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Biomedical subjects

R Rapp

Publications and source records attributed to R Rapp.

At least 37 records · Page 2Linked to original sources
PubMed1993

An investigation of accessory foramina in furcation areas of human primary molars: Part 1. SEM observations of frequency, size and location of accessory foramina in the internal and external furcation areas.

Although the existence of accessory foramina in the furcation area and roots of permanent teeth has been demonstrated, the presence of accessory foramina in furcation areas of primary molars is less certain. This investigation was conducted to determine the presence or absence of accessory foramina in the furcation areas of human primary molars using the scanning electron microscope (SEM). Twenty extracted, carious and noncarious human primary molars were placed in fixative and then mounted in a hard tissue cutting machine: ten teeth were cut transversely 2.0mm coronal to the floor of the pulpal chamber and ten teeth were cut transversely 2.0mm apical to the external furcation. Both the internal and external furcation surfaces of these sectioned molars were debrided with sodium hypochlorite/hydrogen peroxide solutions to remove organic materials, which might obscure visibility of possible foramina and then rinsed in water and dried. The tissues were then prepared for and examined by SEM. Twenty percent of the molars examined by SEM on the internal furcation surface and 50% of the molars examined by SEM on the external furcation surface demonstrated accessory foramina.

Child↗
PubMed1993

An investigation of accessory canals in furcation areas of human primary molars: Part 2. Latex perfusion studies of the internal and external furcation areas to demonstrate accessory canals.

Four classes of accessory canals: "true," "blind," "looping" and "enclosed" canals have been suggested to exist in furcation areas of primary teeth. Although the existence of accessory canals in the furcation areas and roots of permanent teeth has been demonstrated, their presence in furcation areas of primary teeth is uncertain. This investigation was conducted to determine the presence or absence of accessory canals in the furcation areas of human primary molars using a variety of latex perfusion techniques. Twenty extracted, noncarious human primary molars were placed in fixative and then sectioned on a hard tissue cutting machine: ten teeth were cut transversely 2.0 mm coronal to the floor of the pulpal chamber and ten teeth were cut transversely 2.0 mm apical to the external furcation area. The internal and external furcation surfaces of these sectioned molars were debrided with sodium hypochlorite/hydrogen peroxide solutions, rinsed in water and dried to remove organic materials, which might obscure the existence of possible canals. Twenty of these extracted teeth were examined by SEM to detect the possible presence of accessory foramina in the internal and external furcation areas (Part 1). Twenty percent of the molars examined by SEM on the IFA and 50 percent of the molars examined by SEM on the EFA exhibited accessory foramina. Twenty molars were perfused with low viscosity latex using vacuum [negative] pressure (10 molars) and positive pressure (10 molars) to detect the possible existence of the patency and the extent of such accessory canals in the internal and external furcation areas (Part 2).(ABSTRACT TRUNCATED AT 250 WORDS)

Child↗
PubMed1992

In vitro permeability of furcation dentin in permanent teeth.

Extracted unerupted permanent third molars with the occlusal half of the crown and apical half of the roots removed were cemented to Plexiglas blocks. Using a positive pressure system in which the movement of fluid across the dental tubules could be measured, the permeability of furcation dentin was measured before and after alteration of the furcation thickness. Subsequently, measurements of reduction in thickness of cementum and dentin were performed. Furcation dentin permeability was found to increase as the cementum and dentin thickness was reduced and the smear layer removed. The permeability values obtained for the furcation dentin were similar to those found in radicular dentin in general, indicating that root dentin has a low permeability and that it has good barrier properties. The data would suggest that any bone resorption seen under the furcation region of permanent molars is more likely to be due to the presence of accessory canals than due to permeation directly through furcation hard tissues.

Adolescent↗
PubMed1992

Macroscopic sectioning of undecalcified tissues.

An inexpensive laboratory apparatus designed to section undecalcified teeth and bone has been constructed. It consists of an electric motor with a mandrel bearing a carborundum sectioning disk centered within a Plexiglas enclosure. A coolant flows from a reservoir positioned in the upper portion of the Plexiglas enclosure to prevent desiccation or burning of the tissues. Undecalcified tissue can be cut into a series of thin, 0.5-1 mm slices to facilitate studies of pulpal enzymes, tooth morphology and design of dental cavity preparations.

Humans↗
PubMed1992

Vascular pathways within pulpal tissue of human primary teeth.

The vascular distribution within pulps of human primary teeth has not been as well studied as those within human permanent teeth. Such information is useful to those who diagnose and treat dental conditions in children. The purpose of this study was to determine the architecture of the vascular structures, in contrast to the histological appearances, of noncarious human primary teeth during root completion, root resorption and dental caries attack. Following extraction, primary teeth were perfused with an opaque injection mass and photographed to trace the courses of the arterioles, venules and capillaries within the crowns and roots. The architectural morphology of similar vascular structures in permanent pulps are included to provide a comparative reference. Arterioles entered the apical foramina and traveled throughout the root canal(s) to the pulpal chamber, giving off branches which passed toward the dentinal walls. Within the pulpal chamber, the arterioles passed toward the occlusal and proximal surfaces and arborized profusely to form a subodontoblastic plexus of capillaries. The capillaries lead to larger diameter venules, which exited the pulp through apical foramina. Many unusual vascular pathways existed within the root structure. No communication existed between the pulp chamber and periodontal membrane through the furcation dentin and cementum. Many lateral canals were seen along the root structures.

Child↗
PubMed1990

[Air pollution--consequences for the general practitioner].

Air pollution can also be considered a health risk for those living in Switzerland. During short episodes of high pollution (smog), protection from exposure can be recommended. The continuous air pollution problem, however, implies for the physician a complex educational task with regard to his patients. As the patient does not perceive a direct improvement in his personal health, it is difficult to promote ecologically acceptable behaviour. In view of the long term effects of continuous exposure to air pollution on the health of the population, such preventative activity is considered necessary.

Air Pollution↗
PubMed1988

Characterization of the protein which binds insulin-like growth factor in human serum.

The binding of the 125I-labelled insulin-like growth factors I and II (125I-IGF I and 125I-IGF II) to the high-molecular-mass binding protein of human serum was characterized. With diluted human serum both growth factors showed optimal specific binding at 4 degrees C and pH 5-6. When 0.1% Triton X-100 was present in the incubation buffer an increase in the affinity of the IGF-binding protein was induced, which produced an enhanced binding of IGF I and IGF II. Competition experiments with various peptide hormones revealed that the native IGF-binding protein complex binds both the IGF I and IGF II with high specificity. Analysis of binding data according to the method of Scatchard resulted in linear plots for IGF I and IGF II respectively, indicating that in human serum only a single class of non-interacting binding sites is present. At optimal binding conditions the dissociation constants were determined to be 0.28 x 10(-9) M for IGF I binding and 0.66 x 10(-9) M for IGF II. Human serum was gel-filtered on Sepharose CL-6B at neutral pH and the eluate was assayed for binding activity with both IGF I and IGF II. One peak with an apparent molecular mass of 175 kDa and a Stokes radius of 4.8 nm was determined for both growth factors. Thus, our data suggest that human serum contains one class of high-molecular-mass binding protein with comparable binding characteristics for IGF I and IGF II.

Binding Sites↗
PubMed1987

Generation of oligomeric insulin receptor forms by intramolecular sulfhydryl-disulfide exchange. Involvement of masked sulfhydryl groups.

Insulin receptors from rat liver membranes were labelled with a 125I-labelled photoreactive insulin analogue or by iodination using lactoperoxidase and analysed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Under nonreducing conditions different receptor forms with Mr 400,000 (alpha 2 beta 2), 360,000 (alpha 2 beta beta'), 330,000 (alpha 2 beta' beta'), 320,000 (alpha 2 beta), 280,000 (alpha 2 beta'), 240,000 (alpha 2), 210,000 (alpha beta), 165,000 (alpha beta') and 115,000 (alpha) were detected. The subunit composition of these receptor forms was determined by two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis in the absence and presence of dithioerythritol. During denaturation in sodium dodecyl sulfate in the absence of reductants, the Mr 400,000 receptor form (alpha 2 beta 2) was converted into the Mr 320,000 (alpha 2 beta) and Mr 240,000 (alpha 2) receptor form. This conversion was prevented either by N-ethylmaleimide, oxidants, or low pH. In contrast, alkylation of the receptor with N-ethylmaleimide under non-denaturing conditions did not prevent the appearance of intermediate-sized receptor forms. Furthermore, the inhibition of receptor cleavage by N-ethylmaleimide during denaturation was also observed when the amount of free sulfhydryl groups was reconstituted by the addition of an unlabelled and non-alkylated receptor sample to the alkylated and photoaffinity-labelled receptor. These results suggest, that the generation of different oligomeric receptor forms detected by sodium dodecyl sulfate polyacrylamide gel electrophoresis is due at least in part to the cleavage of one or both beta-subunits from the insulin receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Affinity Labels↗
PubMed1987

The effect of nutritional support on outcome from severe head injury.

Fifty-one brain-injured patients with peak 24-hour admission Glasgow Coma Scale (GCS) scores of 4 to 10 were prospectively randomly assigned to receive total parenteral (TPN) or enteral (EN) nutrition. Patients were studied from hospital admission to 18 days postinjury. Outcome was assessed by the Glasgow Outcome Scale at 3 months, 6 months, and 1 year postinjury. The TPN group received a significantly higher cumulative mean intake of protein than the EN group (mean +/- standard error of the mean: 1.35 +/- 0.12 vs. 0.91 +/- 0.9 gm/kg/day; p = 0.004). Mean cumulative caloric balance was also significantly higher in the TPN than in the EN group (75.6% +/- 5.13% vs. 59% +/- 4.26%; p = 0.02). Nitrogen balance was significantly more negative in the EN group during the 1st week postinjury (p = 0.002). The incidence of pneumonia, urinary tract infections, septic shock, and infections was not significantly different between groups. Classic nutritional assessment parameters such as anergy screens, total lymphocyte counts, and albumin levels were not significantly different between groups. The 11 patients in the EN group who did not tolerate tube feedings for 1 week postinjury had a significantly higher incidence of septic shock (p = 0.008). The change over time in GCS scores between groups was significantly different, with the TPN group showing a mean four-point increase in GCS score compared with a three-point increase in the EN group (p = 0.02). At 3 months the TPN group had a significantly higher percentage of favorable outcomes (43.5% vs. 17.9%, respectively; p = 0.05). At 6 months, 43.5% of the TPN group had a favorable outcome while 32.1% of the EN group had a favorable outcome (p = 0.29). By 1 year, 47.8% of the TPN group and 32.1% of the EN group had a favorable outcome (p = 0.20). In conclusion, more calories and protein usually can be administered to acute brain injury patients via the TPN route than by EN feedings via nasogastric or nasoduodenal routes. Traditional parameters for nutritional assessment are not useful in studying the efficacy of nutritional support during the first 2 weeks after head injury. Neurological recovery from head injury occurs more rapidly in patients with better early nutritional support.

Craniocerebral Trauma↗
PubMed1987

The patient with critical neurological disease.

The known metabolic abnormalities and nutritional requirements of the brain injury, spinal cord injury, and acute stroke patient have been presented. Further investigations are required in all these conditions to identify specific nutritional requirements and metabolic abnormalities. The specific role of nutritional support on outcome, immune function, and body structure requires further study.

Acute Disease↗
PubMed1987

Moral pioneers: women, men and fetuses on a frontier of reproductive technology.

As one of the new reproductive technologies, amniocentesis is rapidly becoming routinized, especially for pregnant women in their mid-thirties and older. Prenatal diagnosis has been evaluated medically, economically, and bioethically. But we know very little about how pregnant women and their families who use, or might use, this new technology respond to its benefits and burdens. This article reports on a two-year field study in New York City. Responses of genetic counselors, a multicultural patient population using and refusing amniocentesis, women who had received "positive" diagnoses, and families with children who have the conditions that can now be diagnosed prenatally were all elicited through participant-observation. My goal in this study is to assess the social impact and cultural meaning of one new reproductive technology.

Adult↗
PubMed1986

The nonclassical insulin binding of insulin receptors from rat liver is due to the presence of two interacting alpha-subunits in the receptor complex.

The binding characteristics of the insulin receptor tetramer (alpha 2 beta 2) and dimer (alpha beta) were examined. Unlabelled insulin enhanced the dilution-induced dissociation only of the receptor tetramer-bound 125I-insulin. Furthermore, when both the receptor forms had been preincubated with anti-receptor-antibodies (B9-antiserum), insulin binding only to the receptor tetramer but not to the dimer was inhibited. However, both oligomers are not immunologically distinct since more than 80% of the two forms were immunoprecipitated by the antiserum. These results suggest that both insulin and anti-receptor-antibodies induce cooperative interactions between the two linked alpha-subunits of the receptor tetramer leading to a decrease in insulin binding of this receptor form.

Affinity Labels↗
PubMed1986

Characterization of solubilized insulin receptors from rat liver microsomes. Existence of two receptor species with different binding properties.

Insulin receptors were solubilized from rat liver microsomes by the nonionic detergent Triton X-100. After gel filtration of the extract on Sepharose CL-6B, two insulin-binding species (peak I and peak II) were obtained. The structure and binding properties of both peaks were characterized. Gel filtration yielded Stokes radii of 9.2 nm (peak I) and 8.0 nm (peak II). Both peaks were glycoproteins. At 4 degrees C peak I showed optimal insulin binding at pH 8.0 and high ionic strength. In contrast, peak II had its binding optimum at pH 7.0 and low ionic strength, where peak I binding was minimal. For peak I the change in insulin binding under different conditions of pH and ionic strength was due to a change in receptor affinity only. For peak II an additional change in receptor number was found. Both peaks yielded non-linear Scatchard plots under most of the buffer conditions examined. At their binding optima at 4 degrees C the high affinity dissociation constants were 0.50 nM (peak I) and 0.55 nM (peak II). Sodium dodecyl sulfate/polyacrylamide gel electrophoresis of peak I revealed five receptor bands with Mr 400 000, 365 000, 320 000, 290 000, and 245 000 under non-reducing conditions. For peak II two major receptor bands with Mr 210 000 and 115 000 were found. The peak II receptor bands were also obtained after mild reduction of peak I. After complete reduction both peaks showed one major receptor band with Mr 130 000. The reductive generation of the peak II receptor together with molecular mass estimations suggest that the peak I receptor is the disulfide-linked dimer of the peak II receptor. Thus, Triton extracts from rat liver microsomes contain two receptor species, which are related, but differ considerably in their size and insulin-binding properties.

Affinity Labels↗
PubMed1986

On the surface lattice of microtubules: helix starts, protofilament number, seam, and handedness.

The tubulin monomers of brain microtubules reassembled in vitro are arranged on a 3-start helix, irrespective of whether the number of protofilaments is 13 or 14. The dimer packing is that of the B-lattice described for flagellar microtubules. This implies that the tubulin core of microtubules contains at least one helical discontinuity. Neither 5-start nor 8-start helices have a physical significance and thus cannot be implicated in models of microtubule elongation, but the structure is compatible with elongation of protofilaments by dimers or protofilamentous oligomers. The inner and outer surfaces of the microtubule wall can be visualized by propane jet freezing, freeze fracturing, and metal replication, at a resolution of at least 4 nm. The 3-start helix is left-handed, in contrast to a previous study based on negative staining and shadowing. The reasons for this discrepancy are discussed.

Cytoskeleton↗
PubMed1986

Microtubule structure studied by quick freezing: cryo-electron microscopy and freeze fracture.

Microtubules have been quickly frozen and examined by electron microscopy using several techniques: (1) freezing of a thin layer of solution by plunging into cryogen, followed by cryoelectron microscopy of the unstained vitrified samples; (2) freezing by the propane-jet method, followed by freeze fracturing and metal replication. The unstained frozen-hydrated microtubules show a structure in agreement with X-ray diffraction data; they differ from negatively stained particles mainly by the better preservation of cylindrical shape. Secondly, they reveal a supertwist of the profilaments that is not detected reliably by other methods. This allows a determination of the number of protofilaments and the polarity. The structural resolution of unstained microtubules is similar to that of stained ones (about 2-3 nm); it is limited by low contrast and lack of crystalline order. Propane-jet or cryo-block freezing followed by freeze fracturing reveals the structures of the inner and outer surfaces of the microtubule wall at a resolution of 4 nm or better. The outside is dominated by the longitudinal protofilaments whereas on the inside one observes tilted cross-striations. Although the freezing temperatures of the two methods are different (liquid nitrogen or helium) they yield similar results for the case of thin layers of protein solution.

Animals↗