Spinal cord injuries (SCI) sever communication between supraspinal centers and the central pattern generator (CPG) responsible for locomotion. Because the CPG is intact and retains the ability to initiate locomotor activity, it can be accessed electrically and pharmacologically. The goal of this thesis was to identify and characterize a novel spinal cord surface site along the sacral dorsal column (sDC) for electrically evoking locomotor-like activity in the neonatal rat spinal cord. Stimulation of the sDC robustly activated rhythmic left-right alternation in flexor-related ventral roots that was dependent on the activation of high-threshold C fiber afferents. The C fibers synapsed onto spinal neurons, which project to the lumbar segments as part of a pathway dependent on purinergic, adrenergic, and cholinergic receptor activation. In ventral roots containing only somatic efferents, rhythmic activity was rarely recruited. However, in ventral roots containing both autonomic and somatic efferents, sacral dorsal column stimulation recruited autonomic efferent rhythms, which subsequently recruited somatic efferent motor rhythms. The efferent rhythms revealed a half-center organization with very low stimulation frequencies, and the evoked alternating bursts entrained to the stimuli. Similar entrainment was seen when sDC stimuli were applied during ongoing neurochemically-induced locomotor rhythms. The rhythmic patterns evoked by sDC stimulation operated over a limited frequency range, with a discrete burst structure of fast-onset, frequency-independent peaks. In comparison, neurochemically-induced locomotor bursts operated over a wide frequency range and had slower time to peaks that varied with burst frequency. The overall findings support the discovery of an autonomic efferent pattern generator that is recruited by sacral visceral C fiber afferents. It is hoped that this research will advance the understanding of afferent activation of the lumbar central pattern generator and potentially provide insight useful for future development and design of neuroprosthetic devices.

A transmissão sináptica é essencial para o funcionamento do sistema nervoso. A neuromodulação permite regular esse processo de forma precisa. Um desses mecanismos modulatórios é a regulação da liberação de neurotransmissores. A adenosina é um importante modulador da transmissão sináptica. Além disso, a ativação do subtipo A2a dos receptores para adenosina está envolvida com a facilitação da liberação de neurotransmissores no sistema nervoso central. O presente trabalho teve como objetivo avaliar os efeitos modulatórios da ativação do receptor A2a de adenosina sobre a liberação de neurotransmissores e sua via de sinalização intracelular em modelo in vitro. Além disso, a tese contempla a construção histórica dos conceitos abordados no trabalho permitindo uma visão clara de sua evolução. Esse projeto foi o pioneiro no Brasil a utilizar o sensor biossintético fluorescente de liberação de vesículas sinápticas (supereclipse sinapto-pHluorina), o qual foi gentilmente cedido pelo professor Gero Miensenboeck do Sloan-Kettering Institute for Cancer Research. Nossos resultados demonstraram que o tratamento com o agonista do receptor A A2a de adenosina aumentou a fluorescência do supereclipse sinapto-pHluorina, assim como os níveis de glutamato e noradrenalina. Além disso, foi demonstrado que o inibidor da proteína cinase dependente de AMPc aboliu o aumento nos níveis do glutamato e noradrenalina, tal como a fosforilação da proteína sináptica sinapsina I evocado pelo agonista do receptor A2a de adenosina. Desta forma, nossos dados sugerem que a ativação do receptor A2a de adenosina em cultura de células do bulbo de ratos Wistar modula a liberação de neurotransmissores e a fosforilação da sinapsina I, assim como a proteína cinase dependente do AMPc pode ser o modus operandi desse fenômeno modulatório / Synaptic transmission is a sine qua non process for nervous system physiology. Such precise process is accomplished in part due to modulation of neurotransmitter release. Adenosine is a putative synaptic transmission modulator. Moreover, adenosine A2a receptor facilitates neurotransmitter release in the Central Nervous System. The present study focuses on the modulation of neurotransmission by adenosine A2a receptor and its intracellular signaling pathway in in vitro model. Here, we provided evidence that adenosine A2a receptor agonist increases an optical biosynthetic sensor of synaptic vesicle release (supereclipct synapto-pHluorin), as well as glutamate and noradrenaline. Furthermore, it was demonstrated that cAMP-dependent protein kinase inhibitor abolished glutamate and norepinephrin increase, as well as synapsin I phosphorylation evoked by adenosine A2a receptor agonist. Therefore, our data suggest that adenosine A2a receptor activation modulates neurotransmitter release and synapsin I phosphorylation in cultured cells from medulla oblongata of Wistar rats, as well as cAMP-dependent protein kinase might be the modus operandi of this modulatory phenomenon

Introdução: Após décadas de experimentação em estimulação transcraniana por corrente contínua (ETCC), poucos protocolos alcançaram robusta aceitação científica. Protocolos de ETCC foram sugeridos para influenciar alterações no controle postural de indivíduos saudáveis e pacientes após acidente vascular cerebral. No entanto, a escassa literatura nesta área revela a indispensável investigação do efeito doseresposta das estimulações cerebrais a fim de elaborar protocolos mais eficazes. O presente trabalho teve por objetivo verificar o efeito dependente de polaridade e intensidade após o uso da estimulação transcraniana por corrente contínua de alta definição (HD-ETCC) na junção têmporo-parietal (JTP) do hemisfério cerebral direito na assimetria da postura espontânea. Métodos: Este é um ensaio clínico fatorial cruzado, randomizado, controlado por placebo e duplo cego. Foram incluídos 21 indivíduos saudáveis, com idade média de 24,2±4,1 anos, 61,9% mulheres. A intervenção consistiu na aplicação do HD-ETCC com um eletrodo central e 3 eletrodos periféricos posicionados sobre JTP no hemisfério cerebral direito. A descarga de peso corporal (DPC) na posição ortostática foi realizada utilizando uma plataforma de força sobre cada pé do participante, e avaliada durante 2 minutos na medida basal e 5 minutos após cada estimulação. A fim de melhorar a tolerância dos participantes à HD-ETCC, foi realizado um protocolo de acomodação composto por 3 repetições de estimulação com duração e intervalo de 5 segundos cada, nas intensidades fixas de 1, 2 e 3mA. Após um repouso de 5 minutos, foi aplicado o protocolo de estimulação constituído por 3 tipos de polaridade (anodo central; catodo central; placebo) realizadas randomicamente em 3 dias diferentes com intervalo mínimo de 24 horas. Cada sessão de estimulação incluiu 3 repetições de HD-ETCC com duração de 2 minutos em 3 diferentes intensidades (1, 2 e 3mA) com intervalo de 5 minutos. A ordem das intensidades de HD-ETCC foi randomizada. Escala visual analógica foi utilizada para avaliar o grau de desconforto de cada estimulação e efeitos adversos após cada sessão foram registrados. A aquisição de dados foi realizada no Laboratório de Biomecânica e Controle Motor na Escola de Educação Física e Esportes da Universidade de São Paulo-USP. Resultados: A aplicação do HD-ETCC sobre a JTP resultou em efeitos polaridade dependente, provocando assimetria corporal com descarga de peso para o lado direito quando usado condição catodo central em relação à condição placebo nas intensidades de 2mA (Kruskal Wallis: p=0,037; Tukey Post-hoc: p=0,029) e 3mA (Kruskal Wallis: 0,009; Tukey Post-hoc: p=0,049). A DPC mediana na condição cátodo central foi, respectivamente, medida basal de 1,78%[-1,76;4,67]; após 1mA: 2,12%[-0,63;7,08]; após 2mA: 2,33%[- 1,57;6,25]; após 3mA: 2,40%[-0,53;7,16]. Não foi observado efeito dependente de intensidade. Todos os participantes apresentaram boa tolerância dos protocolos de acomodação e estimulação. Conclusão: O protocolo aplicado revelou ser seguro e apresentar boa tolerância dos participantes. Esta é a primeira evidência de que HDETCC aplicada sobre a JTP pode influenciar no controle postural de forma polarizada, o pequeno efeito observado sugere a utilização de protocolos com maior tempo de estimulação. Os resultados deste trabalho favorecem a elaboração da hipótese de aplicação da HD-ETCC no tratamento de desequilíbrio postural / Introduction: After decades of experimentation in transcranial direct current stimulation (tDCS), few protocols achieved robust scientific acceptance. Stimulation protocols were suggested to influence postural control in healthy subjects and patients after stroke. However, the scarce literature in this area reveals imperative investigation of physiological and clinical effects of transcranial stimulations to elaborate more efficient protocols. The aim of the present study was to verify the polarity and intensity dependent effects of high-definition tDCS (HD-tDCS) over the right temporo-parietal junction (JTP) in the weight-bearing asymmetry (WBA). Methods: This is a randomized, double-blind, factorial, crossover controlled clinical trial. We included 21 healthy subjects, mean age of 24,2±4,1 years, and 61.9% women. The intervention consisted of the application of HD-tDCS over the right temporo-parietal junction (TPJ). The WBA in the upright static position was measured using one force plate under each participant\'s foot, assessed during 2 minutes at baseline and 5 minutes after each stimulation. In order to increase participants\' tolerance of the HD-tDCS, we applied an accommodation protocol consisted of 3 stimulation repetitions with 5 seconds of duration and interval, under fixed stimulation intensities of 1, 2 and 3mA. After 5 minutes of rest, the stimulation protocol consisted of 3 types of polarity (anode center; cathode center; sham) applied randomly in different days with a minimal interval of 24 hours. Each stimulation session comprised of 3 repetitions of 2 minutes HD-tDCS in different intensities (1, 2 and 3 mA). Visual analog scale was used to assess discomfort degree after each stimulation and adverse events after each session were registered. The evaluations were carried out in the Biomechanics and Motor Control Laboratory at the Ribeirão Preto School of Physical Education and Sport-USP. Results: The application of HD-tDCS over TPJ resulted in polarity-dependent effects, causing load bearing to the right leg when using central cathode condition in relation to sham at 2mA (Kruskal Wallis: p=0,037; Tukey Post-hoc: p=0,029) and 3mA Kruskal Wallis: 0,009; Tukey Post-hoc: p=0,049). The median WBA of cathode center condition was, respectively, 1,78% [-1,76;4,67] at baseline, 2,12% [-0,63;7,08] after 1mA; 2,33% [- 1,57;6,25] after 2mA; and 2,40% [-0,53;7,16] after 3mA. No intensity dependent effects were observed. Conclusion: The present protocol was feasible and presented good tolerance of participants. This is the first evidence that HD-TDCS over TPJ can influence postural balance. The small effect observed suggests the usage of longer protocols of HD-tDCS. The results of this study enable to hypothesize the application of HD-tDCS over TPJ to treat postural imbalance.

L'étude de la dynamique des circuits neuronaux est primordiale pour la compréhension des troubles neurologiques et psychiatriques. Ces processus, classiquement étudiés in vivo ou ex vivo, peuvent être appréhender in vitro grâce à des micro-technologies. Les technologies microfluidiques offrent la possibilité de reconstruire des réseaux de neurones orientés et de manipuler indépendamment les deux populations neuronales ainsi connectées. Dans cette étude, une caractérisation de la mise en place et de la rythmogénèse des réseaux cortico-striataux a été entreprise par imagerie calcique. Par la suite, nous avons démontré que des modifications chroniques des rythmes pré-synaptiques corticaux conduisaient à des phénomènes d¿excitotoxicité trans-synaptique. L'avancée des recherches a montré que les maladies neurodégénératives et psychiatriques pouvaient partager des points communs, notamment des altérations de la transmission synaptique et de l'activité des réseaux de neurones. Pour évaluer ces effets, une modulation de l'expression de Disrupted-In-Schizophrenia-1 a été réalisée dans nos réseaux cortico-striataux. Une altération de la différenciation des neurones striataux a été objectivée mais sans impact sur l'activité rythmique des réseaux neuronaux. Cependant, les expériences de surexpression ont montré la capacité de DISC-1 à participer à la formation des granules de stress, et à recruter dans celles-ci des protéines impliquées dans la transmission synaptique. Au final, ce projet démontre que les réseaux reconstruits in vitro possèdent des caractéristiques similaires aux réseaux in vivo et permettent l'étude de pathologies du système nerveux central. / Neural circuit dynamics need to be elucidated for understanding neurological and psychiatric disorders such as Parkinson's disease and schizophrenia. While this is classically studied in vivo or ex vivo, micro-technological approaches permit “brain-on-chip” models recapitulating some intrinsic neuronal network properties. In this study, parameters of cortico-striatal connection were monitored. Glutamatergic neuronal network activity was monitored using calcium imaging. Dopamine and Dopaminergic receptor 2 agonist decreased firing frequency and disrupted striato-striatal synchrony. Then, we demonstrated that both acute and chronic alterations of cortical neurons activity led to impairment of striatal survival through trans-synaptic degeneration. In psychiatric diseases, network rhythm alterations do not lead to neuronal death but to behavior disorders. To study how those alterations appeared, we investigated the impact of DISC-1 expression modulation on the establishment of cortico-striatal network and its activity. Alteration of DISC-1 expression led to deficits in striatal differentiation processes and seemingly did not drive network rhythms variation. Interestingly, DISC-1 overexpression experiments showed its aggregation in stress granules concomitant with an ability to recruit others proteins involved in synaptic transmission and neuronal plasticity. These results seem to show that DISC-1 could be involved in degenerative processes and not only in psychiatric diseases. The present data demonstrate that cortico-striatal networks reconstructed in a microfluidic environment present characteristics similar to in vivo cortico-striatal networks.

abstract: Electromagnetic fields (EMFs) generated by biologically active neural tissue are critical in the diagnosis and treatment of neurological diseases. Biological EMFs are characterized by electromagnetic properties such as electrical conductivity, permittivity and magnetic susceptibility. The electrical conductivity of active tissue has been shown to serve as a biomarker for the direct detection of neural activity, and the diagnosis, staging and prognosis of disease states such as cancer. Magnetic resonance electrical impedance tomography (MREIT) was developed to map the cross-sectional conductivity distribution of electrically conductive objects using externally applied electrical currents. Simulation and in vitro studies of invertebrate neural tissue complexes demonstrated the correlation of membrane conductivity variations with neural activation levels using the MREIT technique, therefore laying the foundation for functional MREIT (fMREIT) to detect neural activity, and future in vivo fMREIT studies. The development of fMREIT for the direct detection of neural activity using conductivity contrast in in vivo settings has been the focus of the research work presented here. An in vivo animal model was developed to detect neural activity initiated changes in neuronal membrane conductivities under external electrical current stimulation. Neural activity was induced in somatosensory areas I (SAI) and II (SAII) by applying electrical currents between the second and fourth digits of the rodent forepaw. The in vivo animal model involved the use of forepaw stimulation to evoke somatosensory neural activations along with hippocampal fMREIT imaging currents contemporaneously applied under magnetic field strengths of 7 Tesla. Three distinct types of fMREIT current waveforms were applied as imaging currents under two inhalants – air and carbogen. Active regions in the somatosensory cortex showed significant apparent conductivity changes as variations in fMREIT phase (φ_d and ∇^2 φ_d) signals represented by fMREIT activation maps (F-tests, p <0.05). Consistent changes in the standard deviation of φ_d and ∇^2 φ_d in cortical voxels contralateral to forepaw stimulation were observed across imaging sessions. These preliminary findings show that fMREIT may have the potential to detect conductivity changes correlated with neural activity. / Dissertation/Thesis / Doctoral Dissertation Biomedical Engineering 2020

Lors du vieillissement sain, et malgré une augmentation de la fréquence d’apparition du manque du mot, les personnes âgées manifestent une préservation des performances de dénomination orale d’objets (DO), suggérant la mise en place de stratégies efficaces de récupération et de sélection de l’information lexicale. Dans ce travail de thèse, nous avons utilisé une approche méthodologique multimodale afin d’évaluer la nature de ces stratégies. Nous nous sommes plus spécifiquement intéressés aux mécanismes de réorganisation cérébrale ainsi qu’aux activités sociales comme facteur de réserve cognitive. Ce travail de thèse se décompose en cinq études et aborde une perspective homogène (effet de l’âge) et hétérogène (effet des performances) du vieillissement. Nos résultats mettent en évidence l’existence de différents mécanismes de compensation associés au vieillissement sain. Tout d’abord, nous observons que les personnes âgées sont plus lentes que les jeunes adultes lors de la DO, mais obtiennent un taux de précision similaire. D’après la perspective homogène, le maintien des performances de DO s’expliquerait par le recrutement d’une stratégie de nature sémantique. Au niveau cérébral, nous observons une augmentation de l’asymétrie intra-hémisphérique gauche des régions temporo-pariétales chez les personnes âgées, ainsi qu’un transfert de la connectivité normalement observée du gyrus frontal inférieur (GFI) gauche avec le gyrus temporal latéral au gyrus temporal médial gauche. D’après la perspective hétérogène, le maintien des performances de DO s’expliquerait par l’utilisation d’une stratégie de nature exécutive, reflétée par une réduction de l’asymétrie inter-hémisphérique frontale chez les personnes âgées dont les temps de réponse de DO sont courts. Par ailleurs, nous proposons que l’encodage lexico-phonologique module également le taux de précision de DO, via la connectivité effective entre le GFI gauche et le gyrus temporal supérieur gauche. Enfin, nous observons une relation significative entre la fréquence de participation aux activités sociales, notamment collectives, et les performances de DO. Cette relation est partiellement médiée au niveau cérébral par l’activité du gyrus frontal supérieur médian gauche, via un mécanisme de réserve neurale. Sur la base de nos résultats, nous proposons un modèle neurocognitif des stratégies de récupération et de sélection de l’information lexicale, utilisant une approche multimodale et plurifactorielle du vieillissement sain. / Despite increased difficulties to find words in the daily life, older adults show preserved object naming performances when compared to younger ones. This suggests a supplementary recruitment of compensatory strategies in order to retrieve and select words. In this research work, we have used a multimodal methodological approach to evaluate the nature of these strategies, by using an object naming task. Specifically, we have evaluated these strategies in terms of mechanisms of cerebral reorganization. We were also interested to know how these strategies are modulated by the frequency of social activities, considered as a factor of cognitive reserve. This thesis work is composed of five studies performed under a homogeneous (effect of age) and a heterogeneous (effect of performance) perspective. Based on results, we suggest that aging is associated with multiple compensatory mechanisms to maintain a correct level of performance. Specifically, according to the homogeneous perspective, we consider that preserved object naming performances in older adults might be explained by the use of a semantic strategy. Indeed, in older compared to younger adults and at a cerebral level, we observed increased left hemispheric asymmetry with significant recruitment of the temporo-parietal regions. In addition, the inferior frontal gyrus (IFG) that is connected to the lateral temporal cortex in younger adults, seems to “switch” its connectivity toward the left medial temporal gyrus in older adults. In addition, according to the heterogeneous perspective, preserved object naming performances in older adults can be also explained by the use of an executive strategy, reflected by reduced inter-hemispheric asymmetry of frontal regions, specifically in more performant older adults (with shorter response latencies). Furthermore, we suggest that lexico-phonological processes mediate naming accuracy as reflected by the increased connectivity from the left IFG to the left superior temporal gyrus. A final result that we report in this work indicates that the frequency of participation to group social activities correlates to naming performance in older adults. This relation is partially mediated by the left superior medial frontal gyrus and is assimilated to a neural reserve mechanism. Overall, based on our findings, we propose a neurocognitive model of lexical retrieval and selection strategies in normal aging, based on a multimodal dataset and a multifactorial approach.

No description available.

No description available.

No description available.

No description available.