15 research outputs found
Membranove vlastnosti gliovych bunek a jejich uloha v iontove a objemove homeostaze CNS.
No full textSystematic study of the electrophysiological properties of glial cells, astrocytes and oligodendrocytes, began during the sixties, when their possible role in the buffering of K plus, which accumulates in the extracellular space of the central nervous system (CND) during neuronal activity, was first formulated. Even though glial cells and neurons develop from the same type of precursor cell, they have distinct electrophysiological properties, which are determined by the presence of transport protein. It was suggested that transport proteins in glial cells play an important role in various processes in normal nervous tissue, during development as well as during pathological states. Activation of ionic channels and transporters in glial cells takes place during the maintenance of ionic homeostasis, during the regulation of metabolism and the release of hormones, and during communication with surrounding cells. As a result of ionic shifts, the cell volume of glial cells changes, affecting the size and geometry of the extracellular space (ECS), which is the microenvironment of neurons and glial cells. The composition and size of the ECS change dynamically during neuronal activity as well as during pathological states. Following their release, a number of neuroactive substances, including ions, mediators, metabolites and neurotransmitters, diffuse via the ECS to targets distant form their release sites. Glial cells affect the composition and volume of the ECS and therefore also extracellular diffusion, particularly during development, aging and ptahological states such as ischemia, injury, X-irradiation, gliosis, demyelination and often in grafted tissue. Recent studies also indicate that diffusion in the ECS is affected by ECS volume inhomogeneities, which are the result of a more compacted space in certain regions. Besides glial cells, the extracellular matrix also changes ECS geometry and forms diffusion barrier, which may also result in diffusion anisotropy. Glial cells therefore play an important role in extrasynaptic transmission, for example in functions such as vigilance, sleep, depression, chronic pain, LTP, LTD, memory formation and other plastic changes in the CNS. In turn, ECS diffusion parameters affect neuron-glia communication, ionic homeostasis and the movement and/or accumulation of neuroactive substances in the brain. Chvatal, AlexandrSummary and text also in EnglishAvailable from STL, Prague, CZ / NTK - National Technical LibrarySIGLECZCzech Republi
Differential calcium signalling in neuronal-glial networks
No full textCalcium ions are the probably the most ancient, the most universal and omnipresent intracellular signalling molecules, which are involved in regulation of a host of cellular functional reactions. In the nervous system Ca 2+ signalling is intimately involved in information transfer and integration within neural circuits. Local Ca2+ signals or Ca 2+ microdomains control neurotransmitter release; more global Ca 2+ signals regulate synaptic strength and accomplish postsynaptic processing. In the glial syncytium Ca2+ ions provide for glial "Ca2+ excitability", convey long-range signalling by means of propagating Ca2+ waves and control the release of gliotransmitters. Differential Ca2+ signals in various elements of neural circuits represent therefore molecular mechanisms of integration in the nervous system
Impact of global cerebral ischemia on K+ channel expression and membrane properties of glial cells in the rat hippocampus
No full textThree-dimensional confocal morphometry reveals structural changes in astrocyte morphology in situ
No full textHigh extracellular K+ evokes changes in voltage-dependent K+ and Na+ currents and volume regulation in astrocytes
No full textCell Death/Proliferation and Alterations in Glial Morphology Contribute to Changes in Diffusivity in the Rat Hippocampus after Hypoxia—Ischemia
No full text To understand the structural alterations that underlie early and late changes in hippocampal diffusivity after hypoxia/ischemia (H/I), the changes in apparent diffusion coefficient of water (ADCW) were studied in 8-week-old rats after H/I using diffusion-weighted magnetic resonance imaging (DW-MRI). In the hippocampal CA1 region, ADCW analyses were performed during 6 months of reperfusion and compared with alterations in cell number/cell-type composition, glial morphology, and extracellular space (ECS) diffusion parameters obtained by the real-time iontophoretic method. In the early phases of reperfusion (1 to 3 days) neuronal cell death, glial proliferation, and developing gliosis were accompanied by an ADCW decrease and tortuosity increase. Interestingly, ECS volume fraction was decreased only first day after H/I. In the late phases of reperfusion (starting 1 month after H/I), when the CA1 region consisted mainly of microglia, astrocytes, and NG2-glia with markedly altered morphology, ADCW, ECS volume fraction and tortuosity were increased. Three-dimensional confocal morphometry revealed enlarged astrocytes and shrunken NG2-glia, and in both the contribution of cell soma/processes to total cell volume was markedly increased/decreased. In summary, the ADCW increase in the CA1 region underlain by altered cellular composition and glial morphology suggests that considerable changes in extracellular signal transmission might occur in the late phases of reperfusion after H/I. </jats:p
Erdos--Ko--Rado Theorems: New Generalizations, Stability Analysis and Chvatal's Conjecture
No full textabstract: The primary focus of this dissertation lies in extremal combinatorics, in particular intersection theorems in finite set theory. A seminal result in the area is the theorem of Erdos, Ko and Rado which finds the upper bound on the size of an intersecting family of subsets of an n-element set and characterizes the structure of families which attain this upper bound. A major portion of this dissertation focuses on a recent generalization of the Erdos--Ko--Rado theorem which considers intersecting families of independent sets in graphs. An intersection theorem is proved for a large class of graphs, namely chordal graphs which satisfy an additional condition and similar problems are considered for trees, bipartite graphs and other special classes. A similar extension is also formulated for cross-intersecting families and results are proved for chordal graphs and cycles. A well-known generalization of the EKR theorem for k-wise intersecting families due to Frankl is also considered. A stability version of Frankl's theorem is proved, which provides additional structural information about k-wise intersecting families which have size close to the maximum upper bound. A graph-theoretic generalization of Frankl's theorem is also formulated and proved for perfect matching graphs. Finally, a long-standing conjecture of Chvatal regarding structure of maximum intersecting families in hereditary systems is considered. An intersection theorem is proved for hereditary families which have rank 3 using a powerful tool of Erdos and Rado which is called the Sunflower Lemma.Dissertation/ThesisPh.D. Mathematics 201
Tunable soft-matter optofluidic waveguides assembled by light
No full textDevelopment of artificial materials exhibiting unusual optical properties is one of the major strands of current photonics research. Of particular interest are soft-matter systems reconfigurable by external stimuli that play an important role in research fields ranging from physics to chemistry and life sciences. Here, we prepare and study unconventional self-assembled colloidal optical waveguides (CWs) created from wavelength-size dielectric particles held together by long-range optical forces. We demonstrate robust non-linear optical properties of these CWs that lead to optical transformation characteristics remarkably similar to those of gradient refractive index materials and enable reversible all-optical tuning of light propagation through the CW. Moreover, we characterize strong optomechanical interactions responsible for the CW self-assembly; in particular, we report self-sustained oscillations of the whole CW structure tuned so that the wavelength of the laser beams forming the CW is not allowed to propagate through. The observed significant coupling between the mechanical motion of the CW and the intensity of light transmitted through the CW can form a base for designing novel mesoscopic-scale photonic devices that are reconfigurable by light
Valid inequalities for mixed-integer linear programming problems
No full textIn this work we focus on various cutting-plane methods for Mixed-integer Linear Programming (MILP) problems. It is well-known that MILP is a fundamental hard problem and many famous combinatorial optimization problems can be modeled using MILP formulations. It is also well-known that MILP formulations are very useful in many real life applications. Our first, rather theoretical, contribution is a new family of superadditive valid inequalities that are obtained from value functions of special surrogate optimization problems. Superadditive functions hold particular interest in MILP as they are fundamental in building integer programming duality, and all ``deepest valid inequalities'' are known to arise from superadditive functions. We propose a new family of superadditive functions that generate inequalities that are at least as strong as Chvatal-Gomory (CG-) inequalities. A special subfamily provides a new characterization of CG-cuts. Value functions of optimization problems are known to be super additive. We look at special surrogate optimization problems, and measure their complexity in terms of the number of integer variables in them. It turns out that the lowest possible nontrivial complexity class here includes all CG-cuts, and provides some stronger ones, as well. Our next contribution is a practically efficient, polynomial time method to produce ``deepest'' cuts form multiple simplex rows for the so called corner polyhedra. These inequalities have been receiving considerable attention lately. We provide a polynomial time column-generation algorithm to obtain such inequalities, based on an arbitrary (fixed) number of rows of the simplex tableau. We provide numerical evidence that these inequalities improve the CPLEX integrality gap at the root node on a well-known set of MILP instances, MIPLIB. In the last chapter, we consider a particular MILP instance, Optimal Resilient Distribution Grid Design Problem (ORDGDP). This is a problem of critical importance to infrastructure security and recently attracted a lot of attention from various government agencies (e.g. Presidential Policy Directive of Critical Infrastructure Security 2013). We formulate this problem as a MILP and propose various efficient solution methods blending together well-known decomposition ideas to overcome the numerical intractability encountered using commercial MILP software such as CPLEX.Ph.D.Includes bibliographical referencesby Emre Yamangi
Physiology of spontaneous [Ca2+]i oscillations in the isolated vasopressin and oxytocin neurones of the rat supraoptic nucleus
No full textThe magnocellular vasopressin (AVP) and oxytocin (OT) neurones exhibit specific electrophysiological behaviour, synthesise AVP and OT peptides and secrete them into the neurohypophysial system in response to various physiological stimulations. The activity of these neurones is regulated by the very same peptides released either somato-dendritically or when applied to supraoptic nucleus (SON) preparations in vitro. The AVP and OT, secreted somato-dendritically (i.e. in the SON proper) act through specific autoreceptors, induce distinct Ca2+ signals and regulate cellular events. Here, we demonstrate that about 70% of freshly isolated individual SON neurones from the adult non-transgenic or transgenic rats bearing AVP (AVP-eGFP) or OT (OT-mRFP1) markers, produce distinct spontaneous [Ca2+]i oscillations. In the neurones identified (through specific fluorescence), about 80% of AVP neurones and about 60% of OT neurones exhibited these oscillations. Exposure to AVP triggered [Ca2+]i oscillations in silent AVP neurones, or modified the oscillatory pattern in spontaneously active cells. Hyper- and hypo-osmotic stimuli (325 or 275 mOsmol/l) respectively intensified or inhibited spontaneous [Ca2+]i dynamics. In rats dehydrated for 3 or 5 days almost 90% of neurones displayed spontaneous [Ca2+]i oscillations. More than 80% of OT-mRFP1 neurones from 3 to 6-day-lactating rats were oscillatory vs. about 44% (OT-mRFP1 neurones) in virgins. Together, these results unveil for the first time that both AVP and OT neurones maintain, via Ca2+ signals, their remarkable intrinsic in vivo physiological properties in an isolated condition
