Search

Major depression is a psychiatric disorder relying on different neurobiological mechanisms. In particular, a hypersensitivity of the hypothalamic-pituitary-adrenal axis leading to an excess of cortisol in blood and a deficit in monoaminergic neurotransmission have been associated with mood disorders. In keeping with these mechanisms, currently available antidepressant drugs act by increasing the extracellular levels of monoamines in the synaptic cleft. Since the discovery of the rapid and long-lasting antidepressant effects of ketamine, an NMDA receptor antagonist, a growing attention in psychiatry is paid to the pharmacological tools able to attenuate glutamatergic neurotransmission. Astrocytes play an important role in the excitatory/inhibitory balance of the central nervous system through the regulation of glutamate reuptake and secretion. Interestingly, the release of this excitatory amino acid is controlled, at least in part, by plasma membrane proteins (i.e. connexins) that cluster together to form gap junctions or hemichannels. Preclinical evidence suggests that these functional entities play a critical role in emotional behaviour. After a brief overview of the literature on mood disorders and related treatments, this review describes the role of astrocytes and connexins in glutamatergic neurotransmission and major depression. Moreover, we highlight the arguments supporting the therapeutic potential of connexins blockers but also the practical difficulties to target the hemichannels while maintaining gap junctions intact.Rôle des connexines astrocytaires dans la régulation des taux extracellulaires de glutamate : implication pour le traitement des épisodes dépressifs majeurs.La dépression majeure est une pathologie psychiatrique reposant sur différents mécanismes neurobiologiques. Parmi ces mécanismes, on trouve une hypersensibilité de l’axe hypothalamo-hypophyso-surrénalien associée à un excès de cortisol dans le sang et un déficit de neurotransmission monoaminergique. Ainsi, l’efficacité thérapeutique des antidépresseurs actuels repose sur leur capacité à augmenter les taux extracellulaires de monoamines dans la fente synaptique. Depuis la découverte des effets antidépresseurs rapides et durables de la kétamine, un antagoniste des récepteurs NMDA, un intérêt croissant est porté sur les moyens pharmacologiques atténuant l’action du glutamate pour traiter la dépression majeure. Les astrocytes jouent un rôle prépondérant dans la balance excitation/inhibition du système nerveux central en régulant la recapture et la sécrétion du glutamate. De manière intéressante, la libération de cet acide aminé excitateur est contrôlée, du moins en partie, par des canaux membranaires regroupés au niveau de jonctions intercellulaires de type « gap » ou d’hémicanaux formés par les connexines 30 et 43. Les données précliniques suggèrent que ces deux entités fonctionnelles ont des effets sur les comportements émotionnels dans différents modèles murins de dépression. Après un bref rappel sur les troubles de l’humeur et leurs traitements, cette revue de la littérature décrit le rôle des astrocytes et des connexines dans la neurotransmission glutamatergique et la dépression majeure. Les arguments avancés soulignent l’intérêt thérapeutique potentiel du blocage des connexines astrocytaires mais aussi les difficultés pratiques à cibler la fonction hémicanal sans impacter la fonction « gap ».

Positron emission tomography imaging is still an expanding field of preclinical and clinical investigations exploring the brain and its normal and pathological functions. In addition to technological improvements in PET scanners, the availability of suitable radiotracers for unexplored pharmacological targets is a key factor in this expansion. Many radiotracers (or radiopharmaceuticals, when administered to humans) have been developed by multidisciplinary teams to visualize and quantify a growing numbers of brain receptors, transporters, enzymes and other targets. The development of new PET radiotracers still represents an exciting challenge, given the large number of neurochemical functions that remain to be explored. In this article, we review the development context of the first preclinical radiotracers and their passage to humans. The main current contributions of PET radiotracers are described in terms of imaging neuronal metabolism, quantification of receptors and transporters, neurodegenerative and neuroinflammatory imaging. The different approaches to functional imaging of neurotransmission are also discussed. Finally, the contributions of PET imaging to the research and development of new brain drugs are described.L’imagerie TEP pour une meilleure compréhension de la neurotransmission normale et pathologique.La neuroimagerie des récepteurs cérébraux a commencé au début des années 1980. Aujourd’hui, quelque quarante ans plus tard, l’imagerie par tomographie d’émission de positons (TEP) est toujours un domaine en expansion dans les études précliniques et cliniques cherchant à explorer le cerveau et son fonctionnement normal et pathologique. Outre les améliorations apportées aux caméras TEP et à l’analyse d’images, la disponibilité de radiotraceurs est un facteur déterminant de cette expansion. De nombreux radiotraceurs (ou radiopharmaceutiques, lorsque injectés chez l’Homme) ont été mis au point par des équipes pluridisciplinaires pour visualiser et quantifier un nombre croissant de récepteurs, transporteurs, enzymes et autres cibles moléculaires du cerveau. Le développement de nouveaux radiotraceurs TEP représente un défi passionnant, du fait du grand nombre de cibles et de fonctions neurochimiques qui restent encore à explorer. Dans cet article, nous resituons le contexte de développement des premiers radiotraceurs précliniques et leur passage à l’Homme. Les principales contributions actuelles des radiotraceurs TEP sont décrites en termes d’imagerie du métabolisme neuronal, de quantification des récepteurs et des transporteurs, d’imagerie neurodégénérative et neuroinflammatoire. Les différentes approches d’imagerie fonctionnelle de la neurotransmission sont également abordées. Enfin, les apports de l’imagerie TEP à la recherche et au développement de nouveaux médicaments du cerveau sont décrits.

Data accumulated over the two last decades have demonstrated that astrocytes play key roles in the regulation of synaptic transmission and plasticity. This is due to their capability to detect and regulate synaptic transmission by expressing receptors and releasing gliotransmitters, respectively. However, astrocytes become reactive in pathological condition such as Alzheimer’s disease, and neuronal activity regulation by these glial cells is likely to be altered.The main objective of this thesis is to study the role of astrocytes as integrators and modulators of synaptic transmission under both physiological and pathological conditions.First, we have shown that a single astrocyte is able to detect and in turn up-regulate basal synaptic transmission at individual synapses in juvenile rats. Whether this upregulation is still present in adults and whether it is affected by the synaptic activity occurring at neighboring synapses present within the same astroglial domain is unknown. Using STED imaging on fixed tissue and electrophysiological recordings on acute hippocampal slices of adult male rats we here show that the upregulation pathway previously described in juvenile rats is also present in adults. Indeed, as in juvenile, astrocytes detect basal glutamatergic transmission at individual synapses through mGluR5 and in turn upregulate it by releasing purines and activating presynaptic A2A receptors. More importantly, our data suggest strongly that an individual astrocyte is able to adapt its purine-mediated regulation of glutamatergic transmission as a function of the number of synapses activated in its domain. When the number of afferent inputs activated is small, astrocytes facilitate synaptic efficacy through a purine-mediated process. Interestingly, this process is no longer present when a higher number of afferences is activated, suggesting the astrocytes integrate the incoming information and adapt its response in terms of purine release.Second, studies on Alzheimer’s disease models have reported changes in several astrocyte functions such as its ability to regulate synaptic transmission. However, the contribution of astrocytic reactivity in this pathology remains largely unknown and debated as the reported changes in these studies can have beneficial, deleterious or even mixed effects on neurons. Indeed, reactive astrocytes display a morphological, molecular and functional heterogeneity that could explain their controversial effects in this pathology. To understand how astrocyte reactivity contributes to Alzheimer's disease and to find therapeutic pathways, it is crucial to develop a new strategy that efficiently modulates all types of reactive astrocytes. Here, we used cell type-specific approaches in vivo and identified the JAK2/STAT3 pathway, as necessary and sufficient for the induction and maintenance of astrocyte reactivity. Modulation of this cascade by viral gene transfer in mouse astrocytes efficiently controlled several morphological and molecular features of reactivity. Inhibition of this pathway in mouse models of Alzheimer's disease improved key pathological hallmarks by reducing amyloid deposition and improving spatial learning. Combining this viral gene transfer with electrophysiological recordings, we specifically showed in our lab that reducing astrocyte reactivity by inhibiting JAK2/STAT3 cascade in astrocytes restores synaptic transmission and plasticity deficits observed in a 3xTg mouse model of Alzheimer's disease. In conclusion, the JAK2/STAT3 cascade operates as a master regulator of astrocyte reactivity in vivo. Its inhibition offers new therapeutic opportunities for Alzheimer's disease., Les données accumulées au cours des deux dernières décennies ont montré que l’astrocyte joue un rôle clé dans la régulation de la transmission synaptique. Cela est dû à sa capacité à détecter, via des récepteurs, et réguler, via la libération de gliotransmetteurs, la transmission synaptique. Cependant, les astrocytes deviennent réactifs dans des conditions pathologiques comme la maladie d’Alzheimer et la régulation de l’activité neuronale par ces cellules est susceptible d’être altérée.L'objectif principal de cette thèse est d'étudier le rôle de l‘astrocyte en tant qu'intégrateur et modulateur de la transmission synaptique dans des conditions physiologique et pathologique.Premièrement, nous avons montré qu’un astrocyte est capable de détecter et d’augmenter la transmission synaptique de base au niveau d’une synapse chez des rats jeunes. On ignore si cette régulation est toujours présente chez les adultes et si elle est affectée par l'activité synaptique des synapses voisines présentes dans le même domaine astrocytaire. En utilisant l’imagerie STED et des enregistrements électrophysiologiques sur des tranches d’hippocampes de rats adultes, nous montrons ici que la voie de régulation décrite précédemment est également présente chez les adultes. En effet, les astrocytes détectent la transmission glutamatergique de base au niveau de synapses individuelles par le biais des mGluR5 et l’augmente en libérant des purines qui activent les récepteurs présynaptiques A2A. Plus important encore, nos données suggèrent fortement qu'un astrocyte est capable d'adapter sa régulation de la transmission glutamatergique en fonction du nombre de synapses activées dans son domaine. Lorsque le nombre d’afférences activées est faible, les astrocytes facilitent l'efficacité synaptique par un mécanisme dépendant des purines. Fait intéressant, ce processus n’est plus présent lorsqu’un plus grand nombre d’afférences est activé, ce qui suggère que les astrocytes sont capables d’intégrer différemment les informations entrantes et d’adapter leur réponse en termes de libération de purine.Deuxièmement, des études sur des modèles de la maladie d’Alzheimer ont rapporté que plusieurs fonctions astrocytaires, comme leur capacité à réguler la transmission synaptique, étaient perturbées. Cependant, la contribution de la réactivité astrocytaire dans cette pathologie reste méconnue et débattue du fait que les modifications rapportées dans ces études peuvent être bénéfiques et/ou néfastes pour les neurones. En effet, les astrocytes réactifs présentent une hétérogénéité morphologique, moléculaire et fonctionnelle qui peut expliquer leurs effets controversés dans cette pathologie. Pour comprendre comment la réactivité astrocytaire contribue à la maladie d'Alzheimer et trouver des voies thérapeutiques, il est essentiel de développer une nouvelle stratégie qui module efficacement tous les types d'astrocytes réactifs. Ici, nous avons utilisé des approches in vivo visant spécifiquement les astrocytes et identifié la voie JAK2/STAT3, comme étant nécessaire et suffisante pour l'induction et le maintien de la réactivité astrocytaire. La modulation de cette cascade par approche virale contrôle efficacement plusieurs caractéristiques morphologiques et moléculaires de la réactivité. De plus, son inhibition chez des modèles murins de la maladie d'Alzheimer améliore des caractéristiques pathologiques clés en réduisant les dépôts amyloïdes et en améliorant l'apprentissage spatial. En combinant l’approche virale avec des enregistrements électrophysiologiques, notre équipe a montré que réduire la réactivité astrocytaire en inhibant la voie JAK2/STAT3 rétablit les déficits de transmission synaptique et de plasticité observés chez un modèle 3xTg de la maladie d'Alzheimer. En conclusion, la cascade JAK2/STAT3 est un régulateur principal de la réactivité astrocytaire in vivo. Son inhibition offre de nouvelles opportunités thérapeutiques pour la maladie d'Alzheimer.

Data accumulated over the two last decades have demonstrated that astrocytes play key roles in the regulation of synaptic transmission and plasticity. This is due to their capability to detect and regulate synaptic transmission by expressing receptors and releasing gliotransmitters, respectively. However, astrocytes become reactive in pathological condition such as Alzheimer’s disease, and neuronal activity regulation by these glial cells is likely to be altered.The main objective of this thesis is to study the role of astrocytes as integrators and modulators of synaptic transmission under both physiological and pathological conditions.First, we have shown that a single astrocyte is able to detect and in turn up-regulate basal synaptic transmission at individual synapses in juvenile rats. Whether this upregulation is still present in adults and whether it is affected by the synaptic activity occurring at neighboring synapses present within the same astroglial domain is unknown. Using STED imaging on fixed tissue and electrophysiological recordings on acute hippocampal slices of adult male rats we here show that the upregulation pathway previously described in juvenile rats is also present in adults. Indeed, as in juvenile, astrocytes detect basal glutamatergic transmission at individual synapses through mGluR5 and in turn upregulate it by releasing purines and activating presynaptic A2A receptors. More importantly, our data suggest strongly that an individual astrocyte is able to adapt its purine-mediated regulation of glutamatergic transmission as a function of the number of synapses activated in its domain. When the number of afferent inputs activated is small, astrocytes facilitate synaptic efficacy through a purine-mediated process. Interestingly, this process is no longer present when a higher number of afferences is activated, suggesting the astrocytes integrate the incoming information and adapt its response in terms of purine release.Second, studies on Alzheimer’s disease models have reported changes in several astrocyte functions such as its ability to regulate synaptic transmission. However, the contribution of astrocytic reactivity in this pathology remains largely unknown and debated as the reported changes in these studies can have beneficial, deleterious or even mixed effects on neurons. Indeed, reactive astrocytes display a morphological, molecular and functional heterogeneity that could explain their controversial effects in this pathology. To understand how astrocyte reactivity contributes to Alzheimer's disease and to find therapeutic pathways, it is crucial to develop a new strategy that efficiently modulates all types of reactive astrocytes. Here, we used cell type-specific approaches in vivo and identified the JAK2/STAT3 pathway, as necessary and sufficient for the induction and maintenance of astrocyte reactivity. Modulation of this cascade by viral gene transfer in mouse astrocytes efficiently controlled several morphological and molecular features of reactivity. Inhibition of this pathway in mouse models of Alzheimer's disease improved key pathological hallmarks by reducing amyloid deposition and improving spatial learning. Combining this viral gene transfer with electrophysiological recordings, we specifically showed in our lab that reducing astrocyte reactivity by inhibiting JAK2/STAT3 cascade in astrocytes restores synaptic transmission and plasticity deficits observed in a 3xTg mouse model of Alzheimer's disease. In conclusion, the JAK2/STAT3 cascade operates as a master regulator of astrocyte reactivity in vivo. Its inhibition offers new therapeutic opportunities for Alzheimer's disease.; Les données accumulées au cours des deux dernières décennies ont montré que l’astrocyte joue un rôle clé dans la régulation de la transmission synaptique. Cela est dû à sa capacité à détecter, via des récepteurs, et réguler, via la libération de gliotransmetteurs, la transmission synaptique. Cependant, les astrocytes deviennent réactifs dans des conditions pathologiques comme la maladie d’Alzheimer et la régulation de l’activité neuronale par ces cellules est susceptible d’être altérée.L'objectif principal de cette thèse est d'étudier le rôle de l‘astrocyte en tant qu'intégrateur et modulateur de la transmission synaptique dans des conditions physiologique et pathologique.Premièrement, nous avons montré qu’un astrocyte est capable de détecter et d’augmenter la transmission synaptique de base au niveau d’une synapse chez des rats jeunes. On ignore si cette régulation est toujours présente chez les adultes et si elle est affectée par l'activité synaptique des synapses voisines présentes dans le même domaine astrocytaire. En utilisant l’imagerie STED et des enregistrements électrophysiologiques sur des tranches d’hippocampes de rats adultes, nous montrons ici que la voie de régulation décrite précédemment est également présente chez les adultes. En effet, les astrocytes détectent la transmission glutamatergique de base au niveau de synapses individuelles par le biais des mGluR5 et l’augmente en libérant des purines qui activent les récepteurs présynaptiques A2A. Plus important encore, nos données suggèrent fortement qu'un astrocyte est capable d'adapter sa régulation de la transmission glutamatergique en fonction du nombre de synapses activées dans son domaine. Lorsque le nombre d’afférences activées est faible, les astrocytes facilitent l'efficacité synaptique par un mécanisme dépendant des purines. Fait intéressant, ce processus n’est plus présent lorsqu’un plus grand nombre d’afférences est activé, ce qui suggère que les astrocytes sont capables d’intégrer différemment les informations entrantes et d’adapter leur réponse en termes de libération de purine.Deuxièmement, des études sur des modèles de la maladie d’Alzheimer ont rapporté que plusieurs fonctions astrocytaires, comme leur capacité à réguler la transmission synaptique, étaient perturbées. Cependant, la contribution de la réactivité astrocytaire dans cette pathologie reste méconnue et débattue du fait que les modifications rapportées dans ces études peuvent être bénéfiques et/ou néfastes pour les neurones. En effet, les astrocytes réactifs présentent une hétérogénéité morphologique, moléculaire et fonctionnelle qui peut expliquer leurs effets controversés dans cette pathologie. Pour comprendre comment la réactivité astrocytaire contribue à la maladie d'Alzheimer et trouver des voies thérapeutiques, il est essentiel de développer une nouvelle stratégie qui module efficacement tous les types d'astrocytes réactifs. Ici, nous avons utilisé des approches in vivo visant spécifiquement les astrocytes et identifié la voie JAK2/STAT3, comme étant nécessaire et suffisante pour l'induction et le maintien de la réactivité astrocytaire. La modulation de cette cascade par approche virale contrôle efficacement plusieurs caractéristiques morphologiques et moléculaires de la réactivité. De plus, son inhibition chez des modèles murins de la maladie d'Alzheimer améliore des caractéristiques pathologiques clés en réduisant les dépôts amyloïdes et en améliorant l'apprentissage spatial. En combinant l’approche virale avec des enregistrements électrophysiologiques, notre équipe a montré que réduire la réactivité astrocytaire en inhibant la voie JAK2/STAT3 rétablit les déficits de transmission synaptique et de plasticité observés chez un modèle 3xTg de la maladie d'Alzheimer. En conclusion, la cascade JAK2/STAT3 est un régulateur principal de la réactivité astrocytaire in vivo. Son inhibition offre de nouvelles opportunités thérapeutiques pour la maladie d'Alzheimer.

International audience; Spasticity after spinal cord injury has considerable quality of life implications, impacts on rehabilitation efforts and necessitates long-term multi-disciplinary pharmacological and non-pharmacological management. The potassium chloride co-transporter (KCC2) plays a central role in intracellular chloride homeostasis and the inhibitory function of mature neurons. Animal studies consistently have demonstrated a downregulation of KCC2 activity after spinal cord transection, causing a shift from the inhibitory action of gamma-aminobutyric acid and glycine to an excitatory effect. Furosemide, a recognized KCC2 antagonist in animals, blocks the formation of inhibitory post-synaptic potentials in spinal motoneurons without affecting excitatory post-synaptic potentials. Based on observations in animals studies, we hypothesized that furosemide may be used to unmask KCC2 downregulation after spinal cord injury in humans, which contributes to reflex hyperexcitability. We have shown previously that furosemide reduces both pre-synaptic and post-synaptic inhibition in healthy subjects without altering monosynaptic excitatory transmission. These findings provide evidence that furosemide may be used in humans to evaluate inhibitory synapses in the spinal cord. In this present study, we show that furosemide fails to modulate both pre- and post-synaptic inhibitions relayed to soleus spinal motor neurons in persons with spinal cord injury. The lack of furosemide effect after spinal cord injury suggests KCC2 dysfunction in humans, resulting in reduced inhibitory synaptic transmission in spinal neurons. Our findings suggest that KCC2 dysfunction may be an important etiological factor in hyperreflexia after spinal cord injury. These observations may pave the way to novel therapeutic strategies against spasticity centered on chloride homeostasis.

Addiction is a chronic disease that has serious consequences, both in terms of public health and economy. Clear characteristics distinguish recreational and controlled use from addiction. Thus, today, addiction includes the notions of compulsive drug use, associated with a loss of control over consumption, leading to craving. When consumption is stopped, withdrawal symptoms may emerge: a negative emotional state, cognitive problems and physical symptoms with some products (alcohol and opiates, for example). Relapse episodes may occur during this withdrawal period, countering the negative effects of withdrawal. Relapse episodes can also be observed after long periods of abstinence. They can be precipitated by re-exposure to the context in which the drugs were taken, or by stress. Regardless of the stage of addiction (e.g., development of the addictive behavior, or relapse) changes in brain function and structure can be observed. Some brain structures are therefore modified, such as the prefrontal cortex, where several neuroadaptations have been identified. Some of these changes are described in this paper.Circuits neuronaux et neuromédiateurs impliqués dans les effets des drogues psychoactives – État de l’art avec un focus sur la cocaïne.L’addiction est une maladie chronique qui engendre de lourdes conséquences, à la fois en termes de santé publique et au niveau économique. Des caractéristiques claires distinguent bien l’usage récréatif et contrôlé, de l’addiction. Ainsi, aujourd’hui, l’addiction inclut les notions de recherche compulsive de la drogue, associées à une perte de contrôle sur sa prise, favorisant l’émergence d’un désir persistant et irrépressible pour la drogue (appelé craving). À l’arrêt de la consommation, des symptômes de sevrage peuvent émerger : un état émotionnel négatif, des troubles cognitifs et des symptômes physiques avec certains produits (alcool et opiacés, par exemple). Les épisodes de rechute peuvent survenir au cours de cette période de sevrage pour contrer les effets négatifs du sevrage. De tels épisodes peuvent aussi être observés après de longues périodes d’abstinence. Ils peuvent être précipités par une réexposition au contexte dans lequel les prises de drogues s’effectuaient, ou encore par un stress. Quel que soit le stade auquel on se place (e.g., mise en place de l’addiction, ou rechute), des changements dans les fonctions et la structure du cerveau peuvent être observés. Certaines structures cérébrales sont donc modifiées, comme le cortex préfrontal, où plusieurs neuroadaptations ont été mises en évidence. Certaines de ces modifications sont revisitées dans cet article.

Synaptic plasticity consists in a change in structure and composition of presynaptic and postsynaptic compartments. For a long time, synaptic plasticity had been thought as a neuronal mechanism only under the control of neural network activity. However, recently, with the growing knowledge about glial physiology, plasticity has been reviewed as a mechanism influenced by the synaptic environment. Thus, it appears that astrocytes and microglia modulate these mechanisms modifying neural environment by clearance of neurotransmitters, releasing essential factors and modulating inflammation. Moreover, glia can change its own activity and the expression pattern of many factors that modulate synaptic plasticity according to the environment. Hence, these populations of "non-neuronal" cells in the central nervous system seem to be active players in synaptic plasticity. This review discusses how glia modulates synaptic plasticity focusing on long-term potentiation and depression, and questions the role of the signaling processes between astrocytes and microglia in these mechanisms.

Since the work of Johnson and North, it is known that opiates increase the activity of dopaminergic neurons by a GABA neuron-mediated desinhibition. This model should however be updated based on recent advances. Thus, the neuroanatomical location of the GABA neurons responsible for this desinhibition has been recently detailed: they belong to a brain structure in continuity with the posterior part of the ventral tegmental area and discovered this past decade. Other data also highlighted the critical role played by glutamatergic transmission in the opioid regulation of dopaminergic neuron activity. During protracted opiate withdrawal, the inhibitory/excitatory balance exerted on dopaminergic neurons is altered. These results are now leading to propose an original hypothesis for explaining the impact of protracted opiate withdrawal on mood.

La sclérose latérale amyotrophique est une maladie neurodégénérative fatale caractérisée par la dégénérescence progressive des neurones moteurs centraux et périphériques. L’un des premiers signes de la maladie est la dénervation de la jonction neuromusculaire (JNM). Les diverses unités motrices (UM) ne présentent toutefois pas la même vulnérabilité à la dénervation dans la SLA: les UM rapide fatigables sont en fait les plus vulnérables et les UM lentes sont les plus résistantes. Alors que des études précédentes ont démontré dans plusieurs modèles animaux de la SLA de nombreuses variations synaptiques, les découvertes ont été contradictoires. Par ailleurs, le type d’UM n’a pas été tenu en compte dans ces divers travaux. Nous avons donc émis l’hypothèse que la présence de la mutation SOD1 pourrait affecter différemment la transmission synaptique des UM, en accord avec leur vulnérabilité sélective. En effectuant des enregistrements électrophysiologiques et de l’immunohistochimie, nous avons étudié la transmission synaptique des différents types d’UM du muscle à contraction rapide Extensor Digitorum Longus (EDL; rapide fatigable (FF) MU) et du muscle à contraction lente Soleus (SOL; lente (S) and rapide fatigue-résistante (FR) MU) de la souris SOD1G37R et leur congénères WT. Pour identifier le type d’UM, un marquage par immunohistochimie des chaînes de myosine a été effectué. Un triple marquage de la JNM a également été effectué pour vérifier son intégrité aux différents stades de la maladie. À P160, dans la période asymptomatique de la maladie, alors qu’aucune altération morphologique n’était présente, l’activité évoquée était déjà altérée différemment en fonction des UM. Les JNMs FF mutantes ont démontré une diminution de l’amplitude des potentiels de plaque motrice (PPM) et du contenu quantique, alors que les JNMs lentes démontraient pratiquement le contraire. Les JNMs FR montraient quant à elles une force synaptique semblable au WT. À P380, dans la période présymtomatique, de nombreuses altérations morphologiques ont été observées dans le muscle EDL, incluant la dénervation complète, l’innervation partielle et les extensions du nerf. La transmission synaptique évoquée des UM FF étaient toujours réduites, de même que la fréquence des potentiels de plaque motrice miniatures. À P425, à l’apparition des premiers symptômes, l’activité synaptique des JNMs S était redevenue normale alors que les JNMs FR ont montré à ce moment une diminution du contenu quantique par rapport au contrôle. De manière surprenante, aucun changement du ratio de facilitation n’a été observé malgré les changements flagrants de la force synaptique. Ces résultats révèlent que la fonction de la JNM est modifiée différemment en fonction de la susceptibilité des UM dans l’ALS. Cette étude fournit des pistes pour une meilleure compréhension de la physiologie de la JNM durant la pathologie qui est cruciale au développement d’une thérapie adéquate ciblant la JNM dans la SLA., Amyotrophic lateral sclerosis (ALS) is a fatal late-onset neurodegenerative disease characterized by the progressive loss of upper and lower motor neurons. Denervation of the neuromuscular junction (NMJ) is an early pathological event in various ALS models. Motor units (MU) appear unequally susceptible to denervation, the fast fatigable (FF) MU being the most vulnerable and the slow (S) MU the most resistant. While previous studies in several ALS models have consistently reported alterations in synaptic transmission, their findings have been contradictory. Interestingly, the MU types were not taken into account in these studies, which could explain these discrepancies. We hypothesized that the MU selective vulnerabilities observed in ALS will be associated with MU-specific NMJ alterations throughout the disease course. Using electrophysiology, we studied synaptic transmission of different types of MU in the fast-twitch Extensor Digitorum Longus (EDL; fast fatigable (FF) MU) and the slow-twitch Soleus (SOL; slow (S) and fast fatigue resistant (FR) MU) of the SOD1 mice and their WT littermates. MU types were identified using immunohistochemical labelling of the respective myosine heavy chains. Immunohistochemistry was also performed to assess NMJ integrity by using antibodies against main NMJ components. At a presymptomatic stage (P160), while no morphological alterations of NMJs were seen in both muscles, evoked activity was altered in a MU-specific manner in SOD1 mice. FF MU from SOD1 mice showed a decrease in EPP amplitude and quantal content whereas S MU showed the opposite. Mutant FR MU showed no difference in evoked activity compared to WT. At presymptomatic stage (P380), various morphological alterations were seen in the SOD1 EDL, including denervation, partial innervation and nerve sprouting. Evoked activity was still reduced in FF MU, as well as mEPP frequency. In contrast, at disease onset (P425), synaptic strength of the S MU was now similar to WT MU, whereas FR NMJs showed a decrease in EPP amplitude and quantal content. Surprisingly, paired-pulse facilitation was not altered in any MU type and at any age despite changes in synaptic strength. Taken together, these results reveal that NMJ function is differentially modified according to MU susceptibility in ALS. This study provides insights for a better understanding of NMJ physiology during the illness that is crucial to the development of a proper NMJ-targeted treatment in ALS.

One of major obstacles in neuroscience research is the difficulty of directly accessing the brain function to understand the biological mechanisms underlying brain dysfunctions in psychiatric disorders. As an anatomical and developmental extension of the central nervous system, the retina could afford to offer an indirect access to brain neurological functions. Investigating the retinal function provides the unique opportunity to study in an objective way a complex neuronal network which shares similar properties with the brain. Cannabis is a neurotoxic substance identified as modulating brain synaptic transmission through the cannabinoid system, but the precise mechanisms underpinning these anomalies are poorly understood. The first part of this work is dedicated to present the neurobiological basis and pathophysiological hypotheses justifying the study of retinal function in cannabis users and is based on the presence of the cannabinoid system in the retina and its involvement in the regulation of synaptic neurotransmission. The second part discusses the interest of the study of retinal function with electrophysiological methods in psychiatric research. The last part presents the retinal dysfunctions detected in cannabis users, after acute or regular use, and assessed by electrophysiological techniques such as electroretinogram. All these data reinforce the relevance of the retina as a site of brain investigation and possibly open the prospect for the development of functional markers, Un des obstacles majeurs de la recherche en neurosciences est la difficulté d’accéder de manière directe au fonctionnement du cerveau afin de comprendre les mécanismes biologiques à l’origine des dysfonctionnements cérébraux dans les troubles psychiatriques. En tant qu’extension anatomique et développementale du système nerveux central, la rétine pourrait permettre d’offrir un accès indirect aux fonctions neurologiques cérébrales. Ainsi, l’investigation de la fonction rétinienne apporte l’unique opportunité d’étudier de manière objective un réseau neuronal complexe présentant des similarités avec celui du cerveau. Le cannabis est une substance neurotoxique identifiée comme modulant la transmission synaptique cérébrale par l’intermédiaire du système cannabinoïde mais les mécanismes précis à l’origine de ces anomalies sont peu connus. La première partie de ce travail consiste à présenter les bases neurobiologiques et les hypothèses physiopathologiques justifiant l’étude de la fonction rétinienne chez les usagers de cannabis, en se basant sur la présence du système cannabinoïde dans la rétine et son implication dans la régulation de la libération synaptique de neurotransmetteurs. La seconde partie discute l’intérêt de l’étude de la fonction rétinienne dans la recherche en psychiatrie avec des méthodes électrophysiologiques. Enfin, la dernière partie présente les dysfonctions rétiniennes présentes chez les usagers de cannabis, après un usage aigu ou régulier, évaluées par les techniques électrophysiologiques comme l’électrorétinogramme. Toutes ces données renforcent la pertinence de la rétine comme site d’investigation du cerveau et ouvrent éventuellement la perspective au développement de marqueurs fonctionnels

Numerous studies have now demonstrated that sleep has a beneficial influence on memory but also impact forgetting. We have submitted rats to behavioral tasks involving different levels of forgetting. These tasks, implying reference memory (RM) or working memory (WM) with different level of interferences, were executed in the same behavioral apparatus. Whereas we observed an increase of paradoxical sleep (PS) during the RM training, the WM tasks requiring forgetting are dependent on slow-wave sleep (SWS). Only the RM trained rats exhibited an increase in theta bursts during PS, as well as spindles during SWS. These results thus indicate the role of PS in long-term spatial learning, whereas behavioral flexibility required by WM tasks is dependent on SWS. Numerous pieces of evidence suggest that learning is caused by modifications of synaptic connections, and different theories suggest different roles of the SWS and PS to optimize these changes. We sought to understand the evolution of synaptic transmission in the hippocampal network but also between the hippocampus (HPC) and the medial prefrontal cortex (mPFC), as well as between the HPC and the nucleus accumbens (NAc). While SWS increases synaptic transmission in the HPC, PS decreases it rapidly. In contrast and regarding hippocampal efferents, SWS reduces transmission to the mPFC while PS enhances transmission to the NAc. In contrast to the hypotheses posing that sleep promotes a global process common to the entire brain; our results suggest that SWS and PS redirect data flows between different networks, and that this switch between different information pathways could be modulated by the various sleep oscillations, Le sommeil a un effet sur la mémoire mais également sur l'oubli. Nous avons soumis des rats à des tâches impliquant différents degrés d'oubli. Ces tâches, impliquant mémoire de référence (MR), ou mémoire de travail (MT) avec différents niveaux d'interférences, ont été réalisées dans un même dispositif comportemental. Alors que nous avons observés une augmentation du sommeil paradoxal (SP) lors de la tâche de MR, les performances en MT nécessitant l'oubli sont dépendantes du sommeil lent (SL). Seuls les rats entrainés en MR montrent une augmentation du thêta phasique durant le SP, ainsi que des fuseaux durant le SL. Ces résultats indiquent donc un rôle du SP dans les apprentissages spatiaux à long terme alors que la flexibilité comportementale requise en MT semble dépendante du SL. Il existe de nombreuses évidences suggérant que l'apprentissage résulte de modifications synaptiques, et différentes théories suggèrent des rôles différents du SL et du SP dans ces changements. Nous avons donc ensuite examiné l'évolution de la transmission synaptique dans l'hippocampe (HPC), mais aussi entre l'HPC et le cortex préfrontal médian (CPFm) ainsi que le noyau accumbens (NAc). Alors que le SL accroit la transmission synaptique dans l'HPC, le SP la diminue. Au niveau des efférences de l'HPC, le SL diminue la transmission vers le CPFm alors que les épisodes de SP favorisent la communication vers le NAc. Plutôt que de favoriser globalement des processus communs à l'ensemble du cerveau, nos résultats suggèrent que le SL et le SP permettent de rediriger les flux d'informations entre différents réseaux, et que cet aiguillage de l'information est modulé par les oscillations du sommeil

One of major obstacles in neuroscience research is the difficulty of directly accessing the brain function to understand the biological mechanisms underlying brain dysfunctions in psychiatric disorders. As an anatomical and developmental extension of the central nervous system, the retina could afford to offer an indirect access to brain neurological functions. Investigating the retinal function provides the unique opportunity to study in an objective way a complex neuronal network which shares similar properties with the brain. Cannabis is a neurotoxic substance identified as modulating brain synaptic transmission through the cannabinoid system, but the precise mechanisms underpinning these anomalies are poorly understood. The first part of this work is dedicated to present the neurobiological basis and pathophysiological hypotheses justifying the study of retinal function in cannabis users and is based on the presence of the cannabinoid system in the retina and its involvement in the regulation of synaptic neurotransmission. The second part discusses the interest of the study of retinal function with electrophysiological methods in psychiatric research. The last part presents the retinal dysfunctions detected in cannabis users, after acute or regular use, and assessed by electrophysiological techniques such as electroretinogram. All these data reinforce the relevance of the retina as a site of brain investigation and possibly open the prospect for the development of functional markers, Un des obstacles majeurs de la recherche en neurosciences est la difficulté d’accéder de manière directe au fonctionnement du cerveau afin de comprendre les mécanismes biologiques à l’origine des dysfonctionnements cérébraux dans les troubles psychiatriques. En tant qu’extension anatomique et développementale du système nerveux central, la rétine pourrait permettre d’offrir un accès indirect aux fonctions neurologiques cérébrales. Ainsi, l’investigation de la fonction rétinienne apporte l’unique opportunité d’étudier de manière objective un réseau neuronal complexe présentant des similarités avec celui du cerveau. Le cannabis est une substance neurotoxique identifiée comme modulant la transmission synaptique cérébrale par l’intermédiaire du système cannabinoïde mais les mécanismes précis à l’origine de ces anomalies sont peu connus. La première partie de ce travail consiste à présenter les bases neurobiologiques et les hypothèses physiopathologiques justifiant l’étude de la fonction rétinienne chez les usagers de cannabis, en se basant sur la présence du système cannabinoïde dans la rétine et son implication dans la régulation de la libération synaptique de neurotransmetteurs. La seconde partie discute l’intérêt de l’étude de la fonction rétinienne dans la recherche en psychiatrie avec des méthodes électrophysiologiques. Enfin, la dernière partie présente les dysfonctions rétiniennes présentes chez les usagers de cannabis, après un usage aigu ou régulier, évaluées par les techniques électrophysiologiques comme l’électrorétinogramme. Toutes ces données renforcent la pertinence de la rétine comme site d’investigation du cerveau et ouvrent éventuellement la perspective au développement de marqueurs fonctionnels

Cochlear inner hair cells (IHCs) encode acoustic signals into nerve impulses at their ribbon synapses formed with the auditory afferent fibers. The exocytosis of glutamatergic vesicles is triggered by voltage activation of Cav1.3 channels and requires otoferlin, the putative intracellular Ca2+ sensor. The precise molecular mechanisms of exocytosis still remain elusive, notably the mechanisms allowing the temporal precision, the high rates of vesicular fusion (high frequency phase-locking with sound) and the indefatigability of the process. We show here that exocytosis in auditory and vestibular hair cells relies on a specific tight spatial organization of Cav1.3 channels at the active zones. Auditory IHCs use different Cav1.3isoforms, notably short C-terminal isoforms (Cav1.343S et Cav1.342A). These short Cav1.3isoforms essentially trigger the RRP exocytosis (Readily Releasable Pool of vesicles) and are at the origin of its fast adaptation. This fast exocytotic adaptation is based both on an intracellularCa2+ dependant inactivation of the Ca2+ current and on its extracellular block by exocytosed protons. Long Cav1.3 isoforms (Cav1.342L et Cav1.3∆44) regulate the vesicular recruitment at the active zones. Furthermore, our results show that a synaptic actin cytoskeleton is essential for the tight spatial organization of the Cav1.3 channels at the ribbons. Clarin 1 (Usher IIIA protein),through its interactions with the F-actin network, harmonin (PDZ protein, Usher IC) and the Ca2+channel β2 subunit, is required to maintain the tight organization of Cav1.3 channels at the ribbon synapses., Les cellules ciliées internes (CCIs) de la cochlée encodent les signaux acoustiques en impulsions électriques au niveau des synapses à ruban formées avec les fibres afférentes du nerf auditif. L'exocytose des vésicules glutamatergiques par les CCIs est déclenchée par l'activation des canaux calciques Cav1.3 et par l'otoferline, le senseur calcique intracellulaire présumé. Les mécanismes moléculaires précis régulant cette exocytose restent encore mal compris, notamment ceux à l’origine de sa précision temporelle, sa vitesse élevée en phase avec le signal acoustique("phase-locking" jusqu'à 1-2 kHz) et son infatigabilité. Nous montrons que la spécificité des synapses à ruban auditive et vestibulaire passe par une organisation spatiale spécifique des canaux Cav1.3 dans les zones actives. Les CCIs utilisent différentes isoformes de canaux Cav1.3, notamment des isoformes courtes tronquées dans leur partie C-terminale. Ces isoformes courtes (Cav1.343S et Cav1.342A) sont essentiellement impliquées dans le déclenchement et dans l'adaptation rapide de l'exocytose. Cette adaptation se réalise au niveau des canaux Cav1.3 à la fois en intracellulaire par le Ca2+ et en extracellulaire parles protons secrétés lors de l'exocytose. Les isoformes longues (Cav1.342L et Cav1.3∆44),positionnées en périphérie du ruban, réguleraient le recrutement vésiculaire. Par ailleurs, nous montrons que l'organisation spatiale des canaux Cav1.3 est dépendante d'un cytosquelette d'actine-F au ruban synaptique. La clarine 1 (protéine Usher IIIA) interagirait avec l'actine-F, l'harmonine (protéine PDZ, Usher IC) et la sous-unité β2 des canaux calciques pour organiser les canaux Cav1.3 dans les zones actives.

The work of this thesis aims to apply modeling and simulation techniques to mechanisms underlying neuronal activity, in order to promote drug discovery for the treatment of nervous system diseases. The models are developed and integrated at different scales: 1) the so-called "elementary models" permit to simulate dynamics of receptors, ion channels and biochemical reactions in intracellular signaling pathways; 2) models at the neuronal level allow to study the electrophysiological activity of these cells; and 3) microcircuits models help to understand the emergent properties of these complex systems, while maintaining the basic mechanisms that are the targets of pharmaceutical molecules. After a bibliographic synthesis of necessary elements of neurobiology, and an outline of the implemented mathematical and computational tools, the manuscript describes the developed models, as well as their validation process, ranging from the neurotransmitter receptor to the microcircuit. Moreover, these developments have been applied to three studies aiming to understand: 1) pharmacological modulation of the long-term potentiation (LTP) of glutamatergic synapses in the hippocampus, 2) mechanisms of neuronal hyperexcitability in the mesial temporal lobe epilepsy (MTLE), based on in vitro and in vivo experimental results, and 3) cholinergic modulation of hippocampal activity, particularly the theta rhythm associated with septo-hippocampal pathway.; Les travaux de cette thèse ont pour but de mettre en œuvre des outils de modélisation et de simulation numériques de mécanismes sous-tendant l’activité neuronale, afin de promouvoir la découverte de médicaments pour le traitement des maladies du système nerveux. Les modèles développés s’inscrivent à différentes échelles : 1) les modèles dits « élémentaires » permettent de simuler la dynamique des récepteurs, des canaux ioniques, et les réactions biochimiques des voies de signalisation intracellulaires ; 2) les modèles de neurones permettent d’étudier l’activité électrophysiologique de ces cellules ; et 3) les modèles de microcircuits permettent de comprendre les propriétés émergentes de ces systèmes complexes, tout en conservant les mécanismes élémentaires qui sont les cibles des molécules pharmaceutiques. À partir d’une synthèse bibliographique des éléments de neurobiologie nécessaires, et d’une présentation des outils mathématiques et informatiques mis en œuvre, le manuscrit décrit les différents modèles développés ainsi que leur processus de validation, allant du récepteur de neurotransmetteur au microcircuit. D’autre part, ces développements ont été appliqués à trois études visant à comprendre : 1) la modulation pharmacologique de la potentialisation à long terme (LTP) dans les synapses glutamatergiques de l’hippocampe, 2) les mécanismes de l'hyperexcitabilité neuronale dans l'épilepsie mésio-temporale (MTLE) à partir de résultats expérimentaux in vitro et in vivo, et 3) la modulation cholinergique de l'activité hippocampique, en particulier du rythme thêta associé à la voie septo-hippocampique.

The dorsal horn of the spinal cord (DH) is an important site of integration and modulation of somatosensory information and deep laminae of the DH play an important role in the modulation of nociceptive information in the neuronal network of the spinal cord.Our aim was to characterize the effects of NA on synaptic transmission in deep laminae of the DH.We show that NA facilitates inhibitory synaptic transmission in laminae III-IV of the DH. This phenomenon involves the activation of alpha1, alpha2, and beta adrenoceptors and requires intact interlaminar communications between laminae III-IV and V. Glial cell metabolism inhibition has the same consequences as a mechanical section between laminae IV and V. These results indicate that an interaction between glial cell and deep laminae neurons of the DH seems essential for the facilitatory effect of NA on inhibitory synaptic communications in laminae III-IV of the DH., La corne dorsale de la moelle épinière (CDME) est un site d’intégration et de modulation de l’information somatosensorielle. Les laminae profondes de la CDME jouent un rôle important dans la modulation des informations nociceptives. Notre objectif a été de caractériser les effets de la NA sur la transmission synaptique des laminae profondes de la CDME. Nous montrons que la NA facilite la transmission synaptique inhibitrice dans les laminae III-V de la CDME. Ce phénomène met en jeu l’activation d’adrénocepteurs alpha1, alpha2, et bêta et nécessite une communication interlaminaire intacte entre les laminae III-IV et V. L’inhibition du métabolisme glial produit les mêmes effets qu’une section mécanique entre les laminae IV et V. Une interaction entre les cellules gliales et les neurones des laminae profondes la CDME semble donc indispensable à l’effet facilitateur de la NA.

Brain functionning is gouverned by two master forces : excitation, mainly supported by glutamatergic transmission, and inhibition, mainly supported by GABAergic transmission. The mutual and balanced influence of these two forces is instrumental to establish and maintain a physiological neuronal activity, particulary in neuronal networks involving several interconnected brain area and neuron types. The metabotropic glutamate receptor type 7, mGlu7, modulates both glutamatergic and GABAergic transmission, but its precise localization andsynaptic role are still widly unknown. Recently, a genetic mouse model has highlighted mGlu7a receptor's involvement into the functionning of a particular network supporting somatosensory perception during arousal and loss of consciousness during sleep, as well as absence epileptic seizures : the thalamo-cortical network. This thesis aims at understanding physiological functions mediated by the mGlu7a receptor in the thalamo-cortical circuit. I have dissected localization and electrophysiologicalprocesses triggered by the receptor in thalamic synapses. The mGlu7a receptor was proved as essential to control oscillatory rythmes in the thalamus, associated with both sleep-related waves (spindles) and absence epileptic seizures.This receptor was supposed to function only during high neuronal activities. In addition, our study highlights a constitutive activity of mGlu7a receptor in excitatory and inhibitory synapses. It thus exerts a permanent brake on Ca2+ presynaptic entry, which is crucial for neuronal developpement, synaptic transmission, excitability and plasticity. I found that this mechanism modulates glutamate and GABA release, but also short term plasticity in thestudied network. Moreover, mGlu7a receptor slows down the inhibitory tonus in the thalamus and thalamic excitability.Surprisingly for a glutamate receptor, these data suggest that the physiological action of mGlu7a receptor is highly involved in the control of the excitability of inhibitory thalamic and cortical neurons. By decreasing synchronous activities of the network, its action leads in fine to the maintenance of a conscious, awake state of a subject, that is necessary for sensorial informations processing, learning and memory.; Le fonctionnement cérébral est régit par deux grandes forces : un système excitateur, principalement supporté par la transmission gluue,tamatergiq qui s'oppose à un système inhibiteur, principalement supporté par la transmission GABAergique. L'influence mutuelle et équilibrée de ces deux forces est déterminante pour établir et maintenir une activité neuronale physiologique au sein des réseaux neuronaux. Le récepteur métabotropique du glutamate de type 7, mGlu7, est capable de moduler à la fois la transmission glutamatergique et GABAergique, mais sa localisation et son rôle synaptique précis restent largement méconnus à l'heure actuelle. Il semble important pour contrôler le fonctionnement d'une circuiterie particulière supportant notamment la perception sensorielle lors de l'éveil ou la perte de conscience lors de l'endormissement, mais aussi les crises épileptiques d'absence lors d'un dysfonctionnement : le circuit thalamo-cortical. Cette thèse porte sur l'étude des fonctions physiologiques médiées par le récepteur mGlu7a au sein du réseau thalamo-cortical chez la souris. Pour cela, j'ai décortiqué la localisation et les processus électrophysiologiques engendrés par le récepteur dans les synapses thalamiques constituant la circuiterie thalamo-corticale. Le récepteur mGlu7a s'estavéré essentiel dans le contrôle des rythmes oscillatoires au sein du thalamus, associés à la fois au sommeil (les fuseaux de sommeil) et aux épilepsies de type absence.Ce récepteur était présumé ne fonctionner que lors d'activités neuronales intenses. Cette étude complète ce tableau. Elle met en évidence une activité constitutive du récepteur mGlu7a au sein des synapses excitatrices et inhibitrices. Il exerce donc un frein permanent sur l’entrée de Ca2+ dans les présynapses, un acteur crucial pour le développement du système nerveux, la transmission synaptique, l'excitabilité et la plasticité neuronales. Je montre que cette activitémodule la libération de glutamate et de GABA, mais aussi la plasticité à court terme dans certaines synapses du circuit. De plus, le récepteur mGlu7a limite le tonus inhibiteur au sein du thalamus et ainsi l'excitabilité globale thalamique.De façon surprenante pour un récepteur du glutamate, l'ensemble de ces résultats suggère une action physiologique du récepteur mGlu7a particulièrement impliquée dans le contrôle de l'état d'excitabilité des neurones GABAergiques thalamiques et corticaux. En limitant l'apparition d'activités synchrones au sein de la circuiterie, son action abouti in fine au maintien d'un état conscient de l'individu, nécessaire aux traitements des informations sensorielles, mais aussi à l'apprentissage et la mémoire.

In recent years, discovery of ketamine's fast and powerful antidepressant effects for treatment-resistant depression (TRD) has led to rethinking of the pathophysiology of depression. Numerous studies in humans and animals have focused on mechanisms of action underlying this effect, producing a number of explanatory pathways.The aim of this article is to summarize the various hypotheses underlying rapid antidepressant action of ketamine and therefore to better understand the mechanisms underlying depression and antidepressant action.Ketamine unique antidepressant properties have led to many studies on its neurobiological grounds. Intracellular signaling pathways such as mTOR, GSK3 or eEF2 seem to play a key role and are associated with an increased synaptic plasticity. Other hypotheses are discussed such as ketamine effects on neuro-inflammation, the role of anterior cingulate cortex in brain changes induced by ketamine, and the potential benefits of analgesic properties of ketamine in depressive disorders.Our review highlights the potential role of the glutamatergic system in the pathophysiology and treatment of mood disorders. Understanding which pathways underlie the fast antidepressant effect of ketamine paves the way for the development of new antidepressants.

The knowledge on neurobiology of drug dependence substantially progressed with animal models. All drug of abuse share the effect of an increase of dopamine in nucleus accumbens that contributes to induce dependence. Chronic drug use disrupts numerous neurotransmission systems (glutamate, serotonin, neuropeptides…) and this may participate in relapse. Therapeutic approaches are classified in two types: agonist strategies consist of drug replacement by medicine acting on the same target and strategies using medicines acting on multiple neurotransmission systems.

International audience; Synesthetes, a small fraction of the population, experience systematic, additional associations. For example, they may arbitrarily associate a specific color to each letter or number. Synesthesia has offered for the last ten years to cognitive science a unique opportunity to study the neural bases of subjective experience, drawing on individual differences just like in neuropsychology, but with healthy people. Here we review the current knowledge and propose a new theory, the "palimpsest hypothesis", a variant of the recycling hypothesis for reading. The neural development of written language expertise (a recent cultural invention acquired without any genetic modification) requires indeed the recycling of brain regions predisposed to expertise acquisition into reading regions. The palimpsest hypothesis supposes that for synesthetes recycling involves neuronal networks that were already specialized for color perception. Synesthetic colors would be the remains of this former expertise.

Experiments performed in mammals, including non-human primates, have demonstrated an increase in neuronal death rates normally seen in normal brain development. Such an increase is encountered in diseases but also after exposure of the brain to various class of anaesthetics. In living animals, it can (but not always) result in persistent cognitive impairment. Most of the experiments have been conducted in animals which were never exposed to any pain, which questions their relevancy. On the clinical side, all data comes from retrospective studies. Given the multiple bias, they cannot definitely state that a protocol, if toxic, is more or less when compared to another. Until now, prospective follow-up of children exposed to anaesthetics in utero or during the first months of life do not suggest a major deleterious effect. Yet, a minor one, if existing, would be hard to detect among polluting variables (e.g. pathology requiring anaesthesia, long hospitalization after birth, preterm birth, environmental stress...). For sure, when surgery is mandatory during pregnancy, it is generally for maternal indication and should not be a motif strong enough for foetal extraction, especially in terms where the baby has few chances to survive. Second, it is known for years than anaesthesia before 1 year of age is much riskier than after 1 year, whatever the theorical neurotoxicity is. Third, this enforces the need to develop tools enhancing the precision of anaesthesia as much as possible. Meanwhile, when an infant has undergone numerous general anaesthesias, we strongly recommend a long-time neurological follow-up.

Pain is brought into play by a system which detects and transmits messages signaling pain. Opioids negatively modulate nociception, but paradoxically also contribute to hyperalgesia. A nutritional approach with low polyamine contents helps to reduce this phenomenon without the harmful side effects of antihyperalgesic drugs.

International audience; INTRODUCTION: Many metals like iron (Fe), copper (Cu) or zinc (Zn) fulfil various essential biological functions and are thus vital for all living organisms. For instance, they play important roles in nervous tissue, participating in a wide range of processes such as neurotransmitter synthesis, myelination or synaptic transmission. STATE OF THE ART: As in other tissues, brain cells tightly control the concentration of metals but any excess or deficit can lead to deleterious responses and alter cognitive functions. Of note, certain metals such as Zn, Fe or Cu accumulate in specific brain structures over lifespan and several neurodegenerative diseases are associated with a dysregulation of the homeostatic mechanisms controlling the concentration of these cations. CONCLUSION AND PERSPECTIVES: This review will address some of the cellular and molecular processes controlling the entry and distribution of selected metals (mainly Zn and Fe) in the brain, as well as their roles in synaptic transmission, in the pathogenesis of some neurologic diseases such as Parkinson's disease and Alzheimer's disease, and their impact on cognitive functions.

Mental retardation (MR) occurs in 2 to 3 % of the general population and is still not therapeutically addressed. Milder forms of MR result from deficient synaptogenesis and/or impaired synaptic plasticity during childhood. These alterations would result from disequilibrium in signalling pathways regulating the balance between long term potentiation (LTP) and long term depression (LTD) in certain neurons such as hippocampus neurons. To provide mentally retarded children with increased cognitive abilities, novel experimental approaches are currently being developed to characterize signalling status associated with MR and to identify therapeutic targets that would restore lost equilibrium. Several studies also highlighted the major role played by molecular switches like kinases, phosphatases, small G proteins and their regulators in the coordination and integration of signalling pathways associated with synaptic plasticity. These proteins may therefore constitute promising therapeutic targets for a number of cognitive deficiencies.

Etiological diagnosis of mild cognitive impairment (MCI) or dementia requires combined clinical, neuropsychological, biological and neuro-imaging clues. The diagnostic value of biological and neuro-imaging biomarkers has recently increased according to neuropathological studies. Biomarkers help for making the in vivo diagnosis of underlying histological lesions, sometimes of combined lesions. Sensitivity and specificity of CSF biomarkers, i.e. tau, phospho-tau and amyloid, is now over 85% for Alzheimer's disease (AD) diagnosis at the dementia and MCI stages. Brain MRI can suggest mild AD when depicting medial temporal lobe atrophy. DAT-SCAN(R) is indicated in cases suspected to have Lewy body dementia when parkinsonism is lacking. Metabolism and blood flow impairments observed by PET and SPECT in posterior cortical areas, in particular in posterior cingulate and parieto-temporo-occipital junction, are highly suggestive of AD in atypical cases. International research is currently focalised on research of possible serum biomarkers and neuro-imaging techniques using tracers targeting the specific AD lesions.

Despite the fact that the neurotransmitter dopamine was discovered more than 50 years ago, we still have limited knowledge of its physiological and pathological roles. Recent work has unveiled novel and surprising properties of dopamine neurons and of other key players involved in regulating the dopamine system. For example, the integration of the dopamine signal by its receptors depends on many proteins of diverse signaling pathways and also of other types of receptors that interact with and regulate dopamine receptors: many new promising interactions have been reported during the past few years. Also, we are beginning to discover that chronic treatment with dopamine receptor ligands or other molecules affecting dopaminergic pathways induce long-term molecular, structural and functional rearrangements that could ultimately force us to revisit the mechanism of action of established therapeutic agents. Finally, the discovery of glutamate co-release by dopamine neurons is leading us to reconsider some keys aspects of dopamine neuron physiology.

In the brain of vertebrates, glutamate receptor ion channels (iGluR) mediate fast neurotransmission at excitatory synapses. They exist as distinct subfamilies (AMPA, Kainate and NMDA) differing in their functional properties. Yet, all iGluR are tetramers sharing a common molecular architecture, and a common scheme applies for the general mechanisms of their activation, which are discussed in this review. The dissection of the molecular mechanisms responsible for the operation of iGluR explain how they match their physiological requirements and paves the way to new strategies for pharmacological regulations of these receptors. This could prove useful for the discovery of drugs of therapeutic interest, such as cognitive enhancers, pain killers or anti-psychotics.

In vivo intracellular electrophysiology offers the unique possibility of listening to the "synaptic rumor " of the cortical network, captured by a recording electrode in a single V1 cell. It allows one to reconstruct the distribution of input sources in space and time, i.e. the effective network dynamics. We have used a reverse engineering method to demonstrate the propagation of visually evoked activity through lateral (and feedback) connectivity in the primary cortex of higher mammals. This approach, based on synaptic echography, is compared here with a real-time brain imaging technique based on voltage-sensitive dye imaging. The former method gives access to the microscopic convergence processes of single neurons, whereas the latter describes the macroscopic divergence process on the neuronal map. A combination of the two techniques can be used to elucidate the cortical origin of low-level (non attentive) binding processes participating in the emergence of Gestalt percepts.

Autism is a neurodevelopmental disorder characterized by a deficit of language and communication both associated with a restricted repertoire of activities and interests. The current prevalence of autistic disorder stricto sensu is estimated at 1/500 whereas autism spectrum disorders (ASD) increases up to 1/150 to 1/200. Mental deficiency (MD) and epilepsy are present in numerous autistic individuals. Consequently, autism is as a major public health issue. Autism was first considered as a non biological disease; however various rational approaches for analysing epidemiological data suggested the possibility of the influence of genetic factors. In 2003, this hypothesis was clearly illustrated by the characterization of genetic mutations transmitted through a mendelian manner. Subsequently, the glutamate synapse appeared as a preferential causal target in autism because the identified genes encoded proteins present in this structure. Strikingly, the findings that an identical genetic dysfunction of the synapse might also explain some MD suggested the possibility of a genetic comorbidity between these neurodevelopmental conditions. To date, various identified genes are considered indifferently as "autism" or "MD" genes. The characterization of mutations in the NLGN4X gene in patients with Asperger syndrome, autism without MD, or MD without autism, was the first example. It appears that a genetic continuum between ASD on one hand, and between autism and MD on the other hand, is present. Consequently, it is likely that genes already involved in MD will be found mutated in autistic patients and will represent future target for finding new factors in autism.

Conceptual advances about chemical neurotransmission during the last 40 years have benefited a lot from histocytochemical approaches and from a particular experimental model, the endocrine hypothalamic neurons. New concepts like cotransmission, neuronal versatility, somatodendritic release of neurotransmitters, volume transmission, differential routing or cooperative synthesis of mediators, have often been issued from this set of methodologies and from their application to neurosecretory neurons. This review, mainly based on the results of our group, is aiming at illustrating how the peculiar metabolism of these neurons and their location at the neuro-endocrine interface have allowed discovering new aspects of neurotransmission, first considered as exceptions but then generalized to the whole nervous system. These new concepts shed lights on the normal functioning of the brain and definitely contribute to diversify pharmacological approaches of pathological neurotransmission.

Thrombolysis remains the main therapeutic strategy used in stroke, but with a limited use to only a part of stroke patients. A neuroprotective approach would be necessary with a double objective : (1) to serve as an add-on treatment with thrombolysis to improve safety and increase therapeutic window ; (2) to limit infarct area by delaying neuronal death. While numerous molecules failed in clinical trials in stroke, pharmacological development is on-going with pleiotropic drugs targeting both neuronal and vascular parts of neurovascular unit. Another approach targets the functional rehabilitation and the neurorepair using pharmacological ways or cell therapy.

The skeletal neuromuscular junction has been considered as a model of chemical synapses due to its relatively simple organization. It is made up of three cellular partners including the motoneuron nerve terminals, the peri-synaptic Schwann cells and a specialized region of skeletal muscle fibers. It has been extensively studied revealing its ultrastructural complexity involving many molecular actors. The neuromuscular junction is a highly specialized structure, optimized for the rapid transmission of information from the presynaptic nerve terminal to the post-synaptic muscle fiber. This rapid transmission requires a very close apposition of plasmic membranes of pre- and post-synaptic partners, and a strict structural and molecular arrangement on both sides of the narrow synaptic cleft separating nerve terminal and muscle membranes. In this short review, we summarize the knowledge regarding pre- and post-synaptic ultrastructural specializations and give an overview of some functional aspects of neuromuscular transmission, including the quantal acetylcholine release process, which will help to better understand the pharmacological actions of botulinum toxins in esthetic and corrective dermatology.

Several bacteria of the Clostridium genus (C. botulinum) produce 150 kDa di-chainal protein toxins referred as botulinum neurotoxins or BoNTs. They associate with non-toxic companion proteins and form a complex termed botulinum toxin. BoNTs specifically inhibit vesicular neurotransmitter release. The cellular action of BoNTs can be depicted according to a multi-step model : The toxin's heavy chain mediates binding to specific receptors comprised of a ganglioside moiety and a vesicular protein (SV2 for BoNT type A, synaptotagmin for BoNT type B), followed by endocytotic internalisation of the BoNT/receptor complex. Vesicle recycling induces BoNT internalisation. Upon acidification of vesicles, the light chain of the neurotoxin is translocated into the cytosol. Here, this zinc-endopeptidase cleaves one or two among three synaptic proteins (VAMP-synapto-brevin, SNAP25, and syntaxin). As the three protein targets of BoNT play major role in fusion of synaptic vesicles at the release sites, their cleavage is followed by blockade of neurotransmitter exocytosis. Importantly, as the BoNT receptors and intracellular targets are present in all nerve terminals, the BoNTs are not specific for cholinergic transmission. Duration of their inhibitory action is mainly determined by the the life-time of the toxin's light chain in the cytosol. Sprouting of new nerve-endings, which are retracted when the poisoned nerve terminals have recovered full functionality, may lead to anticipated recovery of the poisoned nerve terminals.

Botulinum toxin is a multi-molecular complex comprised of a neuro-active moiety (i.e. botulinum neurotoxin) and several associated non-toxic proteins. The toxin dissociates rapidly at plasmatic pH, thereby releasing neurotoxin. Nerve terminals only take up the neurotoxin. In the peripheral nerve system, the neurotoxin mainly blocks acetylcholine release. When acting at the neuromuscular junctions, this results in paralysis of the muscle fibers. The duration of the neurotoxin action is mainly determined by the life-time of neurotoxin molecules inside the nerve terminals. Inhibition of cholinergic transmission induces rapid atrophy of the muscle fibres, and, sometimes, sprouting from poisoned nerve terminals. These effects, as well as the acetylcholine release blockade are entirely reversible. When injected in the periphery, a direct action of botulinum neurotoxin in the central nervous system remains unlikely despite its retrograde ascent demonstrated in animal models. However, indirect effects are numerous. The constituting proteins of the toxin complex can lead to immunisation against the non-toxic associated proteins and neurotoxin. Only the antibodies directed against neurotoxin are potentially neutralizing.

Gait disorders form part of the axial symptoms observed in Parkinson's disease (PD) and also represent a major source of therapeutic failure in the later stages of PD, with the appearance of freezing of gait (FOG) and falls. Double-blind clinical trials and, above all, clinical experience have demonstrated that l-DOPA is effective in reducing FOG. Dopaminergic agonists appear to be less effective than l-DOPA and lack formal proof of their efficacy. The enzyme inhibitors provide modest benefits, which need to be confirmed. Hence, these symptoms appear to be partially doparesistant and justify investigation of other major neurotransmission systems. Of the various drugs with partial noradrenergic activity, methylphenidate may improve FOG and attention disorders. Memantine has shown some value in improving motor symptoms and gait in fluctuating parkinsonian patients - possibly by reducing the effect of glutamatergic hyperactivation of the subthalamic nucleus on the pedunculopontine nucleus (PPN). The PPN's dense cholinergic innervation also suggests that cholinesterase inhibitors may be of use, although any benefits must be set against a potential aggravation of rest tremor. The many interactions between the serotoninergic and dopaminergic systems require the implementation of clinical studies on the complex motor impact of serotoninergic treatments, which may aggravate the parkinsonian syndrome while improving gait (as is the case with paroxetine and ritanserin). This review seeks to develop the various pathophysiological hypotheses prompted by the results of fundamental studies and pilot clinical trials, with a view to justifying the implementation of confirmatory, double-blind, placebo-controlled therapeutic trials.

Le réseau neuronal de l’hippocampe joue un rôle central dans la mémoire en modifiant de façon durable l’efficacité de ses synapses. Dans les interneurones de la couche oriens/alveus (O/A), l’induction de la potentialisation à long terme (PLT) requiert les courants postsynaptiques excitateurs évoqués par les récepteurs métabotropes du glutamate de sous-type 1a (CPSEmGluR1a) et l’entrée subséquente de Ca2+ via des canaux de la famille des transient receptor potential (TRP). Le but de ce projet était d’identifier les canaux TRP responsables des CPSEmGluR1a et d’explorer les mécanismes moléculaires régulant leur ouverture. Nous avons déterminé par des enregistrements électrophysiologiques que les CPSEmGluR1a étaient spécifiques aux interneurones O/A et qu’ils étaient indépendants de la phospholipase C. Nous avons ensuite examiné l’expression des TRPC et leur interaction avec mGluR1a par les techniques de RT-PCR, d’immunofluorescence et de co-immunoprécipitation. Nos résultats montrent que TRPC1 et mGluR1a s’associent dans l’hippocampe et que ces deux protéines sont présentes dans les dendrites des interneurones O/A. En revanche, TRPC4 ne semble s’associer à mGluR1a qu’en système recombinant et leur colocalisation paraît limitée au corps cellulaire. Finalement, nous avons procédé à des enregistrements d’interneurones dans lesquels l’expression des TRPC a été sélectivement supprimée par la transfection d’ARN interférant et avons ainsi démontré que TRPC1, mais non TRPC4, est une sous-unité obligatoire du canal responsable des CPSEmGluR1a. Ces travaux ont permis de mieux comprendre les mécanismes moléculaires à la base de la transmission synaptique des interneurones O/A et de mettre en évidence un rôle potentiel de TRPC1 dans la PLT., The hippocampal neuronal network plays a crucial role in memory by producing long lasting changes in the efficacy of its synapses. In interneurons of stratum oriens/alveus (O/A), long term potentiation (LTP) induction requires metabotropic glutamate receptor subtype 1a (mGluR1a)-evoked excitatory postsynaptic currents (EPSCs) and subsequent Ca2+ entry through transient receptor potential (TRP) channels. The objectives of this project were to identify the TRP channels that mediate mGluR1a-evoked EPSCs and to explore molecular mechanisms that underlie their activation. Electrophysiological recordings showed that mGluR1a-evoked EPSCs were specifically observed in O/A interneurons and they were phospholipase C-independent. We then examined TRPC expression and their interaction with mGluR1a by RT-PCR, immunofluorescence and co-immunoprecipitation techniques. Our results show that TRPC1 and mGluR1a associate in hippocampus and that both proteins have overlapping distributions in dendrites of O/A interneurons. In contrast, TRPC4 seems to associate with mGluR1a only in recombinant system and their co-localization appears to be limited to the cell body. Finally, we performed recordings of interneurons in which TRPC expression was selectively suppressed by small interfering RNAs and we found that TRPC1, but not TRPC4, is an obligatory subunit of the channel that mediate mGluR1a-evoked EPSCs. This work brought new insight on molecular mechanisms underlying synaptic transmission of O/A interneurons and uncovered a potential role for TRPC1 in LTP.

The diagnosis of myasthenia gravis is above all clinical, however electroneuromyography (ENMG) and laboratory tests can be helpful. ENMG testing is readily available and with immediate results. Useful with emergent symptoms, it is equally so in the event of more acute pictures found in generalized motor deficit and bulbar findings of respiratory failure. It can be performed in out-patient clinics or at the bedside. ENMG is based on an assessment of repetitive nerve stimulations (RNS), which can be sensitized, and more rarely on jiter studies using single-fiber electromyography (SFEMG). RNS recordings from multiple sites, depending on symptoms, are preferable. The usefulness of these tests varies depending on the clinical situation, not only for diagnosis but also during follow-up, in order to obtain objective evidence of the effects of treatment.

The D2 dopamine receptors play a pivotal role in the physiopathology of schizophrenia. Their over-stimulation in the limbic area, resulting from a hyperactivity of the mesolimbic dopaminergic neurones, is linked to positive expressions of the disease, whereas their lack of stimulation in cortical regions, depending on a hypoactivity of mesocortical dopaminergic neurones, underlies the negative expressions of the disease. Concerning the extrapyramidal side effects which emanate from treatments by neuroleptic drugs, they are triggered by the blockade of nigro-striatal dopaminergic transmissions. The ligands of D2 dopamine receptors can be characterized by their intrinsic activity (alpha). Dopamine, which is their physiological ligand, is a full agonist (alpha=1). On the contrary, neuroleptic drugs, by suppressing the constitutive activity of these receptors (spontaneous activity even without occupation by dopamine) are inverse agonists (alpha0). Thus, they not only oppose the effects of dopamine but they also induce diametrically opposed effects. Between these extremes, are located the partial agonists, the so-called agonists-antagonists (1alpha0-1), illustrated by OPC 14597=aripiprazole. This partial agonist, by stimulating D2 and D3 dopamine autoreceptors, moderates the functioning of hyperactive dopaminergic neurones. In addition, by taking the place of dopamine on D2 post-synaptic receptors, it changes their intense stimulation into a lesser one, which reduces positive expressions (delusions, hallucinations, agitation...). On the other hand, the occupation by aripiprazole of the D2 receptors that are not stimulated by dopamine (on account of an insufficient presynaptic dopaminergic activity) restores a certain amount of stimulation, which partly alleviates negative expressions of schizophrenia. Simultaneously to these actions, both on productive as well as on negative expressions of the disease, this agonist-antagonist is virtually devoid of several adverse effects developed by neuroleptic drugs (extrapyramidal side effects) and new antipsychotic drugs (hyperprolactinemia, sedation, late dyskinesia, modifications in thermoregulation, bulimia, overweight, depression...).

The ketogenic diet is a high-fat, low-protein, low-carbohydrate diet that has been employed as a nonpharmacologic therapy for intractable epilepsy. Several multicenter or randomized studies have demonstrated the anticonvulsive properties of the ketogenic diet. The reports on the clinical efficacy have described a greater than 50% reduction in seizure frequency for about 60% of patients on a ketogenic diet. Efficacy has been reported both for child-teenager and adult patients. Patients who were responders to the ketogenic diet exhibited a decrease in seizure frequency within two months of treatment onset. Underlying mechanisms remain unknown. The current hypotheses are: anticonvulsive properties of ketone bodies, variation in excitatory or inhibitory brain neurotransmissions, modulation of cell excitability or implication of polyunsaturated fatty acids. Ketogenic diet is a fastidious and restrictive therapy. Moreover, side effects have been reported. In order to facilitate patient tolerability and palatability, the diet protocols are gradually modified including changes in ratios of the fat versus non fat components, initiation of the diet with or without fasting, fatty acids composition. A modified Atkins diet seems to be a possible alternative diet with a comparable efficacy on intractable epilepsy. This diet induces ketosis without fluid, calorie or protein restriction, nor the requirement for fasting and food weighing. Furthermore, 10 to 20 grams carbohydrates are allowed per day to increase patient tolerability and palatability. New data suggest that ketogenic diet and its variants should not be considered like a "last chance" treatment.

ICU-acquired neuromyopathy (NMAR) and delirium are the two most frequent and severe neurological complications of intensive care medicine. Their mechanisms still remain to be elucidated. The objective of this review is to address the potential role of sedation in occurrence of these complications. There is no evidence that sedation is involved in NMARs. However, the hypothesis that muscle inactivity induced by sedation fosters NMAR is an argument to discontinue or reduce sedatives infusion whenever possible. It is also recommended not to administer propofol more than 48 h at an infusion rate above 5 mg/kg per hour in patients with systemic inflammatory response syndrome, because of the risk of propofol infusion syndrome, which includes notably rhabdomyolysis. The relationship between delirium and sedation are controversial because in most studies, patients were considered delirious though being still sedated and multivariate analysis was lacking. One study showed that lorazepam given continuously was an independent risk factor for daily transition to delirium 24 h later with a 20% increase risk of every unit dose (expressed as log(e)mg). The impact of deepness, daily interruption or titration of sedation on the prevalence of delirium has never been assessed but it seems that deep sedation has to be avoided.