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A Hillebrand

Publications and source records attributed to A Hillebrand.

At least 19 recordsLinked to original sources
PubMed2006

Semantic and phonological task-set priming and stimulus processing investigated using magnetoencephalography (MEG).

In this study the neural substrates of semantic and phonological task priming and task performance were investigated using single word task-primes. Magnetoencephalography (MEG) data were analysed using Synthetic Aperture Magnetometry (SAM) to determine the spatiotemporal and spectral characteristics of cortical responses. Comparisons were made between the task-prime conditions for evidence of differential effects as a function of the nature of the task being primed, and between the task-prime and the task performance responses for evidence of parallels in activation associated with preparation for and completion of a specific task. Differential priming effects were found. Left middle temporal and inferior frontal voxels showed a statistically significant power decrease associated with the semantic task-prime, and a power increase associated with the phonological task-prime, within beta and gamma frequency bands respectively. Similarities between the task-related differential effects associated with task-prime presentation and those associated with target stimulus presentation were also found. For example, within the semantic task condition, left superior frontal and middle temporal regions showed a significant power decrease within both task-prime and target epochs; within the phonological task condition there were significant parietal and cerebellar power decreases within both types of epoch. In addition there was evidence within the priming epochs of dissociable patterns of activity which could be interpreted as indices of de-activation of task-irrelevant networks. Following a phonological task-prime, significant power increases were observed in those inferior frontal and middle temporal regions in which significant power decreases were associated with semantic task priming and performance.

Brain Mapping↗
PubMed2004

Co-registration of magnetoencephalography with magnetic resonance imaging using bite-bar-based fiducials and surface-matching.

OBJECTIVE: To introduce a new technique for co-registration of Magnetoencephalography (MEG) with magnetic resonance imaging (MRI). We compare the accuracy of a new bite-bar with fixed fiducials to a previous technique whereby fiducial coils were attached proximal to landmarks on the skull. METHODS: A bite-bar with fixed fiducial coils is used to determine the position of the head in the MEG co-ordinate system. Co-registration is performed by a surface-matching technique. The advantage of fixing the coils is that the co-ordinate system is not based upon arbitrary and operator dependent fiducial points that are attached to landmarks (e.g. nasion and the preauricular points), but rather on those that are permanently fixed in relation to the skull. RESULTS: As a consequence of minimizing coil movement during digitization, errors in localization of the coils are significantly reduced, as shown by a randomization test. Displacement of the bite-bar caused by removal and repositioning between MEG recordings is minimal ( approximately 0.5 mm), and dipole localization accuracy of a somatosensory mapping paradigm shows a repeatability of approximately 5 mm. The overall accuracy of the new procedure is greatly improved compared to the previous technique. CONCLUSIONS: The test-retest reliability and accuracy of target localization with the new design is superior to techniques that incorporate anatomical-based fiducial points or coils placed on the circumference of the head.

Brain↗
PubMed2004

Dissociating the spatio-temporal characteristics of cortical neuronal activity associated with human volitional swallowing in the healthy adult brain.

Human swallowing represents a complex highly coordinated sensorimotor function whose functional neuroanatomy remains incompletely understood. Specifically, previous studies have failed to delineate the temporo-spatial sequence of those cerebral loci active during the differing phases of swallowing. We therefore sought to define the temporal characteristics of cortical activity associated with human swallowing behaviour using a novel application of magnetoencephalography (MEG). In healthy volunteers (n = 8, aged 28-45), 151-channel whole cortex MEG was recorded during the conditions of oral water infusion, volitional wet swallowing (5 ml bolus), tongue thrust or rest. Each condition lasted for 5 s and was repeated 20 times. Synthetic aperture magnetometry (SAM) analysis was performed on each active epoch and compared to rest. Temporal sequencing of brain activations utilised time-frequency wavelet plots of regions selected using virtual electrodes. Following SAM analysis, water infusion preferentially activated the caudolateral sensorimotor cortex, whereas during volitional swallowing and tongue movement, the superior sensorimotor cortex was more strongly active. Time-frequency wavelet analysis indicated that sensory input from the tongue simultaneously activated caudolateral sensorimotor and primary gustatory cortex, which appeared to prime the superior sensory and motor cortical areas, involved in the volitional phase of swallowing. Our data support the existence of a temporal synchrony across the whole cortical swallowing network, with sensory input from the tongue being critical. Thus, the ability to non-invasively image this network, with intra-individual and high temporal resolution, provides new insights into the brain processing of human swallowing.

Adult↗
PubMed2002

A quantitative assessment of the sensitivity of whole-head MEG to activity in the adult human cortex.

MagnetoEncephaloGraphy (MEG) relies on the detection of cortical current flow by measurement of the associated magnetic field outside the head. The amplitude of this magnetic field depends strongly on the depth of the electrical brain activity. Additionally, radially orientated sources are magnetically silent in a concentrically homogeneous volume conductor, giving rise to the anecdotal assumptions that MEG is insensitive to both deep and gyral sources. Utilising cortical surfaces extracted from Magnetic Resonance Images (MRIs) of two adult brains we constructed all possible single source elements and examined the proportion of active neocortex that is actually detectable with a whole-head MEG system. We identified those electrically active regions to which MEG is maximally sensitive by analytically computing the probability of detecting a source within a specified confidence volume. Our findings show that source depth, and not orientation, is the main factor that compromises the sensitivity of MEG to activity in the adult human cortex. There are thin strips (approximately 2 mm wide) of poor resolvability at the crests of gyri; however, these strips account for only a relatively small proportion of the cortical area and are abutted by elements with nominal tangential component yet high resolvability due to their proximity to the sensor array. Finally, we varied the extent of the patches of cortical activity, showing that small patches have a small net-current moment and are therefore less visible whereas large patches have a strong net-current moment, are generally more visible to the MEG system, yet are less appropriately modelled as single dipoles.

Adult↗
PubMed2000

Glycosylation-site-selective synthesis of N-acetyl-lactosamine repeats in bis-glycosylated human lysozyme.

We have studied the elongation of oligosaccharides containing N-acetyl-lactosamine repeats using glycosylated human lysozyme mutants as a model. We reported previously that a combination of glycosylation sites at the 49th (site IV) and 68th (site II) amino acid residues of the protein particularly stimulates the synthesis of N-acetyl-lactosamine repeats [Melcher, Grosch, Grosse and Hasilik (1998) Glycoconjugate J. 15, 987-993]. In the present study we show that it is the carbohydrate attached to site IV that is selectively affected. It contains more N-acetyl-lactosamine repeats when site II is glycosylated in the same molecule. As a corollary of the glycosylation at site II, the synthesis of a third antenna at site IV is increased. The triantennary oligosaccharides at site IV contain more N-acetyl-lactosamine repeats than the biantennary ones. Thus placing a carbohydrate at site II stimulates the branching and the elongation of the carbohydrate at the other site.

Amino Acid Sequence↗
PubMed1996

Variability of fatty acid content in pumpkin seeds (Cucurbita pepo L.).

Pumpkin (Cucurbita pepo L.) seed oil is a common salad oil which is produced in Slovenia, Hungary and the southern parts of Austria. It is dark green and has a high content of free fatty acids. The seed itself can be eaten. Due to its colour and the foam formation, the oil cannot be used for cooking. The content of vitamin E, especially gamma-tocopherol, is very high. The oil content of the pumpkin seed is about 50%. The variability in the oil content is very high resulting from a broad genetic diversity. Thus a breeding programme for increasing the oil productivity is very promising. The four dominant fatty acids are palmitic, stearic, oleic and linoleic acids. These four fatty acids make up 98 +/- 0.13% of the total amount of fatty acids, others being found at levels well below 0.5%.

Austria↗
PubMed1996

Variability of vitamin E content in pumpkin seeds (Cucurbita pepo L.).

Pumpkin (Cucurbita pepo L.) seed oil is a common salad oil which is produced in the southern parts of Austria, Slovenia and Hungary. It is dark green and has a high content of free fatty acids. Due to its colour, the oil cannot be used for cooking. The content of vitamin E, especially gamma-tocopherol, is very high. The oil content of the pumpkin seed is about 50%. The seed itself can be eaten. Therefore a pumpkin variety with high vitamin E content is desirable. The aim of this work was to find a variety of Cucurbita pepo which has a high oil yield and a high vitamin E content. A total of 100 breeding lines were tested for their tocopherol content. The tocopherols and tocotrienols are extracted with hexane and analysed by NP-HPLC/FLD with hexane/dioxan (96/4) as eluent, with fluorescence detection at 292/335 nm. The gamma-tocopherol content, which is about 5-10 times as much as that of alpha-tocopherol varies over a broad range (41-620 mg/kg dry pumpkin seeds). Beta- and delta-tocopherol are found at low levels.

Chromatography, High Pressure Liquid↗
PubMed1996

Hydration-scanning tunneling microscopy as a reliable method for imaging biological specimens and hydrophilic insulators.

The recently discovered high lateral conductivity of molecularly thin adsorbed water films enables investigation of biological specimens, and even of surfaces of hydrophilic insulators by scanning tunneling microscopy (STM). Here we demonstrate the capabilities of this method, which we call hydration-STM (HSTM), with images of various specimens taken in humid atmosphere: We obtained images of a glass coverslip, collagen molecules, tobacco mosaic virus, lipid bilayers and cryosectioned bovine achilles tendon on mica. To elucidate the physical mechanism of this conduction phenomenon we recorded current-voltage curves on hydrated mica. This revealed a basically ohmic behavior of the I-V curves without a threshold voltage to activate the current transport and indicates that electrochemistry probably does not dominate the surface conductivity. We assume that the conduction mechanism is due to structuring of water at the surface.

Aluminum Silicates↗
PubMed1994

Scanning tunneling microscopy of insulators and biological specimens based on lateral conductivity of ultrathin water films.

Scanning tunneling microscopy is based on the flow of an electrical current and thus cannot be used to directly image insulating material. It has been found, however, that a very thin film of water (about one monolayer) adsorbed to a surface exhibits a surprisingly high conductivity that is sufficient to allow scanning tunneling microscope imaging at currents below 1 picoampere. Hydrophilic insulators, such as glass and mica, can thus be imaged in humid air. The same is true for biological specimens deposited on such surfaces, as demonstrated by the scanning tunneling microscope imaging of plasmid DNA on mica.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1990

Albumin binding proteins are highly expressed in actively proliferating fetal and adult tissues.

The expression of albumin binding proteins (ABP, 31 and 18 kDa peptides) in various organs as a function of their ontogenic development was investigated in fetuses (20 days old), neonates (1 day old) and adult rabbits. At each of these stages, tissue extracts of brain, lung, thymus, heart, skeletal muscle and liver as well as whole embryos (11 days old) were examined by ligand blotting and quantitative immunoblot assays. Blots were either incubated with [125I]albumin followed by autoradiography and radioassay or exposed to a radioiodinated antibody raised against affinity-isolated 31 kDa peptide. Anti-31 kDa IgG cross-reacted with both 31 and 18 kDa peptides. Both methods used revealed that ABP are well expressed in embryos and in all fetal organs investigated. By comparison, in neonates, the ABP expression was diminished (by approximately 2-fold) in brain, heart and skeletal muscle. These changes were even more pronounced in the adult rabbit brain, heart, skeletal muscle and liver; no significant modification was detected in the lung. Prompted by these results, which inferred a high level of ABP in actively proliferating/differentiating tissues, we checked for the presence of ABP in other adult cells and tissues. In bone marrow cells, thymocytes and splenocytes, the 31 and 18 kDa peptides represented the major sodium dodecyl sulfate-urea extracted proteins, whereas in mature circulating white blood cells they were moderately expressed. The results indicate that ABP 1) are present early in embryogenesis, 2) are particularly well expressed in organs (fetal or adult) and cells characterized by active proliferation and differentiation, and 3) are not tissue specific.(ABSTRACT TRUNCATED AT 250 WORDS)

Albumins↗
PubMed1983

The conserved part of the T-region in Ti-plasmids expresses four proteins in bacteria.

The T-region of Ti-plasmids expresses four proteins (mol. wts. 74,000, 49,000, 28,000 and 27,000) in Escherichia coli minicells. Promoter activities are determined by sequences within the T-region, and the protein-coding regions map in that part of the T-region which is highly conserved in octopine and nopaline plasmids and which is responsible for shoot and root inhibition when expressed in plant cells. Three of the regions expressed in bacteria correlate with three regions which are transcribed in transformed plant cells; the fourth protein-coding region has no corresponding transcript in plants. At least three of the proteins synthesized in E. coli minicells are also expressed in cell-free systems prepared from E. coli and from Agrobacterium tumefaciens; the fourth protein (mol. wt. 49,000) is poorly expressed in both cell-free extracts. The possibility is discussed that the same genes are expressed in Agrobacteria and in transformed plant cells and that in both cases the gene products mediate growth regulatory effects to non-transformed plant cells.

Agrobacterium tumefaciens↗
PubMed1981

Expression of plant tumor-specific proteins in minicells of Escherichia coli: a fusion protein of lysopine dehydrogenase with chloramphenicol acetyltransferase.

Fragment EcoRI 7 from Ti-plasmid pTi Ach5, a part of the T-DNA in octopine tumors, was cloned in both orientations into pACYC184 and expressed in E. coli minicells. The cells synthesized four proteins from four different coding regions on EcoRI 7. Two of the proteins (Mr 25.000 and 26.000) were expressed with promoters from the Ti-plasmid fragment, while transcription for the two other proteins (Mr 18.000 and 74.000) started with a promoter on pACYC184. The Mr 18.000 protein represented a fusion product between chloramphenicol acetyltransferase (CAT) on pACYC184 and a part of lysopine dehydrogenase (LpDH), the enzyme synthesizing octopine and lysopine in plant tumor cells. The results suggest that E. coli minicells are a valuable system to study the proteins coded for by the T-region of Ti-plasmids.

Acetyltransferases↗
PubMed1975

An experimental study concerning the accessory nerve in the chicken and turkey.

The retrograde degeneration consecutive to accessory nerve transection proved that the real origin of this nerve in the chicken and turkey is represented exclusively by the ipsilateral dorso-central motor column described by BECCARI (1943). This nucleus, with a moniliform aspect, extends into the first two cervical neuromeres and enters the bulb, where it is continuous with the alpha subdivision of the hypoglossal nucleus. The accessory nerve of the two species of birds is homologous with the external ramus of the same nerve in mammals. An internal ramus is absent in birds.

Accessory Nerve↗