Following unilateral stroke there is significant loss of function in the body side contralateral to the damage and a robust degenerative-regenerative cascade of events in both hemispheres. It is natural to compensate for loss of function by relying more on the less-affected body side to accomplish everyday living tasks (e.g. brushing teeth, drinking coffee). This is accompanied by a “learned disuse” of the impaired side thought to occur due to repeated experience with its ineptness. However, as investigated in these studies, it may also be due to brain changes instigated by experience with the intact body side. The central hypothesis of these dissertation studies is that experience with the intact forelimb, after unilateral sensorimotor cortex (SMC) damage, disrupts functional recovery with the impaired forelimb and interferes with peri-lesion neural plasticity. Following unilateral ischemic lesions, rats were trained on a skilled reaching task with their intact (less-affected) forelimb or received control procedures. The impaired forelimb was then trained and tested on the same skilled reaching task. Intact forelimb experience worsened performance with the impaired forelimb even when initiated at a more delayed time point following lesions. Intact forelimb training also reduced peri-lesion expression of FosB/ΔFosB, a marker of neuronal activation, and caudal forelimb motor map areas compared to animals without intact forelimb training. It was further established that it is focused training of the intact forelimb and not experience with this limb per se, as animals trained with both forelimbs in an alternating fashion did not exhibit this effect. Transections of the corpus callosum blocked the maladaptive effect of intact forelimb experience on impaired forelimb recovery, suggesting a disruptive influence of the intact hemisphere onto the lesion hemisphere that is mediated by experience. Together these dissertation studies provide insight into how experience with the less-affected, intact body side, can influence peri-lesion neural plasticity and recovery of function with the impaired forelimb. The findings from these studies suggest that compensatory use of the less-affected (intact) body side following unilateral brain damage is not advantageous if the ultimate goal is to improve function in the impaired body side. / text

The neurotransmitter dopamine (DA) represents a neural substrate for positive motivation as its spatiotemporal distribution across the brain is responsible for goaldirected behavior and learning reward associations. The critical determinant of DA release throughout the brain is the firing pattern of DA-producing neurons. Synchronized bursts of spikes can be triggered by sensory stimuli in these neurons, evoking phasic release of DA in target brain areas to drive reward-based reinforcement learning and behavior. These bursts are generated by NMDA-type glutamate receptors (NMDARs). This dissertation reports a novel form of long-term potentiation (LTP) of NMDARmediated excitatory transmission at DA neurons as a putative cellular substrate for changes in DA neuron firing during reward learning. Patch-clamp electrophysiological recording from DA neurons in acute brain slices from young adult rats demonstrated that synaptic NMDARs exhibit LTP in an associative manner, requiring coordinated pre- and postsynaptic burst firing. Ca2+ signals produced by postsynaptic burst firing needed to be amplified by preceding metabotropic neurotransmitter inputs to effectively drive plasticity. Activation of NMDARs themselves was also necessary. These two coincidence detectors governed the timingdependence of NMDAR plasticity in a manner analogous to the timing rule for cuereward learning paradigms in behaving animals. Further mechanistic study revealed that PKA, but not PKC, activity gated LTP induction by regulating the magnitude of Ca2+ signal amplification via the inositol 1,4,5-triphospate (IP3) receptor and release of Ca2+ from intracellular stores. Plasticity of NMDARs was input specific and appeared to be expressed postsynaptically, but was not associated with a change in NMDAR subunit stoichiometry. LTP of NDMARs was DA-independent, and was specific for NMDARs: the same induction protocol produced long-term depression of AMPA receptors. NMDARs that had undergone LTP could be depotentiated in a spike-conditional manner, consistent with active unlearning. Finally, repeated, in vivo amphetamine experience dramatically increased facilitation of spike-evoked Ca2+ signals, which in turn drove enhanced plasticity. NMDAR plasticity thus represents a potential neural substrate for conditioned DA neuron burst responses to environmental stimuli acquired during reward-based learning as well a novel therapeutic target for intervention-based therapy of addictive disorders. / text

Recent experiences from the Darfield and Canterbury, New Zealand earthquakes have shown that the soft soil condition of saturated liquefiable sand has a profound effect on seismic response of buildings, bridges and other lifeline infrastructure. For detailed evaluation of seismic response three dimensional integrated analysis comprising structure, foundation and soil is required; such an integrated analysis is referred to as Soil Foundation Structure Interaction (SFSI) in literatures. SFSI is a three-dimensional problem because of three primary reasons: first, foundation systems are three-dimensional in form and geometry; second, ground motions are three-dimensional, producing complex multiaxial stresses in soils, foundations and structure; and third, soils in particular are sensitive to complex stress because of heterogeneity of soils leading to a highly anisotropic constitutive behaviour. In literatures the majority of seismic response analyses are limited to plane strain configuration because of lack of adequate constitutive models both for soils and structures, and computational limitation. Such two-dimensional analyses do not represent a complete view of the problem for the three reasons noted above. In this context, the present research aims to develop a three-dimensional mathematical formulation of an existing plane-strain elasto-plastic constitutive model of sand developed by Cubrinovski and Ishihara (1998b). This model has been specially formulated to simulate liquefaction behaviour of sand under ground motion induced earthquake loading, and has been well-validated and widely implemented in verifcation of shake table and centrifuge tests, as well as conventional ground response analysis and evaluation of case histories. The approach adopted herein is based entirely on the mathematical theory of plasticity and utilises some unique features of the bounding surface plasticity formalised by Dafalias (1986). The principal constitutive parameters, equations, assumptions and empiricism of the existing plane-strain model are adopted in their exact form in the three-dimensional version. Therefore, the original two-dimensional model can be considered as a true subset of the three-dimensional form; the original model can be retrieved when the tensorial quantities of the three dimensional version are reduced to that of the plane-strain configuration. Anisotropic Drucker-Prager type failure surface has been adopted for the three-dimensional version to accommodate triaxial stress path. Accordingly, a new mixed hardening rule based on Mroz’s approach of homogeneous surfaces (Mroz, 1967) has been introduced for the virgin loading surface. The three-dimensional version is validated against experimental data for cyclic torsional and triaxial stress paths.

Activity-dependent and synapse-specific translation of mRNAs is required for long-term changes in synaptic strength (or efficacy). However, many of the components mediating repression, transport and activation of mRNAs are unknown. Translational control in neurons is a highly conserved process and mediated by a ribonuclear particle (RNP). This study shows that RNPs in Drosophila neurons are similar not only to mammalian neuronal RNA granules but also to yeast P-bodies, cytoplasmic foci involved in translational repression and RNA decay. The evolutionarily conserved proteins Me31b and Trailer Hitch localize to RNA granules. Me31b and Trailer Hitch are required for normal dendritic growth. Mutations in Me31b and Trailer Hitch suppress phenotypes resulting from overexpression of Fragile X Mental Retardation protein, suggesting that both proteins may act as translational repressors. In addition, this study reports the identification of novel translational repressors in neurons. Using the overexpression phenotype of Fragile X Mental Retardation protein in a candidate-based genetic screen, I identified dominant suppressor mutations in five genes, including Doubletime/Discs Overgrown, Orb2/CPEB, PolyA Binding Protein, Rm62/Dmp68 and SmD3. Like Me31b and Trailer Hitch, all five proteins localize to neuronal RNPs. Overexpression of each proteins affects dendritic branching of sensory neurons in Drosophila. Identification and further characterization of these novel RNP granule components and dFMR1-interacting proteins may provide further insights into the mechanisms controlling translational in dendrites.

Unprecedented rates of anthropogenic environmental change have resulted in dramatic decreases in biodiversity worldwide. In order to persist during changes in both the abiotic and biotic environment resulting from anthropogenic stressors such as climate change and habitat degradation, populations must be able to respond or face extirpation. Predicted population-level responses to environmental change include i) range shifts as individuals disperse into more suitable regions, ii) phenotypic plasticity allowing for shifts in the mean phenotype of the population or iii) microevolution resulting from a genetic change within the population. The goal of this thesis is to assess how species within a community respond to a dramatic change in the environment. This study used the sediment record of a Subarctic pond to investigate the impacts of a rapid increase in salinity on two species of the crustacean zooplankton Daphnia. One species, Daphnia tenebrosa, was unable to persist in the high salinity conditions and is believed to have been extirpated from the system. The other species, Daphnia magna, was tolerant of the new environmental conditions and was present throughout the sediment record. To investigate the changes in life history of D. magna, resting eggs from the sediment were hatched to compare iso-female lines from pre- and post-disturbance time periods. No differences were observed between the clone lines, suggesting that phenotypic plasticity allowed D. magna to persist despite the rapidly changing environmental conditions, and that microevolution in salinity tolerance may not have occurred in this population. This study suggests that, in environments with moderate levels of post environmental change, pre-existing phenotypic plasticity may play a greater role than microevolution in species response to environmental changes. However, not all species from a community display the same response to environmental changes, as seen in this study with the extirpation of D. tenebrosa. To better understand how communities will be affected by future environmental change, further investigations need to be made on what factors influence species response. Identifying species response may allow conservation efforts to focus on species that are unlikely to adapt to environmental change, and are most at risk. / Thesis (Master, Biology) -- Queen's University, 2013-09-29 21:54:34.881

Non-competitive antagonists of the glutamate N-methyl-D-aspartate receptor (NMDAR) induce a broad range of schizophrenia-like symptoms in humans. Consequently hypothesis has emerged suggesting that glutamate or NMDAR hypofunction may occur in schizophrenia. The NMDAR is localised at dendritic spines of neurons and is embedded in a multi-protein complex called the post-synaptic density (PSD). The biochemical composition of the postsynaptic membrane and the structure of dendritic spines are continuously modulated by glutamatergic synaptic activity. The activity-dependent interaction between glutamate receptors and proteins of the PSD stimulate intracellular signalling pathways underlying learning and memory processes. These may be disturbed in schizophrenia. In the present study we hypothesised that molecules of the PSD may be disturbed in expression in the premotor cortex of patients with schizophrenia. Postmortem premotor cortex from patients with schizophrenia, major depressive disorder, bipolar disorder and healthy controls were processed for PSD extraction and purification. Protein expression of the PSD fraction was assessed using co-immunoprecipitation (co-IP) and Western blotting (WB) methods. The expression of NMDAR subunit NR2A, PSD-95, Ca2+/calmodulin-dependent protein kinase II subunit β (CaMKIIβ) and truncated isoform of the tropomyosin receptor kinase type B (TrkB-T1) were significantly reduced in schizophrenia. A significant decrease in the expression of NR2A was also observed in patients with major depressive disorder relative to controls. A decrease in the abundance of key PSD proteins in schizophrenia provides strong evidence that PSD function and possibly synaptic plasticity may be disturbed in the premotor cortex in the disease. There may also be more subtle disturbances in PSD function in major depressive disorder.

<p>All organisms live in complex habitats that shape the course of their evolution by altering the phenotype expressed by a given genotype (a phenomenon known as phenotypic plasticity) and simultaneously by determining the evolutionary fitness of that phenotype. In some cases, phenotypic evolution may alter the environment experienced by future generations. This dissertation describes how genetic and environmental variation act synergistically to affect the evolution of glucosinolate defensive chemistry and flowering time in Boechera stricta, a wild perennial herb. I focus particularly on plant-associated microbes as a part of the plant’s environment that may alter trait evolution and in turn be affected by the evolution of those traits. In the first chapter I measure glucosinolate production and reproductive fitness of over 1,500 plants grown in common gardens in four diverse natural habitats, to describe how patterns of plasticity and natural selection intersect and may influence glucosinolate evolution. I detected extensive genetic variation for glucosinolate plasticity and determined that plasticity may aid colonization of new habitats by moving phenotypes in the same direction as natural selection. In the second chapter I conduct a greenhouse experiment to test whether naturally-occurring soil microbial communities contributed to the differences in phenotype and selection that I observed in the field experiment. I found that soil microbes cause plasticity of flowering time but not glucosinolate production, and that they may contribute to natural selection on both traits; thus, non-pathogenic plant-associated microbes are an environmental feature that could shape plant evolution. In the third chapter, I combine a multi-year, multi-habitat field experiment with high-throughput amplicon sequencing to determine whether B. stricta-associated microbial communities are shaped by plant genetic variation. I found that plant genotype predicts the diversity and composition of leaf-dwelling bacterial communities, but not root-associated bacterial communities. Furthermore, patterns of host genetic control over associated bacteria were largely site-dependent, indicating an important role for genotype-by-environment interactions in microbiome assembly. Together, my results suggest that soil microbes influence the evolution of plant functional traits and, because they are sensitive to plant genetic variation, this trait evolution may alter the microbial neighborhood of future B. stricta generations. Complex patterns of plasticity, selection, and symbiosis in natural habitats may impact the evolution of glucosinolate profiles in Boechera stricta.</p> / Dissertation

<p>Multiple lines of evidence reveal that activation of the tropomyosin related kinase B (TrkB) receptor is a critical molecular mechanism underlying status epilepticus (SE) induced epilepsy development. However, the cellular consequences of such signaling remain unknown. To this point, localization of SE-induced TrkB activation to CA1 apical dendritic spines provides an anatomic clue pointing to Schaffer collateral-CA1 synaptic plasticity as one potential cellular consequence of TrkB activation. Here, we combine two-photon glutamate uncaging with two photon fluorescence lifetime imaging microscopy (2pFLIM) of fluorescence resonance energy transfer (FRET)-based sensors to specifically investigate the roles of TrkB and its canonical ligand brain derived neurotrophic factor (BDNF) in dendritic spine structural plasticity (sLTP) of CA1 pyramidal neurons in cultured hippocampal slices of rodents. To begin, we demonstrate a critical role for post-synaptic TrkB and post-synaptic BDNF in sLTP. Building on these findings, we develop a novel FRET-based sensor for TrkB activation that can report both BDNF and non-BDNF activation in a specific and reversible manner. Using this sensor, we monitor the spatiotemporal dynamics of TrkB activity during single-spine sLTP. In response to glutamate uncaging, we report a rapid (onset less than 1 minute) and sustained (lasting at least 20 minutes) activation of TrkB in the stimulated spine that depends on N-methyl-D-aspartate receptor (NMDAR)-Ca2+/Calmodulin dependent kinase II (CaMKII) signaling as well as post-synaptically synthesized BDNF. Consistent with these findings, we also demonstrate rapid, glutamate uncaging-evoked, time-locked release of BDNF from single dendritic spines using BDNF fused to superecliptic pHluorin (SEP). Finally, to elucidate the molecular mechanisms by which TrkB activation leads to sLTP, we examined the dependence of Rho GTPase activity - known mediators of sLTP - on BDNF-TrkB signaling. Through the use of previously described FRET-based sensors, we find that the activities of ras-related C3 botulinum toxin substrate 1 (Rac1) and cell division control protein 42 (Cdc42) require BDNF-TrkB signaling. Taken together, these findings reveal a spine-autonomous, autocrine signaling mechanism involving NMDAR-CaMKII dependent BDNF release from stimulated dendritic spines leading to TrkB activation and subsequent activation of the downstream molecules Rac1 and Cdc42 in these same spines that proves critical for sLTP. In conclusion, these results highlight structural plasticity as one cellular consequence of CA1 dendritic spine TrkB activation that may potentially contribute to larger, circuit-level changes underlying SE-induced epilepsy.</p> / Dissertation

A systematic investigation is presented into the microstructural and micromechanical influences on ductile damage nucleation with an emphasis on grain boundaries in polycrystals. Microstructures obtained from experiments on copper polycrystals are characterized using Electron Backscatter Diffraction (EBSD) and near-field High-Energy Diffraction Microscopy (nf-HEDM) and the occurrence of damage is compared with micromechanical values obtained using an elasto-viscoplastic model based on the Fast- Fourier Transform (EVPFFT). The model produces full-field solutions for the stress and strain in voxelized polycrystalline microstructures. In order to resolve the fields onto interfaces, local Cartesian moments of the polycrystalline grain structure are used to extract the normals of grain boundaries and the tangents of triple junctions directly from the voxelized microstructure. Thus projecting the stress yields a parameter with potential significance, i.e. the grain boundary surface tractions. We identify “traction hotspots”, i.e. regions with tractions that are significantly above the mean, for the case of uniaxial tension. These show correlations with the angle between the grain boundary normal and the loading axis, a trend that some experiments also show when boundaries that nucleated voids are analyzed using EBSD, though differences present between the simulation and experiment hint that further criteria are needed. Nf-HEDM was used to record microstructure images of a polycrystalline sample before and after it undergoes damage. The damage locations in the post-shocked image are mapped onto the pre-shocked image, allowing stress and strain values from the EVPFFT model in the regions that eventually nucleated damage to be correlated with the locations of the void. The unexpected result was that differences in plastic work across boundaries correlated with voids, whereas vi quantities such as triaxiality and normal forces across boundaries did not.

In the pathophysiology of traumatic brain injury (TBI), the amygdala remains understudied, despite involvement in processing emotional and stressful stimuli associated with anxiety disorders, such as post-traumatic stress disorder (PTSD). Because the basolateral amygdala (BLA) integrates inputs from sensory and other limbic structures coordinating emotional learning and memory, injury-induced changes in circuitry may contribute to psychiatric sequelae of TBI. This study quantified temporal changes in dendritic complexity of BLA neurons after experimental diffuse TBI, modeled by midline fluid percussion injury. At post-injury days (PIDs) 1, 7, and 28, brain tissue from sham and brain-injured adult, male rats was processed for Golgi, glial fibrillary acidic protein (GFAP), or silver stain and analyzed to quantify BLA dendritic branch intersections, activated astrocytes, and regional neuropathology, respectively. Compared to sham, brain-injured rats at all PIDs showed enhanced dendritic branch intersections in both pyramidal and stellate BLA neuronal types, as evidenced by Sholl analysis. GFAP staining in the BLA was significantly increased at PID1 and 7 in comparison to sham. However, the BLA was relatively spared from neuropathology, demonstrated by an absence of argyrophilic accumulation over time, in contrast to other brain regions. These data suggest an early and persistent enhancement of dendritic complexity within the BLA after a single diffuse TBI. Increased dendritic complexity would alter information processing into and through the amygdala, contributing to emotional symptoms post-TBI, including PTSD.