L’élément constitutif des synapses centrales est le site synaptique individuel, comprenant une zone active du côté présynaptique et une densité postsynaptique associée. Du fait de limitations techniques nos connaissances sur le mode de fonctionnement d’un site synaptique restent insuffisantes. Pour faire progresser cette question nous projetons d’effectuer des enregistrements en paires entre interneurones de la couche moléculaire du cervelet. Ces neurones forment des synapses qui ont des signaux élémentaires quantiques de grande taille, et les synapses comprennent parfois un seul site synaptique, ce qui fait qu’ils offrent des avantages décisifs pour ce projet. Les réponses postsynaptiques à des trains de potentiels d’action seront étudiées dans différentes conditions expérimentales. Les résultats seront interprétés par un modèle supposant que les vésicules synaptiques doivent se lier à un petit groupe de sites d’arrimage avant l’exocytose. / The unitary element of central synaptic transmission is a single synaptic site, with one active zone as presynaptic component and the postsynaptic density as postsynaptic partner. Due to technical limitations there is much uncertainty on the mode of functioning of a single synaptic site. To address this issue it is planned to perform paired recordings between interneurons of the molecular layers of the cerebellum. These neurons form synapses with a large quantal size, and occasionally displaying a single release site, and are thus favorable for this study. Postsynaptic responses will be studied in response to trains of presynaptic action potentials under various conditions. The results will be compared to a model supposing the obligatory binding of vesicles to a small complement of docking sites prior to exocytosis.

No / Acute administration of the psychotomimetic phencyclidine (PCP) can mimic some features of schizophrenia, while a repeated treatment regimen of PCP may provide a more effective way to model in animals the enduring cognitive dysfunction observed in many schizophrenic patients. The present study aims to investigate behavioural and neuropathological effects of sub-chronic PCP administration. The cognitive deficit induced by sub-chronic PCP was examined using a previously established operant reversal-learning paradigm. Subsequently, the effect of sub-chronic PCP on parvalbumin-immunoreactive (parvalbumin-IR) neurons was assessed using immunohistochemical techniques. Rats were trained to respond for food in an operant reversal-learning paradigm for approximately 6 weeks, followed by sub-chronic administration of PCP (2mg/kg) or vehicle twice daily for 7 days followed 7 days later by behavioural testing. Six weeks post PCP, brains were analysed using immunohistochemical techniques to determine the size and density of parvalbumin-IR in the frontal cortex and hippocampus. Sub-chronic PCP significantly reduced (p <0.001) percentage correct responding in the reversal phase relative to the initial phase, an effect that persisted throughout the experimental period (4 weeks). The density of parvalbumin-IR neurons was reduced in the hippocampus, with significant reductions in the dentate gyrus and CA2/3 regions (p <0.001). There were significant changes in the frontal cortex, with a reduction (p <0.01) in the M1 (motor area 1) region and increases in the M2 (motor area 2) region and cingulate cortex (p <0.01-p <0.001). These results parallel findings of profound hippocampal and more subtle cortical deficits of parvalbumin-IR neurons in schizophrenia, and provide evidence to suggest that sub-chronic PCP can induce a lasting cognitive deficit, an effect that may be related to the observed neuronal deficits.

Die Neurone des Neokortex lassen sich in exzitatorische und inhibitorische Neurone unterteilen. Bei den inhibitorischen Neuronen, die 20-30% der Neurone ausmachen, handelt es sich um GABA freisetzende Interneurone, die anhand ihrer morphologischen, elektrophysiologischen und molekularen Merkmale voneinander unterschieden werden können. Man unterscheidet drei große Gruppen von GABAergen Interneuronen, die Parvalbumin (PV)-exprimierenden, die Somatostatin (SOM)-exprimierenden und die ionotropen Serotonin-Rezeptor 5HT3a-exprimierenden Interneurone. Die 5HT3a-Rezeptor-exprimierenden Interneurone stellen eine sehr heterogene Gruppe dar und bestehen zu 40% aus vasoaktives intestinales Polypeptid (VIP)-exprimierenden Interneuronen. Für die vorliegende Studie wurde die transgene VIPcre/tdTomato-Maus verwendet, die mit Hilfe der Cre/loxP-Technik generiert wurde. In dieser Maus sollten VIP-exprimierende Zellen mit dem fluoreszenten tdTomato-Protein markiert sein. Ziel der vorliegenden Arbeit war es, die VIP-exprimierenden Neurone im somatosensorischen Kortex (Barrel-Kortex) mittels Immunhistochemie und Fluoreszenz-in-situ-Hybridisierung neurochemisch zu charakterisieren. Dafür wurden die Proteine vasoaktives intestinales Polypeptid, Somatostatin, Parvalbumin, Glutamatdecarboxylase (GAD 67) und der vesikuläre Glutamattransporter 1 (VGLUT1) als zu identifizierende molekulare Bestandteile genutzt. Ferner konnten Aussagen über die Zelldichte und Zellverteilung von VIP/tdTomato-positiven Zellen in den Schichten I-VI des Barrel-Kortex getroffen werden, um eine schichtenspezifische Charakterisierung der VIPcre/tdTomato-Maus durchzuführen. Außerdem wurde nach möglichen Kolokalisationen zwischen VIP und SOM und VIP und PV gesucht. Durch den Einsatz der Sonden Gad1 und Vglut1 konnten Rückschlüsse auf die exzitatorischen bzw. inhibitorischen Eigenschaften von VIP-exprimierenden Interneuronen gezogen werden. Durch den Einsatz zweier verschiedener VIP-Antikörper und einer Vip-Sonde konnte nachgewiesen werden, dass es sich bei den tdTomato-fluoreszenten Zellen tatsächlich um VIP-exprimierende Interneurone handelt. Zwischen den VIP/tdTomato-positiven Zellen und dem PV-Antikörper bzw. der Pvalb-Sonde wurde niemals eine Kolokalisation nachgewiesen. Für den SOM-Antikörper bzw. die Sst-Sonde konnte nur eine ganz geringe Anzahl an Kolokalisationen mit den VIP/tdTomato-Zellen gezeigt werden. Dadurch bestätigt sich, dass es sich bei der VIPcre/tdTomato-Maus um ein verlässliches Mausmodell zur Untersuchung von VIP-exprimierenden Interneuronen handelt. Die Vglut1-Sonde hatte niemals eine VIP/tdTomato-Zelle markiert, wodurch sich exzitatorische Eigenschaften der VIP-Zellen nicht nachweisen ließen. Hingegen markierte die Gad1-Sonde den Großteil aller VIP/tdTomato-Zellen, wodurch sich bestätigen lässt, dass es sich bei den VIP-exprimierenden Interneuronen um inhibitorische GABAerge Interneurone handelt. Die größte Population an GABAergen Interneuronen in der VIPcre/tdTomato-Maus stellen die PV-exprimierenden Interneurone dar. In den Schichten IV und Vb wurden die meisten PV-positiven Zellen nachgewiesen. Die SOM-exprimierenden Interneurone stellen die zweitgrößte Zellpopulation dar. Die meisten SOM-positiven Zellen befinden sich in den neokortikalen Schichten Vb und VI. Bei den VIP-exprimierenden Interneuronen konnte die größte Anzahl an Zellen in Schicht II/III gefunden werden.

La mise en place des circuits neuronaux fonctionnels se construit autour d'une grande diversité cellulaire et nécessite l'accomplissement d'une série d'évènements complexes incluant la prolifération, la migration, la différenciation, le guidage axonal, la reconnaissance cellulaire et la synaptogenèse des progéniteurs neuronaux. Dans le cervelet, les interneurones GABAergiques de la couche moléculaire (IGCM) s‘intègrent au cours des deux premières semaines post-natales et se différencient en deux sous-types cellulaires, les cellules en panier (CP) qui innervent le segment initial de la cellule de Purkinje, cellule principale du cervelet, et les cellules étoilées qui innervent l'arbre dendritique de la cellule Purkinje. Bien que ces deux types cellulaires possèdent des morphologies distinctes et innervent des sous-domaines cellulaires spécifiques, aucun marqueur moléculaire ne permet de les discriminer. Depuis près d'un siècle, la controverse existe concernant leur identité et deux théories s'affrontent. La première suggère que ces deux cellules sont des variantes issues d'un même progéniteur et que les différences morphologiques sont dues à un changement progressif de l'environnement cellulaire alors qu'une autre hypothèse suggère que ces deux cellules proviennent de progéniteurs neuronaux différents. Au cours de ma thèse j'ai étudié l'intégration des IGCM au sein de la couche moléculaire (CM) en caractérisant deux étapes clés de la formation des circuits GABAergiques, la migration et l'innervation de leur cible. En utilisant une combinaison de techniques telles que la microscopie bi-photonique et les greffes in vivo de progéniteurs neuronaux, j'ai mis en évidence que durant la première semaine post-natale, les IGCM quittent leur lieu de naissance pour rejoindre la CM en réalisant une seule étape de migration radiale. De manière intéressante certains IGCM accomplissent une étape de migration supplémentaire inédite tangentiellement à la surface piale pendant la deuxième semaine post-natale. Cette nouvelle phase de migration tangentielle des IGCM se déroule au sein de la couche granulaire externe où résident les cellules granulaires pré-migratoires dont les fibres qui expriment TAG-1 jouent un rôle essentiel en tant que support physique et participent à l'établissement des IGCM en mode “inside-out”. De plus, nos résultats suggèrent que seule une sous-population de type cellule étoilée effectuerait cette étape supplémentaire, montrant ainsi une première divergence dans le processus de maturation des IGCM. Par la suite, je me suis intéressée à l'innervation des cellules de Purkinje par les CP nouvellement différenciées. En utilisant des techniques d'immuno-histochimie, j'ai tout d'abord montré que la Neuropiline-1 (NRP1), un des récepteurs de la Sémaphorine-3A, était exprimé au niveau des terminaisons axonales des CP. Enfin, grâce à l'analyse d'un mutant conditionnel pour NRP1, j'ai pu mettre en évidence qu'en plus de son rôle crucial dans le guidage axonal des CP, NRP1 est également impliquée dans l'innervation spécifique du segment initial axonal des cellules de Purkinje en interagissant avec une molécule d'adhésion cellulaire de la famille L1CAM, la Neurofascine. Ces résultats démontrent pour la première fois un rôle de NRP1 dans la transition entre l'étape de guidage avec celle de la reconnaissance cellulaire par les CP. En conclusion, nos résultats suggèrent fortement que les deux sous-types d'IGMC possèdent un programme génétique spécifique leur permettant de s'intégrer de manière unique au sein de la CM. / The establishment of functional neural circuits is built around a large cell diversity and requires the completion of a series of complexe events including proliferation, migration, differentiation, axon guidance, cell recognition and synaptogenesis of neural precursors. In the cerebellum, molecular layer GABAergic interneurons (MLGI) reach their final location during the first two post-natal weeks and differentiate into two cellular subtypes, the basket cells (BC) that innervate the Purkinje cell initial segment and the stellate cells that innervate the dendritic tree of the Purkinje cell, the principal cell of cerebellar cortex. Although these two cell types have distinct morphologies and innervate specific subcellular domains, no molecular marker allows to discriminate between them. For nearly a century, controversy exists concerning their identity and two theories exist. The first one suggests that these two cell types are variants derived from a single progenitor and that morphological divergence is due to a gradual change in the cellular environment while the other hypothesis suggests that these two cell types come from different progenitors. During my thesis, I studied the integration of the MLGI in the molecular layer (ML) characterizing two key steps in the formation of GABAergic circuits, migration and innervation of their target. Using a combination of techniques such as two-photon microscopy and in vivo transplantation of neural progenitors, I highlighted that during the first post-natal week, MLGI leave their birthplace to join the ML by performing a single radial migration step. Interestingly, some MLGI perform an unexpected additional migration step tangentially to the pial surface during the second post-natal week. This new phase of MLGI tangential migration takes place in the external granule cell layer where resident pre-migratory granule cells whose fibers expressing TAG-1 play an essential role as physical support and participate in the establishment of MLGI « inside-out » mode. In addition, our results suggest that only a stellate-like subpopulation would perform this extra step, bringing the first indication of an early divergence during MLGI maturation process. Then, I was interested in the innervation of Purkinje cells by newly differentiated BC. Using immunohistochemistry experiments, I first showed that Neuropilin-1 (NRP1), a Semaphorin-3A receptor, was expressed in the BC axon terminals. Finally, through the analysis of a NRP1 conditional mutant, I brought out that, in addition to its critical implication in axon guidance, NRP1 is also involved in the specific innervation of the Purkinje cell axon initial segment by interacting with a cell adhesion molecule belonging to the L1 family, Neurofascin. These results demonstrate for the first time a role of NRP1 in the transition between the guidance and the cell recognition steps by BC. In conclusion, our results strongly support that the two MLGI subtypes have a specific genetic program allowing them to integrate within the ML in a unique manner.

No description available.

Les Sémaphorines de classe 3 modulent de nombreux comportement neuritiques lors de la formation du système nerveux central. Leur liaison sur des complexes récepteurs composés de la sous unité obligatoire de liaison au ligand, les Neuropilines1,2 (Nrp1,2) et de la sous unité de signalisation, les PléxinesA1-4, permet d'assurer la spécificité fonctionnelle. Cependant, les mécanismes moléculaires contrôlant la formation de ces complexes récepteurs ne sont pas connus. Au cours de ma thèse, j'ai étudié l'assemblage des complexes récepteurs des Sémaphorines de classe 3 par une approche FRET. J'ai pu montrer que Nrp1,2 forment des homo et hétéro-oligomères à la membrane plasmique. Nrp1 peut former des hétero-oligomères avec les PléxinesA1,2 et 4 mais apparemment pas avec PléxineA3. La délétion du domaine Séma de PléxineA3 (PléxinesA3∆sem) suffit pour induire la formation d'hétéro-complexes Nrp1-PléxinesA3∆sem. Ces résultats suggèrent que le domaine Séma de PléxineA3 adopte une conformation différente des autres PléxinesA et empêche l'interaction entre PléxineA3 et Nrp1. De plus, toutes les PléxinesA peuvent former des homo-oligomères de manière indépendante du domaine Séma. Ces résultats suggèrent que les récepteurs des Sémaphorines de classe 3 pourraient former des complexes oligomériques plus important, composés d'homo-dimères de Nrps et de PléxinesA. Dans la deuxième partie de ma thèse, j'ai étudié la spécificité de signalisation des PléxinesA dans les interneurones GABAergiques du cervelet. Au laboratoire, nous avons montré que Séma3A induit la formation de branches des interneurones GABAergiques du cervelet par l'intermédiaire de Fyn. Mais l'identité des complexes récepteurs Séma3A impliquée dans ce processus n'était pas connue. Nous avons montré que les interneurones GABAergiques expriment PléxineA1,A2 A3 mais pas A4. Alors que les PléxinesA1,2 et 3 interagissent avec la protéine Fyn, seule l'activation des voies de signalisation de PléxineA1 et A2 induit la formation de branches in vitro. De manière intéressante, Fyn interagit avec les PléxinesA1 et A2 via son domaine SH3 alors qu'elle utilise son domaine SH2 pour l'interaction avec PléxineA3, suggérant l'importance du mode d'interaction de Fyn avec les PléxinesA pour sa fonction. Enfin nous avons pu montrer que PléxineA1 est la seule Pléxine in vivo capable d'induire un défaut de formation de branches des interneurones GABAergiques du cervelet. / Secreted class 3 Semaphorin (Sema3) modulates a wide variety of axon behavior during central nervous system formation. Sema3 family functions are triggered through binding to specific receptor complexes that include the obligate binding subunit Neuropilins-1 and 2 (Nrp1-2) and the signalling subunit plexin-A1-4. Yet, the exact mechanism controlling Sema3 receptor complex formation is not known. Here, we investigate Sema3 cell surface receptor formation using a time resolved FRET approach. We showed that Nrp-1 and 2 formed homo and hetero-oligomers at the cell surface of leaving cells. Nrp-1 can form hetero-oligomers with PlexinA1, A2 and A4 but not with PlexinA3. Deletion of the Plexin-Sema domain of PlexinA3 (PlexinA3∆sem) induced the formation of Nrp1 and PexinA3∆sem hetero-complexes. These results showed that PlexinA3-sema domain adopts a different conformation from the other PlexinAs and inhibited the interaction with Nrp1. Furthermore, PlexinAs can form homo-oligomers independently of the Plexin-Sema domain. These results further suggest that Sema3 receptors could form higher oligomeric complex that include homodimers of both neuropilins and PlexinAs. Understanding the basic principles of Sema3 receptor assembly will be pivotal to decipher how ligand binding translates into specific pathways of cellular signaling. In the second part of my thesis we investigated PlexinA specific signaling in cerebellar GABAergic interneurons. Sema3A induced GABAergic axonal branching in cerebellar cortex in a Fyn dependent manner (Cioni et al.,2013). However the identity of Sema3A receptor complexes involved in this process needed further investigation. We showed that PlexinA1, A2 and A3, but not PlexinA4, are expressed in GABAergic interneurons. While PlexinA1-3 are associated with FYN, only PlexinA1 and A2 induced axon branching. Interestingly, Fyn interaction with PlexinA1 and A2 is mediated via the SH3 domain while the interaction with PlexinA3 is through the SH2 domain, suggesting that the binding mode of Fyn to PlexinA is important. These results were further supported by in vivo characterization of PlexinA1-4 deficient mice that showed GABAergic axon branch deficit only in PlexinA1 mutant.

No description available.

No description available.

A sinalização muscarínica exerce função modulatória sobre diferentes aspectos da cognição e emoções. Todos os cinco subtipos de receptores muscarínicos (mAChR), M1 a M5, são expressos no hipocampo de mamíferos e são ativados de forma sobreposta pela maioria dos fármacos, dificultando avanços significativos na compreensão da contribuição de cada componente desse sistema. A toxina muscarínica 3 (MT3) é um antagonista seletivo para o subtipo M4, permitindo a investigação das ações modulatórias deste receptor no aprendizado, memória e plasticidade sináptica. Os M4 são receptores acoplados à proteína G (GPCRs) que atuam via Gi/o desencadeando efeitos inibitórios sobre as células em que estão presentes. Estudos comportamentais anteriores indicam que a administração de MT3 imediatamente após o treino em uma tarefa aversiva produz efeito amnéstico, enquanto que a administração antes da evocação, causa facilitação. Uma explicação para estes resultados é que os circuitos locais envolvidos na consolidação e na evocação da memória diferem em sua natureza. Nesse contexto, sugere-se que o efeito amnéstico da MT3 sobre a consolidação seja consequência da supressão da inibição de interneurônios GABAérgicos; enquanto que na evocação, esse efeito se daria sobre as sinapses glutamatérgicas. Assim, no presente trabalho, com o objetivo de investigar como o receptor M4 modula a plasticidade sináptica de longa duração e interage com uma dessas sinalizações, no caso a GABAérgica, utilizou-se a técnica de eletrofisiologia in vivo de hipocampo de ratos anestesiados. Para tanto, foram realizados registros extracelulares do potencial excitatório pós-sináptico de campo (fEPSP) de CA1 evocados por estimulação contralateral da via Colateral de Schaffer com infusão dos fármacos 15 min antes ou depois da estimulação elétrica de alta ou baixa frequência (HFS: 10 trens 0,5 Hz, 20 pulsos 100 Hz; ou LFS: 600 pulsos 1 Hz, respectivamente). MT3 (4,0 μg/μl), bicuculina (0,06 μg/μl), baclofen (0,2 μg/μl) e veículo, isoladamente ou combinados, não alteraram a amplitude da resposta evocada basal ou a facilitação por pulso pareado (FPP) 15 min após a infusão. MT3 aparentemente atenuou, mas não de forma significativa, a potenciação de longa duração (LTP) em relação ao controle (potenciação 60 min após a HFS de 31,8% e 66,0%, respectivamente). Além disso, não houve diferença significativa entre a amplitude do fEPSP no período basal e 60 min após a HFS sob ação da MT3. Bicuculina, embora não tenha abolido a LTP e nem causado alteração na FPP, produziu uma potenciação de apenas 36,4%. Baclofen promoveu uma potenciação semelhante à dos controles. A administração de baclofen também reduziu significativamente a FPP em relação ao basal. A administração conjunta de MT3 com bicuculina ou baclofen promoveu uma potenciação semelhante ao controle. MT3 não apresentou efeito sobre a manutenção da LTP quando aplicada 15 min após a HFS. Por fim, não foi possível induzir a depressão de longa duração (LTD) com o protocolo de LFS utilizado. Embora não tenha ocorrido diferença estatisticamente significativa entre os grupos devido ao baixo número de animais utilizados, os dados sugerem a possibilidade de uma amplitude reduzida da LTP quando da injeção de bicuculina. Baclofen alterou a FPP em relação ao fEPSP basal, o mesmo não tendo sido observado no grupo controle. Com a administração concomitante de MT3, tais alterações deixam de ser identificadas. Ainda que os achados experimentais sejam inconclusivos e preliminares, este trabalho permitiu a padronização da técnica de eletrofisiologia in vivo em animal anestesiado o que abre portas para futuras investigações. / The cholinergic muscarinic system exerts modulatory function over different aspects of cognition and emotion. All five muscarinic receptors subtypes (mAChR), M1 to M5, are expressed at mammals hippocampus and at least two of them are simultaneously activated by most of the drugs, hindering significant advances on the role of each component of this system. The muscarinic toxin 3 (MT3) is a selective antagonist for the M4 subtype, allowing the investigation of the modulatory actions of this receptor over learning, memory and synaptic plasticity. The M4 are G protein coupled receptors (GPCRs) that act through Gi/o triggering inhibitory effects on which cells they are occur. Previous behavioral studies have shown that administration of MT3 soon after aversive task training exerts amnestic effects over memory, while administration prior to recall, leads to facilitation. A possible explanation to these results could be that the local circuits involved on memory consolidation and recall are different in nature. On this perspective, the amnestic effect of MT3 over memory consolidation should be consequence of GABAergic interneurons inhibition suppression; while the effect on recall, should be over glutamatergic synapses modulation. Thereby, the present work, with the objective to investigate how the M4 receptor modulates long-term synaptic plasticity and interacts with the GABAergic system, in vivo electrophysiological approach of anesthetized rats’ hippocampus was applied. Hence, field excitatory postsynaptic potentials (fEPSP) from CA1 were recorded after stimulation of contralateral Schaffer Collateral pathway with drugs infusion 15 min before or after high or low frequency electric stimulation (HFS: 10 trains 0.5 Hz, 20 pulses 100 Hz; LFS: 600 pulses 1 Hz, respectively). Neither MT3 (4.00 μg/μl), bicuculline (0.06 μg/μl), baclofen (0.20 μg/μl) nor vehicle, isolated or combined, changed the baseline evoked response amplitude 15 min after infusion nor the paired-pulse facilitation ratio (PPF). MT3 apparently attenuated, but not significantly, the long-term potentiation (LTP) compared to control (31.8% and 66.0% potentiation 60 min after HFS, respectively). In addition, there was no significant difference between baseline and 60 min after HFS fEPSP amplitude at MT3 group. Bicuculline, although did not abolish LTP neither changed PPF, it did produce a potentiation of only 36.4%. Baclofen induced a potentiation similar to control group. Baclofen administration also significantly reduced PPF compared to baseline. The simultaneous administration of MT3 and bicuculline or baclofen led to a potentiation similar to the control group. MT3 did not show any effect over LTP maintenance when applied 15 min after HFS. Lastly, it was not possible to induce long-term depression (LTD) with the used LFS protocol. Although there was no statistical significance between groups due to the low animal numbers used, data suggest that bicuculline had reduced LTP amplitude. Baclofen did alter PPF and the same was not observed on control group. When bicuculline or baclofen were injected with MT3, those alterations were not observed. These are inconclusive and preliminary results, notwithstanding this work allowed to set up the in vivo electrophysiology technique in anesthetized animals what will provide new tools for future research.

A sinalização muscarínica exerce função modulatória sobre diferentes aspectos da cognição e emoções. Todos os cinco subtipos de receptores muscarínicos (mAChR), M1 a M5, são expressos no hipocampo de mamíferos e são ativados de forma sobreposta pela maioria dos fármacos, dificultando avanços significativos na compreensão da contribuição de cada componente desse sistema. A toxina muscarínica 3 (MT3) é um antagonista seletivo para o subtipo M4, permitindo a investigação das ações modulatórias deste receptor no aprendizado, memória e plasticidade sináptica. Os M4 são receptores acoplados à proteína G (GPCRs) que atuam via Gi/o desencadeando efeitos inibitórios sobre as células em que estão presentes. Estudos comportamentais anteriores indicam que a administração de MT3 imediatamente após o treino em uma tarefa aversiva produz efeito amnéstico, enquanto que a administração antes da evocação, causa facilitação. Uma explicação para estes resultados é que os circuitos locais envolvidos na consolidação e na evocação da memória diferem em sua natureza. Nesse contexto, sugere-se que o efeito amnéstico da MT3 sobre a consolidação seja consequência da supressão da inibição de interneurônios GABAérgicos; enquanto que na evocação, esse efeito se daria sobre as sinapses glutamatérgicas. Assim, no presente trabalho, com o objetivo de investigar como o receptor M4 modula a plasticidade sináptica de longa duração e interage com uma dessas sinalizações, no caso a GABAérgica, utilizou-se a técnica de eletrofisiologia in vivo de hipocampo de ratos anestesiados. Para tanto, foram realizados registros extracelulares do potencial excitatório pós-sináptico de campo (fEPSP) de CA1 evocados por estimulação contralateral da via Colateral de Schaffer com infusão dos fármacos 15 min antes ou depois da estimulação elétrica de alta ou baixa frequência (HFS: 10 trens 0,5 Hz, 20 pulsos 100 Hz; ou LFS: 600 pulsos 1 Hz, respectivamente). MT3 (4,0 μg/μl), bicuculina (0,06 μg/μl), baclofen (0,2 μg/μl) e veículo, isoladamente ou combinados, não alteraram a amplitude da resposta evocada basal ou a facilitação por pulso pareado (FPP) 15 min após a infusão. MT3 aparentemente atenuou, mas não de forma significativa, a potenciação de longa duração (LTP) em relação ao controle (potenciação 60 min após a HFS de 31,8% e 66,0%, respectivamente). Além disso, não houve diferença significativa entre a amplitude do fEPSP no período basal e 60 min após a HFS sob ação da MT3. Bicuculina, embora não tenha abolido a LTP e nem causado alteração na FPP, produziu uma potenciação de apenas 36,4%. Baclofen promoveu uma potenciação semelhante à dos controles. A administração de baclofen também reduziu significativamente a FPP em relação ao basal. A administração conjunta de MT3 com bicuculina ou baclofen promoveu uma potenciação semelhante ao controle. MT3 não apresentou efeito sobre a manutenção da LTP quando aplicada 15 min após a HFS. Por fim, não foi possível induzir a depressão de longa duração (LTD) com o protocolo de LFS utilizado. Embora não tenha ocorrido diferença estatisticamente significativa entre os grupos devido ao baixo número de animais utilizados, os dados sugerem a possibilidade de uma amplitude reduzida da LTP quando da injeção de bicuculina. Baclofen alterou a FPP em relação ao fEPSP basal, o mesmo não tendo sido observado no grupo controle. Com a administração concomitante de MT3, tais alterações deixam de ser identificadas. Ainda que os achados experimentais sejam inconclusivos e preliminares, este trabalho permitiu a padronização da técnica de eletrofisiologia in vivo em animal anestesiado o que abre portas para futuras investigações. / The cholinergic muscarinic system exerts modulatory function over different aspects of cognition and emotion. All five muscarinic receptors subtypes (mAChR), M1 to M5, are expressed at mammals hippocampus and at least two of them are simultaneously activated by most of the drugs, hindering significant advances on the role of each component of this system. The muscarinic toxin 3 (MT3) is a selective antagonist for the M4 subtype, allowing the investigation of the modulatory actions of this receptor over learning, memory and synaptic plasticity. The M4 are G protein coupled receptors (GPCRs) that act through Gi/o triggering inhibitory effects on which cells they are occur. Previous behavioral studies have shown that administration of MT3 soon after aversive task training exerts amnestic effects over memory, while administration prior to recall, leads to facilitation. A possible explanation to these results could be that the local circuits involved on memory consolidation and recall are different in nature. On this perspective, the amnestic effect of MT3 over memory consolidation should be consequence of GABAergic interneurons inhibition suppression; while the effect on recall, should be over glutamatergic synapses modulation. Thereby, the present work, with the objective to investigate how the M4 receptor modulates long-term synaptic plasticity and interacts with the GABAergic system, in vivo electrophysiological approach of anesthetized rats’ hippocampus was applied. Hence, field excitatory postsynaptic potentials (fEPSP) from CA1 were recorded after stimulation of contralateral Schaffer Collateral pathway with drugs infusion 15 min before or after high or low frequency electric stimulation (HFS: 10 trains 0.5 Hz, 20 pulses 100 Hz; LFS: 600 pulses 1 Hz, respectively). Neither MT3 (4.00 μg/μl), bicuculline (0.06 μg/μl), baclofen (0.20 μg/μl) nor vehicle, isolated or combined, changed the baseline evoked response amplitude 15 min after infusion nor the paired-pulse facilitation ratio (PPF). MT3 apparently attenuated, but not significantly, the long-term potentiation (LTP) compared to control (31.8% and 66.0% potentiation 60 min after HFS, respectively). In addition, there was no significant difference between baseline and 60 min after HFS fEPSP amplitude at MT3 group. Bicuculline, although did not abolish LTP neither changed PPF, it did produce a potentiation of only 36.4%. Baclofen induced a potentiation similar to control group. Baclofen administration also significantly reduced PPF compared to baseline. The simultaneous administration of MT3 and bicuculline or baclofen led to a potentiation similar to the control group. MT3 did not show any effect over LTP maintenance when applied 15 min after HFS. Lastly, it was not possible to induce long-term depression (LTD) with the used LFS protocol. Although there was no statistical significance between groups due to the low animal numbers used, data suggest that bicuculline had reduced LTP amplitude. Baclofen did alter PPF and the same was not observed on control group. When bicuculline or baclofen were injected with MT3, those alterations were not observed. These are inconclusive and preliminary results, notwithstanding this work allowed to set up the in vivo electrophysiology technique in anesthetized animals what will provide new tools for future research.