Long-term potentiation (LTP) and depression (LTD) are important forms of activity-dependent synaptic plasticity believed to play a role in memory at the cellular level. It has previously been described that synthesis of new proteins is needed to maintain LTP longer than a few hours. Other reports argue that sufficient proteins for stable LTP are already available. The present study aims to examine the role of protein synthesis in LTD, the presumed mirror mechanism of LTP. Experiments were carried out in hippocampal slices from young (12-45 days) and old (12-18 weeks) Sprague-Dawley rats. Extracellular techniques were used to study synaptic responses in the Schaffer-collateral-commissural pathway. Plasticity was induced electrically by low frequency stimulation (2-3 trains at 1 Hz for 15 min) or chemically by brief exposure to certain glutamate receptor agonists (NMDA at 20 µM for 3 min or DHPG at 100 µM for 10 min). Whole slice protein synthesis was quantified by assessing 3H-leucine incorporation. Stable LTD (> 8 h) was be obtained by either electrical or chemical activation. Protein synthesis inhibitors anisomycin (40 uM) and cycloheximide (100 uM) both failed to influence the magnitude of LTD. Moreover, no age difference was found, in terms of stable LTD in both young and old rats under inhibition of protein synthesis. The potency of the inhibitors was found to be high, depressing synthesis down to a few percent. It is concluded that sufficient proteins for generating stable LTD are normally present in the brain, implying a large safety-margin for cellular memory.

Die KE-Familie ist das am ausführlichsten untersuchte Beispiel für eine angeborene spezifische Sprachstörung. Die Sprachstörung in dieser Familie wird durch eine heterozygote Punktmutation im FoxP2-Gen hervorgerufen, die R553H-Mutation. Die betroffenen Mitglieder der Großfamilie haben Defizite beim Erlernen komplexer orofazialer Bewegungsabläufe als Grundlage des fließenden Sprechens und zeigen Störungen beim Sprachverständnis und beim Schreiben. Untersuchungen an der KE-Familie und an Knockout-Tieren hatten Hinweise auf eine Beteiligung des Kleinhirns an der Sprachstörung der KE-Familie geliefert. Entsprechend war zu erwarten, dass genauere Kenntnisse über den Einfluss vom FoxP2-Gen auf Entwicklung und Funktion des Kleinhirns helfen könnten, die Funktion von FoxP2 und seine Rolle bezüglich dieser Sprachstörung, aber auch in Hinblick auf die Sprachfähigkeit des Menschen weiter aufzuschlüsseln. Die Experimente, die der vorliegenden Promotionsarbeit zu Grunde liegen, erforschten erstmals den Einfluss der KE-Mutation im FoxP2-Gen auf synaptischer Ebene durch Untersuchungen am in der Literatur ausführlich beschriebenen erregenden Schaltkreis im Kleinhirnkortex von heterozygoten R552H-Mäusen. Elektrophysiologische Messungen dienten dazu, die Verschaltung der Parallelfasern und Kletterfasern auf die Purkinjezelle auf Veränderungen der Übertragungseigenschaften zu prüfen. Durch Induktion von Langzeitdepression und Paarpulsbahnung an der Parallelfaser-Purkinjezell-Synapse sollte die synaptische Plastizität untersucht werden. Es zeigten sich eine intakte Verschaltung der erregenden Eingänge auf die Purkinjezelle, jedoch Veränderungen der Langzeit- und der Kurzzeitplastizität: Nach Induktion von Langzeitdepression entwickelte sich diese signifikant schneller. Die Paarpulsbahnung war bei kurzen Interstimulusintervallen signifikant verstärkt. Die Befunde sprechen für einen Einfluss des FoxP2-Gens auf die synaptischen Eigenschaften im Kleinhirnkortex. Die Aufschlüsselung dieses Einflusses und seine Bedeutung für die Sprachstörung der KE-Familie und die Sprachentwicklung beim Menschen ist Gegenstand weiterer Forschung.

Synaptic plasticity is thought to be integral to learning and memory. The two most common forms of plasticity are long-term potentiation (LTP) and long-term depression (LTD), both of which can be supported either by presynaptic changes in transmitter release probability (Pr), or by postsynaptic changes in AMPA receptor number. It is generally thought that the induction of LTP and LTD at Schaffer-collateral synapses in the hippocampus depends on the activation of NMDA receptors (GluN). Recent studies, however, have demonstrated that both increases and decreases in Pr can be induced under blockade of postsynaptic GluN receptors, suggesting that the activation of postsynaptic GluN receptors by glutamate is only a strict requirement for postsynaptic plasticity. In this thesis, I therefore re-examined the role of glutamate in presynaptic plasticity. I used single synapse imaging along with electrophysiological and pharmacological techniques to independently manipulate and monitor the levels of glutamatergic signalling during synaptic activity. I discovered that glutamate is inhibitory and unnecessary for the induction of LTP at the presynaptic locus. My findings support a novel model of presynaptic plasticity in which the net activity-dependent changes in Pr at an active presynaptic terminal is jointly determined by two opposing processes that can be simultaneously active: 1) postsynaptic depolarization, which, via the activation of L-type voltage-gated Ca²⁺ channels, increases Pr by driving the synthesis and release of nitric oxide from neuronal dendrites and 2) glutamate release, which through the activation of presynaptic GluN receptors, decreases Pr. Computationally, this model suggests that plasticity functions to reduce prediction-errors that arise during synaptic activity, and, thereby offers a biologically plausible mechanism by which neuronal networks may optimize learning at the level of single synapses.

Tinnitus is a common and often severely disabling symptom that is characterized by the perceived sensation of sound in the absence of an external stimulus. Traditional treatment approaches have limited efficacy. It is assumed, that tinnitus is connected with dysfunctional activation of neuronal plasticity induced by altered sensory and somatosensory input. Adaptive neuroplastic processes alter the balance between excitatory and inhibitory function of the auditory system at several levels. Functional imaging studies in tinnitus patients have revealed increased neronal activity of primary auditory cortex (PAC). Repetitive transcranial magnetic stimulation (rTMS) induces changes of neuronal activity that outlast the stimulation period. Low-frequency rTMS over the PAC region results in a decrease of cortical activity by inducing long term depression (LTD) and leads to reduced tinnitus perception. The aim of this study was to assess in prospective randomized placebo- controlled study the ability of active low-frequency rTMS guided by frameless stereotaxy to affect symptoms of chronic tinnitus compared to placebo stimulation. Treatment outcome was assessed by subjective specific questionnaires; Tinnitus Handicap Inventory (THI), Tinnitus Questionnaire (TQ) and Visual analogue scales (VAS1, VAS2)...

Cannabinoids have been shown to alter synaptic plasticity but the mechanism by which this occurs at hippocampal CA3-CA1 synapses in vivo is not yet known. Utilizing in vivo electrophysiological recordings of field excitatory postsynaptic potentials (fEPSP) on anesthetized rats and mice as well as three lines of conditional knockout mouse models, the objective was to show a two-part mechanistic breakdown of cannabinoid-evoked CA3-CA1 long-term depression (LTD) in its induction as well as early and later-phase expression stages. It was determined that this cannabinoid-induced in vivo LTD requires cannabinoid type-1 receptors (CB1Rs) on astrocytes, but not CB1Rs on glutamatergic or GABAergic neuronal axons/terminals. Pharmacological testing determined that cannabinoid-induced in vivo LTD also requires activation of NMDA receptors (NMDAR) and subsequent postsynaptic endocytosis of AMPA receptors (AMPAR). There exists a clear role for NR2B-containing NMDARs in a persistent, transitory form, potentially related to prolonged or delayed glutamate release (possibly as a result of the astrocytic network). A key determination of the expression phase is the involvement of new protein synthesis (using translation and transcription inhibitors) – further evidence of the long-term action of the synaptic plasticity from a single cannabinoid dose.

O núcleo talâmico mediodorsal (Tmd) e o córtex pré-frontal (CPF) comunicam-se mutuamente, formando um circuito envolvido em funções executivas e transtornos psiquiátricos. As funções executivas estão sujeitas aos níveis de alerta gerados pela atividade oscilatória talamocortical, que por sua vez é controlada pela transmissão colinérgica. Possivelmente, a plasticidade sináptica do circuito Tmd-CPF é sensível tanto aos padrões oscilatórios do próprio circuito quanto à modulação colinérgica. Porém, esta possibilidade ainda não foi testada, muito menos dissociando-se a participação dos receptores muscarínicos e nicotínicos. Assim, nosso objetivo foi examinar como a plasticidade Tmd-CPF é modulada sob estados oscilatórios globais mediados pelo sistema colinérgico, e se esta modulação varia com os tipos de receptores recrutados. Anestesiamos ratos com uretana e implantamos um eletrodo de estimulação no Tmd, um eletrodo de registro no CPF e uma cânula de microinjeção acima do ventrículo. Emitimos 90 pulsos elétricos no Tmd (0,05 Hz) para evocação de potenciais pós-sinápticos de campo (PPSCs) basais no CPF por 30 min. Em seguida, aplicamos injeção intraventricular do agonista muscarínico pilocarpina (PILO), do agonista nicotínico nicotina (NIC), ou veículo-controle (VEIC). Os efeitos das substâncias sobre potenciais de campo locais (eletrencefalograma) foram monitorados através dos mesmos eletrodos. PILO e NIC induziram aumento das oscilações rápidas (4-80 Hz) e proporcional redução das oscilações lentas mantidas pela anestesia (0,5-4 Hz) e tais efeitos duraram ~10-15 min, conforme padronização prévia das concentrações das drogas. Justamente durante este período, aplicamos estimulação em alta frequência (EAF) ou baixa frequência (EBF) para indução de, respectivamente, potencialização (PLD) ou depressão (DLD) de longa duração, que são modelos bem conhecidos de plasticidade sináptica. Em grupos-controle, a injeção de PILO, NIC ou VEIC foi desacompanhada de EAF/EBF. Por fim, retomamos a coleta de PPSCs a 0,05 Hz por 240 min. Os resultados mostraram que a EAF não afetou os PPSCs quando aplicada após VEIC. Porém, nos ratos PILO e NIC, os PPSCs tiveram amplitude aumentada a partir de 150 min após EAF, indicando que a pré-ativação colinérgica foi necessária à indução de uma PLD tardia. Inversamente, quando a EBF foi aplicada após VEIC, a amplitude dos PPSCs foi reduzida de modo estável por 240 min. Isto não ocorreu quando a EBF foi aplicada após PILO e NIC, sugerindo que a modulação colinérgica suprimiu a DLD. Nos grupos-controle, PILO, NIC e VEIC sozinhos não afetaram os PPSCs em longo prazo, confirmando que os resultados de PLD e DLD são devidos a uma interação entre a pré-ativação colinérgica e mecanismos sinápticos desencadeados pela EAF/EBF.Portanto,as oscilações rápidas induzidas pela transmissão colinérgica favorecem a PLD no circuito Tmd-CPF, enquanto dificultam sua DLD. Além disto, os efeitos muscarínicos e nicotínicos sobre a plasticidade de longo prazo são iguais, apesar de os mecanismos celulares destes receptores serem diferentes. Nossos achados ajudam a esclarecer a regulação do sinal talâmico no CPF sob modulação colinérgica fisiológica (atenção e sono paradoxal) e disfuncional (esquizofrenias e doença de Alzheimer). / The mediodorsal thalamic nucleus (MD) and the prefrontal cortex (PFC) communicate with each other, constituting a circuit involved in executive functions and psychiatric disorders. Executive functions are subject to arousal levels driven& by the thalamocortical oscillatory activity, which in turn is controlled by the cholinergic neurotransmission. Possibly, the MD-PFC synaptic plasticity is susceptible to both the oscillatory patterns within the MD-PFC circuit and the cholinergic modulation. However, this likelihood is still untested, as well as the specific roles of muscarinic and nicotinic receptors. Thus, our aim was to evaluate whether and how the MD-PFC plasticity is modulated under cholinergic system-dependent oscillatory states of the forebrain, and if such modulation varies with the subtypes of activated cholinergic receptors. For that, we anesthetized rats with urethane to implant a stimulating electrode into the MD, a recording electrode into the PFC, and a microinjection cannula above the ventricle. We applied 90 monophasic square pulses into the MD (0.05 Hz) for recording of basal field postsynaptic potentials (fPSPs) in the PFC for 30 min. Then, we did an intraventricular injection of either the muscarinic agonist pilocarpine (PILO), the nicotinic agonist nicotine (NIC), or a control vehicle (Veh). The drug effects on local field potentials (electroencephalogram) were monitored through the same electrodes. PILO and NIC induced an increase in theta, beta and gamma oscillations (4-80 Hz) with proportional reduction of urethane-driven delta waves (0.5-4 Hz), and these effects survived approximately 10-15 min according to pilot-experiments on PILO and NIC concentrations. During this period, we applied either high-frequency (HFS) or low-frequency stimulation (LFS) for induction of respectively long-term potentiation (LTP) or depression (LTD), which are well-known synaptic plasticity models. In control groups, the injection of PILO, NIC or Veh was not followed by the HFS/LFS. Lastly, we resumed the evoking of fPSP at 0.05 Hz for an additional 240 min. The results showed that the HFS did not affect the fPSPs when applied after the Veh. However, in PILO and NIC rats the fPSP had their amplitudes increased from 150 min after HFS, indicating that the cholinergic pre-activation was required for the induction of a late-phase LTP. On the other hand, when the LFS was applied after the Veh, the fPSP amplitudes were stably decreased for 240 min, which did not occur when the LFS was applied after PILO and NIC, suggesting that the cholinergic modulation suppressed the LTD. In the control groups, PILO, NIC, and Veh by themselves did not change fPSPs in the long term, reinforcing that the LTP and LTD were due to an interaction between the cholinergic pre-activation and synaptic mechanisms triggered by the HFS/LFS. Therefore, the rapid oscillations induced by the cholinergic transmission favor LTP in the MD-PFC loop, while occlude its LTD. Moreover, the muscarinic and nicotinic effects on long-term plasticity were equal, although their quite distinct cell mechanisms. Our findings might help clarify the regulation of thalamic signals on the PFC both under physiological (attention and rapid-eye-movement sleep) and dysfunctional (schizophrenia symptoms and Alzheimer\'s) cholinergic drive.

Dopamine (DA) neurons of the substantia nigra pars compacta (SNc) have a key role in regulation of voluntary movement control. Their death is a hallmark of Parkinson’s disease, characterised by inhibited motor control, including muscle rigidity and tremor. Excitatory input to SNc-DA neurons is primarily from the subthalamic nucleus, and in PD these afferents display a higher frequency firing, as well as increased burst firing, which could cause increased excitatory activity in SNc-DA neurons. NMDA receptors (NMDARs) bind the excitatory neurotransmitter glutamate, and are essential for learning and memory. In SNc-DA neurons, NMDARs have a putative triheteromeric subunit arrangement of GluN1 plus GluN2B and/or GluN2D. Wild type (WT) mice, and those lacking the gene for GluN2D (Grin2D-null), were used to explore its role in various aspects of DA neuronal function and dysfunction using patch-clamp electrophysiology, viability assaying, and immunofluorescence. Pharmacological intervention using subunit-specific inhibitors ifenprodil and DQP-1105 on elicited NMDAR-EPSCs suggested a developmental shift from primarily GluN2B to GluN2B/D. Activity dependent regulation was assessed by high frequency burst stimulation of glutamatergic afferents: in comparison to controls, significant downregulation of NMDARs was observed in SNc-DA neurons, though no differences were observed based on genotype. This regulatory function may be a neuroprotective or homeostatic response. Ambient extracellular glutamate elicits tonic NMDAR activity in SNc-DA neurons, which may be important for maintaining basal levels of excitability: the role of GluN2D was assessed by recording the deflection in baseline current caused by application of competitive NMDAR antagonist D-AP5. There was a significantly larger NMDAR-mediated current in WT vs Grin2D-null mice, indicating that GluN2D has a role in binding ambient glutamate. Dysfunction of glutamate uptake could be a secondary pathophysiological occurrence in the SNc, leading to increased ambient glutamate: the effect of this was explored by application of the competitive glutamate transporter blocker TBOA. Here, the NMDAR-mediated portion of this current was significantly higher in WT mice in comparison to Grin2D-null. Interestingly, dose-response data obtained from bath application of NMDA showed significantly larger currents in Grin2D-null animals vs WT, but only at the top of the response curve (~1-10 mM), which may indicate a capability for larger conductance in Grin2D-null animals at high NMDAR saturation due to replacement of GluN2D with GluN2B. GluN2D may therefore be neuroprotective, by attenuating peak current flow in response to very high agonist concentrations. Lastly, GluN2D has been found to decrease NMDAR open probability under hypoxic conditions, potentially conferring resistance to hypoxia / ischemia related excitotoxicity. Therefore, low (15% O2 / 80% N2 / 5% CO2) vs high (95% O2 / 5% CO2) oxygen conditions were used along with immunofluorescent propidium iodide cell death assaying and immunofluorescent labeling for DA neurons in order to compare levels of DA neuronal death in the SNc based on oxygen status and genotype. Whilst there was a significant submaximal effect based on O2 status, genotype did not confer a practical resistance under these conditions. In summary, NMDARs have diverse roles in SNc-DA neurons which may both serve to maintain normal function and protect the cell against potentially pathological conditions.

O núcleo talâmico mediodorsal (Tmd) e o córtex pré-frontal (CPF) comunicam-se mutuamente, formando um circuito envolvido em funções executivas e transtornos psiquiátricos. As funções executivas estão sujeitas aos níveis de alerta gerados pela atividade oscilatória talamocortical, que por sua vez é controlada pela transmissão colinérgica. Possivelmente, a plasticidade sináptica do circuito Tmd-CPF é sensível tanto aos padrões oscilatórios do próprio circuito quanto à modulação colinérgica. Porém, esta possibilidade ainda não foi testada, muito menos dissociando-se a participação dos receptores muscarínicos e nicotínicos. Assim, nosso objetivo foi examinar como a plasticidade Tmd-CPF é modulada sob estados oscilatórios globais mediados pelo sistema colinérgico, e se esta modulação varia com os tipos de receptores recrutados. Anestesiamos ratos com uretana e implantamos um eletrodo de estimulação no Tmd, um eletrodo de registro no CPF e uma cânula de microinjeção acima do ventrículo. Emitimos 90 pulsos elétricos no Tmd (0,05 Hz) para evocação de potenciais pós-sinápticos de campo (PPSCs) basais no CPF por 30 min. Em seguida, aplicamos injeção intraventricular do agonista muscarínico pilocarpina (PILO), do agonista nicotínico nicotina (NIC), ou veículo-controle (VEIC). Os efeitos das substâncias sobre potenciais de campo locais (eletrencefalograma) foram monitorados através dos mesmos eletrodos. PILO e NIC induziram aumento das oscilações rápidas (4-80 Hz) e proporcional redução das oscilações lentas mantidas pela anestesia (0,5-4 Hz) e tais efeitos duraram ~10-15 min, conforme padronização prévia das concentrações das drogas. Justamente durante este período, aplicamos estimulação em alta frequência (EAF) ou baixa frequência (EBF) para indução de, respectivamente, potencialização (PLD) ou depressão (DLD) de longa duração, que são modelos bem conhecidos de plasticidade sináptica. Em grupos-controle, a injeção de PILO, NIC ou VEIC foi desacompanhada de EAF/EBF. Por fim, retomamos a coleta de PPSCs a 0,05 Hz por 240 min. Os resultados mostraram que a EAF não afetou os PPSCs quando aplicada após VEIC. Porém, nos ratos PILO e NIC, os PPSCs tiveram amplitude aumentada a partir de 150 min após EAF, indicando que a pré-ativação colinérgica foi necessária à indução de uma PLD tardia. Inversamente, quando a EBF foi aplicada após VEIC, a amplitude dos PPSCs foi reduzida de modo estável por 240 min. Isto não ocorreu quando a EBF foi aplicada após PILO e NIC, sugerindo que a modulação colinérgica suprimiu a DLD. Nos grupos-controle, PILO, NIC e VEIC sozinhos não afetaram os PPSCs em longo prazo, confirmando que os resultados de PLD e DLD são devidos a uma interação entre a pré-ativação colinérgica e mecanismos sinápticos desencadeados pela EAF/EBF.Portanto,as oscilações rápidas induzidas pela transmissão colinérgica favorecem a PLD no circuito Tmd-CPF, enquanto dificultam sua DLD. Além disto, os efeitos muscarínicos e nicotínicos sobre a plasticidade de longo prazo são iguais, apesar de os mecanismos celulares destes receptores serem diferentes. Nossos achados ajudam a esclarecer a regulação do sinal talâmico no CPF sob modulação colinérgica fisiológica (atenção e sono paradoxal) e disfuncional (esquizofrenias e doença de Alzheimer). / The mediodorsal thalamic nucleus (MD) and the prefrontal cortex (PFC) communicate with each other, constituting a circuit involved in executive functions and psychiatric disorders. Executive functions are subject to arousal levels driven& by the thalamocortical oscillatory activity, which in turn is controlled by the cholinergic neurotransmission. Possibly, the MD-PFC synaptic plasticity is susceptible to both the oscillatory patterns within the MD-PFC circuit and the cholinergic modulation. However, this likelihood is still untested, as well as the specific roles of muscarinic and nicotinic receptors. Thus, our aim was to evaluate whether and how the MD-PFC plasticity is modulated under cholinergic system-dependent oscillatory states of the forebrain, and if such modulation varies with the subtypes of activated cholinergic receptors. For that, we anesthetized rats with urethane to implant a stimulating electrode into the MD, a recording electrode into the PFC, and a microinjection cannula above the ventricle. We applied 90 monophasic square pulses into the MD (0.05 Hz) for recording of basal field postsynaptic potentials (fPSPs) in the PFC for 30 min. Then, we did an intraventricular injection of either the muscarinic agonist pilocarpine (PILO), the nicotinic agonist nicotine (NIC), or a control vehicle (Veh). The drug effects on local field potentials (electroencephalogram) were monitored through the same electrodes. PILO and NIC induced an increase in theta, beta and gamma oscillations (4-80 Hz) with proportional reduction of urethane-driven delta waves (0.5-4 Hz), and these effects survived approximately 10-15 min according to pilot-experiments on PILO and NIC concentrations. During this period, we applied either high-frequency (HFS) or low-frequency stimulation (LFS) for induction of respectively long-term potentiation (LTP) or depression (LTD), which are well-known synaptic plasticity models. In control groups, the injection of PILO, NIC or Veh was not followed by the HFS/LFS. Lastly, we resumed the evoking of fPSP at 0.05 Hz for an additional 240 min. The results showed that the HFS did not affect the fPSPs when applied after the Veh. However, in PILO and NIC rats the fPSP had their amplitudes increased from 150 min after HFS, indicating that the cholinergic pre-activation was required for the induction of a late-phase LTP. On the other hand, when the LFS was applied after the Veh, the fPSP amplitudes were stably decreased for 240 min, which did not occur when the LFS was applied after PILO and NIC, suggesting that the cholinergic modulation suppressed the LTD. In the control groups, PILO, NIC, and Veh by themselves did not change fPSPs in the long term, reinforcing that the LTP and LTD were due to an interaction between the cholinergic pre-activation and synaptic mechanisms triggered by the HFS/LFS. Therefore, the rapid oscillations induced by the cholinergic transmission favor LTP in the MD-PFC loop, while occlude its LTD. Moreover, the muscarinic and nicotinic effects on long-term plasticity were equal, although their quite distinct cell mechanisms. Our findings might help clarify the regulation of thalamic signals on the PFC both under physiological (attention and rapid-eye-movement sleep) and dysfunctional (schizophrenia symptoms and Alzheimer\'s) cholinergic drive.

Die KE-Familie ist das am ausführlichsten untersuchte Beispiel für eine angeborene spezifische Sprachstörung. Die Sprachstörung in dieser Familie wird durch eine heterozygote Punktmutation im FoxP2-Gen hervorgerufen, die R553H-Mutation. Die betroffenen Mitglieder der Großfamilie haben Defizite beim Erlernen komplexer orofazialer Bewegungsabläufe als Grundlage des fließenden Sprechens und zeigen Störungen beim Sprachverständnis und beim Schreiben. Untersuchungen an der KE-Familie und an Knockout-Tieren hatten Hinweise auf eine Beteiligung des Kleinhirns an der Sprachstörung der KE-Familie geliefert. Entsprechend war zu erwarten, dass genauere Kenntnisse über den Einfluss vom FoxP2-Gen auf Entwicklung und Funktion des Kleinhirns helfen könnten, die Funktion von FoxP2 und seine Rolle bezüglich dieser Sprachstörung, aber auch in Hinblick auf die Sprachfähigkeit des Menschen weiter aufzuschlüsseln. Die Experimente, die der vorliegenden Promotionsarbeit zu Grunde liegen, erforschten erstmals den Einfluss der KE-Mutation im FoxP2-Gen auf synaptischer Ebene durch Untersuchungen am in der Literatur ausführlich beschriebenen erregenden Schaltkreis im Kleinhirnkortex von heterozygoten R552H-Mäusen. Elektrophysiologische Messungen dienten dazu, die Verschaltung der Parallelfasern und Kletterfasern auf die Purkinjezelle auf Veränderungen der Übertragungseigenschaften zu prüfen. Durch Induktion von Langzeitdepression und Paarpulsbahnung an der Parallelfaser-Purkinjezell-Synapse sollte die synaptische Plastizität untersucht werden. Es zeigten sich eine intakte Verschaltung der erregenden Eingänge auf die Purkinjezelle, jedoch Veränderungen der Langzeit- und der Kurzzeitplastizität: Nach Induktion von Langzeitdepression entwickelte sich diese signifikant schneller. Die Paarpulsbahnung war bei kurzen Interstimulusintervallen signifikant verstärkt. Die Befunde sprechen für einen Einfluss des FoxP2-Gens auf die synaptischen Eigenschaften im Kleinhirnkortex. Die Aufschlüsselung dieses Einflusses und seine Bedeutung für die Sprachstörung der KE-Familie und die Sprachentwicklung beim Menschen ist Gegenstand weiterer Forschung.

L’objectif principal de mon projet de thèse a été d’identifier les mécanismes neuronaux adaptatifs se mettant en place au niveau des circuits de la récompense et des circuits activés en réponse à un stress aigu. Plus spécifiquement, nous avons étudié le rôle du noyau du lit de la strie terminale (BNST) au sein de ces deux circuits. Mon hypothèse est que le BNST appartient à un circuit de structures interconnectées dans lequel il intègre des informations contextuelles (hippocampe ventral) et des informations émotionnelles (cortex préfrontal médian) afin, d’une part, de réguler les niveaux d’anxiété innés ainsi que les réponses induites par les centres du stress suite à un épisode de stress aigu mais également, d’adapter l’activité des neurones dopaminergiques de l’aire tegmentale ventrale (VTA) en vue de motiver ou d’empêcher la reproduction d’un comportement associé à un stimulus récompensant ou aversif. Afin de tester cette hypothèse, nous avons mis en place et développé différents projets de recherche combinant des approches d’électrophysiologie in vivo, anatomiques et comportementales. Dans un premier temps, nous nous sommes intéressés au BNST en tant que structure clef participant à la régulation des centres de stress. Grâce à l’utilisation d’approches d’électrophysiologie in vivo chez la souris anesthésiée, nous avons montré qu’après l’exposition à un stress aigu, les neurones du BNST adaptent leur réponse suite à la stimulation du cortex préfrontal médian et passent d’une dépression à long terme (LTD) en situation contrôle à une potentialisation à long terme (LTP) après un stress aigu. Nous avons disséqué une partie des mécanismes permettant l’élaboration de ces plasticités grâce à l’utilisation de souris génétiquement modifiés pour le récepteur aux endocannabinoïdes de type 1 (CB1-R). Ainsi, nous avons trouvé que la LTD et la LTP mis en place dans le BNST sont médiées par le système endocannabinoïde via les récepteurs CB1. Ensuite, nous avons étudié le rôle du ventral subiculum (vSUB) dans la régulation des neurones du BNST ainsi que l’impact de l’activation de cette voie vSUB-BNST sur l’autre voie glutamatergique ILCx-BNST. Tout d’abord, nous avons montré par des approches électrophysiologiques et anatomiques, qu’un même neurone du BNST est capable d’intégrer des informations provenant à la fois du ventral subiculum et du cortex infralimbic (ILCx). Nous avons induit in vivo une LTP NMDA dépendante dans la voie vSUB-BNST suite à un protocole de stimulation haute fréquence dans le vSUB alors qu’en parallèle ce même protocole induit une LTD sur ces mêmes neurones dans la voie ILCx–BNST. Deplus, nous avons noté que ces adaptations plastiques se mettant en place dans le BNST suiteà une simple stimulation haute fréquence dans le vSUB permettent à long terme de diminuerles niveaux d’anxiété innés chez le rat. Enfin, nous avons mis en évidence que le BNST est un relai excitateur entre le vSUBet la VTA. Nous avons montré qu’une stimulation à haute fréquence dans le vSUBpotentialise in vivo l’activité des neurones dopaminergiques (DA) de la VTA. Or le vSUBne projette pas de manière directe sur les neurones DA de la VTA. Nous avons observé quece protocole de stimulation haute fréquence dans le vSUB induit dans un premier temps uneLTP NMDA dépendante dans les neurones du BNST projetant à la VTA qui est nécessairepour observer cette potentialisation des neurones DA. En dernier lieu, nous avons montréque cette potentialisation des neurones DA de la VTA augmente la réponse locomotrice à unchallenge avec de la cocaine.Ainsi, l’ensemble de ces projets nous ont permis de confirmer et de préciser lafonction majeure du BNST dans la régulation du stress et de l’anxiété ainsi que dans lecircuit de la motivation. / The main goal of my PhD was to identify the adaptive neuronal mechanismsdeveloping in the reward circuit and in the circuit implicated in the regulation of stressresponses. More specifically, we have studied the function of the bed nucleus of the striaterminalis (BNST) in both circuits.My hypothesis was that, the BNST belongs to interconnected circuits in whichintegrates contextual (from ventral hippocampus) and emotional informations (from medialprefrontal cortex). Thus, the BNST diffuses these informations in order to regulate the basalinnate level of anxiety and stress centers responses induced after acute stress exposure, butalso to adapt the activity of dopaminergic neurons of the ventral tegmental area (VTA) thatcan promote or prevent a behavioral task associated with a rewarding or aversive stimulus.To test this hypothesis, we decided to develop several research projects usingelectrophysiological, anatomical and behavioral approaches.Firstly, we focused our interest on the stress circuit in which the BNST is a keystructure which participates in regulating the responses of stress centers after acute stressexposure. By using in vivo electrophysiology approach in anesthetized mice, we haveshown that after acute restraint stress, BNST neurons adapt their plastic responses inducedby the tetanic stimulation of the medial prefrontal cortex: switch from long term depression(LTD) under control condition to long term potentiation (LTP) after acute stress condition.Furthermore, we demonstrated that both LTD and LTP are endocannabinoid dependent byusing genetic modified mice for the type 1 endocannabinoid receptors and localpharmacological approach in the BNST.In a second step, we studied the function of the ventral subiculum (vSUB) in theregulation of BNST neurons and the impact of the vSUB-BNST pathway activation on theother glutamatergic ILCx-BNST pathway. In a first set of experiments, we showed that asame single BNST neuron could integrate informations from both vSUB and the infralimbiccortex. By using high frequency stimulation (HFS) protocols, we induced in vivo NMDAdependentLTP in the vSUB-BNST pathway whereas the same protocol led to LTD in thesame BNST neurons in the ILCx-BNST pathway. Moreover, we noted single application ofHFS protocol in the vSUB induced a long term decrease of the basal innate level of anxietyin rats.Lastly, we presented the BNST as a key excitatory relay between the vSUB and theVTA. Here, we have shown that in vivo HFS protocols in the vSUB potentiate the activity ofdopaminergic (DA) neurons of the VTA. However, the vSUB does not directly project to theVTA. We observed that a HFS protocol in the vSUB first induce NMDA-dependent LTP inBNST neurons that project to the VTA, which is necessary to promote the potentiation of7VTA DA neurons. In the last step, we demonstrated in vivo that the potentiation of VTA DAneurons increases the locomotor response to cocaine challenge.All together, these projects allow us to confirm and detail the major function of theBNST in the regulation of stress and anxiety and also in the motivational circuit.