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

In mammals, tectal and tegmental divisions of the brainstem are involved in attentional mechanisms and responses to threatening stimuli such as predators. These centers are regulated by ascending connections, but the anatomical and neurochemical details of this drive are not fully known. The nucleus incertus (NI) in the pontine tegmentum is the source of ascending GABA projections to forebrain cognitive/emotional centers and NI neurons contain a number of neuropeptides, including relaxin-3 (RLN3). Tract-tracing studies have described NI projections within the tectum; and in this study we describe the distribution of relaxin-3 fibers within tectal and tegmental areas/nuclei of rat brain. RLN3-immunostained sections were also reacted with antisera against other neurochemical markers, as synaptophysin, nitric oxyde synthetase, tyrosine hydroxylase, calbindin, calretinin and 5-HT, to assist in demarcation of the area. RLN3-containing fibers were concentrated in the medial, olivary and ventrolateral pretectal nuclei; the medial intermediate grey layer of superior colliculus; and the pericentral area of inferior colliculus. Some labeled fibers were also detected in the cuneiform, parabigeminal and sagulum nuclei. RLN3 fibers were concentrated around the commissural bundles along the midline of the tectum, in the dorsal columns of the periaqueductal gray and in the dorsal raphe. In all areas, RLN3 and synaptophysin staining co-existed, indicating an association of the peptide with synapses. RLN3 projections target structures within the tectum and tegmentum that comprise the defensive system involved in detection of and response to unexpected threatening stimuli. NI neurons, which are a major source of RLN3 fibers and express corticotrophin-releasing factor receptors, may contribute to these responses following activation by stress-related stimuli. / Nos mamíferos, as divisões tectal e tegmental do tronco cerebral estão envolvidas em mecanismos de atenção e de respostas a estímulos ameaçadores, como os predadores. Esses centros são regulados por conexões ascendentes, mas os detalhes anatômicos e neuroquímicos desta unidade não são totalmente conhecidos. O núcleo incertus (NI) no tegmento pontino é a fonte de projeções ascendentes de GABA para prosencéfalo cognitivo/centros emocionais, e os neurônios do NI contêm alguns neuropeptídeos, incluindo relaxina-3 (RLN3). Estudos com traçadores descreveram projeções do NI para o tectum, e neste estudo, descrevemos a distribuição de fibras relaxina-3 nas áreas tectal e tegmental. Foram feitas imunocitoquímica para RLN3 conjugadas com outros marcadores neuroquímicos, tais como, sinaptofisina, óxido nítrico sintase neuronal, tirosina hidroxilase, calbindina, calretinina e 5-HT, para ajudar na demarcação da área. Fibras contendo RLN3 estavam concentradas na nucleos pretectais ventrolaterais, olivar e medial; na camada intermediária medial cinzenta do colículo superior; e na área pericentral de colículo inferior. Algumas fibras marcadas também foram detectadas nos núcleos cuneiforme, parabigeminal e sagulum. Fibras RLN3 foram concentradas em torno da feixes comissurais ao longo da linha mediana do tectum, nas colunas dorsais da substância cinzenta periaquedutal e na rafe dorsal. Em todas as áreas, a marcação para RLN3 e sinaptofisina co-existiu, indicando uma associação do péptideo com as sinapses. Estruturasalvo para as projeções de RLN3 do tecto e tegmento compõem o "sistema defensivo" envolvidos na detecção e resposta a estímulos ameaçadores. Neurônios do NI, são uma importante fonte de fibras RLN3 e expressam fatores de liberação de receptores para corticotropina, que podem contribuir para a respostas ao estímulos de estresse.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / The effects of the acute administration of yangambin (25, 50 and 75 mg/kg intraperitoneal and oral), were studied in some animals behavioral models (open field, rotarod, forced swimming test, barbiturate-induced sleeping time, hole board, elevated plus maze, pentilenotetrazole-induced convulsion). Binding in vitro with differents concentrations of yangambin (0.5-200 microlitre), had been carried out to evaluate its interaction with the dopaminergic receptors (D1- and D2-like), muscarinic receptors (M1+M2)-like and serotonergic receptors (5-HT2)-like, as well as, HPLC studies to determine the effects of yangambin (25, 50 e 75 mg/kg, i.p.) after 24 h of its acute administration on the monoamines levels and its metabolites in mice motor cortex and striatum. The results showed that yangambin induced a significant reduction in the locomotor activity and the frequencies of rearing and grooming in the open field test, indicative of possible ansiolytic-like effect. These results can have related with the dopaminergic system, since that it had interaction of the yangambin with D1- e D2-sÃmile receptors, in striatum and D2-sÃmile in motor cortex, followed by a dopamine reduction, indicating a probable dopaminergic antagonistic action. The yangambin did not cause alteration in the motor coordination of the animals in the rotarod test, suggesting that the reduction of the locomotor activity can involve central action. It had a significant increase in the immobility of the mice in the forced swimming test induced by the yangambin. This effect, taken together with the reduction of the dopamine, noradrenaline and serotonin induced by yangambin in striatum, can explain its depressant effect in this model. Moreover, corroborating these results, the yangambin increased pentobarbital-induced sleeping time in treated mice, suggestive of central depressant effect. Yangambin in the doses used in this work, did not protect the animals from pentilenotetrazole-induced convulsions, suggesting that this effect depends on the used dose. In the hole board test, the yangambin increased the number of the head dips, in all the doses studied, intraperitoneal or oral, demonstrating ansiolytic activity. The ansiolytic effect of yangambin (75 mg/kg, i.p. and 25, 50 and 75 mg/kg, p.o.) was also confirmed in the elevated plus maze, where it presented significant increase in the percentage of the entries number in the open arms and the percentage of the time of permanence in the open arms. Yangambin 50 and 75 mg/kg, p.o., also increased the number of entries and the time of permanence in the open arms, respectively. However, yangambin 25 and 50 mg/kg, i.p., presented ansiogenic effect evidenced by the reduction of the time of permanence in the open arms which probably due to the absence of the formation of some active metabolite generated in the first-pass metabolism. The ansiolytic effect induced for yangambin 75 mg/kg, p.o., in the plus maze, was reverted with flumazenil (2.5 mg/kg, i.p.), indicating the possible participation of the GABAergic receptors in its mechanism of action. The ansiolytic effect of the yangambin, observed in the hole board and the plus maze test, was followed by a reduction of noradrenaline and serotonin in striatum, however, in the motor cortex, yangambin (75 mg/kg, i.p.), induced an increase of the noradrenaline levels, as well as yangambin (25, 50 and 75 mg/kg, i.p.) induced serotonin increase, demonstrating that the ansiolytic effect associated to the reduction of noradrenaline and serotonin depends on the cerebral area. The blockade of the dopaminergic receptors induced by yangambin was synergic to its agonist action on the cholinergic receptors, since that it did not modify the reduction of the locomotive activity of the animals in the open field test. The present work shows an interaction between the systems dopaminergic, cholinergic, serotonergic and GABAergic, that suggest the importance of yangambin in illnesses that modify these systems of neurotransmission. The yangambin presented compatible behavioural and neurochemical alterations with ansiolytic-like effect. / Os efeitos da administraÃÃo aguda da iangambina (25, 50 e 75 mg/kg, por via intraperitoneal e oral), foram estudados em vÃrios modelos animais de comportamento (campo aberto, rota rod, nado forÃado, tempo de sono induzido por pentobarbital, placa perfurada, labirinto em cruz elevado, convulsÃo induzida por pentilenotetrazol). Binding in vitro com diferentes concentraÃÃes de iangambina (0,5-200 microlitros), foram realizados para avaliar sua interaÃÃo com os receptores dopaminÃrgicos (D1- e D2-sÃmile), receptores muscarÃnicos (M1+M2)-sÃmile e receptores serotonÃrgicos (5-HT2)-sÃmile, bem como, estudo em HPLC para determinar os efeitos da iangambina (25, 50 e 75 mg/kg,i.p.) apÃs 24 horas de sua administraÃÃo aguda sobre os nÃveis de monoaminas e seus metabÃlitos em cÃrtex motor e corpo estriado de camundongos. Os resultados mostraram que a iangambina induziu uma diminuiÃÃo significativa na atividade locomotora e nas freqÃÃncias de rearing e grooming no teste de campo aberto, indicativo de possÃvel efeito ansiolÃtico. Estes resultados podem estar relacionados com o sistema dopaminÃrgico, desde que houve interaÃÃo da iangambina com os receptores D1- e D2-sÃmile, em corpo estriado e D2-sÃmile em cÃrtex motor, acompanhado de uma reduÃÃo de dopamina, indicando uma provÃvel aÃÃo antagonista dopaminÃrgica. A iangambina nÃo causou alteraÃÃo na coordenaÃÃo motora dos animais no teste de rota rod, sugerindo que a reduÃÃo da atividade locomotora possa envolver aÃÃo central. Houve um aumento significativo na imobilidade dos camundongos no teste do nado forÃado induzido pela iangambina. Este efeito, juntamente com a reduÃÃo da dopamina, noradrenalina e serotonina induzida pela iangambina em corpo estriado, pode explicar seu efeito depressor neste modelo. AlÃm disso, corroborando estes resultados, a iangambina potenciou o tempo de sono induzido pelo pentobarbital em camundongos, sugestivo de efeito depressor central. Iangambina nas doses empregadas neste trabalho, nÃo protegeu os animais das convulsÃes induzidas por pentilenotetrazol, sugerindo que este efeito depende da dose usada. No teste da placa perfurada, a iangambina aumentou o nÃmero de head dips, em todas as doses estudadas, por via intraperitoneal ou oral, demonstrando atividade ansiolÃtica. O efeito ansiolÃtco da iangambina (75 mg/kg, i.p e 25, 50 e 75 mg/kg, v.o.) tambÃm foi confirmado no teste do labirinto em cruz elevado, onde apresentou aumento significativo na percentagem do nÃmero de entradas nos braÃos abertos e na percentagem do tempo de permanÃncia nos braÃos abertos. Iangambina (50 e 75 mg/kg, v.o.) tambÃm aumentou o nÃmero de entradas e o tempo de permanÃncia nos braÃos abertos, respectivamente. No entanto, iangambina 25 e 50 mg/kg, i.p., apresentou efeito ansiogÃnico evidenciado pela reduÃÃo do tempo de permanÃncia nos braÃos abertos o que provavelmente pode dever-se a ausÃncia da formaÃÃo de algum metabÃlito ativo gerado no metabolismo de primeira passagem. O efeito ansiolÃtico induzido pela iangambina 75 mg/kg, v.o., no modelo do labirinto, foi revertido com o flumazenil (2,5 mg/kg,i.p), indicando a possÃvel participaÃÃo dos receptores GABAÃrgicos no seu mecanismo de aÃÃo. O efeito ansiolÃtico da iangambina, observado no teste da placa perfurada e no labirinto em cruz elevado, foi acompanhado por uma reduÃÃo de noradrenalina e serotonina em corpo estriado, no entanto, em cÃrtex motor, iangambina (75 mg/kg, i.p.), induziu um aumento dos nÃveis de noradrenalina, assim como iangambina (25, 50 e 75 mg/kg, i.p.) induziu aumento de serotonina, demonstrando que o efeito ansiolitico associado a reduÃÃo de noradrenalina e serotonina depende da Ãrea cerebral. A iangambina interagiu com receptores muscarÃnicos em cÃrtex motor e corpo estriado. O bloqueio dos receptores dopaminÃrgicos induzido pela iangambina foi sinÃrgico à sua aÃÃo agonista sobre os receptores colinÃrgicos, desde que nÃo alterou a reduÃÃo da atividade locomotora dos animais no modelo de campo aberto. O presente trabalho mostra uma interaÃÃo entre os sistemas dopaminÃrgico, colinÃrgico, serotonÃrgico e GABAÃrgico, revelando a importÃncia da iangambina em doenÃas que alteram estes sistemas de neurotransmissÃo. A iangambina apresentou alteraÃÃes comportamentais e neuroquÃmicas compatÃveis com efeito ansiolÃtico-sÃmile.

Une prise de décision inadaptée est au centre de nombreuses pathologies neuropsychiatriques, telle que la toxicomanie, mais concerne également certains sujets sains, pour lesquels les gratifications immédiates prévalent sur les conséquences à long terme. Afin de mieux comprendre les bases neuropsychologiques et neurobiologiques de la prise de décision dans un cadre normal et pathologique, les sujets sains inadaptés constituent un modèle prometteur. Une tâche de mesure de la prise de décision chez le rat (le Rat Gambling Task, RGT) a récemment été validée dans l’équipe, très similaire à l’Iowa Gambling Task chez l’homme et permettant de révéler, parmi une population saine de rats, une majorité de sujets performants, et une minorité de non performants. Ces rats persistent à choisir les options immédiates les plus récompensantes, mais associées à de fortes pénalités imprédictibles, entrainant un faible gain final. Nous avons montré que tous ces rats sont inflexibles et moins efficaces dans la qualité du caractère dirigé de l’action. Ils présentent également une motivation accrue pour les récompenses, qui dépend d’une balance complexe coût/bénéfice, étroitement liée à l’effort à fournir, à la palatabilité de la récompense mais pas à la perception de la sensation plaisante ou des besoins métaboliques. Par ailleurs, nous avons montré qu’il n’existe pas de relation directe entre les capacités de mémoire de travail et la prise de décision. Sur le plan neurobiologique, nous avons montré 1) que la qualité du caractère dirigé de l’action dépend d’une balance d’activité PL/SDM et 2) que la prise de décision dans le RGT engage différemment des structures spécifiques selon les performances dans la tâche et la cinétique d’élaboration des choix. Ainsi, le fort recrutement de l’OFC et du Nacc shell serait un marqueur de choix adaptés, alors que celui de PL/SDM serait modulé selon la rapidité à préférer les choix favorables. Le CgA, IL et l’amygdale se désengageraient lorsque les choix sont établis. Les rats non performants présentent une hypoactivité préfrontale associée à une activité persistante de l’amygdale, suggérant un contrôle cognitif préfrontal déficient, couplé à une altération dans les associations liées à la valeur des options, induisant un déficit d’acquisition et de ré-actualisation de la valeur incitative des choix. Nous avons également montré que les différences inter-individuelles dans le RGT sont associées à des différences dans le fonctionnement basal du système monoaminergique. Les rats non performants présentent notamment (1) des métabolismes DA- et 5HT-ergique plus élevés au niveau d’IL, en accord avec l’impulsivité motrice de ces rats, et/ou la moindre qualité du caractère dirigé de l’action et (2) un métabolisme DA-ergique plus élevé au niveau du Nacc core et 5HT-ergique plus faible au niveau du BLA, suggérant une relation étroite avec leur motivation accrue et la qualité des associations liées à la valeur des options. Finalement, ces données sont intéressantes au regard des modifications dans le fonctionnement monoaminergique de base induites par des polymorphismes génétiques, conduisant à une prise de décision inadaptée, ainsi qu’à certaines pathologies psychiatriques. Toutes ces caractéristiques comportementales et neurobiologiques qui forment un ensemble cohérent pourraient correspondre à un endophénotype de troubles mentaux. Les études à l’avenir devront investir la relation directe avec la pathologie, telle que l’addiction, et l’exploration de ces caractéristiques au niveau génétique. / Decision-making is profoundly impaired in several psychiatric disorders such as addiction, but also in some healthy individuals for whom immediate gratifications prevail over long term gain. To better elucidate the neuropsychological and neurobiological bases of good and poor decision making in normal and pathological conditions, healthy poor decision-makers represent a promising model. Recently, a Rat Gambling Task, aimed at measuring decision-making like in the Iowa gambling Task in humans has been validated. It allows the identification, among a normal population of rats, of majority of good decision-makers, and a minority of poor decision-makers that prefer immediate larger reward despite suffering large loses. We demonstrated that all poor decision makers are unflexible and less efficient in goal-directed behavior. They also have a higher motivation for reward that depends on a complex cost/benefice balance, related to the effort to make, to food palatability, but not to the perception of the pleasant feeling or to metabolic needs. Moreover, we demonstrated the absence of relationship between decision making performance and working memory. At the neurobiological level, we demonstrated 1) that efficiency in goal-directed behavior depends on balance of activity between PL and SDM and 2) that decision making depends on specific brain regions, with a level of activity related to the performance, as well as the time course to make choices. Higher OFC and Nacc shell activities are systematically associated with good decision making, whereas the recruitment of PL/SDM is modulated according to the time course to make good choices. CgA, IL and the amygdala would be disengaged when choices are established. Poor decision makers display a prefrontal hypoactivity associated with a persistent involvement of the amygdala, suggesting an alteration in the prefrontal cognitive control, combined with deficits in reward-based associations, leading to an impaired acquisition and/or re-updating of the incentive value of the options. Moreover, we demonstrated that inter-individual differences in the RGT are associated with distinct DA- and 5HT basal functions. Poor decision makers notably displayed (1) high DA- and 5HT-ergic metabolisms in IL, supporting their motor impulsivity and/or lower efficiency in goal-directed behavior and (2) a higher DA-ergic metabolism in the Nacc core, and lower 5HT-ergic in BLA, that could be related to their higher motivation, and the quality of reward-based associations. These data support the relationship between genetic polymorphisms inducing distinct basal monoaminergic functioning, and poor decision making as well as psychiatric disorders. All these cognitive/behavioural and neurobiological characteristics that make a consistent framework could be an endophenotype of mental disorders. Further experiments should examine the direct relationship between poor decision making and psychiatric disorders, such as addiction, and the genetic background related to this specific profile.

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