PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Microscopy, Electron”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 271 records · Page 15Linked to original sources
PubMed2003

Observations of the intestinal mucosa using environmental scanning electron microscopy (ESEM); comparison with conventional scanning electron microscopy (CSEM).

In order to evaluate the potential use of environmental scanning electron microscopy (ESEM) in biology, structural changes of the jejunal villi of rats were studied after periods of fasting and refeeding, using a conventional scanning electron microscope (CSEM) and ESEM. While observation using the CSEM, involves chemical fixation, drying and coating, observation of fresh, unprepared materials can be directly realized with the ESEM. Environmental microscopy provides a relatively new technology for imaging hydrated materials without specimen preparation and conductive coating. Direct observation of biological samples in their native state is therefore possible with an ESEM. After fasting, the jejunal mucosa is dramatically reduced in size, splits and holes appearing at the tip of the villi. These changes were observed whatever the type of technique used. Artifacts due to the sample preparation for CSEM observation (drying, coating) can therefore be excluded. However, CSEM and ESEM must be used jointly. While, CSEM must be preferred for surface analysis involving high magnifications, ESEM observation, on the other hand, can prove valuable for determining the living aspect of the samples.

Animals↗
PubMed2001

Field emission scanning electron microscopy and freeze-fracture transmission electron microscopy of mouse cerebellar synaptic contacts.

Samples of albino mice were processed by the cryofracture method for scanning electron microscopy and examined with the field emission scanning electron microscope (FESEM). Freeze-etching direct replicas of mice cerebellar cortex were also studied with the transmission electron microscope (FFTEM), as a complementary technique for obtaining higher resolution, three-dimensional correlative images of cerebellar synaptic contacts. At the granular, Purkinje cells and molecular layers, the cryofracture method for FESEM selectively removed the neuroglial cell investment, facilitating the visualization of the outer and inner surfaces of cerebellar synaptic contacts. In addition, FFTEM showed the real extension of perisynaptic neuroglial investment. The outer surface of mossy fiber rosettes and their digitiform processes were seen at the granular layer, making flat and invaginated synaptic contacts with the granule cell dendrites. At the molecular layer, the longitudinal traject of parallel fibers or nonsynaptic segments and their synaptic varicosities were characterized. These latter established synaptic contacts with Purkinje dendritic spines. Fractured parallel fiber endings showed the SE-I images of clustered spheroidal synaptic vesicles and mitochondria and the surrounding cotton-like appearance of Bergmann glial cell cytoplasm. Climbing fibers showed a characteristic crossing-over bifurcation pattern in the white matter and in the three-layer structure of cerebellar cortex, formation of tendril collaterals in the granular layer, topographical relationship with Purkinje cell soma and retrograde collaterals in the molecular layer. The climbing fiber synaptic relationship with Purkinje dendritic spines was characterized, by means of FFTEM, by the presence of large synaptic endings and aggregation of intramembrane particles at the P and E faces of presynaptic endings, characteristic of excitatory synapses.

Animals↗
PubMed1995

Monitoring morphology and signal during non-radioactive in situ hybridization procedures by reflection-contrast microscopy and transmission electron microscopy.

We analyzed the effects of steps in RNA in situ hybridization (ISH) procedures on morphology and hybridization signal with reflection-contrast microscopy (RCM) and transmission electron microscopy (TEM). In chessboard experiments, a range of fixatives containing formaldehyde, glutaraldehyde, or both, and various permeabilization protocols, including ethanol and pepsin treatment, were investigated. A transfected rat fibroblast cell line that harbors an inducible human cytomegalovirus immediate early (IE) transcription unit, and specific probes for 28S ribosomal RNA and IE messenger RNA were used for this purpose. Probes were labeled with digoxigenin and hybrids were detected with anti-digoxigenin F(ab)2 fragments conjugated to horseradish peroxidase, followed by diaminobenzidine/H2O2 reaction. Effects of fixation and pre-treatments on RNA detection efficiency and morphology were monitored by RCM on whole cells. After Epon embedding and ultra-thin cross-sectioning, the corresponding TEM images were obtained. With the pre-treatments analyzed, it appeared impossible to find an acceptable balance between ISH signals and preservation of ultrastructural morphology: when good signal-to-noise ratios are obtained, the ultrastructural morphology is already deteriorated. We discuss the parameters that influence the fragile balance between high RNA detection efficiency and good preservation of ultrastructure and the benefit of RCM monitoring in the development and procedures for pre-embedding electron microscopic ISH.

Animals↗
PubMed1981

Structure and porosity of human cervical enamel studied by polarizing microscopy and transmission electron microscopy.

Dehydration by alcohols and concentrated solutions of highly soluble salts caused refractive changes in enamel which were enhanced in the cervical regions. Electron microscopy showed crystals in cervical enamel to vary from normal orientation, size and habit to marked disorientation and reduced size. Consequent increases in surface area and inter-crystalline volume could account for the exaggerated optical behaviour. The changes in optical properties of enamel occurred only when the osmotic pressures of the imbibing solutions exceeded 500 atm. It is proposed that the internal pore system may take up water freely but exclude large hydrated molecules and ions which thereby create a negative pressure on the water contained in these pores. Once this negative pressure exceeds the tensile strength of the water-pore system, molecules may be torn from their attachment sites, and possibly from each other, so that a sudden evacuation of the pores is accompanied by a simultaneous reduction in refractive index. It is likely that such sudden evacuation would alter the potential of the pore surfaces to react with small molecules and ions subsequently invading the tissue.

Absorption↗
PubMed1989

Preparation of cross-sectional transmission electron microscopy samples by electron beam lithography and reactive ion etching.

A cross-sectional sample preparation technique is described that relies on lithographic and dry-etching processing, thus avoiding metallographic polishing and ion milling. The method is capable of producing cross-sectional transmission electron microscopy samples with a large amount of transparent area (1 micron x 2.5 mm) which allows the examination of many patterned test sites on the same sample from the same chip of a silicon wafer. An example of the application of the technique is given for localized oxidation through a mask.

Microscopy, Electron↗
PubMed2005

Assessing transferrin modification of liposomes by atomic force microscopy and transmission electron microscopy.

Site-specific delivery of drugs and therapeutics can significantly reduce drug toxicity and increase the therapeutic effect. Transferrin (Tf) is one suitable ligand to be conjugated to drug delivery systems to achieve site-specific targeting, due to its specific binding to transferrin receptors (TfR), expressed on several cell types of therapeutic interest. TfRs have been reported to be highly expressed on the surfaces of tumour cells and the well-characterised and efficient mechanism of internalisation of Tf has been exploited for the delivery of anticancer drugs, proteins, and therapeutic genes into primarily proliferating malignant cells. Liposomes are effective vehicles for drugs, genes and vaccines and can be easily modified with proteins, antibodies, and other appropriate ligands, resulting in attractive formulations for targeted drug delivery. In this study, we used atomic force microscopy (AFM) and transmission electron microscopy (TEM) to confirm the conjugation of Tf to liposomes by three different coupling methods. In addition, the conventional assays for quantification of protein amount (BCA) and phospholipid content (according to Steward) were performed. AFM and TEM were able to display Tf-molecules on the liposomal surfaces and can be routinely used to obtain additional visual information on the protein-drug carrier conjugation in a fast and reliable manner.

Drug Delivery Systems↗
PubMed1998

Compatibility study between ibuproxam and pharmaceutical excipients using differential scanning calorimetry, hot-stage microscopy and scanning electron microscopy.

Differential scanning calorimetry (DSC) was used as a screening technique for assessing the compatibility of ibuproxam with some currently employed pharmaceutical excipients. The influence of processing effects (simple blending, cogrinding or kneading) on drug stability was also evaluated. On the basis of DSC results, ibuproxam was found to be compatible with corn starch, avicel and sodium carboxymethylcellulose. Some drug-excipient interaction was observed with polyethyleneglycol 4000, palmitic acid, stearic acid, Ca and Mg stearate. Actual solid-phase interactions of the drug with polyvinylpolypyrrolidone and polyvinylpirrolidone K30 were induced by mechanical treatments. Hot-stage microscopy (HSM) and scanning electron microscopy (SEM) were of help in interpreting the DSC results and excluding in all cases relevant pharmaceutical incompatibilities.

Benzeneacetamides↗
PubMed2001

Specific surface area of snow samples determined by CH4 adsorption at 77 K and estimated by optical microscopy and scanning electron microscopy.

Snow is a divided medium that can adsorb atmospheric trace gases. Evaluating the impact of the snow cover on atmospheric chemistry therefore requires the knowledge of the specific surface area (SSA) of snow. This paper compares the results of three methods used to measure or estimate the SSA of four snow samples: CH4 adsorption at 77 K, optical microscopy (OM), and scanning electron microscopy (SEM, used only on two samples). Within error bars, CH4 adsorption and OM yield similar results on three of the four snow samples. Values for the 4th sample are within a factor of 2. For both samples where CH4 adsorption, OM, and SEM are used, all three methods yield similar results, but CH4 adsorption always has a better accuracy and a much better precision. Thus, despite its ease of use, estimates from OM images are often not accurate enough to monitor the evolution of snow SSA. The main sources of error in the OM method are the difficulty to determine snow crystal thicknesses and to take into account the topography of the snow crystal surface. The combination of CH4 adsorption and OM or SEM can provide useful information on the evolution of both the SSA and the shape of snow crystals. This will be useful to evaluate the respective contributions of adsorption/desorption and sublimation/condensation processes to the impact of the snow cover on atmospheric chemistry.

Adsorption↗
PubMed1980

[Surface ultrastructure of the human uterine exfoliated endometrial cells--comparative studies of the same cell by light microscopy and scanning electron microscopy (author's transl)].

The preparations for observations of the same cells by light microscopy (LM) and scanning electron microscopy (SEM) were examined and the exfoliated endometrial cells of the uterus obtained by the newly introduced brush and cannula was evaluated. 1) The degree of shrinkage of the area was not significant between the air drying method and critical point drying method. In the air drying group, adhesion, entanglement and disappearance of microvilli (mv) and the adhesion of cilia, and the collapse of cells were noted morphologically. 2) Papanicolaou stain had no effect on the degree of shrinkage of the area and the shape of cilia or mv. 3) When the samples were transferred from ethanol to critical point drying, without immersion in isoamyl acetate, artifacts appeared in small granulated form. 4) The menopausal phase was divided into two groups which showed a shift of the maturation Index (MI) to center and had a slender mv and the other group which showed a shift to the left and granular mv. The nether surface of the cells showed a wrinkled and irregular undulations and did not show cilia or mv. 5) In adenomatous hyperplasia, the ratio of ciliated cell to no ciliated cell was four to one. It was two to one in cystic glandular hyperplasia. 6) The dense and short mv were observed in well-differentiated adenocarcinoma and poorly-differentiated adenocarcinoma showed neither mv nor cilia. Morphologic changes of mv and cilia in carcinomatous change of uterine endometrium commenced with a decrease in cilia, shifted to the shortening and disappearance disappearance of mv.

Adenocarcinoma↗
PubMed1990

Ultra structural studies of the surface of Hymenolepis nana by scanning and transmission electron microscopy.

Scanning electron microscopy of the surface of Hymenolepis nana indicated that dense populations of microtriches occur on scolex proper, suckers and strobila, with an average density of 20/micron2. The excellent preservation of microtriches proves the efficacy of the critical point drying method for preparing cestodes for study of SEM. The cytological structure of the tegument of H. nana corresponds in general to that of other tapeworms.

Animals↗
PubMed1992

Insect crossbridges, relaxed by spin-labeled nucleotide, show well-ordered 90 degrees state by X-ray diffraction and electron microscopy, but spectra of electron paramagnetic resonance probes report disorder.

The structure of glycerinated Lethocerus insect flight muscle fibers, relaxed by spin-labeled ATP and vanadate (Vi), was examined using X-ray diffraction, electron microscopy and electron paramagnetic resonance (e.p.r.) spectra. We obtained excellent relaxation of MgATP quality as determined by mechanical criteria, using vanadate trapping of 2' spin-labeled 3' deoxyATP at 3 degree C. In rigor fibers, when the diphosphate analog is bound in the absence of Vi, the probes on myosin heads are well-ordered, in agreement with electron microscopic and X-ray patterns showing that myosin heads are ordered when attached strongly to actin. In relaxed muscle, however, e.p.r. spectra report orientational disorder of bound (Vi-trapped) spin-labeled nucleotide, while electron microscopic and X-ray patterns both show well-ordered bridges at a uniform 90 degrees angle to the filament axis. The spin-labeled nucleotide orientation is highly disordered, but not completely isotropic; the slight anisotropy observed in probe spectra is consistent with a shift of approximately 10% of probes from angles close to 0 degrees to angles close to 90 degrees. Measurements of probe mobility suggest that the interaction between probe and protein remains as tight in relaxed fibers as in rigor, and thus that the disorder in relaxed fibers arises from disorders of (or within) the protein and not from disorder of the probe relative to the protein. Fixation of the relaxed fibers with glutaraldehyde did not alter any aspect of the spectrum of the Vi-trapped analog, including the slight order observed, showing that the extensive inter- and intra-molecular cross-linking of the first step of sample preparation for electron microscopy had not altered relaxed crossbridge orientations. Two models that may reconcile the apparently disparate results obtained on relaxed fibers are presented: (1) a rigid myosin head could possess considerable disorder in the regular array about the thick filament; or (2) the nucleotide site could be on a disordered, probably distal, domain of myosin, while a more proximal region is well ordered on the thick filament backbone. Our findings suggest that when e.p.r. probes signal disorder of a local site or domain, this is complementary, not contradictory, to signals of general order. The e.p.r. spectra show that a portion of the myosin molecule can be disordered at the same time as the X-ray diffraction and electron microscopy show the bulk of myosin head mass to be uniformly oriented and regularly arrayed.

Animals↗
PubMed1988

Gut-associated lymphoid tissue in the large intestine of calves. II. Electron microscopy.

Scanning electron microscopy of lymphoid tissue in the large intestine of three germfree calves (age 3, 6, and 7 days) revealed two different units: propria nodules and lymphoglandular complexes (LGC). Propria nodules had lymphoid tissue predominantly in lamina propria and were covered by distinct follicle-associated epithelium which lacked goblet cells; nodules were surrounded by wide crypts, which were also lined by follicle-associated epithelium towards the luminal side. Lymphoglandular complexes had lymphoid follicles in the tunica submucosa; epithelial diverticulae extended through the muscularis mucosae branching into the lymphoid nodule. In centers of lymphoglandular complexes, protrusions of lymphoid tissue were covered with distinct follicle-associated epithelium. By transmission electron microscopy cells compatible with M cells in the small intestine of calves and cells with characteristics of both enteroabsorptive and M cells were found. Follicle-associated epithelium of propria nodules and lymphoglandular complexes differed only in the relative frequency of cell types.

Animals↗
PubMed1998

Sutural mineralization of rat calvaria characterized by atomic-force microscopy and transmission electron microscopy.

The application of transmission electron microscopy (TEM) and atomic-force microscopy (AFM) aid the acquisition of detailed structural information on the process of hard tissue formation. The sutural mineralization of rat calvaria is taken as a model for a collagen-related mineralization system. After cryofixation or chemical fixation an anhydrous tissue preparation technique with no staining procedures is used. The atomic-force microscope and the transmission electron microscope are used for structural analysis of the mineralizing region of the sutural tissue. With the application of AFM the collagen macroperiod is shown to be well represented in the unmineralized sutural tissue. At the mineralization front the collagen fibrils are found to be thickened and to change to a characteristic stacked platelet structure. Using TEM the macroperiod is faintly visible before mineral crystallites have formed and is more prominent after the apatite crystallization has started in the fibrils. In this step a needle-like structure of the newly formed apatitic crystals is visible.

Animals↗
PubMed2002

Computer-assisted simulation of high-voltage electron microscopy using serial images recorded by conventional transmission electron microscopy.

Here we describe a computer-assisted method which, based on conventional transmission electron microscopy, renders simulated high-voltage electron micrographs. We perform arithmetic minimum filtering on stacks of aligned serial transmission electron microscopic images. In this way, the structural information of the separate images is fused into one compound image that highlights organization patterns otherwise easily overlooked or impossible to comprehend. Our method, like high-voltage electron microscopy, offers the possibility to build stereo-pairs for high-resolution three-dimensional analysis of tissue layers 1-2 microm thick. The use of background elimination and the development of a depth enhancement routine improved the three-dimensional effect and facilitated the analysis of the interior of objects. As an example, we use the method to display the distribution of axonal organelles at nodes of Ranvier and the shape and contents of a highly branched hippocampal dendritic spine.

Animals↗