A neuron’s function depends critically on the shape, size, and territory of its dendritic field. We have only recently begun to understand how diverse dendritic arbors are built and how the morphology and territory of these arbors support diverse neural functions. In this thesis, I use the Drosophila larval peripheral nervous system (PNS) as a model for studying these questions, as these neurons are very amenable to genetic manipulation and in vivo imaging. First, I examined the relationship between dendritic fields and sensory activity in the proprioceptive neurons of the body wall. In collaboration with Elizabeth Hillman’s lab, we used a high-speed volumetric microscopy technique, Swept Confocally Aligned Planar Excitation (SCAPE) microscopy, to simultaneously image the dendrite deformation dynamics and sensory activity of body wall neurons in crawling Drosophila larvae. We imaged a set of proprioceptive neurons with diverse dendrite morphologies and territories, revealing that each neuron subtype responds in sequence during crawling. These activities could conceivably provide a continuum of position encoding during locomotion. Activity timing is related to the dynamics of each neuron’s dendritic arbors, suggesting arbor shape and targeting endow each proprioceptor with a specific role in monitoring body wall deformation. Furthermore, our results provide new insights into the body-wide activity dynamics of the proprioceptive system, which will inform models of sensory feedback during locomotion. To investigate how dendritic arbors are built to support sensory function, I focused on proprioceptive (class I) and touch-sensing (class II-III) dendritic arborization (da) neurons. Proprioceptive and touch-sensing dendrite territories tend to target non-overlapping, neighboring, areas of the body wall. How is territory coverage specified during development, and how does this coverage support a specific sensory function? Ablation studies indicate that repulsive interactions between heterotypic dendrites are not required for territory patterning. Instead, dendrite boundaries correlate with Anterior (A)-Posterior (P) compartment boundaries in the underlying epidermal substrate: proprioceptive class I dendrites target the P compartment, while touch-sensing dendrites tend to avoid that region. I found that genetic expansion of the P compartment leads to expansion of class I proprioceptive dendrites, suggesting compartmentalized epidermal cues instruct dendrite targeting. Furthermore, SCAPE imaging revealed that the P compartment coincides with a major body wall fold that occurs during crawling. These results support a model in which dendrite targeting by compartment cues reliably tunes neurons for predictable stimuli on the body wall: proprioceptive dendrites target areas that bend predictably during crawling, while touch-sensing dendrites could be avoiding those areas to be tuned for external mechanosensory stimuli. To investigate the molecular identity of the substrate cues guiding the compartmental organization of dendrites, I tested candidate cues and sought new potential cues. I first tested cues that are known to be expressed in a compartmental fashion (Hedgehog and EGFR pathways). Interestingly, the overall dendrite territory footprint of class I proprioceptive cells is unaffected by known compartment cues. To reveal new candidates, I performed cell sorting and RNA sequencing. I identified 290 cell surface and secreted molecules with differential expression in the A and P compartments. I provide initial findings from a knockdown and misexpression screen testing the role of these candidates for class I and class III territory patterning. Taken together, these results provide new insights into how dendritic fields are patterned to support proper neural function.

The purpose of this study is to determine the effect of short-time cold pack cryotherapy in thermoreceptors, therefore, proprioception via deep sensation receptors and sense of balance on ankle joint in healthy adults. In the subject, I refer to other studies using the word proprioception when measuring the cold effect in the balance of the ankle joint. Mainly, cold therapy is affecting to the thermoreceptors but there might be input also to change neuromuscular transmission. The aim of the experimental process is to identify if the cold application on the ankle joint for 20 minutes is decreasing dynamic postural stability and the sense of balance in laboratory environment. Short term cryotherapy effect is measured within 12 participants divided into two groups: control and study group. Both groups went through the first measurement, 20 minutes rest with or without cold application and second measurement directly after the rest period. The dynamic posturography machine SMART Balance Master System (NeuroCom) was used to evaluate somatosensory outcome in the experiment. In the systematic review the previous studies are investigated within same settings as on experimental process, short time cold application on ankle joint measuring the effect on ankle proprioception and joint position sense. The...

Shoulder injuries may be associated with proprioceptive deficits, however, it is unknown whether these changes are due to the experience of pain, tissue damage, or a combination of these. The aim of this study was to investigate the effect of experimentally-induced sub-acromial pain on proprioceptive variables. Sub-acromial pain was induced via hypertonic saline injection in 20 healthy participants. Passive joint replication (PJR) and threshold to detection of movement direction (TTDMD) were assessed with a Biodex System 3 Pro isokinetic dynamometer for baseline control, experimental pain and recovery control conditions with a starting position of 60° shoulder abduction. The target angle for PJR was 60° external rotation, starting from 40°. TTDMD was tested from a position of 20° external rotation. Repeated measures ANOVAs were used to determine differences between PJR absolute and variable errors and TTDMD for the control and experimental conditions. Pain was elicited with a median 7 on the Numeric Pain Rating Scale. TTDMD was significantly decreased for the experimental pain condition compared to baseline and recovery conditions (≈30%, P=0.003). No significant differences were found for absolute (P=0.152) and variable (P=0.514) error for PJR. Movement sense was enhanced for the experimental sub-acromial pain condition, which may reflect protective effects of the central nervous system in response to the pain. Where decreased passive proprioception is observed in shoulders with injuries, these may be due to a combination of peripheral tissue injury and neural adaptations that differ from those due to acute pain.

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Le contenu de cette thèse traite: 1) des différences entre les jeunes adultes et les aînés au niveau des caractéristiques de l'exécution du premier pas de marche, 2) de l'intégration des informations sensorielles à l'amorce de la marche, notamment, de la modification des informations prorioceptives et vestibulaires sur les caractéristiques de l'amorce de la marche. Les études présentées ici ont pour objectif de : Déterminer les caractéristiques du patron d'amorce de marche chez les jeunes adultes, les aînés et chez les aînés chuteurs. Pour cela, les caractéristiques spatiales et temporelles, notamment la variabilité du premier pas et la durée des phases de double support sont mises en évidence pour les trois groupes. La variabilité du premier pas pourrait être un facteur prédictif du risque de chute. Déterminer les modalités sensorielles affectant l'amorce du patron de marche chez les jeunes adultes et chez les aînés: Les effets d'une perturbation proprioceptive sur la variabilité du premier pas de marche et sur les déplacements du centre / de masse et du centre de pression chez les jeunes adultes et chez les aînés. Déterminer l'effet combiné d'une perturbation proprioceptive et vestibulaire sur l'amorce de la marche. Les résultats de ces études montrent que l'exécution du premier pas de marche est déterminée par la qualité des informations sensorielles. La variabilité du premier pas de marche permet de discriminer les chuteurs des non chuteurs. La position du corps dans l'espace, déterminée par les afférences proprioceptives et vestibulaires modifie la phase anticipée et la phase d'exécution à l'amorce de lamarche.

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L'objectif de ce travail de thèse était d'étudier les effets de l'hyperthermie sur la proprioception et leurs répercussions sur la cinématique de la course à pied. Nous avons élaboré un protocole expérimental composé de deux études pour répondre à cette question. La première expérimentation a exploré l'hyperthermie induite en mode passif et son effet sur la proprioception. Notre hypothèse était que les perturbations neuromusculaires induites par une hyperthermie passive générale pourraient affecter la proprioception et l'équilibre. 14 participants ont réalisé une série de tests de la fonction neuromusculaire ainsi que des tests de proprioception et d'équilibre statique et dynamique dans une chambre environnementale en conditions chaude (44°C-50°C) et contrôle (24°C). Les résultats de cette 1ère étude ont montré qu'une augmentation de la température rectale (39.0°C vs. 36.9°C) et cutanée (37.9°C vs. 32°C) en ambiance chaude par rapport à la situation de contrôle était associée à une réduction de l'amplitude du reflexe H, une diminution de l'acuité proprioceptive et des perturbations de l'équilibre statique et dynamique. Ces résultats suggèrent que l'hyperthermie passive détériore la proprioception et l'équilibre, ce qui pourrait affecter le geste sportif. Afin d'explorer les effets de l'hyperthermie active sur la proprioception, nous avons par la suite réalisé le test de proprioception active chez 12 coureurs entrainés avant et après un test de 30 minutes en course à pied dans des conditions chaude (39°C) et contrôle (22°C). Les résultats de cette étude ont montré une augmentation plus importante des contraintes thermiques, perceptives et cardiovasculaires en ambiance chaude comparé à la condition tempérée. En plus, nous avons observé une diminution de l'acuité proprioceptive suite à l'exercice en ambiance chaude mais pas tempérée. Ces résultats montrent que les altérations identifiées en situation d'hyperthermie passive lors de la première étude sont également spécifiques à un exercice en ambiance chaude. Lors de ce protocole expérimental, nous avons également exploré les répercussions de ces perturbations de la proprioception sur la cinématique de la course à pied. Pour ce faire, les paramètres spatio-temporels et cinématiques angulaires de la foulée ont été mesurés à vitesse constante (i.e., 70% de la vitesse maximale aérobie) lors de la première et dernière minute de l'exercice (la vitesse étant librement choisie de la 2ème à la 29ème minute). Nous avons ainsi montré une diminution de la fréquence et une augmentation de la longueur des foulées avec la fatigue dans les deux conditions ; accompagnée de changement des paramètres angulaires limités à un redressement du bassin et une diminution de l'angle de la cheville. Cependant, Il n'y avait aucun effet de la condition thermique ou d'interaction entre la fatigue et l'environnement thermique pour les paramètres spatio-temporels et cinématiques angulaires. Ces résultats suggèrent que l'hyperthermie induite par un exercice de course à pied affecte la proprioception de la cheville, mais que cette altération n'affecte pas la cinématique de la course à pied. Suite à ces travaux, nous pouvons donc conclure que la proprioception est affectée par l'hyperthermie induite soit par des méthodes passives ou actives. Ces altérations pourraient provenir des effets de l'hyperthermie sur les fonctions neuromusculaire et cognitive. Cependant, la dégradation de l'acuité proprioceptive avec une augmentation de la température rectale au-delà de 39°C n'affecte pas la cinématique de la course à pied, ce qui suggère une forte stabilité du pattern de course malgré une proprioception et des fonctions neuromusculaires affectées / The objective of this PhD was to investigate the effects of hyperthermia on proprioception and their impact on running gait kinematics. We developed an experimental protocol consisting of two studies to answer this question.The first experiment explored passive hyperthermia and its effects on proprioception and balance. We hypothesized that neuromuscular disturbances induced by passive hyperthermia would impair proprioception and balance. 14 participants performed a series of tests of neuromuscular function, proprioception, as well as static and dynamic balance in an environmental chamber under hot (44°C - 50°C) and control (24°C) conditions. The results of this first study showed that an increase in rectal (39.0°C vs. 36.9°C) and skin (37.9°C vs. 32°C) temperatures in hot compared to control ambient conditions was associated with a reduction in the amplitude of the Hoffman reflex, a decrease in the proprioceptive acuity and impairments in static and dynamic balance. These results suggest that passive hyperthermia deteriorates proprioception and balance, something that could potentially affect sports movement. ln order to explore the effects of active hyperthermia on proprioception, we subsequently performed the active discrimination test in 12 trained runners before and just after a 30-minute running time-trials under hot (39°C) and control (22°C) conditions. The results of this study showed a larger increase in thermal, perceptual and cardiovascular stresses when running in the heat as compared to running in a temperate environment. ln addition, we observed a decrease in proprioceptive acuity following exercising in the heat only. This showed that the proprioceptive impairments identified during the first study are also present following exercise-induced hyperthermia, but not exercise-induced fatigue without hyperthermia. During this study, we have also explored the impact of hyperthermia-induced alterations in proprioception on running gait kinematics. To do so, we measured angular kinematics and spatiotemporal stride parameters at a constant speed (i.e., 70% of the maximum aerobic speed) during the first and last minute of the exercise (whilst speed was freely chosen from the 2nd to the 29th minute). Results showed that fatigue decreased step frequency and increase step length under both conditions, along inducing a few little changes in the angular kinematic parameters limited to an increase of the PELVlS angle and a decrease of the ANKLE angle. However, no interaction effect was found for any of the spatiotemporal or angular stride parameters. These results suggest that exercise-induced hyperthermia impairs ankle proprioception, but that this alteration does not affect running kinematics. ln summary, proprioception is affected by hyperthermia induced either by passive or active methods. These alterations could be due to the effects of hyperthermia on neuromuscular and cognitive functions. However, the degradation of proprioceptive acuity with an increase in rectal temperature above 39 °C does not affect the kinematics of running, suggesting that running pattern remains stable despite proprioception and neuromuscular functions impairments

Thèse d'exercice : Médecine : Nancy 1 : 2008. / Titre provenant de l'écran-titre.

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