Biomedical subjects

Thomas Schmidt

Publications and source records attributed to Thomas Schmidt.

7 recordsLinked to original sources

PubMed2003

Different time courses for visual perception and action priming.

Visual stimuli may remain invisible but nevertheless produce strong and reliable effects on subsequent actions. How well features of a masked prime are perceived depends crucially on its physical parameters and those of the mask. We manipulated the visibility of masked stimuli and contrasted it with their influence on the speed of motor actions, comparing the temporal dynamics of visual awareness in metacontrast masking with that of action priming under the same conditions. We observed priming with identical time course for reportable and invisible prime stimuli, despite qualitative changes in the masking time course. Our findings indicate that experimental variations that modify the subjective visual experience of masked stimuli have no effect on motor effects of those stimuli in early processing. We propose a model that provides a quantitative account of priming effects on response speed and accuracy.

Adult↗

PubMed2003

Divergence of satellite DNA and interspersion of dispersed repeats in the genome of the wild beet Beta procumbens.

Several repetitive sequences of the genome of Beta procumbens Chr. Sm., a wild beet species of the section Procumbentes of the genus Beta have been isolated. According to their genomic organization, the repeats were assigned to satellite DNA and families of dispersed DNA sequences. The tandem repeats are 229-246 bp long and belong to an AluI restriction satellite designated pAp11. Monomers of this satellite DNA form subfamilies which can be distinguished by the divergence or methylation of an internal restriction site. The satellite is amplified in the section Procumbentes, but is also found in species of the section Beta including cultivated beet (Beta vulgaris). The existence of the pAp11 satellite in distantly related species suggests that the AluI sequence family is an ancient component of Beta genomes and the ancestor of the diverged satellite subfamily pEV4 in B. vulgaris. Comparative fluorescent in-situ hybridization revealed remarkable differences in the chromosomal position between B. procumbens and B. vulgaris, indicating that the pAp11 and pEV4 satellites were most likely involved in the expansion or rearrangement of the intercalary B. vulgaris heterochromatin. Furthermore, we describe the molecular structure, and genomic and chromosomal organization of two repetitive DNA families which were designated pAp4 and pAp22 and are 1354 and 582 bp long, respectively. The families consist of sequence elements which are widely dispersed along B. procumbens chromosomes with local clustering and exclusion from distal euchromatic regions. FISH on meiotic chromosomes showed that both dispersed repeats are colocalized in some chromosomal regions. The interspersion of repeats of the pAp4 and pAp22 family was studied by PCR and enabled the determination of repeat flanking sequences. Sequence analysis revealed that pAp22 is either derived from or part of a long terminal repeat (LTR) of an Athila-like retrotransposon. Southern analysis and FISH with pAp4 and pAp22 showed that both dispersed repeats are species-specific and can be used as DNA probes to discriminate parental genomes in interspecific hybrids. This was tested in the sugar beet hybrid PRO1 which contains a small B. procumbens chromosome fragment.

Alu Elements↗

PubMed2002

Screening crystallisation conditions using fluorescence correlation spectroscopy.

We investigate the potential of fluorescence correlation spectroscopy (FCS) in screening for crystallisation conditions. Solutions that nucleate protein crystals must have different interactions than solutions that do not give rise to crystals. Due to these different interactions the average mean squared displacement of the individual proteins changes. By monitoring protein self-diffusion, we can distinguish crystallizing from non-crystallizing solutions. The method introduced can be applied at extremely low concentrations in femtoliter volumes as an early diagnostic for molecular association. Based on our preliminary findings FCS has the potential to become a routine screening method for crystallography.

Apoferritins↗

PubMed2002

Painting of parental chromatin in Beta hybrids by multi-colour fluorescent in situ hybridization.

Sugar beet (Beta vulgaris L.) is a relatively young crop and has a narrow gene pool. In order to introduce genetic variability into the crop, interspecific hybrids, selected from crosses with wild beets of the sections Corollinae and Procumbentes, have been generated. The introgressed B. procumbens chromatin carries resistance genes to beet cyst nematode Heterodera schachtii Schm. These lines are important for breeding of nematode-resistant sugar beet, while Corollinae species are potential donors of tolerance to biotic and abiotic stresses such as drought or saline soils. We have used in situ hybridization of genomic DNA to discriminate the parental chromosomes in these interspecific hybrids. Suppression of cross-hybridization by blocking DNA was not necessary indicating that the investigated Beta genomes contain sufficient species-specific DNA enabling the unequivocal determination of the genomic composition of the hybrids. Interspecific hybrid lines with an additional chromosome (2n = 18 + 1), chromosome fragment (2n = 18 + fragment) or translocation of B. procumbens (2n = 18) were analysed by genomic in situ hybridization (GISH) at mitosis and meiosis. Species-specific satellites and ribosomal genes used in combination with genomic DNA or in rehybridization experiments served as landmark probes for chromosome identification in hybrid genomes. The detection of a B. procumbens translocation of approx. I Mbp demonstrated the sensitivity and resolution of GISH and showed that this approach is a powerful method in genome analysis projects of the genus Beta.

Animals↗

PubMed2002

The finger in flight: real-time motor control by visually masked color stimuli.

Current theories of dual visual systems suggest that color is processed in a ventral cortical stream that eventually gives rise to visual awareness but is only indirectly involved in visuomotor control mediated by the dorsal stream. If the dorsal stream is indeed less sensitive to color than the ventral stream, color stimuli blocked from awareness by visual masking should also be blocked from guiding fast motor responses. In this study, pointing movements to one of two isoluminant color targets were preceded by consistent or inconsistent color primes. Trajectories were strongly affected by priming, with kinematics implying a continuous flow of color information into executive brain areas while the finger was already moving. Motor effects were more sensitive to color of the primes than were deliberate attempts to identify the primes in forced-choice tasks based on visual awareness. Priming was observed even when masking was complete.

Adolescent↗

PubMed1999

Symbolic dynamics of jejunal motility in the irritable bowel.

Different studies of the irritable bowel syndrome (IBS) by conventional analysis of jejunal motility report conflicting results. Therefore, our aim is to quantify the jejunal contraction activity by symbolic dynamics in order to discriminate between IBS and control subjects. Contraction amplitudes during fasting motility (phase II) are analyzed for 30 IBS and 30 healthy subjects. On the basis of a particular scale-independent discretization of the contraction amplitudes with respect to the median, IBS patients are characterized by increased block entropy as well as increased mean contraction amplitude. In a further more elementary level of analysis these differences can be reduced to specific contraction patterns within the time series, namely the fact that successive large contraction amplitudes are less ordered in IBS than in controls. These significant differences in jejunal motility may point to an altered control of the gut in IBS, although further studies on a representative number of patients have to be done for a validation of these findings. (c) 1999 American Institute of Physics.

Journal Article↗

PubMedDate not supplied

[Accidental injury of medial rectus muscle in endoscopic surgery of ethmoidal sinus: case report and survey of literature].

BACKGROUND: Ophthalmologic complications of endoscopic sinus surgery are rare, consequences may be serious. PATIENTS: Two patients are presented who suffered lesions of the internal rectus muscles during endoscopic ethmoidectomy. The clinical picture of this rare complication resembles that of a paralysis of the medial rectus muscle. THERAPY AND COURSE: In one patient the very thinned medial rectus muscle was tucked in a first surgical step. In the second step the external rectus muscle was recessed. Fusion in primary gaze was possible. In the second patient surgery was planned, he died however. CONCLUSION: Because of the anatomy the medial rectus muscle is endangered in endoscopic ethmoidectomy. Considered to the frequency of this surgery the incidence however is rare.

Aged↗