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Biomedical subjects

J M Underwood

Publications and source records attributed to J M Underwood.

8 recordsLinked to original sources
PubMed2005

Pulse energy dependence of subcellular dissection by femtosecond laser pulses.

Precise dissection of cells with ultrashort laser pulses requires a clear understanding of how the onset and extent of ablation (i.e., the removal of material) depends on pulse energy. We carried out a systematic study of the energy dependence of the plasma-mediated ablation of fluorescently-labeled subcellular structures in the cytoskeleton and nuclei of fixed endothelial cells using femtosecond, near-infrared laser pulses focused through a high-numerical aperture objective lens (1.4 NA). We find that the energy threshold for photobleaching lies between 0.9 and 1.7 nJ. By comparing the changes in fluorescence with the actual material loss determined by electron microscopy, we find that the threshold for true material ablation is about 20% higher than the photobleaching threshold. This information makes it possible to use the fluorescence to determine the onset of true material ablation without resorting to electron microscopy. We confirm the precision of this technique by severing a single microtubule without disrupting the neighboring microtubules, less than 1 micrometer away.

Actins↗
PubMed1999

Lipid deposition in rat aortas with intraluminal hemispherical plug stenosis. A morphological and biophysical study.

A new method was devised to create a stenosis in the rat abdominal aorta. To restrict blood flow, a hemispherical plug was inserted into the aorta through a renal artery. This type of intrinsic (intraluminal) stenosis minimizes possible intramural effects associated with external compression or ligation which severely deform the arterial wall. In the aorta of hypercholesterolemic rats, lipid deposits were distributed in crescent-shaped patches proximal and distal to the plug, whereas lipid deposition in the opposite aortic wall was inhibited. Based on enlarged physical scale models used to study the flow field, the regions of lipid deposition were found to coincide with regions of low shear stress, stagnation, and recirculation. Shear stress was elevated at the wall opposite the plug. These results show that when confounding mural effects are minimized, lipid deposition is promoted in regions of low shear stress with recirculation and inhibited in regions of elevated shear stress.

Animals↗
PubMed1994

Electron microscopic and immunochemical studies in a patient with hepatitis C virus infection and mixed cryoglobulinemia type II.

The authors describe patient with hepatitis C virus (HCV) infection and mixed cryoglobulinemia type II in whom multiorgan failure was associated with deposits of typical, electron-microscopically visualized paracrystalline tubules in the organs studied. The patient's plasma cryoprecipitate was comprised of monoclonal IgM rheumatoid factor, polyclonal IgG, HCV RNA, and complement component C3. Of the polyclonal IgG, almost half was anti-HCV. The molar ratio between IgG and IgM was approximately 1.5 to 1. On peripheral blood films the cryoprecipitate formed cloudlike structures, which may be a useful diagnostic clue in mixed cryoglobulinemia type II. The ultrastructure of plasma cryoprecipitate and of deposits in skin, renal glomerular capillaries, and blood monocytes was identical. The cross-sectional diameter of the tubules was 30.7 +/- 1.6 nm (mean +/- 1 SD), and they appeared to be surrounded by eight electron-lucent dots. Deposition in organs of complexes containing HCV antigens and antibodies, rheumatoid factor, and C3 contributed to the multiorgan disease in this patient.

Adult↗
PubMed1990

Capillary leakage in inflammation. A study by vascular labeling.

The local injection of pure inflammatory mediators induces venular leakage. To test the effect of endogenous mediators from dying tissue on vascular leakage, the authors devised an experimental model simulating an infarct, whereby living vessels would be exposed to fragments of organs undergoing aseptic necrosis. Tissues from donor rats were implanted aseptically in the cremasteric sac. Control rats were implanted with materials deemed to be as close as possible to nonirritating: boiled tissues and spheres of Teflon or glass. At different points the rats were injected intravenously with carbon black and killed an hour later. Whole cremaster mounts showed that vascular labeling was strictly venular up to 8 hours, mixed with capillary labeling between 12 and 24 hours, and mainly or exclusively capillary at 48 hours. Histology showed an acute inflammatory infiltrate in the labeled areas. A similar but weaker labeling pattern accompanied by milder inflammation was seen in controls. These results indicate that the vascular leakage in aseptic inflammation is biphasic, first venular, then capillary; and that the capillary phase is induced by the inflammatory reaction itself, possibly through a form of diffuse angiogenesis.

Animals↗
PubMed1985

The significance of endothelial stomata and stigmata in the rat aorta. An electron microscopic study.

Perfusion of arteries with dilute silver nitrate produces in the endothelium (a) a pattern of pericellular black lines, which we earlier interpreted as a marker of the physiological electrolyte pathway (Zand et al. 1982), and (b) focal black deposits on or between the cells, either ring-shaped (stomata) or solid (stigmata). The purpose of this study was to clarify the nature and significance of these controversial structures. A glutaraldehyde-fixed normal rat aorta was perfused with silver nitrate; 17 typical stomata and stigmata were photographed en face, then studied on ultrathin serial sections. When seen en face, they fell into three groups: (I) 4 stomata in endothelial cells; (II) 6 stigmata in endothelial cells; (III) 7 stigmata on intercellular junctions. By electron microscopy, (I) all the stomata in endothelial cells corresponded to myoendothelial herniae. (II) Of the 6 stigmata in endothelial cells, 4 corresponded again to myoendothelial herniae, 2 corresponded to blebs (it seemed likely that these blebs had existed in vivo, but the possibility of a fixation artefact could not be excluded). (III) Of the 7 stigmata on intercellular junctions, one corresponded to the diapedesis of a mononuclear cell; the other 6 did not correspond to visible endothelial changes and are best interpreted as points of normally higher permeability. We conclude that stomata and stigmata (under the conditions of our experiments) can be explained in at least 4 different ways, depending in part on their location (in cells, on junctions). These ancient terms therefore remain useful for descriptive purposes, as long as it is realized that their significance in any given case must be determined by electron microscopic study.

Animals↗
PubMed1982

Endothelium and "silver lines". An electron microscopic study.

The significance of endothelial "silver lines" was studied by TEM in rat aortas after perfusion with glutaraldehyde followed by silver nitrate. Standard TEM technique proved unsatisfactory (coarse silver granules, imprecise localization, artefacts). Exposure of the silver-treated aortas to photographic fixer markedly improved the image of the deposits leaving fine, stable, uniform "residual granules" about 100 A in diameter. Most of these granules were localized along the intercellular junctions; they also tended to pool in the basement membrane beneath each junction. This image suggests that the Ag+ ions pass through the junction, and react with its contents as well as with the basement membrane beyond it. A scheme is proposed to explain the reaction of Ag+ ions with anions and negatively charged radicals within the junction. It is concluded that the "silver lines" represent not only a histochemical effect, but also the visualization of a transendothelial electrolyte pathway.

Animals↗
PubMed1978

A comparison of two indirect methods for localizing the site of urinary infection: beta glucuronidase levels and the presence of antibody-coated bacteria.

A comparison of two of the indirect methods used for localization of the site of urinary tract infection was made for 218 obstetric patients. There was no correlation between urinary beta glucuronidase activity and the presence of a positive fluorescent antibody test. The ranges of beta glucuronidase activity were so variable that this test could not differentiate between the presence of renal, bladder, or absence of infection.

Bacteria↗