids↗