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

The structure of nitrogen-fixing nodules produced by Rhizobium infection of the non-legume Parasponia andersonii was examined by light and electron (both SEM and TEM) microscopy. Comparisons were made with the nodules previously described on P. rugosa. Like the nodules on different non-legumes formed by other types of endophytes, the Rhizobium nodules on Parasponia resembled modified roots by having a central vascular bundle surrounded by an endophyte-infected zone. The intimate association between the Rhizobium and the host nodule cell was compared with the Rhizobium association found in legumes. The rhizobia were not released from the infection thread as happens in the legume. The infection thread, which propagates the Rhizobium infection to new cells, was transformed within a nodule cell from a darkly stained (light microscopy) or very electron-dense (TEM) structure to a number of thread types. The walls of the threads varied greatly in thickness and often the thread structures were without rigid walls and were only enclosed by a plasma membrane. If the rhizobia are transformed into bacteroids, as in the legumes, it would have to occur when the threads had reached their mature size, when bacterial division had ceased. Nitrogen fixation was considered to occur in all thread types.
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PMID:Structure of nitrogen-fixing nodules formed by Rhizobium on roots of Parasponia andersonii Planch. 47 39

Plastic coverslips made of polymethylpentene serve as excellent substrates for growth of bovine endothelial cells, and are easily processed for both transmission (TEM) and scanning (SEM) electron microscopy. Portions of the same coverslip (monolayer) are used for both SEM and TEM examination and are fixed, postfixed, and dehydrated as a single entity. The portion of the coverslip for SEM is then excised, critical point dried, and mounted for sputter coating prior to viewing. The remaining piece of coverslip used for TEM is Epon-Araldite embedded, polymerized, separated from the coverslip by liquid nitrogen immersion, and sectioned either "en face" or in cross section for viewing. Coated glass coverslips are not required and organic solvents such as propylene oxide, acetone, and amyl acetate can be used for dehydration and infiltration. Furthermore, specimens do not require re-embedding or blocks to be glued onto blank capsules before sectioning. The number of cells needed to achieve a monolayer is significantly reduced compared to the usual culture flasks, but are abundant enough to assess ultrastructural changes accurately. Support films may be required to prevent folding of the ultrathin section which can obstruct viewing of cells located on the edge of the section.
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PMID:Transmission and scanning electron microscopy of cell monolayers grown on polymethylpentene coverslips. 49 32

Fine structural alterations of liver sinusoids in young and adult albino rats breathing 6% oxygen in nitrogen at normal atmospheric pressure for periods from 3 to 30 h were described by use of TEM and SEM. After short-term hypoxia the fenestrated areas of endothelial cells were partially destroyed. After long--term hypoxia wide gaps could be visualized in the endothelium, too. In the liver specimens of all hypoxic animals electron lucent membrane bounded blebs arose from the endothelial lining. Cytoplasmic protrusions of hepatocytes bulged into the sinusoidal lumen. In the space of Disse and the sinusoidal lumen bleblike corpuscles and parts of cytoplasmic membrane being discharged from liver cell vacuoles could be observed. The find structure of liver sinusoids in hypoxia was very similar in young and adult albino rats. The findings suggest a discharge of metabolites and cellular components from endothelial cells and hepatocytes in a state of energetic insufficiency by forming cellular blebs and protrusions. It was supposed, that the combined effects of hypoxia and shearing of circulating blood were responsible for the development of holes and gaps in the endothelial lining.
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PMID:[On the influence of hypoxia on the sinus endothelial cells of rat liver. A scanning and transmission electron microscopic investigation (author's transl)]. 82 Dec 46

Samples of human semen frozen in liquid nitrogen ( - 196 degrees C) with no glycerol, 5 and 10% glycerol were compared with samples that were untreated, with 10% glycerol but not frozen, and spermatozoa frozen at -20 degrees C. SEM and TEM of the samples indicates that 10% glycerol caused fewer surface changes of the spermatozoa than other treatments. Motility counts after the various freezing treatments were also highest when 10% glycerol was used as the cryoprotectant. Nonetheless, cryopreservation is detrimental to spermatozoa and often causes considerable damage to the acrosome with a leakage of the acrosomal contents.
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PMID:Surface structure of spermatozoa frozen for artificial insemination. 88 75

Soft X-ray contact absorption edge images of unfixed, unstained biological specimens were made using monochromatic synchrotron radiation. X-ray contact replicas of unfixed, hydrated biological specimens at the nitrogen absorption edge and above and below the CaLIII absorption edge were compared to comparative conventional morphological and elemental high-resolution imaging methods (scanning and transmission electron microscopy, TEM-histochemistry and TEM-X-ray microanalysis). Soft X-ray absorption edge images made above the calcium absorption edge clearly revealed morphological detail and identified regions ladened with calcium as verified by TEM histochemistry of identical spores. Similarly, nitrogen absorption edge images identified residual nitrogenous material in the spore resuspension medium, and non-viable spores with nitrogen loss due to protoplast disaggregation.
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PMID:Biological calcium absorption edge imaging using monochromatic synchrotron radiation. 175 14

With foam components removed, mixed saliva from three donors were solidified in liquid nitrogen and sectioned, mounted, and fixed. Examination by transmission (TEM) and scanning (SEM) electron microscopy and energy-dispersive X-ray (EDAX) analysis were performed for paraformaldehyde-fixed sections, some of which were OsO4-postfixed. The TEM and certain SEM examinations showed the presence of fine and dense salivary network structures, seemingly originating from the major fibrous components. In OsO4-treated sections, TEM pictures showed reticulated arrangements with open cellular diameters down to 0.2 microns. The EDAX analyses particularly showed the presence of Ca, Fe, K, P, and S, with increased Ca readings in major components. Untreated sections showed that strands, with diameters of more than 1-2 microns, had more electron-dense central portions than peripheries and sometimes had interior, very electron-dense, granules. The observed features indicate that saliva has internal structures consistent with its colloid chemical characteristics.
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PMID:Electron microscopic studies of human mixed saliva. 271 56

As a pilot trial, a semen sample was diluted with a glucose-citrate-egg yolk diluent and frozen in 0.5 ml PVC paillettes in liquid nitrogen vapor. Motility and acrosome integrity of the sample were evaluated before and after freezing, and longevity was monitored up to 6 h postthaw. Acrosome integrity was assessed by comparing Spermac-stained thin smears with TEM. Acrosome damage was found to be progressive, and four main types of acrosome state were identified and illustrated.
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PMID:Ultrastructural changes in the acrosome of human sperm during freezing and thawing: a pilot trial. 382 89

Normal and ischemic myocardium was prepared by slicing and cryofracture techniques for examination with the SEM. The tissues were dehydrated in ethanol and Freon 113 (slicing method) or were cryofractured in Freon 113 cooled with liquid nitrogen, followed by critical point drying and coating with gold and palladium. Some osmicated tissue pieces were treated with thiocarbohydrazide for examination without metal coating. Some hearts were infiltrated with silver particles and were examined with backscattered electron imaging technique (BSI). The cryofractured tissue provided the most useful and consistent surface features of the cell organelles with a minimum of mechanical disorder compared to other methods. Although the myocardium prepared by slicing method revealed the interior of the cells, it contained several frayed edges and loose myofibrils making interpretation of the ischemic myocardium difficult. The normal cells exhibited myofibrils covered by transverse tubules at the level of Z bands as confirmed by BSI using silver particles as an extracellular tracer and numerous oval to elongated mitochondria located between the myofibrils. An extensive network of tubules (sarcoplasmic reticulum) over the sarcomeres and nuclei were observed. The changes observed by SEM in the ischemic hearts were consistent with those seen in TEM. With prolonged coronary ligation the changes became obvious. The T-tubules were often broken and nuclei were distorted. The myofibrils were disorganized and formed homogeneous bands. These SEM studies suggest that myocardium prepared by cryofracture technique yields information on normal and ischemic cell structure consistent with data obtained by TEM.
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PMID:Preparation of normal and ischemic myocardial tissue for scanning electron microscopy. 716 67

An attempt to determine the ideal temperature and duration of storage of human foetal chondrocytes yielded highly cellular preparations with no alteration in morphology or loss of viability. Initial digestion with activated papain was followed by incubation in 0.5 per cent collagenase. Trypan blue exclusion test revealed a viability count of 95-99 per cent and radioactive thymidine uptake a corresponding labelling index. On TEM no subcellular damage was evident. The isolated viable chondrocytes were further banked at varying temperatures of +4 degrees, -4 degrees, -30 degrees, -79 degrees and -196 degrees C, in Eagles MEM with 10 per cent dimethyl sulfoxide. Post storage morphology and viability of these cells, thawed after durations of 20 h, 1 wk, 1, 2, 3, 4 and 6 months, were compared with prestorage readings in an attempt to define the ideal temperature for banking. Storage in liquid nitrogen at -196 degrees C demonstrated excellent preservation even at the end of six months with minimal subcellular change. Electron microscopy and labelling index were found to be superior to Trypan blue exclusion test in assessing the stored chondrocytes for retention of their functions.
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PMID:Isolation & cryo-preservation of human foetal articular chondrocytes. 813 36

Four Trypanosoma species were examined for damage following prolonged storage in liquid nitrogen (-196 degrees C). The stabilates were successfully recovered after a cryopreservation period of approximately 30 years. The structure of specimens was studied by means of light microscopy and scanning (SEM) and transmission (TEM) electron microscopy. All of the species tested--T. evansi, T. equinum, T. brucei, and T. congolense--proved to be infective to mice. However, as compared with controls, the trypomastigote bloodstream forms, which had been frozen and later recovered, showed clear differences. Formerly deep-frozen organisms usually appeared to have shrunk as a result of solution effects, which occur during freezing and thawing. Ultrastructural changes such as separation of the cytoplasm from the pellicle, the occurrence of large vacuoles in the cytoplasm and karyoplasm, a loss of cytoplasmatic ribosomes, membrane injuries, enlargement of the flagellar pocket, and denaturation of chromatin became obvious. The extent of the ultrastructural alterations appeared to be much greater after a cryopreservation period of approximately 30 years than those previously reported after a 13-year storage period. These changes, however, did not result in a complete loss of infectivity to mice.
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PMID:Ultrastructural changes on various Trypanosoma spp. after a 30-year storage period in liquid nitrogen. 889 7


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