This research delves into idiopathic autism spectrum disorder (ASD), investigating the role of TrkB signaling pathways and BDNF regulation in the cortex. Additionally, it explores offering insights into maternal influences on mouse models. / Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by challenges in social interactions and repetitive behaviors. Prevalence of ASD is estimated to be 1 in 54 globally and is rising recently in many countries including Canada. ASD affects individuals differently, making diagnosis challenging. At present, no molecular diagnosis of ASD is available. Further, available medications only manage some symptoms of the disease and have adverse side effects in children. Therefore, there is a need for accurate molecular diagnostic tools to aid in molecular detection and treatment of ASD. To this end, a better understanding of the underlying molecular mechanisms that link ASD etiology to ASD-related behavior is crucial. While genetic factors contribute to syndromic ASD, most cases of ASD are idiopathic with unknown causes, influenced by a combination of epigenetic and environmental factors. TrkB and its downstream signaling pathways, such as Akt and Erk, are hyper-activated in syndromic ASD and hypo-activated in idiopathic cases. Therefore, drugs like rapamycin that inhibit the mTOR pathway downstream of TrkB are beneficial for syndromic ASD but not idiopathic cases. Additionally, insulin-like growth factor 1 (IGF-1), which mitigates ASD-related synaptic disruptions via Akt and Erk signaling, shows unchanged mRNA and protein levels along with its receptor in the idiopathic ASD fusiform gyrus. In ASD with either genetic or epigenetic/environmental causes, disruptions in synaptic connectivity are observed. Synaptic function is regulated by signaling pathways involving brain-derived neurotrophic factor (BDNF) and its receptor, tropomyosin-related kinase B (TrkB), as well as their downstream signaling cascades such as MAPK and Akt. The existing literature suggests that there is an association between BDNF and TrkB signaling pathways and ASD. However, a serious gap in knowledge about the precise molecular role of TrkB in ASD pathology is that our current understanding is correlational in nature and based on observational studies that lack causal experiments. This underscores the importance of further research to understand the causative role of TrkB and its related molecular events in idiopathic ASD. The present work aims to provide a deeper understanding about the causative role of molecular mechanisms underlying TrkB signaling in ASD. ASD mouse models exhibit behaviors and molecular features resembling those observed in human ASD. Therefore, these mouse models are helpful tools for studying ASD. However, understudied physiological confounding factors, such as maternal age and parity, can introduce biases and add to data variability, thus negatively impacting the reproducibility and translational value of ASD mouse models. To achieve a reliable mouse model of ASD, we conducted our first study that examines the impact of maternal age and parity on pregnancy complications, neurodevelopment, and social behavior in mice. Results demonstrate that older maternal age and prior motherhood interact to ensure a normal, steady developmental rate and provide protective effects against anxiety, social impairment, and olfactory deficits. Given the current lack of clarity regarding the causative impact of TrkB on ASD pathology, our subsequent investigation sought to establish a causal relationship between TrkB signaling and ASD. We used the TrkB agonist, LM22A-4 treatment in a validated ASD mouse model. Our results demonstrate that treatment with LM22A-4 effectively rescues the core symptoms associated with ASD (social impairment and repetitive behavior). These findings indicate that impaired TrkB signaling is responsible for ASD-like behavior of valproic acid (VPA)-exposed mice. However, unlike TrkB-related molecular events occurring in the fusiform gyrus of idiopathic ASD, TrkB isoform protein levels, BDNF species, Akt, and Erk total protein levels and activation remained unchanged in VPA-exposed cortices compared to healthy control mice. Since our VPA mouse model does not replicate human idiopathic ASD, our study cannot draw a conclusion on how disruptions in these signaling pathways may contribute to the development and manifestation of ASD symptoms. Cortex is responsible for various aspects of social behavior that are impaired in ASD. However, regulatory mechanisms that are involved in ASD upstream of cortical TrkB and BDNF are not well known. BDNF expression is highly cell-and tissue-specific and is regulated by different sets of transcription factors in specific tissues. While NURR1, the BDNF regulator in midbrain neurons, is associated with ASD pathology, its specific role in regulation of cortical BDNF is not yet well-established. Our third study aimed to understand the role of NURR1 in regulating BDNF specifically in the cortex. We showed that in resting and depolarized neurons, when NURR1 is knocked down, BDNF mRNA levels remained unchanged, suggesting that NURR1 does not regulate BDNF in cortical neurons and highlighting the tissue-specificity of BDNF regulation. In summary, we address the understudied effects of maternal factors on mouse models, which enhances the reliability of ASD research. Further, our studies significantly enhance the understanding of ASD by elucidating the role of TrkB and its downstream signaling pathways in the behavioral aspects of the disorder. We also contribute to the knowledge of BDNF regulation in the cortex, a brain tissue with crucial roles in various aspects of social behavior. In a forward-looking approach, the results of our studies provide valuable insights into mouse modeling of idiopathic ASD and the potential role of TrkB in ASD behavioral symptoms. / Thesis / Candidate in Philosophy / Autism spectrum disorder (ASD) is a condition that is accompanied by challenges in social interaction and repetitive behaviors. ASD is a complicated condition because we do not fully understand all the details of how it works in the body. Studying ASD is important as it is the most challenging condition in children and it is becoming more common, especially in the last two decades. While scientists are developing molecular tools to improve ASD diagnosis and understand its biology, these tools are not widely used in clinics for ASD diagnosis yet. Also, the approved medications available can only help with managing some of the behavioral symptoms like self-harming behavior. Despite the pressing need to find a solution, our recent advancements have not yet brought us closer to a cure for ASD, mainly because of the complexity of the disorder. Therefore, identifying the specific ASD-related mechanisms at the molecular level that contribute to ASD-related behaviors is crucial for gaining a deeper understanding of the disease. In ASD, there are problems with how brain cells communicate with each other. This communication is controlled by certain molecules in the brain, such as brain-derived neurotrophic factor (BDNF) and its receptor, tropomyosin-related kinase B (TrkB), along with other molecules. There is evidence suggesting a link between these molecules and ASD, but we have not fully understood their precise roles because most of the current knowledge is based on observations and correlations, rather than on establishing cause-and-effect relationships. To bridge this gap, our research focused on understanding TrkB's role in ASD. We required reliable mouse models. Since we aimed to induce ASD-like behaviors in mice using an ASD-causing chemical, it was crucial to ensure they were healthy beforehand. We needed to confirm that any social deficits or repetitive behaviors were not due to other factors, such as adverse infancy experiences or impaired interactions between mother and infant. We discovered that sexually mature dams aged between 3 to 6 months, with a history of previous pregnancies and motherhood, give birth to healthier litters. These litters can serve as a more dependable source for our animal behavioral studies. Many cases of ASD in humans are caused by non-genetic factors such as environmental influences like pesticides, air pollution, and the use of certain drugs during pregnancy. In cases of human ASD triggered by non-genetic factors, there is an increase in proBDNF, the precursor of BDNF. However, this proBDNF does not efficiently convert to BDNF. With insufficient BDNF and TrkB receptors, molecules like Akt (protein kinase B, also PKB) and Erk (Extracellular Signal-Regulated Kinase), which are crucial for neuron communication, are also less active downstream. This imbalance disrupts neuron connections, leading to ASD behaviors. In our research, the ASD-causing chemical which we used is valproic acid. It is originally an anti-seizure medication. When pregnant women took valproic acid, the chance of their child having ASD increased. Scientists used this information to inject pregnant mice with valproic acid, and as a result, all the offspring showed ASD-like behaviors. We anticipated that by isolating the brains of these offspring and measuring protein levels of BDNF, TrkB, Akt, and Erk, we would observe a similar pattern to that seen in humans with non-genetic ASD cases. We focused on studying the cortex, a region of the brain responsible for regulating social behaviors in both mice and humans. Since ASD is associated with challenges in social behaviors, we isolated the cortex from mouse brains to analyze protein levels. A chemical known as LM22A-4 with a structure resembling BDNF can bind to TrkB and activate it. We expected that the offspring of pregnant dams injected with valproic acid, which led to reduced TrkB axis activation in their brains, would show improvement in ASD behavior. This anticipation stems from the understanding that LM22A-4 activates the TrkB axis, thus compensating for its reduction, which is thought to be causing ASD-like behaviors. The offspring of mothers injected with valproic acid exhibited ASD-like behaviors, unlike the control mice. Control mice were offspring of pregnant dams injected with a solution containing only the substances used to dissolve valproic acid, typically water and salt (saline). Mice prenatally exposed to valproic acid (VPA) exhibited ASD-like behaviors, but treatment with LM22A-4 helped alleviate these behaviors, promoting more typical behavior patterns. LM22A-4, by activating TrkB receptors, helped to protect the brain from harm caused by exposure to valproic acid before birth. This could mean that valproic acid-induced changes in TrkB-related molecular mechanisms are involved in social behavior difficulties and increased repetitive behaviors seen in autism. Nevertheless, the levels of TrkB, BDNF, proBDNF, Akt, and Erk in the cortex of offspring from mothers injected with valproic acid were like those in the offspring from mothers injected with the saline solution. Therefore, the BDNF and TrkB signaling pathways remained unchanged in the cortex of our valproic acid model in this study, and they differ from those observed in human idiopathic ASD. We also speculated that a protein, called NURR1 acting upstream of BDNF and TrkB might be involved in the process. NURR1 acts as a regulatory protein that binds to the BDNF, increasing the production of copies from the BDNF. We also used a small RNA that targets a specific region in the Nurr1 and inhibits its protein production We anticipated a reduction in Nurr1 levels. As NURR1 acts as an upregulator of BDNF, lower levels of Nurr1 would result in decreased BDNF production. Activating NURR1 resulted in increased BDNF mRNA levels. However, when NURR1 was reduced, BDNF mRNA levels remained unaffected. This led us to conclude that if NURR1 levels decrease, other proteins may step in to maintain BDNF mRNA levels. Therefore, in the cortex, unlike in some other brain regions, the presence of NURR1 is not essential for regulating Bdnf. In summary, before inducing ASD-like behavior in mice using valproic acid, it is crucial to ensure the health of the mice. We used sexually mature mothers with prior pregnancy experience to provide a healthy baseline. We showed valproic acid induced ASD-like behaviors in mice offspring. We also observed that LM22A-4 treatment alleviated ASD-like behaviors of offspring. In our study, we demonstrated that the levels of BDNF, TrkB, Erk, and Akt proteins in the cortex of mice exposed to valproic acid were not affected. For this reason, our mouse model does not resemble human non-genetic ASD. Finally, NURR1's role in BDNF regulation varies by brain region. Lowering NURR1 did not affect BDNF mRNA levels, suggesting compensatory mechanisms. Our findings suggest new directions for further research to better understand the roles of TrkB and BDNF in non-genetic ASD. Overall, this study provides valuable knowledge that can contribute to advancing our understanding of idiopathic ASD-related molecular mechanisms.

La perception visuelle implique une interaction complexe entre les yeux, le cerveau et les processus cognitifs, transformant les stimuli visuels en une représentation interne de l'environnement. Bien qu'une fraction limitée des informations parviennent à notre conscience visuelle, le cerveau traite une quantité considérable d'informations de manière inconsciente. Des recherches en imagerie par résonance magnétique fonctionnelle (IRMf) ont visé à mieux discerner les corrélats neuronaux associés à la perception consciente et inconsciente. Cependant, l'identification précise des régions cérébrales impliquées dans la génération d'une perception consciente, et leur modulation par l'expérience ou par des lésions cérébrales, demeure un défi. Cette thèse examine le traitement conscient et inconscient de l'information visuelle à l'aide de tâches visuelles et de neuroimagerie, pour comprendre comment ces processus se reflètent dans l'activation cérébrale et l'impact de lésions du cortex visuel. L'article 1 vise à identifier de manière empirique les zones d'activation fonctionnelle associées au traitement visuel conscient et inconscient chez les individus neurotypiques, en menant deux méta-analyses quantitatives de données de neuroimagerie. Les résultats révèlent que le traitement conscient mobilise la jonction fronto-inférieure, le sillon intrapariétal, le cingulum antérieur dorsal, le gyrus angulaire, le cortex temporo-occipital et l'insula antérieure. Le traitement visuel inconscient sollicite davantage les régions postérieures, comme le complexe occipital latéral. L'article 2 traite des processus cognitifs associés à la modulation de l'activation fonctionnelle suite à une lésion du cortex visuel. La déficience visuelle cérébrale (DVC) est caractérisée par une perte des fonctions visuelles due à un dommage cérébral plutôt qu'à une atteinte des yeux. Bien que la majorité des individus ne regagnent pas une vision normale, dans certains cas fascinants une amélioration peut être notée avec le temps en raison de la capacité du cerveau à se réorganiser. La perte visuelle peut s'accompagner du blindsight, où les individus sont capables de traiter de l'information visuelle tout en niant l'avoir vue. Cet article novateur utilise un paradigme de détection de mouvement pour évaluer l'activation des structures corticales et sous-corticales lors d'une performance de blindsight chez un individu avec DVC. Cette contribution significative met en évidence des corrélats neuronaux indépendants des aires visuelles primaires, associés à des structures spécifiques pendant la détection de mouvement en blindsight. Le chapitre 4 présente une base de données d'IRM haute résolution pour la perception du mouvement visuel d'individus neurotypiques et atteints de DVC. Les données incluent des mesures d'IRM structurelles, fonctionnelles, et de diffusion, des évaluations comportementales et de suivi du regard, des mesures électrophysiologiques, en plus de données prétraitées, le code et des métriques de contrôle de la qualité. L'article 3 caractérise les conséquences neurologiques des lésions cérébrales chez les participants DVC, ainsi que l'impact sur leur capacité à traiter divers stimuli de mouvement, comparés à un groupe de contrôles neurotypiques, en utilisant des techniques comportementales et d'IRM fonctionnelle à haute résolution. La détection automatisée des lésions a permis de quantifier de manière fiable l'étendue des dommages cérébraux et les participants ont été catégorisés selon leur capacités visuelles résiduelles. Les résultats confirment que le cerveau peut traiter des informations visuelles malgré l'absence de zones visuelles primaires intactes. Les participants DVC ont présenté des altérations fonctionnelles étendues, contrairement aux participants neurotypiques, qui ont montré une activation focalisée dans des régions spécialisées pour le traitement visuel et de mouvement. L'hémisphère lésé présente une activation plus synergique dans l'aire temporale médiane et le complexe occipital latéral. Dans l'hémisphère intact, ce dernier peut répondre à une stimulation du champ visuel atteint. Le thalamus et le pulvinar ipsilésionnels ont montré une dominance ipsilatérale en réponse au mouvement, contrairement à la dominance controlatérale dans l'hémisphère intact et chez les participants DVC avec des capacités visuelles résiduelles comparables à celles des contrôles. Cette thèse, par une approche multimodale, étudie les mécanismes neuronaux du traitement visuel chez les individus neurotypiques et atteints de DVC. L'utilisation d'étapes empiriques séquentielles, notamment une étude de cas, des analyses de groupes et des méta-analyses, renforce la fiabilité et l'applicabilité de la recherche, et vise à cartographier l'adaptation cérébrale après une lésion du cortex visuel. / Visual perception involves the intricate interplay of the eyes, brain, and cognitive processes, enabling photons of visible light to be captured on the retina, processed through specific pathways in the brain and transformed into a rich internal representation of our surroundings. While only a fraction of information reaches conscious awareness, the brain can process the remaining unconsciously. Functional magnetic resonance imaging studies have sought to understand the neural signals associated with conscious versus unconscious perception. However, comprehensively understanding the core brain regions involved in generating a conscious perception and their modulation through experience or brain damage remains a challenge. In this thesis, we investigate the conscious and unconscious processing of visual information through a series of visual tasks. We aim to understand how these processes are reflected in brain activation and how they can be modulated by damage to the visual cortex. Article 1 aimed to empirically identify and characterize areas of reliable convergence in functional activation of regions engaged during either conscious or unconscious visual processing in neurotypical participants by conducting two distinct quantitative meta-analyses. The findings reveal that conscious visual processing readily engages a constellation of regions comprising the inferior frontal junction, intraparietal sulcus, dorsal anterior cingulate, angular gyrus, temporo-occipital cortex and anterior insula, whereas unconscious processing recruits posterior regions, mainly the lateral occipital complex. The aim of Article 2 was to provide a detailed understanding of cognitive constructs and functional alterations following visual cortex damage. Cerebral visual impairment (CVI) refers to a loss of visual function caused by damage to the brain rather than the eyes. While most individuals do not recover intact vision, some cases have demonstrated improvement over time due to the brain's ability to reorganize itself. In certain instances of visual loss, blindsight can occur, allowing individuals to process visual information without conscious awareness. To our knowledge, this article was the first to propose the use of an event-related motion detection paradigm to assess functional activation in cortical and subcortical structures, independant of primary visual areas, during a CVI individual's blindsight performance. Chapter 4 aimed to conceptualize and acquire a unique high-resolution MRI dataset for studying visual motion perception in neurotypical and CVI individuals. This comprehensive dataset encompasses multiple modalities, including structural, functional task-based, resting-state and diffusion MRI, behavioral and evaluations, electrophysiological measures, and eyetracking data, in addition to preprocessed data, code and quality control metrics. Article 3 aimed to understand the functional consequences of brain damage in CVI individuals and the resulting impact on their ability to process diverse visual motion stimuli, including looming and biological motion, compared to a group of neurotypical controls, using behavioral and high-resolution neuroimaging techniques. Automatic lesion mapping enabled to reliably quantify the extent of brain damage and participants were categorized based on their residual visual ability. The findings demonstrate that the brain can process and represent visual information, without intact primary visual areas. CVI participants exhibited broad functional alterations, contrasting the focused activation in visual and motion processing regions for neurotypical controls. Specifically, the lesioned hemisphere displayed synergistic activation in the middle temporal area and lateral occipital complex, while the intact hemisphere's lateral occipital complex responded to impaired visual field stimulation. The ipsilesional thalamus and pulvinar demonstrated an ipsilateral dominance in response to looming motion, in contrast to the contralateral dominance in the intact hemisphere and among CVI participants with residual visual abilities akin to neurotypical controls. By employing a multi-modal approach integrating behavioral assessments, structural and functional neuroimaging methods, this thesis comprehensively investigates the neural mechanisms underlying visual processing in both neurotypical individuals and those with CVI. The use of sequential steps in empirical science, namely a case study, group analyses, and meta-analyses, enhances the reliability and applicability of the research, and effectively contributes to help map brain adaptation post visual cortex injury and further inform neurotypical visual information processing.

Les neurones du cortex visuel primaire (aire 17) du chat adulte répondent de manière sélective à différentes propriétés d’une image comme l’orientation, le contraste ou la fréquence spatiale. Cette sélectivité se manifeste par une réponse sous forme de potentiels d’action dans les neurones visuels lors de la présentation d’une barre lumineuse de forme allongée dans les champs récepteurs de ces neurones. La fréquence spatiale (FS) se mesure en cycles par degré (cyc./deg.) et se définit par la quantité de barres lumineuses claires et sombres présentées à une distance précise des yeux. Par ailleurs, jusqu’à récemment, l’organisation corticale chez l’adulte était considérée immuable suite à la période critique post-natale. Or, lors de l'imposition d'un stimulus non préféré, nous avons observé un phénomène d'entrainement sous forme d'un déplacement de la courbe de sélectivité à la suite de l'imposition d'une FS non-préférée différente de la fréquence spatiale optimale du neurone. Une deuxième adaptation à la même FS non-préférée induit une réponse neuronale différente par rapport à la première imposition. Ce phénomène de "gain cortical" avait déjà été observé dans le cortex visuel primaire pour ce qui est de la sélectivité à l'orientation des barres lumineuses, mais non pour la fréquence spatiale. Une telle plasticité à court terme pourrait être le corrélat neuronal d'une modulation de la pondération relative du poids des afférences synaptiques. / Primary visual cortex neurons in adult cat are selective to different image properties as orientation, contrast and spatial frequency. This selectivity is characterized by action potentials as electrical activity from the visual neurons. This response occurs during the presentation of a luminous bar in the receptive fields of the neurons. Spatial frequency is the amount of luminous bars in a grating presented from a precise distance from the eyes and is measured in cycles per degree. Furthermore, it was establish until recently that cortical organisation in the adult remains inflexible following the critical period after birth. However, our results have revealed that spatial frequency selectivity is able to change after an imposition of a non-preferred spatial frequency, also called adapter. Following cortical activity recordings, there is a shift of the spatial frequency tuning curves in the direction of the adapter. A second adaptation at the same non-preferred spatial frequency produced a different neural response from the first adaptation. This “short-term plasticity” was already observed in the primary visual cortex for orientation selective neurons but not yet for spatial frequency. The results presented in this study suggest that such plasticity is possible and that visual neurons regulate their electrical responses through modulation of the weights of their synaptic afferences.

Le co-transporteur KCC2 spécifique au potassium et chlore a pour rôle principal de réduire la concentration intracellulaire de chlore, entraînant l’hyperpolarisation des courants GABAergic l’autorisant ainsi à devenir inhibiteur dans le cerveau mature. De plus, il est aussi impliqué dans le développement des synapses excitatrices, nommées aussi les épines dendritiques. Le but de notre projet est d’étudier l’effet des modifications concernant l'expression et la fonction de KCC2 dans le cortex du cerveau en développement dans un contexte de convulsions précoces. Les convulsions fébriles affectent environ 5% des enfants, et ce dès la première année de vie. Les enfants atteints de convulsions fébriles prolongées et atypiques sont plus susceptibles à développer l’épilepsie. De plus, la présence d’une malformation cérébrale prédispose au développement de convulsions fébriles atypiques, et d’épilepsie du lobe temporal. Ceci suggère que ces pathologies néonatales peuvent altérer le développement des circuits neuronaux irréversiblement. Cependant, les mécanismes qui sous-tendent ces effets ne sont pas encore compris. Nous avons pour but de comprendre l'impact des altérations de KCC2 sur la survenue des convulsions et dans la formation des épines dendritiques. Nous avons étudié KCC2 dans un modèle animal de convulsions précédemment validé, qui combine une lésion corticale à P1 (premier jour de vie postnatale), suivie d'une convulsion induite par hyperthermie à P10 (nommés rats LHS). À la suite de ces insultes, 86% des rats mâles LHS développent l’épilepsie à l’âge adulte, au même titre que des troubles d’apprentissage. À P20, ces animaux presentent une augmentation de l'expression de KCC2 associée à une hyperpolarisation du potentiel de réversion de GABA. De plus, nous avons observé des réductions dans la taille des épines dendritiques et l'amplitude des courants post-synaptiques excitateurs miniatures, ainsi qu’un déficit de mémoire spatial, et ce avant le développement des convulsions spontanées. Dans le but de rétablir les déficits observés chez les rats LHS, nous avons alors réalisé un knock-down de KCC2 par shARN spécifique par électroporation in utero. Nos résultats ont montré une diminution de la susceptibilité aux convulsions due à la lésion corticale, ainsi qu'une restauration de la taille des épines. Ainsi, l’augmentation de KCC2 à la suite d'une convulsion précoce, augmente la susceptibilité aux convulsions modifiant la morphologie des épines dendritiques, probable facteur contribuant à l’atrophie de l’hippocampe et l’occurrence des déficits cognitifs. Le deuxième objectif a été d'inspecter l’effet de la surexpression précoce de KCC2 dans le développement des épines dendritiques de l’hippocampe. Nous avons ainsi surexprimé KCC2 aussi bien in vitro dans des cultures organotypiques d’hippocampe, qu' in vivo par électroporation in utero. À l'inverse des résultats publiés dans le cortex, nous avons observé une diminution de la densité d’épines dendritiques et une augmentation de la taille des épines. Afin de confirmer la spécificité du rôle de KCC2 face à la région néocorticale étudiée, nous avons surexprimé KCC2 dans le cortex par électroporation in utero. Cette manipulation a eu pour conséquences d’augmenter la densité et la longueur des épines synaptiques de l’arbre dendritique des cellules glutamatergiques. En conséquent, ces résultats ont démontré pour la première fois, que les modifications de l’expression de KCC2 sont spécifiques à la région affectée. Ceci souligne les obstacles auxquels nous faisons face dans le développement de thérapie adéquat pour l’épilepsie ayant pour but de moduler l’expression de KCC2 de façon spécifique. / The potassium-chloride cotransporter KCC2 decreases intracellular Cl- levels and renders GABA responses inhibitory. In addition, it has also been shown to modulate excitatory synapse development. In this project, we investigated how alterations of KCC2 expression levels affect these two key processes in cortical structures of a normal and/or epileptic developing brain. First, we demonstrate that KCC2 expression is altered by early-life febrile status epilepticus. Febrile seizures affect about 5% of children during the first year of life. Atypical febrile seizures, particularly febrile status epilepticus, correlate with a higher risk of developing cognitive deficits and temporal lobe epilepsy as adults, suggesting that they may permanently change the developmental trajectory of neuronal circuits. In fact, the presence of a cerebral malformation predisposes to the development of atypical febrile seizures and temporal lobe epilepsy. The mechanisms underlying these effects are not clear. Here, we investigated the functional impact of this alteration on subsequent synapse formation and seizure susceptibility. We analyzed KCC2 expression and spine density in the hippocampus of a well-established rodent model of atypical febrile seizures, combining a cortical freeze lesion at post-natal day 1 (P1) and hyperthermia-induced seizure at P10 (LHS rats). 86% of these LHS males develop epilepsy and learning and memory deficits in adulthood. At P20, we found a precocious increase in KCC2 protein levels, accompanied by a negative shift of the reversal potential of GABA (EGABA) by gramicidin-perforated patch. In parallel, we observed a reduction in dendritic spine size by DiI labelling and a reduction of miniature excitatory postsynaptic current (mEPSC) amplitude in CA1 pyramidal neurons, as well as impaired spatial memory. To investigate whether the premature expression of KCC2 played a role in these alterations in the LHS model, and on seizure susceptibility, we reduced KCC2 expression in CA1 pyramidal neurons by in utero electroporation of shRNA using a triple-probe electrode. This approach lead to reduced febrile seizure susceptibility, and rescued spine size shrinkage in LHS rats. Our results show that an increase of KCC2 levels induced by early-life insults affect seizure susceptibility and spine development and may be a contributing factor to the occurrence of hippocampal atrophy and associated cognitive deficits in LHS rats. Second, we investigated whether KCC2 premature overexpression plays a role in spine alterations in the hippocampus. We overexpressed KCC2 in hippocampal organotypic cultures by biolistic transfection and in vivo by in utero electroporation. In contrast to what was previously published, we observed that both manipulations lead to a decrease in spine density in the hippocampus, as well as an increase in spine head size in vivo. In fact, it has been previously shown that overexpressing KCC2 leads to an increase of spine density in the cortex in vivo. To prove that this discrepancy is due to brain regional differences, we overexpressed KCC2 in the cortex by in utero electroporation, and similarly found an increase in spine density and length. Altogether, our results demonstrate for the first time, that alterations of KCC2 expression are brain circuit-specific. These findings highlights the obstacles we will face to find adequate pharmacological treatment to specifically modulate KCC2 in a region-specific and time-sensitive manner in epilepsy.

Myosin 1c (Myo1c) is a molecular motor involved in regulation of tension-gated ion channels, exocytosis, endocytosis, motility and other membrane-related events. Moreover, it acts as a dynamic linker between the cell membrane and cortical actin network, contributing to the maintenance of plasma membrane tension. In contrast, nuclear myosin 1 (NM1), an isoform of Myo1c, has been described only in the nucleus where it participates in various nuclear processes, including transcription or chromatin remodeling. However, although traditionally regarded as exclusively cytoplasmic or nuclear, all myosin 1c isoforms participate in nuclear functions and they are present in the cytoplasm as well. The main focus of this study was to characterize the functional significance of NM1 in the cytoplasm. We have found that NM1 localizes to plasma membrane and shows a uniform punctuated distribution with a high concentration at the cell periphery. Moreover, atomic force microscopy measurements of mouse NM1 KO fibroblasts revealed a significant increase in an overall plasma membrane elasticity in comparison to WT cells, indicating a disruption in the regulation of plasma membrane tension caused by the loss of NM1. Since a higher membrane elasticity and deformability is a characteristic marker of cancer cells,...

This work deals with issue of human wrist and appropriate total wrist implant allowing a restoration of hand mobility approaching physiological condition after traumatic and degenerative diseases. Treating these diseases are very complex. These issues including a biological and medical issues. To determine the appropriate treatment method and select right total wrist implant is important to know the behavior the human wrist at all stages in terms of medical and biomechanical. For this reason, it was developed a biomechanical study including computation model of human wrist allowing solution of strain and stress of hand in physiological and pathological conditions and condition after total wrist implant. The frost remodeling of bone tissue was used for analysis of human wrist bone tissues and bone tissues after application of total wrist implant RE-MOTION™ Total Wrist.

Wir untersuchen globale dynamische Phänomene, die sich von dem Zusammenspiel zwischen Netzwerktopologie und Dynamik der einzelnen Elementen ergeben. Im ersten Teil untersuchen wir relativ kleine strukturierte Netzwerke mit überschaubarer Komplexität. Als geeigneter theoretischer Rahmen für erregbare Systeme verwenden wir das Kuramoto und Shinomoto Modell der sinusförmig-gekoppelten "aktiven Rotatoren" und studieren das Kollektivverhalten des Systems in Bezug auf Synchronisation. Wir besprechen die Einschränkungen, die durch die Netzwerktopologie auf dem Fluss im Phasenraum des Systems gestellt werden. Insbesondere interessieren wir uns für die Stabilitätseigenschaften von Fluss-invarianten Polydiagonalen und die Entwicklungen von Attraktoren in den Parameterräume solcher Systeme. Wir untersuchen zweidimensionale hexagonale Gitter mit periodischen Randbedingungen. Wir untersuchen allgemeine Bedingungen auf der Adjazenzmatrix von Netzwerken, die die Watanabe-Strogatz Reduktion ermöglichen, und diskutieren verschiedene Beispiele. Schließlich präsentieren wir eine generische Analyse der Bifurkationen, die auf der Untermannigfaltigkeit des Watanabe-Strogatz reduzierten Systems stattfinden. Im zweiten Teil der Arbeit untersuchen wir das globale dynamische Phänomen selbstanhaltender Aktivität (self-sustained activity / SSA) in neuronalen Netzwerken. Wir betrachten Netzwerke mit hierarchischer und modularer Topologie , umfassend Neuronen von verschiedenen kortikalen elektrophysiologischen Zellklassen. Wir zeigen, dass SSA Zustände mit ähnlich zu den experimentell beobachteten Eigenschaften existieren. Durch Analyse der Dynamik einzelner Neuronen sowie des Phasenraums des gesamten Systems erläutern wir die Rolle der Inhibierung. Darüber hinaus zeigen wir, dass beide Netzwerkarchitektur, in Bezug auf Modularität, sowie Mischung aus verschiedenen Neuronen, in Bezug auf die unterschiedlichen Zellklassen, einen Einfluss auf die Lebensdauer der SSA haben. / In this work we study global dynamical phenomena which emerge as a result of the interplay between network topology and single-node dynamics in systems of excitable elements. We first focus on relatively small structured networks with comprehensible complexity in terms of graph-symmetries. We discuss the constraints posed by the network topology on the dynamical flow in the phase space of the system and on the admissible synchronized states. In particular, we are interested in the stability properties of flow invariant polydiagonals and in the evolutions of attractors in the parameter spaces of such systems. As a suitable theoretical framework describing excitable elements we use the Kuramoto and Shinomoto model of sinusoidally coupled “active rotators”. We investigate plane hexagonal lattices of different size with periodic boundary conditions. We study general conditions posed on the adjacency matrix of the networks, enabling the Watanabe-Strogatz reduction, and discuss different examples. Finally, we present a generic analysis of bifurcations taking place on the submanifold associated with the Watanabe-Strogatz reduced system. In the second part of the work we investigate a global dynamical phenomenon in neuronal networks known as self-sustained activity (SSA). We consider networks of hierarchical and modular topology, comprising neurons of different cortical electrophysiological cell classes. In the investigated neural networks we show that SSA states with spiking characteristics, similar to the ones observed experimentally, can exist. By analyzing the dynamics of single neurons, as well as the phase space of the whole system, we explain the importance of inhibition for sustaining the global oscillatory activity of the network. Furthermore, we show that both network architecture, in terms of modularity level, as well as mixture of excitatory-inhibitory neurons, in terms of different cell classes, have influence on the lifetime of SSA.

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Establishing and maintaining successful communication stands as a critical prerequisite for achieving the goals of inducing and studying advanced computation in small-scale living neuronal networks. The following work establishes a novel and effective method for communicating arbitrary "sensory" input information to cultures of living neurons, living neuronal networks (LNNs), consisting of approximately 20 000 rat cortical neurons plated on microelectrode arrays (MEAs) containing 60 electrodes. The sensory coding algorithm determines a set of effective codes (symbols), comprised of different spatio-temporal patterns of electrical stimulation, to which the LNN consistently produces unique responses to each individual symbol. The algorithm evaluates random sequences of candidate electrical stimulation patterns for evoked-response separability and reliability via a support vector machine (SVM)-based method, and employing the separability results as a fitness metric, a genetic algorithm subsequently constructs subsets of highly separable symbols (input patterns). Sustainable input/output (I/O) bit rates of 16-20 bits per second with a 10% symbol error rate resulted for time periods of approximately ten minutes to over ten hours. To further evaluate the resulting code sets' performance, I used the system to encode approximately ten hours of sinusoidal input into stimulation patterns that the algorithm selected and was able to recover the original signal with a normalized root-mean-square error of 20-30% using only the recorded LNN responses and trained SVM classifiers. Response variations over the course of several hours observed in the results of the sine wave I/O experiment suggest that the LNNs may retain some short-term memory of the previous input sample and undergo neuroplastic changes in the context of repeated stimulation with sensory coding patterns identified by the algorithm.

Grundlage der vorgelegten Arbeit sind die bei der Alzheimerschen Erkrankung beobachtbaren pathologischen Merkmale, wie die progressive Akkumulation von β-Amyloid-Plaques, cholinerger Dysfunktion und zerebrovaskuläre Abnormalitäten. Die in englischer Sprache verfasste Dissertation ist eine tierexperimentelle Studie, die versucht, den Zusammenhang von β-Amyloid, cholinerger Neurotransmission und zerebralem Gefäßsystem bei der Alzheimerschen Erkrankung näher zu charakterisieren. An Hirnmaterial aus der transgenen Maus Tg2576, die die schwedische Mutation des humanen Amyloidpräkursorproteins als Transgen trägt und ab dem 10. Lebensmonat durch humane β-Amyloid-Plaqueablagerungen in der Hirnrinde imponiert, wurden im Altersverlauf (4 bis 18 Monate) immunhistochemische Untersuchungen zur morphologischen Integrität der zerebralen Mikrogefäße, der kortikalen cholinergen Nervterminalen und der intrazerebralen cholinergen neurovaskulären Innervation durchgeführt. Am somatosensorischen Kortex werden beispielhaft die Expression des Glukosetransporters 1 oder Solanum tuberosum Lektin als Kapillarmarker und des vesikulären Acetylcholintransporters als Marker für cholinerge Fasern mittels Immunfluoreszenz und Laser-Scanning Mikroskopie erfasst, einer semiquantitativen Computer-gestützten Bildanalytischen Auswertung unterzogen und mit dem Ausmaß der kortikalen Plaquebeladung korreliert. So konnte gezeigt werden, dass die Dichte der Blutgefäße und cholinergen Fasern im somatosensorischen Kortex von transgenen Tieren mit dem Alter im Vergleich zu nichttransgenen Kontrolltieren abnimmt, was mit einer Reduktion der perivaskulären cholinergen Innervation einhergeht. Die erhobenen Befunde stützen die von J.C. de la Torre und T. Mussivand schon im Jahre 1993 formulierte „vaskuläre Hypothese“, wonach bei der sporadischen Form der Alzheimerschen Erkrankung alters- und Lebensstil-bedingte Schädigungen des zerebralen Gefäßsystems eine zentrale Rolle bei der Manifestierung der Erkrankung spielen.