Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Les CPGs (Central Pattern Generators) sont des circuits neuronaux capables de générer de façon autonome des comportements rythmiques essentiels à la vie tels que la respiration ou la locomotion. Chez la larve de Drosophile, le CPG locomoteur est composé de motoneurones (MNs) et d’une grande diversité d’interneurones (INs). Combien d’entre eux sont nécessaires pour former une CPG fonctionnel et comment ils interagissent reste un mystère. Au cours de mon doctorat, j’ai étudié une population neuronale restreinte caractérisée par son expression du facteur de transcription (FT) de la famille des Maf, Traffic Jam (TJ). En utilisant une technique d’intersection génétique et grâce à une lignée TJ-Flp générée au cours de mon doctorat, j’ai démontré pour la première fois que différentes sous-populations de neurones TJ+ ont des fonctions distinctes dans le comportement locomoteur de la larve de Drosophile. Au travers de cette sous-division fonctionnelle, j’ai finalement identifié 3 neurones TJ+ per+ GABAergic par segment qui régulent la vitesse de locomotion des larves. Une caractérisation moléculaire poussée de ces cellules a permis de confirmer qu’elles appartiennent au groupe connu des « midline cells », et plus particulièrement des mnb progeny, dont la fonction était jusqu’à maintenant inconnue. Par ailleurs, le code combinatoire de FTs trouvé chez ces mnb progeny rappelle celui exprimé par les V2b, une population d’interneurones qui régulerait également la vitesse de locomotion chez les vertébrés. Ces similarités entre mnb progeny et V2b laissent à penser que cette population de neurones pourrait être conservée au cours de l’évolution. En outre, des résultats préliminaires suggèrent que les interneurones TJ+ ont également un rôle chez la mouche adulte. / CPGs (Central Pattern Generators) are neural networks able to autonomously generate essential rhythmic behaviours such as walking or breathing. In Drosophila larvae, the locomotor CPG is made up of motoneurons (MNs) and a huge variety of interneurons (INs). How many are actually necessary to constitute a functional CPG and how they interact is not known. During the course of this PhD, I studied a discrete neuronal population singled out by its expression of the Maf transcription factor (TF) Traffic Jam (TJ). Thanks to an intersectional genetics approach and a TJ-Flp line generated during my PhD, I showed for the first time that TJ+ neurons subpopulations have distinct functions in Drosophila larva locomotion. Functional subdivision of TJ+ population eventually led to the identification of 3 TJ+ per+ GABAergic neurons that regulate the speed of locomotion. Thorough molecular characterization of this population permitted to identify them as mnb progeny neurons, a well studied subgroup of midline cells whose function had never been described before. The TF combinatorial code expressed by these cells is highly reminiscent of the one found in V2b INs, a population in vertebrates thought to regulate the speed of locomotion as well in vertebrates; this opens the possibility of a functional conservation across evolution. Preliminary results furthermore suggest that TJ+ INs would have functional roles in the adult fly.

Le syndrome de Down (SD), ou Trisomie 21, est l’aneuploïdie la plus fréquente chez l’humain. Le désordre génomique est tel qu’aucun traitement unique ne peut pallier à tous les symptômes (retard mental, troubles moteurs...). C’est pourquoi l’utilisation de modèles murins permet d’étudier l’impact de régions partielles du Hsa21 dans l’apparition des déficits. Mon projet de thèse s’est orienté sur un locus télomérique encadré par les gènes Abcg1 et U2af1. Mes recherches se sont focalisées sur deux modèles, Ts1Yah et Ms2Yah, dédiés à cette région. L’étude de ces lignées, combinées à d’autres modèles transgéniques, a montré la contribution de l’intervalle génique dans l’optimisation de l’apprentissage locomoteur. Dans un deuxième temps, le gène Cbs, candidat à la perte de fonction de mémoire, a permis de mettre en évidence un sauvetage fonctionnel dans une expérience à effets de doses. Cette découverte ouvre la voie à de nouvelles perspectives thérapeutiques. / The Down syndrome (DS), or Trisomy21, is the most frequent aneuploidy in human. The genomic disorder is such an extent that any single cure could overcome all the symptoms (mental retardation, motor defects…). That’s why mouse models’ using allows studies on Hsa21 regions impact in deficits apparition. My PhD project was turned toward the telomeric locus of the Hsa21 framed between Abcg1 and U2af1. We focused our research on two models, Ts1Yah and Ms2Yah, dedicated to this region. The study of those lines, combined with several other transgenic ones, showed the contribution of the interval into the optimisation of motor learning. In a second step, the Cbs gene, candidate on memory loss of function, has highlighted a functional rescue in dose-effect experiment. This discovery paves the way to new therapeutic perspectives.

Dois modelos mecânicos, o pêndulo-invertido e o massa-mola, explicam como os mecanismos pendular e elástico minimizam o dispêndio energético advindo dos músculos durante caminhada e corrida humana. A presente tese testa dois efeitos que, para nosso conhecimento, todavia não possuem respostas conclusivas da literatura, nomeadamente o processo de envelhecimento na mecânica da corrida humana e o efeito da inclinação do terreno na velocidade ótima da caminhada. Para estudar o primeiro efeito, as forças de reação do solo provenientes de uma plataforma de força (4m x 0,50m), foram usadas para a posterior comparação de: i) trabalho mecânico, ii) parâmetros do sistema massa-mola e, iii) assimetrias contatodespregue entre jovens e idosos. Os idosos produzem menos força durante a fase de trabalho mecânico positivo com uma menor oscilação vertical total e oscilação durante a fase aérea. Conseqüentemente a capacidade de armazenar e re-utilizar energia elástica dos tendões é prejudicada contribuindo para o maior dispêndio energético neste grupo quando comparado com jovens.Para o modelo do custo eletromiográfico (EMG) da caminhada humana criou-se duas abordagens: experimental e teórica. Em ambas as abordagens, informações da atividade EMG de dezesseis músculos, sendo 8 posturais e 8 propulsores foram coletadas e analisadas a partir da integral EMG. A abordagem teórica parece ter uma melhor relação com as evidências experimentais sobre a energética da caminhada humana em inclinações. Os principais mecanismos envolvidos na nova hipótese são i) músculos posturais que não realizam trabalho muscular, exercem uma função importante na determinação do dispêndio energético total e ii) a presente hipótese leva em consideração a co-contração de músculos antagonistas no dispêndioenergético total. Mais experimentos são necessários para confirmar o modelo apresentado neste estudo. Além disso, através de estratégias de otimização e predição linear, um modelo teórico foi delineado a fim de determinar parâmetros mecânicos (comprimento de passada e velocidade de progressão) e energéticos da locomoção terrestre em situações onde as informações disponíveis são apenas a massa e uma curva força de reação vertical versus tempo. Os resultados advindos do modelamento correspondem aos parâmetros determinados experimentalmente. Laboratórios que detenham apenas uma plataforma de força, ou nas áreas onde as informações de entrada do atual modelo sejam as únicas informações (e.g. paleontologia, biomecânica forênsica, etc), a predição de variáveis primárias da locomoção podem ser preditas com razoável acurácia. / Two mechanical models, the inverted pendulum and spring-mass, explain how do the pendular and elastic mechanisms minimizing energy expenditure from muscles during human walking and running. Here, we test two effects that, to our knowledge, do not have yet conclusive responses from literature, specifically the ageing effects on mechanics of human running, and the effect of gradient on walking optimal speed. In order to check the former effect, the ground reaction forces came from a force platform (4m x 0.5m) were used for a later comparison: i) mechanical work, ii) spring-mass parameters and, iii) landing-takeoff asymmetries. The old subjects produce less force during positive work resulting in a smaller overall and aerial vertical oscillation of the centre of mass. Consequently, the potential for restore elastic energy from tendons is reduced contributing to greater energy expenditure than in young subjects. In relation to Electromyographical (EMG) Cost of human walking we created two approaches: experimental and theoretical. In both approaches, information from EMG activity of sixteen muscles, eight postural and eight propulsor were collected and analysed. The theoretical approach seems to fit better with the energy expenditure during gradient walking. The main mechanisms involved in this new hypothesis are i) postural muscles that do not perform muscular work, play an important role in the total energy expenditure and ii) the present hypothesis take the co-contraction into account of the antagonist muscles in the total energy expenditure. Further experiments are necessary to confirm this hypothesis. Besides, using optimization and linear prediction procedures, a theoretical model was designed to estimate mechanical parameters (stride length and velocity of progression) and energetic variables of terrestrial locomotion when available information consists only of mass and one vertical ground reaction force versus time.The results from this modelling are similar to experimentally obtained data. Laboratories with just one force platform, or in areas where the present model’s input information be the unique accessible data (e.g. palaeontology, forensic biomechanics, etc) the prime variables of locomotion may be estimated with reasonable accuracy.

In aspiration to achieve naturalistic character animation, some difficulty does show up, both in 3D-CGI, 2D-CGI as in traditional handmade animation. The reason why difficulty appears in the task of achieving naturalism is for instance because of the simulated natural laws in the digital world which cannot affect the characters cinematic movement. The result of illustrating the natural law manually by hand can affect the illusion of the movement as not naturalistic or inconsistent, which can result in that the spatial adaptation to space is not perceived as naturalistic. It is most often up to the animator to make a believable illusion of the natural laws. This study examines a deeper understanding of the human way to behave and to adapt to the physical reality and through that, apply this movement on character animation. The purpose of a deeper understanding of movement's phenomena is to find a clearer method dedicated to naturalistic movement that can be adapted to all forms of character animation, regardless of the character anatomy. Unfortunately, it would not be possible to study all aspects of the physically adaptive behaviors as to the size of the topic. This study will therefore orbit the human locomotion, also known as walking. Focus will therefore be on the bottom part of the body, from the pelvis down to the ankles. There are scientists that do argue about a connection between the golden ratio and the human locomotion. This study is an attempt to apply the golden ratio on 3D-characters. This study has been devoted to a different approach in the character animation, where its starting point will be mathematical equations. For this study, it has meant an application of the golden section in a temporary form, that is in motion. The result is therefore a mathematically based method dedicated to imitating naturalistic movement in terms of time, that is to say human locomotion. The method has been proved to be useful even in the imitation of characters movements that do not possess human proportions. / I en strävan efter naturalistisk karaktäranimation uppstår vissa hinder på vägen i 3D-CGI som 2D-CGI animation. Svårigheter i att uppnå naturalism beror bland annat på att det inte finns några simulerade naturlagar i den digitala världen som kan påverka karaktärens kinematiska rörelser. Resultatet av att behöva illustrera naturlagar och liknande externa påverkningar manuellt för hand kan orsaka en rumslig känsla om onaturlighet eller inkonsekvens. Vilket kan resultera i att den rumsliga anpassningen till rummet inte upplevs som naturalistisk. Ofta är det upp till animatören att skapa en trovärdig illusion om naturlagarna. Målet med denna studie är att utforska och ge animatören en djupare förståelse för människans sätt att förhålla och anpassa sig till den fysiska verkligheten. Syftet med en djupare förståelse för rörelsers företeelser är att finna en tydligare metod dedikerad åt naturalistisk rörelse som går att anpassa för alla former av karaktärsanimation, oberoende av karaktärens anatomi. Tyvärr skulle det inte vara möjligt att täcka alla aspekter av det fysiskt adaptiva beteendet på grund av ämnets storlek. Denna studie har därför avgränsats till mänsklig lokomotion, även känt som vandring. Fokus riktas därför mot bäckenet och knäleden ner till anklarna. Det finns forskning som argumenterar för en koppling mellan det gyllene snittet och mänskliga rörelser. Denna studie är ett försök att tillämpa lokomotion uträknat ifrån gyllene snittet på en digital tredimensionell karaktär. Denna studie har ägnats ett annorlunda angreppsätt i karaktärsanimationen där dess utgångspunkt består av matematiska ekvationer. Det har för studien inneburit ett applicerande av gyllene snittet i en temporär form, det vill säga i rörelse. Resultatet är därför en matematiskt baserad metod dedikerad för att efterlikna naturalistisk rörelse i form av gång, alltså mänsklig lokomotion. Metoden har visat sig användbar även vid efterliknandet av karaktärers rörelser som inte besitter mänskliga proportioner.

Dois modelos mecânicos, o pêndulo-invertido e o massa-mola, explicam como os mecanismos pendular e elástico minimizam o dispêndio energético advindo dos músculos durante caminhada e corrida humana. A presente tese testa dois efeitos que, para nosso conhecimento, todavia não possuem respostas conclusivas da literatura, nomeadamente o processo de envelhecimento na mecânica da corrida humana e o efeito da inclinação do terreno na velocidade ótima da caminhada. Para estudar o primeiro efeito, as forças de reação do solo provenientes de uma plataforma de força (4m x 0,50m), foram usadas para a posterior comparação de: i) trabalho mecânico, ii) parâmetros do sistema massa-mola e, iii) assimetrias contatodespregue entre jovens e idosos. Os idosos produzem menos força durante a fase de trabalho mecânico positivo com uma menor oscilação vertical total e oscilação durante a fase aérea. Conseqüentemente a capacidade de armazenar e re-utilizar energia elástica dos tendões é prejudicada contribuindo para o maior dispêndio energético neste grupo quando comparado com jovens.Para o modelo do custo eletromiográfico (EMG) da caminhada humana criou-se duas abordagens: experimental e teórica. Em ambas as abordagens, informações da atividade EMG de dezesseis músculos, sendo 8 posturais e 8 propulsores foram coletadas e analisadas a partir da integral EMG. A abordagem teórica parece ter uma melhor relação com as evidências experimentais sobre a energética da caminhada humana em inclinações. Os principais mecanismos envolvidos na nova hipótese são i) músculos posturais que não realizam trabalho muscular, exercem uma função importante na determinação do dispêndio energético total e ii) a presente hipótese leva em consideração a co-contração de músculos antagonistas no dispêndioenergético total. Mais experimentos são necessários para confirmar o modelo apresentado neste estudo. Além disso, através de estratégias de otimização e predição linear, um modelo teórico foi delineado a fim de determinar parâmetros mecânicos (comprimento de passada e velocidade de progressão) e energéticos da locomoção terrestre em situações onde as informações disponíveis são apenas a massa e uma curva força de reação vertical versus tempo. Os resultados advindos do modelamento correspondem aos parâmetros determinados experimentalmente. Laboratórios que detenham apenas uma plataforma de força, ou nas áreas onde as informações de entrada do atual modelo sejam as únicas informações (e.g. paleontologia, biomecânica forênsica, etc), a predição de variáveis primárias da locomoção podem ser preditas com razoável acurácia. / Two mechanical models, the inverted pendulum and spring-mass, explain how do the pendular and elastic mechanisms minimizing energy expenditure from muscles during human walking and running. Here, we test two effects that, to our knowledge, do not have yet conclusive responses from literature, specifically the ageing effects on mechanics of human running, and the effect of gradient on walking optimal speed. In order to check the former effect, the ground reaction forces came from a force platform (4m x 0.5m) were used for a later comparison: i) mechanical work, ii) spring-mass parameters and, iii) landing-takeoff asymmetries. The old subjects produce less force during positive work resulting in a smaller overall and aerial vertical oscillation of the centre of mass. Consequently, the potential for restore elastic energy from tendons is reduced contributing to greater energy expenditure than in young subjects. In relation to Electromyographical (EMG) Cost of human walking we created two approaches: experimental and theoretical. In both approaches, information from EMG activity of sixteen muscles, eight postural and eight propulsor were collected and analysed. The theoretical approach seems to fit better with the energy expenditure during gradient walking. The main mechanisms involved in this new hypothesis are i) postural muscles that do not perform muscular work, play an important role in the total energy expenditure and ii) the present hypothesis take the co-contraction into account of the antagonist muscles in the total energy expenditure. Further experiments are necessary to confirm this hypothesis. Besides, using optimization and linear prediction procedures, a theoretical model was designed to estimate mechanical parameters (stride length and velocity of progression) and energetic variables of terrestrial locomotion when available information consists only of mass and one vertical ground reaction force versus time.The results from this modelling are similar to experimentally obtained data. Laboratories with just one force platform, or in areas where the present model’s input information be the unique accessible data (e.g. palaeontology, forensic biomechanics, etc) the prime variables of locomotion may be estimated with reasonable accuracy.

Les créatures à n-pattes, comme les quadrupèdes, les arachnides ou les reptiles, sont une partie essentielle de n’importe quelle simulation et ils participent à rendre les mondes virtuels plus crédibles et réalistes. Ces créatures à n-pattes doivent être capables de se déplacer librement vers les points d’intérêt de façon réaliste, afin d’offrir une meilleure expérience immersive aux utilisateurs. Ces animations de locomotion sont complexes en raison d’une grande variété de morphologies et de modes de déplacement. Il convient d’ajouter à cette problématique la complexité des environnements où ils naviguent. Un autre défi lors de la modélisation de tels mouvements vient de la difficulté à obtenir des données sources. Dans cette thèse nous présentons un système capable de générer de manière procédurale des animations de locomotion pour des dizaines de créatures à n-pattes, en temps réel, sans aucune donnée de mouvement préexistante. Notre système est générique et contrôlable. Il est capable d’animer des morphologies différentes, tout en adaptant les animations générées à un environnement dynamique complexe, en temps réel, ce qui donne une grande liberté de déplacement aux créatures à n-pattes simulées. De plus, notre système permet à l’utilisateur de contrôler totalement l’animation produite et donc le style de locomotion / Multi-legged characters like quadrupeds, arachnids, reptiles, etc. are an essential part of any simulation and they greatly participate in making virtual worlds more life-like. These multi-legged characters should be capable of moving freely and in a believable way in order to convey a better immersive experience for the users. But these locomotion animations are quite rich due to the complexity of the navigated environments and the variety of the animated morphologies, gaits, body sizes and proportions, etc. Another challenge when modeling such animations arises from the lack of motion data inherent to either the difficulty to obtain them or the impossibility to capture them.This thesis addresses these challenges by presenting a system capable of procedurally generating locomotion animations fordozens of multi-legged characters in real-time and without anymotion data. Our system is quite generic thanks to the chosen Procedural-Based techniques and it is capable of animating different multi-legged morphologies. On top of that, the simulated characters have more freedom while moving, as we adapt the generated animations to the dynamic complex environments in real-time. Themain focus is plausible movements that are, at the same time,believable and fully controllable. This controllability is one of the forces of our system as it gives the user the possibility to control all aspects of the generated animation thus producing the needed style of locomotion

Dois modelos mecânicos, o pêndulo-invertido e o massa-mola, explicam como os mecanismos pendular e elástico minimizam o dispêndio energético advindo dos músculos durante caminhada e corrida humana. A presente tese testa dois efeitos que, para nosso conhecimento, todavia não possuem respostas conclusivas da literatura, nomeadamente o processo de envelhecimento na mecânica da corrida humana e o efeito da inclinação do terreno na velocidade ótima da caminhada. Para estudar o primeiro efeito, as forças de reação do solo provenientes de uma plataforma de força (4m x 0,50m), foram usadas para a posterior comparação de: i) trabalho mecânico, ii) parâmetros do sistema massa-mola e, iii) assimetrias contatodespregue entre jovens e idosos. Os idosos produzem menos força durante a fase de trabalho mecânico positivo com uma menor oscilação vertical total e oscilação durante a fase aérea. Conseqüentemente a capacidade de armazenar e re-utilizar energia elástica dos tendões é prejudicada contribuindo para o maior dispêndio energético neste grupo quando comparado com jovens.Para o modelo do custo eletromiográfico (EMG) da caminhada humana criou-se duas abordagens: experimental e teórica. Em ambas as abordagens, informações da atividade EMG de dezesseis músculos, sendo 8 posturais e 8 propulsores foram coletadas e analisadas a partir da integral EMG. A abordagem teórica parece ter uma melhor relação com as evidências experimentais sobre a energética da caminhada humana em inclinações. Os principais mecanismos envolvidos na nova hipótese são i) músculos posturais que não realizam trabalho muscular, exercem uma função importante na determinação do dispêndio energético total e ii) a presente hipótese leva em consideração a co-contração de músculos antagonistas no dispêndioenergético total. Mais experimentos são necessários para confirmar o modelo apresentado neste estudo. Além disso, através de estratégias de otimização e predição linear, um modelo teórico foi delineado a fim de determinar parâmetros mecânicos (comprimento de passada e velocidade de progressão) e energéticos da locomoção terrestre em situações onde as informações disponíveis são apenas a massa e uma curva força de reação vertical versus tempo. Os resultados advindos do modelamento correspondem aos parâmetros determinados experimentalmente. Laboratórios que detenham apenas uma plataforma de força, ou nas áreas onde as informações de entrada do atual modelo sejam as únicas informações (e.g. paleontologia, biomecânica forênsica, etc), a predição de variáveis primárias da locomoção podem ser preditas com razoável acurácia. / Two mechanical models, the inverted pendulum and spring-mass, explain how do the pendular and elastic mechanisms minimizing energy expenditure from muscles during human walking and running. Here, we test two effects that, to our knowledge, do not have yet conclusive responses from literature, specifically the ageing effects on mechanics of human running, and the effect of gradient on walking optimal speed. In order to check the former effect, the ground reaction forces came from a force platform (4m x 0.5m) were used for a later comparison: i) mechanical work, ii) spring-mass parameters and, iii) landing-takeoff asymmetries. The old subjects produce less force during positive work resulting in a smaller overall and aerial vertical oscillation of the centre of mass. Consequently, the potential for restore elastic energy from tendons is reduced contributing to greater energy expenditure than in young subjects. In relation to Electromyographical (EMG) Cost of human walking we created two approaches: experimental and theoretical. In both approaches, information from EMG activity of sixteen muscles, eight postural and eight propulsor were collected and analysed. The theoretical approach seems to fit better with the energy expenditure during gradient walking. The main mechanisms involved in this new hypothesis are i) postural muscles that do not perform muscular work, play an important role in the total energy expenditure and ii) the present hypothesis take the co-contraction into account of the antagonist muscles in the total energy expenditure. Further experiments are necessary to confirm this hypothesis. Besides, using optimization and linear prediction procedures, a theoretical model was designed to estimate mechanical parameters (stride length and velocity of progression) and energetic variables of terrestrial locomotion when available information consists only of mass and one vertical ground reaction force versus time.The results from this modelling are similar to experimentally obtained data. Laboratories with just one force platform, or in areas where the present model’s input information be the unique accessible data (e.g. palaeontology, forensic biomechanics, etc) the prime variables of locomotion may be estimated with reasonable accuracy.

Au cours de la métamorphose, les amphibiens subissent une réorganisation complète de leur anatomie et de leur physiologie. Chez Xenopus laevis le système locomoteur est un des plus affecté au cours de cette phase développementale, l’animal passant d’une nage ondulatoire à une nage appendiculaire. Cette transformation du mode locomoteur implique une réorganisation du réseau locomoteur central. Dans une première étude, nous avons mis en évidence que les muscles axiaux s’activent de manière bilatéralement alternée chez le têtard alors que les muscles équivalents chez l’adulte s’activent de manière synchrone au cours de la nage. Nous avons montré que ce nouveau patron d’activation musculaire, accompagné d’une synchronisation avec les muscles appendiculaires extenseurs, reposent principalement sur la mise en place de nouvelles projections propriospinales lombo-thoraciques. Ces résultats suggèrent l’existence d’un contrôle postural proactif au cours de la locomotion, reposant directement sur le CPG des membres postérieurs. Dans une deuxième étude, nous nous sommes intéressés à l’influence d’un déséquilibre des afférences vestibulaires sur le développement du réseau locomoteur spinal au cours de la métamorphose. Pour cela nous avons réalisé une suppression unilatérale des organes vestibulaires avant ou après la métamorphose. Dans les deux cas, cette lésion aigue génère d’importants troubles locomoteurs et posturaux. Nous avons montré que la lésion chronique au cours de la métamorphose entraîne une modification ipsi-lésionnelle du développement du réseau locomoteur lombo-thoracique, de manière concomitante à une compensation comportementale. De façon intéressante, cette plasticité développementale ainsi que la compensation des troubles locomoteurs sont absentes chez les animaux lésés au stade adulte. Ces résultats suggèrent que les informations sensorielles sont un facteur déterminant pour le développement du réseau locomoteur spinal. Enfin, dans une troisième étude, nous avons analysé le développement du réseau locomoteur supra-spinal et en particulier les propriétés de déclenchement et de contrôle de la région locomotrice mésencéphalique (MLR). Nous avons mis en évidence l’existence fonctionnelle des deux noyaux de cette structure, le noyau pédonculopontin (PPN) et le noyau latérodorsal du tegmentum (LDT) tout au long de la métamorphose du xénope, ainsi qu’une fréquence d’activation optimale de 10-20 Hz pour le PPN. / Throughout the course of metamorphosis, amphibians undergo a complete anatomical and physiological reorganization. In Xenopus laevis, the locomotor system is one of the most affected during this developmental phase where the animal passes from undulatory swimming to limb-based propulsion. This transformation implies a parallel reorganization of the central locomotor network. In an initial study we showed that axial muscles which are activated in bilateral alternation in tadpoles mature to dorsal muscles that are synchronously active during adult locomotion. We found that this new pattern, accompanied by coordination of dorsal and hindlimb muscle activities, is principally sustained by the development of new propriospinal lumbo-thoracic projections, suggesting proactive postural control coming from the hindlimb CPG during ongoing locomotion. In a second study, we examined the influence of disequilibrium in vestibular inputs on the metamorphic development of the spinal locomotor network. To induce this sensory asymmetry we performed unilateral removal of vestibular end organs either before or after metamorphosis. Acutely, in both cases, the lesion induced dramatic postural and locomotor changes. Chronically, the lesion altered the metamorphic development of the lumbo-thoracic network on the lesioned side, concomitantly with compensation for locomotor defects. Interestingly, animals lesioned after metamorphosis neither compensated nor expressed this developmental spinal plasticity. Altogether, these results suggest that descending sensory inputs are crucial cues for the development of the spinal locomotor network. Finally, we studied the metamorphic development of the supra-spinal network, focusing our attention on the locomotor triggering and control properties of the mesencephalic locomotor region (MLR). We showed that both subparts of this structure, the laterodorsal tegmentum (LDT) and the pedunculopontine (PPN) nuclei, are present and functional during the entire period of metamorphosis and that the PPN has an optimal activation frequency of 10-20 Hz.

L’organisation biologique, du niveau moléculaire jusqu’au niveau des performances de l’organisme. La locomotion est une fonction neurophysiologique hautement intégrée illustrant un tel processus multi-échelle. Le déclin des performances de locomotion avec l’âge, comme la vitesse maximale, a été observé pour de nombreuses espèces, aussi bien en captivité qu’en milieu naturel. Cependant, ces descriptions restent souvent succinctes, sans précision sur la progression de ces performances au cours du vieillissement. Dans ces travaux, nous utilisons une équation bi-phasique pour décrire la relation entre performance de locomotion et âge sur l’ensemble de la durée de la vie pour Caenorhabditis elegans, Mus domesticus, Canis familiaris, Equus caballus et Homo sapiens. Les performances maximales de locomotion se révèlent être des bio-marqueurs robustes pour suivre la progression des performances sur l’ensemble de la durée de vie des animaux, permettant ainsi d’estimer le pic physiologique et le début du déclin des performances. De plus, dans tous les cas, nous remarquons que la forme de progression des performances maximales selon l’âge est similaire et conservée d’une espèce à l’autre ; seule varie la pente dans le temps, dépendant de l’espèce et la performance mesurée. L’observation des performances selon le genre ne montre pas de différence dans la forme de l’enveloppe. Néanmoins, elle révèle des écarts variables dans les performances maximales entre femelles et mâles selon les espèces. Enfin, les conditions thermiques affectent les performances maximales de locomotion, mais la forme de l’enveloppe reste aussi préservée. Nous avons ensuite étudié le développement et l’expansion de cette dynamique au cours du siècle dernier pour les performances athlétiques maximales d’Homo sapiens. Cette étude révèle que la forme s’est progressivement précisée au cours du temps en s’étendant à tous les âges et suivant homothétiquement la progression des records du monde. Néanmoins, la progression semble ralentir au cours des dernières décennies, laissant présager l’atteinte possible des limites biologiques d’Homo sapiens. Ces travaux offrent de nouvelles perspectives sur l’utilité des approches comparatives et l’utilisation d’un bio-marqueur comme les performances de locomotion pour suivre les dynamiques sur l’ensemble de la durée de vie à différentes échelles. Elles apportent aussi un regard novateur sur la progression des performances avec l’âge, en intégrant à la fois les processus de développement et de vieillissement, permettant ainsi de préciser les pics physiologiques et la forme des progressions des performances sur toute la durée de la vie. / Aging is a complex, multi-scale process that affects all levels of biological organization from molecular structure to individual behavior. Locomotion is a highly integrated neurophysiological function that illustrates this process. The functional decline in locomotion with age has been described in a wide-range of species, both domestic and wild, and appears as a common aspect of senescence among animals. However, in most cases these descriptions remain incomplete and the dynamics of age-related changes are poorly understood. Here, we use a conceptual feature to describe age-related changes in locomotor performances for Caenorhabditis elegans, Mus domesticus, Canis familiaris, Equus caballus and Homo sapiens. We show that measurements of locomotor performance are consistent biomarkers of age-related changes, with a well preserved pattern regardless of the type of effort or duration. We also show that age-related pattern for locomotor performance are modulated by gender and environment. Nevertheless, in every case, the pattern remains similar and very well preserved. The second part of this work introduces the concept of phenotypic expansion and focuses on the expansion of the age-related pattern for Homo sapiens during the last century. Since the first edition of modern Olympic Games in 1896, athletes have consistently improved previous records, echoing scientific and industrial progress. Their data constitute privileged and accurate biomarkers, as sport performances reflect highly integrated neuro-physiological traits based on complex multifactorial interactions. Following the progression of the world records, the age-related pattern expanded gradually during the 20th century. However, the last decades show a slow-down in the expansion, following again the recent asymptotic levelling off of world records, which no longer supports the historical motto “Citius, Altius, Fortius”. This work provides new insights about the utility of an age-based comparative approach to provide a thorough understanding of aging processes and also for gaining insights into aging at different levels of biological organization and in an evolutionary perspective.