Although neurotrophins are conventionally associated with the proper growth and survival of developing neurons, there is increasing evidence that they play an equally significant role in the functions of adult neurons. Specifically, brain derived neurotrophic factor activation of its preferred receptor TrkB is essential in the regulation of motoneuronal activity. Neurotrophin‐dependent and independent activation of TrkB regulates the motoneuronal dendritic integrity, and maintains unique classes of synapses. In addition, it regulates the expression and function of ion channels as well as the strength of inhibitory and excitatory synapses via different intracellular pathways. The recent physiological findings in the regulatory roles of TrkB are implicative of its presence on motoneuronal dendrites. Although, the expression of TrkB in the soma has long been confirmed, its distribution on the dendritic tree of motoneurons remains unknown. We aimed to examine the distribution of TrkB in the cytoplasm and membrane‐associated regions of the dendritic tree of adult neck motoneurons. We have determined, via confocal microscopy, that TrkB is present and abundant throughout the cytoplasm and the membrane‐associated regions of motoneuronal dendrites as well as the soma. TrkB is organized in clusters and its distribution is best described as punctated. We then developed a technique to separately extract and quantify the TrkB immunoreactivity associated with the membrane and the cytoplasm as function of distance from the soma and dendritic tree. We have demonstrated that there is no bias in TrkB immunoreactivity to a specific region of the dendritic tree in five trapezius motoneurons. These observations were confirmed for both cytoplasmic and membrane‐associated TrkB. There is compelling evidence that both mature full‐length and immature hypoglycosylated TrkB isoforms are active in strengthening the response to excitatory synapses in motoneurons. We identified the full length TrkB as well as 3 hypoglycosylated isoforms in cervical spinal segments that contain trapezius motoneurons and phrenic motoneurons. Taken together, these data indicate that TrkB is likely involved in regulating and maintaining different classes of ion channels and synapses on the dendrites as well as the soma. Various isoforms of TrkB may also be involved in regulating motoneuronal activity. / Thesis (Master, Neuroscience Studies) -- Queen's University, 2014-01-14 12:48:21.357

We adopt a novel topological approach for graphs, in which edges are modelled as points as opposed to arcs. The model of classical <i>topologized graphs</i> translates graph isomorphism into topological homeomorphism, so that <i>all</i> combinatorial concepts are expressible in purely topological language. This allows us to extrapolate concepts from finite graphs to infinite graphs equipped with a compatible topology, which, dropping the classical requirement, need not be unique. We bring standard concepts from general topology to bear upon questions of a combinatorial inspiration, in an infinite setting. We show how (possibly finite) graph-theoretic paths are, without any technical subterfuges, a subclass of a broad category of topological spaces, namely paths, that includes Hausdorff arcs, the real line and all connected orderable spaces (of arbitrary cardinality). We show that all paths, and the topological generalizations of cycles, are topologized graphs. We use feeble regularity to explore relationships between the topologies on the vertex set and the whole space. We employ compactness and weak normality to prove the existence of our analogues for minimal spanning sets and fundamental cycles. In this framework, we generalize theorems from finite graph theory to a broad class of topological structures, including the facts that fundamental cycles are a basis for the cycle space, and the orthogonality between bond spaces and cycle spaces. We show that this can be accomplished in a setup where the set of edges of a cycle has a loose relationship with the cycle itself. It turns out that, in our model, feeble regularity excludes several pathologies, including one identified previously by Diestel and Kuehn, in a very different approach which addresses the same issues. Moreover, the spaces surgically constructed by the same authors are feebly regular and, if the original graph is 2-connected, compact. We consider an attractive relaxation of the <i>T</i>₁ separation axiom, namely the <i>S</i>₁ axiom, which leads to a topological universe parallel to the usual one in mainstream topology. We use local connectedness to unify graph-theoretic trees with the dendrites of continuum theory and a more general class of well behaved dendritic spaces, within the class of <i>ferns</i>. We generalize results of Whyburn and others concerning dendritic spaces to ferns, and show how cycles and ferns, in particular paths, are naturally <i>S</i>₁ spaces, and hence may be viewed as topologized hypergraphs. We use topological separation properties with a distinct combinatorial flavour to unify the theory of cycles, paths and ferns. This we also do via a setup involving total orders, cyclic orders and partial orders. The results on partial orders are similar to results of Ward and Muenzenberger and Smithson in the more restrictive setting of Hausdorff dendritic spaces. Our approach is quite different and, we believe, lays the ground for an appropriate notion of completion which links Freudenthal ends of ferns simultaneously with the work of Polat for non-locally-finite graphs and the paper of Allen which recognizes the unique dendritic compactification of a rim-compact dendritic space as its Freudenthal compactification.

The establishment of correct neural circuitry in the nervous system requires the interplay, integration, and coordination of a diverse set of cells and signals during development and in the adult. Two important events are the regulated initiation and growth of dendrites that receive and process synaptic information, and the establishment and maintenance of appropriate neural connectivity. The goals of this study are to identify the molecular mechanisms underlying dendrite growth and initiation, and to understand how neural connectivity is maintained in the adult nervous system. I first identified a novel intracellular signal transduction pathway involving two kinases important in regulating dendrite development. I showed that the ILK-GSK3beta pathway is required for dendrite growth and initiation in both peripheral and central nervous system neurons. I then asked how neural connectivity is maintained in the adult nervous system by examining the role of myelin in the intact nervous system. My results indicate that when myelin contacts aberrantly growing axons, it activates on those axons the p75 neurotrophin receptor (p75NTR), which in turn causes the local degeneration of those axons. I further identified the signal transduction pathway required for axon degeneration consisting of p75NTR and intracellular signaling proteins activated by this receptor, Rho-GDI, Rho, and caspase 6. This data establishes p75NTR as an important regulator of neural connectivity and identifies for the first time a degeneration-inducing signal transduction pathway activated by myelin. It also provides an explanation for why myelin inhibits regeneration of injured central nervous system axons. Taken together, I identified a new signaling pathway important for regulating dendrite initiation and growth, and a novel role for myelin in maintaining neural connectivity. Both of these findings contribute to our knowledge of how such connectivity is established during development and maintained in the adult nervous system.

The establishment of correct neural circuitry in the nervous system requires the interplay, integration, and coordination of a diverse set of cells and signals during development and in the adult. Two important events are the regulated initiation and growth of dendrites that receive and process synaptic information, and the establishment and maintenance of appropriate neural connectivity. The goals of this study are to identify the molecular mechanisms underlying dendrite growth and initiation, and to understand how neural connectivity is maintained in the adult nervous system. I first identified a novel intracellular signal transduction pathway involving two kinases important in regulating dendrite development. I showed that the ILK-GSK3beta pathway is required for dendrite growth and initiation in both peripheral and central nervous system neurons. I then asked how neural connectivity is maintained in the adult nervous system by examining the role of myelin in the intact nervous system. My results indicate that when myelin contacts aberrantly growing axons, it activates on those axons the p75 neurotrophin receptor (p75NTR), which in turn causes the local degeneration of those axons. I further identified the signal transduction pathway required for axon degeneration consisting of p75NTR and intracellular signaling proteins activated by this receptor, Rho-GDI, Rho, and caspase 6. This data establishes p75NTR as an important regulator of neural connectivity and identifies for the first time a degeneration-inducing signal transduction pathway activated by myelin. It also provides an explanation for why myelin inhibits regeneration of injured central nervous system axons. Taken together, I identified a new signaling pathway important for regulating dendrite initiation and growth, and a novel role for myelin in maintaining neural connectivity. Both of these findings contribute to our knowledge of how such connectivity is established during development and maintained in the adult nervous system.

We adopt a novel topological approach for graphs, in which edges are modelled as points as opposed to arcs. The model of classical <i>topologized graphs</i> translates graph isomorphism into topological homeomorphism, so that <i>all</i> combinatorial concepts are expressible in purely topological language. This allows us to extrapolate concepts from finite graphs to infinite graphs equipped with a compatible topology, which, dropping the classical requirement, need not be unique. We bring standard concepts from general topology to bear upon questions of a combinatorial inspiration, in an infinite setting. We show how (possibly finite) graph-theoretic paths are, without any technical subterfuges, a subclass of a broad category of topological spaces, namely paths, that includes Hausdorff arcs, the real line and all connected orderable spaces (of arbitrary cardinality). We show that all paths, and the topological generalizations of cycles, are topologized graphs. We use feeble regularity to explore relationships between the topologies on the vertex set and the whole space. We employ compactness and weak normality to prove the existence of our analogues for minimal spanning sets and fundamental cycles. In this framework, we generalize theorems from finite graph theory to a broad class of topological structures, including the facts that fundamental cycles are a basis for the cycle space, and the orthogonality between bond spaces and cycle spaces. We show that this can be accomplished in a setup where the set of edges of a cycle has a loose relationship with the cycle itself. It turns out that, in our model, feeble regularity excludes several pathologies, including one identified previously by Diestel and Kuehn, in a very different approach which addresses the same issues. Moreover, the spaces surgically constructed by the same authors are feebly regular and, if the original graph is 2-connected, compact. We consider an attractive relaxation of the <i>T</i>₁ separation axiom, namely the <i>S</i>₁ axiom, which leads to a topological universe parallel to the usual one in mainstream topology. We use local connectedness to unify graph-theoretic trees with the dendrites of continuum theory and a more general class of well behaved dendritic spaces, within the class of <i>ferns</i>. We generalize results of Whyburn and others concerning dendritic spaces to ferns, and show how cycles and ferns, in particular paths, are naturally <i>S</i>₁ spaces, and hence may be viewed as topologized hypergraphs. We use topological separation properties with a distinct combinatorial flavour to unify the theory of cycles, paths and ferns. This we also do via a setup involving total orders, cyclic orders and partial orders. The results on partial orders are similar to results of Ward and Muenzenberger and Smithson in the more restrictive setting of Hausdorff dendritic spaces. Our approach is quite different and, we believe, lays the ground for an appropriate notion of completion which links Freudenthal ends of ferns simultaneously with the work of Polat for non-locally-finite graphs and the paper of Allen which recognizes the unique dendritic compactification of a rim-compact dendritic space as its Freudenthal compactification.

<p>Dendrite shape is a defining component of neuronal function. Yet, the mechanisms specifying diverse dendritic morphologies, and the extent to which their functioning depends on these morphologies, remain unclear. Here, we demonstrate a dendrite-specific requirement for the microtubule severing protein Katanin p60-like 1 (Kat-60L1) in regulating the elaborate branch morphology and nocifensive functions of Drosophila melanogaster larval class IV dendritic arborization (da) neuron dendrites. Through genetic loss of function analysis we show that loss of kat-60L1 reduced dendrite branching and process length, particularly during a period of normally extensive growth. This morphological defect was paralleled by a reduction in nocifensive responsiveness mediated by these neurons, indicating a tight correlation between neuronal function and the full extent of the dendritic arbor. To understand the mechanism underlying Kat-60L1's effects, we used in vivo imaging of the microtubule plus-end binding protein EB1, and found fewer polymerizing microtubules within mutant dendrites. Kat-60L1 thus promotes microtubule growth within class IV dendrites to establish the full arbor complexity and nocifensive functions of these neurons. </p><p>Although reduction of the related microtubule severing protein Spastin also compromised class IV dendrite arborization and nocifensive responses, microtubule polymerization in dendrites was unchanged in spastin mutants, and behavioral defects arose from generally compromised neuronal excitation. Kat-60L1 and Spastin thus function in distinct neuronal compartments to establish the complex dendritic morphology and sensory functions of class IV da neurons via distinct mechanisms of microtubule regulation. Whereas Spastin regulates stable microtubules affecting both pre- and post-synaptic compartments of these neurons, Kat-60L1 function is required specifically in dendrites to promote their complex arborization through the addition of growing microtubule numbers. Double mutant analysis demonstrated that Kat-60L1 and Spastin function antagonistically to promote dendritic aborization, likely involving other molecular players involved in regulating the microtubule cytoskeleton. Lastly, we identified Mi-2 as a transcriptional regulator of both kat-60L1 and spastin and show a genetic interaction between mi-2 and kat-60L1 in the class IV dendritic arbor, demonstrating that Mi-2 antagonizes Kat-60L1 function, possibly through the parallel upregulation of spastin. These data support a key role for the differential utilization of microtubule severing in generating distinct neuronal morphologies and subsequent function.</p> / Dissertation

abstract: Methyl-CpG binding protein 2 (MECP2) is a widely abundant, multifunctional regulator of gene expression with highest levels of expression in mature neurons. In humans, both loss- and gain-of-function mutations of MECP2 cause mental retardation and motor dysfunction classified as either Rett Syndrome (RTT, loss-of-function) or MECP2 Duplication Syndrome (MDS, gain-of-function). At the cellular level, MECP2 mutations cause both synaptic and dendritic defects. Despite identification of MECP2 as a cause for RTT nearly 16 years ago, little progress has been made in identifying effective treatments. Investigating major cellular and molecular targets of MECP2 in model systems can help elucidate how mutation of this single gene leads to nervous system and behavioral defects, which can ultimately lead to novel therapeutic strategies for RTT and MDS. In the work presented here, I use the fruit fly, Drosophila melanogaster, as a model system to study specific cellular and molecular functions of MECP2 in neurons. First, I show that targeted expression of human MECP2 in Drosophila flight motoneurons causes impaired dendritic growth and flight behavioral performance. These effects are not caused by a general toxic effect of MECP2 overexpression in Drosophila neurons, but are critically dependent on the methyl-binding domain of MECP2. This study shows for the first time cellular consequences of MECP2 gain-of-function in Drosophila neurons. Second, I use RNA-Seq to identify KIBRA, a gene associated with learning and memory in humans, as a novel target of MECP2 involved in the dendritic growth phenotype. I confirm bidirectional regulation of Kibra by Mecp2 in mouse, highlighting the translational utility of the Drosophila model. Finally, I use this system to identify a novel role for the C-terminus in regulating the function of MECP in apoptosis and verify this finding in mammalian cell culture. In summary, this work has established Drosophila as a translational model to study the cellular effects of MECP2 gain-of-function in neurons, and provides insight into the function of MECP2 in dendritic growth and apoptosis. / Dissertation/Thesis / Doctoral Dissertation Neuroscience 2015

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19314号 / 工博第4111号 / 新制||工||1634(附属図書館) / 32316 / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 安部 武志, 教授 作花 哲夫, 教授 陰山 洋 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

This dissertation presents the development of numerical models based on lattice Boltzmann (LB) and cellular automaton (CA) methods for solving phase change and microstructural evolution problems. First, a new variation of the LB method is discussed for solving the heat conduction problem with phase change. In contrast to previous explicit algorithms, the latent heat source term is treated implicitly in the energy equation, avoiding iteration steps and improving the formulation stability and efficiency. The results showed that the model can deal with phase change problems more accurately and efficiently than explicit LB models. Furthermore, a new numerical technique is introduced for simulating dendrite growth in three dimensions. The LB method is used to calculate the transport phenomena and the CA is employed to capture the solid/liquid interface. It is assumed that the dendritic growth is driven by the difference between the local actual and local equilibrium composition of the liquid in the interface. The evolution of a threedimensional (3D) dendrite is discussed. In addition, the effect of undercooling and degree of anisotropy on the kinetics of dendrite growth is studied. Moreover, effect of melt convection on dendritic solidification is investigated using 3D simulations. It is shown that convection can change the kinetics of growth by affecting the solute distribution around the dendrite. The growth features of twodimensional (2D) and 3D dendrites are compared. Furthermore, the change in growth kinetics and morphology of Al-Cu dendrites is studied by altering melt undercooling, alloy composition and inlet flow velocity. The local-type nature of LB and CA methods enables efficient scaling of the model in petaflops supercomputers, allowing the simulation of large domains in 3D. The model capabilities with large scale simulations of dendritic solidification are discussed and the parallel performance of the algorithm is assessed. Excellent strong scaling up to thousands of computing cores is obtained across the nodes of a computer cluster, along with near-perfect weak scaling. Considering the advantages offered by the presented model, it can be used as a new tool for simulating 3D dendritic solidification under convection.

Previous research has demonstrated that augmented prenatal sensory stimulation can influence the emergence of normal or species-typical patterns of intersensory perception. For example, unusually early visual experience can produce a facilitative effect on subsequent postnatal perceptual responsiveness, while substantially augmented prenatal visual stimulation can interfere with early postnatal responsiveness. In constructing a link between early experience and neuronal plasticity, it has been established that unusual visual experience can produce measurable changes in post-synaptic structures, particularly dendritic morphology, in brain areas responsible for vision. In avian species, the brain area responsible for vision is the visual Wulst, thought to be analogous to the mammalian visual cortex. This study examined the effects of differing amounts of augmented prenatal visual stimulation on the plasticity of neurons in the visual Wulst and on subsequent postnatal visual responsiveness to maternal cues in bobwhite quail chicks. Results revealed that the pattern of neuronal organization and postnatal behavior was influenced by the amount of prenatal visual experience subjects were provided. Specifically, chicks exposed to 240 min of prenatal visual stimulation during the last 24 hr prior to hatching had neurons with significantly fewer spines/10 mm dendrite and displayed accelerated patterns of species-typical visual responsiveness. In contrast, chicks provided 900 min of prenatal visual stimulation had more complex neurons (including more spines, longer dendrites, and more branches) and failed to display normal species-specific visual responsiveness in the days following hatching. These results suggest that neuronal organization in the bobwhite Wulst proceeds in a selective fashion, molded by experience, and appears to influence early perceptual development and organization during the perinatal period / Ph. D.