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Query: UMLS:C0276640 (TEM)
 20,729 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The need to screen potential chemical pollutants for mutagenicity has increased with the increasing volume of such materials being introduced into natural water. The present study demonstrates the utility of a fish, the guppy (Poecilia reticulata), as a model test system in which water-borne chemical mutagens may be assayed for dominant lethal effects. Mature male guppies were injected with three doses of triethylenemelamine (0.1, 0.2 and 0.4 mg/kg) in addition to a control sham treatment. Each male was subsequently mated to virgin females. In an alternative test, male fish were allowed to swim in triethylenemelamine solutions of known concentration for a period of 24 h prior to being mated to virgin female guppies. 10 days following matings, females were dissected, and numbers of live and dead embryos were recorded. Significant dose effects were demonstrated by analysis of variance techniques in both the injection and the emersion tests with the results showing higher percentages of dead embryos and lower total number of embryos with increasing doses of TEM.
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PMID:Dominant lethal effects of triethylenemelamine in the guppy Poecilia reticulata. 36 86

The aim of the paper is to provide pertinent, information about scanning electron microscopy (SEM), with a detailed survey on the great possibilities of SEM which is becoming increasingly important in research and practical work of forensic medicine. The electronoptical characteristics of the method are discussed and the basic preparation methods to be selected are described. The areas of forensic medicine where these methods have already been used, as well as the results obtained, are briefly surveyed. The present state of affairs as well as personal experiences with hairs, bones, muscle and skin are described in detail. The experience with the critical point drying method is described. This method according to the reviewers, is very useful for work with hairs, bones, nails and sometimes with skin although the preparation may result in secondary destructions of the tissues of high water content to such an extent that the evaluation will be interfered with or becomes impossible. Further possibilities of these perspectivic methods are under research. The discussion of the physiological data is preceded by a historical description of the SEM and TEM systems and the basic principles of its function, which should facilitate reading of the text.
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PMID:On the possibilities of the application of scanning electron microscopy in the forensic medicine. 60 50

The water-rich phase (tissue channels) of the intersititial tissue in rat ileum, knee joint capsules, kidneys, and implanted Guyton's capsules was examined electron microscopically by the SEM of plastic injection models, and by TEM and HVEM of ferrocyanide and ferritin as tracers. It was shown that the channels do in fact exist, and are not just vacuoles. Quantitative estimations of their numbers and diameters were made. These agreed well with estimates made by other methods.
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PMID:The quantitative morphology of interstitial tissue channels in some tissues of the rat and rabbit. 72 12

This paper describes a simple technique for consistent production of clean, unwrinkled, flat thin (500-1000 A) sections for TEM and thick (1/2-1 micron) sections for HVEM mounted on Formvar-covered slot grids for use in conventional and high voltage electron microscopy. The technique centers around use of a Formvar-covered aluminum supporting rack onto which slot grids that contain sections suspended in water are placed.
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PMID:A simple procedure for mounting wrinkle-free sections on formvar-coated slot grids. 80 Jun 84

Ultrastructural analysis including scanning and transmission electron microscopic studies (SEM and TEM) were carried out on oyster gill tissue after exposure either to serum fractions from individuals homozygous or heterozygous for cystic fibrosis (CF), to comparable serum fractions from normal individuals, or to sea water. In 4 of the experiments examined topologically (SEM), the CF sera (either heterozygous or homozygous) stimulated the production of mucus that was found in close association with the cilia. The association of excessive mucus with the cell surface could be responsible, in part, for the well-known inhibition of ciliary activity by a factor in CF serum. In 3 additional SEM experiments involving shorter treatment times, very little difference could be observed between homozygous CF, heterozygous CF, and normal serum-fraction-treated oyster tissues. In parallel experiments, ultrathin sections of gill tissue were examined by means of TEM. Those samples that were responsive, as determined by TEM, displayed several characteristic features, including enlarged and partially exuded goblet cells, altered mucus structure along with twisted and matted cilia. An overall swelling of the gill filament was also observed in the responsive tissues. From TEM analysis no detectable alteration in fine structure was apparent in gill tissues that were treated with sera from heterozygous or normal individuals.
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PMID:Effects of cystic fibrosis serum ciliary inhibitor on oyster gill ultrastructure: analysis by scanning and transmission electron microscopy. 99 86

Using STEM dark field images, we have determined linear mass densities and radial density profiles of vitrified helical particles. The samples studied are: TMV, RNA-free helical polymers of TMV coat protein (TMV-P), Salmonella typhimurium bacterial flagellar filaments and Escherichia coli pili. The difference between the profiles obtained for TMV and TMV-P shows a maximum at a radius of about 4 nm, corresponding to the RNA in TMV. Of the peaks that are resolved in X-ray diffraction analysis we can resolve the ones for TMV at radii of approximately 4.2 and approximately 6.7 nm and a shoulder at approximately 7.8 nm. Density peaks in bacterial flagellar filaments appear at radii of approximately 4.2, approximately 6.5, approximately 8.5, and approximately 10.5 nm. Accurate mass data can be obtained if the filaments are embedded in ice layers of uniform thickness; their diameters need to be similar to that of the mass standard (TMV) when these data are measured in a comparative manner. Ice layers are often not uniform, and thickness variations are well revealed in STEM dark field. The signal-to-noise ratio and contrast for the transverse projections are lower than those measured for freeze-dried specimens: half an order and one order of magnitude, respectively. The thinnest uniformly thick ice layer still containing a single layer of particles is approximately 10-15 nm thicker than the particles. Radial mass density functions that are directly determined in STEM may have a potential use as substitutes for the unreliable equatorial data in helical reconstructions of TEM bright field images of vitrified specimens.
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PMID:Radial mass density functions of vitrified helical specimens determined by scanning transmission electron microscopy: their potential use as substitutes for equatorial data. 136 14

This paper describes four investigations of the olfactory mucosa of the brown trout: 1) the ultrastructure of the olfactory mucosa as revealed by scanning (SEM), conventional transmission (TEM), and high voltage (HVEM) electron microscopy; 2) light and electron-microscopic investigations of retrograde transport of the tracer macromolecule horseradish peroxidase (HRP) when applied to the cut olfactory nerve; 3) SEM and TEM investigations of the effects of olfactory nerve transection on cell populations within the olfactory epithelium; and 4) ultrastructural investigations of reversible degeneration of olfactory receptors caused by elevated copper concentrations. The trout olfactory epithelium contains five cell types: ciliated epithelial cells, ciliated olfactory receptor cells, microvillar olfactory receptor cells, supporting cells, and basal cells. The ciliated and microvillar olfactory receptor cells and a small number of basal cells are backfilled by HRP when the tracer is applied to the cut olfactory nerve. When the olfactory nerve is cut, both ciliated and microvillar olfactory receptor cells degenerate within 2 days and are morphologically intact again within 8 days. When wild trout are taken from their native stream and placed in tanks with elevated copper concentrations, ciliated and microvillar cells degenerate. Replacement of these trout into their stream of origin is followed by morphologic restoration of both types of olfactory receptor cells. Ciliated and microvillar receptor cells are primary sensory bipolar neurons whose dendrites make contact with the environment; their axons travel directly to the brain. Consequently, substances can be transported directly from the environment into the brain via these "naked neurons." Since fish cannot escape from the water in which they swim, and since that water may occasionally contain brain-toxic substances, the ability to close off--and later reopen--this anatomic gateway to the brain would confer a tremendous selective advantage upon animals that evolved the "brain-sparing" capacity to do so. Consequently, the unique regenerative powers of vertebrate olfactory receptor neurons may have their evolutionary origin in fishes.
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PMID:Ultrastructural neurobiology of the olfactory mucosa of the brown trout, Salmo trutta. 139 70

Cells cultured on transparent conductive substrates (glass coated with indium oxide) were fixed with aldehyde and osmium tetroxide and then treated with tannic acid, uranyl acetate and lead citrate. The same cell culture preparation could be sequentially studied by light microscopy (in water immersed condition), SEM (after dehydration and critical point drying) and TEM (after embedding in an epoxy resin). This method ensures the preservation of intact cell morphology, cell surface topography and intracellular structures. The treatments used render the cells conductivity and permit to carry out successfully SEM of uncoated cells cultured on conductive substrates. This method also provides a higher contrast of TEM images.
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PMID:[A method for the chemical treatment of cells for the purpose of the subsequent study of the same cell culture preparation by light, scanning and transmission electron microscopy]. 170 38

Human, rat and mouse pituitary tissues have been examined electron microscopically in transmission (TEM), scanning-transmission (STEM) and scanning (SEM) modes for the surface appearance of the secretory granules in tissue sections. Cryofixed and cryosectioned tissue showed only slightly protruding granule profiles which had a smooth surface. Cryofixed, freeze-dried and Epon embedded pituitaries, on the other hand, demonstrated swollen and furrowed surfaces over the granules after contact with water. This topography could also be seen after glutaraldehyde fixation but less after post-fixation in OsO4. The surface alterations in the sections of pituitary secretory granules are thought to be due to differences in the homogeneity of the resin infiltration, leaving resin-free openings where water can enter. It also seems probable that the Epon resin is more influenced by water than has been previously assumed, based on the findings of efficient elimination of osmium from the granules after incubation of tissue sections in water for only 10 min.
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PMID:Pituitary secretory granule topography: influence of different electron microscopic preparation procedures on the surface of Epon sections. 179 Feb 40

The lement concentrations of intracellular compartments of leaf cells of Egeria densa are estimated by X-ray microanalysis. Ultrathin frozen-dried sections are used in TEM mode. The concentrations of Na, Mg, P, Cl, K, and Ca are determined in the cell wall, cytoplasm and chloroplasts. The cell wall represents a Donnan free space with a negative fixed charge concentration of 360 mval/l water. The water fraction of the cytoplasm is between 85 and 90% and strikes the bounds of possibility of that method.
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PMID:Ion distribution in leaf cells of Egeria densa. 208 Feb 91


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