Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2005. / Includes bibliographical references (leaves 136-146). Also available in electronic version.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: Wesley J. Thompson. Vita. Includes bibliographical references.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references (leaves 100-121). Also available in electronic version.

The human cortical temporoparietal junction (TPJ) has been implicated in cognitive processes including attentional reorienting, social cognition, and behavioral inhibition. Functional organization of TPJ remains unclear due to individual differences in anatomy. This dissertation describes functional magnetic resonance imaging (fMRI) experiments examining TPJ at the level of individuals. A method to localize TPJ using fMRI in individual subjects was developed and tested. TPJ subregions for social cognition, behavioral inhibition, and attention reorienting were parcellated. Finally, differences in attention networks between practitioners of focused attention meditation and matched control participants were investigated. Fifty individuals (ages 20-58; 21 women) participated. Experiment 1 (n=10) developed and tested a novel fMRI paradigm ('CueBall') that combined two forms of attentional reorienting; participants directed and shifted attention in a spatial cueing task and were distracted by the infrequent and unexpected presentation of task-irrelevant images ('oddballs'). The contrast of 'oddball distractor' to 'non-oddball' trials robustly identified TPJ in individual brains. Bilateral subdivisions of TPJ were identified in the fundus of the superior temporal sulcus (STS) and in ventral supramarginal gyrus (SMG). Experiment 2 (n=10, including one individual from Experiment 1) employed the CueBall task along with a Stop Signal task and a Theory of Mind task to determine whether these disparate tasks recruit common or distinct cortical areas. The data demonstrated functional overlap in anterior TPJ between the attention and behavioral inhibition tasks and in posterior TPJ for attention and Theory of Mind. Experiment 3 (n=30) investigated neural correlates of focused attention meditation training in the dorsal attention network (DAN), the default mode network (DMN), and ventral attention network (VAN). Meditators demonstrated an increased magnitude of differential activation in DAN vs. DMN in a sustained attention task, relative to matched controls. In contrast, attentional reorienting did not reveal attention network differences between meditators and controls. Taken together, this work validates an attentional fMRI tool, helps disambiguate functional organization of the TPJ, and demonstrates neural correlates of improved attention in humans with meditation experience. / 2020-03-31T00:00:00Z

The neuromuscular junction (NMJ), the synapse formed between lower motor neuron and skeletal muscle fibre, is known to be a target in a number of neurodegenerative conditions, including motor neuron disease (MND). Located in an accessible part of the peripheral nervous system, the NMJ can be used as a ‘model synapse’ in the context of ‘connectomics’ – the study of synaptic connectivity throughout the nervous system as a whole. Although the NMJ has been studied in a number of species, relatively little is known about its structure in humans, complicating the translation of animal models of disease to the human condition. Described here is the first detailed cellular and molecular characterization of the human NMJ. A standardized methodology for comparative morphometric analysis of NMJs was developed and validated (‘NMJ-morph’). NMJ-morph was used to generate baseline data for 2160 NMJs from a single litter of wild type mice, representing 9 distinct muscles across 3 body regions. Principal components analysis (PCA) revealed synaptic size and fragmentation to be the key determinants of synaptic variability. Correlation data revealed the pre-synaptic cell (motor neuron) to be a stronger predictor of synaptic morphology than the post-synaptic cell (muscle fibre). Other factors influencing synaptic variability were in a clear hierarchy: muscle identity accounted for more variation in synaptic form than animal identity, with side having no effect. Human tissue was obtained from 20 patients (aged 34 to 92 years) undergoing lower limb amputation, primarily for the complications of peripheral vascular disease (PVD). Muscle samples were harvested from non-pathological regions of the surgical discard tissue. 2860 human NMJs were analyzed from 4 distinct muscles (extensor digitorum longus, soleus, peroneus longus and peroneus brevis), and compared with equivalent NMJs from wild type mice. Human NMJs displayed unique morphological characteristics, including small size, thin axons, rudimentary nerve terminals and distinctive ‘nummular’ endplates, all of which distinguished them from equivalent mouse NMJs. The previous notion of partial occupancy in human NMJs was disproved. As in mice, the pre-synaptic cell was shown to correlate more strongly with NMJ morphology; in contrast to mice, the human NMJ was found to be relatively stable throughout its 90+ year lifespan. In support of the tissue harvesting procedure, patient co-morbidities (diabetes mellitus and vascular disease) did not significantly impact NMJ morphology. Super-resolution imaging of the NMJ revealed significant differences in the functional architecture of human and mouse active zones. Despite the smaller synaptic size in humans, the total quantity of active zone material was conserved between the species, suggesting a homeostatic mechanism to preserve effective neurotransmission. Parallel proteomic profiling demonstrated further species-specific differences in the broader molecular composition of the NMJ. The cellular and molecular anatomy of the human NMJ is fundamentally different to that of other mammalian species. These differences must be taken into account when translating animal models of disease to the human condition.

Made available in DSpace on 2014-06-11T19:25:26Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-07-15Bitstream added on 2014-06-13T18:26:28Z : No. of bitstreams: 1 cardoso_ff_me_botib.pdf: 693511 bytes, checksum: ce598a499b044fd23ed66dd6f42f2f0a (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Os acidentes envolvendo as serpentes do gênero Bothrops se destacam no Brasil e em outros países da América Latina, representando 90% das notificações. O envenenamento botrópico é caracterizado por intensa mionecrose local que não é eficientemente neutralizada pelo único tratamento disponível, isto é, a soroterapia. Como conseqüência, em casos graves, este acidente pode levar a amputação de membros, desabilitando a vítima. Os principais responsáveis pelo desenvolvimento da mionecrose são proteínas com estruturas homólogas às enzimas fosfolipases A2 (PLA2s). Entre essas se destacam as variantes cataliticamente inativas que apresentam como característica um resíduo de lisina na posição 49 (Lys49-PLA2s). Tradicionalmente, as Lys49-PLA2s são consideradas miotoxinas não-neurotóxicas, uma vez que não induzem paralisia in vivo. No entanto, em preparações isoladas, tal efeito é observado. Recentemente, sugeriu-se que a paralisia muscular in vitro, da mesma forma que a lesão muscular, resultaria da atividade desestabilizadora de membrana da fibra muscular induzida por estas toxinas. O presente estudo teve como objetivo investigar a relação entre os efeitos miotóxico e paralisante das Lys49-PLA2s e contribuir para o esclarecimento do mecanismo de ação e da relação estrutura/atividade dessas toxinas. Sendo assim, realizaram-se estudos miográficos e morfológicos em preparações neuromusculares de camundongos utilizando a PrTX-I (Lys49-PLA2 isolada do veneno de Bothrops pirajai) e potenciais inibidores vegetais (ácido rosmarínico, ácido caféico e ácido aristolóquico). Os resultados obtidos mostraram as diferentes capacidades dos compostos vegetais em neutralizar os efeitos miotóxico e paralisante da PrTX-I. Assim, o ácido rosmarínico neutralizou ambos os efeitos eficientemente... / Accidents caused by Bothrops snake genus stand out in Brazil and other Latin American countries, representing 90% of notifications. Bothropic envenoming is characterized by intense local myonecrosis, not effectively neutralized by serum therapy, the only available treatment. As a result, in severe cases, these accidents can lead to amputation of limbs, disabling the victim. The main responsibles for myonecrosis development are proteins with homologous structures from enzymes phospholipase A2 (PLA2s). Among these stand out catalytically inactive variants that have a characteristic lysine residue at position 49 (Lys49-PLA2s). Traditionally, Lys49-PLA2s myotoxins are considered non-neurotoxic, since they do not induce paralysis in vivo. However, this effect is observed in isolated preparations. It was recently suggested that muscle paralysis in vitro, as well as muscle injury, would result from the destabilizing activity of the muscle fiber membrane induced by these toxins. This study aimed to investigate the relationship between paralyzing and myotoxic effects of Lys49-PLA2s and contribute to the elucidation of the mechanism of action and structure/activity relationship of these toxins. Therefore, myographical and morphological studies were performed in neuromuscular preparations of mice using PrTX-I (Lys49-PLA2 isolated from Bothrops pirajai venom) and potential inhibitors from plants (rosmarinic acid, caffeic acid and aristolochic acid) as experimental tools. The results showed the different skills of plant compounds to neutralize myotoxic and paralyzing effects of PrTX-I. Thus, the rosmarinic acid efficiently neutralized both effects, whereas caffeic acid only partially inhibited the... (Complete abstract click electronic access below)

Orientador: Lea Rodrigues Simioni, Yoko Oshima Franco / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Ciencias Medicas / Made available in DSpace on 2018-08-12T10:25:13Z (GMT). No. of bitstreams: 1 RochaJunior_DimasdosSantos_M.pdf: 1074208 bytes, checksum: 78f54f332c4a0788a9a1522ffdfffefa (MD5) Previous issue date: 2008 / Resumo: O dimetilaminoetanol (DMAE) é comercializado em vários países como suplemento da dieta, amplificador da cognição e também como matéria-prima de produtos cosméticos. No Brasil, a Agência Nacional de Vigilância Sanitária aprovou o uso cosmético em 2002, visando a uma ação antienvelhecimento, após a observação do efeito colateral decorrente da administração oral do medicamento Deanol-®: contração involuntária da musculatura do rosto e do pescoço. Pesquisou-se, neste trabalho, a ação do DMAE em preparação isolada do nervo frênico-diafragma de camundongos, utilizando-se técnicas miográfica e eletrofisiológica. DMAE, sob o parâmetro miográfico, mostrou dois efeitos neuromusculares principais, dependentes da concentração: o facilitador da neurotransmissão (1 mg/mL, n = 6 e 4 mg/mL, n = 11) e o bloqueador neuromuscular completo aos 40 minutos (20 mg/mL, n = 4). Em preparações previamente curarizadas (d-Tubocurarina, 10 µg/mL) e sob estímulo direto, o DMAE (8 mg/mL, n = 3) aumentou a amplitude da contração muscular (30%), mostrando uma ação direta sobre a fibra muscular; enquanto sob estímulo indireto, demonstrou não possuir ação anticolinesterásica. O DMAE, sob o parâmetro eletrofisiológico, agiu pré-sinapticamente sobre a terminação nervosa, constatado pelo aumento gradativo dos valores de conteúdo quântico (1 mg/mL, n = 4). As implicações desses resultados são discutidas neste trabalho. / Abstract: The dimethylaminoethanol (DMAE) is commercialized in several countries as diet supplement, amplifier of the cognition and also as substance in the constitution of cosmetic products. In Brazil, the cosmetic use was approved by the Agência Nacional de Vigilância Sanitária, in 2002, aiming at an antiaging action, after the collateral effect from oral Deanol® administration: the involuntary contraction of the face and the neck muscles. The objective of this work was to study the DMAE action in isolated mouse phrenic nerve-diaphragm preparation, using myographical and electrophysiological techniques. DMAE, under myographical parameter, showed two main neuromuscular and concentration-dependents effects: the facilitatory (1 mg/mL, n = 6 and 4 mg/mL, n = 11) and the neuromuscular blocker at 40 min (20 mg/mL, n = 4). In pre-curarized preparations (d-Tubocurarine, 10 µg/mL) and under direct stimuli, DMAE (8 mg/mL, n = 3) increased the amplitude of muscular contraction (30%), showing a direct action on the muscular fiber; whereas under indirect stimuli, showed to have no anticholinesterasic action. DMAE, under electrophysiological parameter did act presynaptically on the nervous terminal by a gradual increase of quantum content values (1 mg/mL, n = 4). The implications of these results are argued in this work. / Mestrado / Mestre em Farmacologia

Abstract All neurons and macroglial cells of vertebrates derive from the neuroepithelium. Neuroepithelial (NE) cells first proliferate and, after closure of the neural tube, some cells start generating neurons. It is still unclear what triggers differentiation but apparently there is interplay between extrinsic (secreted or transmembrane signals) and intrinsic factors. Diriving from the embryonic ectoderm, the NE cells inherit epithelial characteristics. It has been shown in other developmental systems that epithelial determinants, such as cell-cell contacts and contact to basal laminar components can guide differentiation. The key epithelial features include cell polarity, and tight junctions. We studied these in the NE at two developmental stages, the neural plate, a proliferative stage and the neural tube, a differentiative stage. The polarity of membrane proteins in NE cells was studied with polarly budding viruses. Mouse embryos were infected with Fowl plague- and vesicular stomatitis viruses and cultured in a whole embryo culture system. Viral envelope proteins (HA and G-protein) were localized by indirect immunofluorescence and immunoelectron microscopy. HA was polarized in the plate stage neuroepithelial cells, whereas in the tube it was not polarized anymore. It is also shown by penetrance of apically injected horseradish peroxidase that in the neural plate, NE cells have functional tight junctions. At this stage, they also express occludin, a transmembrane protein of tight junctions, as shown by indirect immunofluorescence. In the neural tube, the paracellular barrier is lost and there is no occludin expression. In contrast, expression of ZO-1, a cytoplasmic protein binding to occiudin, is upregulated. The downregulation of these epithelial features occurs in all NE cells, irrespective of their mode of division and before any neurons are generated in the NE. The change is initiated already at the plate stage and coincides with the switch from E- to N-cadherin. Later, with birth of neurons, the proliferative cell layer also looses contact to basal lamina. This is probably an important step in the regulation of neurogenesis. Furthermore, lack of apico-basolateral polarity of non-anchored membrane proteins may contribute to the mechanism of rapid neuron generation. Until now, it has been impossible to distinguish a neuroepithelial cell preparing for neuron generation from the surrounding cells that give rise to two precursor cells. In this study, the immediate neuron precursors are shown to express the antiproliferative gene TIS2 1. Using this new marker and ISH in serial sections, we show that the switch to differentiation is initiated in single NE cells.

D.Ing. (Electrical & Electronic Engineering ) / In recent years, bipolar transistors have become available with large current ratings (300A-1DODA). The purpose 01 this study is to analyse the modelling 01 these devices, with a view to applying the results to detailed power electronic circuit design (for example base drive and snubber circuits). In contrast to the many curve-filling approaches existing in this field, a model which correctly represents the physical mechanisms is desirable, in order to characterise the device behaviour with a minimum number of parameters. Existing modelling techniques, which have mostly been developed for low current devices, are examined in detail to determine their validity for high current 8JTs. Alter a survey of the literature, the assumptions contained in the lundamental first order theory are investigated, together with the most important second order ellecls. This is followed by a detailed experimental investigation, to establish the dominant mechanisms for both de and dynamic operation. The behaviour 01 large power devices is dominated by conductivity modulation 01 the lightly doped collector region. This means that the Gummel-Poon model, which is based on ellects in the base is not the most appropriate for high current modelling. II also found that the the simple charge control equation can give accurate results for dynamic modelling. The dynamic saturation region 01 operation is described by a simple model, based on the quantity 01 stored charge. This is an improvement on the currently used Gummel-Poon models. The findings are all incorporated into a new model, which is included in a version of the SPICE network simulation program and then tested experimentally. The importance 01 the reverse conduction mode 01 operation is discussed and some techniques for modelling this region are presented, together with some experimental results. II is shown conclusively that the developed device based approach, models the behaviour of the devices adequately for converter design purposes, over a wide range of operating conditions.

Background: The paediatric craniocervical junction has anatomical, physiological and biomechanical properties that make this region unique to that of the adult spine, vulnerable to injury, and contribute to the complexity of management. Traditionally, on-lay fusion with external Halo immobilisation has been used. Instrumented fusion offers intra-operative reduction and immediate stability. Methods: A retrospective review of a single surgeon’s prospectively maintained database was conducted for all cases of paediatric patients that had undergone a fusion involving the occipito-atlanto-axial region. Case notes were reviewed and a radiological analysis was done. Results: Sixteen patients were managed with on-lay fusion and external immobilisation and twentyseven patients were managed with internal fixation using screw-rod constructs. The fusion rates were 80% and 90.5% respectively. Allograft bone grafting was found to be a significant risk factor for non-union. Conclusion: The screws can be safely and predictably placed as confirmed on radiological follow-up with a high fusion rate and an acceptable complication rate. Uninstrumented onlay fusion with Halo immobilization remains an acceptable alternative. Allograft in the form of bone croutons or demineralised bone matrix is a significant risk factor for non-union and posterior iliac crest graft should be used preferentially.