Biomedical subjects

R Reichelt

Publications and source records attributed to R Reichelt.

40 records · Page 3Linked to original sources

PubMed1988

Early ontogeny of the central benzodiazepine receptor in human embryos and fetuses.

The early ontogeny of the central benzodiazepine receptor (BZR) was investigated in human embryos and fetuses between 7 and 26 weeks of gestation. Brain tissue was gained from terminated pregnancies or spontaneous abortions. Binding studies, which were performed with 3H-flunitrazepam (FNZ), revealed that specific benzodiazepine binding is already detectable at an embryonal age of 7 weeks post conceptionem. Binding at this early stage can be displaced potently by clonazepam and the inverse agonist beta-CCE. Additionally, 3H-FNZ binding is enhanced by GABA. Thus, benzodiazepine binding is of the central type. Receptor density increases steeply in whole brain between weeks 8 and 11 of gestation. In frontal cortex receptor density increases gradually between weeks 12 and 26 of gestation. No specific fetal disease entity (including trisomy 21) was consistently associated with exceptionally high or low Bmax-values.

Brain↗

PubMed1988

Processing of quantitative scanning transmission electron micrographs.

While digital image processing is widely used for 3-D structure reconstruction from tilt-series recorded in the electron microscopy (EM), a few scanning transmission electron microscopy (STEM) specific procedures have been developed which provide us with useful quantitative information on the structure of biological macromolecules and their assemblies. These include determination of the mass- or elemental distribution within the structure under investigation. Simple procedures evaluate the mass of proteinous particles, the mass-per-length of filaments or the mass-per-area of sheets. Averaging of STEM elastic darkfield (DF) micrographs from regular structures has demonstrated the possibility of obtaining mass maps, which can reveal domains as small as 1,000 daltons. While the elastic DF image defines the (regular) structure at high-resolution, thereby providing a rule for averaging, much weaker signals are simultaneously acquired by detectors positioned at specific energy losses. Since many (approximately 500) identical subunits from a single multichannel micrograph can be averaged, and many such averages can readily be accumulated due to the precise morphological characterization obtained from the elastic DF image, an element map is expected to emerge from thus averaged electron energy loss windows.

Computer Systems↗

PubMed1986

Contrast and resolution of scanning transmission electron microscope imaging modes.

Image blurring due to delocalization of inelastic events was studied for scanning transmission electron microscopy (STEM) of unstained thin sections. The delocalization probability was obtained from the angular distribution of inelastic scattering, which was calculated from experimental electron loss spectra of organic samples. This probability was implemented in a Monte Carlo program to simulate the effects of multiple scattering and delocalization for STEM images collected by either the annular detector or the spectrometer, and images generated by a combination of these two signals. Depending on the illumination, the detector geometry and the energy-loss range selected for imaging the annular detector image is blurred by a non-negligible fraction of inelastically scattered electrons. Simultaneous acquisition of an inelastic image using a spectrometer allows the blurring to be reduced by calculation of either the ratio or the difference of the two darkfield signals. While inherent nonlinearities reduce the interpretability of ratio-contrast images, difference-contrast improves the visibility of details submerged in a diffuse background without introducing artifacts.

Data Display↗

PubMed1984

Imaging of biological structures with the scanning transmission electron microscope.

The scanning transmission electron microscope (STEM) is discussed in view of biological applications. Theoretical considerations are given, but the emphasis is directed to practical examples from a range of biological projects. The STEM is most efficiently used in elastic and inelastic dark-field modes providing information on the scattering power of the irradiated sample. Thus, the STEM is an ideal tool for quantitative measurements such as mass-mapping or element-mapping at high resolution. Limitations of such methods due to multiple scattering and quantum noise are briefly reviewed.

Animals↗