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J B Tucker

Publications and source records attributed to J B Tucker.

At least 37 records · Page 2Linked to original sources
PubMed1995

Dual modulation of the gamma-aminobutyric acid type A receptor/ionophore by alkyl-substituted gamma-butyrolactones.

Alkyl-substituted gamma-butyrolactones (GBLs) and gamma-thiobutyrolactones exhibit convulsant or anticonvulsant activity, depending on the alkyl substituents. alpha-Substituted lactones with small alkyl substituents are anticonvulsant and potentiate gamma-aminobutyric acid (GABA)-mediated chloride currents, whereas beta-substituted compounds are usually convulsant and block GABAA currents. We have now found that this distinction is not so clear-cut, in that some compounds can both block and augment GABAA currents, but with different time courses. For example, alpha,alpha-diisopropyl-GBL (alpha-DIGBL) potentiates exogenous GABA currents in cultured rat hippocampal neurons but diminishes GABA-mediated inhibitory postsynaptic currents. A more detailed analysis demonstrates a triphasic effect of alpha-DIGBL on GABA currents, with a rapid inhibitory phase, a slower potentiating phase, and then an "off response" when the GABA/alpha-DIGBL perfusion is stopped. Thus, alpha-DIGBL can inhibit and potentiate GABA currents with kinetically different time courses. Inhibition is more rapid, but at steady state potentiation dominates. Using a simplified model of the GABAA receptor/ionophore, we have simulated our experimental observations with alpha-DIGBL. Another lactone, beta-ethyl-beta-methyl-gamma-thiobutyrolactone, also has dual actions, with inhibition predominating at low concentrations and potentiation predominating at high concentrations. We propose two distinct GBL modulatory sites on the GABAA receptor, i.e., an inhibitory "picrotoxin" site and an enhancing "lactone site." New information on the structure of the GABAA receptor/ionophore may allow the molecular dissection of these two sites.

4-Butyrolactone↗
PubMed1994

Reorganization of the centrosome and associated microtubules during the morphogenesis of a mouse cochlear epithelial cell.

Reorganization of centrosomal microtubule-organizing centres and the minus ends of microtubules occurs as the centrosomal ends of large microtubule bundles are repositioned and anchored to cell junctions in certain epithelial cells called inner pillar cells in the mouse organ of Corti. The microtubule bundle that assembles in each cell consists of two distinct microtubule arrays that run closely alongside each other. Both arrays are attached to the cell surface at their upper and lower ends. One of the arrays spans the entire length of a cell but the other is confined to its lower portion. Initially, about 3,000 microtubules elongate downwards from an apically situated centrosome in each cell. Subsequently, the minus ends of these microtubules, and the centrosome and its two centrioles, migrate for about 12 microns to the tip of a laterally directed projection. Then, a meshwork of dense material accumulates to link microtubule minus ends and the centrosome to cell junctions at the tip of the projection. Pericentriolar satellite bodies, which form after the initial burst of microtubule nucleation, may represent a condensed and inactive concentration of microtubule-nucleating elements. Surprisingly, as a cell matures, about 2,000 microtubules are eliminated from the centrosomal end of the microtubule bundle. However, about 2,000 microtubules are added to the basal portion of each bundle at levels that are remote with respect to the location of the centrosome. Possibly, these microtubules have escaped from the centrosome. If this is the case, then both the plus and minus ends of most of the errant microtubules are captured by sites at the cell surface where the ends are finally anchored. Alternatively, each cell possesses at least one other major microtubule-nucleating site (which does not possess centrioles) in addition to its centrosome.

Animals↗
PubMed1993

Microtubule rearrangement and bending during assembly of large curved microtubule bundles in mouse cochlear epithelial cells.

Mature inner pillar cells in the mammalian organ of Corti are curved through about 60 degrees, where they arch over adjacent epithelial cells and the apex of an intercellular space called the tunnel of Corti. This report deals with changes in microtubule organization that are associated with cell bending and tunnel formation during morphogenesis of the mouse organ of Corti. A large bundle of up to 3,000 microtubules assembles in each inner pillar cell. Microtubule rearrangement occurs about 5 days after bundle assembly begins. The lumen of each initially straight hollow tube-shaped microtubule bundle is occluded as the bundle becomes more compact and elliptical in cross section. This event anticipates the once-only bending which subsequently occurs between particular levels (about 9-19 microns) below the top of a bundle as it curves into its final shape about 2 days later. Microtubule rearrangement presumably facilitates bending which is effected in the plane of least mechanical resistance parallel to the short axis of a bundle's elliptical cross-sectional profile. Precocious bending of bundles has been induced about 1.5 days in advance of the natural event. Abnormal positioning of these prematurely curved bundles indicates that bending is effected by a contractile mechanism located within bundles rather than being a response to externally applied forces. The potential importance of such microtubule-associated contractions for active modulation of the vibratory response in the cochlea during hearing is considered.

Animals↗
PubMed1993

Screening for open-angle glaucoma.

Chronic (open-angle) glaucoma is a leading cause of new cases of blindness in the United States. This blindness is a result of increased intraocular pressure and deterioration of the optic nerve. Nearly 2 million Americans have glaucoma. "Ocular hypertension" is the term applied to elevation of the ocular pressure above 21 mm Hg. Glaucoma is defined as a group of diseases that have certain common features, including an intraocular pressure too high for the continued health of the eye, cupping and atrophy of the optic nerve head and visual field loss. Although long-term studies evaluating the success of medical treatment are still in progress, medical intervention remains the standard of care for both ocular hypertension and open-angle glaucoma.

Glaucoma↗
PubMed1993

Arthroscopically assisted proximal quadricepsplasty for patellar instability.

Arthroscopy has come to play a major role in the evaluation and treatment of patellofemoral instability. In fact, most patients sustaining a traumatic dislocation or recurrent subluxations are subjected to, at a minimum, an arthroscopic evaluation to assess intraarticular damage and patellar tracking.

Arthroscopy↗
PubMed1993

Multiple plasma membrane-associated MTOC systems in the acentrosomal cone cells of Drosophila ommatidia.

Multiple plasma membrane-associated microtubule-organizing centers operate in the cone cells of Drosophila ommatidia. A transcellular array of about 250 microtubules assembles in each cone cell during late pupal ommatidial morphogenesis. While these arrays are assembling, cone cells do not possess conventional centriole-containing centrosomal microtubule-organizing centers. The microtubules are associated with plasma membrane-associated plaques at both the apical and basal surfaces. During assembly of the arrays there is a progressive decrease in the number of microtubules/cell cross section at successively lower levels in each cell which is indicative of apicobasal microtubule elongation. In this respect, assembly of the arrays closely resembles that of transcellular 15 protofilament microtubules in late pupal wing cells (Mogensen et al. J. Cell Biol. 108, 1445-1452 (1989)). However, cone cell microtubules are almost certainly of the 13 protofilament variety as found in eukaryotic cells generally. We suggest that plasma membrane-associated microtubule-organizing centers are widely employed in polarized epithelia in Drosophila during late pupal morphogenesis.

Animals↗
PubMed1992

A cell surface-associated centrosomal layer of microtubule-organizing material in the inner pillar cell of the mouse cochlea.

This investigation provides evidence that pericentriolar material is divorced from the immediate vicinities of centrioles and becomes functionally associated with the plasmalemma during the differentiation of a mammalian cell type. Such events occur prior to the assembly of large transcellular microtubule bundles in columnar epithelial cells called inner pillar cells in the mouse organ of Corti. The microtubules do not radiate from a typical centrosome and its centrioles. They elongate from a microtubule-organizing centre (MTOC), which is deployed as a subapical cell surface-associated layer in each cell. Most of the dense material of this layer, and the tops of most of the microtubules, are initially concentrated around the sides of a cell about 1 microns below its apical surface. In addition, a pair of centrioles is located above the layer, which acts as if it is a pericellular concentration of the pericentriolar material of a modified centrosome. Although microtubule nucleation takes place in a centrosome-like region, 13 protofilament fidelity is not exercised. Most of the microtubules have 15 protofilaments. Microtubule assembly progresses in these cells after the organ of Corti has been isolated for in vitro culture. However, large numbers of microtubules elongate from pericentriolar material juxtaposed against the centrioles. Hence, there is some reversion by the centrosomes of cultured cells to the operational configuration regarded as typical for animal tissue cells in general.

Animals↗
PubMed1991

Boxing: the preparticipation evaluation.

Boxing is a controversial sport that has drawn public and physician criticism since its inception in 900 BC. The American Medical Association has recently taken a formal position to ban boxing because of the alleged dangers, including the possibility of the long-term effect of dementia pugilistica. Proponents of amateur boxing are working diligently to document this claim both as premature and false. They cite amateur boxing's purpose as one boxer's attempt to outpoint or outscore his opponent by utilization of superior strength and skill. Despite this medical and political controversy, thousands of primary care patients are boxing. This report offers the physician guidelines for the preparticipation evaluation. Specific disqualifying conditions are addressed.

Boxing↗
PubMed1990

Taxol influences control of protofilament number at microtubule-nucleating sites in Drosophila.

Control of protofilament number has been investigated using Drosophila wings at a stage when 15-protofilament microtubules assemble under normal conditions. Microtubule nucleation still progressed at the usual microtubule-nucleating sites in the presence of taxol. However, provided taxol was introduced before microtubule nucleation began, few microtubules with 15 protofilaments assembled. Most microtubules were composed of 12 protofilaments (a previously undetected value for Drosophila) or 13 protofilaments (which is the value for microtubules in most eukaryotic cells). Unexpectedly, a comparatively mild challenge to control of nucleation (in vitro wing culture) also promoted assembly of 13-protofilament microtubules. Hence, the microtubule-nucleating sites may possess a relatively labile control specifying 15 protofilaments superimposed upon that for maintaining 13-protofilament fidelity.

Alkaloids↗
PubMed1989

Microtubule polarities indicate that nucleation and capture of microtubules occurs at cell surfaces in Drosophila.

Hook decoration with pig brain tubulin was used to assess the polarity of microtubules which mainly have 15 protofilaments in the transcellular bundles of late pupal Drosophila wing epidermal cells. The microtubules make end-on contact with cell surfaces. Most microtubules in each bundle exhibited a uniform polarity. They were oriented with their minus ends associated with their hemidesmosomal anchorage points at the apical cuticle-secreting surfaces of the cells. Plus ends were directed towards, and were sometimes connected to, basal attachment desmosomes at the opposite ends of the cells. The orientation of microtubules at cell apices, with minus ends directed towards the cell surface, is opposite to the polarity anticipated for microtubules which have elongated centrifugally from centrosomes. It is consistent, however, with evidence that microtubule assembly is nucleated by plasma membrane-associated sites at the apical surfaces of the cells (Mogensen, M. M., and J. B. Tucker. 1987. J. Cell Sci. 88:95-107) after these cells have lost their centriole-containing, centrosomal, microtubule-organizing centers (Tucker, J. B., M. J. Milner, D. A. Currie, J. W. Muir, D. A. Forrest, and M.-J. Spencer. 1986. Eur. J. Cell Biol. 41:279-289). Our findings indicate that the plus ends of many of these apically nucleated microtubules are captured by the basal desmosomes. Hence, the situation may be analogous to the polar-nucleation/chromosomal-capture scheme for kinetochore microtubule assembly in mitotic and meiotic spindles. The cell surface-associated nucleation-elongation-capture mechanism proposed here may also apply during assembly of transcellular microtubule arrays in certain other animal tissue cell types.

Animals↗
PubMed1988

Intermicrotubular actin filaments in the transalar cytoskeletal arrays of Drosophila.

Rabbit muscle myosin subfragment S1 decorates 6 nm diameter filaments in Drosophila wing epidermal cells in the arrowhead fashion characteristic of the binding of subfragment S1 to actin filaments. The filaments in question are concentrated between microtubules that are mostly composed of 15 protofilaments and form cell surface-associated transcellular bundles. There are indications that the majority of the actin filaments have the same polarity and that, like the microtubules, they may elongate from sites at the apical surfaces of the cells. The bundles of F actin and microtubules occur in dorsal and ventral epidermal cell layers of a wing blade. They are joined in dorso-ventral pairs by attachment desmosomes. These transalar cytoskeletal arrays may provide an example of a situation where actin filaments operate as stiffeners rather than active generators of force in conjunction with myosin. The arrays probably function as noncontractile pillars to maintain basal cell extensions and keep haemocoelic spaces open in the highly folded and expanding wing blades of late pupae.

Actins↗
PubMed1987

Evidence for microtubule nucleation at plasma membrane-associated sites in Drosophila.

This report is concerned with the nucleation and organization of microtubule bundles that assemble after 'conventional' centrosomal microtubule-organizing centres have been lost. The microtubule bundles in question span the lengths of wing epidermal cells. Bundles extend between hemidesmosomes at the apical cuticle-secreting surfaces of cells and basal attachment desmosomes that unite the dorsal and ventral epidermal layers of developing wing blades. Furthermore, each bundle includes up to 1500 microtubules and most of the microtubules are composed of 15 protofilaments. Individual cells were serially cross-sectioned at an early stage of bundle assembly. The number of microtubule profiles/cell cross-section decreased progressively by up to 59% of the most apical values in section sequences cut from fairly apical to more basal levels in the cells. The apical ends of microtubules were associated with numerous small dense plaque-like sites (diameter 0.1-0.2 micron), which were specialized regions of plasma membranes at the apical surfaces of cells. Many of the microtubules near apical plaques were not well aligned with each other; they 'radiated away' from cell apices. This was in contrast to the situation at more basal levels where most microtubules were oriented parallel to the longitudinal axes of cells. These findings indicate that the relatively dispersed arrays of apical plasma membrane-associated plaques act as microtubule-nucleating sites to initiate basally directed elongation of bundle microtubules. Apical cell surfaces and their plaques seem to operate as microtubule-nucleating and -organizing regions that functionally replace the centrosomal microtubule-organizing centres lost earlier in cell differentiation.

Animals↗
PubMed1986

Supracellular microtubule alignments in cell layers associated with the secretion of certain fish scales.

Intercellularly aligned microtubule arrays are present in cell layers associated with the growth and secretion of scales in the zebra fish Brachydanio rerio and the neon tetra fish Hyphessobrycon innesi. The layers in question are: the osteoblast layer that covers the ossified outer surface of a scale, and the layer of fibroblasts that is situated immediately underneath the inner collagenous surface of a scale's fibrillary plate. In certain osteoblasts, the proximal portions of microtubules (with respect to centrosomes) run closely alongside the anterior margin of each cell where it flanks one of a scale's ridge-shaped circuli. These osteoblasts and microtubule portions are arranged in aligned rows that are parallel to circuli. However, the distal portions of the microtubules curve into an orientation that is approximately at right angles to circuli and they are aligned with each other and similar microtubule portions in adjacent osteoblasts. Such microtubule alignments only occur in osteoblasts that are associated with circuli. In Hyphessobrycon osteoblasts situated elsewhere on a scale's surface, microtubules radiate from cell centres but their distal portions curve into alignment with each other and are oriented alongside cell margins. The proximal portions of fibroblast microtubules radiate from centrally positioned centrosomes but the distal portions curve into alignment with each other and distal microtubule portions in neighbouring fibroblasts. The overall pattern of microtubule alignment is similar to that of collagen fibres, which these fibroblasts are secreting onto the fibrillary plate. The immunofluorescence protocol that was used to demonstrate the microtubule alignments described above did not reveal such alignments in the osteoblast and fibroblast layers associated with scales of the brown trout Salmo trutta fario. These findings are assessed in terms of intra-and inter-cellular control of microtubule alignment, and decentralized reorientation of microtubules at distances of several micrometres from centrosomal microtubule-organizing centres. The functional significance of the relationships between microtubule alignment and supracellular patterns of alignment that take place as collagen deposition and ossification proceed during scale formation is also considered.

Animals↗
PubMed1986

Fieldside management of athletic injuries.

A physician trained in the management of sports-related injuries should be in attendance at athletic events with a potential for significant injury. These are usually contact sports, particularly football. While many of the expected injuries are orthopedic in nature, the risk of serious injury to the larynx, abdomen, eyes and teeth also exists.

Abdominal Injuries↗
PubMed1985

Spindle microtubule differentiation and deployment during micronuclear mitosis in Paramecium.

Spindles underwent a 12-fold elongation before anaphase B was completed during the closed mitoses of micronuclei in Paramecium tetraurelia. Two main classes of spindle microtubules have been identified. A peripheral sheath of microtubules with diameters of 27-32 nm was found to be associated with the nuclear envelope and confined to the midportion of each spindle. Most of the other microtubules had diameters of approximately 24 nm and were present along the entire lengths of spindles. Nearly all of the 24-nm microtubules were eliminated from spindle midportions (largely because of microtubule disassembly) at a relatively early stage of spindle elongation. Disassembly of some of these microtubules also occurred at the ends of spindles. About 60% of the total microtubule content of spindles was lost at this stage. Most, perhaps all, peripheral sheath microtubules remained intact. Many of them detached from the nuclear envelope and regrouped to form a compact microtubule bundle in the spindle midportion. There was little, if any, further polymerization of 24-nm microtubules after the disassembly phase. Polymerization of microtubules with diameters of 27-32 nm continued as spindle elongation progressed. Most microtubules in the midportions of well-elongated spindles were constructed from 14-16 protofilaments. A few 24-nm microtubules with 13 protofilaments were also present. The implications of these findings for spatial control of microtubule assembly, disassembly, positioning, and membrane association, that apparently discriminate between microtubules with different protofilament numbers have been explored. The possibility that microtubule sliding occurs during spindle elongation has also been considered.

Animals↗
PubMed1985

An evaluation of patient satisfaction and level of physician training.

A study evaluating patients' degrees of satisfaction with physicians holding varying levels of medical training in similar practice settings was conducted. Results revealed that there were more satisfied patients relative to physicians who were more completely trained only on questions relating to the accessibility of health care. Since the most highly trained physician group had a different practice ambiance, it is concluded that level of physician training and degree of patient satisfaction are not related. Implications for health care marketing are discussed.

Clinical Competence↗