Es existiert bereits eine Vielzahl von tierexperimentellen Studien bezüglich Einflussfaktoren auf die adulte Neurogenese. Nachdem die Teilungsfähigkeit von neuralen Stammzellen Ende der 1990er Jahre auch im adulten humanen Gehirn nachgewiesen wurde, war es das Ziel der vorliegenden Arbeit, adulte Neurogenese bei psychischen Erkrankungen zu quantifizieren bzw. den Ein-fluss medikamentöser Therapien auf die adulte Neurogenese zu untersuchen. Diese Studie stellt dabei die bislang einzige Arbeit dar, die sich mit der humanen adulten Neurogenese bei psychischen Erkrankungen beschäftigt. Mittels Doppelfärbungen von Ki67 und BrdU an Mausgewebe wurde zunächst nachgewiesen, dass das Ki67-Antigen ein zuverlässiger Marker für sich teilende Zellen ist, woraufhin die Färbeprozedur problemlos auf Humangewebe übertragen werden konnte. Die Quantifizierung von Ki67 positiven Zellen erfolgte entlang der Körnerzellschicht in einem definierten Abstand in der Einheit Zellen pro Millimeter. Die Ergebnisse der hier vorliegenden Studie widersprechen in mehrfacher Hinsicht den Hypothesen, die sich aus tierexperimentellen Studien ergeben. Während die neurale Stammzellproli-feration bei schizophrenen Psychosen signifikant vermindert ist, findet sich kein Unterschied bei affektiven Erkrankungen im Vergleich zu Kontrollen. Weder wird die „Neurogenese-Hypothese“ der Depression bestätigt, noch zeigte sich ein Effekt antidepressiv oder antipsychotisch wirksamer Pharmaka auf die Rate adulter Neurogenese, da eine pharmakologische Therapie jedweder Art keinen Einfluss auf die Zahl Ki67 positiver Zellen hatte. Deshalb scheint eine Steigerung der adulten Neurogenese kein Wirkmechanismus dieser Medikamente zu sein. Ein überraschendes Ergebnis jedoch ist die signifikant reduzierte Rate adulter Neurogenese bei an Schizophrenie erkrankten Patienten. Aufgrund der sehr begrenzten Anzahl untersuchter Patienten ist die vorliegende Studie in ihrer Aussagekraft jedoch eingeschränkt und muss daher an einem größeren Patientenkollektiv wiederholt werden. Eine Vielzahl von Fragen bzgl. des Stellenwerts der adulten Neurogenese bei psychischen Erkrankungen bleibt darüber hinaus weiter ungeklärt, was die Durchführung weiterer Studien am adulten humanen Gehirn verlangt. / The phenomenon of adult neurogenesis (AN), that is, the generation of functional neurons from neural stem cells in the dentate gyrus of the hippocampus, has attracted remarkable attention, especially as it was shown that this process is also active in the human brain. Based on animal studies, it has been suggested that reduced AN is implicated in the etiopathology of psychiatric disorders, and that stimulation of AN contributes to the mechanism of action of antidepressant therapies. As data from human post-mortem brain are still lacking, we investigated whether the first step of AN, that is, the level of neural stem cell proliferation (NSP; as quantified by Ki-67 immunohistochemistry), is altered in tissue from the Stanley Foundation Neuropathology Consortium comprising brain specimens from patients with bipolar affective disorder, major depression, schizophrenia as well as control subjects (n = 15 in each group). The hypothesis was that stem cell proliferation is reduced in affective disorders, and that antidepressant treatment increases NSP. Neither age, brain weight or pH, brain hemisphere investigated nor duration of storage had an effect on NSP. Only in bipolar disorder, postmortem interval was a significant intervening variable. In disease, onset of the disorder and its duration likewise did not affect NSP. Also, cumulative lifetime dose of fluphenazine was not correlated with NSP, and presence of antidepressant treatment did not result in an increase of NSP. Concerning the different diagnostic entities, reduced amounts of newly formed cells were found in schizophrenia, but not in major depression. Our findings suggest that reduced NSP may contribute to the pathogenesis of schizophrenia, whereas the rate of NSP does not seem to be critical to the etiopathology of affective disorders, nor is it modified by antidepressant drug treatment.

Os endocanabinóides (ECs) são neuromoduladores lipídicos que são produzidos por demanda tendo ação retrógrada. Existem duas moléculas que são atualmente reconhecidos como os principais ECs, a anandamida (AEA) e 2-araquidonoilglicerol (2-AG). O hipocampo sintetiza endocanabinóides e expressa seus receptores (CB1, CB2, TRPV1).Existe uma discrepância de efeitos dos 2 endocanabinóides na potenciação á longo prazo (LTP) hipocampal que pode ser um resultado da AEA agir tanto em receptores CB1 quanto em receptores TRPV1.Tendo em vista que a ativação dos receptores TRPV1 potenciam a LTP hipocampal, e não a inibem como é observado com a AEA, então qual seria o mecanismo de ação da AEA em inibir a LTP? Seria possível que a AEA estivesse preferencialmente inibindo a produção de 2-AG e assim inibindo a LTP? Para testar essa hipótese usamos inibidores farmacológicos da degradação hidrolítica do 2-AG e da AEA e também usamos antagonistas dos receptores TRPV1 e um animal knock-out para o receptor TRPV1. Camundongos machos BlackC57 e knockout(KO) para TRPV1 com idade entre 35 a 49 dias foram utilizados para obtenção de fatias do hipocampo (400µm), e a potenciação a longo prazo na via Schaffer-CA1 estudada. Não observamos efeito dos inibidores da degradação hidrolítica e oxidative dos endocanabinóides na LTP. A LTP do camundongo knock-out era inibida, porem o antagonismo farmacológico dos receptores TRPV1 não minetizou esse efeito. Já o agonista dos receptors canabinóides WIN55212-2 inibiu a indução da LTP. Concluimos que o aumento dos endocanabinóides pela inibição da sua degradação não foi eficiente em alterar a LTP hippocampal em nosso modelo experimental. Aprovação do CONCEA-FMRP- nº008/2017 / Endocannabinoids (ECs) are lipid neuromodulators that are produced on demand having retrograde action. There are two molecules that are currently recognized as the major ECs, anandamide (AEA) and 2-arachidonoylglycerol (2-AG). The hippocampus synthesizes endocannabinoids and expresses their receptors (CB1, CB2, TRPV1). There is a discrepancy of endocannabinoid effects on hippocampal long term potentiation (LTP) which may be a result of AEA acting on both CB1 and TRPV1 receptors. Given that the activation of TRPV1 receptors potentiate hippocampal LTP, and do not inhibit it as observed with AEA, then what would be the mechanism of action of AEA in inhibiting LTP? Was it possible that AEA was preferentially inhibiting 2-AG production and thus inhibiting LTP? To test this hypothesis, we used pharmacological inhibitors of the hydrolytic degradation of 2-AG and AEA and also used TRPV1 receptor antagonists and a knock-out animal for the TRPV1 receptor. Male BlackC57 mice and TRPV1 knockout (KO) aged 35 to 49 days were used to obtain hippocampal slices (400 ?m), and the long-term potentiation in the Schaffer-CA1 pathway studied). The LTP of the knock-out mouse was inhibited, but the pharmacological antagonism of TRPV1 receptors did not mimic this effect, whereas the WIN55212-2 cannabinoid receptor agonist inhibited the induction of LTP. We conclude that increasing the levels of endocannabinoids by inhibiting their degradation was not efficient in altering hippocampal LTP in our experimental model Approval of CONCEA-FMRP- nº 008/2017

Les neurones GABAergiques sont une composante majeure des réseaux neuronaux corticaux. Au cours du développement, les neurones GABAergiques pionniers générés aux stades les plus précoces de l’embryogénèse forment une sous-population de neurones « hubs ». Cependant, leurs propriétés et leurs fonctions à l'âge adulte restent inconnus. En combinant différentes techniques, nous montrons que ces neurones pionniers ont également une fonction « hub » dans la région CA1 en développement in vitro et qu’ils maintiennent une forte connectivité fonctionnelle pendant les périodes de veille calme chez la souris adulte in vivo. Ces neurones, peu actifs de façon spontanée chez l’adulte, sont préférentiellement recrutés pendant les activités calciques synchrones souvent associées aux oscillations de type « SWRs ». Ceci est compatible avec leur faible excitabilité intrinsèque, révélée par des enregistrements en courant-imposé. L’étude des connexions synaptiques afférentes des neurones pionniers de CA1 adulte, par optogénétique, révèle un schéma de connectivité remarquable avec des entrées synaptiques GABAergiques issues du septum et la quasi-absence d’entrées thalamiques. Localement, ces neurones reçoivent moins de courants postsynaptiques GABAergiques, témoignant d’une intégration différentielle dans le réseau GABAergique inhibiteur. Enfin, nous montrons qu’une majorité significative de ces neurones pionniers appartiennent à la famille des neurones à projection longue distance. En conclusion, nous montrons que les neurones GABAergiques pionniers sont prédéterminés à occuper une place remarquable dans l’organisation fonctionnelle et structurale de l’hippocampe tout au long de leur vie. / The remarkable diversity of cortical GABAergic neurons is rooted, at least in part, in their embryonic origins. Adding to the spatial control of interneuron specification is a temporal schedule that has significant impact on their fate. In the CA3 region of the hippocampus, GABAergic cells born the earliest (ebGABA) form a sparse subpopulation acting as ‘hubs’ during development and surviving until adulthood. However, their properties and function in adulthood remain elusive. Using a combination of techniques, we demonstrate that ebGABA neurons also operate as “hubs” in the developing CA1 region in vitro and that they seem to maintain such remarkable functional connectivity into adulthood as observed during quiet rest in vivo. EbGABA display a lower spontaneous activity rate, as expected from their lower intrinsic excitability and are preferentially recruited during the synchronous calcium events previously shown to be associated with SWRs. EbGABA also display a remarkable synaptic connectivity scheme as they receive long-range GABAergic septal inputs but are almost excluded from thalamic afferents. Locally, they receive fewer spontaneous inhibitory postsynaptic currents, indicating a particular integration into local GABAergic circuits. Moreover, using combinatorial immunohistochemistry, we have shown that a majority of these ebGABA neurons are long-range projection GABAergic neurons. We conclude that, ebGABA cells are predetermined to become exceptional nodes in the functional and structural organization of the hippocampus, throughout their lifetime.

Experimentally naive rats exhibit varying degrees of novelty exploration. Some rats display high rates of locomotor reactivity to novelty (high responders; HR), and others display low rates (low responders; LR). The novelty-seeking phenotype (LRHR) is introduced as a model of stress responsiveness. In this thesis I examined effects of chronic variable physical and social stress or control handling on the levels of various neurotrophins in the hippocampus, and changes in mossy fibre terminal fields in LRHR rats. A positive correlation is seen between histone deacetylase 2 and brain-derived neurotrophic factor (BDNF) levels both of which are oppositely regulated in LRHR CA3 fields in response to chronic social stress. Increase in BDNF levels in CA3 field accompanied increase in supra-pyramidal mossy fibre terminal field size (SP-MF) in HRs, and decrease in BDNF levels accompanied decrease in SP-MF volume in LRs. Epigenetic regulation of neurotrophic support underlying these structural changes is discussed. / by Ozge Oztan. / Thesis (M.S.)--Florida Atlantic University, 2009. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2009. Mode of access: World Wide Web.

O hipocampo dorsal (HD) é uma estrutura do sistema límbico que está envolvida em processos emocionais, de memória e aprendizado. Alem disso, o HD também exerce influência sobre a atividade autonômica. Durante situações aversivas pode se observar tanto respostas autonômicas (aumento da pressão arterial, frequência cardíaca e queda da temperatura cutânea) quanto comportamentais. O HD está envolvido com diversas alterações associadas a reações defensivas e apresenta conexões com diversas estruturas que modulam essas respostas, fazendo parte de uma via responsável por modular as respostas durante situações aversivas. São observadas aumentos nas respostas autonômicas durante o estresse por restrição (ER). Durante a atividade do HD está aumentada. Além disso, é possível observar aumento dos níveis de glutamato no HD. A ativação de receptores glutamatérgicos do tipo NMDA no sistema nervoso central aumenta a síntese de óxido nítrico (NO) por ativação da isoforma neuronial da óxido nítrico sintase (nNOS). Além disso, esta interação, NMDA/NO, no HD parece ser importante nas reações defensivas. Portanto, no presente estudo nós observamos que a administração de glutamato no HD promove aumentos do sistema cardiovascular, similares a aqueles observados durante situações de estresse. Estas respostas cardiovasculares são associadas com um aumento da atividade simpática. Além disso, os efeitos do glutamato foram inibidos pela administração do AP7, um antagonista NMDA, do N?-Propyl-L-Arginine, um inibidor da nNOS ou do Carboxy-PTIO(S)-3-carboxy-4- hydroxyphenylglicine, um sequestrador de NO. Finalmente, a administração destas drogas foi capaz de reduzir as respostas autonômicas causadas pelo ER. Portanto, nossos achados mostram que o sistema glutamatérgico presente no HD esta envolvido com a modulação autonômica através de receptores do tipo NMDA e a ativação de nNOS. Além disso, esta via NMDA/NO está envolvida na modulação autonômica durante situações de estresse. / The dorsal hippocampus (DH) is a structure of limbic system that is involved in emotional, leaning and memories process. Moreover, the DH also exerts influence on autonomic activity. During aversive situations it is possible observes autonomic responses (increase in blood pressure, heart rate and decrease in cutaneous temperature) associated to defensive behavioral. The DH is involved with alterations associated to defensive reactions and presents connections with several structures which modulate that responses, making part of a pathway involved with behavior and autonomic responses associated with aversive situations. Increase of autonomics responses are observed during restraint stress (RS). During RS the DH activity is increased. Moreover, it is possible observe increases in glutamate levels in DH. In central nervous system the activation of NMDA glutamatergic receptors increases the nitric oxide (NO) synthesis by activate the neuronal isoform of nitric oxide syntase (nNOS). Moreover, this interaction, NMDA/ NO, in the DH appears to important in the defensive reactions. Therefore, in the present work we observed that administration of glutamate in the DH promotes increases of cardiovascular system, similar those observed during stress situation. These cardiovascular responses were associate with an increase of sympathetic activity. Also, the glutamate effects were inhibited by administration of AP7, a NMDA antagonist, N?-Propyl-L-Arginine, a nNOS inhibitor, or Carboxy-PTIO(S)-3- carboxy-4-hydroxyphenylglicine, a NO scavenger. Finally, the administration of these drugs were able to reduces the autonomic responses evoked by RS. Therefore, our findings showed that glutamatergic system present in DH are involved with autonomic modulation through NMDA receptors and nNOS activation. Moreover, this NMDA/ NO is involved with autonomic modulation during stress situation.

O nosso grupo tem investigado os efeitos da Clorfeniramina (CPA), antagonista H1, e da L-histidina (LH), uma droga precursora da síntese de histamina, sobre a ansiedade e a memória emocional. Diante disso, os objetivos desse estudo foram investigar os efeitos LH administrada i.p. e da CPA microinjetada no hipocampo dorsal sobre a ansiedade e a memória emocional de camundongos submetidos ao labirinto em cruz elevado (LCE). O experimento foi realizado em dois dias consecutivos. No primeiro dia (T1) 71 camundongos machos da cepa Suíço-Albino pesando 25-35g foram pré-tratados i.p. com salina (SAL) ou LH (500mg/Kg). Após duas horas, os sujeitos receberam microinjeção de SAL ou CPA (0,016nmol; 0,052nmol; 0,16nmol/0,1l) no hipocampo dorsal. Após cinco minutos, os animais foram expostos ao LCE por cinco minutos. Vinte quatro horas depois, o mesmo protocolo experimental foi adotado na reexposição (T2). Os animais foram distribuídos aleatoriamente em 8 grupos de acordo com o tratamento farmacológico: SAL/SAL (n=9), SAL/CPA1 (n=9), SAL/CPA2 (n=10), SAL/CPA3 (n=8), LH/SAL (n=10), LH/CPA1 (n=8), LH/CPA2 (n=8) e LH/CPA3 (n=9). As três doses de CPA microinjetadas no hipocampo dorsal não alteraram a porcentagem de tempo gasto nos braços abertos (%TBA) na exposição ao LCE: T1 SAL/CPA1 (46,13±4,45); SAL/CPA2 (47,59±4,89); SAL/CPA3 (44,30±6,65) quando comparados com o grupo controle SAL/SAL (35,84±2,77) e não alteraram o número de entradas nos braços fechados (EBF) SAL/CPA1 (8,56±1,06); SAL/CPA2 (9,70±1,10); SAL/CPA3 (9,38±1,25) - quando comparados com o grupo controle SAL/SAL (10,56±1,11). A administração i.p. de LH aumentou a %TBA em T1 para o grupo LH/SAL (59,79±4,71), quando comparado ao grupo controle SAL/SAL (35,84±2,77), mas não alterou o EBF: LH/SAL (9,20±1,78) e SAL/SAL (10,56±1,11). Os animais do grupo LH/CPA3 diminuíram %TBA (32,25±4,81) em T1 quando comparados com o grupo LH/SAL (59,79±4,71). Os animais do grupo SAL/CPA1 não apresentaram diminuição da %TBA em T2 (T1: 46,13±4,45; T2: 39,38±6,53). O mesmo foi observado para os sujeitos dos grupos LH/CPA2 (T1: 50,10±3,99; T2: 40,97±8,22) e LH/CPA3 (T1: 32,25±4,81; T2: 32,16±6,93). Nós concluímos que: a CPA microinjetada no hipocampo dorsal de camundongos não apresenta efeito sobre a ansiedade; a administração intraperitoneal de LH apresenta efeito ansiolítico em camundongos expostos ao LCE e que esse efeito é revertido pela maior dose de CPA (0,16nmol/0,1l); são necessárias maiores doses de CPA para que haja prejuízo na memória emocional de camundongos reexpostos ao LCE quando os níveis de histamina no hipocampo dorsal estão elevados. / Our group has been investigating the effects of Chlorpheniramine (CPA), a histaminergic H1 antagonist, and of L-Histidine (LH), a histamine precursor, on anxiety-related behaviors and emotional memory. Thus the aim of this study was to investigate the effects of LH i.p. injections and of dorsal intra-hippocampal microinjections of Chlorpheniramine (CPA) on anxiety-related behaviors and emotional memory in male mice using elevated plus-maze (EPM). The experiment was performed in two days. On the first day (T1) 71 male Swiss Albino mice of body weight 25- 35g were pre-treated with saline (SAL) i.p. or LH (500mg/Kg) i.p. After two hours they were treated with dorsal intra-hippocampal microinjections of SAL or CPA (0.016nmol; 0.052nmol; 0.16nmol/0,1l). Five minutes after intra-hippocampal microinjections the animals were exposed to EPM for 5 minutes. Twenty four hours later the same protocol was repeated (T2). The animals were randomly assigned to 8 groups based on drug treatment: SAL/SAL (n=9), SAL/CPA1 (n=9), SAL/CPA2 (n=10), SAL/CPA3 (n=8), LH/SAL (n=10), LH/CPA1 (n=8), LH/CPA2 (n=8) and LH/CPA3 (n=9). All three doses of intra-hippocampal microinjections of CPA did not change the percentage of time spent in the open-arms (%OAT) on T1 SAL/CPA1 (46.13±4.45); SAL/CPA2 (47.59±4.89); SAL/CPA3 (44.30±6.65) when compared to control group SAL/SAL (35.84±2.77) and did not change the enclosed arm entries (EAE) SAL/CPA1 (8.56±1.06); SAL/CPA2 (9.70±1.10); SAL/CPA3 (9.38±1.25) when compared to control group SAL/SAL (10.56±1.11). Intraperitoneal injections of LH increased %OAT on T1 on LH/SAL group (59.79±4.71), when compared to control group SAL/SAL (35.84±2.77), but not EAE LH/SAL (9.20±1.78) and SAL/SAL (10.56±1.11). Animals treated with LH and CPA3 (LH/CPA3) decreased %OAT (32.25±4.81) on T1 when compared to LH/SAL (59.79±4.71) group. SAL/CPA1 animals did not decreased %OAT on T2 (T1: 46.13±4.45; T2: 39.38±6.53). The same happened to LH/CPA2 (T1: 50.10±3.99; T2: 40.97±8.22) and LH/CPA3 (T1: 32.25±4.81; T2: 32.16±6.93) groups. Thus, we conclude that: dorsal intra-hippocampal microinjection of Chlorpheniramine has no effect on anxiety-related behaviors in male mice; intraperitoneal injection of L-Histidine has an anxiolytic-like effect in male mice exposed to elevated plus-maze, that is reversed by the higher dose of Chlorpheniramine (0.16nmol/0,1l); higher doses of CPA are necessary to impair emotional memory when the levels of hippocampal histamine are elevated.

La mémoire est communément définie comme la capacité de coder, stocker et rappeler les informations que nous avons perçues. Lorsque nous traversons le monde, nous ressentons des stimuli, nous assistons à des événements, nous constatons des faits, nous étudions des concepts et nous acquérons des compétences. Bien que la mémoire soit un comportement humain inné et familier, les mécanismes cérébraux qui nous fournissent de telles facultés sont loin d'être compris. Des études expérimentales ont montré que, lors des tâches de mémoire, certaines structures cérébrales présentent une activité synchrone qui est censée être corrélée avec le maintien à court terme des stimuli saillants. L'objectif de cette thèse est d'utiliser la modélisation mathématique biologiquement inspirée et des simulations d'activité neuronale pour éclairer les mécanismes permettant l'émergence de ces oscillations synchrones liées à la mémoire. Nous nous concentrons en particulier sur l'activité mnémonique de l'hippocampe pendant l'état éveillé, et l'amnésie et la consolidation inattendue de la mémoire sous anesthésie générale. Nous commençons par présenter un modèle détaillé de neurone pyramidal qui se trouve couramment dans les zones CA3 et CA1 de l'hippocampe. Stimulé par une courte impulsion de courant, le neurone produit une activité persistante maintenue pour de longues périodes (> 30s) au-delà du stimulus uniquement par des récepteurs calciques non spécifiques (CAN). Les paramètres du modèle sont dérivés des enregistrements in vitro de neurones hippocampiques réalisés par nos collaborateurs Beate Knauer et Motoharu Yoshida à l'Université de la Ruhr à Bochum, en Allemagne. Par la suite, nous étudions la dynamique d'une population de ces neurones pyramidaux-CAN interconnectés. Nous supposons que les réseaux de neurones à tir persistant pourraient fournir le mécanisme neuronale pour la maintenance des oscillations hippocampiques mnésiques. Nos résultats montrent que le réseau génère une activité oscillante auto-soutenue dans la fréquence thêta. Lors de la connexion du réseau pyramidal-CAN à des interneurones inhibiteurs, la dynamique du modèle révèle que l'inhibition rétroactive améliore la robustesse des oscillations thêta rapides, en resserrant la synchronisation des neurones pyramidaux. Nous démontrons que, dans le modèle, la fréquence et la puissance spectrale des oscillations sont modulées uniquement par le courant CAN, permettant une large gamme de fréquences d'oscillation dans la bande theta. Il s'agit d'un mécanisme biologiquement plausible pour la maintenance des oscillations thêta synchrones dans l'hippocampe qui vise à étendre les modèles traditionnels d'activité rythmique hippocampique entraînée par le septum. En outre, nous présentons une étude approfondie des effets perturbateurs de l'anesthésie générale sur les oscillations gamma dans l'hippocampe. Nous introduisons un nouveau modèle qui prend en compte les quatre principaux effets de l'agent anesthésique propofol sur les récepteurs GABAA. Nos résultats indiquent que l'inhibition tonique médiée par le propofol contribue à améliorer la synchronisation du réseau dans un réseau d'interneurones de l'hippocampe. Cette synchronisation améliorée pourrait fournir une explication possible pour l'apparition d'une conscience intra-opératoire, d'une formation explicite de la mémoire et même d'une excitation paradoxale sous anesthésie générale, en facilitant la communication entre structures cérébrales qui ne devraient pas être autorisées à le faire lorsqu'elles sont anesthésiées. En conclusion, les résultats décrits dans cette thèse fournissent de nouvelles idées sur les mécanismes sous-jacents de l'activité neuronale mnémonique, à la fois au cours du réveil et de l'anesthésie, en ouvrant des voies convaincantes pour les travaux futurs sur les applications cliniques qui s'attaquent aux maladies de la mémoire neurodégénératives et la surveillance de l'anesthésie. / Memory is commonly defined as the ability to encode, store, and recall information we perceived. As we experience the world, we sense stimuli, we witness events, we ascertain facts, we study concepts, and we acquire skills. Although memory is an innate and familiar human behaviour, the interior workings of the brain which provide us with such faculties are far from being fully unravelled. Experimental studies have shown that during memory tasks, certain brain structures exhibit synchronous activity which is thought to be correlated with the short-term maintenance of salient stimuli. The objective of this thesis is to use biologically-inspired mathematical modelling and simulations of neural activity to shed some light on the mechanisms enabling the emergence of these memory-related synchronous oscillations. We focus in particular on hippocampal mnemonic activity during the awake state, and the amnesia and paradoxical memory consolidation occurring under general anaesthesia. We begin by introducing a detailed model of a type of persistent-firing pyramidal neuron commonly found in the CA3 and CA1 areas of the hippocampus. Stimulated with a brief transient current pulse, the neuron displays persistent activity maintained solely by cholinergic calcium-activated non-specific (CAN) receptors, and outlasting the stimulus for long delay periods (> 30s). Our model neuron and its parameters are derived from experimental in-vitro recordings of persistent firing hippocampal neurons carried out by our collaborators Beate Knauer and Motoharu Yoshida at the Ruhr University in Bochum, Germany. Subsequently, we turn our attention to the dynamics of a population of such interconnected pyramidal-CAN neurons. We hypothesise that networks of persistent firing neurons could provide the neural mechanism for the maintenance of memory-related hippocampal oscillations. The firing patterns elicited by this network are in accord with both experimental recordings and modelling studies. In addition, the network displays self-sustained oscillatory activity in the theta frequency. When connecting the pyramidal-CAN network to fast-spiking inhibitory interneurons, the dynamics of the model reveal that feedback inhibition improves the robustness of fast theta oscillations, by tightening the synchronisation of the pyramidal CAN neurons. We demonstrate that, in the model, the frequency and spectral power of the oscillations are modulated solely by the cholinergic mechanisms mediating the intrinsic persistent firing, allowing for a wide range of oscillation rates within the theta band. This is a biologically plausible mechanism for the maintenance of synchronous theta oscillations in the hippocampus which aims at extending the traditional models of septum-driven hippocampal rhythmic activity. In addition, we study the disruptive effects of general anaesthesia on hippocampal gamma-frequency oscillations. We present an in-depth study of the action of anaesthesia on neural oscillations by introducing a new computational model which takes into account the four main effects of the anaesthetic agent propofol GABAergic hippocampal interneurons. Our results indicate that propofol-mediated tonic inhibition contributes to enhancing network synchronisation in a network of hippocampal interneurons. This enhanced synchronisation could provide a possible mechanism supporting the occurrence of intraoperative awareness, explicit memory formation, and even paradoxical excitation under general anaesthesia, by facilitating the communication between brain structures which should supposedly be not allowed to do so when anaesthetised. In conclusion, the findings described within this thesis provide new insights into the mechanisms underlying mnemonic neural activity, both during wake and anaesthesia, opening compelling avenues for future work on clinical applications tackling neurodegenerative memory diseases, and anaesthesia monitoring

L'hippocampe est une région du cerveau importante pour la formation de mémoire. Des études récentes ont montré que la zone CA2 de l'hippocampe, longtemps ignorée, joue un rôle clef dans certaines formes de mémoire et notamment dans la mémoire sociale. De plus, des études post-mortem ont révélé des altérations spécifiques à la région CA2 chez les patients schizophrènes. Cependant, l’implication des neurones de CA2 dans les circuits de l'hippocampe reste peu connu, tant dans des conditions physiologiques que pathologiques. En combinant pharmacologie, génétique et électrophysiologie sur tranches d’hippocampe de souris, nous avons étudié comment les neurones pyramidaux (NP) CA2 sont recrutés dans les circuits hippocampiques après des changements d’inhibition et comment le recrutement des NP CA2 pourrait moduler l’information sortant de l'hippocampe. D’autre part, nous avons examiné les altérations fonctionnelles de la zone CA2 dans le modèle murin Df(16)A+/- de la microdélétion 22q11.2, le facteur génétique de risque de schizophrénie le plus élevé. Dans la région CA2 de l’hippocampe, les synapses inhibitrices contrôle les afférences des collatérales de Schaeffer (CS) et expriment une dépression à long-terme (DLTi) unique qui dépendant des récepteurs delta-opioïdes (RDO). Contrairement aux synapses CS-CA1, les synapses excitatrices CS-CA2 n’expriment pas de potentialisation à long-terme après application des protocoles d'induction. Cependant, nous avons constaté que différents types d'activités induisent une augmentation durable de l’amplitude des potentiels post-synaptiques (PPS) évoqués aussi bien par une stimulation des CS que des afférences distales des NP CA2, et ceci via une modulation de la balance excitation/inhibition. Nous avons démontré que ces augmentations du rapport excitation/inhibition sont les conséquences directes de la DLTi RDO-dépendante. De plus, la DLTi permet le recrutement des NP CA2 par les NP CA3 alors qu’une inhibition intacte empêche complètement leur activation en réponse aux stimulations des CS. Par ailleurs, le recrutement des pyramides de CA2 par les CS après disinhibition activité-dépendante ajoute une composante polysynaptique (SC-CA2-CA1) au PPS monosynaptique (SC-CA1) dans les NP CA1 et augmente leur activité. De plus, l’inactivation des interneurones exprimant la parvalbumine à l’aide d’outils pharmacogénétiques, a montré que ces cellules inhibitrices contrôlent fortement l'amplitude du PPS et l’activité des NP CA2 en réponse à la stimulation des CS et qu’elles sont nécessaires à l'augmentation RDO-dépendante du rapport excitation/inhibition entre CA3 et CA2. Enfin, l'étude de la zone CA2 chez les souris Df(16)A+/- a révélé plusieurs modifications dépendantes de l'âge dont une réduction de l'inhibition, une altération de la plasticité du rapport excitation/inhibition entre CA3 et CA2 et une hyperpolarisation NP CA2. Ces modifications cellulaires peuvent expliquer les déficiences de mémoire sociale que nous observons chez les souris Df(16)A+/- adultes. L’ensemble de nos études a permis de mettre en évidence le rôle des neurones CA2 dans les circuits de l'hippocampe. Enfin pour conclure, nous postulons que le recrutement des neurones CA2 dans les réseaux neuronaux sous-tend des aspects particuliers de la fonction de l'hippocampe. / The hippocampus is a region of critical importance for memory formation. Recent studies have shown that the long-overlooked hippocampal region CA2 plays a role in certain forms of memory, including social recognition. Furthermore, post-mortem studies of schizophrenic patients have revealed specific changes in area CA2. As yet, the role of CA2 neurons in the hippocampal circuitry remains poorly understood under both normal physiological and pathological conditions. By combining pharmacology, mouse genetics and electrophysiology, we investigated how CA2 pyramidal neurons (PNs) could be recruited in hippocampal circuits in mice hippocampal slices following an activity-dependent change in the strength of their inhibitory inputs. We further investigated how subsequent recruitment of CA2 PNs could modulate hippocampal output. Moreover, we examined the functional alterations of area CA2 in the Df(16)A+/- mouse model of the 22q11.2 microdeletion, a spontaneous chromosomal deletion that is the highest known genetic risk factor for developing schizophrenia. In area CA2, inhibitory synapses exert a powerful control of Schaffer collateral (SC) inputs and undergo a unique long-term depression (iLTD) mediated by delta-opioid receptor (DOR) activation. Unlike SC-CA1 synapses, SC-CA2 excitatory synapses fail to express long-term potentiation after classical induction protocols. However, we found that different patterns of activity persistently increase both the SC and the distal input net excitatory drive onto CA2 PNs via a modulation of the balance between excitation and inhibition. We demonstrated that increases in the excitatory/inhibitory ratio are direct consequences of the DOR-mediated iLTD. Interestingly, we found that the inhibition in area CA2 completely preventing CA3 PNs to activate CA2 PNs, and following iLTD, SC stimulation allows CA2 PNs to fire action potentials. Moreover, the recruitment of CA2 PNs by SC intra-hippocampal inputs after their activity-dependent disinhibition adds a delayed SC-CA2-CA1 response to the SC-CA1 monosynaptic post-synaptic potential (PSP) in CA1 and increases CA1 PN activity. Furthermore, pharmaco-genetic silencing of parvalbumin-expressing interneurons revealed that these inhibitory cells control the PSP amplitude and the firing of CA2 PNs in response to SC stimulation and are necessary for the DOR-mediated increase in excitatory/inhibitory balance between CA3 and CA2. Finally, we found several age-dependent alterations in area CA2 in Df(16)A+/- mouse model of the 22q11.2 microdeletion. These included a reduction in inhibition, an impaired activity-dependent modulation of the excitatory drive between CA3 and CA2 and a more hyperpolarized CA2 PN resting potential. These cellular disruptions may provide a potential mechanism for the social memory impairment that we observe in Df(16)A+/- adult mice. Altogether, our studies highlight the role of CA2 neurons in hippocampal circuitry. To conclude, we postulate that the recruitment of CA2 neurons in neuronal networks underlies key aspects of hippocampal function.

The hippocampal-medial prefrontal circuit has been shown to serve a critical role in decision making and goal directed actions. While the hippocampus (HF) exerts a direct influence on the medial prefrontal cortex (mPFC), there are no direct return projections from the mPFC to the HF. The nucleus reuniens (RE) of the midline thalamus is strongly reciprocally connected with the HF and mPFC and represents the major link between these structures. We investigated the role of RE in functions associated with the hippocampus and the mPFC -- or their interactions. Using two different inactivation techniques (pharmacological and chemogenetic), we sought to further define the role of RE in spatial working memory (SWM) and behavioral flexibility using a modified delayed non-match to sample (DNMS) working memory task. We found that the reversible inactivation of RE with muscimol critically impaired SWM performance, abolished well-established spatial strategies and produced a profound inability to correct non-rewarded, incorrect choices on the T-maze (perseverative responding). We observed similar impairments in SWM following the chemogenetic (DREADDs) inactivation of RE or selective RE projections to the ventral HF. In addition, we showed that the inhibition of RE terminals to the dorsal or ventral HF altered task related behaviors by increasing or decreasing the time to initiate the task or reach the reward, respectively. Finally, we examined discharge properties of RE cells across sleep-wake states in behaving rats. We found that the majority of RE cells discharge at high rates of activity in waking and REM and at significantly reduced rates in SWS, with a subpopulation firing rhythmically in bursts during SWS. We identified five distinct subtypes of RE cells that discharged differently across vigilant states; those firing at highest rates in waking (W1, W2), in REM sleep (R1, R2) and SWS (S1). Given the differential patterns of activity of these cells, we proposed they may serve distinct functions in waking – and possibly in SWS/REM sleep. In sum, our findings indicate that RE is critically involved in mnemonic and executive functions and the heterogeneous activity of these cells support a role for RE in arousal/attention, spatial working memory and cognition. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2018. / FAU Electronic Theses and Dissertations Collection

Male C7BL/6J mice were implanted with bilateral dorsal CA1 guide cannulae. After confirming that intrahippocampal microinfusion of muscimol impaired hippocampal function, demonstrated by impaired performance in the Morris water maze, the influence of intrahippocampal muscimol was tested in the Novel Object Recognition paradigm. During a test session 24 h after the last habituation/sample session, mice were presented with one familiar object and one novel object. Successful retention of object memory was inferred if mice spent more time exploring the novel object than the familiar object. Results demonstrate that muscimol infused into dorsal CA1 region prior to the test session eliminates novel object preference, indicating that the hippocampus is necessary for the retrieval of this non-spatial memory - a topic that has garnered much debate. Understanding the similarities between rodent and human hippocampal function could enable future animal studies to effectively answer questions about diseases and disorders affecting human learning and memory. / by Lisa Rios. / Thesis (M.A.)--Florida Atlantic University, 2011. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2011. Mode of access: World Wide Web.