La stimulation électrique neurale, appliquée au système nerveux périphérique pour la restauration des fonctions motrices ou la neuromodulation, est une technologie en plein essor, en particulier la stimulation implantée avec des électrodes Cuff positionnées autour d’un nerf périphérique. Le principal frein au développement des systèmes de stimulation est la difficulté à obtenir la stimulation ou l’inhibition des fonctions cibles de manière précise et indépendante, c’est-à-dire, obtenir une sélectivité des fonctions. Les paramètres impliqués dans la sélectivité au sens large ne sont pas toujours intuitifs, et le nombre de degrés de libertés (choix de l’électrode, nombre de contacts, forme du pulse etc.) est important. Tester toutes ces hypothèses en expérimentation n’est pas faisable et inenvisageable dans le réglage des neuroprothèses en contexte clinique. La modélisation a priori nous permet d’établir des critères de choix, de déterminer les stratégies les plus efficaces et de les optimiser. Par ailleurs, un grand nombre d’études ont pu prévoir des stratégies de sélectivité inédites grâce à la modélisation, et validées a posteriori par l’expérimentation. Le schéma de calcul scientifique est composé de deux parties. On modélise, d’une part, la propagation du champ de potentiels électriques générés par les électrodes à l’intérieur d’un volume conducteur représentant le nerf (étude biophysique), et d’autre part l’interaction entre ce champ de potentiels et les neurones (réponse électrophysiologique). Notre première contribution propose une méthode originale de modélisation et d’optimisation de la sélectivité spatiale avec une électrode Cuff, sans connaissance a priori de la topographie de nerf. Partant de ce constat, nous déterminons de nouveaux critères, l’efficacité et la robustesse, complémentaires à la sélectivité, nous permettant de faire un choix entre des configurations multipolaires concurrentes. Ainsi, en fonction de la pondération de ces critères, nous avons développé un algorithme d’optimisation pour déterminer la configuration optimale en fonction de la zone choisie, du diamètre des fibres visées ainsi que de la durée de stimulation, pour un pulse type rectangulaire de référence. Des expérimentations sur modèle animal nous ont permis d’évaluer l’efficacité de la méthode et sa généricité. Ce travail est partie intégrante d’un projet plus vaste de stimulation du nerf vague (projet INTENSE), où l’une des applications concerne le traitement des troubles cardiaques. L’objectif est d’activer sélectivement une population spécifique de fibres nerveuses pour obtenir des effets plus ciblés conduisant à une thérapie améliorée, tout en diminuant les effets secondaires. La deuxième contribution consiste à combiner la sélectivité spatiale et la sélectivité au diamètre de fibre avec un modèle générique de nerf et une électrode Cuff à 12 contacts. L’utilisation d’une forme d’onde particulière (prépulse) combinée avec des configurations multipolaires permet d’activer des fibres d’un diamètre défini dans un espace ciblé. Les perspectives cliniques sont nombreuses, notamment sur la réduction de la fatigue liée à l’utilisation prolongée de la stimulation ou la diminution des effets secondaires. Dans le cadre du projet INTENSE, la seconde application liée à la stimulation du nerf vague vise le problème de l’obésité morbide. L’activation des axones cibles liés aux fonctions gastriques nécessite une quantité de charges conséquente. Plusieurs études suggèrent que les formes de pulse non rectangulaires peuvent activer les axones du système nerveux périphérique avec une quantité de charges réduite comparée à la forme de pulse rectangulaire de référence. Notre dernière contribution concerne l’étude expérimentale et de modélisation de ces formes d’ondes complexes. L’approche par modélisation, si elle est bien maîtrisée, apporte une analyse pertinente voire même indispensable au réglage clinique des neuroprothèses. / Neural electrical stimulation, applied to the peripheral nervous system for motor functions restoration or neuromodulation, is a thriving technology, especially implanted stimulation using Cuff electrodes positioned around a peripheral nerve. The main obstacle to the development of stimulation systems is the difficulty in obtaining the independent stimulation or inhibition of specific target functions (i.e. functional selectivity). The parameters involved in selectivity are not always intuitive and the number of degrees of freedom (choice of electrode, number of contacts, pulse shape etc.) is substantial. Thus, testing all these hypotheses in a clinical context is not conceivable. This choice of parameters can be guided using prior numerical simulations predicting the effect of electrical stimulation on the neural tissue. Numerous studies developed new strategies to achieve selectivity based on modeling results that have been validated a posteriori by experimental works. The computation scheme is composed of two parts : the modeling of the potential field generated by the electrodes inside a conductive medium representing the nerve on the one hand; and the determination of the interaction between this field of potentials and neurons on the other. Our first contribution is an original method of modeling and optimization of the spatial selectivity with a Cuff electrode, without prior knowledge of the nerve topography. Based on this observation, we determined new criteria, efficiency and robustness, complementary to selectivity, allowing us to choose between multipolar configurations. Thus, according to the weighting applied to these criteria, we developed an optimization algorithm to determine the optimal configuration as a function of the target zone, fiber diameter and the stimulation duration for a typical rectangular pulse. Experiments on animal model allowed us to evaluate the effectiveness and genericness of the method. This work was performed as part of a larger project on vagus nerve stimulation (INTENSE project) in which one of the applications focused on the treatment of cardiac disorders. The main objective was to selectively activate a specific population of nerve fibers to improve therapy and decrease side effects. In a second contribution, numerical simulations were used to investigate the combination of multipolar configurations and the prepulses technique, in order to obtain fiber recruitment in a spatially reverse order. The main objective was to achieve both spatial and fiber diameter selectivity. Expected clinical perspectives of this work are the reduction of fatigue related to a prolonged use of stimulation and the reduction of side effects. Within the framework of the INTENSE project, the second application investigated vagus nerve stimulation as a therapy for morbid obesity. Activation of target axons related to gastric functions requires a significant amount of charge injection. Several studies suggest that non-rectangular waveforms can activate axons of the peripheral nervous system with a reduced amount of charge compared to the reference rectangular pulse shape. Our last contribution focuses on the experimental study and the modeling of these complex waveforms. The modeling approach, if performed properly and while bearing in mind its limits, provides a relevant and even indispensable analysis tool for the clinical adjustment of neuroprostheses.

<p>My thesis revolves around neuronal circuit dynamics in health and disease. The first part of the thesis characterized cross-regional synchrony within the visual cortical network following visual perceptual experience in healthy mice. This work for the first time described inter-areal 4-8 Hz superficial layer LFP synchrony across mouse visual cortical regions persisting beyond visual stimulation time window, and revealed that the synchrony was expressed specifically between V1 and the higher-order visual area (HVA) with functional preference matching the entrained spatial frequency (SF) and temporal frequency (TF) content, in mice. The discovery of visual familiarity induced inter-areal 4-8 Hz synchrony extends the previous discovery of the 4-8 Hz oscillation in V1 after visual experience from our lab (Kissinger et al., 2018; Kissinger et al., 2020; Gao et al., 2021), and provided the first pivotal evidence supporting the role of 4-8 Hz oscillation in mediating cross-regional communication. Such 4-8 Hz visual cortical network synchrony has been mostly reported in primate studies in contexts of visual attention and working memory (Liebe et al., 2012; Spyropoulos et al., 2018), while our study extended the visual cortical network synchrony research scope to mouse models and in a new context of visual familiarity. The work is a key step for starting cortical network studies in mice, and for starting predictive coding theory study in the context of oscillations in mouse cortical network in the future. Additionally, unit spiking was more strongly modulated by 4-8 Hz oscillations in V1 and HVAs after visual experience. The visually-locked responsive units in V1 and HVAs exihibted either increased or decreased inter-areal spiking synchrony, while most post-stimulus responsive units in V1 and HVA exhibited higher spiking synchrony. </p> <p>The other parts of my dissertation looked at V1 activity in disease and following a novel CNS therapy. One project looked at recovery of visually evoked response in mouse V1 after ischemia through NeuroD1 mediated astrocyte-to-neuron conversion, where we characterized the formation of cortical laminated structure from the converted neurons, longitudinal recovery of visually evoked responses of unit populations in V1, and units’ selective responses to orientations. Another project looked at altered visual cortical activity in an Auxilin knockout mouse model, which demonstrated overall reduced visually evoked responses, less selective responses to orientations, impaired visual adaptive responses and mismatch responses, as well as slower visual experience induced oscillations. These projects utilized the high-density silicon probe recording technique to 1) characterize visual cortical function recovery following a therapy, which provided evidence for its high efficacy for recovering physiological functions, and to 2) phenotype visual cortical functional impairments in a mouse disease model, which provided more basic understanding in visual cortical physiology of Auxilin related disease.</p> <p>In sum, my dissertation work took advantage of the high-density silicon probe recording technique to probe neuronal circuits in health and disease. The discovery of visual experience induced inter-areal 4-8 Hz synchrony paves the way for studying 4-8 Hz activity in relation to stream-dependent visual processing and predictive coding in health and disease.</p>

Spinal muscular atrophy (SMA) is an autosomal recessive neurodegenerative disorder that is the leading genetic cause of infantile death. SMA is caused by homozygous deletion or mutation of the survival of motor neuron 1 gene (SMN1). The SMN2 gene is nearly identical to SMN1, however is alternatively spliced. The close relationship to SMN1 results in SMN2 being a very power genetic modifier of SMA disease severity and a target for therapies. In this study we attempt to characterize novel chemical compounds identified as potential activators of the SMN2 gene. Additionally, we sought to determine the regulatory role individual HDAC proteins use to control expression of full length protein from the SMN2 gene. We used quantitative PCR to determine the effects of novel compounds and shRNA silencing of individual HDACs on the steady state levels of a SMN2-luciferase reporter transcripts. We determined that the compounds identified in multiple reporter high throughput screens increased SMN protein levels via transcriptional activation of the SMN2 gene. Other compounds identified in the same screen functioned post-transcriptionally, possibly stabilizing the SMN protein itself by decreasing degradation. Furthermore, we determined that reduction of individual HDAC proteins was sufficient to increase SMN protein levels in a transgenic reporter system. Knockdown of class I HDAC proteins preferentially activated the reporter by increased promoter transcription. Silencing of class II HDAC proteins maintained transcriptional activity; however silencing of HDAC 5 and 6 also appeared to enhance inclusion of an alternatively spliced exon. This collective work defines a quantitative RNA based protocol to determine mechanism of SMN reporter increase in response to any chosen treatment method. Additionally, this work highlights HDAC proteins 2 and 6 as excellent investigative targets. These data are important to the basic understanding of SMN expression regulation and the refinements of current therapeutic compounds as well as the development of novel SMA therapeutics.

Indiana University-Purdue University Indianapolis (IUPUI) / Methylmercury (MeHg) exposure from occupational, environmental and food sources is a significant threat to public health. MeHg poisonings in adults may result in severe psychological and neurological deficits, and in utero exposures can confer significant damage to the developing brain and impair neurobehavioral and intellectual development. Recent epidemiological and vertebrate studies suggest that MeHg exposure may contribute to dopamine (DA) neuron vulnerability and the propensity to develop Parkinson’s disease (PD). I have developed a novel Caenorhabditis elegans (C. elegans) model of MeHg toxicity and have shown that low, chronic exposure confers embryonic defects, developmental delays, reduction in brood size, decreased animal viability and DA neuron degeneration. Toxicant exposure results in an increase in reactive oxygen species (ROS) and the robust induction of several glutathione-S-transferases (GSTs) that are largely dependent on the PD-associated phase II antioxidant transcription factor SKN-1/Nrf2. I have also shown that SKN-1 is expressed in the DA neurons, and a reduction in SKN-1 gene expression increases MeHg-induced animal vulnerability and DA neuron degeneration. Furthermore, I incorporated a novel genome wide reverse genetic screen that identified 92 genes involved in inhibiting MeHg-induced animal death. The putative multidrug resistance protein MRP-7 was identified in the screen. I have shown that this transporter is likely expressed in DA neurons, and reduced gene expression increases cellular Hg accumulation and MeHg-associated DA neurodegeneration. My studies indicate that C. elegans is a useful genetic model to explore the molecular basis of MeHg-associated DA neurodegeneration, and may identify novel therapeutic targets to address this highly relevant health issue.

Microtubule targeting agents (MTAs) are chemotherapeutics commonly used in the treatment of breast, ovarian, lung, and lymphoma cancers. There are two main classes of MTAs based upon their effects on microtubule stability. The two classes are the destabilizing agents, which include the drug vincristine, and the stabilizing agents, which include paclitaxel and epothilone B. These drugs are highly effective antineoplastics, but their use is often accompanied by several side effects, one of which is peripheral neuropathy. Peripheral neuropathy can be characterized by burning pain, tingling, loss of proprioception, or numbness in the hands and feet. In some patients, the MTA-induced peripheral neuropathy is debilitating and dose-limiting; however, there are no effective prevention strategies or treatment options for peripheral neuropathy as the mechanisms mediating this side effect are unknown. The goal of this work was to investigate MTA-induced effects on neuronal activity and morphology in order to elucidate the underlying mechanisms involved in the development of MTA-induced peripheral neuropathy. As an indicator of sensory neuronal activity, the basal and stimulated release of the putative nociceptive peptide, calcitonin gene-related peptide (CGRP), was measured from sensory neurons in culture after exposure to the MTAs paclitaxel, epothilone B, and vincristine. Neurite length and branching were also measured in sensory neuronal cultures after treatment with these MTAs. The results described in this thesis demonstrate that MTAs alter the stimulated release of CGRP from sensory neurons in differential ways depending on the MTA agent employed, the CGRP evoking-stimulus used, the concentration of the MTA agent, the duration of exposure to the MTA agent, and the presence of NGF. It was also observed that MTA agents decrease neurite length and branching, independent of the concentration of NGF in the culture media. Thus, this thesis describes MTA-induced alterations of sensory neuronal sensitivity and neurite morphology and begins to elucidate the underlying mechanisms involved in MTA-induced alterations of sensory neurons. These findings will undoubtedly be used to help elucidate the mechanisms underlying MTA-induced peripheral neuropathy.

Einleitung: Epidemiologische Studien zeigen den langfristigen Nutzen körperlicher Aktivität zur Prävention neurologischer Erkrankungen und kognitiver Defizite im Alter auf. Sportliche Betätigung kann jedoch, vor allem bei Ausübung von Kontaktsportarten, auch akute und chronische neuronale Schädigungen durch häufige mechanische Beeinflussungen des Gehirns hervorrufen. NSE und S-100B sind laborchemische Marker, die im Rahmen der Diagnostik von Hirnschädigungen zum Einsatz kommen. Einige Forschungsarbeiten fanden erhöhte Konzentrationen dieser Biomarker nach sportlichen Belastungen ohne offensichtliches Vorliegen von traumatischen Ereignissen oder neurologischer Beeinträchtigungen. Daher stellt sich die Frage, ob entsprechende Norm- bzw. Cut-Off-Werte für NSE und S-100B universell im klinischen Alltag geeignet sind oder durch belastungsinduzierte Einflüsse einer differenzierteren Beurteilung unterzogen werden sollten. In vorliegender Arbeit wird diese Fragestellung anhand der klassischen Ausdauersportarten Laufen und Radfahren untersucht. Ergebnisse und Diskussion: Zunächst erfolgte der Nachweis für die Reproduzierbarkeit von NSE bei Ausdauersportlern für Ruhe- und Belastungsbedingungen. Es wurden keine signifikanten Unterschiede für NSE im Belastungsvergleich von Radfahren und Laufen, wie beim Vergleich verschiedener Laufintensitäten im zeitlichen Verlauf festgestellt. Die denkbare Einflussnahme beim Laufen durch leichte Erschütterungen des Gehirns basierend auf dem Impact beim Bodenkontakt des Fußes, ist offensichtlich irrelevant. Physischer Stress, der durch einen Marathonlauf verursacht wird, führt offensichtlich in der Akutphase nach dem Wettkampf zu einem signifikanten Anstieg von NSE und S-100B, welche im späteren Verlauf wieder auf das Ausgangsniveau abfallen. Dies ist unabhängig von Alter und Geschlecht. Über dem Normwert für Gesunde liegende NSE-Konzentrationen nach einer Marathonbelastung, haben offensichtlich keine pathophysiologischen Auswirkungen oder klinische Korrelationen. In der klinischen Praxis sollten erhöhte NSE-Werte entsprechend vorsichtig interpretiert werden. Weitere marathonspezifische Faktoren wie Trainingshäufigkeit, Renneinteilung, Wetterbedingungen und Dysnatriämie, aber auch Alter und Geschlecht zeigten keine Zusammenhänge hinsichtlich der Serum-Konzentration von NSE und S-100B. Ebenfalls fanden sich keine signifikanten Veränderungen bei der Klassifizierung von Notfallpatienten bei Laufveranstaltungen bezüglich Diagnose und Streckenlängen. Fortführende Forschungsaktivitäten mit hohen Fallzahlen sind notwendig, um die Wertigkeit der beiden biochemischen Labormarker unter Einfluss körperlicher Aktivität herauszustellen.:1. Einleitung und allgemeine Problemstellung 1 1.1 Einleitung 1 1.2 Ziele der Arbeit 4 2. Theoretische Grundlagen 5 2.1 Theoretische Grundlagen zu NSE 5 2.2 Theoretische Grundlagen zu S-100B 8 2.3 Einfluss sportlicher Belastungen auf NSE 9 2.4 Einfluss sportlicher Belastungen auf S-100B 10 3. Grundlegende Aspekte zur Methodik dieser Arbeit 12 3.1 Blutanalytik 13 3.2 Messverfahren NSE und S-100B 13 3.3 Ausschluss Hämolyse 14 3.4 Plasmavolumenkorrektur 17 3.5 Leistungsdiagnostik 18 3.6 Auswertung und Statistik 19 4. Teilstudie 1 - Methodische Untersuchungen 21 4.1 Reproduzierbarkeit von NSE unter Ruhe- und Belastungsbedingungen 21 4.1.1 Einleitung 21 4.1.2 Methoden 21 4.1.2.1 Probanden 21 4.1.2.2 Studiendesign 23 4.1.3 Ergebnisse 24 4.1.4 Diskussion 30 4.2 Pilotstudie zur In-vivo-Bestimmung von zerebralen S-100B mittels 1H-Magnetresonanzspetroskopie 35 4.2.1 Einleitung 35 4.2.2 Methoden 35 4.2.2.1 Probanden 35 4.2.2.2 Messverfahren 36 4.2.2.3 Studiendesign 39 4.2.3 Ergebnisse 39 4.2.4 Diskussion 41 5. Teilstudie 2 - Untersuchungen zum Einfluss sportlicher Belastung und NSE 47 5.1 Belastungsart und NSE 47 5.1.1 Einleitung 47 5.1.2 Methoden 47 5.1.2.1 Probanden 47 5.1.2.2 Studiendesign 48 5.1.3 Ergebnisse 50 5.1.4 Diskussion 54 5.2 Belastungsintensität und NSE 56 5.2.1 Einleitung 56 5.2.2 Methoden 56 5.2.2.1 Probanden 56 5.2.2.2 Studiendesign 57 5.2.3 Ergebnisse 57 5.2.4 Diskussion 61 6. Teilstudie 3 - Untersuchungen zum Einfluss von Marathonbelastungen auf NSE und S-100B 62 6.1 Einleitung 62 6.2 Methoden 64 6.2.1 Probanden 64 6.2.2 Sonstige Blutparameter 69 6.2.3 Studiendesign 71 6.3 Ergebnisse 71 6.3.1 Zeitlicher Verlauf 71 6.3.2 Geschlecht und NSE 73 6.3.3 Einfluss des Alters 75 6.3.4 Sportanamnestische Daten 79 6.3.5 Renntaktik 81 6.3.6 Wetterbedingungen 82 6.3.7 Dysnatriämie 84 6.3.8 NSE und S-100B im Zusammenhang mit weiteren belastungsspezifischen Laborparametern 85 6.4 Diskussion 91 6.4.1 Zeitlicher Verlauf 91 6.4.2 Alter und Geschlecht 93 6.4.3 Trainingshäufigkeit und -umfang 94 6.4.4 Renneinteilung 95 6.4.5 Elektrolytstörungen 97 6.4.6 NSE und S-100B im Zusammenhang mit weiteren belastungsspezifischen Laborparametern 98 7. Teilstudie 4 - Untersuchungen bei laufassoziierten Notfällen 104 7.1 Laufassoziierte Notfälle und NSE 104 7.1.1 Einleitung 104 7.1.2 Methoden 105 7.1.2.1 Probanden 105 7.1.2.2 Studiendesign 105 7.1.3 Ergebnisse 106 7.1.4 Diskussion 108 7.2 Einzelfallstudie 111 7.2.1 Einleitung 111 7.2.2 Methoden 111 7.2.2.1 Proband 111 7.2.2.2 Studiendesign 112 7.2.3 Ergebnisse 112 7.2.4 Diskussion 114 8. Abschließende Diskussion 118 9. Zusammenfassung 123 10. Literaturverzeichnis 125 11. Anhang 140 12. Danksagung 145 13. Eidesstattliche Erklärung 146 / Introduction: Epidemiological studies show long term benefits of exercise and sports for neurological diseases and cognitive deficits in elderly populations. In contact sports however also acute and chronic neuronal impairment of the brain itself caused by repetitive mechanical impact have been found. NSE and S-100B are biochemical markers used in diagnostics of brain injuries. Through several studies found increased values of theses markers after exercise without evident existence of traumatological occasion or neurological impairment. Whether NSE and S-100B and its corresponding reference- and cut-off-values can be applied in clinical routine or if exercise-induced effects apply for a more sophisticated evaluation, should herein be examined by the effects of traditionally endurance sports running and cycling. Results and discussion: At first the proof for repeatability of NSE in endurance sportsmen at rest and during physical activity was given. When comparing the effects of cycling and running as well as different training intensities in these sports, no significant changes could be noticed. Possible causes of elevated NSE due to slight concussions of the brain based on repetitive impact forces during running are obviously irrelevant. Running a marathon tends to result in a significant raise of NSE and S-100B in the acute period after the competition. The further process shows a decline to the base level independent of age or gender. NSE values above norm values after completing a marathon have clearly no pathophysiological effects or clinical correlates. Thus high NSE- concentrations should be interpreted with caution in clinical praxis. Further marathon specific factors like training, pacing strategy, weather conditions, dysnatraemia show no significant correlations with NSE or S-100B. Clustering emergency cases by diagnosis and running distance revealed no relationships to NSE. Further research with larger populations is necessary, to emphasize the relevance for NSE and S-100B during exercise.:1. Einleitung und allgemeine Problemstellung 1 1.1 Einleitung 1 1.2 Ziele der Arbeit 4 2. Theoretische Grundlagen 5 2.1 Theoretische Grundlagen zu NSE 5 2.2 Theoretische Grundlagen zu S-100B 8 2.3 Einfluss sportlicher Belastungen auf NSE 9 2.4 Einfluss sportlicher Belastungen auf S-100B 10 3. Grundlegende Aspekte zur Methodik dieser Arbeit 12 3.1 Blutanalytik 13 3.2 Messverfahren NSE und S-100B 13 3.3 Ausschluss Hämolyse 14 3.4 Plasmavolumenkorrektur 17 3.5 Leistungsdiagnostik 18 3.6 Auswertung und Statistik 19 4. Teilstudie 1 - Methodische Untersuchungen 21 4.1 Reproduzierbarkeit von NSE unter Ruhe- und Belastungsbedingungen 21 4.1.1 Einleitung 21 4.1.2 Methoden 21 4.1.2.1 Probanden 21 4.1.2.2 Studiendesign 23 4.1.3 Ergebnisse 24 4.1.4 Diskussion 30 4.2 Pilotstudie zur In-vivo-Bestimmung von zerebralen S-100B mittels 1H-Magnetresonanzspetroskopie 35 4.2.1 Einleitung 35 4.2.2 Methoden 35 4.2.2.1 Probanden 35 4.2.2.2 Messverfahren 36 4.2.2.3 Studiendesign 39 4.2.3 Ergebnisse 39 4.2.4 Diskussion 41 5. Teilstudie 2 - Untersuchungen zum Einfluss sportlicher Belastung und NSE 47 5.1 Belastungsart und NSE 47 5.1.1 Einleitung 47 5.1.2 Methoden 47 5.1.2.1 Probanden 47 5.1.2.2 Studiendesign 48 5.1.3 Ergebnisse 50 5.1.4 Diskussion 54 5.2 Belastungsintensität und NSE 56 5.2.1 Einleitung 56 5.2.2 Methoden 56 5.2.2.1 Probanden 56 5.2.2.2 Studiendesign 57 5.2.3 Ergebnisse 57 5.2.4 Diskussion 61 6. Teilstudie 3 - Untersuchungen zum Einfluss von Marathonbelastungen auf NSE und S-100B 62 6.1 Einleitung 62 6.2 Methoden 64 6.2.1 Probanden 64 6.2.2 Sonstige Blutparameter 69 6.2.3 Studiendesign 71 6.3 Ergebnisse 71 6.3.1 Zeitlicher Verlauf 71 6.3.2 Geschlecht und NSE 73 6.3.3 Einfluss des Alters 75 6.3.4 Sportanamnestische Daten 79 6.3.5 Renntaktik 81 6.3.6 Wetterbedingungen 82 6.3.7 Dysnatriämie 84 6.3.8 NSE und S-100B im Zusammenhang mit weiteren belastungsspezifischen Laborparametern 85 6.4 Diskussion 91 6.4.1 Zeitlicher Verlauf 91 6.4.2 Alter und Geschlecht 93 6.4.3 Trainingshäufigkeit und -umfang 94 6.4.4 Renneinteilung 95 6.4.5 Elektrolytstörungen 97 6.4.6 NSE und S-100B im Zusammenhang mit weiteren belastungsspezifischen Laborparametern 98 7. Teilstudie 4 - Untersuchungen bei laufassoziierten Notfällen 104 7.1 Laufassoziierte Notfälle und NSE 104 7.1.1 Einleitung 104 7.1.2 Methoden 105 7.1.2.1 Probanden 105 7.1.2.2 Studiendesign 105 7.1.3 Ergebnisse 106 7.1.4 Diskussion 108 7.2 Einzelfallstudie 111 7.2.1 Einleitung 111 7.2.2 Methoden 111 7.2.2.1 Proband 111 7.2.2.2 Studiendesign 112 7.2.3 Ergebnisse 112 7.2.4 Diskussion 114 8. Abschließende Diskussion 118 9. Zusammenfassung 123 10. Literaturverzeichnis 125 11. Anhang 140 12. Danksagung 145 13. Eidesstattliche Erklärung 146

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The current study investigates the effect of strain state, strain rate, and membrane planar area on phospholipid bilayer mechanoporation and failure. Using molecular dynamics, a 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) bilayer was deformed biaxially to represent injury-induced neuronal membrane mechanoporation and failure. For all studies, water forming a bridge through both phospholipid bilayer leaflets was used as a failure metric. To examine the effect of strain state, 72 phospholipid structures were subjected to equibiaxial, 2:1 non-equibiaxial, 4:1 non-equibiaxial, strip biaxial, and uniaxial tensile deformations at the von Mises strain rate of 5.45 × 108 s-1. The stress magnitude, failure strain, headgroup clustering, and damage behavior were strain state dependent. The strain state order of detrimentality in descending order was equibiaxial, 2:1 non-equibiaxial, 4:1 non-equibiaxial, strip biaxial, and uniaxial with failure von Mises strains of 0.46, 0.47, 0.53, 0.77, and 1.67, respectively. Additionally, pore nucleation, growth, and failure were used to create a Membrane Failure Limit Diagram (MFLD) to demonstrate safe and unsafe membrane deformation regions. This MFLD allowed representative equations to be derived to predict membrane failure from in-plane strains. To examine the effect of strain rate, the equibiaxial and strip biaxial strain states were repeated at multiple strain rates. Additionally, a 144 phospholipid structure, which was twice the size of the 72 phospholipid structure in the x dimension, was subjected to strip biaxial tensile deformations to examine planar area effect. The applied strain rates, planar area, and cross-sectional area had no effect on the von Mises strains at which pores greater than 0.1 nm2 were detected (0.509 plus/minus 7.8%) or the von Mises strain at failure (0.68 plus/minus 4.8%). Additionally, changes in bilayer planar and cross-sectional areas did not affect the stress response. However, a strain rate increase from 1.4 × 108 to 6.8 × 108 s-1 resulted in a yield stress increase of 44.1 MPa and a yield strain increase of 0.17. Additionally, a stress and mechanoporation behavioral transition was determined to occur at a strain rate of ~1.4 × 108 s-1. These results provide the basis to implement a more accurate mechano-physiological internal state variable continuum model that captures lower-length scale damage.

Neuronal membrane disruption and mechanoporation are nanoscale damage mechanisms that critically affect brain cell viability during traumatic brain injury (TBI). These nanoscale cellular impairments are elusive in experiments and necessitate in silico approaches such as molecular dynamics (MD) simulations. Implementing MD, this research aims to investigate the effects of different key factors related to membrane deformation and damage, including force field resolutions, lipid compositions, and loading conditions. To examine the impact of force field resolution, MD deformation simulations were conducted on 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC) lipid bilayer membranes, using all-atom (AA), united-atom (UA), and coarse-grained Martini (CG-M) force fields. The mechanical responses of the three models progressively changed based on the coarse-graining level. The coarser systems exhibited lower yield stresses and failure strains, and higher mechanoporation damage. To study the influence of lipid components, tensile deformation was applied on seven lipid bilayers, each of which contained a different lipid type commonly found in human brain membrane. Larger headgroup structure, greater degree of unsaturation, and tail-length asymmetry decreased lipid packing, increased the area per lipid (APL), and decreased the failure strain of membrane. Lastly, the deformation behavior of a complex multicomponent MD bilayer (realistically representing human neuronal plasma membrane) under different strain rates and strain states was inspected. The yield stress increased with increasing strain rates and more equibiaxial strain states. Meanwhile, lower strain rates resulted in fewer but larger pores, as well as lower strain and APL at failure. Besides, more equibiaxial strain states exhibited more and larger pores, and lower failure strain. Similar failure APL was obtained regardless of strain states, suggesting that the membrane failed when reaching a critical APL value. In addition, the inclusion of cholesterol was shown to decrease the critical APL. The strain-state dependence results were then used to update the Membrane Failure Limit Diagram (MFLD) that indicates the planar strains for potential membrane failure. Overall, the study provides a non-invasive approach that aids in the current understanding of nanoscale neuronal damage dynamics and essential aspects affecting membrane mechanical responses, and furthermore lays the groundwork for future studies on brain injury biomechanics under various TBI scenarios.