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

We have tested the effects of TEM in 3 strains of mice using the sperm morphology assay. In addition, we have made an attempt to evaluate this test system with respect to experimental design, statistical problems and possible interlaboratory differences. Treatment with TEM results in significant increases in the percent of abnormally shaped sperm. These increases are readily detectable in sperm treated as spermatocytes and spermatogonial stages. Our data indicate possible problems associated with inter-laboratory variation in slide analysis. We have found that despite the introduction of such sources of variation, our data were consistent with respect to the effects of TEM. Another area of concern in the sperm morphology test is the presence of "outlier" animals. In our study, such animals comprised 4% of the total number of animals considered. Statistical analysis of the slides from these animals have shown that this problem can be dealt with and that when recognized as such, "outliers" do not effect the outcome of the sperm morphology assay.
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PMID:Increased frequencies of aberrant sperm as indicators of mutagenic damage in mice. 44 Mar 24

Perforating canals arise exclusively from junctional canals just above the reserve zone and they do not branch after entering the proliferative zone. They are uniformly spaced and arranged in parallel array. The cartilage canals terminate near the beginning of the zone of hypertrophic cartilage cells. Vascular components within the perforating canals consist of a central arteriole surrounded by enlarged, interconnected capillaries which are individually in contact with the adjacent cartilage matrix. TEM shows that the capillary endothelium is extremely attenuated, possesses numerous fenestrations and lacks a continuous basement membrane. The central arteriole is enlarged through the midpart of the canal and then narrows to communicate with the capillaries near the bottom of the canal. The large capillaries ascend from their point of origin and recombine near the top of the growth plate to exit as a single venule. The vascular arrangement therefore describes a system in which the outgoing blood runs in close proximity, but counter to, the incoming blood. This vascular arrangement within the perforating cartilage canal would most likely allow the zone of maturing cartilage cells to receive the highest concentration of nutrients.
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PMID:Morphology of the perforating cartilage canals in the proximal tibial growth plate of the chick. 44 60

Previous light microscopic studies showed that perfusion of the hamster jejunum with 4.8% ethanol (ethanol period) in vivo produced fluid-filled subepithelial blisters (blebs) on the villi. These blebs had virtually disappeared within 45 min after the discontinuation of the ethanol perfusion (recovery period). The present study examined these ethanol-induced changes in the jejunum by scanning (SEM) and transmission (TEM) electron microscopy. TEM revealed that ethanol did not damage epithelial cells in areas where blebs were not present. In these areas the basal surfaces of the epithelial cells were attached to the basal lamina, and the lateral intercellular spaces (LIS) were open. In the areas where blebs formed, the stretched epithelial cells which covered the blebs lost their basal anchoring and so could not maintain their LIS. Both SEM and TEM indicate that there was a decrease in the quantity of glycocalyx at the surfaces of cells which covered blebs. Our findings indicate that ethanol does not directly damage epithelial cells but that the cellular damage is due to detachment over the blebs. It is likely that ethanol at first traverses the epithelial layer and then produces stasis in the villus core. Continued fluid transport by the epithelial layer in the presence of statis results in accumulation of the fluid and widely dilated LIS. With subsequent enlargement of the LIS the bases of the cells detach from the basal lamina and blebs are formed.
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PMID:The ultrastructure of blebs induced in the hamster jejunum by ethanol. 44 32

Maturation ameloblasts of developing molar teeth of the rate were studied by both scanning and transmission electron microscopy. After fixation, teeth were frozen and split. One face of the fractured tooth was used for SEM, the other for TEM. It was found that in some regions proximal junctional complexes separate the interameloblast space from the intercellular space of the papillary layer. Thereby an intercellular ameloblastic compartment is delineated which in some specimens contains a substance interpreted to be colloidal. Elsewhere the proximal junctions of ameloblasts are not present and free communication between the extracellular spaces is evident. The apical pole of ameloblasts varies in structure. Over some areas there is a distinct distal border zone with membranous infoldings which in some regions resembles a striated or ruffled border, but in other regions the membranes show whorl configurations. The distal border zone also contains granules with flocculent material. Elsewhere the ameloblasts display no distal border zone and the cells show a smooth membrane (except for pinocytotic vesicles and hemidesmosomes) facing the enamel surface. The lateral surface of ameloblasts exhibits a variety of surface configurations similar to but not as pronounced as those reported previously in rat incisor maturation ameloblasts.
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PMID:A correlated scanning and transmission electron microscopic study of maturation ameloblasts in developing molar teeth of rats. 45 7

The plasmids from six clinical strains of Salmonella wien have been characterized. All the S. wien strains were found to carry three types of plasmids: an IncFI R-Tc Cm Km Ap (resistance to tetracycline, chloramphenicol, kanamycin, and ampicillin) plasmid, either conjugative or nonconjugative, of large size (90 to 100 megadaltons); an R-Ap Su Sm (resistance to ampicillin, sulfonamide, and streptomycin) plasmid of 9 megadaltons; and a very small (1.4 megadaltons) cryptic plasmid. The characteristics of conjugative R plasmids, recombinant between F'lac pro and the FI nonconjugative plasmid, indicated that regions coding for the donor phenotype were present on this plasmid. The molecular and genetic features of the R plasmids were very close to those described for the R plasmids isolated from S. wien strains of different origin. This fact supported the hypothesis of a clonal distribution of this serotype in Algeria and Europe. The analysis used to identify transposable elements showed the presence of only TnA elements, which were located on both the R-Tc Cm Km Ap and R-Ap Su Sm plasmids. They contained the structural gene for a TEM-type beta-lactamase and had translocation properties analogous to those reported for other TnA's.
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PMID:Plasmids and transposable elements in Salmonella wien. 45 8

Cells from the new strain IMR-90 were examined by scanning (SEM) and transmission (TEM) electron microscopy at early, middle, and late population doubling levels. The cells are characteristically flattened and elongated and arranged in clusters from 1 to several cells thick. Long thin processes extend from the poles and sides of the cells. The number of blebs and microvilli on the cell surface varies. In later population doubling level (PDL) cultures, a larger number of cells have greater quantities of microvilli on their surface. It is suggested that the increased number of microvilli might represent an increased level of differentiation. By TEM the cells typically have elongated to oval shaped nuclei which are sometimes deeply invaginated. The cytoplasm contains a well developed Golgi region, elongated mitochondria, microtubules, filaments, a variety of vesicles, vacuoles and dense bodies and large amounts of RNA in the form of granular endoplasmic reticulum and ribosomes. Cytoplasmic appearance, particularly the number of dense bodies, varies widely at all PDL. With increasing PDL, cells tend to have nuclei with more condensed chromatin, and a cytoplasm containing less mitochondria and granular endoplasmic reticulum and more dense bodies. Also at later PDL there is a higher frequency of cells containing long, thin dense mitochondria as well as bizarre shaped mitochondria. In older populations there are many cells in a state of filamentous degeneration. Cells with large numbbers of surface projections (microvilli) tend to be correlated with an osmiophilic cytoplasm containing many filaments and numerous dense bodies.
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PMID:Fine structure of IMR-90 cells in culture as examined by scanning and transmission electron microscopy. 47 Apr 67

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

We have observed, by light and electron microscopy, fibroblast-like cells which appear to be involved in collagen fiber and filament degradation. These cells are most prominent in the dermis of mature hypertrophic scars which were clinically observed to be in the remodeling phase of wound repair. Total incorporation of collagen filaments within cellular vacuoles, as seen by TEM, appears to precede the enzymatic degradation of the collagen. Cytoplasmic contractile bundles and/or collagen filament remnants found within residual lysosomes were also seen in many of these cells. Evidence of structural reorganization within the tissue was observed by means of SEM. These cells appear to be similar to osteoclasts in function: thus we propose to name them "fibroclasts" and "myofibroclasts."
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PMID:Ultrastructural evidence for the presence of "fibroclasts" and "myofibroclasts" in wound healing tissues. 49 Jun 89

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

High resolution "low-loss" scanning electron microscopy is a relatively new technique which permits an investigator to examine structures that were formerly visualized exclusively by transmission electron microscopy [1]. This paper presents some images of intact bacterial virus T7, viewed at the ultrastructural level. Due to the high resolution capibility of this technique, and the demanding physical prerequisites for visualization of the specimen, current specimen preparation techniques were modified in order to permit 1--2 nm resolution in surface mode. Using this method of microscopy, it is possible to view clearly this small bacteriophage (the smallest of the T-coliphages), adsorbed to its host bacterium, in a scanning mode at magnification (and resolution) comparable to TEM without resorting to the use of replicas, or reconstruction of a two-dimensional image.
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PMID:High resolution SEM of bacterial virus T7. 49 34


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