Biomedical subjects

M Stadler

Publications and source records attributed to M Stadler.

At least 37 records · Page 2Linked to original sources

PubMed2000

Reversal-rate dependent differences in the EEG gamma-band during multistable visual perception.

It is an often reported observation in the literature on multistable perception that the reversal rate within a given observation time is subject to a high interindividual variability. Recently, we reported frontal gamma-band enhancement during multistable visual perception. The aim of the present study was to investigate whether changes in the gamma-band correspond to the variability of the reversal rate. Therefore, a total of 25 observers were divided into two subgroups according to their reversal rate during a 400-s observation period of a reversible pattern based on apparent motion. Subjects with more than 40 reversals within the 400-s were defined as high-rate switchers (HRS). Subjects with a reversal rate below 40 switches were defined as low-rate switchers (LRS). EEG was recorded from frontal, central, parietal, and occipital locations of both hemispheres. The results showed significantly higher gamma activity for the HRS in both phase-locked and non-phase-locked oscillations. Both subgroups showed the highest gamma amplitudes at frontal locations. The results support the involvement of attentional top-down processing in figure reversal. It is concluded that the higher gamma activity for the HRS reflects states of higher arousal, alertness and/or attention according to their fast reversal rate.

Adolescent↗

PubMed2000

Alpha activity decreases during the perception of Necker cube reversals: an application of wavelet transform.

Since the first observation of perceptual reversal by Necker, many theoretical approaches have been proposed. In a previous study, we showed that a positive wave appeared approximately 250 ms prior to the button press of the subjects, indicating perceptual reversal during the observation of the Necker cube figure. A basic difficulty in this type of study is the possible jitter in the latency of the button press due to the variability of the subjects' reaction time during a recording session. To overcome this difficulty, a pattern selection method based on the wavelet transform was proposed in the previous study. A dominant positive wavelet coefficient in the delta band was found to represent the perceptual-reversal-related positivity. In the present study, we aim to analyze the changes in the alpha frequency band during perceptual reversal by using the Necker cube. The RMS values of the alpha frequency band were measured for two time periods: +/- 3 SD around the mean peak latency of the perceptual-reversal-related positivity and a time window of the same length before the positive wave. We found significantly increased delta power and decreased alpha power during the perceptual-reversal-related positivity.

Adult↗

PubMed2000

Noise improves three-dimensional perception: stochastic resonance and other impacts of noise to the perception of autostereograms.

Autostereograms can be perceived in different well-defined spatial levels. Therefore they are an excellent tool with which to examine spatiotemporal processes of multistable three-dimensional perception. We study properties of spatial ambiguity such as phase transitions between different spatial levels and hysteresis in perception with and without noise. We show that the perception of physical noise-which is added to the autostereograms in the form of a random dot pattern-is dependent on the perceived spatial level. We demonstrate that noise can be helpful for the perception of depth in some cases. We show that the signal-to-noise ratio of depth perception is enhanced at an intermediate level of noise strength that is the signature of stochastic resonance in depth perception.

Artifacts↗

PubMed2000

Endotoxin-induced lung inflammation is independent of the complement membrane attack complex.

Several products of the activated complement system are known to modulate endothelial cell function in vitro. It has been shown that the membrane attack complex (MAC) (C5b-C9) can enhance tumor necrosis factor alpha (TNF-alpha)-induced expression of P- and E-selectin and intercellular adhesion molecule type 1 in cell cultures of human umbilical vein endothelial cells. In the present study the potential role of this synegism for lung injury during endotoxin-mediated septic shock in vivo was examined using a model of C6-deficient PVG (C-) (RT1(C)) rats and the congenic PVG (C+) (RT1(C)) strain. Following administration of a high (5 mg/kg) or low (0.5 mg/kg) dose of lipopolysaccharide (LPS) (Escherichia coli O55:B5), we determined the expression of cytokines, chemokines, and adhesion molecules as well as the recruitment of leukocytes in the lung. Challenge with intraperitoneal i.p. injections of LPS resulted in a strong induction of TNF-alpha, interleukin-1alpha/beta, cytokine-induced neutrophil chemoattractant, interferon-inducible protein 10, macrophage inflammatory proteins 1alpha and 2, macrophage chemotactic protein 1, and P-selectin. However, there were no significant differences between PVG (C-) and PVG (C+) rats. Immunoperoxidase staining showed a similar increase of lung infiltration by CD11b/c(+) leukocytes in both rat strains. We therefore conclude that the described synergism between TNF-alpha and the MAC of the complement system on the induction of endothelial adhesion molecules is dispensable for inflammatory processes during endotoxin-mediated septic shock in vivo.

Animals↗

PubMed1999

VEP-interhemispheric transfer time in 20-32 Hz band in man.

This research aimed to investigate callosal transfer in the different frequency bands of VEP to lateralized reversal of checkerboard pattern as stimuli. The chosen band pass filters (4-8 Hz, 8-15 Hz, 15-20 Hz, 20-32 Hz) were applied to the VEPs of subjects, and four different components for each VEP were obtained. Latency differences between hemispheres for digitally unfiltered and filtered VEPs were computed to estimate IHTT. Different IHTTs in the theta (17 ms), alpha (9 ms) and beta1 (7 ms) bands from right to left and from left to right were estimated, supporting the previous report. Furthermore, a transfer within 4.5 ms from right to left in the 20-32 Hz band for the occipital lobe was found. In conclusion, our findings suggest that the frequency analysis of VEP to lateralized stimuli give us additional information, relating to the types of callosal fibers.

Adult↗

PubMed1999

Pigs aerogenously immunized with genetically inactivated (ghosts) or irradiated Actinobacillus pleuropneumoniae are protected against a homologous aerosol challenge despite differing in pulmonary cellular and antibody responses.

Aerosol immunization is a safe way to induce complete protection against pleuropneumonia in pigs caused by the lung pathogenic bacterium Actinobacillus pleuropneumoniae. In order to determine the local immune responses of vaccinees in concomitant with protection, lung lining fluid before and 3 weeks after immunization from pigs immunized three times with aerosols of either genetically inactivated ghosts which represent whole cell envelope preparations, or irradiated bacteria were examined following an homologous aerosol challenge. Specific antibody isotypes in the bronchoalveolar lavage were assayed by whole cell ELISAs. Total and relative numbers of cells including lymphocyte subsets were determined. In both vaccinated groups a net influx of plasma cells and lymphocytes, as well as a significant increase of specific IgG occurred. Concurrently, the CD4+/CD8+ ratio was found to increase after aerosol immunization. The lymphocyte subsets of IgG+ and IgA+ cells were found significantly higher in the group immunized with irradiated bacteria when compared to pigs immunized with bacterial ghosts. The latter group showed a significant increase of IgA, IgM, and a net influx of lymphoid blasts and granulocytes in the bronchoalveolar lining fluid. Although differences between the local immune responses of both immunized groups occurred, a significant increase of specific IgG and a net influx of plasma cells and lymphocytes were found to be associated with complete protection against a homologous aerosol challenge infection.

Actinobacillus Infections↗

PubMed1999

TIF1gamma, a novel member of the transcriptional intermediary factor 1 family.

We report the cloning and characterization of a novel member of the Transcriptional Intermediary Factor 1 (TIF1) gene family, human TIF1gamma. Similar to TIF1alpha and TIF1beta, the structure of TIF1beta is characterized by multiple domains: RING finger, B boxes, Coiled coil, PHD/TTC, and bromodomain. Although structurally related to TIF1alpha and TIF1beta, TIF1gamma presents several functional differences. In contrast to TIF1alpha, but like TIF1beta, TIF1 does not interact with nuclear receptors in yeast two-hybrid or GST pull-down assays and does not interfere with retinoic acid response in transfected mammalian cells. Whereas TIF1alpha and TIF1beta were previously found to interact with the KRAB silencing domain of KOX1 and with the HP1alpha, MODI (HP1beta) and MOD2 (HP1gamma) heterochromatinic proteins, suggesting that they may participate in a complex involved in heterochromatin-induced gene repression, TIF1gamma does not interact with either the KRAB domain of KOX1 or the HP1 proteins. Nevertheless, TIF1gamma, like TIF1alpha and TIF1beta, exhibits a strong silencing activity when tethered to a promoter. Since deletion of a novel motif unique to the three TIF1 proteins, called TIF1 signature sequence (TSS), abrogates transcriptional repression by TIF1gamma, this motif likely participates in TIF1 dependent repression.

Amino Acid Sequence↗

PubMed1999

Visual evoked potential interhemispheric transfer time in different frequency bands.

OBJECTIVE: Visual evoked potentials (VEP) have been used to estimate interhemispheric transfer time (IHTT). However, the complex wave of VEP is most probably formed by different generators of neural populations that act through different frequency channels. If the main peaks of VEP are established by different types of generators, which can also be connected to each other by a different type of callosal fibres, we would be able to estimate a wide range of various IHTT by measuring the latency between time-locked peaks of narrow band-pass filtered VEP. This research aimed to test this hypothesis. METHODS: Nine right-handed men were presented with a reversal of a checkerboard pattern as stimuli at RVF or LVF, and EEG was recorded at O1, O2, P3, P4. The grand-averaged VEPs were transformed to the frequency domain by means of the fast Fourier transform to obtain the amplitude frequency characteristics. Band-pass filters were chosen adequately, according to tuning frequencies indicated by clear peaks in the amplitude frequency characteristics. The chosen band pass filters (4-8 Hz, 8-15 Hz, 15-20 Hz, 20-32 Hz) were applied to the VEP of the subjects, and 4 different components of VEPs for each VEP were obtained. The latency of P100 and N160 of unfiltered VEP was measured. In the band-pass digital filter applied VEPs, positive and negative peaks, which are consistent with P100 and N160, were measured for each subject. Latency differences between hemispheres for digitally unfiltered and filtered VEPs were computed to estimate IHTT. RESULTS: In the different frequency bands, different IHTTs were estimated, ranging from 3 ms to 30 ms. Approximately 16 ms for theta band, 11 ms for alpha band, 6 ms for 15-20 Hz and 3 ms for 20-32 Hz bands were found. CONCLUSIONS: Our findings support the hypothesis which states that unfiltered VEPs provide us with only a rough estimation of IHTT. Also, they are consistent with anatomical findings that describe callosal fibres of varying dimensions, predicting various velocities between hemispheres.

Adult↗

PubMed1999

Differences in top-down influences on the reversal rate of different categories of reversible figures.

Understanding the mechanisms underlying the multistability of reversible figures may provide valuable insights into the normal functioning of our visual system. The proposed factors that control the perceptual alternations of reversible figures can be classified into bottom-up and top-down processes. In the present study, we report differences in top-down effects on the reversal rate depending on whether a structural perspective (Necker cube, Schröder staircase) or a meaningful content (duck/rabbit figure, chef/dog figure) is subject to the reversal phenomenon. In order to activate top-down mechanisms explicitly the subjects had the instruction to bring the reversal rate under voluntary control. The results indicated that both slowing down and speeding up the rate of alternations was more effective for the content-reversal figures (duck/rabbit, chef/dog) than for the rather abstract perspective-reversal figures (Necker cube, Schröder staircase). In order to investigate the effect of meaningfulness in figure/ground reversals, the effect of the same instructional variable was also determined for Rubin's vase/faces and the Maltese cross. The results showed a similar tendency as in the case of the comparison between perspective reversals and content reversals. Possible cognitive processes that may play a role in top-down influences on figure reversal and theoretical implications of these findings for the interaction of bottom-up and top-down processes are discussed.

Analysis of Variance↗

PubMed1999

Degradation of ciprofloxacin by basidiomycetes and identification of metabolites generated by the brown rot fungus Gloeophyllum striatum.

Ciprofloxacin (CIP), a fluoroquinolone antibacterial drug, is widely used in the treatment of serious infections in humans. Its degradation by basidiomycetous fungi was studied by monitoring 14CO2 production from [14C]CIP in liquid cultures. Sixteen species inhabiting wood, soil, humus, or animal dung produced up to 35% 14CO2 during 8 weeks of incubation. Despite some low rates of 14CO2 formation, all species tested had reduced the antibacterial activity of CIP in supernatants to between 0 and 33% after 13 weeks. Gloeophyllum striatum was used to identify the metabolites formed from CIP. After 8 weeks, mycelia had produced 17 and 10% 14CO2 from C-4 and the piperazinyl moiety, respectively, although more than half of CIP (applied at 10 ppm) had been transformed into metabolites already after 90 h. The structures of 11 metabolites were elucidated by high-performance liquid chromatography combined with electrospray ionization mass spectrometry and 1H nuclear magnetic resonance spectroscopy. They fell into four categories as follows: (i) monohydroxylated congeners, (ii) dihydroxylated congeners, (iii) an isatin-type compound, proving elimination of C-2, and (iv) metabolites indicating both elimination and degradation of the piperazinyl moiety. A metabolic scheme previously described for enrofloxacin degradation could be confirmed and extended. A new type of metabolite, 6-defluoro-6-hydroxy-deethylene-CIP, provided confirmatory evidence for the proposed network of congeners. This may result from sequential hydroxylation of CIP and its congeners by hydroxyl radicals. Our findings reveal for the first time the widespread potential for CIP degradation among basidiomycetes inhabiting various environments, including agricultural soils and animal dung.

Basidiomycota↗

PubMed1999

Down-regulation of MHC class II expression on bovine retinal pigment epithelial cells by cytokines.

To determine the effect of interleukin-10 (IL-10) and transforming growth factor-beta (TGF-beta) on the down-regulation of MHC class II antigens, bovine retinal pigment epithelial (RPE) cells were incubated with interferon-gamma (IFN-gamma) in different concentrations. Subsequently, the IFN-gamma pretreated RPE cells were cultured with TGF-beta or IL-10 in distinct concentrations and treatment modi. About 10% of native (totally untreated) RPE cells were positive for MHC class II antigens detected with immunocytostaining. Under the influence of IFN-gamma (1,000 U/ml), the number of MHC class II-bearing cells increased to 49.9 +/- 4.5% positive cells after 8 days' incubation. Expression decreased under the most effective TGF-beta treatment (5 ng/ml) to 2.0 +/- 0.9% after 24 h incubation, and under similar IL-10 treatment (200 U/ml) to 3.8 +/- 1.4% after 72 h. This decreasing number of the MHC class II-positive cells may be useful for various eye research studies and, more especially, to RPE cell transplantation in the future.

Animals↗

PubMed1999

Degradation products of factor VIII which can lead to increased immunogenicity.

The biochemical and immunochemical aspects of the development of inhibitors with a plasma-derived, double-virus inactivated factor VIII (FVIII) concentrate (marketed as Octavi SDPlus in Germany and Bisinact in Belgium) are described. A total of 12 cases of inhibitor formation (predominantly type II) were reported in Germany, 8 in Belgium but none in Portugal. Initially, the only difference between the non-pasteurised, SD virus-inactivated product Octavi and the pasteurised product Octavi SDPlus appeared to be pasteurisation, though subsequently, the quality of source material for the product was found to differ in different countries. Separation studies revealed the presence of a 40 kDa peptide fragment in some batches. It was subsequently shown that there was a strong correlation between inhibitor development and batches containing the 40 kDa marker, and a relationship between elevated markers of coagulation activation (FPA in particular) and the occurrence of the 40 kDa marker. Further work revealed that analytical methods commonly used for quality control were not suitable to highlight batch-to-batch differences. It was concluded that inhibitor potential (neoantigenicity) in Octavi SDPlus arose due to two effects; degradation of FVIII already present in source material; and heating of unstable FVIII degradation products. In this case, inhibitors were not caused by the overall production process, nor by GMP failures. The problem of inhibitor potential can be avoided if appropriate preventive measures are taken. Further work is needed to prove non-neoantigenicity and to reinforce the scientific findings, and to characterise pilot batches.

Chromatography, High Pressure Liquid↗

PubMed1998

Analysis of the electroencephalographic activity during the Necker cube reversals by means of the wavelet transform.

In previous studies, a perceptual switching related potential was obtained during the observation of a multistable dynamic reversal pattern, where the averaging of the single responses was triggered by subjects pressing a button. The present methodological study aims to increase the signal quality of perceptual switching related potentials considering the dependence of the measurement method on the reaction time of the subject, which may vary significantly during a session, leading to low-amplitude waveform in the averaged event-related-potential (ERP). To overcome this problem in measuring the electrophysiological correlate of an internal event, a pattern selection method based on the wavelet transform (WT) is proposed to choose a subset of single ERPs with more homogenous latencies. Nine subjects observed a Necker cube and were instructed to press the button immediately after perceptual switching. A slow, low-amplitude positive wave with frontocentral amplitude maxima was observed around 250 ms prior to the button press. After the application of a 5 octave WT on single sweeps, the time-frequency coefficients obtained in each octave were averaged across trials. The most dominant feature representing the averaged ERP was the delta (0.5-4 Hz) coefficient occurring between 250 and 125 ms before the button press. By averaging the subset of the single sweeps containing this property, a sharpening and significant amplitude increase of the response peak was observed.

Animals↗

PubMed1998

Distinct functions of interferon-gamma for chemokine expression in models of acute lung inflammation.

Challenge of the immune system with bacterial superantigens or endotoxin induces the systemic release of cytokines followed by lethal septic shock. The lung is particularly susceptible to systemic toxin exposure resulting in acute leucocyte infiltration and vascular damage. In the present study, the functions of interferon-gamma (IFN-gamma) and tumour necrosis factor (TNF) for chemokine regulation during acute lung inflammation were examined. Following administration of the superantigen, staphylococcal enterotoxin B (SEB), lung mRNA levels of the chemokines cytokine-induced neutrophil chemo-attractant (KC), lipopolysaccharide-induced CXC chemokine (LIX), macrophage chemotactic protein-1 (MCP-1), macrophage inflammatory protein (MIP)-1alpha and MIP-2 were increased to a similar extent both in controls and in mice deficient for the IFN-gamma or 55 000 MW TNF receptors. In contrast, interferon-inducible protein-10 (IP-10) and monokine induced by IFN-gamma (Mig) mRNA expression was markedly reduced in mice deficient for IFN-gamma or IFN-gamma receptor, but not in 55 000 MW TNF receptor knockout mice. In situ hybridization experiments demonstrated that IP-10 was highly expressed in lung interstitial macrophages of C57BL/6, but not of IFN-gamma receptor-deficient mice. In contrast to SEB administration, treatment with lipopolysaccharide resulted in a strong induction of IP-10 and Mig in IFN-gamma receptor-deficient mice. Together, these results establish a critical function of IFN-gamma for chemokine induction in acute lung inflammation that is dependent on the nature of the inflammatory stimulus.

Acute Disease↗

PubMed1998

In-vitro methods to decrease MHC class II-positive cells in retinal pigment epithelium cell grafts.

Rejection of RPE transplants may be caused by expression of MHC class II molecules on the graft. We wanted to determine if passage level, hyperoxia, low temperature, or magnetic separation had an influence on this expression or on several other physiological parameters of bovine RPE cells. For this, bovine RPE cells were cultured under normal conditions for several passages (1-5) or were incubated with a high level of oxygen (75%) for 24 h or at low temperature (24 degrees C) for seven days. Magnetic beads coated with monoclonal antibody against MHC class II antigens were used to separate the positive cells from the total cell population. The number of MHC class II-positive RPE cells was not affected by increased passage, oxygen concentration, or low temperature. Using magnetic beads, approximately 7.5% of the cells were separated from the total RPE population as MHC class II-positive cells. Hyperoxia initially increased the number of RPE cells to 178% that of the untreated controls, but the subsequent MTT test showed a decrease in proliferation to 95% of control levels. Similarly, low temperature increased cell number of 110% that of controls, but prolonged proliferation decreased to 76% of the controls. None of the experimental conditions had a significant influence on the viability of the cells. Culture conditions can be modified to increase the yield of RPE cells, and MHC class II-positive RPE cells can be detected and selectively separated from the total cell population, both of which may prove to be useful for RPE cell transplantation.

Animals↗

PubMed1997

Histone H4 mRNA from the nematode Ascaris lumbricoides is cis-spliced and polyadenylated.

A histone H4 gene from Ascaris lumbricoides contains an intron of approx. 2040 bp. Transcripts of the gene are spliced and polyadenylated. This is the first intron-containing H4 gene described for a metazoan. Notably, H4 mRNA from another nematode, Caenorhabditis elegans, is intron-less and lacks poly A (Roberts, S.B., Emmons, S.W. and Childs, G. (1989) J. Mol. Biol. 206, 567-577).

Animals↗

PubMed1996

Induction of protective immunity by aerosol or oral application of candidate vaccines in a dose-controlled pig aerosol infection model.

In order to outline basic concepts for the design of a bacterial aerosol infection model, the development of a pig model with Actinobacillus pleuropneumoniae is described. First, reproducibility of aerosol parameters should be maintained by optimizing generating and sampling conditions. Survival rates of the chosen strain must be predictable. Secondly, inhalation conditions for the recipients have to be standardized to enable the determination of deposition sites and the dose administered. Subsequently, dose-response relationship should be evaluated to find a suitable challenge dose. Furthermore, it seems necessary to establish methods to obtain local specimens for determination of the local immune responses. The present study demonstrates that after aerosol challenge pigs were completely protected after inhalation and partially protected after oral application of A. pleuropneumoniae vaccines and describes techniques to administer bacteria in a dose-dependent, viable way. Using the infection model several stages of the disease from acute pleuropneumonia to chronic infection can be induced for research purposes.

Actinobacillus Infections↗

PubMed1996

Continuous phase transitions in the perception of multistable visual patterns.

The phenomenon of stroboscopic alternative motion exhibits five different percepts that are seen with an increase in the frequency of presentation: (a) succession, (b) fluttering motion, (c) reversible clockwise and counter-clockwise turning motion, (d) oppositional motion and (e) simultaneity. From a synergetic point of view the increase in frequency is a control parameter and the different percepts are order parameters with phase transitions in between. The neural network model of Carmesin and Arndt is applied to receive predictions about hysteresis and phase transitions between these order parameters. Empirical data show the different motion percepts (b), (c) and (e) have lognormal distributions. Following the theoretical model, it is argued that there are three different phases, (a), (c) and (e), with two continuous phase transitions, (b) and (d), between them. The experimental data substantially match the theoretical assumptions.

Animals↗