Abstract not available

The nervous system, including the brain, is a complex network with billions of complex neurons. Ion channels mediate the electrical signals that neurons use to integrate input and produce appropriate output, and could thus be thought of as key instruments in the neuronal orchestra. In the field of neuroscience we are not only curious about how our brains work, but also strive to characterize and develop treatments for neural disorders, in which the neuronal harmony is distorted. By modulating ion channel activity (pharmacologically or otherwise) it might be possible to effectively restore neuronal harmony in patients with various types of neural (including channelopathic) disorders. However, this exciting strategy is impeded by the gaps in our understanding of ion channels and neurons, so more research is required. Thus, the aim of this thesis is to improve the understanding of how specific ion channel types contribute to shaping neuronal dynamics, and in particular, neuronal integration, excitability and memory. For this purpose I have used computational modeling, an approach which has recently emerged as an excellent tool for understanding dynamically complex neurophysiological phenomena. In the first of two projects leading to this thesis, I studied how neurons in the brain, and in particular their dendritic structures, are able to integrate synaptic inputs arriving at low frequencies, in a behaviorally relevant range of ~8 Hz. Based on recent experimental data on synaptic transient receptor potential channels (TRPC), metabotropic glutamate receptor (mGluR) dynamics and glutamate decay times, I developed a novel model of the ion channel current ITRPC, the importance of which is clear but largely neglected due to an insufficient understanding of its activation mechanisms. We found that ITRPC, which is activated both synaptically (via mGluR) and intrinsically (via Ca2+) and has a long decay time constant (τdecay), is better suited than the classical rapidly decaying currents (IAMPA and INMDA) in supporting low-frequency temporal summation. It was further concluded that τdecay varies with stimulus duration and frequency, is linearly dependent on the maximal glutamate concentration, and might require a pair-pulse protocol to be properly assessed. In a follow-up study I investigated small-amplitude (a few mV) long-lasting (a few seconds) depolarizations in pyramidal neurons of the hippocampal cortex, a brain region important for memory and spatial navigation. In addition to confirming a previous hypothesis that these depolarizations involve an interplay of ITRPC and voltage-gated calcium channels, I showed that they are generated in distal dendrites, are intrinsically stable to weak excitatory and inhibitory synaptic input, and require spatial and temporal summation to occur. I further concluded that the existence of multiple stable states cannot be ruled out, and that, in spite of their small somatic amplitudes, these depolarizations may strongly modulate the probability of action potential generation. In the second project I studied the axonal mechanisms of unmyelinated peripheral (cutaneous) pain-sensing neurons (referred to as C-fiber nociceptors), which are involved in chronic pain. To my knowledge, the C-fiber model we developed for this purpose is unique in at least three ways, since it is multicompartmental, tuned from human microneurography (in vivo) data, and since it includes several biologically realistic ion channels, Na+/K+ concentration dynamics, a Na-K-pump, morphology and temperature dependence. Based on simulations aimed at elucidating the mechanisms underlying two clinically relevant phenomena, activity-dependent slowing (ADS) and recovery cycles (RC), we found an unexpected support for the involvement of intracellular Na+ in ADS and extracellular K+ in RC. We also found that the two major Na+ channels (NaV1.7 and NaV1.8) have opposite effects on RC. Furthermore, I showed that the differences between mechano-sensitive and mechano-insensitive C-fiber types might reside in differing ion channel densities. To conclude, the work of this thesis provides key insights into neuronal mechanisms with relevance for memory, pain and neural disorders, and at the same time demonstrates the advantage of using computational modeling as a tool for understanding and discovering fundamental properties of central and peripheral neurons. / <p>QC 20120914</p>

Thesis (Ph. D.)--University of Virginia, 2007. / Includes bibliographical references. Also available online through Digital Dissertations.

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

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2007. / Härtill 3 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2002. / Härtill 5 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2003. / Härtill 4 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2003. / Härtill 5 uppsatser.

Orientadores: Carlos Amilcar Parada, Helder José Ceragioli / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-19T15:58:34Z (GMT). No. of bitstreams: 1 Ferreira_PriscilaAmaral_M.pdf: 1496649 bytes, checksum: a3c769ea7d0b4a3fe45913f836d3615c (MD5) Previous issue date: 2011 / Resumo: Nanopartículas são estruturas com dimensões nanométricas que vem demonstrando um potencial para várias aplicações, inclusive na área biológica. De acordo com o seu processo de síntese e crescimento estas partículas podem possuir propriedades magnéticas com maior ou menor magnitude. O objetivo deste trabalho foi avaliar se a administração no espaço sub-aracnóide da medula espinal, de nanopartículas magnéticas altera o limiar de resposta a estímulos mecânicos aplicados em patas de ratos. As nanopartículas de carbono (nanotubos ou nanofibras) foram caracterizadas através do espectro de Raman e o seu comportamento magnético caracterizado pelo ferromagnetismo foi avaliado através da curva de histerese. As nanopartículas foram administradas via intratecal em ratos Wistar machos levemente anestesiados com Isoflorano. A resposta comportamental ao estímulo mecânico foi avaliada por um analgesímetro eletrônico (Von Frey eletrônico) que mede o limiar mecânico de retirada da pata (nocicepção mecânica). As nanopartículas foram classificadas de acordo com o comportamento magnético em: alto magnetismo e baixo magnetismo. A administração de nanopartículas (5, 20 ou 80 ?g) com alto magnetismo, mas não com baixo magnetismo, diminuiu o limiar mecânico de retirada da pata, quando comparada com a administração do seu solvente propilenoglicol (20?L). A diminuição do limiar mecânico foi observada nos tempos de 15, 30 e 60 minutos após a administração de 20?g de nanopartículas com alto magnetismo, sendo que após este período as respostas retornaram aos seus limiares basais. Por outro lado, a administração intraplantar das nanopartículas não alterou o limiar mecânico quando comparados com as respostas basais. Portanto, a administração na medula espinal, mas não no tecido periférico, de nanopartículas com alto magnetismo diminuiu o limiar mecânico. Em conclusão, os dados deste trabalho sugerem que a transmissão neuronal na medula espinal envolve uma atividade eletromagnética / Abstract: Nanoparticles are structures with nanometer dimensions that are emerging to various applications, including that one involved in biological area. According to their synthesis and growth techniques these particles can have magnetic properties with greater or lesser magnitude. The objective of this study was to evaluate whether the magnetic nanoparticles administration in the subarachnoid space of the spinal cord induces changes in the mechanical nociceptive threshold in rats hind-paw. The carbon nanoparticles (nanotubes or nanofibers) were characterized by Raman spectrum and their magnetic characterized by the ferromagnetism behavior was evaluated by the hysteresis curve. The nanoparticles were intrathecally administered in Wistar rats lightly anesthetized with Isoflorano. The behavioral response to mechanical stimulation was assessed by an electronic analgesimeter (electronic Von Frey) that measures the withdrawal mechanical threshold (mechanical nociception). The nanoparticles were classified according to their magnetic behavior in: high magnetism and low magnetism. The administration (5, 20 or 80 ?g) of high magnetism nanoparticles, but not of low magnetism nanoparticles, decreased the mechanical withdrawal threshold of the hind-paw, when compared with the administration of propylene glycol (20 ?L). Decreasing in mechanical withdrawal threshold was observed at 15, 30 and 60 minutes after administration of 20?g of high magnetism nanoparticles. After this period, the mechanical withdrawal thresholds returned to their normal baseline. In contrast, intraplantar administration of the nanoparticles did not alter the mechanical withdrawal threshold. Therefore, administration of high magnetic nanoparticles in the spinal cord, but not in peripheral tissue, decreases the mechanical withdrawal threshold. In conclusion, our data suggest that neuronal transmission in the spinal cord involves an electromagnetic activity / Mestrado / Fisiologia / Mestre em Biologia Funcional e Molecular

Chez les vertébrés, la douleur est perçue par des neurones spécialisés, les nocicepteurs, dont le corps cellulaire est localisé dans les ganglions de la racine dorsale (DRG) et qui présentent une grande hétérogénéité. Nous cherchons donc à identifier de nouveaux marqueurs des sous populations de nocicepteurs afin de pouvoir comprendre cette diversité et d’attribuer des fonctions physiologiques précises à ces différentes sous-populations neuronales. Nous avons identifié le gène GINIP, spécifiquement exprimé dans une sous populations de nocicepteurs non peptidergiques et définissant deux classes particulières de neurones : les neurones MRGPRD+ et les C-Low Threshold MecanoReceptors (C-LTMRs). Durant ma thèse, j’ai cherché à savoir quelles modalités sensorielles sont détectées et transmises par la population GINIP+. Pour cela, j’ai tiré avantage d’un modèle murin ginip généré au laboratoire, permettant d’éliminer spécifiquement les neurones GINIP+ au sein des neurones du DRG. J’ai pu démontrer que l’ablation ciblée de ces neurones entraine une diminution de la douleur induite par l’injection de formaline, cela sans affecter la sensibilité thermique ou mécanique. Sachant que les neurones MRGPRD positifs ne sont pas impliqués dans la réponse douloureuse induite par l’injection de formaline, mais jouent un rôle primordial dans la mécano sensibilité en condition normale et pathologique, notre étude montre que la réponse douloureuse induite par l’injection de formaline est due à l’activation des C-LTMRs. En conclusion, notre étude révèle que les C-LTMRs agissent en tant que puissants modulateurs des douleurs chimiques et mécaniques. / Primary sensory neurons are heterogeneous by myriad of molecular criteria. However, the functional significance of this remarkable heterogeneity is just emerging. Here we used our recently generated ginip mouse model to selectively ablate the cutaneous free nerve endings MRGPRD+ neurons and the C-Low threshold mechanoreceptors (C-LTMRs). Ablation of GINIP-expressing neurons led to a significant decrease of formalin-evoked first pain and a complete absence of the second phase pain response, without affecting thermal or mechanical sensitivity. Knowing that MRGPRD+ neurons are dispensable for formalin-evoked pain and that these neurons play a critical role in acute and injury-induced mechanical pain, our data demonstrate that formalin-induced pain hypersensitivity is primarily transduced via C-LTMRs, and suggest that C-LTMRs and MRGPRD+ neurons play antagonistic roles in transduction of acute and injury-induced mechanical pain. Therefore, our results suggest that C-LTMRs act as strong modulators of chemical and mechanical pain signals.