Muitas evidências demonstram que o peptídeo liberador de gastrina (GRP) é um fator de crescimento que afeta funções neuroendócrinas, incluindo proliferação e diferenciação celular, comportamento alimentar, formação de memória, respostas a estresses, desenvolvimento de neoplasias, desordens neurológicas e psiquiátricas. Porém, os eventos moleculares pelos quais isso ocorre ainda não são totalmente compreendidos. No presente estudo, nós avaliamos as interações entre o receptor do peptídeo liberador de gastrina (GRPR) e a via de sinalização celular da PKA, tanto na proliferação celular de glioblastoma humano (in vitro) quanto na consolidação da memória no hipocampo de ratos Wistar (in vivo). Mostramos que o GRP age em sinergismo com agentes que estimulam a via do cAMP/PKA, promovendo a proliferação de células de glioblastoma humano, pois o tratamento com GRP combinado com um ativador de adenilil ciclase (AC), forskolin, ou um análogo de cAMP, 8-Br-cAMP, ou um inibidor do tipo IV de fosfodiesterase, rolipram, aumentaram a proliferação das células de U- 138MG, quando avaliadas pelo método de MTT. Nenhum destes compostos teve efeito sozinho. O mRNA de GRPR e a expressão protéica em U-138MG foram detectados pelas técnicas de RT-PCR e imuno-histoquímica. No estudo in vivo a bombesina em baixas doses induziu um aumento na consolidação da memória. O resultado foi potencializado na combinação com um ativador do receptor de dopamina D1/D5 (D1R), além de ser prevenido quando combinado com um inibidor da via da PKA. Os resultados sugerem que GRP e GRPR interagem com a via de sinalização cAMP/PKA tanto na estimulação da proliferação celular em linhagem de câncer humano quanto na modulação da memória no hipocampo de ratos. / Increasing evidence indicates that gastrin-releasing peptide (GRP) acts as an autocrine growth factor for brain tumors as well as been implicated in memory formation, however, underlying molecular events are poorly understood. In the present study, we examined interactions between the GRPR and cellular signaling pathways in influencing memory consolidation in the hippocampus and on proliferation of glioblastoma cell in vitro. We show here that GRP acts synergistically with agents that stimulate the cAMP/PKA pathway to promote proliferation of human gliobastoma cells. Treatment with GRP combined with the adenylyl cyclase (AC) activator forskolin, the cAMP analog 8-Br-cAMP, or the phosphodiesterase type IV (PDE4) inhibitor rolipram increased proliferation of U138-MG cells in vitro measured by MTT assay. None of the compounds had an effect when given alone. GRP receptor (GRPR) mRNA and protein expression in U138-MG cells was detected by reverse transcriptase polymerase chain reaction (RT-PCR) and immunohistochemistry. We investigated the interactions between the GRPR and the PKA pathway in male Wistar rats. BB-induced enhancement of consolidation was potentiated by co infusion of activators of the dopamine D1/D5 receptor (D1R) pathway and prevented by a PKA inhibitor. The results suggest that GRP and the GRPR interact with the cAMP/PKA signaling pathway in stimulating a cancer cell line proliferation and in memory modulation by hippocampal.

Cette thèse illustre une recherche sur les assemblées de cellules, groupes de neurones étroitement liés et co-activés, considérés comme les unités de la mémoire. Après une revue des majeures avancées expérimentales et théoriques dans ce domaine, et des techniques de physique statistique et d'inférence pour l'étude de neurones en interaction, on présente une nouvelle méthode pour dévoiler les assemblées decellules à partir des données neuronales et on montre son application à des enregistrements multi-électrodes dans le cortex préfrontal de rats pendant l'exécution d'une tâche et les époques de sommeil précédant et suivant. La méthode est basée sur l'inférence d'un réseau d'Ising d’interactions effectives entre les neurones et sur la simulation du modèle inféré en présence d'une entrée globale uniforme: quand l'entrée augmente, on découvre des configurations d'activité élevée (assemblées de cellules), qui s'activent dans les données à des échelles de temps de dizaines de ms en présence de stimuli transitoires. Les assemblées sont robustes par rapport au bruit. La comparaison des réseaux d'interactions et des résultats des simulations à travers les trois phases expérimentales révèle des règles empiriques pour la modification des assemblées de cellules. Le modèle inféré est également exploité pour estimer la réactivation (replay) des assemblées pendant le sommeil, important pour la consolidation de la mémoire. Inférence et échantillonnage d'un modèle linéaire généralisé montrent qu'il n'y a pas un ordre d'activation spécifique des neurones. On discute enfin une application de statistique descriptive à l'étude de la plasticité synaptique in vitro dans un cadre optogénétique. / This thesis illustrates a research on cell assemblies, groups of closely connected, synchronously activating neurons, which are thought to be the units of memory. After a review of the main experimental and theoretical advances in this field, and of the techniques of statistical physics and inference for the study of interacting neurons, a new method to unveil cell assemblies from neuronal data is illustrated and applied to multi-electrode recordings in the prefrontal cortex of rats during performance of a task and during the preceding and following sleep epochs. The method is based on the inference of an Ising network of effective interactions between the neurons and on the simulation of the inferred model in the presence of a global uniform drive: as the drive increases, configurations of high activity (cell assemblies) are unveiled, which activate in the data on time scales of tens of ms, in the presence of transient stimuli. The assemblies are robust with respect to noise. Comparisonof the interaction networks and of the results of the simulations across the three experimental phases reveals empirical rules for the modification of cell assemblies. The inferred model is also exploited to estimate the reactivation (replay) of the cell assemblies during sleep, important for memory consolidation. Inference and sampling of a generalized linear model show that there is not a specific order of activation of the neurons in the groups. It is finally discussed an application of descriptive statistics to the study of synaptic plasticity of neurons in vitro in an optogenetic framework.

La grande diversité des réponses de stress observée entre individus a pour origine des facteurs génétiques en interaction avec des facteurs environnementaux. Certaines réponses peuvent être moins adaptées et accroitre la vulnérabilité de l’individu aux divers troubles et pathologies liées au stress. La CBG est une glycoprotéine plasmatique impliquée dans la biodisponibilité des glucocorticoïdes, un des principaux médiateurs de la réponse au stress. Des études génétiques ont montré que des polymorphismes du gène codant la CBG ont un impact significatif sur la réponse des glucocorticoïdes au stress. Pour comprendre les mécanismes de l’impact de la CBG sur l’action des glucocorticoïdes et les conséquences sur les réponses endocriniennes et comportementales de stress, notre équipe a développé un modèle de souris déficiente pour le gène Cbg. Ces souris présentent une réponse diminuée des glucocorticoïdes au stress, associée à un niveau élevé de comportement émotionnel de type dépressif. Cette thèse a pour but d’explorer plus en profondeur les altérations physiologiques et comportementales des souris Cbg ko. Nous avons montré que le niveau plus faible de glucocorticoïdes observé chez la souris Cbg ko provient d’une élimination plasmatique plus importante. Une étude chez la souris Cbg ko femelles a montré que les estrogènes se surimposent à la déficience en CBG pour induire des comportements de type dépressif. Nous avons également démontré que la déficience en CBG conduit a une atténuation de la sensibilité comportementale et endocrinienne au stress chronique. Enfin, nous avons observé une détérioration de la mémoire long terme de ces souris. Par ailleurs, nous montrons que dans des conditions de stress chronique associé à un régime alimentaire déséquilibré le métabolisme du glucose était altéré chez les animaux déficients en CBG. Ces résultats renforcent l’importance du rôle de la CBG influençant l’ensemble des mécanismes d’actions des glucocorticoïdes par la modulation de leurs niveaux et de leur disponibilité. / The great diversity in the response to stress observed among individuals originates from their genetic background in interaction with environmental factors. Some responses can be less adaptive and increase the vulnerability to develop stress-associated disorders. CBG is a plasma glycoprotein that regulates the bioavailability of glucocorticoids, one of the main mediators of the stress response. Genetic studies pointed out variations in the gene coding for CBG as a major factor influencing the glucocorticoid response to stress. To better understand the mechanisms involved and the consequences on endocrine and behavioral responses to stress, our team has developed a mouse model of CBG deficiency. These mice present blunted glucocorticoid response to stress associated with increased despair-like behaviors. This thesis aimed at further exploring the physiological and behavioral alterations presented by the Cbg ko mice. We showed that the lower glucocorticoid levels observed in Cbg ko mice stems from their higher clearance from plasma. A study performed on Cbg ko female mice revealed that estrogens outpass CBG deficiency in inducing despair-like behavior. Additionally, we evidenced that CBG deficiency leads to lower behavioral and endocrine sensitivity to chronic stress, and we observed impairment of hippocampal-dependent long-term memory in these mice. Finally, we found that chronic stress combined to high-fat diet leads to alteration in glucose metabolism in CBG deficient animals. These findings reinforce the important role of CBG influencing the broad range of actions of glucocorticoids by modulating their levels and availability.

A leading theory for why we sleep focuses on memory consolidation - the process of stabilizing and strengthening newly acquired memories into long-term storage. Consolidation of memory for cognitive strategies and problem-solving skills is enhanced as compared to a period of daytime wakefulness. Importantly, sleep preferentially enhances memory for the cognitive strategy per se, over-and-above the motor skills that are used to execute the strategy. Although it has been known for some time that sleep benefits this type of memory, it is not known how this process unfolds during sleep, or how sleep transforms this memory trace in the brain. Sleep is classified into rapid eye movement (REM) sleep and non-REM (NREM) sleep. The role of REM sleep for consolidation of memory for problem-solving skills remains controversial. In addition, little attention has been paid to the possible distinct roles of phasic REM sleep (i.e., when bursts of eye movements occur) and tonic REM sleep (i.e., the presence of isolated eye movements and the absence of eye movement bursts). REM sleep might favour procedural memory consolidation for cognitive strategies and problem-solving skills, and the specific role of REM sleep in this process might be discernible only by differentiating between phasic and tonic REM states. In addition, fMRI studies have revealed that sleep-related consolidation of the memory trace for simple motor procedural skills is associated with strengthened activity of, and functional connectivity between, key memory-related brain areas (i.e., hippocampal, striatal, and neocortex). However, fMRI techniques have not yet been employed to investigate sleep-related consolidation of procedural memory for cognitive strategies and problem-solving skills. Participants (n=60) performed a procedural memory task involving a cognitive strategy while undergoing functional magnetic resonance imaging (fMRI) before and after a condition of Sleep, Nap, or Wake. Those in the Sleep and Nap condition underwent polysomnography (PSG) to further study the learning-related changes in sleep macrostructure and microstructure. This thesis not only shows that a period of sleep or a nap afford a greater benefit to memory consolidation of a procedural strategy than a period of wake, but more specifically: In Study 1, during sleep, phasic REM sleep theta power was directly associated with overnight improvement on the task, whereas tonic REM sleep sensorimotor rhythm power was greater following a night of learning compared to a non-learning control night. In Study 2, we show that distinct hippocampal, striatal, and cortical areas associated with strategy learning are preferentially enhanced. Study 3 reveals that the functional communication among these brain areas is greater following sleep compared to a daytime nap or day of wakefulness. Sleep-related changes in brain activation and functional connectivity were both correlated with improved performance from before to after a period of sleep. Overall, findings from this thesis support the benefit of sleep at the behavioural and systems level for consolidating procedural memory involving cognitive strategies used to solve problems. The findings suggest that the multifaceted nature of REM sleep must be examined separately by its phasic and tonic states, to identify the active role of REM sleep for consolidating memory. Further, the consolidation of the memory trace is reflected through activation of, and communication between hippocampal, striatal, and neocortical brain areas. In summary, this thesis shows that sleep actively consolidates memory for cognitive strategies and problem-solving skills.

Sharp wave-ripple Komplexe (SWRs) sind kurze Ereignisse von kohärenter Netzwerkaktivität im Hippocampus. SWRs spielen eine wichtige Rolle bei der Konsolidierung von expliziten Gedächtnisinhalten, die Mechanismen sind aber bis heute ungeklärt. Pyramidenzellen (PYR) und Parvalbumin-positive Korbzellen (PV+BCs) feuern während SWRs besonders häufig, wohingegen sie außerhalb beinahe inaktiv sind. SWRs treten spontan auf, und können durch Stimulation von PYR und PV+ Zellen hervorgerufen werden. Um die Rolle von PV+ Zellen in SWR Generierung zu klären, untersuche ich wie das Zusammenspiel von exzitatorischen Neuronen (PYR) und zwei Klassen von Interneuronen (PV+BCs und derzeit unbekannte Anti-SWR-Zellen) die Entstehung und die Häufigkeit von SWRs beeinflusst. Erstens entwickle ich ein Netzwerk aus feuernden Neuronen, das spontane Übergänge vom Anti-SWR-Zustand zum SWR-Zustand zeigt. Die Aktivität von PV+BCs, die die Aktivität von PYR disinhibieren, dominiert den SWR-Zustand. SWRs können hervorgerufen werden durch Stimulation von PYR oder PV+BCs, und durch Inaktivierung von Anti-SWR-Zellen. Durch Kurzzeitdepression der synaptischen Verbindung von PV+BCs zu Anti-SWR-Zellen wird die Dauer der SWRs reguliert. Die Koexistenz von Anti-SWR- und SWR-Zuständen bei konstanten Stärken der synaptischen Depression erlaubt die Untersuchung der Bistabilität des Netzwerks. Durch eine Mean-field-Näherung können Voraussetzungen für bistabile Netzwerkaktivität analytisch hergeleitet werden. Das Modell prognostiziert die Existenz von Anti-SWR-Zellen. Im letzten Teil dieser Arbeit zeige ich erste experimentelle Ergebnisse, die die Existenz von CA3-Interneuronen belegen, die anti-moduliert sind bezüglich SWRs. Durch die Untersuchung der Rolle von Interneuronen hinsichtlich der Generierung von SWRs trägt diese Arbeit zu einem tieferen Verständnis der neuronalen Schaltkreise im Hippocampus bei, die essentiell für den Erwerb und die Konsolidierung expliziter Gedächtnisinhalte sind. / Sharp wave-ripple complexes (SWRs) are events of coordinated network activity originating in the hippocampus. SWRs are thought to mediate the consolidation of explicit memories, but the mechanisms underlying their occurrence remain obscure. Pyramidal cells (PYR) and parvalbumin-positive basket cells (PV+BCs) preferentially fire during SWRs and are almost silent outside. SWRs emerge spontaneously or by activating PYR or PV+ cells. To understand how the activation of PV+ interneurons can result in an increase of PYR firing, I explore how the interaction of excitatory neurons (PYR) and two groups of interneurons (PV+BCs and a class of anti-SWR cells) contributes to the initiation, termination, and incidence of SWRs. First, I show that a biophysically constrained network of spiking neurons can exhibit spontaneous transitions from a non-SWR state to a SWR state, in which active PV+BCs disinhibit PYR by suppressing anti-SWR cells. SWR events can be triggered by activating PYR or PV+BCs, or inactivating anti-SWR cells. Short-term synaptic depression at the PV+BCs-to-anti-SWR cells connections regulates the termination of SWR events. The coexistence of states for intermediate values of the depression allows to study the network behavior in terms of bistability. To this end, I consider a mean-field approximation of the spiking network, where conditions for the emergence of a bistable configuration are derived analytically. This allows to unveil the mechanisms regulating the existence of bistable disinhibitory networks. The model predicts the existence of a class of anti-SWR cells. In the last part of this work, I show the first experimental evidence for CA3 interneurons anti-modulated with respect to SWRs, and discuss their involvement in the SWR generation process. Overall, the results of this thesis elucidate the role of interneurons in SWR generation and broaden our understanding of the microcircuits supporting the dynamics of memory-related networks.

Posttraumatic stress disorder is a debilitating anxiety disorder that can develop in the aftermath of a traumatic or life–threatening event involving extreme horror, intense fear or bodily harm. The disorder is typified by a symptom triad consisting of re–experiencing, hyperarousal and avoidance symptoms. Approximately 15–25% of trauma–exposed individuals go on to develop PTSD, depending on the nature and severity of the trauma. Although dysfunctional adaptive responses exist in multiple neurobiological pathways in the disorder, e.g. glutamate, GABA, glucocortocoids and serotonin, the noradrenergic system is particularly prominent and represents an important pharmacological target in attempts at preventing the development of PTSD posttrauma. However, current literature shows opposing and conflicting results regarding the effect of selective noradrenergic agents in memory processing, and the effect of modulation of selective noradrenergic receptors are spread over diverse protocols and paradigms of learning and fear also employing different strains of animals. Fear conditioning is a behavioural paradigm that uses associative learning to study the neural mechanisms underlying learning, memory and fear. It is useful in investigating the underpinnings of disorders associated with maladaptive fear responses. Performing fear conditioning experiments with the aim of applying it to an animal model of PTSD, and relating these behavioural responses to a defined neural mechanism, will assist both in the elucidation of the underlying pathology of the disease, as well as the development of more effective treatment. This project has set about to re–examine the diverse and complex role of noradrenergic receptors in the conditioned fear response with relevance to PTSD. To the best of my knowledge, this study represents the first attempt at studying a range of noradrenergic compounds with diverse actions and their ability to modify conditioned fear in a single animal model. This work thus introduces greater consistency and comparative relevance not currently available in the literature, and will also provide much needed pre–clinical evidence in support of treatment strategies targeting the noradrenergic system in the prevention of PTSD posttrauma. The first objective of this study was to set up and validate a passive avoidance fear conditioning protocol under our laboratory conditions using the Gemini Avoidance System. The noradrenergic system plays a prominent role in memory consolidation and fear conditioning, while administration of –adrenergic blockers, such as propranolol, have been shown to abolish learning and fear conditioning in both humans and animals. Propranolol has also demonstrated clinical value in preventing the progression of acute traumatic stress syndrome immediately posttrauma to full–blown PTSD. To confer predictive validity to our model, the centrally active –adrenergic antagonist, propranolol, and the non–centrally acting –adrenergic antagonist, nadolol, were administered to Wistar rats after passive avoidance fear conditioning training in the Gemini Avoidance System. Wistar rats were used because of their recognised enhanced sensitivity to stress. Evidence from this pilot study confirmed that propranolol 10 mg/kg significantly inhibits the consolidation of learned fear in rats, whereas nadolol is ineffective. This effectively validated our protocol and the apparatus for further application in this study and also confirmed the importance of a central mechanism of action for –adrenoceptor blockade in the possible application of these drugs in preventing the development of PTSD posttrauma. The second objective of this study was to investigate the role of 1–, 2–, 1–, and 2–receptors in a conditioned fear passive avoidance paradigm. This was done in order to investigate how selective pharmacological modulation of these receptors may modify the conditioned fear response, and whether any of these receptor systems might exert opposing effects in passive fear conditioning. Various centrally active noradrenergic agents were employed over a 3–tiered dose response design, including the 1–antagonist, prazosin, the 2–agonist, guanfacine, the 2–antagonist, yohimbine, the 1–antagonist, betaxolol and the 2–antagonist ICI 118551. The effect of post–exposure administration of these drugs on conditioned fear was compared to that of propranolol 10 mg/kg. Selected doses of betaxolol (10 mg/kg) and ICI 118551 (1 mg/kg) attenuated fear conditioning to an extent comparable to propranolol, as did prazosin (0.1 mg/kg). Yohimbine tended to boster fear learning at all doses tested, albeit not significantly, while guanfacine did not produce any significant effect on memory retention at any of the doses studied. This latter observation was surprising since yohimbine tended to bolster fear conditioning while earlier studies indicate that 2–agonism impairs conditioned fear. Concluding, this study has conferred validity to our passive avoidance model and has provided greater insight into the separate roles of noradrenergic receptors in contextual conditioned fear learning. The study has provided supportive evidence for a key role for both 1– and 2–antagonism, as well as 1–antagonism, in inhibiting fear memory consolidation and hence as viable secondary treatment options to prevent the development of PTSD posttrauma. However, further study is required to delineate the precise role of the 2–receptor in this regard. / Thesis (M.Sc. (Pharmacology))--North-West University, Potchefstroom Campus, 2012.

Posttraumatic stress disorder is a debilitating anxiety disorder that can develop in the aftermath of a traumatic or life–threatening event involving extreme horror, intense fear or bodily harm. The disorder is typified by a symptom triad consisting of re–experiencing, hyperarousal and avoidance symptoms. Approximately 15–25% of trauma–exposed individuals go on to develop PTSD, depending on the nature and severity of the trauma. Although dysfunctional adaptive responses exist in multiple neurobiological pathways in the disorder, e.g. glutamate, GABA, glucocortocoids and serotonin, the noradrenergic system is particularly prominent and represents an important pharmacological target in attempts at preventing the development of PTSD posttrauma. However, current literature shows opposing and conflicting results regarding the effect of selective noradrenergic agents in memory processing, and the effect of modulation of selective noradrenergic receptors are spread over diverse protocols and paradigms of learning and fear also employing different strains of animals. Fear conditioning is a behavioural paradigm that uses associative learning to study the neural mechanisms underlying learning, memory and fear. It is useful in investigating the underpinnings of disorders associated with maladaptive fear responses. Performing fear conditioning experiments with the aim of applying it to an animal model of PTSD, and relating these behavioural responses to a defined neural mechanism, will assist both in the elucidation of the underlying pathology of the disease, as well as the development of more effective treatment. This project has set about to re–examine the diverse and complex role of noradrenergic receptors in the conditioned fear response with relevance to PTSD. To the best of my knowledge, this study represents the first attempt at studying a range of noradrenergic compounds with diverse actions and their ability to modify conditioned fear in a single animal model. This work thus introduces greater consistency and comparative relevance not currently available in the literature, and will also provide much needed pre–clinical evidence in support of treatment strategies targeting the noradrenergic system in the prevention of PTSD posttrauma. The first objective of this study was to set up and validate a passive avoidance fear conditioning protocol under our laboratory conditions using the Gemini Avoidance System. The noradrenergic system plays a prominent role in memory consolidation and fear conditioning, while administration of –adrenergic blockers, such as propranolol, have been shown to abolish learning and fear conditioning in both humans and animals. Propranolol has also demonstrated clinical value in preventing the progression of acute traumatic stress syndrome immediately posttrauma to full–blown PTSD. To confer predictive validity to our model, the centrally active –adrenergic antagonist, propranolol, and the non–centrally acting –adrenergic antagonist, nadolol, were administered to Wistar rats after passive avoidance fear conditioning training in the Gemini Avoidance System. Wistar rats were used because of their recognised enhanced sensitivity to stress. Evidence from this pilot study confirmed that propranolol 10 mg/kg significantly inhibits the consolidation of learned fear in rats, whereas nadolol is ineffective. This effectively validated our protocol and the apparatus for further application in this study and also confirmed the importance of a central mechanism of action for –adrenoceptor blockade in the possible application of these drugs in preventing the development of PTSD posttrauma. The second objective of this study was to investigate the role of 1–, 2–, 1–, and 2–receptors in a conditioned fear passive avoidance paradigm. This was done in order to investigate how selective pharmacological modulation of these receptors may modify the conditioned fear response, and whether any of these receptor systems might exert opposing effects in passive fear conditioning. Various centrally active noradrenergic agents were employed over a 3–tiered dose response design, including the 1–antagonist, prazosin, the 2–agonist, guanfacine, the 2–antagonist, yohimbine, the 1–antagonist, betaxolol and the 2–antagonist ICI 118551. The effect of post–exposure administration of these drugs on conditioned fear was compared to that of propranolol 10 mg/kg. Selected doses of betaxolol (10 mg/kg) and ICI 118551 (1 mg/kg) attenuated fear conditioning to an extent comparable to propranolol, as did prazosin (0.1 mg/kg). Yohimbine tended to boster fear learning at all doses tested, albeit not significantly, while guanfacine did not produce any significant effect on memory retention at any of the doses studied. This latter observation was surprising since yohimbine tended to bolster fear conditioning while earlier studies indicate that 2–agonism impairs conditioned fear. Concluding, this study has conferred validity to our passive avoidance model and has provided greater insight into the separate roles of noradrenergic receptors in contextual conditioned fear learning. The study has provided supportive evidence for a key role for both 1– and 2–antagonism, as well as 1–antagonism, in inhibiting fear memory consolidation and hence as viable secondary treatment options to prevent the development of PTSD posttrauma. However, further study is required to delineate the precise role of the 2–receptor in this regard. / Thesis (M.Sc. (Pharmacology))--North-West University, Potchefstroom Campus, 2012.

Des études récentes ont montré le rôle clé de la ligne médiane ventrale du thalamus (noyaux Reuniens et Rhomboïde; ReRh) dans la persistance d’une mémoire spatiale chez le Rat qui nécessite un dialogue hippocampo-préfrontal pour une consolidation au niveau des systèmes. Etant donné que l’environnement enrichi (EE) favorise la récupération d’une mémoire de type déclarative après une lésion diencéphalique (thalamus antérieur) et augmente la plasticité neuronale, nous avons évalué son impact sur la consolidation/rappel d'une mémoire spatiale ancienne en piscine de Morris (25 jours post-acquisition) chez le rat après une lésion des noyaux ReRh. Pour cela, nous avons exposé les animaux pendant 40 jours à un environnement enrichi débutant 2 semaines après la lésion excitotoxique thalamique. En outre, l’expression du gène précoce, c-fos, a été cartographiée en immunohistochimie comme marqueur de l'activité neuronale dans l'hippocampe dorsal, le cortex préfrontal médian (mPFC), les noyaux intralaminaires du thalamus et l’amygdale. L’EE a permis la récupération des capacités de persistance d’une mémoire spatiale chez les rats lésés ReRh, accompagnée d’effets bénéfiques sur l'anxiété et l'habituation à un nouvel environnement. L’immunohistochimie de la protéine Fos a montré un recrutement plus élevé des neurones du mPFC associé à la récupération fonctionnelle chez les rats ReRh enrichis, alors que les rats ReRh élevés en condition standard ont présenté un défaut d’activation dans cette région associé à une altération des performances de mémoire. De plus, l’hyperactivité de l’amygdale induite par la lésion chez les rats ReRh standard à la fois en condition basale et après le rappel d’une mémoire a été significativement atténuée dans le groupe ReRh enrichi. Ainsi, nous avons suggéré que l'amygdale pourrait être impliquée dans les effets de la lésion ReRh sur la perte des capacités de rappel d’une mémoire ancienne, mais aussi dans la récupération fonctionnelle associée à la restauration de l’activité du mPFC au rappel de cette mémoire chez les rats lésés enrichis. / Recent studies have shown the key role of the ventral midline thalamus (Reuniens and Rhomboid nuclei; ReRh) in spatial memory persistence in rats, which requires a hippocampo- prefrontal dialogue for consolidation at the systems-level. As enriched environment (EE) promotes the recovery of declarative-like memories after diencephalic (anterior thalamus) lesion, and enhances neuronal plasticity, we tested its impact on the effects of the ReRh lesion upon the consolidation/retrieval of a remote spatial memory in a Morris water maze (i.e. 25 post-acquisition days). For this purpose, we exposed rats for 40 days to an enriched environment beginning 2 weeks after fiber-sparing excitotoxic thalamic lesions. In addition, the expression of the immediate early gene, c-fos, was mapped by immunohistochemistry as a marker of functional activity in the dorsal hippocampus, the median prefrontal cortex (mPFC), the intralaminar thalamic nuclei and the amygdala. Enriched housing allows the recovery of spatial memory persistence capacities in ReRh rats, with additional beneficial effects on anxiety and habituation to a novel environment. Immunohistochemistry of the Fos protein showed a higher recruitment of the mPFC, concomitant with memory capacities recovery in enriched ReRh rats, while in standard ReRh rats, Fos expression in the mPFC was significantly decreased together with the alteration of memory performance. The lesion-induced amygdala hyperactivity in basal and memory conditions was significantly attenuated in the ReRh enriched group. We suggested that amygdala might be involved in the effect of ReRh lesion on memory persistence, and also in the functional recovery associated with the restoration of the mPFC activity during remote memory retrieval in enriched ReRh rats.

Les modifications post-traductionnelles des histones jouent un rôle majeur dans la régulation de l’expression de gènes impliqués dans la plasticité et la mémoire. Parmi ces modifications, l’acétylation des histones permet le maintien de la chromatine dans un état « permissif », accessible pour la transcription. Nos travaux visent à identifier le rôle joué par l’acétylation de deux histones, H3 et H4, dans la formation de différentes formes de mémoire mettant en jeu les systèmes hippocampique et striatal chez la souris. Nous avons également recherché si des perturbations d’acétylation des histones sont responsables des déficits mnésiques observés au cours du vieillissement. Nous avons utilisé deux types d’apprentissage en piscine de Morris permettant de dissocier la mémoire spatiale, impliquant principalement l’hippocampe et la mémoire procédurale/indicée, impliquant le striatum. Nos résultats mettent en lumière une régulation différentielle de l’acétylation des histones dans l’hippocampe et le striatum selon la nature de la tâche et l’âge des animaux. L’apprentissage spatial induit une augmentation de l’acétylation des histones sélectivement dans l’hippocampe (CA1 et gyrus denté) alors que la tâche indicée augmente l’acétylation des histones spécifiquement dans le striatum. Nous montrons également que des changements opposés de l’acétylation de H3 (augmentation) et de H4 (diminution) dans l’hippocampe pourraient contribuer aux déficits de mémoire spatiale observés chez les souris âgées. Lors d’un test de compétition en piscine de Morris, durant lequel les souris ont le choix entre les stratégies spatiale et indicée pour résoudre la tâche, l’injection intra-hippocampique de Trichostatine A (TSA), un inhibiteur des histones déacétylases, immédiatement après l’apprentissage, perturbe la fonction striatale et favorise l’utilisation préférentielle de la stratégie spatiale hippocampique. Cependant, cet effet de la TSA est absent chez les souris âgées dont la fonction hippocampique est altérée. Dans une dernière série d’expérience, l’analyse des effets d’une injection intra-hippocampique de TSA, après un apprentissage spatial, a permis de préciser les contributions respectives des histones H3/H4 et du facteur de transcription CREB dans les déficits mnésiques associés au vieillissement. Dans leur ensemble, nos travaux apportent des éléments importants concernant l’importance de l’acétylation des histones dans la modulation des interactions entre systèmes de mémoire hippocampique et striatal. / Post-translational modifications of histone proteins play a crucial role in regulating plasticity and memory-related gene expression. Among these modifications, histone acetylation leads to a relaxed or “opened” chromatin state, permissive for transcription. Our work aims to identify the role played by histone H3 and H4 acetylation in the formation of different forms of memory involving hippocampal and striatal systems in mice. We also examined whether alterations of histone acetylation are responsible for age-associated memory deficits. We used two versions of the Morris water maze learning task to dissociate a spatial form of memory that relies on the hippocampus and a procedural/cued memory supported by the striatum. Our results highlight a differential regulation of histone acetylation within the hippocampus and striatum depending on the nature of the task and age of animals. Spatial and cued learning elicited histone acetylation selectively in the hippocampus (CA1 region and dentate gyrus) and the striatum, respectively. Age-related spatial memory deficits were associated with opposite changes in H3 acetylation (increase) and H4 (decrease) selectively in the hippocampus. During a water maze competition task in which mice can choose between spatial and cue-guided strategies, intra-hippocampal injection of Trichostatin A (TSA), an histone deacetylase inhibitor, immediately post-acquisition, impaired striatal function and promoted the use of a hippocampus-based spatial strategy. However, this effect of TSA was absent in old mice in which hippocampal function is impaired. In a final series of experiments, analysis of the effects of intra-hippocampal TSA injection immediately after a spatial training helped to clarify the respective contributions of histone H3/H4 and the transcription factor CREB in spatial memory deficits associated with aging. Taken together, our work provides important information regarding the importance of histone acetylation in modulating interactions between hippocampal and striatal memory systems.

Slow-wave sleep plays an important role in consolidation of declarative memory. From electrophysiological point of view, this process is dependent on a common occurrence and mutual integration of neocortical slow oscillations (< 1 Hz), hippocampal sharp-wave ripples (150-250 Hz) and thalamo-cortical sleep spindles (10-15 Hz). Previous studies demonstrated that periodic acoustic stimulation by pink noise pulses applied at frequency of sleep slow oscillation during slow wave sleep leads to prolongation of slow wave sleep and to enhancement in declarative memory performance in normal sleepers. Our study investigated this kind of periodic acoustic stimulation in its relation to sleep architecture and declarative memory of people suffering from insomnia due to which there often comes to a reduction in slow wave sleep which positively correlates with worsening of declarative memory performance. Our aim was to investigate if this kind of comparatively non-invasive brain stimulation has a potential to increase a total length of slow wave sleep and enhance declarative memory performance in insomnia. Our study revealed acoustic stimulation neither improved declarative memory performance nor it increased total length of slow-wave sleep. No positive association was found between level of declarative memory...