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Biomedical subjects

R B Johnson

Publications and source records attributed to R B Johnson.

At least 145 records · Page 8Linked to original sources
PubMed1985

Neonatal sepsis.

Neonates are susceptible to infection since several elements of the immune system are deficient. At present, the most common pathogens are Group B streptococci and Escherichia coli. Prolonged rupture of membranes with amnionitis is a high-risk setting. Clinical signs suggesting neonatal sepsis include respiratory distress, poor feeding, hypothermia, seizures and hypotonia. After the sepsis work-up is completed, the initial choice of antibiotics is based on the prevailing organisms and antibiotic sensitivities within the community.

Anti-Bacterial Agents↗
PubMed1984

SAR in rats exposed in 2,450-MHz circularly polarized waveguides.

Average specific absorption rates (SARs) for live rats exposed in 2,450-MHz circularly polarized waveguides were estimated from the total system loss determined from measurements using five power meters, and a correction factor representing actual SAR/apparent SAR. The actual SAR was measured by twin-well calorimetry and the apparent SAR by power meters. Values were obtained for carcasses of various body masses for five orientations. The average SAR with free movement in the cages changed less than threefold as the rats grew from 200 to 700 g. The ratio of peak to average SAR in the body was less than 3. These results indicate relatively constant energy disposition in rats exposed in the circularly polarized waveguide.

Animals↗
PubMed1983

Specificity of fibronectin--fibrin cross-linking.

Our experiments indicate that (1) non-covalent binding of fibronectin to fibrin is mediated by sites in a 27 kd NH2-terminal region and a 31 kd COOH-terminal region of fibronectin; (2) the 31 kd region is probably present in both chains of the fibronectin dimer; and (3) covalent (factor XIIIa-mediated) cross-linking of fibronectin and fibrin is between a glutaminyl residue in the 27 kd region of fibronectin and a lysyl residue in the COOH-terminal two-thirds of the fibrin alpha chain.

Amino Acid Sequence↗
PubMed1983

In vitro formation of disulfide-bonded fibronectin multimers.

Fibronectin purified from a plasma protein side fraction in the absence of denaturant contained 1.5 to 1.9 cryptic free sulfhydryl groups per 200- to 250-kDa subunit. Exposure of sulfhydryl groups in physiologic salt solutions required at least 1 M guanidine, and 3 M guanidine was required for optimal exposure. The sulfhydryl groups were not exposed by collagen, a fibronectin-binding collagen fragment, fibrinogen, heparin, hyaluronic acid, calcium ion, EDTA, deoxycholate, or methylamine. One- and two-dimensional gel electrophoresis indicated that a molecule of 40-60 kDa was disulfide-bonded to a minor portion of the fibronectin in whole human plasma and in preparations of purified fibronectin. In addition, traces of disulfide-bonded multimers were present in preparations of purified fibronectin. The proportion of fibronectin in disulfide-bonded multimers increased in guanidine-containing solutions. Compared to dimeric fibronectin, these multimers had limited solubility in physiologic buffers, could be readily cross-linked by Factor XIIIa, and exhibited altered tryptic susceptibility. In free sulfhydryl groups were blocked by prior alkylation with N-ethylmaleimide or iodoacetamide, fibronectin did not form disulfide-bonded multimers in guanidine-containing solutions. The patterns of altered tryptic susceptibility and cyanide cleavage suggested that multimer formation is mediated by both sulfhydryls of fibronectin. The transition from dimeric to multimeric fibronectin can serve as a model for the formation of disulfide-bonded fibronectin multimers in the extracellular matrix.

Disulfides↗
PubMed1983

A new look at the mineralized and unmineralized components of intraosseous fibers of the interdental bone of the mouse.

The degree of mineralization of deeply embedded intraosseous fibers has been the subject of speculation. However, there were few available descriptive morphological studies addressing this question. The present study demonstrated that morphological differences were evident between intraosseous fibers of different levels of the interdental septum. It also revealed that the degree of mineralization of intraosseous fibers was often different at the wall of the tooth socket in comparison to that at deeper levels of interdental bone. Except in the superior crestal third, intraosseous fibers became less mineralized as they passed from the wall of the tooth socket to the midline of the interdental septum. They were surrounded by sheaths throughout their distribution. It was concluded that there might be significant differences in the morphology of intraosseous fibers of the mouse in comparison to the morphology of intraosseous fibers of the dog, which have previously been described in detail.

Alveolar Process↗
PubMed1983

A new technique for exposure of osteocytes and transalveolar fibres of the interdental septum in the mouse for scanning electron microscopy.

The technique selectively removes the fibrous component of the interdental septum. Mandibles were fixed, demineralized and incubated at 37 degrees C in 0.1 per cent bacterial collagenase. Samples were post-fixed in 2 per cent buffered osmium tetroxide for 24 h prior to dehydration in ascending grades of acetones. While in pure acetone, tissue was ultrasonicated at 80 kHz for 5 min and conventionally processed for scanning electron microscopy. Ultrasonication of tissue without prior collagenase digestion did not expose transalveolar fibres in their entirety. After 6 h exposure to collagenase followed by ultrasonication, bone matrix and osteocytes were removed exposing transalveolar fibres which passed through the interdental septum without interruption, becoming continuous with the periodontium of the adjacent tooth.

Alveolar Process↗
PubMed1983

Synthetic analogues of the N-terminal lipid part of bacterial lipoprotein are B-lymphocyte mitogens in vitro and in vivo.

Two analogues of the N-terminal part of bacterial lipoprotein, S-[2,3-bis(palmitoyloxy)-(2RS)propyl]-N-palmitoyl-(R)-cysteine methyl ester ("tripalmitoyl cysteine") and S [-2,3-bis(palmitoyloxy)-(2RS)-propyl]-N-palmitoyl-(R)-cysteinyl-(S)-seryl-(S)-seryl-(S)-asparaginyl-(S)-alanine ("tripalmitoyl pentapeptide") were synthesized and tested for mitogenic activity. The compounds were potent mitogens towards mouse spleen cell cultures, as measured by 3H-thymidine incorporation and by hemolytic plaque assays. This activity was not dependent on the presence of serum. Tripalmitoyl pentapeptide had little, if any, effect on thymocytes. When injected intravenously into Balb/c mice, the synthetic compounds induced splenomegaly and polyclonal B-cell activation, the latter was evident from an increase in the number of plaque-forming cells against trinitrophenylated sheep red blood cells. Thus, a synthetic fragment of a bacterial surface component was shown to exhibit marked biological activity in vitro as well as in vivo.

Animals↗
PubMed1983

The role of antibody in the interaction of Salmonella and listeria with peritoneal macrophages.

That in vitro killing by normal and activated macrophages of S. typhimurium and other gram-negative organisms is dependent on the presence of antibody has been confirmed. It has been shown that antibody is required for the binding of S. typhimurium to the surfaces of macrophages. This binding can be inhibited by the Fc portion of immunoglobulin, indicating that the Fc receptors on macrophages are used for binding S. typhimurium. It has also been confirmed that antibody does not appear to be necessary for killing of L. monocytogenes to occur. The organisms bind to the surface of macrophages by different receptors. Binding of L. monocytogenes occurs in the absence of added antibody and Fc fragments of immunoglobulin do not affect the binding. Attachment can be inhibited, however, by removal of divalent cations, a treatment that has no effect on antibody-mediated binding as, under these conditions, the binding of L. monocytogenes to macrophages can be enhanced by antibody. The significance of these findings is discussed.

Animals↗
PubMed1983

Polyclonal activation of B-lymphocytes in vivo by Salmonella typhimurium lipoprotein.

Lipoprotein prepared from the outer membrane of Salmonella typhimurium is a polyclonal activator of murine B-lymphocytes. It was shown to be mitogenic for splenic cultures, stimulating increased incorporation of [3H]thymidine into DNA. When injected intravenously into mice, the lipoprotein induced splenomegaly and polyclonal B-cell activation. The latter was evident from an increase in the number of plaque-forming cells against trinitrophenylated sheep erythrocytes. Similar results were obtained with Escherichia coli lipoprotein.

Animals↗
PubMed1983

Transalveolar fibers of the mouse periodontium: a scanning electron microscopic study.

Transalveolar fibers have been described by many authors using techniques of light microscopy. However, a study of these fibers using techniques of scanning electron microscopy has not been reported. In the present study, scanning electron microscopic techniques revealed that transalveolar fibers were composed of a bundle of smaller fibers. This fiber bundle passed through channels in bone and was attached to the bone by anchoring fibers. Transalveolar fibers branched within bone. Near points of branching, channels were often dilated. Channels were continuous with the connective tissue space of the periodontal ligament at the bone margin. The results presented herein suggested a revised concept for the anchorage of fibers of the periodontal ligament to bone.

Animals↗
PubMed1983

The relationship of proteoglycans to developing transalveolar fibres in the alveolar bone of the mouse.

Proteoglycans are of interest because of their complex role in the development and maintenance of connective tissues. The present study demonstrates changes in the distribution of proteoglycans in the developing alveolar bone of the mouse using techniques of light and high-voltage electron microscopy. In early development proteoglycans are uniformly distributed throughout the interdental septum. By day 25 there is a loss of proteoglycans, probably as a result of mineralization and the maturation of the collagen of transalveolar fibres. By day 45 proteoglycans are distributed only in tissues adjacent to transalveolar fibres. These proteoglycans occupy the channels surrounding transalveolar fibres and the adjacent bone matrix. It is proposed by the authors that these proteoglycans are involved in the maintenance of the collagen of the transalveolar fibres. Because of the absence of fibroblasts adjacent to transalveolar fibres, proteoglycans are thought to be essential carriers of tropocollagen to these large fibres.

Alveolar Process↗
PubMed1983

A re-examination of the osteocytic network of interdental bone.

A new method for removal of bone minerals and matrix was used in this study to expose osteocytes and osteocytic processes for examination by techniques of scanning electron microscopy. Osteocytes demonstrated more numerous Type II junctions with osteocytic processes than had previously been recognized. The network of osteocytic processes was extensive and exhibited several structural modifications for more efficient transport: rings and branching. Adjacent osteocytes were connected by osteocytic processes suggesting a functional syncytium. The study suggests that the network of osteocytes and osteocytic processes is more extensive and complex than previously recognized.

Animals↗
PubMed1982

Pyoderma gangrenosum. Occurrence with altered cellular immunity and a circulating serum factor.

Aberrations of cellular immune functions in pyoderma gangrenosum (PG) may lead to nonspecific activation of inflammatory cells or to an imbalance of suppression leading to autoaggression (chronic ulceration). A patient with severe unremitting PG had anergy to a battery of seven skin test antigens. Mixed lymphocyte reactions, autologous mixed lymphocyte reactions, lymphocyte proliferative responses to antigens, and the production of leukocyte inhibitory factor were substantially suppressed, while the lymphocyte responses to mitogens were unaffected. Quantitative immunoglobulin and complement levels were normal. The inhibition of cellular immune functions was mediated by a factor in the patient's serum. This factor also inhibited lymphocyte functions of normal unrelated control subjects. Preliminary studies demonstrated that the factor is nondialyzable, heat stable, and not adsorbed by Staphylococcus A protein. Pulse therapy with large doses of corticosteroids resulted in dramatic clinical improvement.

Adult↗
PubMed1982

Development of intraosseous fibers of the mouse periodontium: a high-voltage electron microscopic study.

Development of intraosseous fibers was studied in mandibles of Swiss white mice, age 17 days to 45 days. Light microscopic (LM) and high-voltage electron microscopic (HVEM) techniques were used. In LM, Wilder's reticular stain revealed intraosseous fibers throughout the interdental septum by day 17. fibers were composed of unit collagen fibrils with abundant interfibrillar matrix. As development proceeded, fibers exhibited less interfibrillar matrix. Channels surrounding the intraosseous fibers became evident. Anchoring fibers attached the intraosseous fiber to bone. Fibroblasts appeared to be absent, suggesting that maintenance of the intraosseous fiber might be the function of the osteocyte. The presence of intraosseous fibers suggested a reevaluation of the fibrous attachment of teeth to bone. The concept of intraosseous fibers may simplify concepts of tooth movement and approximal drift.

Animals↗