In the last decades our knowledge concerning cardiovascular risk factors has grown rapidly through results from longitudinal studies. However, despite new treatment, in Western countries coronary heart disease remains the leading cause of death and stroke is still the leading cause of severe disability. The studies reported in these papers examine the relationships between stroke/transient ischaemic attack (TIA) and a number of different factors measured on two different occasions in men born in Uppsala 1920-1924 and are epidemiological in their character. The findings indicate that in addition to already established risk factors, indices of an unhealthy dietary fat intake and high serum lipoprotein(a) are independent predictors of stroke/TIA. Among different glucometabolic variables a low insulin sensitivity index derived from the euglycaemic insulin clamp and proinsulin carries a high predictive value for later stroke, independently of diabetes. Moreover, cognitive test performance measured with Trail Making Test B at age 70 is a strong and independent predictor of brain infarction, indicating that the risk is already increased in the subclinical phase of milder cognitive dysfunction. Performance at a pre-stroke Trail Making Test is also of predictive value for mortality after first-ever stroke/TIA, but none of the studied pre-stroke variables or cognitive tests was found to be related to dependency after an event. In summary these studies provide further knowledge about predictors of stroke and of mortality after first-ever stroke. They also indicate the possible importance of new markers of risk, such as the level of lipoprotein(a), profile of fatty acids in the diet, low insulin sensitivity derived from clamp investigations, level of proinsulin, and cognitive performance measured with Trail Making Tests.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2007. / Härtill 5 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2005. / Härtill 5 uppsatser.

Our senses are constantly bombarded with information. How does the brain integrate such a variety of inputs to generate appropriate behaviours? Innate defensive behaviours are a good model to address this question. They are essential for animal survival and the brain circuits that control them are highly conserved across species. Moreover, the sensory inputs and behavioural outputs can be well defined and reliably reproduced in the lab. This allows us to study function of the individual components of the circuit controlling these behaviours. Ventromedial hypothalamus (VMH) is a key brain region for controlling responses to predators; it has been shown that inactivating the VMH can reduce defensive behaviours. Interestingly, activating the VMH output neurons (SF1+ cells) can produce a variety of different behaviours, from immobility to escape, depending on the intensity of activation. During my PhD I used a variety of approaches to address the question of the function of the VMH in control of defensive behaviours. At first I hypothesised that the VMH might act as a centre responsible for choosing an appropriate behavioural response according to the stimulus. I set to investigate how different activation levels of SF1+ neurons can produce such different behavioural outputs, and how this activity is modulated in vivo in response to predator stimuli. I began the project by quantifying mouse defensive behaviours in response to olfactory and auditory predator cues, as well as to the optogenetic activation of SF1+ neurons. I then questioned whether there was heterogeneity within the population of SF1+ neurons, which could explain their ability to trigger different behaviours. I performed patch clamp recordings from acute brain slices and conducted a study of the electrophysiological properties of SF1+ neurons. I next investigated how SF1+ neurons integrate excitatory inputs from the medial amygdala, a region which receives olfactory inputs from the accessory olfactory bulb. By combining optogenetics with slice electrophysiology and behavioural assessment, I described the physiology and relevance of this connection. Finally, I investigated in vivo activity in the VMH in response to predator cues by performing calcium imaging of the VMH neurons in freely moving mice. By presenting different sensory stimuli, I addressed the question of heterogeneity of the input pattern to the VMH neurons and the relationship between the VMH activity and the behavioural output. Taken all together, the results of this project have led to a hypothesis whereby the function of the VMH is to facilitate rather than directly control the choice of an appropriate behavioural response.

Made available in DSpace on 2015-05-14T13:00:06Z (GMT). No. of bitstreams: 1 parte1.pdf: 1450137 bytes, checksum: 1838bf2efddf0ca147f276df88417bb6 (MD5) Previous issue date: 2009-09-24 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / It was been demonstrated that curine and reticuline, induced a vasodilator effect in the rat small mesenteric arteries through inhibition of voltage-gated Ca2+ channels (VGCC). These compounds, curine and reticuline were isolated from the root barks of Chondrondendron platyphyllum and Ocotea duckei Vattimo, respectively, therefore the aim of this work was to evaluate the vasodilator mechanism of curine and reticuline, bisbenzylisoquinoline alkaloids (BBA), isolated from the root barks of Chondrondendron platyphyllum and Ocotea duckei Vattimo, respectively, using functional and molecular approaches. Tension measurements in aorta rings, whole-cell patch-clamp and confocal techniques were employed to study the action of these alkaloids. The A7r5 smooth muscle derived cell line was used for Ca2+ currents measuring and the intracellular calcium concentration ([Ca2+]i) were evaluated using confocal microscopy. The main results are as follows: in aortic rings, curine (3 - 300 μM) antagonized KCl (60 mM) and Bay K8644 (3 x 10-7 M) induced contractions. In whole-cell configuration, curine reduced the voltage-activated peak amplitude of ICa,L in a concentration-dependent manner. However, the Ca+2 current density versus voltage relationship and maximal activation voltage of ICa,L were not changed. Moreover curine did not also affect the steady-state activation of ICa,L, but shifted the steady-state inactivation curve of ICa,L for more negative potentials, however this effect was not changed in the presence of IBMX, dbcAMP and 8-brcGMP, suggesting that cyclic mononucleotides, such as cAMP and cGMP, are not involved in curine effect. In confocal experiments, curine inhibited the rise on the [Ca2+]i induced by KCl (60 mM) in dispersed vascular smooth muscle cells. In reference to reticuline (3 300 μM) was verified that alkaloid agonized CaCl2 and KCl-induced contractions and elicited vasorelaxation in aortic rings. In whole-cell configuration, reticuline reduced the voltage-activated peak amplitude of ICa,L in a concentration-dependent manner, but did not change the characteristics of current density versus. voltage relationship. Reticuline shifted leftwards the steady-state inactivation curve of ICa,L, however this effect was not changed after application of dibutyryl cyclic adenosine monophosphate to the cell. In cells pretreated with forskolin, an adenylate cyclase activator, the addition of reticuline caused further inhibition of the Ca2+ currents suggesting an additive effect, indicating that cyclic mononucleotides were not involved. Taken together the results have shown that curine and reticuline elicits vasorelaxation due to the blockade of the L-type voltage-dependent Ca2+ current in rat aorta smooth muscle cells. The reported effect may contribute to the potential cardioprotective efficacy of curine and reticuline. / Curina e reticulina são alcalóides isolados das cascas do caule e raízes de Chondrondendron platyphyllum e de Ocotea duckei Vattimo, respectivamente. Estudos anteriores demonstraram que esses alcalóides são capazes de induzir efeito vasodilatador em artéria mesentérica e aorta de rato, respectivamente, devido possível inibição dos canais para Ca2+ dependentes de voltagem (VGCC). O objetivo deste trabalho foi investigar o mecanismo vasodilatador de curina e reticulina realizando experimentações funcionais e moleculares. Foram utilizadas medidas de tensão em anéis de aorta de rato, e empregadas técnicas de patch-clamp e de microscopia confocal para estudos da ação desses alcalóides. Também foram utilizadas células A7r5, uma linhagem de células musculares lisas embrionária derivada de aorta torácica de rato, que foram usadas para medir as correntes de Ca2+ macroscópicas e a concentração de cálcio intracelular ([Ca2+]i), que foram avaliadas usando a técnicas de patch-clamp e microscopia confocal, respectivamente. Os principais resultados são: em anéis de aorta, curina (3 - 300 μM) antagonizou as contrações induzidas por KCl (60 mM) e Bay K8644 (3 x 10-7 M). Na configuração whole-cell patch clamp , curina reduziu a amplitude da corrente de cálcio do tipo L (ICa,L) de maneira dependente de concentração. Porém, curina não alterou as características das correntes na relação corrente-voltagem. A voltagem de ativação máxima para ICa,L não foi diferente em relação ao controle. Além disso, curina também não afetou a ativação no estado estacionário das ICa,L, mas deslocou a curva da inativação estacionária para potenciais mais negativos. No entanto, esse efeito promovido por curina não foi alterado na presença de IBMX, dbcAMP e 8- brcGMP, sugerindo que os mononucleotídeos cíclicos, como APMc e GMPc, não estão envolvidos no efeito da curina. Em experimentos com microscopia confocal curina inibiu os transientes de cálcio intracelulares, e reduziu o aumento de [Ca2+]i induzidos por KCl (60 mM) em células de músculo liso vascular. Em relação à reticulina (3 300 μM), foi verificado que esse alcalóide antagonizou as contrações induzidas por CaCl2 e KCl, provocando vasorelaxamento em anéis de aorta. Na configuração whole-cell patch clamp , reticulina também reduziu a amplitude das ICa,L de maneira dependente de concentração, mas não mudou as características da corrente na relação corrente-voltagem. A reticulina deslocou para potenciais mais negativos a curva de inativação estacionária para as ICa,L. Porém, esse efeito não foi alterado após a aplicação de dbcAMP e 8-brcGMP. Em células pré-tradadas com forskolina, um ativador da adenilil ciclase, a adição da reticulina causou uma inibição adicional das correntes de Ca2+ que sugere um efeito aditivo da reticulina, indicando que os mononucleotídeos cíclicos não estão envolvidos. Dessa forma, curina e reticulina provocaram vasorelaxamento, devido ao bloqueio das correntes de Ca2+ dependentes de voltagem do tipo-L em células de músculo liso, em cultura e recémdispersas, de aorta de rato, revelando que esses alcalóides têm um importante potencial como modelo químico para a concepção e posterior desenvolvimento de novos fármacos com propriedade protetora cardiovascular.

Made available in DSpace on 2014-06-12T15:54:28Z (GMT). No. of bitstreams: 2 arquivo6489_1.pdf: 1208262 bytes, checksum: c1b40f981f11c014c773e3922d544d81 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2011 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / A caracterização de canais iônicos em células tronco é importante pelo fato destas estruturas atuarem no controle da proliferação e diferenciação destas células. Há poucos trabalhos focados nos canais iônicos presentes nas membranas plasmáticas das células tronco e nenhum deles trata das células tronco mesenquimais da geléia de Wharton do cordão umbilical humano (whMSC). O cordão umbilical é uma fonte importante de células tronco para tão esperada terapia celular. Estes fatos motivaram o estudo dos canais iônicos das whMSC como objetivo maior do presente trabalho. Foi utilizada a técnica de patch-clamp na configuração whole-cell e a atuação de inibidores específicos para identificar os canais iônicos presentes nas whMSC. Os inibidores escolhidos foram: tetraetilamonio (TEA) e 4-aminopiridina (4-AP) como inibidores de canais de potássio dependentes de voltagem e de Ca2+, Glibenclamida (GB) um inibidor de canais de potássio dependentes de ATP, canais aniônicos dependentes de volume celular e CFTR e 5-nitro-2-(3-phenylpropylamino) ácido benzóico (NPPB) um potente bloqueador dos canais de cloreto, mas que também é capaz de bloquear os canais de potássio dependentes de Ca2+ de condutância intermediária. Os resultados mostraram que as correntes iônicas ativadas por voltagem das whMSC podem ser bloqueadas consideravelmente por TEA (10 mM), 4-AP (5 mM) e NPPB (100 μM) indicando a presença dos canais de K+ dependentes de voltagem e de Ca2+ e de canais de Cl- dependentes de voltagem conforme descrito para células tronco de outras origens. Utilizando GB (100 μM) observamos um aumento (estimulação) significativo da corrente. Este é um resultado inédito, pois estudos anteriores demonstram que o GB atua inibindo a corrente iônica transmembrana. Em todos os casos, com todos os inibidores testados, os efeitos foram reversíveis. Estes resultados demonstram que as membranas citoplasmáticas das whMSC possuem canais de K+ dependentes de voltagem e de Ca2+ e canais de Cl- dependentes de voltagem. O surpreendente efeito da glibenclamida indica a presença de canais iônicos desconhecidos nas membranas das whMSC

Abstract Excitation-contraction coupling (ECC) is a process linking the electrical excitation of the muscle cell (myocyte) membrane to the contraction of the cell. In this study the possibilities of mathematical modeling were studied in current ECC research. Mathematical modeling was employed in two distinct ECC research areas, the enzymatic regulation of ECC and ECC during cardiac myocyte development. Despite the distinction, both of these are extremely complex biological systems characterized by diverse and partly contradictory reported experimental results, with a large part based on genetically engineered animal models. Novel mathematical models were developed for both of these research areas. The model of ventricular myocyte ECC with calmodulin-dependent protein kinase II (CaMKII)-mediated regulation faithfully reproduced the heart-rate dependent regulation of ECC. This regulation is thought to be the major effect of CaMKII-mediated regulation. The model of the embryonic ventricular myocyte provided the first comprehensive system analysis of how the embryonic heartbeat is generated at the cellular level. A similar type of model was also developed to show the notable differences between neonatal and adult ventricular myocyte ECC. The mathematical models of ECC presented in this study were further used to simulate ECC in genetically engineered myocytes. The cellular mechanisms of genetically engineered animal models could be better understood by employing mathematical modeling in parallel to experimental characterization of the animal model. It was found in simulations that the indirect consequences and the compensatory mechanisms induced by genetic modification may have a more significant effect on ECC than the direct consequences of the modification. To understand the overwhelming complexity of biological systems including ECC, competent system analysis tools, such as mathematical modeling, are required. The purpose of mathematical modeling is not to replace the experimental studies, but to provide a more comprehensive system analysis based on the experimental data. This system analysis will help in planning subsequent experiments needed to gain the most relevant information about the studied biological system.

Les motoneurones tiennent une place remarquable dans l'organisme : ils constituent l'interface entre le système nerveux central et le système musculaire. Leur excitabilité est une caractéristique primordiale dans le comportement moteur puisqu'elle définit la force musculaire développée en réponse à la commande motrice. Chez la souris, la décharge des motoneurones est marquée par la présence d'oscillations de mode mixte (MMOs) entre les potentiels d'action. Ces MMOs permettent la décharge des motoneurones à basse fréquence et sont responsables d'un régime de décharge particulier nommé zone sous-Primaire, pendant lequel la fréquence de décharge est très variable et le gain de la relation courant-Fréquence élevé. Nous avons étudié les mécanismes responsables de l'apparition de ces MMOs à la fois de manière expérimentale, dans une préparation in vivo de souris anesthésié, incluant l'utilisation du Dynamic Clamp, et théorique, au moyen d'un modèle mono-Compartimental de motoneurone. Nos résultats ont montré que ces MMOs étaient causées par les courants sodiques et potassiques responsables des potentiels d'action et qu'elles émergeaient d'un état de faible excitabilité de la membrane, dû à l'inactivation lente des courants sodiques. Nous avons également montré que le courant de post-Hyperpolarisation pouvait paradoxalement augmenter l’excitabilité des motoneurones et réduire les MMOs en dé-Inactivant le courant sodique. La Sclérose Latérale Amyotrophique (SLA) conduit à la dégénérescence spécifique de ces motoneurones qui s'accompagne d'une vacuolisation de leur arborisation dendritique. L'augmentation précoce de l'excitabilité des motoneurones dans la maladie a largement été évoquée pour rendre compte de leur atteinte. Une hyperexcitabilité, aussi bien d'origine intrinsèque qu'extrinsèque pourrait en effet produire une excitotoxicité délétère pour la cellule. Si une telle modification de l'excitabilité est en cause dans la maladie, elle devrait persister jusqu'aux âges auxquels se produisent les premières dénervations des jonctions neuromusculaires. Nous avons enregistré les propriétés électrophysiologiques des motoneurones dans une préparation in vivo de souris adultes SOD1-G93A, modèle de la SLA. Nos résultats ont montré que leur conductance d'entrée était augmentée dans les jours qui précèdent les premières dénervations de leurs jonctions neuromusculaires. Malgré cela, leur excitabilité n'était pas modifiée. Loin d'être intrinsèquement hyperexcitables, une fraction d'entre eux perdaient même leur capacité à décharger de manière répétée. Nous avons finalement étudié la vacuolisation qui prend place dans les dendrites des motoneurones au cours de la maladie et son lien avec la couverture synaptique. Nous avons montré que la vacuolisation dendritique prenait place avant les dénervations et que la taille des vacuoles augmentait avec l'âge des souris SOD1-G93A. De manière intéressante, cette progression semblait plus rapide dans les motoneurones les plus sensibles à la maladie. Bien que la couverture synaptique n'était pas modifiée au cours de la maladie, nous avons mis en évidence une densité de synapses excitatrices et inhibitrices plus importante sur les régions dendritiques qui se vacuolisent. Ces résultats suggèrent un lien entre l'activité synaptique et la formation de vacuoles dans les motoneurones au cours de la SLA. Les motoneurones ne présentant pas d'hyperexcitabilité intrinsèque, une excitotoxicité d'origine synaptique pourrait alors être responsable de leur dégénérescence. / Motoneurones hold a remarkable position in the organism: they are the interface between the central nervous system and the muscular system. Their excitability is a crucial characteristic in motor behavior since it determines the muscular force produced in response to motor command. In mice, motoneurone discharge is marked by the presence of sub-Threshold oscillations between action potentials which create a behavior of mixed mode oscillations (MMOs). These MMOs allow the motoneurones to fire at low frequency and are responsible for a sub-Primary range of discharge during which the firing frequency is irregular and the slope of current-Frequency relation is steep. We investigated the mechanisms responsible for these MMOs by in vivo recordings in anesthetized mice, using Dynamic Clamp, and by theoretical modelization in a monocompartimental model of motoneurone. Our results showed that MMOs were caused by sodium and potasium currents responsible for action potentials and that they emerged from a state of low membrane excitability caused by a slow inactivation of the sodium current. Paradoxically, we also showed that the after-Hyperpolarization current was able to increase the membrane excitability and to reduce MMOs by de-Inactivating the sodium current. Amyotrophic Lateral Sclerosis (ALS) leads to the specific degeneration of these motoneurones and is accompanied by a vacuolation of their dendritic trees. An early increase in motoneurons excitability during the disease has been widely proposed to account for their degeneration. Indeed, a motoneuron hyperexcitability of intrinsic or extrinsic origin could produce a deleterious excitotoxicity. If such a change of excitability is involved in the disease, it should last until the ages where the first denervation of neuromuscular junctions occurs. We recorded the electrophysiological properties of motoneurones in an in vivo preparation of adult SOD1-G93A mice, model of ALS. Our results showed that their input conductance was increased before the first denervation of their neuromuscular junctions. Nevertheless, their excitability was not modified. Far from being intrinsically hyperexcitable, a fraction of them even lost their ability to discharge repeatedly. We finally studied the vacuolation that takes place in dendrites of motoneurones during the disease and its relation with synaptic coverage. We have shown that the dendritic vacuolation takes place before the denervation and that the size of these vacuoles increases with age in SOD1-G93A mice. Interestingly, this increase was faster in the most vulnerable motoneurones. Although synaptic coverage was not altered in the disease, we ¬revealed higher densities of excitatory and inhibitory synapses on dendritic regions that vacuolate. These results suggest a link between synaptic activity and vacuoles formation in motoneurones during ALS. Motoneurones were not intrinsically hyperexcitable, instead, an excitotoxicity from a synaptic origin may be responsible for their degeneration.

Les champs récepteurs corticaux se réorganisent en réponse aux changements de l'environnement. Par exemple, suite à une lésion périphérique, les modalités sensorielles préservées gagnent de l'espace cortical au détriment de celles lésées. L'étude du cortex somatosensoriel en tonneau des rongeurs a fourni des données importantes pour la compréhension des mécanismes synaptiques à l'origine de cette réorganisation corticale. En condition normale, les neurones de chaque colonne corticale répondent préférentiellement à la stimulation d'une seule vibrisse principale ("Principal Whisker, PW"). Au contraire, suite à l'amputation de l'ensemble des vibrisses sauf une ("Single Whisker Experience, SWE"), les neurones des colonnes associées aux vibrisses amputées répondent à la stimulation de la vibrisse conservée, à l'origine du renforcement et de l'expansion des représentations corticales des vibrisses conservées. Bien que des preuves indirectes aient révélées un rôle de la potentialisation à long terme ("Long-Term Potentiation, LTP") de synapses préexistantes dans la modification des cartes corticales, probablement via une augmentation du nombre des récepteurs AMPA (AMPARs) aux synapses, un lien direct entre la LTP, la réorganisation des cartes corticales, et l'adaptation des comportements sensori-moteurs suite à une altération des entrées sensorielles n'a pas encore été démontré. L'objectif de cette thèse a donc été de mettre en évidence cette relation de façon expérimentale et en condition physiologique. Pour cela, nous avons mis au point une stratégie in vivo combinant des enregistrements électrophysiologiques, de l'imagerie biphotonique et l'analyse du comportement d'exploration chez la souris contrôle ("Full Whisker Experience, FWE) et amputée de certaines vibrisses (SWE). Nous avons d'abord confirmé que la stimulation rythmique de la PW ("Rhytmic Whisker Swtimulation, RWS") renforce les synapses excitatrices (RWS-LTP) in vivo des souris anesthésiées FWE. Au contraire des souris FWE, les neurones pyramidaux des souris SWE présentent une augmentation de l'excitabilité neuronale et une absence de RWS-LTP, indiquant ainsi que les synapses corticales associées à la vibrisse intacte ont été potentialisées en réponse au protocole SWE. Pour mieux comprendre l'implication de la RWS-LTP dans la réorganisation des cartes corticales et l'adaptation des comportements sensori-moteurs, nous avons développé une nouvelle approche pour manipuler la LTP in vivo grâce à l'immobilisation des AMPARs par des anticorps extracellulaires ("cross-linking"). En effet, notre équipe a montré précédemment que le cross-linking des AMPARs empêche la LTP in vitro. Par ailleurs, une accumulation des AMPARs au niveau post-synaptique a été démontrée in vivo par imagerie biphotonique au cours d'une stimulation RWS, suggérant un rôle de la mobilité de ces récepteurs dans cette RWS-LTP. Au cours de cette thèse, nous avons démontré que le cross-linking des AMPARs in vivo bloque également l'expression de la RWS-LTP, mais sans affecter la transmission synaptique basale, ni l'induction de la RWS-LTP, indiquant ainsi que la mobilité des AMPARs est également fondamental pour l'expression de la LTP in vivo. De façon importante, le cross-linking des AMPARs de façon chronique, au cours du SWE, permet non seulement de rétablir la RWS-LTP et l'excitabilité neuronale, et donc de bloquer la réorganisation corticale, mais aussi de modifier les capacités de récupération sensori-motrices des souris amputées. Dans l'ensemble, nos données démontrent pour la première fois un rôle critique et direct de la RWS-LTP dans le réarrangement des circuits en réponse à l'amputation de certaines vibrisses. La réorganisation des cartes corticales serait ainsi assurée par le renforcement de la transmission synaptique, et constituerait alors un mécanisme compensatoire pour optimiser le comportement sensorimoteur de l'animal lors de l'altération des entrées sensorielles. / Neuronal receptive fields in the cerebral cortex change in response to peripheral injury, with active modalities gaining cortical space at the expense of less active ones. Experiments on the mouse whisker-to-barrel cortex system provided important evidences about the synaptic mechanisms driving this cortical remapping. Under normal conditions, neurons in each barrel-column have receptive fields that are strongly tuned towards one principal whisker (PW). However, trimming all the whiskers except one (single-whisker experience, SWE) causes layer (L) 2/3 pyramidal neurons located in the deprived and spared-related columns to increase their response towards the spared input. This results in a strengthening and expansion of the spared whisker representation within the barrel sensory map. Indirect evidences suggest that these cortical alterations might depend on the activity-dependent potentiation of pre-existing excitatory synapses (LTP), likely through increased levels of postsynaptic AMPA receptors (AMPARs). However, a clear link between LTP, cortical remapping, and the adaptation of sensorimotor skills following altered sensory experience has not yet convincingly been demonstrated. Here, we combined in vivo whole-cell recordings, 2-Photon calcium imaging and a whisker-dependent behavior protocol to directly demonstrate this relationship. It has been described that rhythmic whisker stimulation potentiates cortical synapses (RWS-LTP) in vivo. An accumulation of postsynaptic AMPARs during similar sensory stimulation was also reported by imaging evidences. Our data demonstrates that this potentiation is occluded by SWE, suggesting that cortical synapses are already potentiated by this trimming protocol. This is translated into an increased neuronal excitability in the spared column and sensorimotor recovery by the spared whisker. To better understand the implication of LTP in cortical remapping, we developed a novel approach to manipulate LTP in vivo without affecting overall circuit properties. Our team showed previously that the blockage of AMPARs synaptic recruitment by extracellular antibody cross-linking prevents LTP in vitro. Here, we report that in vivo cross-linking of AMPARs blocks the expression but not the induction of RWS-LTP, suggesting that the synaptic recruitment of AMPARs is fundamental for in vivo LTP as well. Moreover, chronic AMPAR cross-linking during SWE reverts RWS-LTP occlusion and the increased neuronal excitability caused by whisker trimming. As consequence, the sensorimotor performance by the spared whisker is permanently impaired by the blockage of cortical remapping. Altogether, these evidences led us to define a critical role for synaptic LTP on circuit re-arrangement after whisker trimming. Our data shows that LTP-driven cortical remapping is a compensatory mechanism to optimize animal’s sensorimotor behavior upon altered sensory experience.

Pentameric ligand-gated ion channels (pLGICs) are membrane-embedded receptors found extensively in pre- and post-synaptic membranes throughout the nervous system where they play an important role in neurotransmission. The function of the prototypic pLGIC, the nicotinic acetylcholine receptor (nAChR) is highly sensitive to changes in its lipid environment, while other pLGICs display varying lipid sensitivities. This thesis presents a multidisciplinary investigation into the features of the transmembrane domain (TMD) that determine the unique functional and physical traits of different pLGICs. Using two prokaryotic homologues of the nAChR, ELIC and GLIC, as models, I focus on the outermost, lipid-exposed α-helix, M4, which, despite being distant from the primary allosteric pathway coupling agonist binding to channel gating, exercises significant control over channel function. Here, I present evidence that M4 acts as a lipid sensor, detecting changes in the surrounding lipids and transmitting these changes to the channel pore via contacts with the adjacent TMD α-helices, M1 and M3, and/or with structures in the extracellular domain. Using ELIC and GLIC chimeras, I first show that the TMD is the main driver of pLGIC thermal stability. I then demonstrate that the M4 α-helices in each channel play different roles in channel maturation and function, which suggests a divergent evolutionary path. Following this, I show that the M4 C-terminus is essential to both maturation and function in GLIC, while in ELIC its role is less defined, again showcasing possible evolutionary differences. Building on these findings, I examined the role of aromatic residues at the M4 – M1/M3 interface, and found that they predictably determine the interactions between M4 and M1/M3. Notably, the addition of aromatic residues to enhance M4-M1/M3 interactions in ELIC promotes channel function, while the elimination of aromatic residues at the M4-M1/M3 interface in GLIC is detrimental to channel function. Furthermore, I show that these same aromatics alter the strength of pLGIC lipid sensing and the sensitivity to certain disease-causing mutations, both indicating that aromatic residues are key players in channel function, stability and modulation. Finally, I and my collaborators identified and characterized a novel desensitization-linked lipid binding site in ELIC. Extensive mutagenesis studies coupled with biophysical measurements allowed us to develop a model describing how lipid binding influences the rates of ELIC desensitization to shape the agonist-induced response.