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R Niederman

Publications and source records attributed to R Niederman.

At least 55 records · Page 3Linked to original sources
PubMed1988

Microtubule-granule relationships in motile human polymorphonuclear leukocytes.

We examined the relationship of microtubules to the granule organization in stimulated human polymorphonuclear leukocytes (PMNs). Electron microscopic (EM) observations of critical-point-dried PMNs revealed that only a portion of the granules appeared in close association to microtubules. These closely associated granules appeared to be attached to the microtubule via smaller-diameter filaments. The remaining granules appeared either attached to microtubules at a further distance, via smaller-diameter filaments such as actin, or unassociated with microtubules. EM observations of PMNs treated with either the microtubule promoter drug taxol or the microtubule depolymerization drugs nocodozole and colchicine revealed a redistribution of granules towards the nucleus. Granule clustering at the periphery of the cell was also noted with nocodozole and colchicine. With cytochalasin B, a uniform distribution of granules was noted. However, granule clustering was noted when PMNs were coincubated with cytochalasin B and colchicine. These results indicate that microtubules may have both a direct and indirect role (through other cytoskeletal elements) in the organization of PMN granules.

Alkaloids↗
PubMed1984

The organization of actin filaments in human polymorphonuclear leukocytes.

Actin constitutes a major component of the cytoskeleton of human polymorphonuclear leukocytes (PMNs). In this study, we present a comprehensive view of the organization of actin in various PMN regions and functional states. Transmission electron microscopic observations were made on whole mount, migrating, and phagocytizing PMNs. Positive identification of actin filaments was made through S-1 myosin subfragment labeling. In all PMNs studied, actin filaments were primarily organized as a three-dimensional meshwork. The density of this meshwork was greatest within the cell cortex. At peripheral regions of nonpolarized (viz., no distinct head or tail region) and polarized PMNs, actin filaments organized into parallel bundles or overlapping arcs. These bundles or arcs were oriented either perpendicular or parallel to the cell periphery. At the base of the PMN, actin filaments converged upon dense, plaquelike condensations. This latter pattern of actin organization was also observed in some pseudopods at the cell front and in phagocytic processes engulfing bacteria. In areas of internalized bacteria, the surrounding actin appeared as a loose meshwork. Treatment of PMNs with the antiactin drug, cytochalasin B, revealed shearing of the peripheral actin meshwork, condensation of the meshwork around the nuclear region, and dissolution of the basal plaquelike condensations.

Actins↗
PubMed1984

Chronic treatment with hydrogen peroxide. Is it safe?

The regular application of hydrogen peroxide to gingival tissues is becoming widely used as part of dental hygiene. Since hydrogen peroxide can be toxic under certain experimental conditions, proof of both safety and efficacy of its chronic administration should be available before prescription to the general public.

Animals↗
PubMed1983

Three-dimensional structure of actin filaments and of an actin gel made with actin-binding protein.

Purified muscle actin and mixtures of actin and actin-binding protein were examined in the transmission electron microscope after fixation, critical point drying, and rotary shadowing. The three-dimensional structure of the protein assemblies was analyzed by a computer-assisted graphic analysis applicable to generalized filament networks. This analysis yielded information concerning the frequency of filament intersections, the filament length between these intersections, the angle at which filaments branch at these intersections, and the concentration of filaments within a defined volume. Purified actin at a concentration of 1 mg/ml assembled into a uniform mass of long filaments which overlap at random angles between 0 degrees and 90 degrees. Actin in the presence of macrophage actin-binding protein assembled into short, straight filaments, organized in a perpendicular branching network. The distance between branch points was inversely related to the molar ratio of actin-binding protein to actin. This distance was what would be predicted if actin filaments grew at right angles off of nucleation sites on the two ends of actin-binding protein dimers, and then annealed. The results suggest that actin in combination with actin-binding protein self-assembles to form a three-dimensional network resembling the peripheral cytoskeleton of motile cells.

Actins↗
PubMed1982

Native bare zone assemblage nucleates myosin filament assembly.

Native myosin filaments from rabbit psoas muscle are always 1.5 micrometer long. The regulated assembly of these filaments is generally considered to occur by an initial antiparallel and subsequent parallel aggregation of identical myosin subunits. In this schema myosin filament length is controlled by either a self-assembly or a Vernier process. We present evidence which refines these ideas. Namely, that the intact myosin bare zone assemblage nucleates myosin filament assembly. This suggestion is based on the following experimental evidence. (1) A native bare zone assemblage about 0.3 micrometer long can be formed by dialysis of native myosin filaments to either a pH 8 or a 0.2 M-KCl solution. (2) Upon dialysis back to 0.1 M-KCl, bare zone assemblages and distal myosin molecules recombine to form 1.5 micrometer long bipolar filaments. (3) The bare zone assemblage can be separated from the distal myosin molecules by column chromatography in 0.2 M-KCl. Upon dialysis of the fractionated subsets back to 0.1 M-KCl, the bare zone assemblage retains its length of about 0.3 micrometer. However, the distal molecules reassemble to form filaments about 5 micrometers long. (4) Filaments are formed from mixes of the isolated subsets. The lengths of these filaments vary with the amount of distal myosin present. (5) When native filaments, isolated bare zone assemblages or distal myosin molecules are moved sequentially to 0.6 M-KCl and then to 0.1 M-KCl, the final filament lengths are all about 5 micrometers. The capacity of the bare zone assemblage to nucleate filament assembly may be due to the bare zone myosin molecules, the associated M band components or both.

Animals↗
PubMed1982

The cytoskeleton of human polymorphonuclear leukocytes: phagocytosis and degranulation.

Current evidence indicates that polymorphonuclear leukocyte (PMN) chemotaxis and phagocytosis are effected by an actin-myosin contractile system. However, the structural relationship of the contractile cytoskeleton to cell motility is still in question. In addition, while evidence suggests that microtubules are responsible for orientation during chemotaxis, the role of microtubules in degranulation is unresolved. To determine the organizational relationship between these cytoskeletal elements and phagocytosis, we examined whole-mount preparations of PMNs engulfing bacteria. These preparations were examined in the transmission electron microscope (EM) and photographed as stereo pairs. Two important observations were made. First, there was an increased density of cytoskeletal elements in the pseudopod surrounding bacteria. Second, microtubule elements were intimately associated with lysosomal granules, vesicles, and phagosomes. Lysosomal granules and vesicles aligned along microtubules and clustered around phagosomes. This suggests that the microtubules may provide a tracking mechanism whereby lysosomes are specifically parceled out to phagocytic vacuoles. These results also suggest that phagocytosis and degranulation may involve different effector mechanisms.

Cell Movement↗
PubMed1981

Oral Hygiene Skill Achievement Index I.

The oral hygiene Skill Achievement Index (S.A.I.) is a general method for the direct, quantitative evaluation of oral hygiene skill. The S.A.I. evaluates a person's ability to manipulate a toothbrush and floss in a given fashion. It is applicable to any brushing or flossing procedure. The Index was developed to fulfill all the postulated requirements of a perfect measuring instrument. The key feature of the Index is the evaluation of the position and the motion of the cleaning device on each tooth surface. Consequently, the Index provides a format for the instruction and evaluation of oral hygiene skill. Furthermore, if used in conjunction with other dental indices, it enables one evaluate hygiene procedures and devices in a controlled fashion.

Achievement↗
PubMed1981

Oral Hygiene Skill Achievement Index II.

The utility of any index depends on its validity, reliability, and administrative feasibility. The Oral Hygiene Skill Achievement Index (S.A.I.) was found to be a valid measure of oral hygiene skill in that registered dental hygienists received greater than 90% of the total possible points. The S.A.I. was found to have an initial reliability of r greater than or equal to 0.91 and a repeat reliability of r greater than or equal to 0.96. The S.A.I. requires less than 10 minutes to administer, 40 minutes to teach, and 1 hour and 40 minutes to learn. The results suggest that S.A.I. should be a useful instrument for both clinical and research use.

Achievement↗
PubMed1979

The appearances of common dental diseases on radionuclide bone images of the jaws.

Radionuclide images of hospital patients were examined for abnormal areas within the jaws. Fourteen of 25 subjects studied showed one or more abnormal image areas, most of which were attributable to common dental lesions revealed by oral examinations. The lesions detectable on images included healing bone sites, periodontal and pulpal disease, residual osteitis and irritations caused by ill-fitting dentures.

Adult↗
PubMed1978

Bone scan in dental diseases.

Bone images of the jaws and related dental structures were obtained in 25 patients undergoing skeletal surveys. The upper and lower jaws were divided into eight quadrants to facilitate comparisons between scintigraphic image findings and the results of dental examination. Fourteen of these 25 patients had at least one jaw quadrant with a positive image. The areas of positive uptake correlated well with dental examination findings, which included healing extraction sites and common dental diseases, such as pulpal and periodontal infections and irritations from ill-fitting dentures. The potential usefulness of bone imaging as an adjunct in dental diagnosis is discussed.

Adult↗
PubMed1975

Human platelet myosin. II. In vitro assembly and structure of myosin filaments.

We have used electron microscopy and solubility measurements to investigate the assembly and structure of purified human platelet myosin and myosin rod into filaments. In buffers with ionic strengths of less than 0.3 M, platelet myosin forms filaments which are remarkable for their small size, being only 320 nm long and 10-11 nm wide in the center of the bare zone. The dimensions of these filaments are not affected greatly by variation of the pH between 7 and 8, variation of the ionic strength between 0.05 and 0.2 M, the presence or absence of 1 mM Mg++ or ATP, or variation of the myosin concentration between 0.05 and 0.7 mg/ml. In 1 mM Ca++ and at pH 6.5 the filaments grow slightly larger. More than 90% of purified platelet myosin molecules assemble into filaments in 0.1 M KC1 at pH 7. Purified preparations of the tail fragment of platelet myosin also form filaments. These filaments are slightly larger than myosin filaments formed under the same conditions, indicating that the size of the myosin filaments may be influenced by some interaction between the head and tail portions of myosin molecules. Calculations based on the size and shape of the myosin filaments, the dimensions of the myosin molecule and analysis of the bare zone reveal that the synthetic platelet myosin filaments consists of 28 myosin molecules arranged in a bipolar array with the heads of two myosin molecules projecting from the backbone of the filament at 14-15 nm intervals. The heads appear to be loosely attached to the backbone by a flexible portion of the myosin tail. Given the concentration of myosin in platelets and the number of myosin molecules per filament, very few of these thin myosin filaments should be present in a thin section of a platelet, even if all of the myosin molecules are aggregated into filaments.

Actomyosin↗
PubMedDate not supplied

Benchmarking the dental implant evidence on MEDLINE.

The purpose of this study was to estimate the quantity of dental implant literature available on MEDLINE for evidence-based clinical decision-making and to identify its location. A search strategy based on Medical Subject Headings for dental implants was developed to examine MEDLINE using the Ovid Web Gateway search engine. Sensitive and specific methodologic search filters identified 4 categories of information: etiology, diagnosis, therapy, and prognosis. The results were then subdivided by year to identify trends and sorted to identify the sources of publications. The searches identified 4,655 articles published in English between 1989 and 1999 on human dental implants on MEDLINE. The mean number of articles (+/- SD) per year ranged from 15 +/- 11 for specific searches to 107 +/- 50 for sensitive searches. The number of articles increased by 14% to 43% each year for the sensitive search. When subdivided by clinical category, the mean numbers of articles per year for sensitive and specific searches were, respectively: diagnosis 12 +/- 7.5 and 1.5 +/- 1.6, etiology 58 +/- 33 and 1.9 +/- 2.5, therapy 23 +/- 15 and 0.3 +/- 0.5, and prognosis 67 +/- 33 and 12 +/- 8.3. Four dental journals account for approximately half of these publications. These results provide 6 key central findings: (1) there appears to be a substantial literature of clinically relevant information on implants upon which to base clinical decisions; (2) the implant literature is significantly biased toward articles addressing prognosis; (3) to stay current, one would need to read between 1 and 2 articles per week 52 weeks per year, and this number increases significantly each year; (4) approximately 50% of the articles were published in 4 journals, whereas the remainder reside in approximately 97 other journals, making it difficult to stay current; (5) these trends reaffirm the need for lifelong learning; (6) these trends also suggest the need for computer-based clinical knowledge systems.

Analysis of Variance↗