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PubMed1987

Influence of substratum on the retrograde response of the rat superior cervical ganglion in vitro.

To study the role of the substratum on the retrograde response of injured peripheral noradrenergic neurons, embryonic rat superior cervical ganglia were grown in vitro on four different substrata: collagen, poly-D-lysine, fibronectin, or tissue culture plastic. The rate and pattern of neurite outgrowth were determined for a 2-week period following injury with explantation. In addition, changes in the activity of tyrosine hydroxylase, the neurotransmitter enzyme that has been shown to be altered during the retrograde response, was measured. The pattern and rate of neurite outgrowth varied directly with the ability of the neuronal growth cone to adhere to the underlying substratum. On poly-D-lysine and collagen, neurites grew as individual processes with extensive branching, whereas on plastic and fibronectin there was little branching and marked neurite fasciculation. The rate of neurite elongation on poly-D-lysine (0.75 mm/day) was faster than on collagen (.53 mm/day), fibronectin (0.33 mm/day), or plastic (0.15 mm/day). On plastic, neurons of the superior cervical ganglion showed a severe and prolonged retrograde response as characterized by a reversible decrease in tyrosine hydroxylase activity to 28% of control which persisted until the 10th day in culture. In contrast, on collagen, there was a smaller, but still significant, decrease in tyrosine hydroxylase activity to 73% of control which lasted only 5 to 6 days. On poly-D-lysine, there was no measureable change in the activity of that enzyme after injury. These studies provide quantitative evidence showing an important role of the microenvironment, and in particular the extracellular matrix, in determining the ability of neurons to respond successfully to injury.

Adrenergic Fibers↗
PubMed1991

Cells showing immunoreactivity for calcitonin or calcitonin gene-related peptide (CGRP) in the central nervous system of some invertebrates.

In the central nervous system of some species of several invertebrate phyla, including land planarians (Platyhelminthes), ribbon worms (Nemertina), slugs (Mollusca), polychaetes, earthworms and leeches (Annelida), pill bugs (Arthropoda), and beard worms (Pogonophora), salmon calcitonin-immunoreactive cells and rat calcitonin gene-related peptide (CGRP)-immunoreactive cells were found by immunohistochemistry. These immunoreactive cells were located in the region surrounding the neuropile, although the sizes of the cells varied according to species. Some of them were round or polygonal and regarded as apolar nerve cells because of their lack of cytoplasmic processes, whereas others were spindle-shaped or elongated, being comparable with unipolar nerve cells because of extension of their cytoplasmic processes in the direction of the neuropile. In some cases, it was noted that the cytoplasmic processes had complicated branches or formed loop-like structures at their ends. These observations suggest that a calcitonin-like or CGRP-like substance is extensively present in invertebrates as well as vertebrates.

Animals↗
PubMed1982

Salivary gland of the tick vector of East Coast fever. III. The ultrastructure of sporogony in Theileria parva.

Sporogony of the sporozoan Theileria parva in the salivary gland of the tick vector of East Coast fever was studied in electron micrographs. The findings differ in several respects from previous interpretations based upon light microscopy. Cytokinesis of the primary sporoblast to form secondary and tertiary sporoblasts is not substantiated. Instead it is suggested that the parasite develops as a ramifying, multinucleate syncytium rapidly increasing in size and complexity until it gives rise to myriad sporozoites in a terminal episode of cytoplasmic fission. The proliferating nuclei initially occupy peripheral lobules that are continuous with a central labyrinth of branching and anastomosing processes which present a very large surface area for interchange of metabolites with the host cell cytoplasm. The membrane of the labyrinth is rich in cytostomes, but no evidence if found to bulk uptake of host cytoplasmic matrix or organelles into food vacuoles. Rhoptries are the first of the polar organelles of the parasite to develop and are associated with dense plaques irregularly distributed on the inner aspect of the parasite membrane. Micronemes form independently of the rhoptries at a later stage. After 3-4 days of tick feeding, sporogeny is complete and the infected salivary gland cell contains up to 50, 000 spherical or ovoid sporozoites about 1 micrometer in diameter. These are limited by a simple plasma membrane. The inner layer of the 'pellicle', the polar ring, and the conoid described for zoites of other Apicomplexa are lacking. Maturational changes are noted in sporozoites after sporogony is completed. Micronemes appear to increase in size, and possibly in number, from days 3-5 and the majority take up positions immediately subjacent to the plasmalemma.

Animals↗
PubMed1985

In situ degranulation of human nasal mucosal mast cells: ultrastructural features and cell-cell associations.

Mucosal mast cells in human nasal turbinates obtained at surgery were studied by electron microscopy before and after exposure en bloc to a degranulating stimulus. Mast cells occurred as solitary cells and in islets typically containing one mast cell and one to three mononuclear cells. All islets and most solitary mast cells were associated with thin cytoplasmic processes of distinctive, branched stromal cells that also phagocytosed debris from pyknotic mast cells. Mast cells were grouped into three categories based largely on published ultrastructural criteria. Resting (nondegranulating) mast cells possessed secretory granules that typically packed the cytoplasm and contained a densely stained amorphous material and scroll-like crystalline profiles. Granules in some resting cells were larger, more polymorphic, and appeared nearly homogeneous. Secretory granules of degranulating mast cells possessed crystalline, scroll-like, or reticular constituents predominantly with interspersed amorphous material. Granules were fewer in number and were often concentrated in the peripheral cytoplasm. Few degranulating mast cells exhibited labyrinth formation or exocytosis of granule contents. Largely degranulated mast cells had few if any typical granules but possessed small vacuoles containing recognizable granule remnants. Resting and degranulating mast cells possessed very long cell surface projections that, in places, interdigitated to form stacks of parallel folds above the plasmalemma, resulting in a threefold increase in cell-surface area. The surface membrane of the folds appeared to be continuous with that lining intracytoplasmic channels extending from the cell surface to the Golgi zone.

Cell Membrane↗
PubMed2006

T-type calcium channels: the never ending story.

T-type, or low-voltage-activated (LVA), tiny and transient Ca2+ currents pare more and more recognised as universal players in a plethora of cell functions and are also more and more connected to several diseases. This short introduction reviews the discovery of T-type Ca2+ channels, describes its basic properties and sketches its cloning and physiological impact. Finally, an overview is given how research on T-type Ca2+ channels has developed in the last years and in which topics it is branching out, a process, which is still ongoing.

Animals↗
PubMed2006

Tissue-specific laminin expression facilitates integrin-dependent association of the embryonic wing disc with the trachea in Drosophila.

The interaction of heterologous tissues involves cell adhesion mediated by the extracellular matrix and its receptor integrins. The Drosophila wing disc is an ectodermal invagination that contacts specific tracheal branches at the basolateral cell surface. We show that an alpha subunit of laminin, encoded by wing blister (wb), is essential for the establishment of the interaction between the wing and trachea. During embryogenesis, wing disc cells present Wb at their basolateral surface and extend posteriorly, expanding their association to more posteriorly located tracheal branches. These migratory processes are impaired in the absence of the trachea, Wb, or integrins. Time-lapse and transmission electron microscopy analyses suggest that Wb facilitates integrin-dependent contact over a large surface and controls the cellular behavior of the wing cells, including their exploratory filopodial activity. Our data identify Wb laminin as an extracellular matrix ligand that is essential for integrin-dependent cellular migration in Drosophila.

Animals↗
PubMed1992

Structural comparison of metarhodopsin II, metarhodopsin III, and opsin based on kinetic analysis of Fourier transform infrared difference spectra.

Fourier transform infrared difference spectra were measured at 30-s intervals after a complete bleach of rhodopsin (rho) samples at 20 degrees C and three different pH values. At each pH, all of the spectra could be fit globally to two exponential decay processes. Using a branched unimolecular kinetic model in which metarhodopsin II (meta II) is hydrolyzed to opsin and retinal both directly and through metarhodopsin III (meta III), we calculated rho-->meta II, rho-->meta III, and rho-->opsin difference spectra at each of the pH values and obtained estimates for the microscopic rate constants at each pH. Because of assumptions that had to be made about the branching ratio between the meta II decay pathways, some uncertainties remain in our calculated rho-->meta III difference spectrum at each pH. Nevertheless, our data covering long time ranges, especially those obtained at pH 8, place significant new constraints on the spectrum of meta III and thus on its structure. The rho-->meta II spectrum shows no significant pH dependence over the range examined (pH 5.5-8). However, the rho-->meta III and rho-->opsin spectra each include a limited subset of pH-dependent peaks, which are mostly attributable to titratable amino acid side chains. Our observations can be used to refine an earlier conclusion that the visual pigment refolds to a rhodopsin-like conformation during meta II decay (Rothschild, K.J., J. Gillespie, and W.J. DeGrip. 1987 Biophys. J. 51:345-350). Most of this refolding occurs in the same way at pH values ranging from 5.5 to 8 and whether meta II decays to meta III or opsin. Meta II displays unique spectral perturbations that are mostly attributable to a few residues, probably including three to four aspartic or glutamic acids and an arginine.

Animals↗
PubMed2005

Model predictive control of discrete-time hybrid systems with discrete inputs.

This paper proposes and discusses a model predictive control approach to hybrid systems with discrete inputs only. The algorithm, which takes into account a model of a hybrid system, described as a mixed logical dynamical system, is based on a performance-driven reachability analysis. The algorithm abstracts the behavior of the hybrid system by building a "tree of evolution." The nodes of the tree represent the reachable states of a process, and the branches connect two nodes if a transition exists between the corresponding states. A cost-function value is associated with each node, and based on this value the exploration of the tree is driven. As soon as the exploration of the tree is finished, the corresponding input is applied to the system and the procedure is repeated.

Journal Article↗
PubMed2000

Localization of arginine vasotocin (AVT) mRNA in extrasomal compartments of magnocellular neurons in the chicken hypothalamo-neurohypophysial system.

In the chicken, arginine vasotocin (AVT) is produced in and secreted by magnocellular neurons in the supraoptic (SON) and paraventricular (PVN) nuclei. To test the hypothesis of axonally transported AVT mRNA, the localization of AVT mRNA within extrasomal, axonal/dendritic compartments in the chicken hypothalamo-neurohypophysial system (HNS) were examined using AVT specific in situ hybridization histochemistry (ISHH) and RT-PCR. Many perikarya in the PVN and external--but none in the ventral subgroup of the SON show ISHH signals clearly extended into one or two processes, some with branching collaterals, traceable over a distance of more than 100 microns. Furthermore by using RT-PCR, AVT mRNA was detected in the median eminence and neurohypophysis representing the distal parts of the HNS, mainly consisting of axons and/or axon terminals. These observations of axonal mRNA offer new insights to the organization and function of the avian HNS.

Animals↗
PubMed2002

Preparation and dissolution characteristics of griseofulvin solid dispersions with saccharides.

To improve the solubility of poorly water-soluble drugs, we studied physical characteristics of griseofulvin (GF) solid dispersions with saccharides as the dispersion carrier using a roll mixing method. In all carriers tested, roll mixtures of GF and saccharides gradually became amorphous, and the solubility of GF increased. The solubility of GF was higher in the mixtures with higher molecular weight carriers such as corn starch and processed starch. The dissolution of GF was markedly improved by the GF-Britishgum roll mixture. The initial dissolution rate of these mixtures was 170-fold higher than GF alone. The surface tension of carrier aqueous solutions was low in the processed starch with branched sugar chains. The initial dissolution rate of GF in physical mixtures was correlated with the surface tension of carrier aqueous solutions. The stability of the amorphous state of GF at a high humidity was maintained in the mixtures with carriers with a high molecular weight. These results indicated that the solubility of GF was markedly improved in the roll mixtures. It was suggested that the saccharides with a high molecular weight are useful carriers for solid dispersions.

Chemistry, Pharmaceutical↗
PubMed1999

Painless aortic dissection presenting as hoarseness of voice: cardiovocal syndrome: Ortner's syndrome.

Most of the neurological manifestations of the aortic dissection are due to neuronal ischemia secondary to either extension of the dissection process into a branch artery, or compression of an artery by the false lumen of the dissecting aortic hematoma. However, the enlarging false lumen may directly compress on an adjacent nerve, causing neuronal injury resulting in neurological symptoms. This may particularly take place when a distal intimal tear does not decompress the false lumen, resulting in formation of an expanding blind pouch. About 10% of aortic dissections are painless and may present with symptoms secondary to the complications of the dissection. Although cardiovocal syndrome, or Ortner's syndrome (hoarseness of voice due to involvement of recurrent laryngeal nerve in cardiovascular diseases) has been described with aortic dissection, it has not been reported as an initial presenting feature of this disorder. This report describes the first case of painless aortic dissection presenting with hoarseness of voice, the cardiovocal syndrome. The hoarseness remained the only symptom throughout the entire course of the disease. The aortic dissection was not suspected initially. During surgical exploration, the recurrent laryngeal nerve was found compressed by the false lumen at the level of aortic arch. Aortic root replacement was performed successfully, resulting in complete resolution of the hoarseness. The neurological manifestations of aortic dissection, and the cardiovocal syndrome, are discussed.

Aortic Dissection↗
PubMed2002

Drosophila windpipe codes for a leucine-rich repeat protein expressed in the developing trachea.

The embryonic tracheal system of Drosophila provides an important model for understanding the process of epithelial branching morphogenesis. Here we report the sequence and expression analysis of a novel tracheal gene, named windpipe (wdp). wdp is identical to the predicted gene CG3413 and encodes a transmembrane, leucine-rich repeat family member. wdp transcripts appear abruptly at stage 15 and are restricted to primary tracheal branches that give rise to secondary branches.

Amino Acid Sequence↗
PubMed2004

Mechanisms and products of surface-mediated reductive dehalogenation of carbon tetrachloride by Fe(II) on goethite.

Natural attenuation processes of chlorinated solvents in soils and groundwaters are increasingly considered as options to manage contaminated sites. Under anoxic conditions, reactions with ferrous iron sorbed at iron(hyro)xides may dominate the overall transformation of carbon tetrachloride (CCl4) and other chlorinated aliphatic hydrocarbons. We investigated mechanisms and product formation of CCl4 reduction by Fe(II) sorbed to goethite, which may lead to completely dehalogenated products or to chloroform (CHCl3), a toxic product which is fairly persistent under anoxic conditions. A simultaneous transfer of two electrons and cleavage of two C-Cl bonds of CCl4 would completely circumvent chloroform production. To distinguish between initial one- or two-bond cleavage, 13C-isotope fractionation of CCl4 was studied for reactions with Fe(II)/ goethite (isotopic enrichment factor epsilon = -26.5% percent per thousand) and with model systems for one C-Cl bond cleavage and either single-electron transfer (Fe(II) porphyrin, epsilon = -26.1 percent per thousand) or partial two-electron transfer (polysulfide, epsilon = -22.2 percent per thousand). These epsilon values differ significantlyfrom calculations for simultaneous cleavage of two C-Cl bonds (epsilon approximately equal to -50 percent per thousand), indicating that only one C-Cl bond is broken in the critical first step of the reaction. At pH 7, reduction of CCl4 by Fe(II)/ goethite produced approximately 33% CHCl3, 20% carbon monoxide (CO), and up to 40% formate (HCOO-). Addition of 2-propanol-d8 resulted in 33% CDCl3 and only 4% CO, indicating that both products were generated from trichloromethyl radicals (*CCl3), chloroform by reaction with hydrogen radical donors and CO by an alternative pathway likely to involve surface-bound intermediates. Hydrolysis of CO to HCOO-was surface-catalyzed by goethite butwastoo slow to account for the measured formate concentrations. Chloroform yields slightly increased with pH at constant Fe(II) sorption density, suggesting that pH-dependent surface processes direct product branching ratios. Surface-stabilized intermediates may thus facilitate abiotic mineralization of CCl4, whereas the presence of H radical donors, such as natural organic matter, enhances formation of toxic CHCl3.

Carbon Tetrachloride↗
PubMed2005

Detailed modeling of the reaction of C2H5 + O2.

Modeling of low-temperature ethane oxidation requires an accurate description of the reaction of C(2)H(5) + O(2), because its multiple reaction channels either accelerate the oxidation process via chain branching, or inhibit it by forming stable, less reactive products. We have used a steady-state chemical-activation analysis to generate pressure and temperature dependent rate coefficients for the various channels of this system. Input parameters for this analysis were obtained from ab initio calculations at the CBS-QB3 level of theory with bond-additivity corrections, followed by transition state theory calculations with Wigner tunneling corrections. The chemical-activation analysis used QRRK theory to determine k(E) and the modified strong collision (MSC) model to account for collisional deactivation. This procedure resulted in a C(2)H(5) + O(2) submechanism which was either used directly (possibly augmented with a few C(2)H(5) generating and consuming reactions) or as part of a larger extended mechanism to predict the temperature and pressure dependencies of the overall loss of ethyl and of the yields of ethylene, ethylene oxide, HO(2), and OH. A comparison of the predictions using both mechanisms allowed an assessment of the sensitivity of the experimental data to secondary reactions. Except for the time dependent OH profiles, the predictions using the extended mechanism were in good agreement with the observations. By replacing the MSC model with master equation approaches, both steady-state and time dependent, it was confirmed that the MSC assumption is adequate for the analysis of the C(2)H(5) + O(2) reaction. The good overall performance of the C(2)H(5) + O(2) submechanism developed in this study suggests that it provides a good building block for an ethane oxidation mechanism.

Journal Article↗
PubMed1997

Neurotrophic effects of L-DOPA in postnatal midbrain dopamine neuron/cortical astrocyte cocultures.

L-DOPA is toxic to catecholamine neurons in culture, but the toxicity is reduced by exposure to astrocytes. We tested the effect of L-DOPA on dopamine neurons using postnatal ventral midbrain neuron/cortical astrocyte cocultures in serum-free, glia-conditioned medium. L-DOPA (50 microM) protected against dopamine neuronal cell death and increased the number and branching of dopamine processes. In contrast to embryonically derived glia-free cultures, where L-DOPA is toxic, postnatal midbrain cultures did not show toxicity at 200 microM L-DOPA. The stereoisomer D-DOPA (50-400 microM) was not neurotrophic. The aromatic amino acid decarboxylase inhibitor carbidopa (25 microM) did not block the neurotrophic effect. These data suggest that the neurotrophic effect of L-DOPA is stereospecific but independent of the production of dopamine. However, L-DOPA increased the level of glutathione. Inhibition of glutathione peroxidase by L-buthionine sulfoximine (3 microM for 24 h) blocked the neurotrophic action of L-DOPA. N-Acetyl-L-cysteine (250 microM for 48 h), which promotes glutathione synthesis, had a neurotrophic effect similar to that of L-DOPA. These data suggest that the neurotrophic effect of L-DOPA may be mediated, at least in part, by elevation of glutathione content.

Animals↗
PubMed2002

Reelin, Disabled 1, and beta 1 integrins are required for the formation of the radial glial scaffold in the hippocampus.

The extracellular matrix molecule Reelin is required for the correct positioning of neurons during the development of the forebrain. However, the mechanism of Reelin action on neuronal migration is poorly understood. Reelin is assumed to act on neurons directly, but it may also affect the differentiation of glial cells necessary for neuronal migration. Here we show that a regular glial scaffold fails to form in vivo in the dentate gyrus of mice deficient of Reelin or Disabled 1, a neuronal adaptor protein in the Reelin signaling pathway. A subset of these defects is observed in mice that lack beta(1)-class integrins, known to bind Reelin. Moreover, recombinant Reelin induced branching of glial processes in vitro. Our data suggest that Reelin affects glial differentiation via Disabled 1 and beta(1)-class integrin-dependent signaling pathways.

Animals↗
PubMed1993

RuvA and RuvB proteins of Escherichia coli exhibit DNA helicase activity in vitro.

The SOS-inducible ruvA and ruvB gene products of Escherichia coli are required for normal levels of genetic recombination and DNA repair. In vitro, RuvA protein interacts specifically with Holliday junctions and, together with RuvB (an ATPase), promotes their movement along DNA. This process, known as branch migration, is important for the formation of heteroduplex DNA. In this paper, we show that the RuvA and RuvB proteins promote the unwinding of partially duplex DNA. Using single-stranded circular DNA substrates with annealed fragments (52-558 nucleotides in length), we show that RuvA and RuvB promote strand displacement with a 5'-->3' polarity. The reaction is ATP-dependent and its efficiency is inversely related to the length of the duplex DNA. These results show that the ruvA and ruvB genes encode a DNA helicase that specifically recognizes Holliday junctions and promotes branch migration.

Amino Acid Sequence↗
PubMed1994

Kinetics of an RNA conformational switch.

The spliced leader RNA from Leptomonas collosoma has two competing secondary structures of nearly equal free energy. Short, complementary oligonucleotides can drive the structure from one form of the other. We report stopped-flow rapid-mixing and temperature-jump measurements of the kinetics of the structural switch. At high concentrations of oligonucleotide, the rate of binding becomes limited by the rate of the structural switch, which occurs on a time scale of a fraction of a second. The low activation energy observed for the process implies a branch migration type of mechanism in which portions of the two competing helices transiently coexist.

Animals↗