456 research outputs found
Variedades fitoquímicas en plantas aromáticas argentinas
No full textLas investigaciones fotoquímicas sobre plantas silvestres o cultivadas de Argentina desde el punto de vista de sus variaciones para una misma especie, es decir, de sus diferencias en la composición química de las mismas, han sido hasta ahora muy poco estudiadas.
En el presente trabajo se pasan en revista siete especies en la composición química de cuyas esencias volátiles se ha encontrado notables variaciones. Dichas especies son Acantholippia seriphioides (A. GRAY) MOLD., Mentha piperita L., Mentha spicata HUDS., Mentha rotundifolia L., Limpia alba (MILL.) N. E. BR. y Satureja odora (GRIS.) EPL., de las cuales tres se hallan representadas en la flora mendocina.
Parecería que las variaciones registradas fueran debidas a factores mesológicos lo que abriría un vasto campo a nuevas investigaciones fotoquímicas.Fil: Fester, Gustavo A.
fester, a Candidate Allorecognition Receptor from a Primitive Chordate
No full textSummaryHistocompatibility in the primitive chordate, Botryllus schlosseri, is controlled by a single, highly polymorphic locus, the FuHC. By taking a forward genetic approach, we have identified a locus encoded near the FuHC, called fester, which is polymorphic, polygenic, and inherited in distinct haplotypes. Somatic diversification occurs through extensive alternative splicing, with each individual expressing a unique repertoire of splice forms, both membrane bound and potentially secreted, all expressed in tissues intimately associated with histocompatibility. Functional studies, via both siRNA-mediated knockdown and direct blocking by monoclonal antibodies raised against fester, were able to disrupt predicted histocompatibility outcomes. The genetic and somatic diversity, coupled to the expression and functional data, suggests that fester is a receptor involved in histocompatibility
Estrus cyclicity of spinogenesis: underlying mechanisms
Get PDFHippocampal spine density varies with the estrus cycle. The cyclic change in estradiol levels in serum was hypothesized to underlie this phenomenon, since treatment of ovariectomized animals with estradiol induced an increase in spine density in hippocampal dendrites of rats, as compared to ovariectomized controls. In contrast, application of estradiol to hippocampal slice cultures did not promote spinogenesis. In addressing this discrepancy, we found that hippocampal neurons themselves are capable of synthesizing estradiol de novo. Estradiol synthesis can be suppressed by aromatase inhibitors and by knock-down of Steroid Acute Regulatory Protein (StAR) and enhanced by substrates of steroidogenesis. Expression of estrogen receptors (ERs) and synaptic proteins, synaptogenesis, and long-term potentiation (LTP) correlated positively with aromatase activity in hippocampal cultures without any difference between genders. All effects due to inhibition of aromatase activity were rescued by application of estradiol to the cultures. Most importantly, gonadotropin-releasing hormone (GnRH) increased estradiol synthesis dose-dependently via an aromatase-mediated mechanism and consistently increased spine synapse density and spinophilin expression. As a consequence, our data suggest that cyclic fluctuations in spine synapse density result from pulsative release of GnRH from the hypothalamus and its effect on hippocampal estradiol synthesis, rather than from varying levels of serum estradiol. This hypothesis is further supported by higher GnRH receptor (GnRH-R) density in the hippocampus than in the cortex and hypothalamus and the specificity of estrus cyclicity of spinogenesis in the hippocampus, as compared to the cortex
3D mechanical analysis of aeronautical plain bearings: Validation of a finite element model from measurement of displacement fields by digital volume correlation and optical scanning tomography
Get PDFOn Airbus aircraft, spherical plain bearings are used on many components; in particular to link engine to pylon or pylon to wing. Design of bearings is based on contact pressure distribution on spherical surfaces. To determine this distribution, a 3D analysis of the mechanical behaviour of aeronautical plain bearing is presented in this paper. A numerical model has been built and validated from a comparison with 3D experimental measurements of kinematic components. For that, digital volume correlation (DVC) coupled with optical scanning tomography (OST) is employed to study the mechanical response of a plain bearing model made in epoxy resin. Experimental results have been compared with the ones obtained from the simulated model. This comparison enables us to study the influence of various boundary conditions to build the FE model. Some factors have been highlighted like the fitting behaviour which can radically change contact pressure distribution. This work shows the contribution of a representative mechanical environment to study precisely mechanical response of aeronautical plain bearings
The <it>fester</it> locus in <it>Botryllus schlosseri</it> experiences selection
Get PDFAbstract Background Allorecognition, the ability of an organism to distinguish self from non-self, occurs throughout the entire tree of life. Despite the prevalence and importance of allorecognition systems, the genetic basis of allorecognition has rarely been characterized outside the well-known MHC (Major Histocompatibility Complex) in vertebrates and SI (Self-Incompatibility) in plants. Where loci have been identified, their evolutionary history is an open question. We have previously identified the genes involved in self/non-self recognition in the colonial ascidian Botryllus schlosseri, and we can now begin to investigate their evolution. In B. schlosseri, colonies sharing 1 or more alleles of a gene called FuHC (Fusion Histocompatibility) will fuse. Protein products of a locus called fester, located ~300 kb from FuHC, have been shown to play multiple roles in the histocompatibility reaction, as activating and/or inhibitory receptors. We test whether the proteins encoded by this locus are evolving neutrally or are experiencing balancing, directional, or purifying selection. Results Nearly all of the variation in the fester locus resides within populations. The 13 housekeeping genes (12 nuclear genes and mitochondrial cytochrome oxidase I) have substantially more structure among populations within groups and among groups than fester. All polymorphism statistics (Tajima's D, Fu and Li's D* and F*) are significantly negative for the East Coast A-type alleles, and Fu and Li's F* statistic is significantly negative for the West Coast A-type alleles. These results are likely due to selection rather than demography, given that 10 of the housekeeping loci have no populations with significant values for any of the polymorphism statistics. The majority of codons in the fester proteins have ω values 95% posterior probability of ω values > 1. Conclusion Fester proteins are evolving non-neutrally. The polymorphism statistics are consistent with either purifying selection or directional selection. The ω statistics show that the majority of the protein is experiencing purifying selection (ω 1 is compatible with either scenario. The distribution of variation within and among populations points towards balancing selection and away from directional selection. While these data do not provide unambiguous support for a specific type of selection, they contribute to our evolutionary understanding of a critical biological process by determining the forces that affect loci involved in allorecognition.</p
Synaptopodin is regulated by aromatase activity
No full textLocally synthesized estradiol plays an important role in synaptic plasticity in the hippocampus. We have previously shown that in hippocampal neurons, activity of the enzyme aromatase, which converts testosterone into estradiol, is reduced via Ca2+-dependent phosphorylation. Synaptopodin is a highly estrogen responsive protein, and it has been shown that it is an important regulator of synaptic plasticity, mediated by its close association with internal calcium stores. In this study, we show that the expression of synaptopodin is stronger in the hippocampus of female animals than in that of male animals. Phosphorylation of aromatase, using letrozole, however, down-regulates synaptopodin immunohistochemistry in the hippocampus of both male and females. Similarly, in aromatase knock-out mice synaptopodin expression in the hippocampus is reduced sex independently. Using primary-dissociated hippocampal neurons, we found that evoked release of Ca2+ from internal stores down regulates aromatase activity, which is paralleled by reduced expression of synaptopodin. Opposite effects were achieved after inhibition of the release. Calcium-dependent regulation of synaptopodin expression was abolished when the control of aromatase activity by the Ca2+ transients was disrupted. Our data suggest that the regulation of aromatase activity by Ca2+ transients in neurons contributes to synaptic plasticity in the hippocampus of male and female animals as an on- site regulatory mechanism.Deutsche Forschungsgemeinschaf
Cholesterol-Promoted Synaptogenesis Requires the Conversion of Cholesterol to Estradiol in the Hippocampus
No full textCholesterol of glial origin promotes synaptogenesis (Mauch et al., (2001) Science 294:1354-1357). Because in the hippocampus local estradiol synthesis is essential for synaptogenesis, we addressed the question of whether cholesterol-promoted synapse formation results from the function of cholesterol as a precursor of estradiol synthesis in this brain area. To this end, we treated hippocampal cultures with cholesterol, estradiol, or with letrozole, a potent aromatase inhibitor. Cholesterol increased neuronal estradiol release into the medium, the number of spine synapses in hippocampal slice cultures, and immunoreactivity of synaptic proteins in dispersed cultures. Simultaneous application of cholesterol and letrozole or blockade of estrogen receptors by ICI 182 780 abolished cholesterol-induced synapse formation. As a further approach, we inhibited the access of cholesterol to the first enzyme of steroidogenesis by knock-down of steroidogenic acute regulatory protein, the rate-limiting step in steroidogenesis. A rescue of reduced synaptic protein expression in transfected cells was achieved by estradiol but not by cholesterol. Our data indicate that in the hippocampus cholesterol-promoted synapse formation requires the conversion of cholesterol to estradiol. (C) 2009 Wiley-Liss, Inc.Deutsche Forschungsgemeinschaft [Ru 436/4-4
Estrogen-regulated synaptogenesis in the hippocampus: Sexual dimorphism in vivo but not in vitro
No full textHippocampal neurons are capable of synthesizing estradiol de novo. Estradiol synthesis can be suppressed by aromatase inhibitors and by knock-down of steroid acute regulatory protein (StAR), whereas elevated levels of substrates of steroidogenesis enhance estradiol synthesis. In rat hippocampal cultures, the expression of estrogen receptors (ERs) and synaptic proteins, as well as synapse density, correlated positively with aromatase activity, regardless of whether the cultures originated from males or females. All effects induced by the inhibition of aromatase activity were rescued by application of estradiol to the cultures. In vivo, however, systemic application of letrozole, an aromatase inhibitor, induced synapse loss in female rats, but not in males. Furthermore, in the female hippocampus, density of spines and spine synapses varied with the estrus cycle. In addressing this in vivo-in vitro discrepancy, we found that gonadotropin-releasing hormone (GnRH) regulated estradiol synthesis via an aromatase-mediated mechanism and consistently regulated spine synapse density and the expression of synaptic proteins. Along these lines, GnRH receptor density was higher in the hippocampus than in the cortex and hypothalamus, and estrus cyclicity of spinogenesis was found in the hippocampus, but not in the cortex. Since GnRH receptor expression also varies with the estrus cycle, the sexual dimorphism in estrogen-regulated spine synapse density in the hippocampus very likely results from differences in the GnRH responsiveness of the male and the female hippocampus. This article is part of a Special Issue entitled 'Neurosteroids'. (C) 2011 Elsevier Ltd. All rights reserved.Deutsche Forschungsgemeinschaf
Endocrine regulation of estrogen synthesis in the hippocampus?
No full textEstradiol synthesis in the ovaries is regulated via feedback mechanisms mediated by gonadotrophin-releasing hormone (GnRH) and gonadotrophins, secreted by the hypothalamus and the pituitary, respectively. Estradiol synthesis also takes place in the hippocampus. In hippocampal slice cultures of female animals, GnRH regulates estradiol synthesis dose-dependently. Hence, both hippocampal and ovarian estradiol synthesis are synchronized by GnRH. Hippocampus-derived estradiol is essential to synapse stability and maintenance because it stabilizes the spine cytoskeleton of hippocampal neurons. Inhibition of hippocampal estradiol synthesis in mice, however, results in loss of spines and spine synapses in females, but not in males. Stereotaxic application of GnRH to the hippocampus of female rats confirms the regulatory role of GnRH on estradiol synthesis and synapse density in the female hippocampus in vivo. This regulatory role of GnRH necessarily results in estrus cyclicity of spine density in the hippocampus of females. (C) 2013 Elsevier GmbH. All rights reserved.Deutsche Forschungsgemeinschaf
Numerical simulation of flexural tests in metal ceramic composites
Get PDFTCC (graduação) - Universidade Federal de Santa Catarina. Campus Joinville. Engenharia Naval.O presente trabalho tem como objetivo simular com um software o processo de produção (compactação e sinterização) e ensaios de flexão em materiais compósitos de metal e cerâmica. Tais compósitos são compostos de particulados e/ou grãos dentro de uma matriz. Esses materiais particulados são simulados utilizando o Método de Elementos Discretos (MED), que calcula o movimento de um número finito de partículas de um sistema ou durante um processo. Com o programa de MED é possível realizar a produção de vigas em microescala pela compactação de partículas de alumina e aço, com três variações de composição. Um modelo de ligação é utilizado para simular o material após a sinterização e posteriormente essas vigas são submetidas a um teste de flexão de três pontos, onde é possível obter o módulo de elasticidade do material compósito. Resultados satisfatórios foram obtidos ao comparar com dados de experimentos reais. O modelo de ligação foi validado para o material a partir da análise da microestrutura simulada e dos resultados do módulo de elasticidade.The objective of the the present work is to simulate with a software the production process (compaction and sintering) and flexural tests in a metal ceramic composite. This composite is composed of particles or flakes inside a matrix. This kind of particulate materials are simulated with the Discret Element Method (DEM), which calculates the movement of a finite number of particles in a sistem or during a process. With the DEM software, it is possible to carry out the production of beams in a microscale by the compaction of steel and alumina particles, with three variations of composition. A bonding model is used to simulate the material after the sintering process. Afterwards, three point bending test are carried out in the beams and the elastic modulus of the material is obtained. Satisfatory results were obtained by comparing with real experimental data. The bonding model was validated for the material by the analisys of the simulated microstructure and the results on the elastic modulus
- …
