The high composition of fruits and vegetables in the daily diet is associated with cognitive well-being, especially in the elderly population. The phytonutrients are shown to have effects as antioxidants that neutralize oxidative stressors and can interact with molecular pathways to signal neuron survival. Adult hippocampal neurogenesis is a dynamic lifelong process of generating functional newborn neurons in the granular layer of the dentate gyrus from adult precursor cells. This process contributes to brain plasticity and plays a role in learning and memory. External stimuli such as environmental enrichment and physical activity are known to positively regulate this process. However, the role of nutrition and whether nutritional compounds have pro-neurogenic effects on adult hippocampal precursor cells are still elusive. In this study, I investigated the impact of dietary compounds in apples, a significant source of phytonutrients in our food, on adult hippocampal neurogenesis. I demonstrated that quercetin, the most abundant polyphenol in apple, induces cell cycle exit and differentiation of adult hippocampal precursor cells in monolayer culture. Furthermore, this compound also increases the number of surviving cells upon differentiation in vitro, through the activation of endogenous antioxidants in the Nrf2-Keap1 pathway and the prosurvival Akt pathway. Quercetin supplementation in vivo is also shown to significantly increase the number of surviving cells and new neurons in the dentate gyrus. To search for other potential active compounds in apple, I performed bioassay-guided fractionation whereby the flesh extract from apples of the Pinova cultivar was subjected to liquid- and solid phase separation and the active fraction was determined using primary neurosphere assays using cells derived from adult mouse dentate gyrus. Using mass spectometry, we revealed that the active compounds in the apple flesh extract are dihydroxybenzoate glycosides, which are non-flavonoid benzoic acid derivatives. I also confirmed that the isomers of these compounds; 2,3- and 3,5 dihydroxybenzoic acids significantly increase the number of neurospheres. Interestingly, 3,5 dihdroxybenzoic acid is an agonist of lactate receptor hydroxycarboxylic acid receptor 1 (HCAR1), with an even higher affinity than lactate. This receptor is suggested to mediate neurotrophic actions such as increasing production and release of BDNF. I also demonstrated for the first time that this receptor is presence in adult hippocampal precursor cells. To observe whether customary fruits or fruit-related products consumption affects adult hippocampal neurogenesis, I performed an experiment giving apple juice supplementation ad libitum to mice. I did not find a significant increase in net neurogenesis or the performance in the Morris water maze after apple juice supplementation. This is likely due to the low concentration of active compounds in apple juice failing to reach an effective concentration in the body. I conclude that apples provide potential proneurogenic compounds that can influence adult hippocampal neurogenesis through the activation of endogenous antioxidant mechanisms and molecular pathways for cell survival. Further studies are necessary to investigate the role of HCAR1 activation on adult hippocampal neurogenesis, which is a potential new mechanism to explain the health benefits of fruit and vegetable consumption. / Eine Ernährung die täglich reich an Obst und Gemüse ist, hat insbesondere bei älteren Menschen einen positiven Einfluss auf kognitive Fähigkeiten. Pflanzeninhaltsstoffe wirken als natürliche Antioxidantien, indem sie oxidative Stressoren neutralisieren. Weiterhin beeinflussen pflanzliche Nährstoffe molekulare Signalwege welche beim Überleben von Neuronen eine Rolle spielen. Die adulte hippocampale Neurogenese ist ein dynamischer, lebenslanger Prozess, bei dem aus Vorläuferzellen funktionelle neue Neuronen in der Körnerzellschicht des Gyrus dentatus gebildet werden. Dieser Prozess trägt zur Plastizität des Gehirns bei und spielt eine bedeutende Rolle beim Lernen und für das Gedächtnis. Externe Stimuli wie zum Beispiel eine reizreiche Umgebung und körperliche Aktivität wirken als positive Regulatoren und begünstigen die adulte hippocampale Neurogenese. Welche Rolle die Ernährung dabei spielt und ob Nahrungsbestandteile einen proneurogenen Effekt auf adulte hippocampale Vorläuferzellen haben ist kaum bekannt. In diesem Projekt habe ich den Effekt von Nahrungsbestandteilen aus Äpfeln, welche eine bedeutende Quelle von pflanzlichen Nährstoffen in unserer Ernährung darstellen, auf die adulte hippocampale Neurogenese untersucht. Ich habe gezeigt, dass Querzetin, das am reichlichsten in Äpfeln enthaltende Polyphenol, in der Monolayer-Zellkultur den Austritt aus dem Zellzyklus induziert und die Differenzierung von adulten hippocampalen Vorläuferzellen fördert. Des Weiteren steigert Querzetin nach der Differenzierung in vitro die Anzahl an überlebenden Zellen. Dies geschieht durch die Aktivierung von endogenen Antioxidantien des Nrf2-Keap1-Signalweges und des für das Überleben von Zellen förderlichen Akt-Signalweges. Die Verabreichung von Querzetin in vivo als Nahrungsergänzungsmittel führte ebenfalls zu einem signifikanten Anstieg der Anzahl an überlebenden Zellen und neu gebildeten Nervenzellen im Gyrus dentatus. Um weitere potentiell aktive Wirkstoffe von Äpfeln zu bestimmen, habe ich eine Bioassay-ausgerichtete Fraktionierung durchgeführt, wobei der Fruchtfleischextrakt von Äpfeln der Sorte Pinova einer Fest-/ Flüssig-Separation unterzogen wurde. Die aktive Fraktion wurde anhand der primären Neurosphäre-Assay-Methode mit Zellen aus dem Gyrus dentatus adulter Mäuse ermittelt. Mittels spektrometrischer Analyse habe ich gezeigt, dass die aktiven Wirkstoffe im Fruchtfleischextrakt von Äpfeln zur Gruppe der Dihydroxybenzol-Glykosiden gehören, welche den nicht-flavonoiden Benzoesäure-Derivaten zuzuordnen sind. Im in vitro Neurosphäre-Assay habe ich zudem gezeigt, dass die Isomere dieser Wirkstoffe, die 2,3- und die 3,5-Dihydroxybenzoesäuren, die Anzahl der Neurosphären signifikant erhöhen. Interessanterweise ist die 3,5-Dihydroxybenzoesäure ein Agonist des Laktatrezeptors Hydroxycarboxylic acid receptor 1 (HCAR1) und weist sogar eine noch höhere Affinität als Laktat auf. Es wird suggeriert, dass dieser Rezeptor neurotrophische Wirkungen vermittelt, wie zum Beispiel eine erhöhte Produktion von BDNF und dessen Ausschüttung. Zudem habe ich das Vorkommen dieses Reporters erstmalig bei adulten hippocampalen Vorläuferzellen nachgewiesen. Um zu untersuchen, ob der Konsum handelsüblicher Obstprodukte die adulte hippocampale Neurogenese beeinflusst, habe ich Mäusen Apfelsaft ad libitum verabreicht. Nach der Gabe von Apfelsaft sah ich keinen signifikanten Anstieg der Gesamtneurogenese und keine Verbesserung der Leistungsfähigkeit im Morris-Wasserlabyrinth-Test. Dies ist bedingt durch eine zu geringe Konzentration der aktiven Wirkstoffe im Apfelsaft wodurch die wirksame Konzentration im Körper nicht erreicht wird. Ich schlussfolgere, dass in Äpfeln potentielle pro-neurogene Inhaltsstoffe enthalten sind, welche die adulte hippocampale Neurogenese beeinflussen. Dies wird insbesondere durch die Aktivierung endogener antioxidativer Mechanismen und molekularer Signalwege vermittelt, die für das Überleben von Zellen von Bedeutung sind. Weitere Studien sind nötig, um zu bestimmen wie sich die Aktivierung von HCAR1 auf die adulte hippocampale Neurogenese auswirkt. Dies stellt einen potentiellen neuen Wirkmechanismus dar, welcher die gesundheitlichen Vorteile von Obst- und Gemüsekonsum belegt.

O sistema da procineticina desempenha um papel importante na migração dos neurônios secretores de GnRH e na neurogênese do bulbo olfatório. Camundongos com ablação dos genes que codificam a procineticina 2 (PROK2) e seu receptor (PROKR2) apresentaram fenótipos semelhantes ao da síndrome de Kallmann descrita em humanos. Mutações inativadoras nos genes PROK2 e PROKR2 foram identificadas em pacientes com hipogonadismo hipogonadotrófico isolado. Com base nestes achados, investigamos a presença de alterações estruturais nos genes PROK2 e PROKR2 em 107 pacientes brasileiros (63 com síndrome de Kallmann e 47 com hipogonadismo hipogonadotrófico isolado normósmico). Cem indivíduos brasileiros que relataram desenvolvimento puberal normal foram utilizados como grupo controle. As regiões codificadoras dos genes PROK2 e PROKR2 foram amplificadas utilizando-se oligonucleotídeos intrônicos específicos, seguida de purificação enzimática e sequenciamento automático. Duas mutações no gene PROK2 foram identificadas: a mutação p.G100fsX121 em homozigose presente em dois irmãos com síndrome de Kallmann; e a mutação p.I55fsX56 em heterozigose identiificada em um paciente com HHIn. Quatro mutações foram identificadas no gene PROKR2 (p.R80C, p.Y140X, p.L173R e p.R268C) em cinco pacientes com síndrome de Kallmann e um paciente com HHIn. Essas mutações não foram encontradas no grupo controle. As mutações do tipo missense, p.R80C, p.L173R e p.R268C foram identificadas em heterozigose. Mutações nos genes FGFR1, GnRHR, KiSS-1 e GPR54 foram excluídas nesses pacientes. O paciente portador da mutação p.R268C do PROKR2 apresentou deleção dos exons 1 e 2 do gene KAL1. Adicionalmente, as mutações p.R80C e p.R268C foram identificadas em heterozigose em parentes de primeiro grau assintomáticos dos casos índices. A nova mutação p.Y140X do PROKR2, única alteração em homozigose, foi identificada em um paciente com micropênis, criptorquidia bilateral, anosmia e palato ogival. Os pais deste paciente eram portadores da mutação p.Y140X em heterozigose e relataram desenvolvimento puberal normal e ausência de anormalidades olfatórias. Estudos in vitro da nova mutação p.R80C localizada na primeira alça intracelular demonstraram que o acúmulo de fofatidil-inositol (IP), assim como a ativação da via da MAPK foram significativamente afetadas em células transfectadas com o receptor mutado em relação ao receptor selvagem, indicando que a mutação p.R80C determina uma menor atividade do receptor. Avaliação da expressão por Western blot mostrou uma diminuição na expressão do receptor mutado R80C e uma maior expressão de receptores imaturos. Esses achados sugeriram o papel crítico da arginina localizada na posição 80 na atividade normal do receptor. Em conclusão, expandimos o repertório de mutações deletérias nos genes PROK2 e PROKR2 em pacientes com hipogonadismo hipogonadotrófico isolado. A haploinsuficiência do PROKR2 não foi suficiente para causar síndrome de Kallmann ou HHIn, entretanto mutações inativadoras em homozigose nos genes PROK2 e PROKR2 foram responsáveis pelo fenótipo reprodutivo e olfatório anormal, em concordância com os estudos prévios de ablação gênica em modelos animais. Arginina localizada na posição 80 do PROKR2 desempenha um papel crucial na adequada maturação do receptor / Physiological activation of the prokineticin pathway has a critical role in olfactory bulb morphogenesis and GnRH secretion. Knock-out mice for genes that encode prokineticin 2 (PROK2) and the prokineticin receptor 2 (PROKR2) exhibited a phenotype similar to the Kallmann syndrome (KS). Inactivating mutations in PROK2 and PROKR2 have been identified in patients with isolated hypogonadotropic hypogonadism. Based on these findings, we investigated the presence of inactivating mutations of the genes PROK2 and PROKR2 in Brazilian patients with isolated hypogonadotropic hypogonadism associated or not with olfactory abnormalities and performed in vitro studies of the new identified mutations. We studied 107 patients with HH (63 with Kallmann syndrome and 44 with normosmic HH) and 100 control individuals. The coding regions of PROK2 and PROKR2 were amplified by polymerase chain reaction followed by enzymatic purification and direct automatic sequencing. In PROK2, two known frameshift mutations were identified. Two brothers with Kallmann syndrome harbored the homozygous p.G100fsX121 mutation, whereas one male with normosmic HH harbored the heterozygous p.I55fsX56 mutation. In PROKR2, four distinct mutations (p.R80C, p.Y140X, p.L173R and p.R268C) were identified in five patients with Kallmann syndrome and in one patient with normosmic HH. These mutations were not found in the control group. The p.R80C and p.R268C missense mutations were identified in heterozygous state in the HH patients and in their asymptomatic first-degree relatives. The p.L173R was also identified in heterozygous state. In addition, no mutations of FGFR1, GnRHR, KiSS-1 or GPR54 were identified in these patients. The patient with the PROKR2 mutation p.R268C also has a deletion of the exon 1 and 2 in the gene KAL1. Notably, the new nonsense mutation (p.Y140X) was identified in homozygous state in an anosmic boy with micropenis, bilateral cryptorchidism and high-arched palate. His asymptomatic parents were heterozygous for this severe defect. In vitro studies of the new mutation, p.R80C, were performed in order to access the mechanism by which this mutation could affect the activity of the PROKR2. In vitro studies showed that the amount of fofatidil-inositol (PI) and the activation of MAPK were significantly lower in cells transfected with the R80C mutant receptor than in cells transfected with the wild receptor, indicating that this variant is a loss-of-function mutation. Binding studies and Western blot showed a reduction in the expression levels of the receptor in the plasma membrane and in whole cell, respectively. Additionally, Western blot analysis of R80C PROKR2 revealed an additional smaller molecular weight band that represents the presence of immature unglycosylated receptors. The arginine 80 in ICL1 is important for post-translational processing of PROKR2. In conclusion, we expanded the repertoire of PROK2 and PROKR2 mutations in patients with HH and showed that PROKR2 haploinsufficiency is not sufficient to cause Kallmann syndrome or normosmic HH, whereas homozygous loss-of-function mutations either in PROK2 or PROKR2 are sufficient to cause disease phenotype, in accordance with the Prokr2 and Prok2 knockout mouse models. In vitro studies suggested that the arginine located at position 80 of the receptor seems to play an important role in the receptor function

A experiência vincular, entre o cuidador primário (mãe) e o bebê, no início da vida pós-natal, constitui o contexto da neurogênese, de acordo com os estudos realizados pela Neurociência do Desenvolvimento; e o fundamento do desenvolvimento emocional segundo a teoria do psicanalista Donald W. Winnicott. O objetivo desta pesquisa é aproximar as construções teóricas de autores que estudam diferentes aspectos de uma mesma realidade: as implicações da experiência vincular entre o bebê e o cuidador primário (mãe), que acontecem nas etapas iniciais do desenvolvimento humano, no processo de inter-relação psique-soma considerada a base do desenvolvimento emocional do ser humano. Essas construções pertencem a uma linha de pesquisa em neurociência do desenvolvimento e outra em psicanálise, representada pela teoria de Donald W. Winnicott, sobre os primórdios do desenvolvimento. Considerando-se que o presente trabalho é um estudo teórico-reflexivo, foi realizada uma pesquisa bibliográfica. As conclusões têm o objetivo de fundamentar um conhecimento que possa ampliar a compreensão dos fatores que interferem no desenvolvimento do ser humano, no início da vida pós-natal, que podem ser responsáveis pelo aparecimento de psicopatologias em etapas futuras do ciclo vital. Enfatizam a necessidade do desenvolvimento de estratégias de intervenção precoce na relação mãe-bebê, em programas de assistência à infância, reforçando a importância da psicologia preventiva na proteção do desenvolvimento humano. / The bonding experience between the primary carer (Mother) and the baby, at the start of the post-natal life, forms the context of neurogenesis, according to studies carried out by Developmental Neuroscience; and is also the basis of emotional development, according to the theory of psychoanalyst Donald W. Winnicott. The objective of this study is to investigate the technical constructions of authors who study different aspects of the same reality: the implications of the bonding experience between the baby and the primary carer (mother), which take place in the initial stages of human development, in the process of the interrelation between psyche and soma, which is considered to be the basis for the emotional development the human being. These constructions belong to a line of research in developmental neuroscience, and another in psychoanalysis, represented by the theory of Donald W. Winnicott on the beginnings of development. Considering that this work is a theoretical-reflective study, a bibliographic review was carried out. The conclusions seek to support a knowledge that can further understanding of the factors which influence human development, at the start of the post-natal life, and which may be responsible for the appearance of psychopathologies in future stages of the vital cycle. They also emphasize the need for the development of strategies of early intervention in the relationship between mother and baby, in infant care programs, reinforcing the importance of preventative psychology in the protection of human development.

Les expériences qui jalonnent la vie favorisent la survenue de modifications cérébrales durables et pouvant impacter les fonctions cognitives, ainsi que le développement de troubles cérébraux. L'hippocampe est une structure cérébrale qui joue un rôle essentiel dans l'apprentissage et la mémoire. Dans la première étude, nous avons montré comment l'activité neuronale sous-tendant les processus de la mémoire influence fortement l'intégration des nouveaux neurones hippocampiques dans le cerveau adulte, suggérant une modulation durable de la fonction hippocampique. Dans la deuxième étude, nous avons montré que le séjour en milieu enrichi qui prévient les déficits mnésiques liés à l'âge et induit également des modifications épigénétiques dans le cerveau sain et modèle de la maladie d'Alzheimer. Ceci suggére que des règulations épigénétiques durables pourraient soutenir les effets promnésiques de l'enrichissement environnemental. Ainsi, cette thèse a mis en évidence dans l'hippocampe, l'existence de plasticité dépendante de l'activité dans le cerveau sain et modèle de la maladie d'Alzheimer. Cette plasticité pourrait être une cible pertinente dans le traitement de certaines conditions pathologiques. / Throughout life, environmental challenges promote long-lasting changes within the brain that can affect cognitive function, as well as the development of brain disorders. Within the brain, the hippocampus plays a key role in learning and memory processes. In the first study, we demonstrate how neuronal activity triggered by the learning and memory enhances the synaptic integration of adult-born hippocampal neurons that could support hippocampal function. In the second study, we show that enriched environment prevents age-related memory deficits and induces epigenetic modifications in both healthy and Alzheimer's disease conditions. This suggests that long-lasting epigenetic regulations may participate in sustaining the promnesic effects of environmental enrichment. Altogether, this thesis provides evidence of activity-dependent plasticity in the hippocampus in healthy and diseased brain, and suggests that stimulating such plasticity may contribute to improve pathological conditions.

No description available.

Ce travail de thèse a permis de caractériser avec succès des analogues structuraux de l´allopregnanolone présentant pour certains d'entre eux des effets bénéfiques et des avantages par rapport à la molécule de référence. En particulier, l'analogue O-allyl-AP, qui stimule in vitro la prolifération des cellules progénitrices, la différenciation neuronale et protège les cellules souches neurales adultes contre l'apoptose induite par le peptide Aβ42, est aussi efficace in vivo pour contrecarrer le déclin de la neurogenèse lié à l'âge et améliorer les performances cognitives au cours du vieillissement. De façon intéressante, les effets proliférateur et neuroprotecteur de l´O-allyl-AP semblent impliquer différents mécanismes d'action. Des expériences supplémentaires sont nécessaires pour conclure sur la capacité de l´O-allyl-AP à stabiliser le déclin de l'activité neurologique et à réduire les caractéristiques physiopathologiques de la Maladie d'Alzheimer (MA) chez les souris Tg2576. Nos résultats ouvrent des perspectives intéressantes pour l'application de l´O-allyl-AP dans le développement de stratégies thérapeutiques contre la MA et les maladies neurodégénératives. / This PhD work allowed us to successfully characterize structural analogs of allopregnanolone. Some of these analogs showed beneficial effects and advantages with respect to the molecule of reference. In particular, the analog O-allyl-AP stimulates proliferation of progenitor cells in different neural in vitro models, neuronal differentiation and protects adult neural stem cells against Aβ-induced apoptosis. In addition, O-allyl-AP is effective in counteracting the decline in neurogenesis related to age and in improving cognitive performance during aging. Interestingly, proliferative and neuroprotective effects seem to involve different mechanisms of action. Additional experiments are needed to confirm our preliminary data about the ability of O-allyl-AP to attenuate the decrease of neurogenic activity and to reduce pathophysiological hallmarks of Alzheimer disease (AD) in Tg2576 mice. Our findings provide interesting perspectives for using O-allyl-AP in the development of therapeutic strategies against AD and other neurodegenerative diseases.

L’acide rétinoïque (AR), dérivé actif de la vitamine A (rétinol) circulante, est une petite molécule lipophile contrôlant divers aspects de la mise en place du système nerveux central des vertébrés. L'AR influence notamment le développement précoce du cerveau antérieur, où il contrôle la prolifération et la survie des cellules progénitrices dans l'épithélium neural prosencéphalique. Le développement neural est un processus qui s'articule en trois grandes étapes : la phase d'expansion latérale (E9,5-E10,5 chez la souris), la phase de neurogenèse (E11,5-stades périnataux) et la phase de gliogenèse (stades périnataux-adulte). Nous avons montré que l'AR produit par les méninges à partir de E13 influence la spécification et la migration neuronale au cours de la phase de neurogenèse. De plus, nos travaux suggèrent un rôle plus précoce de l'AR pour la formation et la prolifération des populations progénitrices et neuronales avant et au début de la phase de neurogenèse. Une combinaison de signaux intrinsèques et extrinsèques contrôle divers aspects du développement neural cortical. Nos travaux placent l'AR parmi ces facteurs modulateurs de la neurogenèse corticale. / Retinoic acid (RA), an active vitamin A (retinol) metabolite, is a small lipophilic molecule controlling numerous events during central nervous system development in vertebrates. RA is involved in early forebrain development by controlling cell proliferation and survival in the prosencephalic neuroepithelium. Neural development is a process progressing through three key steps: a phase of lateral expansion (E9.5-E10.5 in the mouse), a phase of neurogenesis (E11.5-perinatal stages) and a gliogenic phase (perinatal stages-adult). My work has shown that RA produced by the developing meninges from E13 influences neuronal specification and migration during the phase of neurogenesis. Moreover, our data suggest an earlier role of RA during the production and proliferation of progenitor and neuronal populations, before and at the onset of the neurogenic phase. A combination of extrinsic and intrinsic signals is required to orchestrate the various aspects of cortical development. RA is likely to be one of such extrinsic factors modulating cortical neurogenesis.

La consommation chronique et excessive d’éthanol provoque des modifications neurobiologiques adaptatives. Les mécanismes qui les contrôlent sont multiples et certains ont été reliés à des régulations épigénétiques conduisant à des modifications structurelles et fonctionnelles. L’éthanol induit également une neurodégénérescence de l’hippocampe responsable de déficits cognitifs. Parmi l’ensemble des modèles animaux qui sont utilisés pour étudier les effets d’une consommation chronique d’alcool, figurent les souris de la lignée C57BL/6J. Ces souris possèdent une appétence naturelle pour l’éthanol faisant d’elles un modèle de choix pour étudier les conséquences de la consommation chronique d’éthanol. Le but de ce travail de thèse a été d’étudier les relations entre les mécanismes épigénétiques et la modulation de la neuroplasticité de l’hippocampe à la suite d’une consommation chronique d’éthanol chez les souris C57BL/6J, et d’en évaluer les conséquences comportementales. Nous avons montré que la consommation chronique d’éthanol induit, au niveau de l’hippocampe, des modulations épigénétiques globales corrélées à un remodelage chromatinien au sein du gène du BDNF, impliquant à la fois les modifications post-traductionnelles des histones et la méthylation de l’ADN. Ces modifications épigénétiques sont certainement responsables de l’augmentation d’expression protéique du BDNF observée dans l’hippocampe, et plus particulièrement dans le gyrus denté, après 3 semaines de consommation chronique d’éthanol en libre choix. L’accroissement de l’expression du BDNF induit une stimulation des voies de la signalisation intracellulaire dépendantes de l’activation du récepteur TrkB du BDNF, et une augmentation de la neurogenèse du gyrus denté. Les effets de l’antagoniste spécifique du récepteur TrkB, ANA 12, démontrent que l’augmentation de la neurogenèse observée chez les souris C57BL/6J après la prise chronique d’éthanol, est sous le contrôle unique du complexe BDNF/TrkB. L’analyse comportementale des souris C57BL/6J ayant consommé de l’éthanol, montre une détérioration des capacités d’apprentissage et de mémoire sans modification de la plasticité synaptique dans l’hippocampe, suggérant ainsi que d’autres mécanismes sont impliqués dans ces déficits cognitifs. L’ensemble de ces données apporte de nouveaux éléments de compréhension concernant la stimulation de la neurogenèse hippocampique chez les souris C57BL/6J lors d’une consommation chronique en libre choix d’éthanol. Il est probable que cette apparente augmentation de plasticité soit un mécanisme adaptatif et compensatoire à la détérioration des fonctions cognitives induite par une consommation chronique d’alcool. / Chronic and excessive ethanol consumption triggers neurobiological adaptations within the central nervous system, which are responsible for the development of an addiction. Ethanol induces adaptive mechanisms linked to epigenetic regulations leading to functional and structural changes, and also provokes a neurodegeneration responsible for the cognitive deficits observed in alcohol abusers. Among the different animal models available for studying the effects of chronic ethanol consumption, C57BL/6J mice are among the most relevant. These mice display high ethanol preference, making them a good model for studying the consequences of chronic and free-choice ethanol consumption. The purpose of this work was to study the links between epigenetic mechanisms and hippocampal neuroplasticity and to evaluate the behavioural consequences induced by chronic ethanol consumption in C57BL/6J mice. We showed that, in the hippocampus, chronic ethanol consumption induced global epigenetic modulations that were correlated with chromatin remodelling at the BDNF gene level. These effects involved post-translational histone modifications and DNA methylation. Epigenetic changes at the BDNF gene level probably allowed the increase in BDNF protein expression observed within the hippocampal dentate gyrus in mice having consumed ethanol for 3 weeks. Upregulation of BDNF expression was linked to both the stimulation of intracellular cascades downstream BDNF/TrkB receptor activation, and the increase in neurogenesis within the dentate gyrus. Using a specific TrkB receptor antagonist, ANA-12, we demonstrated that the hippocampal neurogenesis induced by chronic ethanol intake was under the control of BDNF. Behavioural analysis evidenced learning and memory impairments after ethanol consumption without synaptic plasticity alteration within the hippocampus, suggesting the involvement of other mechanisms in the cognitive deficits. Altogether, these data bring new elements for understanding the hippocampal neurogenesis stimulation observed under chronic and voluntary ethanol consumption in C57BL/6J mice. Moreover, this apparent increase in plasticity might probably be considered as an adaptive and compensatory mechanism in response to the cognitive deficits induced by ethanol consumption.

The nervous system is the most complex system in an organism. Functioning of the nervous system requires proper formation of neural cells, as well as accurate connectivity and signaling among them. While the major events that occur during these processes are known, the finer details are yet to be understood. Hence, an attempt was made to look for novel genes that could be involved in them. The focus of the present study is on CG9650, a gene that was uncovered in a misexpression screen, as a possible player in neuronal development in Drosophila melanogaster. The first chapter of the thesis reviews existing knowledge about neuronal development and function. The first section of this chapter explains in brief the formation and specification of neural stem cells, and their differentiation to neurons and glia. Sections 2 and 3 describe neuronal connectivity and signaling with respect to axon growth, synapse formation, function and plasticity. A comparison of invertebrate and vertebrate neuronal development is provided in section 4 of this chapter. This part also explains the use of Drosophila as a model for neuronal development and function. Chapter 2 describes the expression pattern of CG9650, which was characterized to gain insights into the possible role it plays during Drosophila neurogenesis.CG9650 is expressed in multiple cell types in the nervous system at the embryonic stage. Some of the cell sub-types have been identified from their morphology and position. Expression was restricted to neurons in the larval stage (except in the optic lobe, where it was expressed in precursors also), and continued in the pupal stage. No expression was seen in adults (except in the optic lobe). CG9650 has a putative DNA binding region, which bears homology to the mouse proteins CTIP1 and CTIP2, implying that CG9650 is possibly a transcription factor. In order to understand the function of CG9650, the protein was knocked down panneuronally. The resultant animals showed locomotor defects at both larval and adult stages, which have been described in chapter 3. Knock down larvae showed reduced displacement and speed of movement. The number of peristaltic cycles was also reduced in these animals but the cycle period was normal. In adults, movement was uncoordinated and righting reflex was lost, resulting in inability to walk, climb or fly. These results imply a defect in neuronal signaling. Sensory perception was unaffected in these animals. Stage specific knockdown of CG9650 indicated that the requirement for this protein is primarily during the larval stage. All CG9650-expressing neurons in the ventral nerve cord were glutamatergic, implying that its role in controlling locomotor activity is likely through glutamatergic circuits. Following up on these observations, signaling at the neuromuscular junction was assessed in CG9650 knock down animals. Chapter 4 discusses the signaling defects seen on CG9650 knock down, and the possible role of this protein. Electrophysiological recordings from Dorsal Longitudinal Muscles showed reduced and irregular neuronal firing in the knock down animals. These animals also had reduced bouton and active zone numbers. Moreover, overexpression of BRP, an active zone protein, rescued the locomotor defects caused by knock down of CG9650. Chapter 5 reports the effect of over expression of CG9650. Pan-neural over expression of CG9650 resulted in embryos with severe axon scaffolding defects, as well as aberrant neuronal and glial pattern. However, the incorrectly positioned glial cells in these embryos did not express CG9650, indicating that their aberrant positioning was probably due to incorrect signaling from the neurons. In conclusion, this study reports the requirement for CG9650, a hitherto unknown protein, in locomotor activity and signaling, thus ascribing for it a role in neuronal development and function of Drosophila melanogaster.

Le cerveau des mammifères abrite deux régions spécifiques où la neurogenèse adulte ne cesse pas après l'embryogenèse, mais persiste dans le cerveau postnatal et adulte. Ces deux régions sont la zone sous-granulaire du gyrus denté de l’hippocampe et la zone sous-ventriculaire (SVZ) des ventricules latéraux.Dans la SVZ, des cellules souches neurales génèrent des neuroblastes qui migrent jusqu’au bulbe olfactif (OB) pour coloniser les couches granulaires et glomérulaires et se différencier en différent types d’interneurones dont une petite fraction sont des interneurones dopaminergiques. La découverte de la neurogenèse postnatale et adultes a changé le point de vue de la plasticité du cerveau remarquable et ouvre de nouvelles perspectives pour la thérapie des maladies neurodégénératives. Etant donné que dans la maladie de Parkinson les symptômes moteurs principaux sont causés par la dénervation dopaminergique du striatum, la compréhension de la génération et de la différenciation des neurones dopaminergiques bulbaires a reçu une attention particulière au vu de leur intérêt potentiel pour la thérapie cellulaire. Dans ce contexte, le neuromédiateur dopamine lui-même a été suggéré d'influencer la neurogenèse olfactive et la spécification des interneurones dopaminergique.Dans ma thèse, j'ai analysé l’influence de l’innervation dopaminergique issue du mésencéphale sur la neurogenèse et le destin cellulaire des précurseurs de la SVZ. J'ai combiné un modèle 6-OHDA de dénervation dopaminergique chez la souris postnatale avec l’électroporation in vivo du ventricule latéral pour marquer spécifiquement les progéniteurs latéraux et dorsaux et suivre leur destin dans le OB. / In the postnatal and adult mammalian brain neurogenesis persists in the subgranular zone of the hippocampal dentate gyrus and the subventricular zone (SVZ). In the SVZ slowly dividing stem cells give rise to neuroblasts that migrate to the olfactory bulb (OB) where they reach the granule and glomerular cell layer of the OB and differentiate into different interneuron subtypes including a small fraction of dopaminergic interneurons. The discovery of postnatal and adult neurogenesis has changed the view of the plasticity of the brain remarkably and raised the hope for new therapeutical approaches in the field of neurodegenerative diseases. Since in Parkinson’s disease the main motor symptoms are caused by the dopaminergic denervation of the striatum adjacent to SVZ, the understanding of the generation and differentiation of OB dopaminergic neurons has received special attention. Interestingly, the neurotransmitter dopamine itself has been suggested to influence olfactory bulb neurogenesis via direct innervation of SVZ by midbrain dopaminergic neurons. However, data on this topic have been contradictory. In this study, I investigated how dopaminergic innervation influences SVZ neurogenesis and the fate of SVZ progenitors. I combined a 6-OHDA model of dopaminergic denervation in postnatal mice with in vivo forebrain electroporation to specifically label lateral and dorsal SVZ progenitors and to follow their fate in the olfactory bulb.