Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

No description available.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal.

Há estudos que mostraram que o ácido N-metil-D-aspártico (NMDA), microinjetado nas estruturas do teto mesencefálico (corpos quadrigêmeos) de ratos evoca comportamentos defensivos do tipo pânico que podem ser seguidos por uma resposta antinociceptiva. Tem sido sugerido que respostas defensivas relacionadas ao medo organizadas por neurônios do tronco cerebral podem ser moduladas por projeções ascendentes mediadas pelo neurotransmissor 5-hidroxitriptamina (5-HT) do núcleo dorsal da rafe (NDR), e fenômenos antinociceptivos induzidos pelo medo inato podem ser organizados por vias serotoninérgicas descendentes também originadas no NDR. Os neurônios do NDR que originam tais conexões, por sua vez, podem ser moduladas por monoaminas que recrutam receptores 5-HT2A localizados no NDR. Não obstante, háuma escassez de estudos mostrando o papel dos receptores 5-HT2A do NDR na modulação do comportamento do tipo pânico e da antinocicepção induzida pelo medo inato organizados nos colículos superiores e inferiores. O objetivo deste estudo foi investigar a participação dos receptores 5-HT2A do NDR na modulação do comportamento de defesa organizado pelos corpos quadrigêmeos e da antinocicepção induzida pelo medo evocados por microinjeções de NMDA nos corpos quadrigêmeos. No experimento I, os animais receberam microinjeção de veículo (NaCl 0,9% / 0,2?L) ou 6, 9 e 12 nmol NMDA no CI. No experimento II, foi realizado o pré-tratamento do NDR com microinjeções de veículo ou o antagonista seletivo do receptor 5HT2A (R-96544) nas concentrações de 5, 10 e 15 nM. Dez minutos depois, o NMDA na dose mais efetiva (12 nmol) foi injetado no CI. Em ambos os experimentos, as respostas defensivas foram analisadas quantitativamente durante 10 min e, em seguida, as latências de retirada de cauda foram medidas a intervalos de 10 min durante 70 min. No experimento III, os animais receberam microinjeção de salina fisiológica ou NMDA (6, 9 e 12 nmol) nas cpSC. No experimento IV, a dose mais efetiva de NMDA (12 nmol) ou veículo foi precedida por microinjeções de veículo ou antagonista seletivo do receptor 5HT2A (R- 96544) em diferentes concentrações, 0.5, 5 e 10 nM. Ambos os efeitos pró-eversivos e antinociceptivos provocados pelas injecções intra-cpCS de NMDA foram atenuados pelo pré-tratamento do NDR com R-96544. No experimento V, a análise morfológica mostrou que os receptores 5-HT2A estão presentes nos interneurônios GABAérgicos do NDR. Em conjunto, esses achados sugerem que o bloqueio dos receptores 5-HT2A no NDR é capaz de atenuar tanto o comportamento defensivo do tipo pânico quanto a antinocicepção induzida pelo medo organizada pelos corpos quadrigêmeos. / There are studies that suggest that N-methyl-D-aspartic acid (NMDA) microinjected into the midbrain tectum structures, such corpora quadrigemina, of rats evokes panic-like defensive behaviours that can be followed by an antinociceptive response. It has been suggested that fear-related defensive responses organised by brainstem neurons can be modulated by ascending projections mediated by the neurotransmitter 5-hydroxytryptamine (5-HT) of the dorsal raphe nucleus (DRN), and phenomena of innate fear-induced antinociception can be organised by descending serotonergic pathways also originating from the DRN. The DRN neurons that give rise to such connections, in turn, can be moduled by monoamines that recruit 5-HT2A receptors located in the DRN. Nevertheless, there is a shortage of studies showing the role of DRN 5-HT2A receptors in the modulation of panic-like behaviour and innate fearinduced antinociception organised by superior and inferior colliculi. The purpose of this study was to investigate the participation of DRN 5-HT2A receptors in the modulation of panic-like behaviour and antinociception evoked by corpora quadrigemina injections of NMDA. In experiment I, the animals received microinjection of vehicle (0.9%NaCl/0.2?L) or 6, 9 and 12 nmol NMDA into the IC. In experiment II, it was performed the pretreatment of DRN with microinjections of vehicle or the 5HT2A receptor selective antagonist (R-96544) in a concentration of 5, 10 and 15 nM. Ten minutes later, NMDA at the most effective dose (12nmol) was injected in the IC. In both experiments, the defensive responses were quantitatively analysed for 10 min and then the tail-flick withdrawal latencies were measured at 10 min-intervals for 70 min. In experiment III, the animals received microinjection of physiological saline or NMDA (6, 9 and 12 nmol) into the deep layers of SC (dlSC). In experiment IV, the most effective dose of NMDA (12 nmol) or vehicle was preceded by microinjections of vehicle or 5HT2A receptor selective antagonist (R-96544) at different concentrations (0.5, 5, and 10 nM). Both proaversive and antinociceptive effects elicited by intra-dlSC injections of NMDA were attenuated by the pretreatment of the DRN with R-96544. In experiment V, the morphological analysis showed that 5-HT2A receptors are present in GABAergic interneurons in the DRN. Taken together, these findings suggest that the blockade of DRN 5-HT2A receptors decreased both panic attack-like defensive behaviour and fear- induced antinociception organised by the corpora quadrigemina neurons.

The impacts of exogenous cannabinoids, such as the chemical constituents of Cannabis sativa like cannabidiol (CBD), on brain regions having a modest number of cannabinoid receptors, for example, the ventromedial hypothalamus, are not yet surely knew. A few researches have shown evidence that ventromedial hypothalamus (VMH) neurons play a role in modulating innate fear-induced behavioural reactions in rodents submitted to experimental models of panic attack, for example those based on prey versus wild snake confrontation paradigm. The panic attack-like state was also potentially induced in laboratory animals by N-Methyl-D-aspartate (NMDA), an excitatory amino acid, which stimulates neurons that organize defensive behavioural reactions in the central nervous system. Despite the fact that CB1 receptor-mediated endocannabinoid signaling mechanism underlies the antiaversive effect of exogenous anandamide in medial hypothalamus, there is still a lack of morphological evidence to support the distribution of CB1 receptors in the VMH. Henceforth, this study was designed to explore the specific pattern of distribution of the CB1 receptors in the VMH and, subsequently, the implication of these receptors in the endocannabinoidmodulated defensive behavioural responses followed by fear-induced antinociception evoked by NMDA microinjected in the VMH. A stainless steel guide-cannula was embedded in the rodent\'s brain coordinated towards VMH by means of stareotaxic surgery. Three different doses of cannabidiol (CBD) were microinjected in the VMH. The most effective dose was used after the pretreatment with the CB1 receptor-antagonist AM251, followed by NMDA microinjection in the VMH. The outcomes demonstrated that the defensive behavioural responses evoked in response to intra-VMH administration of NMDA (6 nmol) were decreased by intra-hypothalamic microinjections of CBD at the highest dose (100 nmol).These effects, however, were blocked by the administration of the CB1 receptor-antagonist AM251 (100 pmol) in the VMH. In addition, the fear-induced antinociception elicited by VMH chemical stimulation diminished after the VMH treatment with CBD, an effect reversed by the intra-diencephalic pretreatment with AM251. These findings suggested that CBD causes panicolytic-like effects when administered in the VMH, and that antiaversive effect recruits the CB1 receptor-endocannabinoid signaling mechanism in VMH. / O papel dos canabinoides exógenos nas regiões do cérebro com um número modesto de receptores cannabinoides, por exemplo, o hipotálamo ventromedial, ainda não está plenamente esclarecido. Algumas pesquisas de nosso grupo, não obstante, mostraram o hipotálamo ventromedial (HVM) exerce modulação de reações comportamentais provocadas pelo medo inato em animais submetidos a um modelo de ataques de pânico. Crises de pânico foram induzidas em animais de laboratório por N-metil-D-aspartato (NMDA), um aminoácido excitatório que, ao ser microinjetado em estruturas do sistema encefálico de aversão, estimula reações comportamentais defensivas no sistema nervoso central que mimetizam as respostas defensivas eliciadas por roedores confrontados com serpentes. Apesar do mecanismo de sinalização endocanabinoide mediado pelos receptores CB1 desempenhar um papel na modulação da neurotransmissão excitadora e inibitória no SNC, ainda há escassez de evidências morfológicas que embasem a distribuição dos receptores CB1 no HVM. Por conseguinte, este estudo foi idealizado para explorar a forma específica de distribuição dos receptores CB1 no HVM e, posteriormente, estudar a implicação desses receptores na modulação de respostas comportamentais defensivas, seguidas por antinocicepção induzida pelo medo, moduladas por endocanabinoides e evocadas por microinjetação de NMDA no HVM. Uma cânula-guia feita de aço inoxidável foi implantada no cérebro do roedor, e direcionada para o HVM por meio de cirurgia estareotóxica. Três diferentes doses de cannabidiol (CBD) foram microinjetadas no HVM. A dosagem mais eficaz foi utilizada após o pré-tratamento do hipotálamo medial com um antagonista do receptor CB1, o AM251, seguido da microinjeção NMDA no HVM. Os resultados demonstraram que as respostascomportamentais defensivas evocadas em resposta à administração intra-HVM de NMDA (6 nmol) foram diminuídas por microinjeções intra-hipotalâmicas de CBD na dose mais alta (100 nmol). Estes efeitos, no entanto, foram atenuados pela administração do antagonista do receptor CB1, AM251, na dose de 100 pmol no HVM. Além disso, a antinocicepção induzida pelo medo foi atenuada pela administração intra-diencefálica de CBA, o que foi revertido pelo pré-tratamenot do HVM com AM251. Esses dados sugerem que o CBD causa efeitos panicolíticos, quando administrado no HVM, envolvendo o mecanismo de sinalização do receptor CB1-endocannabinoide.

Im Subikulum der Ratte finden sich zwei unterschiedliche Typen von Pyramidalzellen, die sich auf Grund ihres intrinsischen Entladungsverhaltens unterscheiden. Die Funktion dieser beiden Zelltypen hinsichtlich der synaptischer Neurotransmission ist unklar. Bursterzellen und regulär feuernde Zellen zeigten nach tetanischer Reizung ein unterschiedliches Ausmaß der LTP. Neben der zellspezifischen Ausprägung der LTP fanden sich mehrere Hinweise auf eine zielspezifische Projektion der Efferenzen der vorgeschalteten Area CA1. Die durchgeführten Experimente legen den Schluss nahe, dass Axone von Pyramidalzellen der Area CA1 selektiv auf subikuläre Pyramidenzellen projizieren und so den hippokampalen Informationsfluss steuern und regulieren können. NMDA-Rezeptoren auf beiden Seiten des synaptischen Spaltes spielen hier eine besondere Rolle. Präsynaptische NMDAR der Untereinheit NR2B scheinen an der LTP in Bursterzellen beteiligt zu sein und über einen vermehrten Kalziumeinstrom in die Präsynapse eine langanhaltende Erhöhung der Transmitterausschüttung herbeizuführen. Ebenso zeigten sich abhängig von der Zielzelle Hinweise auf eine unterschiedliche Aktivierung der präsynaptischen Adenylylcyclase-cAMP Kaskade. In Pilokarpin-behandelten Tieren ließ sich nach hochfrequenter Reizung keine langanhaltende Potenzierung der synaptischen Antworten nachweisen. Stattdessen scheinen polysynaptisch latente Verbindungen mittels tetanischer Stimulation aktivierbar zu sein. In einigen Fällen waren diese polysynaptisch latenten Verbindungen per se, in anderen Fällen nach Blockade der GABAergen Neurotransmission aktiv. In Hirnschnittpräparaten von Patienten mit pharmakoresistenter Temporallappenepilepsie konnte im Subikulum spontane rhythmische Aktivität mit einer Frequenz von 0,75 bis 3 Hz aufgezeichnet werden. Diese Aktivität, bestehend aus EPSP/IPSP Sequenzen, wurde sowohl in sklerotischem als auch in nicht sklerotischem Gewebe gefunden. In beiden Gruppen korrelierte die in vitro Aktivität sehr gut mit dem präoperativen Auftreten elektroenzephalografisch detektierter interiktaler Aktivität. Die Blockade GABAerger oder glutamaterger Neurotransmission hob die inhibitorische bzw. exzitatorische Aktivität auf. Dies legt den Schluss nahe, dass sowohl Interneurone wie Pyramidalzellen an der spontanen rhythmischen Aktivität beteiligt sind. / The subiculum plays a key role in processing memory information from the hippocampus to different cortical and subcortical brain regions. Subicular pyramidal cells are classified as regular firing or bursting cells according to their responses to supra-threshold depolarizing current pulses. Synaptic terminals arising from CA1 pyramidal cells do not function as a single compartment but show a specialized synaptic plasticity onto subicular pyramidal cells depending on the discharge properties of the synaptic target. Tetanic stimulation of CA1 axons caused a significantly stronger long-term potentiation (LTP) in bursting cells than in regular firing cells. Postsynaptic bursting was not necessary for the enhanced synaptic potentiation in bursting cells. The LTP in bursting neurons was independent of postsynaptic calcium, induced by presynaptic NR2B-containing autoreceptors and mediated via a adenylyl cylcase-cAMP-dependent signaling cascade. In pilocarpine-treated animals subicular LTP was impaired. A long-lasting increase in synaptic transmission could not be observed after titanic stimulation neither in regular firing cells nor in bursting cells. In human brain slices resected from patients from with drug-resistant temporal lobe epilepsy the subiculum displayed spontaneous rhythmic activity. In sclerotic but also in non-sclerotic hippocampal tissue the subiculum showed cellular and synaptic changes which suffice to generate spontaneous rhythmic activity that is correlated with the occurrence and frequency of interictal discharges recorded in the electroencephalograms of the corresponding patients.

No description available.

DYRK1A es uno de los principales genes candidatos que podrían explicar algunos de los defectos neurológicos asociados al fenotipo Síndrome de Down (SD); desde el retraso mental, rasgo común a todos los individuos con SD hasta los déficits motores, también muy frecuentes entre la población con SD. Con el fin de validar la implicación de DYRK1A en el fenotipo SD se ha desarrollado una estrategia de terapia génica basada en la reducción de la expresión del gen mediante interferencia del RNA, en el modelo transgénico TgDyrk1A, y se han evaluado los efectos en el fenotipo motor de estos animales. Además se ha estudiado la implicación de los receptores glutamatérgicos de tipo NMDA en las alteraciones motoras descritas en el modelo. Los resultados obtenidos en este trabajo ponen de manifiesto la validez de la estrategia desarrollada y apuntan a una desregulación de los receptores de NMDA como uno de los mecanismos moleculares subyacentes de las disfunción motora presente en el modelo TgDyrk1A. / The are growing evidences to consider DYRK1A as a candidate gene for some of the neurological alterations present in DS phenotype such as mental retardation which is a common feature in the syndrome, or motor deficits which show a high prevalence among DS individuals. With the aim to validate the contribution of Dyrk1A to DS phenothype, we have developped a gene therapy strategy based on RNA interference to reduce gene expression in the transgenic model TgDyrk1A, and we have evaluated the effects in the motor phenotype of these animals. Moreover, we have studied the implication of the NMDA glutamate receptor in the motor alterations present in the model. The results obtained validate the strategy developped and suggest the deregulation of the NMDA receptor as one of the main causes underlying motor dysfunction in TgDyrk1A mice.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Les récepteurs ionotropiques du glutamate sont responsables de la vaste majorité de la neurotransmission excitatrice rapide dans le système nerveux central. Parmi eux, les récepteurs NMDA (rNMDA) sont les médiateurs de la plasticité synaptique, fondement cellulaire des processus d’apprentissage et de mémoire. Leurs dysfonctionnements sont impliqués dans de nombreuses pathologies neurologiques et psychiatriques comme les maladies d’Alzheimer et de Parkinson, l’épilepsie et la schizophrénie. Les rNMDA forment des complexes hétérotétramériques massifs (>500 kDa) dotés de propriétés allostériques uniques grâce à un ensemble de 8 domaines extracellulaires bilobés organisé en deux strates superposées : la couche de domaines N-terminaux (NTD) et la couche de domaines de liaison de l’agoniste (ABD). Malgré un nombre croissant de structures complètes de rNMDA, le mécanisme de transduction permettant aux interactions entre ces domaines de contrôler l’activité du récepteur restait inconnu. En combinant analyse expérimentale et computationnelle, nous montrons qu’un mouvement de roulis à l’interface entre les deux dimères de la couche d’ABD est un déterminant clé du processus d’activation et de modulation des rNMDA. Cette rotation des deux dimères d’ABD constitue un commutateur conformationnel qui règle l’ouverture du canal en fonction de la conformation des NTD situés à l’opposé. Ce travail révèle comment des changements conformationnels concertés entre couches de domaines gouvernent l’activité des rNMDA. Il illumine notre compréhension d’un récepteur synaptique majeur du système nerveux central et ouvre la voie à la conception de nouveaux agents pharmacologiques ciblant le mécanisme allostérique élucidé. / Ionotropic glutamate receptors are responsible for the vast majority of fast excitatory neurotransmission in the central nervous system. Among them, NMDA receptors (NMDARs) are key mediators of synaptic plasticity, which is considered as the cellular basis of learning and memory. NMDAR dysfunction is implicated in numerous neurological and psychiatric brain disorders such as Alzheimer and Parkinson’s disease, epilepsy and schizophrenia. NMDAR form massive hetero tetrameric complexes (>500 kDa) endowed with unique allosteric capacity provided by a cluster of eight extracellular clamshell-like domains arranged as two superimposed layers: the Nterminal domain (NTD) layer and the agonist binding domain (ABD) layer. Despite an increasing number of full-length NMDAR structures, the transduction mechanism by which these domains interact in an intact receptor to control its activity remained poorly understood. Combining experimental and in silico analysis, we identify a rolling motion at an interface between the two constitute dimers in the ABD layer as a key determinant in NMDAR activation and modulation pathways. This rotation of the two ABD dimers acts as a conformational switch that tunes channel opening depending on the conformation of the membrane-distal NTD layer. This work unveils how NMDAR domains move and operate in a concerted manner to transduce conformational changes between layers and command receptor activity. It illuminates our understanding of a major synaptic receptor of the central nervous system and paves the way for the development of new pharmacological tools targeting the elucidated allosteric mechanism.