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Biomedical subjects

A Haase

Publications and source records attributed to A Haase.

198 records · Page 11Linked to original sources
PubMed1984

Slow virus visna: reproduction in vitro of virus from extrachromosomal DNA.

Under permissive conditions of growth in tissue culture, the retrovirus visna multiples over the course of a few days to high titer and kills the host cell. We show that in this lytic life cycle, viral DNA is tightly associated with, but not covalently linked to, chromosomal DNA. This finding provides explanations for a number of the unusual properties of the lentivirus subfamily of retroviruses, and suggests potential mechanisms for the block in virus gene expression in vivo responsible for the slow infection in nature.

DNA Replication↗
PubMed1983

Correlation of the 4-5 S form and the 8 S form of the cytosolic androgen receptor in murine skeletal muscle.

Binding experiments with the cytosolic androgen receptor from murine skeletal muscle yield with testosterone a biphasic saturation curve and a biphasic Scatchard plot. These binding characteristics result from the conversion of 8 S receptor (KD = 1,4 X 10(-10) M) into 4-5 S receptor (KD = 1,2 X 10(-9) M). This conversion is androgen dependent and is facilitated in vitro by either UV-irradiation or by methods known to activate steroid hormone receptor complexes to a nuclear binding form (e.g. high ionic strength or elevated temperature). The measured data show that both receptor forms are in a complex dissociation equilibrium. The reassociation of the 4-5 S receptor to form the 8 S complex is inhibited by RNase.

Animals↗
PubMed1981

Persistence and expression of Marek's disease virus DNA in tumour cells and peripheral nerves studied by in situ hybridization.

We have used cloned fragments of Marek's disease virus (MDV) DNA and in situ hybridization to search for virus DNA and study its expression in infected chick embryo fibroblasts (CEF), lymphoblastoid cell lines, tumours and neural lesions. DNA from the HPRS 16/att strain of MDV was cleaved with EcoRI endonuclease and several fragments were cloned in Escherichia coli using the vector PBR322. Seven fragments ranging in size from 2.6 to 11 kbp representing approx. 25% of the MDV genome were labelled in vitro and annealed to EcoRI digests of DNA from infected cells and tumours following separation and transfer according to the Southern blotting procedure. Most of the selected MDV DNA fragments hybridized to fragments of corresponding sizes in EcoRI digests of DNA from cell lines and tumours and failed to hybridize to digests of uninfected chick cell DNA. In situ hydridization using 3H-labelled DNA with specific activity of 10(8) d/min/microgram as probe showed intranuclear MDV DNA in infected CEF, in every cell of two lymphoblastoid cell lines and in the majority of infiltrating or proliferating lymphoid cells found in type 'A' lesions of grossly enlarged peripheral nerves. Both intranuclear and cytoplasmic RNA were detected in cells that contained virus DNA. However, comparatively little virus RNA appears to be transcribed in cell lines and in infected tissues from the regions of virus DNA (25% of genome) used as probe in this study. Our results favour the hypothesis that the accumulation of lymphoid cells in nerves is not the result of an inflammatory response to infected nerve cells but is rather the consequence of proliferating transformed cells.

Animals↗
PubMed1978

Resistance of visna virus to interferon.

Visna is a slow infection of sheep caused by a retrovirus. The persistence of virus despite the immune response of the host is best explained by restricted genetic expression of the virus and consequently prolonged periods of residence inside cells. The purpose of this investigation was to determine whether the restriction in genetic expression of visna virus is mediated by interferon. Sheep interferon induced by polyriboinosinic-polyribocytidylic acid in fetal lambs inhibited the growth of herpes simplex virus, vesicular stomatitis virus, and vaccinia virus, but even highly concentrated interferon did not affect the replication of visna virus in sheep choroid plexus cells. The same results were obtained whether the effects of interferon were assessed in single of multiple cycles of growth and when interferon was added at later times in the growth cycle of the virus. This unusual resistance of visna virus to interferon suggests that restriction of viral expression by the host is probably not mediated in this way.

Animals↗
PubMed1975

[Dose distribution in cobalt-60 irradiation of the axillary efferent lymphatic area in breast cancer].

A method of postoperative irradiation of breast cancer is reported using high dosage in the area of the axillary and subclavicular efferent lymphatic ducts. Within opposite fixed fields it was possible to modify the dose distribution by means of wedges, thus obtaining a maximum value of axillary and clavicular doses, together with a small radiation load on the lymphatic vessels which drain the region of the arm. The dose distributions in the depth of the shoulder are discussed on the basis of measurements at a phantom using different adjustments of the wedge filter. The most favorable dose distribution was noted with 17.5 degree lead wedges whereas, however, the angular aperture in the axillary and clavicular region was reduced to 2.5 degrees. This method is now being tested clinically.

Axilla↗
PubMedDate not supplied

Three-dimensional coronary angiography of the perfused rat heart.

The purpose of this work was to visualize the whole three-dimensional coronary artery tree of the perfused beating rat heart using three-dimensional MRI. The spatial resolution amounts to 140 microns. Also, vessels having smaller diameters could be detected. Different strategies for the visualization of the three-dimensional coronary angiograms including maximum intensity projection, data thresholding, and segmentation, were shown. The coronary artery tree was best visualized by hysteresis threshold segmentation and subsequent surface reconstruction.

Animals↗
PubMedDate not supplied

In vivo quantitative mapping of cardiac perfusion in rats using a noninvasive MR spin-labeling method.

Measurement of myocardial perfusion is important for the functional assessment of heart in vivo. Our approach is based on the modification of the longitudinal relaxation time T1 induced by magnetic spin labeling of endogenous water protons. Labeling is performed by selectively inverting the magnetization within the detection slice, and longitudinal relaxation is measured using a fast gradient echo MRI technique. As a result of blood flow, nonexcited spins enter the detection slice, which leads to an acceleration of the relaxation rate. Incorporating this phenomenon in a mathematical model that describes tissue as two compartments yields a simple expression that allows the quantification of perfusion from a slice-selective and a global inversion recovery experiment. This model takes into account the difference between T1 in blood and T1 in tissue. Our purpose was to evaluate the feasibility and reproducibility of this technique to map quantitatively myocardial perfusion in vivo in rats. Quantitative maps of myocardial blood flow were obtained from nine rats, and the reproducibility of the technique was evaluated by repeating the whole perfusion experiment four times. Evaluation of regions of interest within the myocardium yielded a mean perfusion value of 3.6 +/- .5 ml x min(-1) x g(-1) over all animals, which is in good agreement with previously reported literature values.

Animals↗
PubMedDate not supplied

Rapid three-dimensional MR imaging using the FLASH technique.

Fast low-angle shot (FLASH) imaging is a new technique for rapid magnetic resonance (MR) imaging that reduces acquisition times to seconds while retaining spatial resolution. This article deals with a three-dimensional (3D) variant of the FLASH method that allows the recording of a 3D-data set of 128 X 128 X 128 pixels within an acquisition time of only 4 min. The method is demonstrated using a 2.35 T 40 cm bore MR system. Experiments are carried out on rabbit head and human extremities. Depending on the field of view, the isotropic resolution is 1 mm or even less leading to cross-sectional images with a 1 mm slice thickness. In principle, FLASH imaging techniques are applicable to any MR system without the need of major hardware modifications. However, high-speed computers, large storage capacity, and rapid image display routines greatly facilitate an advantageous use of the 3D-FLASH variant.

Animals↗
PubMedDate not supplied

Inversion recovery snapshot FLASH MR imaging.

Snapshot fast low angle shot (FLASH) magnetic resonance (MR) imaging techniques have been developed to enable real time imaging of MR parameters. The method is based on a 64 x 128 FLASH tomogram acquired within less than 200 ms. This work describes snapshot FLASH MR using a single 180 degrees pulse prior to the acquisition of a series of FLASH images. The experiment creates continuous dynamic inversion recovery (IR) T1 contrast in successive images. The total acquisition time of 16 images displaying the IR behavior is less than 4 s. Representative snapshot FLASH IR MR images of the abdomen of healthy rats and of an implanted hepatic tumor are illustrated.

Animals↗
PubMedDate not supplied

T1 maps by K-space reduced snapshot-FLASH MRI.

The T1 maps evaluated from k-space reduced Snapshot fast low angle shot (FLASH) images provide high contrast parameter images for tissue characterization in vivo of any body region. An algorithm for computing T1 values that allows a fast and reliable evaluation of T1 maps and yields reproducible values of tissue parameters in MR imaging is presented. The algorithm combined with the Snapshot FLASH inversion recovery imaging sequence permits a precise determination of T1 values, even for T1 times as low as 50 ms. Comparison with a spectroscopical inversion recovery method on identical phantoms demonstrates the accuracy of this technique. With its total acquisition time of approximately 2 s, IR Snapshot FLASH is fast enough to be used in monitoring fast T1 dynamics.

Magnetic Resonance Imaging↗
PubMedDate not supplied

[Reducing NMR image artefacts by using optimized materials for diagnostic aids and implants].

Differences in magnetic susceptibility, as occur for example at the boundary between implant materials and the surrounding body tissue, result in artefacts and a signal loss in magnetic resonance imaging. By using materials with a magnetic susceptibility matched to the respective environment, it is possible to minimize both artefacts and signal loss. Such materials can be made by combining two materials of different magnetic susceptibility (e.g. diamagnetic and paramagnetic materials) in such a way that the resulting material has the desired effective magnetic susceptibility.

Artifacts↗
PubMedDate not supplied

Pulsatile flow pattern in cerebral arteries during cardiopulmonary bypass. An evaluation based on transcranial Doppler ultrasound.

Pulsatile wave patterns in basal cerebral arteries were studied by means of transcranial Doppler ultrasound (TCD) in 11 patients undergoing cardiopulmonary bypass (CPB) surgery. Different physiological states and technical parameters were demonstrated influencing wave forms delivered from a pulsatile CPB roller pump. The results gave evidence of the variability of pulsatile perfusion which may explain the inconsistency in the literature concerning its effectiveness in preserving tissue function. TCD proved to be a useful approach to define pulsatility of cerebral blood flow during CPB.

Blood Flow Velocity↗