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Matthias Schmidt

Publications and source records attributed to Matthias Schmidt.

At least 19 recordsLinked to original sources
PubMed2007

Evaluating the spatial relationship of event-related potential and functional MRI sources in the primary visual cortex.

The integration of electroencephalogram (EEG) recordings and functional magnetic resonance imaging (fMRI) can provide considerable insight into brain functionality. However, the direct relationship between neural and hemodynamic activity is still poorly understood. Of particular interest is the spatial correspondence between event-related potential (ERP) and fMRI sources. In the current study we localized sources generated by a checkerboard stimulus presented to eight subjects using both EEG and fMRI. The location of the sources of the visual evoked potential (VEP) were estimated at each timepoint and compared to the location of peak fMRI activity. In the majority of participants we found that the N75 dipole location coincides with a region of positive blood oxygenation level-dependent (BOLD) activation and the P100 dipole location coincides with a region of negative BOLD activation. These findings demonstrate the importance of including the negative BOLD response in combined EEG/fMRI studies.

Adult↗
PubMed2006

Mode of translational activation of the catalase (cat1) mRNA of rye leaves (Secale cereale L.) and its control through blue light and reactive oxygen.

The enzyme catalase (EC 1.11.1.6) is inactivated by light and must be continuously replaced by new synthesis in order to maintain a constant enzyme activity in leaves. In winter rye leaves (Secale cereale L.) posttranscriptional mechanisms determine the rate of new catalase synthesis, including a light-controlled reversible modification of the catalase cat1 mRNA by methylation which greatly enhanced its translation efficiency. The specificity and regulation of this mRNA activation were further investigated. The translation efficiency of the rye cat1 mRNA was much more enhanced by N-7 methylation of the cap than that of an lhcb transcript. Investigations with truncated rye cat1 mRNAs indicated that the translational enhancement resulting from N-7 cap methylation did not require the presence of specific sequences of cat1 5'- and 3'-untranslated regions. Translational activation of the cat1 mRNA in rye leaves was independent of photosynthesis and most effectively induced by blue light. Peroxides (H(2)O(2), tertiary butyl hydroperoxide) and conditions enforcing an H(2)O(2) accumulation in the leaves (aminotriazole, paraquat) also caused an activation of the cat1 mRNA. A search for further signalling systems controlling the replenishment of inactivated catalase in light suggested that an inositol-1,4,5-triphosphate-mediated liberation of Ca(2+) from internal stores and a protein phosphatase played some role. However, these signalling systems did not affect the activation of the cat1 mRNA. After removal of Ca(2+) by EGTA the cat1 mRNA was rapidly degraded.

Catalase↗
PubMed2006

Density functional theory for colloidal mixtures of hard platelets, rods, and spheres.

A geometry-based density-functional theory is presented for mixtures of hard spheres, hard needles, and hard platelets; both the needles and platelets are taken to be of vanishing thickness. Geometrical weight functions that are characteristic for each species are given, and it is shown how convolutions of pairs of weight functions recover each Mayer bond of the ternary mixture and hence ensure the correct second virial expansion of the excess free-energy functional. The case of sphere-platelet overlap relies on the same approximation as does Rosenfeld's functional for strictly two-dimensional hard disks. We explicitly control contributions to the excess free energy that are of third order in density. Analytic expressions relevant for the application of the theory to states with planar translational and cylindrical rotational symmetry--e.g., to describe behavior at planar smooth walls--are given. For binary sphere-platelet mixtures, in the appropriate limit of small platelet densities, the theory differs from that used in a recent treatment [L. Harnau and S. Dietrich, Phys. Rev. E 71, 011504 (2004)]. As a test case of our approach we consider the isotropic-nematic bulk transition of pure hard platelets, which we find to be weakly first order, with values for the coexistence densities and the nematic order parameter that compare well with simulation results.

Journal Article↗
PubMed2006

QT dispersion in comparison to Tl-201-SPECT for detection of myocardial ischaemia.

OBJECTIVE: There is controversy whether the measurement of QT dispersion might provide information about the presence and extent of ischaemic myocardium. It was the aim to analyse the diagnostic value of QT dispersion for the detection of myocardial ischaemia in comparison to Tl-201-SPECT. PATIENTS AND METHODS: 100 patients were randomly selected from patients referred for Tl-201-SPECT. QT duration was measured in all 12 leads in the resting ECG and in the ECG either at maximal bicycle exercise or during peak dipyridamole stress. QT dispersion was calculated and correlated with parameters of ischaemia for all patients and for the bicycle exercise and the dipyridamole group separately. RESULTS: 25 patients had to be excluded from the analysis because QT dispersion could not be measured. Regression analysis did not show significant correlation neither for all 75 patients nor for the bicycle exercise nor for the dipyridamole group correlating grade of myocardial ischaemia, number of ischaemic segments and summed ischaemic stress score with QT dispersion in the resting or the stress ECG and QTd and there was no significant difference between groups. CONCLUSION: QT dispersion could not be measured in 25/100 patients (25%). In the remaining patients QT dispersion did not correlate with the extent or grade of myocardial ischaemia.

Electrocardiography↗
PubMed2006

Diagnostic work-up and outcome of cervical metastases from an unknown primary.

CONCLUSIONS: An intensive diagnostic work-up including (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) detects many unknown primary tumours, leads to a low emergence rate of primary tumours, and selects carcinoma of unknown primary with much more favourable results after neck dissection and postoperative radiotherapy. OBJECTIVE: To investigate the optimal diagnostic approach and best treatment modality for rare head and neck cancer of unknown primary. PATIENTS AND METHODS: In a retrospective study, 69 patients admitted from 1987 to 2002 with cervical lymph node metastases without apparent primary were reviewed. Test characteristics of all diagnostic procedures were calculated. Disease-free and overall survival rates were calculated. Major prognostic factors were analysed uni-variously. RESULTS: At the primary site FDG-PET showed the best sensitivity with 69% and the highest negative predictive value with 87%. Computed tomography and magnetic resonance imaging had a better specificity with 87% and 95%, respectively. The primary tumour was detected in 23 cases (33%). Frequent primary tumour origin was the palatine tonsil (n=8, 35%), base of the tongue (n=6, 26%) and lung (n=4, 17%). All patients with unknown primary were treated by neck dissection. Adjuvant radiotherapy was performed in 26 patients (57%), concurrent radiochemotherapy was performed in 12 patients (26%). The primary emergence rate was 7%. The 5-year overall survival rate was inferior in patients with detected primary in comparison with patients with unknown primary (22% versus 52%). Significant prognostic factors in case of unknown primary were M stage, smoking, alcohol consumption and tonsillectomy. Radiotherapy but not chemotherapy with carboplatin influenced the overall survival.

Adult↗
PubMed2006

Incidence of postradioiodine immunogenic hyperthyroidism/Graves' disease in relation to a temporary increase in thyrotropin receptor antibodies after radioiodine therapy for autonomous thyroid disease.

BACKGROUND: The aim of the study was to analyze retrospectively the incidence of postradioiodine immunogenic hyperthyroidism/Graves' disease in relation to a temporary increase in TSH-receptor antibodies without overt hyperthyroidism after radioiodine therapy for autonomous thyroid disease. PATIENTS AND METHODS: Between May 2000 and May 2003 all patients (n = 1,357) who had undergone radioiodine therapy for autonomous thyroid disease were retrospectively analyzed for development of postradioiodine immunogenic hyperthyroidism. On pretreatment evaluation 565 of 1,357 patients (41.6%) had unifocal autonomous thyroid disease (UFA), 693 of 1,357 patients (51.1%) had multifocal autonomous thyroid disease (MFA), and 99 of 1,357 patients (7.3%) had diffuse thyroid disease (DISS). Free triiodothyronine (FT(3)), free thyroxine (FT(4)), thyrotropin (TSH), and thyroid antibodies were measured. Ultrasound examinations and thyroid scintigraphy were performed before and after radioiodine therapy. A sensitive assay with the human TSH receptor as antigen was chosen for measurement of the TSH receptor antibody and the study was limited to analysis of data obtained since introduction of this assay. RESULTS: Fifteen of 1,357 patients (1.1%) (UFA, 8/565 = 1.4%; MFA, 6/693 = 0.9%; DISS 1/99 = 1.0%) developed postradioiodine hyperthyroidism between 1 and 13 months after radioiodine therapy with clinically overt hyperthyroidism and an elevation of TSH receptor antibodies. Patients with elevated thyroid peroxidase (TPO) antibodies before radioiodine therapy had an almost 10-fold (6/57 patients =10.5%) higher risk of developing postradioiodine immunogenic hyperthyroidism. Thirteen of 999 patients (1.3%) with antibody measurements after radioiodine therapy (UFA, 2/421 = 0.5%; MFA, 9/494 = 1.8%, DISS, 2/84 = 2.4%) had increased levels of TSH receptor antibodies and, to some extent, TPO antibodies without development of clinically overt hyperthyroidism. CONCLUSIONS: There is an estimated 1.1% risk of developing postradioiodine immunogenic hyperthyroidism/Graves' disease in patients undergoing radioiodine therapy for autonomous thyroid disease and this increases approximately 10-fold when TPO antibody levels are elevated before radioiodine therapy. Furthermore, there is an estimated 1.3% risk of a temporary increase of TSH receptor antibodies after radioiodine therapy for autonomous thyroid disease without development of clinically overt hyperthyroidism.

Graves Disease↗
PubMed2006

Localization of 131I-labelled monoclonal antibody ERIC1 in a subcutaneous xenograft model of neuroblastoma in SCID mice.

PURPOSE: To evaluate a novel strategy of immunolocalization of human neuroblastoma by targeting the neural cell adhesion molecule (NCAM), which is over-expressed on neuroblastoma. METHODS: NCAM expression on the cell surface of established neuroblastoma cells was shown by flow cytometry. A SCID mouse model using IMR5-75 neuroblastoma cells to induce subcutaneous tumour growth was established. 131I was used to label monoclonal NCAM specific ERIC1 antibodies generating the 131I-ERIC1 antibody, which showed a high affinity to NCAM also after labelling (KD=9 x 10(-8) mol . l(-1)). RESULTS: Measurement of organ-specific radioactivity showed low organ-specific uptake (5.33%ID/g (percent of injected dose per gram of tissue) after 72 h), which continuously decreased over the 96 h investigation period, demonstrating clearance of radioactivity. In contrast, tumours accumulated radioactivity continuously up to a peak of 42.07%ID/g at the 96 h time point (31.07%ID/g at 72 h). This specific uptake could be blocked by application of unlabelled ERIC1 antibodies. Measurement of blood specific radioactivity revealed a characteristic clearance over the first 72 h. With 37 Gy, tumour-specific radioactivity reached therapeutic doses after 96 h. CONCLUSIONS: These results indicate that 131I-labelled ERIC1 has the ability to probe NCAM-expressing tumour cells in vivo with high efficiency and is a promising reagent for the diagnosis and treatment of NCAM-positive human tumours, especially for neuroblastoma.

Animals↗
PubMed2005

Lattice density functional for colloid-polymer mixtures: comparison of two fundamental measure theories.

We consider a binary mixture of colloid and polymer particles with positions on a simple cubic lattice. Colloids exclude both colloids and polymers from nearest neighbor sites. Polymers are treated as effective particles that are mutually noninteracting, but exclude colloids from neighboring sites; this is a discrete version of the (continuum) Asakura-Oosawa-Vrij model. Two alternative density functionals are proposed and compared in detail. The first is based on multioccupancy in the zero-dimensional limit of the bare model, analogous to the corresponding continuum theory that reproduces the bulk fluid free energy of free volume theory. The second is based on mapping the polymers onto a multicomponent mixture of polymer clusters that are shown to behave as hard cores; the corresponding property of the extended model in strong confinement permits direct treatment with lattice fundamental measure theory. Both theories predict the same topology for the phase diagram with a continuous fluid-fcc freezing transition at low polymer fugacity and, upon crossing a tricritical point, a first-order freezing transition for high polymer fugacities with rapidly broadening density jump.

Journal Article↗
PubMed2005

Mixtures of charged colloid and neutral polymer: influence of electrostatic interactions on demixing and interfacial tension.

The equilibrium phase behavior of a binary mixture of charged colloids and neutral, nonadsorbing polymers is studied within free-volume theory. A model mixture of charged hard-sphere macroions and ideal, coarse-grained, effective-sphere polymers is mapped first onto a binary hard-sphere mixture with nonadditive diameters and then onto an effective Asakura-Oosawa model [S. Asakura and F. Oosawa, J. Chem. Phys. 22, 1255 (1954)]. The effective model is defined by a single dimensionless parameter-the ratio of the polymer diameter to the effective colloid diameter. For high salt-to-counterion concentration ratios, a free-volume approximation for the free energy is used to compute the fluid phase diagram, which describes demixing into colloid-rich (liquid) and colloid-poor (vapor) phases. Increasing the range of electrostatic interactions shifts the demixing binodal toward higher polymer concentration, stabilizing the mixture. The enhanced stability is attributed to a weakening of polymer depletion-induced attraction between electrostatically repelling macroions. Comparison with predictions of density-functional theory reveals a corresponding increase in the liquid-vapor interfacial tension. The predicted trends in phase stability are consistent with observed behavior of protein-polysaccharide mixtures in food colloids.

Journal Article↗
PubMed2005

Simulation and theory of fluid demixing and interfacial tension of mixtures of colloids and nonideal polymers.

An extension of the Asakura-Oosawa-Vrij model of hard sphere colloids and nonadsorbing polymers is studied with grand canonical Monte Carlo simulations and density functional theory. Polymer nonideality is taken into account through a repulsive step-function pair potential between polymers. Simulation results validate previous theoretical findings for the shift of the bulk fluid demixing binodal upon increasing strength of polymer-polymer repulsion, indicating suppression of phase separation. For increasing strength of the polymer-polymer repulsion, simulation and theory consistently predict the interfacial tension of the free interface between the colloidal liquid and the colloidal gas phase to decrease significantly for fixed colloid density difference in the coexisting phases, and to increase for fixed polymer reservoir packing fraction.

Journal Article↗
PubMed2005

Wall-fluid and liquid-gas interfaces of model colloid-polymer mixtures by simulation and theory.

We perform a study of the interfacial properties of a model suspension of hard sphere colloids with diameter sigma(c) and nonadsorbing ideal polymer coils with diameter sigma(p) . For the mixture in contact with a planar hard wall, we obtain from simulations the wall-fluid interfacial free energy, gamma(wf) , for size ratios q =sigma(p)/sigma(c) =0.6 and 1, using thermodynamic integration, and study the (excess) adsorption of colloids, Gamma(c) , and of polymers, Gamma(p) , at the hard wall. The interfacial tension of the free liquid-gas interface, gamma(lg) , is obtained following three different routes in simulations: (i) from studying the system size dependence of the interfacial width according to the predictions of capillary wave theory, (ii) from the probability distribution of the colloid density at coexistence in the grand canonical ensemble, and (iii) for state points where the colloidal liquid wets the wall completely, from Young's equation relating gamma(lg) to the difference of wall-liquid and wall-gas interfacial tensions, gamma(wl)-gamma(wg) . In addition, we calculate gamma(wf) ,Gamma(c) , and Gamma(p) using density functional theory and a scaled particle theory based on free volume theory. Good agreement is found between the simulation results and those from density functional theory, while the results from scaled particle theory quantitatively deviate but reproduce some essential features. Simulation results for gamma(lg) obtained from the three different routes are all in good agreement. Density functional theory predicts gamma(lg) with good accuracy for high polymer reservoir packing fractions, but yields deviations from the simulation results close to the critical point.

Journal Article↗
PubMed2005

Wetting, drying, and layering of colloid-polymer mixtures at porous interfaces.

The influence of interface porosity on the wetting properties of colloid-polymer mixtures is studied within density functional theory for the Asakura-Oosawa-Vrij model at the surface of a quenched hard-sphere matrix. While the porosity hardly changes the location of the transition from partial to complete wetting at colloidal bulk gas-liquid coexistence, the onset of wetting, as signaled by the first discontinuous layering transition, can be efficiently controlled by tailoring the porosity. We furthermore find that the penetrability of the porous interface induces complete drying into the matrix upon approaching capillary coexistence.

Journal Article↗
PubMed2005

Entropic interfaces in hard-core model amphiphilic mixtures.

We investigate bulk and interfacial properties of a recently proposed hard-body model for a ternary mixture of amphiphilic particles, spheres and needles using density functional theory. The simple model amphiphiles are formed by bonding a vanishingly thin needle tail radially to a hard-sphere head group. Such particles provide a natural amphiphile when added to a binary mixture of spheres and needles. As all interactions are hard, we seek to find whether amphiphilic effects can be driven by entropy without the need to invoke attractive interactions. In order to assess the amphiphilic character of the model we first examine the spatial and orientational distribution of the amphiphiles at the free interface between demixed needle-rich and amphiphile-rich fluid phases of the binary amphiphile-needle subsystem. We then consider the free interface between sphere-rich and needle-rich phases upon adding amphiphiles with low concentration to the demixed system. In both cases the orientational distribution of the particles in the interface provides strong evidence that amphiphilic properties can arise purely from geometrical packing effects.

Journal Article↗
PubMed2005

GABA receptor rho subunit expression in the developing rat brain.

Ionotropic GABA(C) receptors are composed of rho1, rho2 and rho3 subunits. Although the distribution of rho subunit mRNAs in the adult brain has been studied, information on the developmental regulation of different rho subunits in the brain is scattered and incomplete. Here, GABA(C) receptor rho subunit expression was studied in the developing rat brain. In situ hybridization on postnatal brain slices showed rho2 mRNA expression from newborn in superficial gray layer (SGL) of superior colliculus (SuC), and from the first postnatal week in the hippocampal CA1 region and pretectal nucleus of the optic tract. rho2 mRNA was also expressed in the adult dorsal lateral geniculate nucleus. Quantitative RT-PCR revealed expression of all three rho subunits in the hippocampus and superior colliculus from the first postnatal day. In the hippocampus, rho2 mRNA expression clearly dominated over rho1 and rho3, whereas in the superior colliculus, rho1 mRNA expression levels were similar to rho2. In both areas, a clear up-modulation of rho2 and rho3 mRNA during the first postnatal week was detected. GABA(C) receptor protein expression was confirmed in adult hippocampus, superior colliculus and dorsal lateral geniculate nucleus by immunohistochemistry. Our results demonstrate for the first time the expression of all three rho subunit mRNAs in several regions of the developing and adult rat brain. Our quantitative data allows assessment of putative subunit combinations in the superior colliculus and hippocampus. From the selective distribution of rho subunits, it may be hypothesized that GABA(C) receptors are specifically involved in aspects of visual image motion processing in the rat brain.

Animals↗
PubMed2005

Differences between cation-chloride co-transporter functions in the visual cortex of pigmented and albino rats.

Albinism in mammals is accompanied by specific morphological and functional alterations of the visual system. To understand their cellular basis we studied the physiological characteristics and transmembrane currents of pyramidal neurons in 350-microm-thick slices of visual cortex from pigmented and albino rats using whole-cell and gramicidin perforated patch-clamp recordings. The resting membrane potential was significantly more positive and the rheobase was significantly lower in neurons of layers II/III and V in albinos as compared with pigmented rats. No significant differences were found in the input resistance, time constant and chronaxy. Whereas the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor-mediated currents were not significantly different, the maximum gamma-aminobutyric acid (GABA)(A) receptor (GABA(A)R)-mediated currents and miniature inhibitory postsynaptic currents showed significantly lower amplitudes in neurons of layer V in visual cortex of albinos as compared with pigmented rats. The reversal potential of the GABA(A)R-mediated currents (E(GABA)) was significantly shifted to more positive values in albinos. Pharmacological experiments showed that this shift could be caused by an increased action of the inward chloride co-transporter NKCC1 and reduced action of the outward chloride co-transporter KCC2 in albino rats. This difference seems to be restricted to the visual cortex because in pyramidal neurons from frontal cortex E(GABA) was not significantly different in albinos as compared with pigmented rats. These results are discussed in relation to functional alterations in the albino visual system.

Animals↗
PubMed2005

Quality control in urinary stone analysis: results of 44 ring trials (1980-2001).

Urinary stone analysis is the most important diagnostic step after stone removal from the body. The methods employed for these analyses are based on diverse analytical principles. Chemical methods are used for detecting individual ions. Infrared spectroscopy is used for examining molecular structures, and X-ray diffraction for determination of the crystalline structure of a substance. Since 1980, a twice-yearly ring trials quality control survey has been on offer to examine the quality of urinary stone analyses. A summary of the results of 44 ring trials (1980-2001) has been compiled for individual pure substances and binary (two-component) mixtures. On average, 100 laboratories have participated in these ring trials. Initially, over 80% of the participants carried out their analyses using chemical methods. In 2001, this figure decreased to a mere 13%. In contrast, a progressive increase in the use of infrared spectroscopy was observed, up to 79% of all participants employed this method. X-Ray diffraction was only employed in a small number of specialised laboratories (5-9%). The chemical methods produced a very high proportion of errors (6.5-94%) with both the pure substances and binary mixtures, whereas high error rates for infrared spectroscopy and X-ray diffraction were confined to individual substances only. Due to the poor results in the ring trials, the majority of laboratories stopped using chemical analysis, which is now considered to be obsolete. Regarding mixtures, error rates of over 10% also occurred with infrared spectroscopy and X-ray diffraction. Ring trials are indispensable for the quality management of urinary stone analysis.

Diagnostic Errors↗
PubMed2004

Isotropic-nematic transition of hard rods immersed in random sphere matrices.

Using replica density functional theory and Monte Carlo computer simulations we investigate a system of annealed hard spherocylinders adsorbed in a matrix of quenched hard spheres. Theoretical predictions for the partition coefficient, defined as the ratio of density of rods in the matrix and that in a reservoir, agree well with simulation results. Theory predicts the isotropic-nematic transition to remain first order upon increasing sphere packing fraction, and to shift towards lower rod densities. This scenario is consistent with our simulation results that clearly show a jump in the nematic order parameter upon increasing the rod density at constant matrix packing fraction, corresponding to the isotropic-nematic transition, even for sphere matrix packing fractions < or approximately equal to 0.3.

Journal Article↗