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Biomedical subjects

S K Chung

Publications and source records attributed to S K Chung.

At least 109 records · Page 6Linked to original sources
PubMed1985

Immunocytochemical localization of actin in dendritic spines of the cerebral cortex using colloidal gold as a probe.

Immunocytochemical localization of actin in rat cerebral cortex embedded in the resin LR White was performed using 5 nm colloidal gold as a probe. Antigenicity is maintained throughout the embedding procedure and the low electron opacity of LR White permits fine filamentous structures to be visualized. Control experiments included incubating the sections with normal goat serum or mouse IgG instead of the primary antibody, preadsorbing the antibody with actin from bovine muscle or liver acetone powder, and heat treating the primary antibody. Immunoreactive actin was identified primarily in dendritic spines, particularly in the postsynaptic density (PSD), the subsynaptic web, and the spine apparatus and endothelial and smooth muscle cells of blood vessels. Within dendritic spines, actin which is labeled in the PSD is in continuity with the filaments of the subsynaptic web. These filaments, in turn, are in continuity with the spine apparatus and/or the spine membranes adjacent to the PSD. The PSD may therefore function like other submembranous filamentous arrays which communicate events occurring at the membrane, in this case, the postsynaptic membrane, to the underlying cytoskeletal network, i.e., the subsynaptic web of the spine. It is also suggested that the actin present in the spine may play a role in changes in spine shape and synaptic curvature. Some actin was also seen in the presynaptic process in association with synaptic vesicles, the filamentous network that is contiguous with the synaptic vesicle membrane, and the presynaptic dense projections. Actin may be involved in dynamic processes in the presynaptic ending which include vesicle translocation.

Actins↗
PubMed1984

Alteration by estrogen of the nucleoli in nerve cells of the rat hypothalamus.

Estrogen is accumulated from the blood by nerve cells in the ventromedial nucleus of the hypothalamus and can facilitate female reproductive behavior by acting on this region of the brain. This cell group was examined in ovariectomized female rats, given estrogen or control treatment, by use of light and electron microscopy. A significantly greater portion of the nerve cells in the estrogen-treated animals had protuberances on their nucleolar surfaces, apparent under the light microscope. The fine structure of such protuberances included dense, aggregated material, which is shown to contain DNA by the sodium tungstate staining technique. Because increased numbers of such protuberances were found in nuclei of cells of the experimental group where previous studies demonstrated a significant increase in ultrastructural signs of biosynthetic activity, they may be associated with increased RNA synthesis. Thus, they could indicate, ultrastructurally, increased synthetic rates for RNA in nerve cells through which estrogen promotes reproductive behavior.

Animals↗
PubMed1984

Ultrastructure and enzyme digestion of nucleoli and associated structures in hypothalamic nerve cells viewed in resinless sections.

Estrogen has been shown to affect ventromedial hypothalamic (VMH) nerve cell nucleoli in ovariectomized rats, by causing an increase in the number of electron-dense aggregates associated with nucleoli. In order to characterize these nucleolus-associated structures and other nuclear components, we examined the ultrastructure of ventromedial hypothalamic nucleoli and nuclei revealed by enzyme digestions (pepsin, RNase and DNase) in resinless thin sections. Digestion by pepsin did not cause obvious alterations in the morphology of the nucleolus or its related structures. Pepsin treatment followed by RNase, however, reduced the density of the nucleolus, while that of the nucleolus-associated structure and other related structures remained unchanged. Conversely pepsin treatment followed by DNase, reduced the density of nucleolus-associated and other chromatin structures, but had no effect on the density of the nucleolus. Pepsin treatment followed by RNase and then DNase treatment, reduced the density of the nucleolus and nucleolus-associated structures. A residual nucleolus and nucleolus-associated structure remained after this treatment. Stereo viewing of resinless sections shows that the nucleolus, its associated structures, and other related structures, are associated with fine filaments that may comprise the nuclear matrix. The nucleolus-associated structure containing DNA may direct RNA synthesis at an increased rate in estrogen-treated hypothalamic cells.

Animals↗
PubMed1982

Comparison of the antibacterial activity of norfloxacin (MK 0366, AM 715), a new organic acid, with that of other orally absorbed chemotherapeutic agents.

425 randomly selected, fresh clinical isolates were tested for susceptibility to norfloxacin and other orally absorbed agents, i.e. amoxicillin, ampicillin, carbenicillin (available commercially as the indanyl ester), cefaclor, cinoxacin, erythromycin, nalidixic acid, penicillin G, tetracycline, trimethoprim and co-trimoxazole. The results have shown norfloxacin to be the most potent agent in vitro against representative members of the family Enterobacteriaceae, Staphylococcus aureus, Pseudomanas aeruginosa, Acinetobacter spp., Neisseria gonorrhoeae and Haemophilus influenzae. Ninety percent of the isolates in these groups of bacteria were inhibited by less than 1 mg/l, 2 mg/l, 8 mg/l, 32 mg/l, 0.06 mg/l and 0.25 mg/l of norfloxacin, respectively. Although norfloxacin inhibited most streptococci and Ureaplasma at a concentration of 8 mg/l or less, penicillin G proved to be the most active against Streptococcus pygenes and Streptococcus pneumoniae; trimethoprim was the most active against Streptococcus faecalis, and tetracycline the most active against Ureaplasma.

Acinetobacter↗
PubMedDate not supplied

N-butyl-2-cyanoacrylate pulmonary embolism after endoscopic injection sclerotherapy for gastric variceal bleeding.

PURPOSE: The purpose of this work was to describe the radiologic and clinical manifestations of n-butyl-2-cyanoacrylate pulmonary embolism (PE) after endoscopic injection sclerotherapy (EIS) for gastric variceal bleeding. METHOD: From 1992 to 1999, the medical records of 140 patients who had undergone EIS using n-butyl-2-cyanoacrylate were reviewed for identification of respiratory symptoms and amount of injection, and their pre- and postprocedure chest radiographs were reviewed to identify PE. In patients with PE, pre- and postprocedure chest radiographs (6/6), chest CT scans (3/6), lung perfusion scans (3/6), and follow-up chest radiographs (6/6) were analyzed retrospectively. RESULTS: Radiographically evident PE was observed in 6 (4.3%) of 140 patients. In comparison with patients without emboli, these patients received a higher mean volume of injection (4.2 vs. 1.8 ml) (p = 0.0011). Four of the six patients with pulmonary emboli had respiratory symptoms. Chest radiographs and CT scans showed unusual tubular or nodular, radiopaque pulmonary emboli along the pulmonary vessels. Multiple peripheral, wedge-shaped, subsegmental perfusion defects were seen on perfusion lung scans. In five of six patients, the radiographic abnormalities showed complete or partial resolution. There were no fatalities directly associated with PE. CONCLUSION: Radiographically evident PEs are uncommonly observed following EIS and appear to be more common in patients receiving a higher volume of liquid acrylate. Affected patients were either mildly symptomatic or asymptomatic, and there were no direct fatalities of this complication.

Adolescent↗