Showing papers by "Federal University of Rio de Janeiro published in 1999"

Choline and selective antagonists identify two subtypes of nicotinic acetylcholine receptors that modulate GABA release from CA1 interneurons in rat hippocampal slices.

Abstract: Neuronal nicotinic receptors (nAChR) are known to control transmitter release in the CNS. Thus, this study was aimed at exploring the diversity and localization of nAChRs present in CA1 interneurons in rat hippocampal slices. The use of a U-tube as the agonist delivery system was critical for the reliable detection of nicotinic responses induced by brief exposure of the neurons to ACh or to the alpha7 nAChR-selective agonist choline. The present study demonstrated that CA1 interneurons, in addition to expressing functional alpha7 nAChRs, also express functional alpha4beta2-like nAChRs and that activation of both receptors facilitates an action potential-dependent release of GABA. Depending on the experimental condition, one of the following nicotinic responses was recorded from the interneurons by means of the patch-clamp technique: a nicotinic whole-cell current, depolarization accompanied by action potentials, or GABA-mediated postsynaptic currents (PSCs). Responses mediated by alpha7 nAChRs were short-lasting, whereas those mediated by alpha4beta2 nAChRs were long-lasting. Thus, phasic or tonic inhibition of CA1 interneurons may be achieved by selective activation of alpha7 or alpha4beta2 nAChRs, respectively. It can also be suggested that synaptic levels of choline generated by hydrolysis of ACh in vivo may be sufficient to control the activity of the alpha7 nAChRs. The finding that methyllycaconitine and dihydro-beta-erythroidine (antagonists of alpha7 and alpha4beta2 nAChRs, respectively) increased the frequency and amplitude of GABAergic PSCs suggests that there is an intrinsic cholinergic activity that sustains a basal level of nAChR activity in these interneurons.

Structures of the M2 channel-lining segments from nicotinic acetylcholine and NMDA receptors by NMR spectroscopy.

Abstract: The structures of functional peptides corresponding to the predicted channel-lining M2 segments of the nicotinic acetylcholine receptor (AChR) and of a glutamate receptor of the NMDA subtype (NMDAR) were determined using solution NMR experiments on micelle samples, and solid-state NMR experiments on bilayer samples. Both M2 segments form straight transmembrane α-helices with no kinks. The AChR M2 peptide inserts in the lipid bilayer at an angle of 12° relative to the bilayer normal, with a rotation about the helix long axis such that the polar residues face the N-terminal side of the membrane, which is assigned to be intracellular. A model built from these solid-state NMR data, and assuming a symmetric pentameric arrangement of M2 helices, results in a funnel-like architecture for the channel, with the wide opening on the N-terminal intracellular side.

Divergence‐Measure Fields and Hyperbolic Conservation Laws

Abstract: We analyze a class of L 1 vector elds, called divergence-measure elds. We establish the Gauss-Green formula, the normal traces over subsets of Lipschitz boundaries, and the product rule for this class of L 1 elds. Then we apply this theory to analyzeL 1 entropy solutions of initial-boundary-value problems for hyperbolic conservation laws and to study the ways in which the solutions assume their initial and boundary data. The examples of conservation laws include multidimensional scalar equations, the system of nonlinear elasticity, and a class ofm m systems with afne characteristic hypersurfaces. The analysis inL 1 also extends toL p .

Detecting defects in object-oriented designs: using reading techniques to increase software quality

Abstract: Inspections can be used to identify defects in software artifacts In this way, inspection methods help to improve software quality, especially when used early in software development Inspections of software design may be especially crucial since design defects (problems of correctness and completeness with respect to the requirements, internal consistency, or other quality attributes) can directly affect the quality of, and effort required for, the implementationWe have created a set of “reading techniques” (so called because they help a reviewer to “read” a design artifact for the purpose of finding relevant information) that gives specific and practical guidance for identifying defects in Object-Oriented designs Each reading technique in the family focuses the reviewer on some aspect of the design, with the goal that an inspection team applying the entire family should achieve a high degree of coverage of the design defectsIn this paper, we present an overview of this new set of reading techniques We discuss how some elements of these techniques are based on empirical results concerning an analogous set of reading techniques that supports defect detection in requirements documents We present an initial empirical study that was run to assess the feasibility of these new techniques, and discuss the changes made to the latest version of the techniques based on the results of this study

Tests of technical trading strategies in the emerging equity markets of Latin America and Asia

Abstract: This study examines the potential profit of ten Variable Length Moving Average (VMA) technical trading rules in ten emerging equity markets in Latin America and Asia from January 1982 through April 1995. The average difference in buy − sell returns after trading costs for each rule and country are compared to a buy and hold strategy. Taiwan, Thailand and Mexico emerge as markets where technical trading strategies may be profitable. We find no strong evidence of profitability for the other markets. However, we find that 82 out of the 100 country–trading rule combinations tested in ten emerging markets, disregarding their statistical significance, correctly predict the direction of changes in the return series. These findings may provide investors with important asset allocation information.

A review on sisal fiber reinforced polymer composites

Abstract: O uso da madeira como material de construcao continua crescendo mundialmente enquanto a disponibilidade deste recurso natural esta diminuindo. Esta situacao tem conduzido ao desenvolvimento de materiais alternativos. Dentre os varios materiais sinteticos que tem sido explorados, os compositos polimericos reivindicam e buscam uma maior participacao como material de construcao. Nos ultimos anos tem se observado um crescente interesse na utilizacao de fibras naturais como reforco de matrizes polimericas para a producao de materiais de baixo custo. As fibras naturais sao reforcos com grande potencialidade e seu uso tem se dado de forma mais tradicional do que cientifica. Elas tem se prestado a inumeras aplicacoes ao longo do tempo, mas a aplicacao da tecnologia dos materiais visando a sua utilizacao como reforco de matrizes polimericas e relativamente recente. As dificuldades economicos e sociais observadas em muitos dos paises em desenvolvimento, onde as fibras naturais sao abundantes, requerem que cientistas e engenheiros apliquem tecnologias apropriadas para utilizar estas fibras da forma mais eficiente possivel, de tal maneira que se possa produzir materiais compositos polimericos de boa qualidade visando a atender a demanda da populacao por habitacoes e componentes habitacionais. Dentre as varias fibras naturais, a fibra de sisal e de particular interesse uma vez que os compositos que a utilizam como reforco apresentam alta resistencia ao impacto alem de possuirem moderada resistencia a tracao e a flexao. O presente artigo apresenta uma revisao dos trabalhos de pesquisa publicados no campo dos compositos polimericos ecologicos, especialmente no que se refere aos compositos reforcados com fibras de sisal, visando seu uso como material de construcao. Enfase especial e dada a micro-estrutura e propriedades da fibra de sisal, as tecnicas de processamento e as propriedades fisicas e mecânicas dos compositos polimericos reforcados com fibras de sisal.

Effects of recent human colonization on the presence of mercury in amazonian ecosystems

Abstract: Three Hg sources were characterised and mass balance calculations were used to determine their relative contributions to the contamination of the Amazonian environment About an order of magnitude more Hg is emitted to the atmosphere by goldmining activity than by the burning of forest biomass However, anthropogenic atmospheric Hg cannot account for the high Hg burdens found in terrestrial ecosystems: deposition of Hg from goldmining sources is estimated to account for less than 3% of the Hg present in the surface horizons of soils We propose that erosion of deforested soils following human colonization constitutes a major disturbance of the natural Hg cycle Deforestation thus increases soil Hg mobilisation by runoff, which may explain the increase of Hg burdens in Amazonian aquatic ecosystems in newly colonized watersheds

Growth and Chemical Composition of Spirulina Maxima and Spirulina Platensis Biomass at Different Temperatures

Abstract: The influence of temperature on growth and biomass composition of two species of Spirulina, S. maxima and S. platensis used for food was studied. A 4L fermenter with temperature and agitation control was used to cultivate both species. Under continuous light, maximum cell production of 2.4 g l−1 was verified for both cultures studied at temperatures above 25 °C: S. maxima (30 °C and 35 °C) and S. platensis (25 °C and 30 °C). An accentuated lag phase was observed for all cultures at lower temperatures (15–20 °C), and a maximum biomass production of 1.5 g l−1 was achieved. It was also observed that an increase of temperature caused a marked decrease in protein content, while carbohydrate synthesis was stimulated. The concentration of γ-linolenic acid varied from 11–16% for S. maxima and from 12–14% for S. platensis, at the optimum growth temperatures. Greater culture volumes were also studied in order to compare the performance of glass and plastic containers. At optimum growth temperature, S. maxima produced the same cell growth and similar final biomass composition.

Expression of lymphocyte-endothelial receptor-ligand pairs, α4β7/MAdCAM-1 and OX40/OX40 ligand in the colon and jejunum of patients with inflammatory bowel disease

Abstract: BACKGROUND—The interaction between leucocytes and vascular endothelial cells is essential for leucocyte migration into inflammatory sites. AIMS—To study the local expression of the pairs of complementary molecules, α4β7/mucosal addressin cell adhesion molecule (MAdCAM-1) and OX40/OX40 ligand in the lamina propria of the colon and jejunum of patients with inflammatory bowel disease. METHODS—Ten patients with active ulcerative colitis (UC), nine with active Crohn's disease (CD), and seven irritable bowel syndrome (IBS) controls were submitted to endoscopic and peroral jejunal biopsies. Specimens were immunostained by indirect alkaline phosphatase using antibodies against CD3, intercellular adhesion molecule (ICAM) 1, α4β7, MAdCAM-1, and OX40. An OX40-mouse-IgG fusion protein was used to detect OX40 ligand on frozen sections. Immunohistological analysis was carried out by optical microscopy using a computer assisted image analyser. RESULTS—Colonic lamina propria of patients with CD and UC showed increased density of CD3+, α4β7+, and OX40+ cells compared with IBS controls. ICAM-1, MAdCAM-1, and OX40 ligand positive vessels were also increased compared with IBS controls. No significant difference was found in the density of any of these cells in the jejunal mucosa of patients compared with IBS controls. CONCLUSIONS—The expression of MAdCAM-1 and OX40 ligand on gut endothelial and OX40+ cells is increased in sites of mucosal inflammation in patients with inflammatory bowel disease. No evidence was found for increased lamina propria T cells or increased vascular adhesion molecule expression in the proximal intestine of patients with distal inflammatory bowel disease. Keywords: adhesion molecules; mucosal immunity; T lymphocytes; inflammatory bowel disease

P2Z/P2X7 receptor-dependent apoptosis of dendritic cells.

Abstract: Macrophages and thymocytes express P2Z/P2X7 nucleotide receptors that bind extracellular ATP. These receptors play a role in immune development and control of microbial infections, but their presence on dendritic cells has not been reported. We investigated whether extracellular ATP could trigger P2Z/P2X7 receptor-dependent apoptosis of dendritic cells. Apoptosis could be selectively triggered by tetrabasic ATP, since other purine/pyrimidine nucleotides were ineffective, and it was mimicked by the P2Z receptor agonist, benzoylbenzoyl ATP, and blocked by magnesium and the irreversible antagonist, oxidized ATP. RT-PCR analysis confirmed the mRNA expression of the P2Z/P2X7 receptor and the absence of P2X1. Caspase inhibitors and cycloheximide had only a partial effect on the apoptosis, suggesting that a caspase-independent mechanism may also be operative. Brief treatment with ATP led to an increase in the intracellular calcium concentration and permeabilization of the plasma membrane to Lucifer yellow, which diffused throughout the dendritic cell cytosol. Other small extracellular molecules may thus attain a similar intracellular distribution, perhaps activating endogenous proteases that contribute to initiation of apoptosis.

Selective Effect of 2′,6′-Dihydroxy-4′-Methoxychalcone Isolated from Piper aduncum on Leishmania amazonensis

Abstract: 2',6'-Dihydroxy-4'-methoxychalcone (DMC) was purified from the dichloromethane extract of Piper aduncum inflorescences. DMC showed significant activity in vitro against promastigotes and intracellular amastigotes of Leishmania amazonensis, with 50% effective doses of 0.5 and 24 micrograms/ml, respectively. Its inhibitory effect on amastigotes is apparently a direct effect on the parasites and is not due to activation of the nitrogen oxidative metabolism of macrophages, since the production of nitric oxide by both unstimulated and recombinant gamma interferon-stimulated macrophages was decreased rather than increased with DMC. The phagocytic activity of macrophages was functioning normally even with DMC concentrations as high as 80 micrograms/ml, as seen by electron microscopy and by the uptake of fluorescein isothiocyanate-labeled beads. Ultrastructural studies also showed that in the presence of DMC the mitochondria of promastigotes were enlarged and disorganized. Despite destruction of intracellular amastigotes, no disarrangement of macrophage organelles were observed, even at 80 micrograms of DMC/ml. These observations suggest that DMC is selectively toxic to the parasites. Its simple structure may well enable it to serve as a new lead compound for the synthesis of novel antileishmanial drugs.

Does cosmopolitanism result from overconservative systematics? a case study using the marine sponge chondrilla nucula.

Abstract: The sponge species Chondrilla nucula has a simple morphology and a very wide geographical distribution. To verify whether the latter might be an artifact of the former, samples of this species were collected across 10,000 km of its range, in the Mediterranean, the Caribbean, and the southwestern atlantic. The classical (spicule morphology) and molecular (allozymes) systematic approaches were compared, to try to define the geographic limits between populations and detect possible cryptic species. We found five distinct genetic forms within C. nucula that sometimes showed morphological homogeneity and other times plasticity. The difference in size of spicules could not be related to the clear-cut genetic differences, suggesting that the use of spicule sizes for sponge systematics should be reappraised. The population of one of the genetic forms along 3000 km of the Brazilian coast was highly structured (FST = 0.21; Ne m = 0.96). Our results reject the null hypothesis of cosmopolitanism of C. nucula and indicate that the putative worldwide distribution of some marine sponges, and possibly many other benthic invertebrates, may be the result of overly conservative systematics. Cryptic species appear to be particularly prevalent when genera are well defined but species are characterized by only a few morphological characters.

Divergent roles for thyroid hormone receptor β isoforms in the endocrine axis and auditory system

Abstract: Thyroid hormone receptors (TRs) modulate various physiological functions in many organ systems. The TRα and TRβ isoforms are products of 2 distinct genes, and the β1 and β2 isoforms are splice variants of the same gene. Whereas TRα1 and TRβ1 are widely expressed, expression of the TRβ2 isoform is mainly limited to the pituitary, triiodothyronine-responsive TRH neurons, the developing inner ear, and the retina. Mice with targeted disruption of the entire TRβ locus (TRβ-null) exhibit elevated thyroid hormone levels as a result of abnormal central regulation of thyrotropin, and also develop profound hearing loss. To clarify the contribution of the TRβ2 isoform to the function of the endocrine and auditory systems in vivo, we have generated mice with targeted disruption of the TRβ2 isoform. TRβ2-null mice have preserved expression of the TRα and TRβ1 isoforms. They develop a similar degree of central resistance to thyroid hormone as TRβ-null mice, indicating the important role of TRβ2 in the regulation of the hypothalamic-pituitary-thyroid axis. Growth hormone gene expression is marginally reduced. In contrast, TRβ2-null mice exhibit no evidence of hearing impairment, indicating that TRβ1 and TRβ2 subserve divergent roles in the regulation of auditory function.

Generalized Vaidya Solutions

Abstract: A large family of solutions, representing, ingeneral, spherically symmetric Type II fluid, ispresented, which includes most of the known solutions tothe Einstein field equations, such as, the monopole-de Sitter-charged Vaidya ones

Glial fibrillary acidic protein (GFAP): modulation by growth factors and its implication in astrocyte differentiation

Abstract: Intermediate filament (IF) proteins constitute an extremely large multigene family of developmentally and tissue-regulated cytoskeleton proteins abundant in most vertebrate cell types. Astrocyte precursors of the CNS usually express vimentin as the major IF. Astrocyte maturation is followed by a switch between vimentin and glial fibrillary acidic protein (GFAP) expression, with the latter being recognized as an astrocyte maturation marker. Levels of GFAP are regulated under developmental and pathological conditions. Upregulation of GFAP expression is one of the main characteristics of the astrocytic reaction commonly observed after CNS lesion. In this way, studies on GFAP regulation have been shown to be useful to understand not only brain physiology but also neurological disease. Modulators of GFAP expression include several hormones such as thyroid hormone, glucocorticoids and several growth factors such as FGF, CNTF and TGF beta, among others. Studies of the GFAP gene have already identified several putative growth factor binding domains in its promoter region. Data obtained from transgenic and knockout mice have provided new insights into IF protein functions. This review highlights the most recent studies on the regulation of IF function by growth factors and hormones.

Deterministic bell states and measurement of the motional state of two trapped ions

Abstract: We present a method for the deterministic generation of all the electronic Bell states of two trapped ions. It involves the combination of a purely dispersive with a resonant laser excitation of vibronic transitions of the ions. In contrast to other methods presented up to now, our proposal does not require differential laser addressing of the individual ions and may be easily implemented with present available techniques. It is further shown that this excitation scheme is highly adequate for the complete determination of the motional state of the ions.

The Connectionist Inductive Learning and Logic Programming System

Abstract: This paper presents the Connectionist Inductive Learning and Logic Programming System (C-IL^2P). C-IL^2P is a new massively parallel computational model based on a feedforward Artificial Neural Network that integrates inductive learning from examples and background knowledge, with deductive learning from Logic Programming. Starting with the background knowledge represented by a propositional logic program, a translation algorithm is applied generating a neural network that can be trained with examples. The results obtained with this refined network can be explained by extracting a revised logic program from it. Moreover, the neural network computes the stable model of the logic program inserted in it as background knowledge, or learned with the examples, thus functioning as a parallel system for Logic Programming. We have successfully applied C-IL^2P to two real-world problems of computational biology, specifically DNA sequence analyses. Comparisons with the results obtained by some of the main neural, symbolic, and hybrid inductive learning systems, using the same domain knowledge, show the effectiveness of C-IL^2P.

Expression of nicotinic acetylcholine receptor subunits in the cerebral cortex in Alzheimer's disease: histotopographical correlation with amyloid plaques and hyperphosphorylated-tau protein.

Abstract: Impairment of cholinergic transmission and decreased numbers of nicotinic binding sites are well-known features accompanying the cognitive dysfunction seen in Alzheimer's disease (AD). In order to elucidate the underlying cause of this cholinoceptive dysfunction, the expression of two pharmacologically different nicotinic acetylcholine receptor (nAChR) subunits (alpha4, alpha7) was studied in the cerebral cortex of Alzheimer patients as compared to controls. Patch-clamp recordings of 14 dissociated neurons of control cortices showed responses suggesting the existence of alpha4- and alpha7-containing functional nAChRs in the human cortex. In cortices of Alzheimer patients and controls, the pattern of distribution and the number of alpha4 and alpha7 mRNA-expressing neurons were similar, whereas at the protein level a decrease in the density of alpha4- and alpha7-expressing neurons of approximately 30% was observed in Alzheimer patients. The histotopographical correlation of nAChR expression with accompanying pathological changes, e.g. accumulation of hyperphosphorylated-tau (HP-tau) protein and beta-amyloid showed that neurons in the vicinity of beta-amyloid plaques bore both nAChR transcripts. Neurons heavily labelled for HP-tau, however, expressed little or no alpha4 and alpha7 mRNA. These results point to an impaired synthesis of nAChRs on the protein level as a possible cause of the cholinoceptive deficit in AD. Further investigations need to elucidate whether interactions of HP-tau with nAChR mRNA, or alterations in the quality of alpha4 and alpha7 transcripts give rise to decreased protein expression at the level of individual neurons.

Ab Initio Calculations of Absolute pKa Values in Aqueous Solution I. Carboxylic Acids

Abstract: A thermodynamical cycle is proposed to calculate absolute pKa values for a Bronsted acid in aqueous solution. The solvent (water) was represented by a dielectric using the polarizable continuum model (PCM), and the absolute pKa values of some aliphatic carboxylic acids were computed. The results indicate that the proposed methodology seems to be capable of predicting reasonably good absolute pKa values, although in some cases appreciable deviations are observed, which can be related to neglecting the molecular motion contributions (ΔGMm) to the solvation energy (ΔGsolv).

Amamentação: um híbrido natureza-cultura

Abstract: Objective: To contribute to the creation of a new theoretical synthesis about the relationship between the biological and social dimensions of breastfeeding, categorizing it as a nature-nurture hybrid. Sources of data: The methodological approach of the present article was based on the qualitative health research frame, and data were analyzed on the basis of dialectic-hermeneutic principles. Primary sources, comprising historical documents, books, scientific articles and medical theses written in the 19th and 20th centuries were analyzed. Summary of the findings: Depending on the moment in history and on the expectations that surround the act of breastfeeding, the aspects related to nature and nurture, i.e., to biology and society, sometimes separate out and sometimes intermingle. A comprehensive approach to breastfeeding makes possible to see that it had to be considered instinctive, natural and biological in order to be assimilated as a cultural habit, and thus, it is not open to any kind of questioning. On other occasions, particularly in the course of the past decade, there has been a steady tendency to supplant traditional biological reductionism, which yielded cultural interpretations that do not reduce the human being to the status of a mammal like any other. Under this point of view, breastfeeding, in addition to being biologically determined, is socially conditioned, and thus constitutes an act embedded in ideologies and determinants resulting from the concrete conditions of life. In real life, however, a process apparently so natural, so loaded with affection and emotion is, in fact, affected by the most aggressive market interests, very often presented as scientific knowledge and decked out as health provisions. Conclusion: Breastfeeding focused as a nature-culture hybrid symbolizes the theoretical and methodological changes in the field, especially in the late 1990s. These changes reflect a renewed appreciation of biology and a more in-depth approach to interdisciplinary processes.

Partial hyperbolicity and robust transitivity

Abstract: Throughout this paper M denotes a three-dimensional boundaryless compact manifold and Diff(M) the space of gl-diffeomorphisms defined on M endowed with the usual Cl-topology. A ~-invariant set A is transitive if A=w(x) for some xEA. Here w(x) is the forward limit set of x (the accumulation points of the positive orbit of x). The maximal invariant set of ~ in an open set U, denoted by A~(U), is the set of points whose whole orbit is contained in U, i.e. A ~ ( U ) = ~ i e z ~i(U). The set A~(U) is robustly transitive if Ar is transitive for every diffeomorphism r CLclose to ~. A diffeomorphism ~EDiff(M) is transitive if M=w(x) for some xEM, i.e. if A ~ ( M ) = M is transitive. Analogously, ~ is robustly transitive if every r gLclose to also is transitive, i.e. if A ~ ( M ) = M is robustly transitive. In this paper we focus our attention on forms of hyperbolicity (uniform, partial and strong partial) of a maximal invariant set A~(U) derived from its robust transitivity. Observe that U can be equal to M, and then ~ is robustly transitive. On one hand, in dimension one there do not exist robustly transitive diffeomorphisms: the diffeomorphisms with finitely many hyperbolic periodic points (Morse~ Smale) are open and dense in Diff(S1). On the other hand, for two-dimensional diffeomorphisms, every robustly transitive set A~(U) is a basic set (i.e. A~(U) is hyperbolic, transitive, and the periodic points of ~ are dense in A~(U)). In particular, every robustly transitive surface diffeomorphism is Anosov and the unique surface which supports such diffeomorphisms is the torus T 2. These assertions follow from [M3] and [M4]. In dimension bigger than or equal to three, besides Anosov (hyperbolic) diffeomorphisms there are robustly transitive diffeomorphisms of nonhyperbolic type. As far as we know, three types of such diffeomorphisms have been constructed: skew products,