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Des recherches, autant chez l’homme que chez l’animal, proposent qu’il existerait, au sein des réseaux cérébraux, une organisation anatomique parallèle de circuits qui coordonne l’activité des structures qui participent à la planification et à l’exécution d’une action. Dans cette foulée, un modèle émerge qui attribue au cortex préfrontal (CPF) latéral une spécificité anatomo-fonctionnelle basée sur les niveaux de traitement en mémoire de travail (MT). Il s’agit du modèle « niveaux de traitement-dépendant », qui accorde un rôle important au CPF latéral dans l’acquisition et la représentation de règles guidant nos comportements. Des études en neuroimagerie fonctionnelle, utilisant le Wisconsin Card Sorting Task (WCST) ont permis de corroborer ce modèle et de dissocier trois niveaux de traitement en MT non seulement au sein du CPF latéral mais encore aux structures sous- corticales, les ganglions de la base (GB). Ces études suggèrent que certains noyaux des GB seraient topographiquement organisés avec le CPF latéral et contriburaient, sous certaines conditions, à des processus cognitifs et moteurs semblables à leur homologue cortical. Le but de notre étude est d'explorer la généralisation de la contribution des GB et du CPF au modèle niveaux de traitement-dépendant afin de voir si ce dernier est indépendant de la nature des stimuli en mémoire de travail. À cet effet, nous avons modifié le WCST en l’appliquant à un autre domaine, celui du langage. Nous avons remplacé les pictogrammes par des mots et modifié les règles formes, couleurs, nombres, par des règles sémantiques et phonologiques. L’analyse des résultats a démontré que différentes parties des GB de concert avec différentes régions du CPF se différencient quant aux niveaux de traitement en MT et ce, indépendamment de la nature des stimuli. Une deuxième analyse a permis d’évaluer les patrons d’activations liés aux conditions sémantiques et phonologiques. Ces résultats ont mis en évidence que les réseaux préfrontaux semblent liés aux processus exécutifs nécessaires à la réalisation de la tâche, indépendamment de la condition tandis que les aires associatives se dissocient davantage et contiennent des réseaux propres à la sémantique et à la phonologie. / Researches in humans and animals have pointed out the possible existence of a parallel anatomic organization in the core of cerebral networks which could coordinate the activity of different brain regions involved in the planning and execution of an action. Within this framework, the emerging model ascribes an anatomic dissociation to the lateral prefrontal cortex (PFC) based on the level of complexity of the working memory (WM) treatment. This model, namely, the complexity-dependent model, gives an important role to the lateral PFC in the acquiring and representation of the rules guiding our behaviors. This model has been corroborated by functional neuroimaging studies using the Wisconsin Card Sorting Task (WCST). These studies allowed dissociating three levels of complexity of the WM treatment, not restricted to the lateral PFC but also including sub- cortical structures, the basal ganglia (BG), suggesting that some BG nuclei would be topographically organized with the lateral PFC and would contribute to the same cognitive and motor functions. The aim of our study was to investigate whether the BG and the PFC’S contribution to the complexity-dependent model generalizes to different types of stimuli or whether their functions are dependent on the nature of stimuli in WM. To do so, a language version of the WCST was developed to suit a different cognitive domain, i.e. language. The pictograms were replaced with words and rules concerning forms, colors and numbers were substituted with semantic and phonological rules. Data analysis showed that the BG along with the PFC have differential role at different levels of WM processing complexity. In a second analysis, the activation patterns linked to the semantic and phonological conditions were evaluated. Those results indicated that the prefrontal networks seem to be coupled with executive processes needed to perform each condition whereas the employment of different language rules (semantic and phonological) activates specific regions of the phonological and semantic network.

Les antipsychotiques sont utilisés en clinique depuis plus de 50 ans pour pallier aux symptômes de la schizophrénie. Malgré une recherche intensive, les mécanismes cellulaires et moléculaires responsables de l’effet clinique de cette médication demeurent encore nébuleux. Ces drogues sont reconnues comme des antagonistes des récepteurs D2 de la dopamine et peuvent moduler la transcription génique dans le striatum. Au cours des recherches qui ont mené à l'écriture de cette thèse, nous avons exploré l’expression de Nur77, un facteur de transcription de la famille des récepteurs nucléaires, afin de caractériser le rôle de la dopamine, la sérotonine, l’adénosine et le glutamate dans la régulation génique contrôlée par les antagonistes D2. En premier lieu, nous avons examiné l’impact de la co-administration d’agents sérotonergiques et adrénergiques sur l’expression de l’ARNm de Nur77 induite par l’halopéridol, un antipsychotique de première génération. Nous avons observé que le 8-OH-DPAT et le MDL11939 préviennent partiellement l’induction de Nur77 dans le striatum. Au contraire, l’idazoxan potentialise l’effet de l’halopéridol sur l’expression de Nur77 alors que le prazosin reste sans effet. Ces résultats démontrent que l’expression striatale de Nur77 induite par l’halopéridol peut être modulée à la baisse avec un agoniste 5-HT1A ou un antagoniste 5-HT2A. Par la suite, nous avons évalué dans divers paradigmes expérimentaux l’effet de l’éticlopride, un antagoniste spécifique D2, afin d’explorer davantage le mécanisme de l’effet transcriptionnel des antagonistes D2. Étonnamment, la suppression de l’isoforme D2L chez la souris D2L KO ne réduit pas la réponse de l’éticlopride dans le striatum. Par contre, une lésion corticale avec l’acide iboténique bloque l’effet de l’éticlopride sur la transcription de Nur77, suggérant un rôle du glutamate. La combinaison d’un antagoniste des récepteurs métabotropes du glutamate de types 5 (mGluR5) et d’un antagoniste des récepteurs de l’adénosine A2A abolit complètement l’augmentation de la transcription de Nur77 induit par l’éticlopride dans le striatum. La modulation directe de l’expression striatale de Nur77 par les récepteurs mGluR5 et A2A a été confirmée dans un modèle de cultures organotypiques de tranches cérébrales. Ces résultats démontrent clairement que la modulation de l’expression génique dans le striatum, à la suite d’un traitement avec un antagoniste D2 pourrait être indépendante d’une interaction directe avec les récepteurs D2 post-synaptiques, et reposerait plutôt sur son interaction avec les récepteurs D2 hétérosynaptiques des afférences corticostriées et l’activation subséquente des récepteurs post-synaptiques du glutamate et de l’adénosine. En résumé, nos résultats suggèrent que l’interaction des antipsychotiques atypiques avec les récepteurs 5-HT2A et 5-HT1A pourrait expliquer la différence dans le patron d’expression génique induit par ces drogues en comparaison avec les antipsychotiques typiques. De plus, nos résultats révèlent un nouveau mécanisme d’action des antagonistes D2 et supportent un rôle primordial du glutamate et de l’adénosine dans les effets des antipsychotiques de première génération. / Antipsychotic drugs have been used to alleviate schizophrenia symptoms for more than 50 years. Despite extensive research, little is known about the molecular and cellular mechanism responsible for their clinical outcome. These drugs are usually recognized as dopamine D2 antagonists and are known to modulate gene expression in the striatum. In the present thesis, we used the expression of Nur77, a transcription factor of the orphan nuclear receptor family, to explore the role of dopamine, serotonin, glutamate and adenosine receptors in the effect of a dopamine D2 antagonist in the striatum. First, we examined the abilities of serotoninergic and adrenergic receptor drugs to modify the pattern of Nur77 mRNA expression induced by haloperidol, a first generation antipsychotic drug. We observed that 8-OH-DPAT and MDL11939 partially prevent haloperidol-induced Nur77 upregulation. On the contrary, idazoxan consistently potentiated haloperidol-induced Nur77 mRNA levels in the striatum whereas prazosin remained without effect. Taken together, these results show the ability of a 5-HT1A agonist or a 5-HT2A antagonist to reduce haloperidol-induced Nur77 striatal expression. Subsequently, we evaluated in different experimental designs the effect of eticlopride, a specific D2 antagonist, to provide additional information on the mechanism by which D2 antagonist controls transcriptional activity in the striatum. Surprisingly, deletion of the D2L receptor isoform did not reduce eticlopride-induced upregulation of Nur77 mRNA levels in the striatum. However, cortical lesions with ibotenic acid strongly reduced eticlopride-induced upregulation of Nur77 mRNA, suggesting a role for glutamate neurotransmission. A combination of a metabotropic glutamate type 5 (mGluR5) antagonist with an antagonist of its synergistic partner adenosine A2A receptor abolished eticlopride-induced upregulation of Nur77 mRNA levels in the striatum. Direct modulation of striatal Nur77 expression by glutamate and adenosine receptors was confirmed using corticostriatal organotypic cultures. Taken together, these results indicate that modulation of gene expression in the striatum, following a D2 antagonist, might not involve a direct interaction of the drug at postsynaptic D2 receptors, but rather relies on its interaction with corticostriatal presynaptic D2 receptors and subsequent activation of postsynaptic glutamate and adenosine receptors in the striatum. In summary, our results suggest that interaction of atypical antipsychotic drugs with 5-HT2A and 5-HT1A receptors participate in the differential pattern of gene expression induced by these drugs when compared with typical antipsychotic drugs. Moreover, our results uncover a new mechanism of action of D2 antagonists and support a prominent role of glutamate and adenosine in the effect of classic antipsychotic drugs.

Decision-making is necessary to adapt to the variable environment in everyday life. During this process, our goal is to select the most beneficial course of action in order to obtain the best outcome, to develop efficient choice strategies. That is, estimating the probability to obtain any of the available outcomes as well as their value. Moreover, poor decision-making ability is a common symptom to several psychiatric disorders, such as pathological gambling, depression, schizophrenia and bipolar disorder.The cognitive and emotional mechanisms controlling decision-making processes depend, among others, on the striatum, Basal Ganglia’s main input nucleus. The striatum is divided into the dorsal striatum, responsible for motor and cognitive control that initiate actions (Dorsomedial Striatum, DMS) and generate habits (Dorsolateral Striatum, DLS), and Nucleus Accumbens (NAc) which manages reward and the influence of motivation on motor behavior. A2A-expressing and D1-expressing medium spiny neurons (iMSNs and dMSNs, respectively), accounting for 95% of striatal neurons act in coordination to generate adaptive behavioral responses. It has been shown that imbalanced activity between these two populations leads to abnormal behaviors: overactivation of striatonigral neurons promotes an increased locomotion as well as a higher sensitivity for reward, whereas overactivation of striatopallidal neurons produces the exact opposite effects. However, the specific contributions to decision-making of these two populations in each striatal territory remains unclear. Here, we made use of a chemogenetic (DREADD) tool to manipulate striatal projection neurons’ activity within each specific striatal area and tested their role in a decision-making operant protocol. To do so, we used two different mouse models that allowed us to target specifically iMSNs (A2A-Cre mice) or dMSNs (D1-Cre mice) and induce neuronal-specific expression of the hM3Dq DREADD receptor. CNO-mediated activation of these receptors led to neuronal activation. Then, we tested DREADD-dependent activation of MSNs during the Iowa Gambling Task (IGT), a test used to assess the influence of different rewards on choice and to evaluate the ability of mice to develop advantageous choice strategies. We found an exclusive role of DMS’ dMSNs in controlling choice preference, as DREADD-induced activation of these neurons produced a loss of preference. Manipulations of MSNs in other striatal areas led to altered task performance without affecting choice preference.These results contribute to a better understanding of the role of the striatum on decision-making and moreover, suggest the existence of a high level of functional specialization in this area, a fact that could be explained by the local circuits in which each MSN population is involved. / Doctorat en Sciences biomédicales et pharmaceutiques (Médecine) / info:eu-repo/semantics/nonPublished

O transtorno obsessivo compulsivo (TOC) é um transtorno psiquiátrico, caracterizado pela presença de obsessões e / ou compulsões. Estudos de neuroimagem funcional indicam que o TOC é um distúrbio heterogêneo relacionado ao circuito talâmico cortico-estriatal (CSTC) e as áreas que compõem este circuito incluem o nucleus accumbens (NAC), putâmen (PT), núcleo caudado (CN), córtex orbitofrontal (OFC) e o córtex cingulado anterior (ACC). As principais características do CSTC são a inervação do córtex frontal em direção ao estriado e cada pequeno circuito possui características específicas: afetiva/límbica, cognitivo e associativo dorsal e cognitivo ventral e motor. Neste trabalho comparamos o transcriptoma de casos e controles das três áreas estriatais (CN, NAC e PT) separadamente de tecido cerebral post mortem e as redes de co-expressão do striatum e de dois circuitos envolvidos no transtorno. Os resultados mostraram que diferentes processos biológicos, bem como a desregulação da conectividade de rede, são específicos para cada região do estriado e estão de acordo com o modelo tripartido do estriado e contribuem de diferentes formas para a fisiopatologia do TOC. Especificamente, a regulação dos níveis de neurotransmissores, processo pré-sináptico envolvido na transmissão sináptica química foram compartilhados entre NAC e PT. A resposta celular ao estímulo químico, resposta ao estímulo externo, resposta à substância orgânica, regulação da plasticidade sináptica e modulação da transmissão sináptica foram compartilhadas entre CN e PT. A maioria dos genes que possuem variantes comuns e / ou raras previamente associadas ao TOC que são diferencialmente expressas ou que fazem parte de módulos de co-expressão menos preservados em nosso estudo também sugerem especificidade de cada região estriatal. Os módulos de co-expressão preservados e menos preservados nos circuitos afetivo e cognitivo ventral corroboram com as assinaturas transcricionais de cada área e de cada circuito no TOC e nos controles. Este é o primeiro trabalho com a proposta de avaliar a expressão gênica em áreas estriatais, analisadas individualmente, envolvidas com o TOC, bem como as redes de co-expressão do estriado e dos circuitos individualmente / Obsessive compulsive disorder (OCD) is a psychiatric disorder, characterized by the presence of obsessions and/or compulsions. Functional neuroimaging studies indicate that OCD is a heterogeneous disorder related the cortical-striatal thalamic circuitry (CSTC) and the areas that compose this circuitry include the nucleus accumbens (NAC), putamen (PT), caudate nucleus (CN), orbitofrontal cortex (OFC) and subgenual cingulate gyri (ACC). The main characteristics of CSTC is the innervation of the frontal cortex in direction of the striatum and each small circuitries have specific characteristics in the affective, dorsal cognitive and ventral cognitive motor. In this work we compared the cases and controls transcriptome of the three striatal areas (CN, NAC and PT) separately from post mortem brain tissue and the co-expression networks of the striatum and of two circuits involved in the disorder. Results showed that different biological process as well as networks connectivity deregulation were specific for each striatum region according to the striatum tripartite model and contribute in different ways to OCD pathophysiology. Specifically, regulation of neurotransmitter levels, presynaptic process involved in chemical synaptic transmission were shared between NAC and PT. Cellular response to chemical stimulus, response to external stimulus, response to organic substance, regulation of synaptic plasticity, and modulation of synaptic transmission were shared between CN and PT. Most genes harboring common and/or rare variants previously associated with OCD that are differentially expressed or part of a least preserved co-expression modules in our study also suggest striatum sub regions specificity. The co-expression modules preserved and least preserved in affective and ventral cognitive circuitry corroborate with transcriptional signatures of each area and each circuitry in OCD and controls. This is the first work with the proposal to evaluate the gene expression in striatum areas individually, involved with OCD as well evaluate the coexpression networks in striatum and each circuitry

Opióides são substâncias de origem endógena ou sintética, referindo-se a todos os compostos relacionados ao ópio, sendo o protótipo dos agonistas opióides, a morfina, conhecida pela sua capacidade de aliviar a dor intensa com eficácia. A morfina se liga a pelo menos três tipos de receptores conhecidos como &#181;, <font face=\"symbol\">k e <font face=\"symbol\">d. Os opióides parecem ter relação a comportamentos reprodutivos, dentre estes o comportamento maternal (CM). O CM é complexo, instintivo e com características espécie-específicas determinadas por modificações fisiológicas que ocorrem pouco antes ou logo após o parto e deve ajustar-se à uma série de variáveis como disponibilidade de alimentos, por exemplo, e influencia diretamente nos desenvolvimentos físico, neurológico e comportamental das proles, garantindo ou não a perpetuação dessas espécies. Trabalhos mostraram que os estados fisiológico, reprodutivo e a manipulação farmacológica com morfina ao final da gestação de ratas, por si só, são capazes de alterar a habilidade materna, comprometendo o desenvolvimento das proles, bem como podem modular a expressão dos genes que codificam para os receptores opióides em regiões implicadas com o controle do CM, porém são desconhecidos os resultados de ratas tratadas com esse opióide nas fases iniciais da gestação, objetivo deste trabalho, bem como os parâmetros físico e neurocomportamental das proles e na biologia molecular de receptores opióides em diferentes regiões encefálicas tanto nas proles quanto nas mães. Os resultados mostraram que tratamento com morfina no primeiro e segundo terços da gestação de ratas alterou alguns parâmetros do CM como a recuperação dos filhotes, e alterou alguns parâmetros do desenvolvimento físico como o ganho de peso e o desenvolvimento dos órgãos sexuais e desenvolvimento neurocomportamental em ambas as proles, bem como os padrões de expressão gênica e produtos protéicos nas mães e em suas proles no estriado, hipotálamo e PAG. Conclui-se, portanto que o tratamento com morfina durante a gestação de ratas pode alterar o estado fisiológico das mães com implicações diretas nas proles. / Opioids are substances of endogenous or synthetic origin, referring to all related opiate compounds, the prototype of the opioid agonists, morphine, known for its ability to relieve severe pain effectively. Morphine binds to at least three types of receptors known as &#181;, <font face=\"symbol\">d and <font face=\"symbol\">k. Opioids appear to be related to reproductive behaviors among this maternal behavior (CM). The CM is complex, instinctive and species-specific characteristics determined by physiological changes that occur shortly before or after delivery and must adjust to a number of variables such as food availability, for example, and directly influences the physical developments, neurological and behavior of the offspring, or not ensuring the perpetuation of the species. Studies have shown that the physiological and pharmacological manipulation reproductive states with morphine to rats in late pregnancy, by themselves, are capable of altering the maternal ability, affecting the development of the offspring, and can modulate the expression of genes encoding the opioid receptors in regions implicated in the control of CM, are unknown but the results of this opioid-treated rats in the early stages of pregnancy, aim of this work as well as the physical and neurobehavioral parameters of the offspring and molecular biology of opioid receptors in different brain regions both in the offspring as mothers. The results showed that morphine treatment in the first two thirds of pregnancy of rats changed some parameters of the CM as the recovery of the puppies, and changed some of the physical parameters such as weight gain and the development of sex organs and neurobehavioral development in both offspring as well as the patterns of gene expression and protein products in mothers and their offspring in the striatum, hypothalamus and PAG. It follows therefore that treatment with morphine during pregnancy in rats can alter the physiological status of mothers with direct implications in offspring.

Le Trouble Développemental de la Coordination (TDC) se caractérise par une altération des habiletés motrices. Si le déficit du contrôle moteur est univoque, les études testant un déficit d'apprentissage procédural moteur restent peu nombreuses et aboutissent à des résultats divergents. L'objectif principal de ce travail est de mettre en évidence les conditions dans lesquelles les enfants présentant un TDC manifestent ou non un déficit d'apprentissage procédural et de la mémoire procédurale. Quatre études ont été menées pour comparer l'apprentissage procédural moteur d'enfants présentant un TDC et d'enfants contrôles. Nous avons testé des tâches comportementales d'apprentissage variées telles que l'apprentissage d'une nouvelle coordination bimanuelle, l'apprentissage de séquences perceptivo-motrices et l'apprentissage de séquences motrices rythmiques dans différentes conditions. Nous avons investigué les corrélats cérébraux fonctionnels et structurels associés, en utilisant l'électroencéphalographie ou l'imagerie par résonance magnétique. Les résultats indiquent des différences comportementales et cérébrales lors de tâches d'apprentissage, révélées par des variables spécifiques. De plus, certaines conditions expérimentales ont amélioré l'apprentissage procédural et la mémoire procédurale des enfants présentant un TDC. Ces résultats amènent à penser que les conditions favorisant l'apprentissage et la mémoire procédurale des enfants présentant un TDC pourraient contribuer à une meilleure prise en charge. / Developmental Coordination Disorder (DCD) is characterized by impaired motor skills. While the motor control deficit is unambiguous, studies testing motor procedural learning are few and lead to contradictory results. The main objective of this work is to understand the conditions under which children with DCD demonstrate a procedural learning and procedural memory deficits. Four studies were conducted to compare the motor procedural learning of children with and without DCD. We tested various learning behavioural tasks such as learning a new bimanual coordination, learning perceptual-motor sequences and learning rhythmic motor sequences in different conditions. We investigated the associated functional and structural brain correlates, using electroencephalography and magnetic resonance imaging. The results indicate some behavioural and brain differences during learning tasks, revealed by specific variables. In addition, some experimental conditions have improved the procedural learning and procedural memory of children with DCD. These results suggest that conditions in which procedural learning and memory of children with DCD are improved could contribute to better therapeutic interventions.

O transtorno obsessivo compulsivo (TOC) é um transtorno psiquiátrico, caracterizado pela presença de obsessões e / ou compulsões. Estudos de neuroimagem funcional indicam que o TOC é um distúrbio heterogêneo relacionado ao circuito talâmico cortico-estriatal (CSTC) e as áreas que compõem este circuito incluem o nucleus accumbens (NAC), putâmen (PT), núcleo caudado (CN), córtex orbitofrontal (OFC) e o córtex cingulado anterior (ACC). As principais características do CSTC são a inervação do córtex frontal em direção ao estriado e cada pequeno circuito possui características específicas: afetiva/límbica, cognitivo e associativo dorsal e cognitivo ventral e motor. Neste trabalho comparamos o transcriptoma de casos e controles das três áreas estriatais (CN, NAC e PT) separadamente de tecido cerebral post mortem e as redes de co-expressão do striatum e de dois circuitos envolvidos no transtorno. Os resultados mostraram que diferentes processos biológicos, bem como a desregulação da conectividade de rede, são específicos para cada região do estriado e estão de acordo com o modelo tripartido do estriado e contribuem de diferentes formas para a fisiopatologia do TOC. Especificamente, a regulação dos níveis de neurotransmissores, processo pré-sináptico envolvido na transmissão sináptica química foram compartilhados entre NAC e PT. A resposta celular ao estímulo químico, resposta ao estímulo externo, resposta à substância orgânica, regulação da plasticidade sináptica e modulação da transmissão sináptica foram compartilhadas entre CN e PT. A maioria dos genes que possuem variantes comuns e / ou raras previamente associadas ao TOC que são diferencialmente expressas ou que fazem parte de módulos de co-expressão menos preservados em nosso estudo também sugerem especificidade de cada região estriatal. Os módulos de co-expressão preservados e menos preservados nos circuitos afetivo e cognitivo ventral corroboram com as assinaturas transcricionais de cada área e de cada circuito no TOC e nos controles. Este é o primeiro trabalho com a proposta de avaliar a expressão gênica em áreas estriatais, analisadas individualmente, envolvidas com o TOC, bem como as redes de co-expressão do estriado e dos circuitos individualmente / Obsessive compulsive disorder (OCD) is a psychiatric disorder, characterized by the presence of obsessions and/or compulsions. Functional neuroimaging studies indicate that OCD is a heterogeneous disorder related the cortical-striatal thalamic circuitry (CSTC) and the areas that compose this circuitry include the nucleus accumbens (NAC), putamen (PT), caudate nucleus (CN), orbitofrontal cortex (OFC) and subgenual cingulate gyri (ACC). The main characteristics of CSTC is the innervation of the frontal cortex in direction of the striatum and each small circuitries have specific characteristics in the affective, dorsal cognitive and ventral cognitive motor. In this work we compared the cases and controls transcriptome of the three striatal areas (CN, NAC and PT) separately from post mortem brain tissue and the co-expression networks of the striatum and of two circuits involved in the disorder. Results showed that different biological process as well as networks connectivity deregulation were specific for each striatum region according to the striatum tripartite model and contribute in different ways to OCD pathophysiology. Specifically, regulation of neurotransmitter levels, presynaptic process involved in chemical synaptic transmission were shared between NAC and PT. Cellular response to chemical stimulus, response to external stimulus, response to organic substance, regulation of synaptic plasticity, and modulation of synaptic transmission were shared between CN and PT. Most genes harboring common and/or rare variants previously associated with OCD that are differentially expressed or part of a least preserved co-expression modules in our study also suggest striatum sub regions specificity. The co-expression modules preserved and least preserved in affective and ventral cognitive circuitry corroborate with transcriptional signatures of each area and each circuitry in OCD and controls. This is the first work with the proposal to evaluate the gene expression in striatum areas individually, involved with OCD as well evaluate the coexpression networks in striatum and each circuitry

The model of basal ganglia function proposed by Albin, Young and Penney (1989) describes two anatomically independent motor pathways, the direct and indirect. However, under normal conditions striatal dopamine (DA) is required for the expression of motor behavior, and DAergic control of the two pathways (via D1 and D2 receptors, respectively) is dependent on co-activation. We tested for a possible breakdown of D1/D2 synergism using transgenic R6/1 mice bearing the human huntingtin allele (Htt). Motor stereotypy, observed prior to the onset of HD-related symptoms, was rated on a 5-point scale following activation of: A) D1 receptors alone, B) D2 receptors alone, and C) stimulation of both D1 and D2 receptors. Results revealed that mice with the HD allele, like their WT litter mates, depend on the co-activation of the indirect and direct motor pathways to facilitate deliberate behavior.

D’après le postulat de Hebb, les circuits neuronaux ajustent et modifient durablement leurs poids synaptiques en fonction des patrons de décharges de part et d’autre de la synapse. La « spike-timing-dependent plasticity » (STDP) est une règle d’apprentissage synaptique hebbienne dépendante de la séquence temporelle précise (de l’ordre de la milliseconde) des activités appariées des neurones pré- et post-synaptiques. Le striatum, le principal noyau d’entrée des ganglions de la base, reçoit des afférences excitatrices provenant du cortex cérébral et du thalamus dont les activités peuvent être concomitantes ou décalées dans le temps. Ainsi, l’encodage temporal des informations corticales et thalamiques via la STDP pourrait être crucial pour l’implication du striatum dans l’apprentissage procédural. Nous avons exploré les plasticités synaptiques cortico- et thalamo-striatales puis leurs interactions à travers le paradigme de la STDP. Les principaux résultats sont :1. Les « spike-timing-dependent plasticity » opposées cortico-striatales et thalamo-striatales induisent des plasticités hétérosynaptiques. Si la très grande majorité des études sont consacrées à la plasticité synaptique cortico-striatale, peu ont exploré les règles de plasticité synaptique aux synapses thalamo-striatale et leurs interactions avec la plasticité cortico-striatale. Nous avons étudié la STDP thalamo-striatale et comment les plasticités synaptiques thalamo- et cortico-striatales interagissent… / According to Hebbian postulate, neural circuits tune their synaptic weights depending on patterned firing of action potential on either side of the synapse. Spike-timing-dependent plasticity (STDP) is an experimental implementation of Hebbian plasticity that relies on the precise order and the millisecond timing of the paired activities in pre- and postsynaptic neurons. The striatum, the primary entrance to basal ganglia, integrates excitatory inputs from both cerebral cortex and thalamus whose activities can be concomitant or delayed. Thus, temporal coding of cortical and thalamic information via STDP paradigm may be crucial for the role of the striatum in procedural learning. Here, we explored cortico-striatal and thalamo-striatal synaptic plasticity and their interplay through STDP paradigm. The main results described here are:1. Opposing spike-timing dependent plasticity at cortical and thalamic inputs drive heterosynaptic plasticity in striatumIf the vast majority of the studies focused on cortico-striatal synaptic plasticity, much less is known about thalamo-striatal plasticity rules and their interplay with cortico-striatal plasticity. Here, we explored thalamo-striatal STDP and how thalamo-striatal and cortico-striatal synaptic plasticity interplay. a) While bidirectional and anti-Hebbian STDP was observed at cortico-striatal synapses, thalamo-striatal exhibited bidirectional and hebbian STDP...