Biomedical subjects

Hermann Müller

Publications and source records attributed to Hermann Müller.

7 recordsLinked to original sources

PubMed2003

Actively tracking 'passive' stability in a ball bouncing task.

This study investigates the control involved in a task where subjects rhythmically bounce a ball with a hand-held racket as regularly as possible to a prescribed amplitude. Stability analyses of a kinematic model of the ball-racket system revealed that dynamically stable solutions exist if the racket hits the ball in its decelerating upward movement phase. Such solutions are resistant to small perturbations obviating explicit error corrections. Previous studies reported that subjects' performance was consistent with this 'passive' stability. However, some 'active' control is needed to attune to this passive stability. The present study investigates this control by confronting subjects with perturbations where stable behavior cannot be maintained solely from passive stability. Six subjects performed rhythmic ball bouncing in a virtual reality set-up with and without perturbations. In the perturbation trials the coefficient of restitution of the ball-racket contact was changed at every fifth contact leading to unexpected ball amplitudes. The perturbations were compensated for within 2-3 bouncing cycles such that ball amplitudes decreased to initial values. Passive stability was reestablished as indicated by negative racket acceleration. Results revealed that an adjustment of the racket period ensured that the impacts occurred at a phase associated with passive stability. These findings were implemented in a model consisting of a neural oscillator that drives a mechanical actuator (forearm holding the racket) to bounce the ball. Following the perturbation, the oscillator's period is adjusted based on the perceived ball velocity after impact. Simulation results reproduced the major aspects of the experimental results.

Acceleration↗

PubMed2003

The genome of goose hemorrhagic polyomavirus, a new member of the proposed subgenus Avipolyomavirus.

The full-length genome of goose hemorrhagic polyomavirus (GHPV), the ethiologic agent of hemorrhagic nephritis and enteritis of geese, was cloned and sequenced. Transfection of the circular ds DNA with a size of 5256 bp and an organisation typical of polyomaviruses produced viral progeny in cultured goose cells. According to the splicing sites determined by RT-PCR, five open reading frames (ORFs) were found to encode putative proteins with significant similarities to large T antigen and small t antigen as well as VP1, VP2, and VP3 of other polyomaviruses. An additional ORF located in the 5' region of late mRNA, with a coding capacity for 169 amino acids, shows a low degree of homology to VP4 of avian polyomavirus (APV). The alignment of nucleotide sequences and amino acid sequences revealed a relatively close relationship between GHPV and APV. Therefore, grouping of this new polyomavirus into the proposed subgenus Avipolyomavirus is suggested.

Amino Acid Sequence↗

PubMed2003

A randomization method for the calculation of covariation in multiple nonlinear relations: illustrated with the example of goal-directed movements.

A randomization method is developed for the calculation of covariation between multiple variables that are linked nonlinearly to a dependent variable. Covariation is a phenomenon often invoked in the study of movement coordination to capture the fact that in coordinated movement the outcome shows greater than expected consistency from the variability in the component processes. However, in most cases, the problem is that more than two variables covary in a nonlinear fashion, which makes quantification with the bivariate linear covariation and correlation coefficient inapplicable. This paper presents a generalization of the calculation of linear bivariate covariance using a variant of a randomization method that is based on the comparison between the empirically measured variability in the outcome and a covariation-free variability. The latter can be estimated by permuting data sets. A generalized correlation coefficient is derived, and it is shown how errors of estimation can be quantified. The permutation method can also quantify partial multiple nonlinear covariation. The calculations are illustrated in a numerical example of an arm-reaching task. However, the method is applicable to all cases where the internal organization of a nonlinear system of multiple variables needs to be quantified. The relation and applicability of the permutation method compared to other methods using regression and principal component analysis are discussed and illustrated with a numerical example.

Arm↗

PubMed2002

Detection and quantitation of group A rotaviruses by competitive and real-time reverse transcription-polymerase chain reaction.

A competitive reverse transcription-polymerase chain reaction (RT-PCR) was developed to detect and to quantitate the RNA of group A rotaviruses. In the assay, a 433 bp fragment is amplified by a one-tube RT-PCR protocol using primers with binding sites located in a highly conserved region of segment 6 of the rotavirus genome. An in vitro synthesized RNA with a 43-base deletion with respect to the wild-type sequence of this fragment was used as an internal control. Using these transcripts as templates, 10 RNA molecules were amplified reproducibly and detected in ethidium bromide-stained agarose gels or by fluorimetry using the SYBR Green I dye in a real-time RT-PCR assay. The efficiency of the protocol was confirmed by the detection of small amounts of viral RNA of group A rotaviruses in clinical samples obtained from various animal species and man.

Base Sequence↗

PubMed2002

Persistence of Borna disease virus in naturally infected sheep.

To get an insight into Borna disease virus (BDV) epidemiology, an isolated flock of approximately 25 sheep within the region of Southeast Germany to which the disease is endemic was investigated over a 3-year observation period. BDV-specific antibodies and RNA in peripheral blood mononuclear cells were detected in 12.5 (year 1), 11.5 (year 2), and 19.4% (year 3) and 1.6 (year 1), 0 (year 2), and 14.9% (year 3) of the animals, respectively. BDV persisted in asymptomatic sheep for up to 2 years. Significantly higher numbers of antibody-positive animals were detected seasonally in spring and early summer, the times when usually most of the clinical cases of Borna disease occur. In spring of the third year, numbers of antibody-positive and viral-RNA-positive animals increased significantly despite their having no obvious clinical symptoms. The removal of all antibody- and RNA-positive animals from the flock did not reduce the prevalence of BDV infections in the following year. During a 3-month observation period of three antibody-positive animals, viral RNA was repeatedly detected by reverse transcription-PCR in nasal secretions, saliva, and conjunctival fluids. Sequence analysis revealed clustered nucleotide exchanges among sheep BDV p24 genomes, which differed at five positions from the clustered nucleotide exchanges seen in horse BDV p24 genomes.

Animals↗

PubMed2001

Avian polyomavirus agnoprotein 1a is incorporated into the virus particle as a fourth structural protein, VP4.

Agnoproteins, encoded by the 5'-region of the late bicistronic mRNA of some polyomaviruses, are small proteins with largely unknown functions. In avian polyomavirus (APV)-infected cells, mRNAs of seven putative agnoproteins have been observed. Recently, it has been shown that agnoprotein 1a and its truncated variant agnoprotein 1b, encoded by the predominant mRNA species, are essential for APV replication. Here, the presence of agnoprotein 1a is demonstrated in the nucleus of APV-infected cells and in purified APV particles. Interaction between agnoprotein 1a and the major structural protein, VP1, was demonstrated by co-immunoprecipitation experiments using lysates of recombinant baculovirus-infected insect cells. With proteins expressed in E. coli, binding to double-stranded DNA in a sequence-unspecific manner was shown for agnoprotein 1a, whereas agnoprotein 1b failed to bind. A leucine zipper-like motif present in agnoprotein 1a is considered to be involved in DNA binding. Due to the absence of any structural or functional homologies between APV agnoprotein 1a and the agnoproteins of mammalian polyomaviruses, it is suggested that this protein should be renamed VP4, indicating its function as a fourth structural protein of APV.

Amino Acid Sequence↗

PubMed2001

Apoptosis is induced by infectious bursal disease virus replication in productively infected cells as well as in antigen-negative cells in their vicinity.

The kinetics of infectious bursal disease virus (IBDV) replication and induction of apoptosis were investigated in vitro and in vivo. After infection of chicken embryo (CE) cells with IBDV strain Cu-1, the proportion of apoptotic cells increased from 5.8% at 4 h post-infection (p.i.) to 64.5% at 48 h p.i. The proportion of apoptotic cells correlated with IBDV replication. UV-inactivated IBDV particles did not induce apoptosis. Double labelling revealed that, early after infection, the majority of antigen-expressing cells were not apoptotic; double-labelled cells appeared more frequently at later times. Remarkably, apoptotic cells were frequently located in the vicinity of antigen-expressing cells. This indicated that an apoptosis-inducing factor(s) might be released by cells that replicate IBDV. Since interferon (IFN) production has been demonstrated after IBDV infection, IFN was considered to be one of several factors. However, supernatants of infected CE cells in which virus infectivity had been neutralized were not sufficient to induce apoptosis. Similar results were observed in the infected bursae of Fabricius: early after infection, most of the cells either showed virus antigens or were apoptotic. Again, double-labelled cells appeared more frequently late after infection. This suggests that indirect mechanisms might also be involved in the induction of apoptosis in vivo, contributing to the rapid depletion of cells in the IBDV-infected bursa.

Animals↗