Wong, Chun Kit. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves ). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

"We are using genetic and molecular techniques to study a simple model organism, C. elegans, to determine the cues involved in the formation of the nervous system. Two molecules currently being studied in the laboratory play roles in the formation of the IL2 neurons, a class of sensory neurons in C. elegans. The first gene, dig-1, influences the sensory process or dendrite and is involved in adhesion as well as potentially providing directional information during development. The second gene, mig-10, influences the axon and may be involved in a cell signal cascade. Genetic screens of C. elegans using Ethyl methyl sulfonate (EMS) as a mutagen resulted in the isolation of mutants with defects in the IL2 sensory map; sensory processes followed aberrant paths, appearing to be defasciculated. Complementation tests showed that the mutations failed to complement n1321, a known allele of dig-1; thus, these new mutations were alleles of dig-1 (Ryder unpub. results). Several of these new alleles of dig-1, including nu336 and n1480, have been further studied to elucidate the role of this gene in sensory map formation. A dig-1 candidate gene was identified that encodes a protein that is a member of the immunoglobulin super-family (IgSF). The candidate gene is predicted to be a large gene, with a transcript of approximately 45Kb. The encoded protein contains three distinct regions and is similar to the hyalectan family of proteoglycans. N terminal region 1 contains immunoglobulin and fibronectin-like domains. Central region 2 is an area that is highly repeated with a potential to have GAGs attached. C-terminal region 3 contains domains associated with adhesion. Polymerase chain reaction (PCR) products from alleles nu336 and n1480 were amplified and sequenced from the candidate gene. The DNA lesion present in the candidate gene from both alleles fit the method for how that mutation was generated. The point mutation in allele nu336 removes a potential glycosylation site. The large re-arrangement in allele n1480 truncates the transcript, suggesting that the protein is also truncated. The sequencing results along with rescuing data (R. Proenca, personal communication) showed that the candidate gene for dig-1 was the gene of interest. Each of the alleles was further studied to determine how severe that allele was by looking at the neuronal process aspect and the brood size as well as displacement of the gonad. In general, alleles with severe defects in the nervous system also had severe gonad displacement, suggesting the gene functions similarly in the two tissues. To determine if the gene was expressed at the RNA level, reverse transcriptase polymerase chain reaction (RT-PCR) was used. Most of the RT-PCRs amplified a cDNA of the appropriate size that showed dig-1 was expressed at the RNA level. RT-PCR further suggested that all three regions were in one transcript as well as confirming part of the predicted exon structure to be correct. In addition, northern analysis showed the presence of a large transcript in wildtype worms as well as a smaller truncated transcript from allele n1480. To investigate developmental differences mixed stage of RNA and embryonic RNA from wildtype animals were compared using gene specific primers. The initial RT-PCR showed potential alternative splicing occurring at the 5? end of the gene during development. To examine expression at the protein level, two recombinant proteins from dig-1 were successfully made by cloning cDNA products from the 5?and 3? end of dig-1. The constructs were sequenced and shown to be in frame. The recombinant proteins (Ant1Con1 and Ant3Con3) were mass produced and sent to a commercial source for injection into pre-screened rabbits. Western analysis showed the presence of an antibody in the serum from two of the rabbits. These antibodies should prove useful in future determination of correctness of our models of DIG-1 function. IgSF members have been shown to have many roles in nervous system development. DIG-1 could act in either an attractive or a repellent role to position sensory processes during development. DIG-1 might also change its function over time; early in development DIG-1 could be adhesive and later become repellant as more sugars are added. The gene mig-10 is involved in sensory map formation. To localize MIG-10 expression, several transgenic animals were generated by injection of two constructs that should recombine in the worm to create a MIG-10::GFP fusion protein. Ten transgenic lines were generated and screened by PCR for the presence of the correct recombinant construct. If this construct makes functional, rescuing protein, the GFP expression should reflect the expression pattern of the MIG-10 protein."

Diseases which affect the central nervous system present a huge burden to sufferers and caregivers. In tandem with longevity, prevalences of age-related neurodegenerative diseases are increasing. However, despite the evident necessity for pharmaceutical interventions, there has been a distinct lack of drug development to combat these disorders. This is largely attributed to high financial costs of using rodent models. Thus the validation of a more cost-effective in vivo system would facilitate pharmaceutical screening. The work presented in this thesis addresses this issue by assessing the utility of zebra fish in two costly areas of translational neurobiology { lead identi cation and safety pharmacology. An aversive classical conditioning assay was developed and automated as a behavioural screening method. This robust assay allows fast assessment of cognition and cognitive decline. The effect of neurotoxin treatment on aversive learning was then assessed using this assay, demonstrating its efficacy as a screening tool for neurodegeneration research. Subsequently, a transgenic zebra fish line - expressing a mutated form of the Alzheimer's-associated human amyloid precursor protein - was assessed, demonstrating an age-related cognitive impairment. Additionally new genetic zebra fish lines were generated, which over-express genes (both endogenous and transgenic) related to Alzheimer's-like pathologies. Whilst these were not assessed within this thesis, they present promising tools for possible future investigations. Regarding safety pharmacology, regulatory bodies require all CNS-penetrant drugs be assessed for abuse potential. Zebra fish display reward responses to several common drugs of abuse (e.g. amphetamine, cocaine, morphine). Thus, the latter sections of this thesis evaluated the utility of zebra fish for assessing human abuse potential. A CPP paradigm was utilised to test a range of drugs, with the sensitivity and specificity of zebra fish compared to previous reports using rodent. Additionally, the development of a zebra fish drug discrimination assay was attempted. However the paradigms utilised failed to develop an efficacious assay.

The human brain is the most complex structure in the known universe and one of the ultimate goals of humanity is to understand its function. The "bottom-up" approach to developmental neuroscience seeks to assemble a "parts list" of the genes expressed in each neuron and a map of the gene regulatory networks that determine the identity of the diverse neuronal types. A key part of building such a gene regulatory map is to identify the transcription factors that are key nodes in these networks. The goal of my PhD was to study the particular gene regulatory networks that govern the decision of the V5 skin cell to divide, lose its skin fate and decide to make dopamine and glutamate sensory neurons. We chose an unbiased forward genetic screen approach coupled with whole genome sequencing of mutants derived from these screens. In the process, we found several mutants that govern this process and developed a software pipeline that simplifies the analysis of mutants for others who perform forward genetic screens.

The hypothalamus is the central regulator of systemic energy homeostasis, and its dysfunction can result in extreme body weight alterations. This small (3-4 mm in thickness in human) neuro-endocrine brain region, located just above the median eminence, is comprised of cell types that subserve specific metabolic and behavioral aspects of the control of body weight, as well as hepatic glucose production, body temperature, autonomic physiology, neuroendocrine axes, serum osmolarity and circadian rhythms. Insights into the complex cellular physiology of this region are critical to the understanding of obesity pathogenesis and its prevention and treatment; however, human hypothalamic cells are largely inaccessible for direct study. My thesis research focused on establishing an in vitro model for understanding the molecular neurophysiology of obesity using, as "proof-of-principle", neurons derived from human pluripotent stem cells (hPSCs) derived from individuals with monogenic forms of obesity. Three related projects are described in details: I. Differentiation of hypothalamic-like neurons from human pluripotent stem cells (Chapter 2) This project was designed to establish an in vitro model for studying hypothalamic cell-molecular physiology in neurons derived from hPSCs. After screening several morphogens and other molecules affecting neuronal differentiation, we developed a protocol that combined early activation of sonic hedgehog signaling followed by timed NOTCH inhibition resulting in the generation of hypothalamic arcuate nucleus (ARC)-like neurons. Neuronal cells expressing pro-opiomelanocortin (POMC), neuropeptide-Y/agouti-related protein (NPY/AgRP) were generated from human embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) obtained from patients with monogenic forms of obesity. These hypothalamic-like neurons accounted for over 90% of differentiated cells and exhibited transcriptional profiles characteristic of specific hypothalamic neurons (and explicitly lacking pituitary markers). Importantly, these cells displayed hypothalamic neuronal characteristics, including production and secretion of neuropeptides and responsiveness to metabolic hormones such as insulin and leptin. Nkx2.1 progenitor cells at 12 days of differentiation from iPSC integrated into the hypothalamus following injection into the lateral ventricle of NSG mice. Single cell transcriptome analysis of day 27 hESC-derived hypothalamic neurons enabled us to identify specific hypothalamic cell types (e.g. POMC, NPY, MC4R) based on transcript signatures. These findings, in the aggregate, supported the utility of these cells for elucidation of aspects of the cellular/molecular neurophysiology of body weight regulation. II. Using stem cell-derived hypothalamic neurons to investigate the neurophysiology of obesity caused by prohormone convertase 1/3 deficiency (Chapter 3). My second project investigated the use the hPSC-differentiated hypothalamic neurons to assess the cellular physiology of hESC-derived hypothalamic neurons with induced knockdown or mutations of proprotein convertase subtilisin/kexin type 1 (PCSK1, encodes prohormone covertase 1/3 (PC1/3)). Congenital hypomorphism for this gene causes a rare autosomal disorder that impairs the processing of specific proproteins to their more bioactive derivatives, affecting, for example, the processing of POMC, proinsulin and proglucagon. The consequences of inactivating mutations of PCSK1 include obesity, possibly due to impaired function of anorexigenic POMC arcuate neurons. To understand the molecular neurophysiology of the obesity in PC1/3-deficient subjects, we generated PCSK1 deficient hESC lines with CRISPR or by knocking down PCSK1 with shRNA, and assessed the POMC processing in the hypothalamic ARC-like neurons made from these lines. The ratios of adrenocorticotropic hormone (ACTH)/POMC, αMSH/POMC and β endorphin (BEP)/POMC proteins were significantly decreased, while total quantities of POMC peptides were greatly increased in PCSK1-deficient hESC-derived neurons, indicating impaired POMC processing caused by reduced PC1/3 protein. These results are consistent with the elevated plasma POMC and ACTH intermediates levels of in humans segregating for hypomorphic mutations of PCSK1, and the impaired pituitary POMC processing in the PC1/3 mutant mice. Interestingly, in day 28 PC1/3-deficient neurons, in addition to upregulation of POMC gene expression and protein, we found increases in some of the "downstream" proteolytic enzymes for POMC processing and the "upstream" transcription factor that regulates PCSK1 expression. The molecular mechanisms underlying the invocation of these possibly compensatory processes are under study. These findings provide confidence that the hypothalamic neurons generated by the techniques described in Chapter 2 display molecular phenotypes consistent with a mutation in one of the important neuropeptide processing pathways. III. Using iPSC-derived neurons to investigate the molecular pathogenesis of obesity in Bardet-Biedl Syndrome (Chapter 4). To further investigate the use of iPSC-derived neurons in the study of the neurobiology of obesity, I analyzed structural and molecular physiologic phenotypes cells derived from patients with Bardet-Biedl Syndrome (BBS). BBS is a rare autosomal recessive disease characterized by multiorgan dysfunction, including polydactyly, hyperphagic obesity, retinal degeneration, renal cysts and cognitive impairments. Eighteen discrete genes have been implicated in specific instances of BBS, and all cognate proteins that have been identified encode constituents of the basal body of the primary cilium. The primary cilium has also been implicated in other clinical obesities, including the Alstrom syndrome, and the effects of a highly prevalent FTO allele on body weight. We found that ciliogenesis and neurite outgrowth were affected in both BBS1 and BBS10 mutant iPSC-derived neurons as reflected by longer primary cilia, shorter neurite length, and fewer processes. Furthermore, insulin-induced AKT phosphorylation at Thr308 was greatly reduced in both BBS1 and BBS10 mutant neurons compared to controls. Overexpression of BBS10 fully restored insulin signaling in BBS10 mutant neurons by rescue of the tyrosine phosphorylation of insulin receptor. Co-immunoprecipitation assays indicated that both BBS1 and BBS10 interacted physically with the insulin receptor. Leptin signaling was also investigated in BBS mutant fibroblasts and neurons. Both BBS mutations impaired leptin-mediated pSTAT3 activation in both cell lines by affecting either the trafficking or the quantities of leptin receptor in these cells. These data demonstrate that BBS proteins are essential for insulin and leptin signaling in neurons and fibroblasts, in a cellular context independent of the effects of obesity. These studies further confirm the ability of iPSC-derived neurons to reflect aspects of the molecular pathophysiology of the patients from whom they are obtained, and to enable studies of these phenotypes in circumstances isolated from the secondary effects of adiposity per se.

Adult hippocampal neurogenesis—a unique form of plasticity in the dentate gyrus (DG)—is regulated by experience, and when manipulated can have specific effects on behavior. Different methods have been used over the years to study new neurons’ functional role in the hippocampus, many of which focus on ablating neurogenesis. While ablation methods can test the necessity of adult-born granule cells (abGCs) for behavior, these techniques remove all abGCs from the circuit and thus do not allow one to determine which properties of abGCs are required for behavior. Such information is required to understand the mechanism of their action. Thus, new strategies are needed to determine what properties of young abGCs allow them to distinguish themselves from their mature counterparts and uniquely impact behavior. Recent hypotheses have suggested that the enhanced synaptic plasticity exhibited by 4–6-week-old abGCs allows them to uniquely contribute to hippocampal circuit function, and thus behavior. The primary goal of this thesis was to explore the contribution young abGCs’ heightened synaptic plasticity makes to hippocampal function. This was achieved using a transgenic mouse approach that allowed for the conditional deletion of NR2B from abGCs. Overall, iNR2BNes mice generated the same number of new neurons in adulthood as control mice at baseline. These neurons survived and matured with only a slight reduction in dendritic complexity. However, a potentially important electrophysiological property of these neurons—their enhanced synaptic plasticity—had been eliminated. From an electrophysiological standpoint, iNR2BNes mice resemble mice with ablated neurogenesis, while from all other neurogenic standpoints examined they most closely resemble wild-type mice. Consequently, these mice provided a novel model to test the extent to which young abGCs’ enhanced plasticity contributes to hippocampal-dependent behaviors. The results reveal that eliminating NR2B-containing NMDA receptors from abGCs does not alter baseline anxiety or antidepressant (AD)-like behavior. However, iNR2BNes mice differed from controls in measures of cognitive function. These mice were able to learn in the contextual fear conditioning test, but were impaired in the more difficult contextual fear discrimination test. Mice also exhibited a decreased novelty exploration phenotype that impaired their performance in the novel object recognition test. Together, these results indicate that the NR2B-dependent heightened plasticity exhibited by 4–6-week-old abGCs is necessary for responses to novelty and fine contextual discrimination, but does not contribute to baseline anxiety or emotionality. AD treatment increases levels of adult neurogenesis in the hippocampus, and these newborn neurons have been shown to be necessary for some of the behavioral effects of ADs seen in rodents. In addition, the maturation timeline of adult neurogenesis correlates with the onset of behavioral responses to ADs. ADs also enhance a neurogenesis-dependent form of long-term potentiation (LTP) in the DG evoked by medial perforant path stimulation under intact GABAergic tone called ACSF-LTP. Thus, a potential mechanism by which abGCs may contribute to AD behavioral efficacy is by providing extra plastic units to the DG circuit. This theory was tested by once again using the mouse line in which NR2B can be conditionally deleted from abGCs in the DG. Here, we found that deletion of the NR2B subunit significantly attenuated a neurogenesis-dependent behavioral response to fluoxetine in the novelty suppressed feeding test, and additionally blocked fluoxetine’s ability to enhance young abGCs’ maturation and subsequent integration into the hippocampal network. This suggests that eliminating abGCs’ enhanced plasticity decreases their ability to influence DG output resulting in an AD response that is less robust than seen in control mice. Control experiments revealed the specificity of this effect, as NR2B deletion did not impact the effect of fluoxetine in a neurogenesis-independent behavioral assay (tail suspension test) or in an assay that was insensitive to fluoxetine in this strain of mice (elevated plus maze). Our efforts to isolate the contribution of abGCs’ unique physiology from the neurogenic effects of fluoxetine were not entirely successful as the results presented here also revealed slight group differences in neurogenesis between control mice and mice lacking NR2B in young neurons. Yet, this data still supports the idea that fluoxetine increases the ability of abGCs to participate in DG output by increasing the chance that new neurons will be activated during DG stimulation. This may be achieved either by increasing their overall number, increasing their potential to make synaptic connections, or increasing their ability to strengthen their connections. However, due to the close link between activity and maturation that appears to be enhanced with fluoxetine treatment, a different approach with greater temporal resolution is needed to separate the neurogenic effects of fluoxetine from the physiological contribution abGCs make to hippocampal output. With this in mind, a mouse line in which abGCs could be temporally inhibited was also generated. Cellular and behavioral characterization of mice conditionally expressing hM4Di—a mutated muscarinic acetylcholine receptor that is insensitive to endogenous acetylcholine, but can be activated by the biologically inert, highly bioavailable compound, clozapine N-oxide (CNO)—has begun. Results show that acute CNO treatment in mice expressing this designer receptor exclusively activated by a designer drug (DREADD) in DG granule cells can impair encoding of contextual fear memory. Chronically treating these mice had an anxiogenic effect in the open field test, but otherwise anxiety and emotionality in these mice were comparable to controls. Chronic CNO treatment in mice expressing hM4Di in young abGCs effectively decreased these cells’ dendritic complexity, but did not alter proliferation or early survival. Thus, hM4Di DREADDs represent a novel tool that can be used to modulate activity of neurons in a temporally restricted manner, allowing for both acute and chronic manipulations of hippocampal granule cells. The experiments put forth in this thesis will highlight the importance of abGCs enhanced plasticity. The utility as well as potential pitfalls of the mouse models used here to test theories of abGC function will also be explored. Hopefully this analysis will provide an improved framework in which future experiments can be developed with the aim of uncovering novel insights into the hippocampal circuitry that underlies learning and memory and discovering new strategies for the treatment of neurological and psychiatric disorders.

Social context, which includes both the direct social experience of individuals as well as the characteristics of their social network as a whole, has been shown to be an important modulator of behavior across species. However, relatively little is known about the role of social context in regulating the complex relationships between neurobiology, neuroendocrine response, and behavior in mammals. Historically, the neurobiology of social behavior has been studied at the dyadic level, looking at brief social interactions between pairs of individuals. Given that all social species live in groups, rather than pairs, it is essential that we begin to understand the role social context at the group level plays in regulating physiology. Throughout this thesis, I use a novel behavioral housing system to study how the characteristics of stable social groups and how instances of social opportunity, when individuals are ascending up a social hierarchy, are associated with differential brain gene expression, neuroendocrine output, and behavior. I first extensively analyze the social dynamics of male dominance hierarchies, showing that they are both consistent, in that males reliably form significantly linear dominance hierarchies, and unique, in that the characteristics of these hierarchies vary from group to group. I further prove that mice living in these social hierarchies are extremely socially competent, displaying the ability to respond appropriately to individuals of varying social status. I demonstrate that females are capable of forming dominance hierarchies as well, but that their hierarchies differ from those of males. I then use this foundational knowledge to investigate how these different hierarchy characteristics can lead to differences in physiology, how one’s social status is associated with brain gene expression and neuroendocrine response, and how disruption of a hierarchy through removal of the alpha male leads to robust behavioral as well as physiological consequences. Finally, I use the insights gained from this immediate early gene work to demonstrate the crucial role of the infralimbic/prelimbic region of the medial prefrontal cortex in regulating socially competent response to changing social contexts. Taken together, this work establishes the broad role social context plays in regulating the complex relationships between behavior, brain gene expression, neural activation, and neuroendocrine output.

There are more neurons in the human brain than seconds in a lifetime. Given this incredible number how can we hope to understand the computations carried out by the full ensemble of neural firing patterns? And neural activity is not the only substrate available for computations. The incredible diversity of function found within biological organisms is matched by an equally rich reservoir available for computation. If we are interested in the metamorphosis of a caterpillar to a butterfly we could explore how DNA expression changes the cell. If we are interested in developing therapeutic drugs we could explore receptors and ion channels. And if we are interested in how humans and other animals interpret incoming streams of sensory information and process them to make moment-by-moment decisions then perhaps we can understand much of this behavior by studying the firing rates of neurons. This is the level and approach we will take in this thesis. Given this diversity of potential reservoirs for computation, combined with limitations in recording technologies, it can be difficult to satisfactorily conclude that we are studying the full set of neural dynamics involved in a particular task. To overcome this limitation, we augment the study of neural activity with the study of artificial recurrent neural networks (RNNs) trained to mimic the behavior of humans and other animals performing experimental tasks. The inputs to the RNN are time-varying signals representing experimental stimuli and we adjust the parameters of the RNN so its time-varying outputs are the desired behavioral responses. In these artificial RNNs we have complete information about the network connectivity and moment-by-moment firing patterns and know, by design, that these are the only computational mechanisms being used to solve the tasks. If the artificial RNN and electrode recordings of real neurons have the same dynamics we can be more confident that we are studying the sufficient set of biological dynamics involved in the task. This is important if we want to make claims about the types of dynamics required, and observed, for various computational tasks, as is the case in Chapter 2 of this thesis. In Chapter 2 we develop tests to identify several classes of neural dynamics. The specific neural dynamic regimes we focus on are interesting because they each have different computational capabilities, including, the ability to keep track of time, or preserve information robustly against the flow of time (working memory). We then apply these tests to electrode recordings from nonhuman primates and artificial RNNs to understand how neural networks are able to simultaneously keep track of time and remember previous experiences in working memory. To accomplish both computational goals the brain is thought to use distinct neural dynamics; stable neural trajectories can be used as a clock to coordinate cognitive activity whereas attractor dynamics provide a stable mechanism for memory storage but all timing information is lost. To identify these neural regimes we decode the passage of time from neural data. Additionally, to encode the passage of time, stabilized neural trajectories can be either high-dimensional as is the case for randomly connected recurrent networks (chaotic reservoir networks) or low-dimensional as is the case for artificial RNNs trained with backpropagation through time. To disambiguate these models we compute the cumulative dimensionality of the neural trajectory as it evolves over time. Recurrent neural networks can also be used to generate hypotheses about neural computation. In Chapter 3 we use RNNs to generate hypotheses about the diverse set of neural response properties seen during spatial navigation, in particular, grid cells, and other spatial correlates, including border cells and band-like cells. The approach we take is 1) pick a task that requires navigation (spatial or mental), 2) create a RNN to solve the task, and 3) adjust the task or constraints on the neural network such that grid cells and other spatial response patterns emerge naturally as the network learns to perform the task. We trained RNNs to perform navigation tasks in 2D arenas based on velocity inputs. We find that grid-like spatial response patterns emerge in trained networks, along with units that exhibit other spatial correlates, including border cells and band-like cells. Surprisingly, the order of the emergence of grid-like and border cells during network training is also consistent with observations from developmental studies. Together, our results suggest that grid cells, border cells and other spatial correlates observed in the Entorhinal Cortex of the mammalian brain may be a natural solution for representing space efficiently given the predominant recurrent connections in the neural circuits. All the tasks we have considered so far in this thesis require memory, but in Chapter 4 we explicitly explore the interactions between multiple memories in a recurrent neural network. Memory is the hallmark of recurrent neural networks, in contrast to standard feedforward neural networks where all signals travel in one direction from inputs to outputs and the network contains no memory of previous experiences. A recurrent neural network, as the name suggests, contains feedback loops giving the network the computational power of memory. In this chapter we train a RNN to perform a human psychophysics experiment and find that in order to reproduce human behavior, noise must be added to the network, causing the RNN to use more stable discrete memories to constrain less stable continuous memories.

A conversão da proteína príon celular (PrPc) em sua isoforma anormal PrPsc está associada a uma série de doenças neurodegenerativas, genericamente designadas por doenças priônicas. Embora a literatura tenha enfatizado o estudo do PrPsc e o mecanismo de propagação das doenças de príon, pouco tem sido feito para o entendimento do papel fisiológico do PrPc. Em 1997 nosso grupo descreveu um receptor/ligante para o PrPc utilizando o princípio da hidropaticidade complementar. Neste trabalho isolamos e identificamos este ligante de PrPc como sendo a STI-1 (Stress Inducible Protein-1). In vitro, a STI-1interage com o PrPc de maneira específica, saturável e com alta afinidade (Kd=8x10-8M). Paralelamente, mostramos que o PrPc se liga ao domínio RNIAEIIKDI da laminina (Ln) (Kd=2x10-8M). O bloqueio de PrPc na superfície de neurônios hipocampais de embriões de ratos e camundongos, reduziu a neuritogênese induzida por Ln. Além disso, neurônios provenientes de animais PrP -/- são incapazes de estender neuritos sobre o peptídeo RNIAEIIKDI, sugerindo que o PrPc é o único receptor celular para este domínio da Ln. Estes dados indicam que a interação PrPc-Ln seja relevante nos fenômenos de adesão e diferenciação neuronais. A caracterização das interações PrPc-Ln e PrPc-STI-1 representa contribuições importantes para a elucidação do papel biológico do PrPc. / Conversion of the cellular prion protein (PrPc) to its abnormal isoform PrPsc is associated with some neurodegenerative and fatal diseases called prion diseases. Although the literature has been emphasizing the mechanism of PrPsc conversion and illness propagation, little attention has been given to the PrPc physiological role. In 1997, our group described a PrPc receptor/ligand based on the complementary hydropathy theory. Herein, we identify the PrPc receptor/ligand as STI-1, the Stress Inducible Protein-1. In vitro studies showed that STI-1 is a specific, saturable and high affinity ligand for PrPc (Kd=8x10-8M). In parallel, we demonstrated that PrPc interacts with RNIAEIIKDI domain of laminin (Ln) (Kd=2x10-8M). The blockage of PrPc, both from embryonic rats and mice hippocampal neuros, inhibited Ln-induced neurite outgrowth. In addition, neurons from PrPc null mice are unable to extend neurites on RNIAEIIKDI, suggesting that PrPc is the unique cellular receptor for this Ln domain. These data indicate that PrPc-Ln interaction is relevant for neuronal adhesion and differentiation. The characterization of PrPc-Ln and PrPc-STl-1 interactions represents important contributions for the elucidation of the PrPc physiological role.

O mundo ainda está enfrentando uma crise financeira, que começou em meados de 2007 e até o momento está longe de ser resolvida. Os mercados de ações ao redor do mundo reagiram mal e as notícias em tempo real nunca desempenharam um papel tão importante para os investidores, como visto nesta crise. Em outras palavras, o impacto dos meios de comunicação aprofundou a dinâmica de baixa dos mercados financeiros, o que é amplificada pela volatilidade intrínseca do mesmo. Assim, a Neuroeconomia veio como um novo campo de questionamentos, o qual tem a finalidade de estudar a tomada de decisão, tendo em conta o papel desempenhado pela emoção e seus aspectos fisio-patológicos. Se utiliza neste estudo uma amostra de oitenta (80) pessoas, classificados em quarenta alunos de graduação e quarenta (40) trabalhadores experientes do mercado financeiro (traders), ambos igualmente divididos em 50% do sexo masculino e 50% do sexo feminino. O escopo é de avaliar o envolvimento de uma ampla rede de circuitos neurais envolvidos na avaliação de riscos, benefícios e conflitos (esta ponderação está intimamente relacionada à serotonina em caso de riscos e benefícios no caso de dopamina) para cada grupo a fim de verificar como reagem neste ambiente. Compreender a funcionalidade de tais sistemas é de fundamental importância para a compreensão da dinâmica do mercado financeiro e de suas anomalias, ou seja, para registrar a percepção de cada indivíduo em relação ao sentimento geral do mercado, seja ele a favor ou adverso. Portanto, o principal objetivo desta tese é mapear a atividade cerebral usando uma técnica desenvolvida por Rocha (2001, 2004 e 2010), operando uma simulação de negociação da Bolsa de Valores BMF&Bovespa, a fim de compreender melhor a neurodinâmica do processo de decisão no mercado de capitais / The world is still facing a financial crisis, which started in mid 2007 and up to now is far from being solved. Stock markets around the world reacted badly and the real time news has never played such an important role to investors as seen in previous crisis. In other words, the impact of the media deepened the bear dynamics of the markets, that is, it amplified the volatility of it. Thus, Neuroeconomics comes as a new field of inquiring that has the purpose of studying decision making taking into consideration the role played by emotion and its physio-pathological aspects. Here, it is used a sample of eighty (80) volunteers, sorted out into forty undergraduate students and forty (40) experienced financial market practioneers (namely traders), both equally divided into 50% male and 50% female. The scope is to evaluate the involvement of a wide network of neural circuits involved in risk assessments, benefits and conflicts (this weighting is closely related to the serotonin neural circuits in the event of risks and benefits in the case of dopamine) so as to verify how both groups react to this environment. Understanding the functionality of such systems is of fundamental importance for understanding the dynamics of the financial market and its anomalies, ie to record the perception of each individual in relation to the general market sentiment, being it in favour or on the contrary, adverse. Therefore, the main objective of this thesis is then to map brain activity using a technique developed by Rocha et al (2001, 2004 and 2010), operating a simulation of trading within the BMF&Bovespa, in order to better understand the process of neurodynamics decision making in the capital market