Dependence of the network structure of cured styrene butadiene rubber on the sulphur content

An investigation about the dependence of the physical properties of styrene-butadiene rubber copolymers (cured with different sulphur content, in order to obtain various networks) on the crosslink density was carried out by means of dynamical mechanical analysis, differential scanning calorimetry and positron annihilation lifetime spectroscopy. SBR specimens were cured with different sulphur content, in order to obtain various networks. On increasing the crosslink density, the glass transition temperature increases and the fractional free volume decreases. The thermal expansion coefficient of the free volume decreases in the rubbery phase by increasing the crosslink density, owing to the slower rate of expansion of nanoholes; furthermore, it seems influenced by the percentage of polysulfide density. The density of nanoholes is independent of the temperature, but decreases on adding sulphur. The results can be framed within the Simha-Somcynsky free volume theory. © 2004 Published by Elsevier Ltd.Fil: Salgueiro, Walter Alberto. Universidad Nacional del Centro de la Provincia de Buenos Aires; ArgentinaFil: Marzocca, Angel José. Univ. N.; ArgentinaFil: Somoza, A.. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; Argentina. Fisica; Argentina. Universidad Nacional del Centro de la Provincia de Buenos Aires; ArgentinaFil: Consolati, G.. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Cerveny, S.. Univ. N.; Argentina. Politecnico di Milano; ItaliaFil: Quassollo Infanzon, Gonzalo Emiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Goyanes, Silvia Nair. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin

Region-specific dendritic simplification induced by Aβ, mediated by tau via dysregulation of microtubule dynamics: a mechanistic distinct event from other neurodegenerative processes

BACKGROUND: Dendritic simplification, a key feature of the neurodegenerative triad of Alzheimer’s disease (AD) in addition to spine changes and neuron loss, occurs in a region-specific manner. However, it is unknown how changes in dendritic complexity are mediated and how they relate to spine changes and neuron loss. RESULTS: To investigate the mechanisms of dendritic simplification in an authentic CNS environment we employed an ex vivo model, based on targeted expression of enhanced green fluorescent protein (EGFP)-tagged constructs in organotypic hippocampal slices of mice. Algorithm-based 3D reconstruction of whole neuron morphology in different hippocampal regions was performed on slices from APP(SDL)-transgenic and control animals. We demonstrate that induction of dendritic simplification requires the combined action of amyloid beta (Aβ) and human tau. Simplification is restricted to principal neurons of the CA1 region, recapitulating the region specificity in AD patients, and occurs at sites of Schaffer collateral input. We report that γ-secretase inhibition and treatment with the NMDA-receptor antagonist, CPP, counteract dendritic simplification. The microtubule-stabilizing drug epothilone D (EpoD) induces simplification in control cultures per se. Similar morphological changes were induced by a phosphoblocking tau construct, which also increases microtubule stability. In fact, low nanomolar concentrations of naturally secreted Aβ decreased phosphorylation at S262 in a cellular model, a site which is known to directly modulate tau-microtubule interactions. CONCLUSIONS: The data provide evidence that dendritic simplification is mechanistically distinct from other neurodegenerative events and involves microtubule stabilization by dendritic tau, which becomes dephosphorylated at certain sites. They imply that treatments leading to an overall decrease of tau phosphorylation might have a negative impact on neuronal connectivity

RhoA pathway and actin regulation of the golgi/centriole complex

International audienceIn vertebrate cells, the Golgi apparatus is located in close proximity to the centriole. The architecture of the Golgi/centriole complex depends on a multitude of factors, including the actin filament cytoskeleton. In turn, both the Golgi and centriole act as the actin nucleation centers. Actin organization and polymerization also depend on the small GTPase RhoA pathway. In this chapter, we summarize the most current knowledge on how the genetic, magnetic, or pharmacologic interference with RhoA pathway and actin cytoskeleton directly or indirectly affects architecture, structure, and function of the Golgi/centriole complex

The Golgi apparatus in polarized neuroepithelial stem cells and their progeny: Canonical and noncanonical features

Neurons forming the central nervous system are generated by neural stem and progenitor cells, via a process called neurogenesis (Gö}tz and Huttner, Nat Rev Mol Cell Biol, 6:777--788, 2005). In this book chapter, we focus on neurogenesis in the dorsolateral telencephalon, the rostral-most region of the neural tube, which contains the part of the central nervous system that is most expanded in mammals (Borrell and Reillo, Dev Neurobiol, 72:955--971, 2012; Wilsch-Br{äuninger et al., Curr Opin Neurobiol 39:122--132, 2016). We will discuss recent advances in the dissection of the cell biological mechanisms of neurogenesis, with particular attention to the organization and function of the Golgi apparatus and its relationship to the centrosome