Due to global warming, our planet will experience more extreme weather conditions. Plants can protect themselves against these abiotic stress conditions with their stress response, which includes alternative splicing of certain genes. Alternative splicing is a post-transcriptional process where a single gene gives rise to different mRNAs, which in turn produces different proteins. In plants, this is usually done by intron retention. One type of protein that may be involved in this stress response are the non-specific lipid transfer proteins (LTPs). Indeed, evidence of intron retention has been found in the LTP genes in the liverwort Marchantia polymorpha, called MpLTPd. To investigate whether this alternative splicing is caused by abiotic stress or not, I subjected the moss to two different types of stress trials, drought and cold, and compared the general expression of the intron in MpLTPd2 and MpLTPd3 from the stressed samples to samples from a moss grown under normal conditions. I found that the expression of the intron did change in the stressed moss, but none of the differences were significant. This suggests that alterative splicing in MpLTPd2 and MpLTPd3 is not caused by cold and drought and that the intron-containing protein plays no role in the protection of M. polymorpha against abiotic stress.

No description available.

Synapses can be altered due to experiences in a process called synaptic plasticity, which causes memory formations. Synapses can be strengthened through methods known as long-term potentiation (LTP) or weakened through long-term depression (LTD). Stresses can cause changes by altering synapses through either LTP or LTD. Rats were used to study the effects of post-traumatic stress disorder (PTSD)-like symptoms and a prophylactic treatment using pharmaceuticals. The first model used was the single prolonged stress (SPS) with two weeks of chronic light, which was not as effective for causing changes in synaptic plasticity. The second model, seven days of social defeat (SD) with two weeks of chronic light was more effective at inducing PTSD-like behavior symptoms and causing changes in LTP levels in the ventral hippocampus, amygdala, and prefrontal cortex between stressed and non-stressed rats. For the prophylactic treatment, propranolol and mifepristone were administered one week prior to and throughout the two weeks of the social defeat protocol. The drugs were able to prevent the changes due to stress on LTP in the three aforementioned brain regions, but did not change the anxious behavior of the rats. An enzyme-linked immunosorbent assay (ELISA) was used to determine corticosterone and norepinephrine levels between the different groups of rats. No significant differences were detected between SD and control rats, but SD injected rats were different from controls indicating that the injections were causing added stress. Reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) was used to detect changes in the adrenergic, corticoid, AMPA, and NMDA receptors. There were a few significant changes to some of the targets indicating that the stress protocol and drugs were having an effect on the mRNA expression. Propranolol and mifepristone could possibly be used as a prophylactic treatment for traumatic stress. In a separate study, techniques were used to determine the negative effects chronic stress (non-PTSD-like) has on synaptic plasticity in the dorsal hippocampus and to show how exercise was able to mitigate some of those negative stress effects. Electrophysiology showed differences in LTP between four groups of mice: sedentary no stress (SNS), sedentary with stress (SWS), exercise with stress (EWS), and exercise no stress (ENS). SWS had the lowest amount of LTP, whereas ENS had the highest. SNS and EWS had similar levels of LTP, which were in between the SWS and ENS groups. Corticosterone blood levels measured by an ELISA showed significant increases in the stressed groups compared to the non-stressed groups. The radial arm maze showed that both groups of exercise mice made fewer reference memory errors the second week of testing compared to the sedentary groups. RT-qPCR determined that brain-derived neurotrophic factor (BDNF) and corticoid and dopamine 5 receptors were likely causing some of the memory changes.

Synapses can be altered due to experiences in a process called synaptic plasticity, which causes memory formations. Synapses can be strengthened through methods known as long-term potentiation (LTP) or weakened through long-term depression (LTD). Stresses can cause changes by altering synapses through either LTP or LTD. Rats were used to study the effects of post-traumatic stress disorder (PTSD)-like symptoms and a prophylactic treatment using pharmaceuticals. The first model used was the single prolonged stress (SPS) with two weeks of chronic light, which was not as effective for causing changes in synaptic plasticity. The second model, seven days of social defeat (SD) with two weeks of chronic light was more effective at inducing PTSD-like behavior symptoms and causing changes in LTP levels in the ventral hippocampus, amygdala, and prefrontal cortex between stressed and non-stressed rats. For the prophylactic treatment, propranolol and mifepristone were administered one week prior to and throughout the two weeks of the social defeat protocol. The drugs were able to prevent the changes due to stress on LTP in the three aforementioned brain regions, but did not change the anxious behavior of the rats. An enzyme-linked immunosorbent assay (ELISA) was used to determine corticosterone and norepinephrine levels between the different groups of rats. No significant differences were detected between SD and control rats, but SD injected rats were different from controls indicating that the injections were causing added stress. Reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) was used to detect changes in the adrenergic, corticoid, AMPA, and NMDA receptors. There were a few significant changes to some of the targets indicating that the stress protocol and drugs were having an effect on the mRNA expression. Propranolol and mifepristone could possibly be used as a prophylactic treatment for traumatic stress. In a separate study, techniques were used to determine the negative effects chronic stress (non-PTSD-like) has on synaptic plasticity in the dorsal hippocampus and to show how exercise was able to mitigate some of those negative stress effects. Electrophysiology showed differences in LTP between four groups of mice: sedentary no stress (SNS), sedentary with stress (SWS), exercise with stress (EWS), and exercise no stress (ENS). SWS had the lowest amount of LTP, whereas ENS had the highest. SNS and EWS had similar levels of LTP, which were in between the SWS and ENS groups. Corticosterone blood levels measured by an ELISA showed significant increases in the stressed groups compared to the non-stressed groups. The radial arm maze showed that both groups of exercise mice made fewer reference memory errors the second week of testing compared to the sedentary groups. RT-qPCR determined that brain-derived neurotrophic factor (BDNF) and corticoid and dopamine 5 receptors were likely causing some of the memory changes.

En este trabajo de tesis doctoral se ha desarrollado una nueva metodología para monitorizar un viñedo en diferentes fases de cultivo y mejorar su gestión en campo. El núcleo del método propuesto es la confección de mapas de cultivo con origen local único, resolución variable, y sistema de coordenadas global pero con geometría plana. El sistema desarrollado, además, permite la integración de información proveniente tanto de sistemas de adquisición totalmente automáticos como manuales, así como la comparación y correlación de medidas efectuadas en diferentes etapas de crecimiento e incluso a lo largo de diferentes años. El objetivo último consiste en la proposición de modelos predictivos sobre la producción de uva y potencial enológico del futuro vino. Para ello se aplican nuevas tecnologías en una arquitectura de coste moderado, dotada de la flexibilidad y versatilidad necesaria para que un productor promedio del área mediterránea pueda adaptar el sistema propuesto a sus necesidades particulares, utilizando para ello un vehículo convencional de uso agrícola. La arquitectura propuesta, implementada, y validada en campo consiste en un sistema de percepción basado en visión artificial, un sistema de posicionamiento global con corrección diferencial, y un ordenador de abordo que, mediante la metodología propuesta, combina toda la información adquirida y la transforma en mapas de cultivo compatibles entre sí. El sistema de visión ofrece una técnica simple basada en una cámara monocromática sensible en el rango UV-NIR y acondicionada mediante filtros ópticos que optimizan la ejecución del algoritmo de segmentación dinámica. El programa desarrollado e implementado a bordo de un tractor estándar combina imágenes y posicionamiento del vehículo para generar la información para los mapas en tiempo real de vegetación relativa, que serán posteriormente relacionados con otros mapas de interés, tanto generados de forma automática (desnivel del terreno) como manual (rendimiento, compactación del terreno, acidez, etc.). El control de los sistemas de percepción y posicionamiento también se ha simplificado a través de una única interfaz gráfica, que permite la utilización del sistema por operarios no versados en nuevas tecnologías. Los resultados obtenidos indican que un planteamiento simplificado de la agricultura de precisión es informativo siempre y cuando se cuente con un sistema de gestión de información óptimo. Los mapas de cultivo propuestos sirvieron para establecer correlaciones estadísticamente significativas entre variables clave, cuantificando de manera objetiva la variabilidad espacial en cuanto a cantidad de vegetación, producción de uva, compactación del terreno, o propiedades químicas del mosto. La posibilidad de enriquecer los modelos presentados con información proveniente de campañas sucesivas resulta atractivo para el viticultor, que puede contar con modelos predictivos específicamente adaptados a su explotación y que cada vez serán más precisos. Esta metodología está al alcance de pequeños y medianos productores, ya que prescinde de la compra de imágenes digitales de origen aéreo o remoto, y además no requiere la adquisición de un vehículo específico, lo que facilita la generación de mapas de cultivo mientras se efectúan otras labores agrícolas gracias al uso de redes con referencias globales. / Sáiz Rubio, V. (2013). Mapas para mejorar la producción de vino combinando tecnologías de la información y vehículos convencionales [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/31522

Yes / Inhibitory GABAB receptors (GABABRs) can down-regulate most excitatory synapses in the CNS by reducing postsynaptic excitability. Functional GABABRs are heterodimers of GABAB1 and GABAB2 subunits and here we show that the trafficking and surface expression of GABABRs is differentially regulated by synaptic or pathophysiological activation of NMDA receptors (NMDARs). Activation of synaptic NMDARs using a chemLTP protocol increases GABABR recycling and surface expression. In contrast, excitotoxic global activation of synaptic and extrasynaptic NMDARs by bath application of NMDA causes the loss of surface GABABRs. Intriguingly, exposing neurons to extreme metabolic stress using oxygen/glucose deprivation (OGD) increases GABAB1 but decreases GABAB2 surface expression. The increase in surface GABAB1 involves enhanced recycling and is blocked by the NMDAR antagonist AP5. The decrease in surface GABAB2 is also blocked by AP5 and by inhibiting degradation pathways. These results indicate that NMDAR activity is critical in GABABR trafficking and function and that the individual subunits can be separately controlled to regulate neuronal responsiveness and survival. / BBSRC, MRC and the European Research Council

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.

La déficience intellectuelle affecte de 1 à 3% de la population mondiale, ce qui en fait le trouble cognitif le plus commun de l’enfance. Notre groupe à découvert que des mutations dans le gène SYNGAP1 sont une cause fréquente de déficience intellectuelle non-syndromique, qui compte pour 1-3% de l’ensemble des cas. À titre d’exemple, le syndrome du X fragile, qui est la cause monogénique la plus fréquente de déficience intellectuelle, compte pour environ 2% des cas. Plusieurs patients affectés au niveau de SYNGAP1 présentent également des symptômes de l’autisme et d’une forme d’épilepsie. Notre groupe a également montré que SYNGAP1 cause la déficience intellectuelle par un mécanisme d’haploinsuffisance. SYNGAP1 code pour une protéine exprimée exclusivement dans le cerveau qui interagit avec la sous-unité GluN2B des récepteurs glutamatergique de type NMDA (NMDAR). SYNGAP1 possède une activité activatrice de Ras-GTPase qui régule négativement Ras au niveau des synapses excitatrices. Les souris hétérozygotes pour Syngap1 (souris Syngap1+/-) présentent des anomalies de comportement et des déficits cognitifs, ce qui en fait un bon modèle d’étude. Plusieurs études rapportent que l’haploinsuffisance de Syngap1 affecte le développement cérébral en perturbant l’activité et la plasticité des neurones excitateurs. Le déséquilibre excitation/inhibition est une théorie émergente de l’origine de la déficience intellectuelle et de l’autisme. Cependant, plusieurs groupes y compris le nôtre ont rapporté que Syngap1 est également exprimé dans au moins une sous-population d’interneurones GABAergiques. Notre hypothèse était donc que l’haploinsuffisance de Syngap1 dans les interneurones contribuerait en partie aux déficits cognitifs et au déséquilibre d’excitation/inhibition observés chez les souris Syngap1+/-. Pour tester cette hypothèse, nous avons généré un modèle de souris transgéniques dont l’expression de Syngap1 a été diminuée uniquement dans les interneurones dérivés des éminences ganglionnaires médianes qui expriment le facteur de transcription Nkx2.1 (souris Tg(Nkx2,1-Cre);Syngap1). Nous avons observé une diminution des courants postsynaptiques inhibiteurs miniatures (mIPSCs) au niveau des cellules pyramidales des couches 2/3 du cortex somatosensoriel primaire (S1) et dans le CA1 de l’hippocampe des souris Tg(Nkx2,1-Cre);Syngap1. Ces résultats supportent donc l’hypothèse selon laquelle la perte de Syngap1 dans les interneurones contribue au déséquilibre d’excitation/inhibition. De manière intéressante, nous avons également observé que les courants postsynaptiques excitateurs miniatures (mEPSCs) étaient augmentés dans le cortex S1, mais diminués dans le CA1 de l’hippocampe. Par la suite, nous avons testé si les mécanismes de plasticité synaptique qui sous-tendraient l’apprentissage étaient affectés par l’haploinsuffisance de Syngap1 dans les interneurones. Nous avons pu montrer que la potentialisation à long terme (LTP) NMDAR-dépendante était diminuée chez les souris Tg(Nkx2,1-Cre);Syngap1, sans que la dépression à long terme (LTD) NMDAR-dépendante soit affectée. Nous avons également montré que l’application d’un bloqueur des récepteurs GABAA renversait en partie le déficit de LTP rapporté chez les souris Syngap1+/-, suggérant qu’un déficit de désinhibition serait présent chez ces souris. L’ensemble de ces résultats supporte un rôle de Syngap1 dans les interneurones qui contribue aux déficits observés chez les souris affectées par l’haploinsuffisance de Syngap1. / Intellectual disability affects 1-3% of the world population, which make it the most common cognitive disorder of childhood. Our group discovered that mutation in the SYNGAP1 gene was a frequent cause of non-syndromic intellectual disability, accounting for 1-3% of the cases. For example, the fragile X syndrome, which is the most common monogenic cause of intellectual disability, accounts for 2% of all cases. Some patients affected by SYNGAP1 also showed autism spectrum disorder and epileptic seizures. Our group also showed that mutations in SYNGAP1 caused intellectual disability by an haploinsufficiency mechanism. SYNGAP1 codes for a protein expressed only in the brain which interacts with the GluN2B subunit of NMDA glutamatergic receptors (NMDAR). SYNGAP1 possesses a Ras-GAP activating activity which negatively regulates Ras at excitatory synapses. Heterozygote mice for Syngap1 (Syngap1+/- mice) show behaviour abnormalities and learning deficits, which makes them a good model of intellectual disability. Some studies showed that Syngap1 affects the brain development by perturbing the activity and plasticity of excitatory neurons. The excitatory/inhibitory imbalance is an emerging theory of the origin of intellectual disability and autism. However, some groups including ours, showed that Syngap1 is expressed in at least a subpopulation of GABAergic interneurons. Therefore, our hypothesis was that Syngap1 happloinsufficiency in interneurons contributes in part to the cognitive deficits and excitation/inhibition imbalance observed in Syngap1+/- mice. To test this hypothesis, we generated a transgenic mouse model where Syngap1 expression was decreased only in GABAergic interneurons derived from the medial ganglionic eminence, which expresses the transcription factor Nkx2.1 (Tg(Nkx2,1-Cre);Syngap1 mouse). We showed that miniature inhibitory postsynaptic currents (mIPSCs) were decreased in pyramidal cells in layers 2/3 in primary somatosensory cortex (S1) and in CA1 region of the hippocampus of Tg(Nkx2,1-Cre);Syngap1 mice. Those results suggest that Syngap1 haploinsufficiency in GABAergic interneurons contributes in part to the excitation/inhibition imbalance observed in Syngap1+/- mice. Interestingly, we also observed that miniature excitatory postsynaptic currents (mEPSCs) were increased in cortex S1 but decreased in CA1 region of the hippocampus. We further tested whether synaptic plasticity mechanisms that are thought to underlie learning and memory were affected by Syngap1 haploinsufficiency in GABAergic interneurons. We showed that NMDAR-dependent long-term potentiation (LTP) but not NMDAR-dependent long-term depression (LTD) was decreased in Tg(Nkx2,1-Cre);Syngap1 mice. We also showed that GABAA receptor blockade rescued in part the LTP deficit in Syngap1+/- mice, suggesting that a disinhibition deficit is present in these mice. Altogether, the results support a functional role of Syngap1 in GABAergic interneurons, which may in turn contributes to the deficit observed in Syngap1+/- mice.

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

Synaptic long-term modifications following neuronal activation are believed to be at the origin of learning and long-term memory. Recent experiments suggest that these long-term synaptic changes are all-or-none switch-like events between discrete states of a single synapse. The biochemical network involving calcium/calmodulin-dependent protein kinase II (CaMKII) and its regulating protein signaling cascade has been hypothesized to durably maintain the synaptic state in form of a bistable switch. Furthermore, it has been shown experimentally that CaMKII and associated proteins such as protein kinase A and calcineurin are necessary for the induction of long-lasting increases (long-term potentiation, LTP) and/or long-lasting decreases (long-term depression, LTD) of synaptic efficacy. However, the biochemical mechanisms by which experimental LTP/LTD protocols lead to corresponding transitions between the two states in realistic models of such networks are still unknown. We present a detailed biochemical model of the calcium/calmodulin-dependent autophosphorylation of CaMKII and the protein signaling cascade governing the dephosphorylation of CaMKII. As previously shown, two stable states of the CaMKII phosphorylation level exist at resting intracellular calcium concentrations. Repetitive high calcium levels switch the system from a weakly- to a highly phosphorylated state (LTP). We show that the reverse transition (LTD) can be mediated by elevated phosphatase activity at intermediate calcium levels. It is shown that the CaMKII kinase-phosphatase system can qualitatively reproduce plasticity results in response to spike-timing dependent plasticity (STDP) and presynaptic stimulation protocols. A reduced model based on the CaMKII system is used to elucidate which parameters control the synaptic plasticity outcomes in response to STDP protocols, and in particular how the plasticity results depend on the differential activation of phosphatase and kinase pathways and the level of noise in the calcium transients. Our results show that the protein network including CaMKII can account for (i) induction - through LTP/LTD-like transitions - and (ii) storage - due to its bistability - of synaptic changes. The model allows to link biochemical properties of the synapse with phenomenological 'learning rules' used by theoreticians in neural network studies.