Doctorat en Sciences de la motricité / info:eu-repo/semantics/nonPublished

A review of the literature on sodium distribution in muscle has been presented including the evidence for heterogeneous distribution and the possible morphological sites of localization of this sodium. Special attention was paid to influx studies on crustacean muscle. The review reveals that while there is good evidence for a heterogeneous distribution, the morphological sites and their associated concentrations of sodium remain obscure. The experiments described in this thesis were performed on muscle fibers of the giant barnacle Balanus nubilis. Single muscle fibers of Balanus are a unique biological preparation due to their large size and ease of dissection. The major disadvantage to single fiber Balanus preparations is the extent of the extracellular space or cleft system. This cleft system contains approximately half the total fiber sodium in 6% of the fiber volume. The purpose of these experiments was to gain a picture of (22)Na+ entry into these single striated muscle fibers with special emphasis on the role of the extracellular space. A histological study revealed that the cleft system was more extensive than had been reported. From measurements made on light and electron microscope pictures it was concluded that no part of Balanus myoplasm was more than 1 - 2μ from a 0.02μ patent cleft. This study gave a picture of the morphological pathway for (22)Na+ diffusion in the extracellular space. Radioautography and radio isotope counting were two techniques used to examine (22)Na+ exchange between the extracellular space and the myoplasm. Since the extracellular space had a sodium concentration of 10 times the myoplasm, the cleft system should be adequately visualized by radioautography. However, the section thickness (15μ) and the high maximum energy of (22)Na+ (0.540MEV) limited the resolution of the radioautograms to 15 - 17.5μ. This resolution coupled with the extent of the cleft system prevented consistent radioautographic visualization of discrete clefts. Radioautographic analysis of fibers with minimal exposure (0.5 minutes) to (22)Na+ revealed a concentration gradient which could be used to define the extracellular pathway and its diffusion coefficient for Na+. The radius of the fiber cross section was found to be a reasonable approximation of the length of the pathway and the diffusion of (22)Na+ in the extracellular space along the pathway was as rapid as the self diffusion of (22)Na+ in dilute solution. A comparison of fibers that had spent 1.5 minutes in the (22)Na+ bath with similar fibers that had a 0.5 minute sucrose rinse revealed that the 0.5 minute sucrose rinse removed half of the (22)Na+ from the extracellular space. The 1.5 minute fibers and all fibers examined after periods in the (22)Na+ bath revealed a homogenous grain distribution in radioautograms. This data conflicted with the rate of (22)Na+ entry predicted by the 0.5 minute fibers. Inappropriate agitation of the 1.5 minute fibers was responsible for the lack of agreement. A further radioautographic study of (22)Na+ influx with experimental times 5, 20, 60 and 180 minutes was analyzed quantitatively. To substantiate this radioautographic study an influx experiment was done with times 5, 10, 20, 40 and 90 minutes. Each study demonstrated two compartments. An initial rapidly exchanging compartment with a half time of 6 - 10 minutes was identified as the extracellular space. The extracellular space contained approximately half the fiber sodium. Both studies detected a rnyoplasmic influx compartment which was still exchanging when the experiments were terminated. The calculated rate constant for myoplasmic exchange (5.6 x 10(-3)/minute) was in good agreement with the value of Allen and Hinke. In conclusion, a useful technique for the radioautography of soluble substances was developed. Both a morphological and a physiological picture of the pathway for (22)Na+ diffusion in the extracellular space was developed. The size and half time of loading of the extracellular space was verified. The myoplasmic influx component was identified by two methods. From these studies emerges a more comprehensive picture of the extracellular space as a pathway for diffusion in Balanus muscle. The failure to consider this compartment in microinjection or flux studies may result in ambiguous conclusions. / Land and Food Systems, Faculty of / Graduate

Thèse ou mémoire avec insertion d'articles / Introduction : Les muscles du tronc participent au maintien de la posture, ils s'activent pour rigidifier et/ou mouvoir la colonne vertébrale. Il est possible de distinguer deux types de contrôle moteur pour ces derniers: un contrôle volontaire (e.g., extension du dos) et un contrôle postural pour conserver la posture (involontaire). Les patients souffrant d'états de santé tels que les accidents vasculaires cérébraux, les lésions de la moelle épinière et les lombalgies présentent des altérations du contrôle moteur du tronc. Ces altérations peuvent être dues à une lésion du système nerveux central (SNC) (e.g., accident vasculaire cérébral) ou à une réorganisation des circuits neuronaux (e.g., lombalgie) en présence de douleur. Bien que la lombalgie chronique soit à l'origine du plus grand nombre d'années vécues avec incapacité dans le monde, la neurophysiologie du contrôle moteur des muscles paravertébraux lombaires est méconnue. Par exemple, les études sondant les représentations des muscles paravertébraux lombaires avec la stimulation magnétique transcrânienne (TMS) chez l'humain se sont concentrées sur une seule région : le cortex moteur primaire (M1). Pourtant, d'autres circuits de neurones tels que l'aire motrice supplémentaire (SMA) semblent impliqués. Dépendamment de la direction du courant électrique utilisée (postéro-antérieur [PA] vs. antéro-postérieur [AP]), la TMS pourrait activer différents circuits de neurones qui pourraient être impliqués différemment dans le contrôle des muscles du tronc. Il a été suggéré que les circuits recrutés par le courant AP pourraient refléter l'action des structures prémotrices (prémoteur et SMA) sur le M1. L'objectif général de la thèse est d'explorer, à l'aide de techniques de neurophysiologie (TMS et réflexe d'étirement (SR)), le fonctionnement de différents circuits de neurones impliqués dans le contrôle moteur des muscles paravertébraux lombaires chez des individus en santé. Méthode : Une revue systématique de la littérature a été réalisée pour examiner systématiquement les études portant sur le contrôle neuronal des muscles paravertébraux lombaires chez l'homme testé par la TMS. Puis, la TMS a été utilisée dans deux études pour mesurer l'excitabilité corticospinale des muscles érecteurs du rachis lombaire (LES) chez des individus en santé. Dans l'étude 2, l'effet de différentes directions de courant de la TMS (PA- vs. AP-TMS) sur la mesure du contrôle corticomoteur des LES et sur la cartographie de la représentation corticale des LES ont été réalisé pendant une tâche statique de maintien postural. Dans l'étude 3, l'excitabilité des circuits de neurones PA- et AP-TMS ainsi que l'excitabilité spinale (SR) ont été testés lors de la préparation et de l'exécution de tâches posturale et volontaire des LES. Les potentiels moteurs évoqués (MEPs) et SR ont été mesurés à plusieurs intervalles de temps avant l'exécution d'une bascule du bassin (activation volontaire des LES) et d'une flexion bilatérale des épaules (activation posturale des LES). Résultats : Les résultats obtenus dans l'étude 1 suggèrent des projections bilatérales à partir de chaque M1 vers un muscle lombaire et la présence de circuits inhibiteurs et excitateurs intracorticaux dans M1. Dans l'étude 2, l'utilisation du courant AP-TMS a entraîné une latence de réponse plus tardive, une inhibition plus importante avec un protocole de stimulations pairées, et un seuil moteur plus élevé qu'avec le courant PA-TMS. Les résultats de l'étude 3 ont révélé (i) dans la tâche posturale, un changement de l'excitabilité corticospinale et motoneuronale plus élevé pendant l'exécution par rapport à la préparation motrice, quelle que soit la direction du courant et (ii) dans la tâche volontaire, une augmentation de l'excitabilité corticospinale pendant l'exécution par rapport à la préparation motrice uniquement avec le courant AP-TMS. Conclusion : Les connaissances des structures neuronales sous-jacentes du contrôle moteur des muscles paravertébraux lombaires sont influencées par les études menées en neurophysiologie sur le contrôle moteur des muscles distaux (e.g., main). Les résultats de la thèse supportent l'existence de différences entre le contrôle moteur des muscles paravertébraux lombaires et des muscles distaux, notamment par une plus grande contribution des voies descendantes bilatérales. De plus, les résultats soutiennent l'existence de deux circuits de neurones sous-jacents du contrôle moteur des LES recrutés par les courants PA- et AP-TMS. Ces circuits semblent contribuer différemment au contrôle moteur des LES dépendamment du type de tâche à réaliser (posturale ou volontaire) chez des individus en bonne santé. De futures études seront nécessaires pour explorer si ces circuits sont modulés différemment en présence de douleur expérimentale (e.g., stimulation électrique) et clinique (e.g., lombalgie). / Introduction: The muscles of the trunk are essential for maintaining posture, they are activated to stiffen and/or move the spine. Two types of motor control can be distinguished for them: voluntary control (e.g., back extension) and postural control during which the motor system is activated to maintain posture. Patients suffering from various health conditions such as stroke, spinal cord injury and low back pain show alterations in the trunk motor control. These alterations may be due to damage to the central nervous system (CNS) (e.g., stroke) or to a reorganisation of neural circuits (e.g., low back pain) in the presence of pain. Although chronic low back pain accounts for the largest number of years lived with disability in the world, the neurophysiology of motor control of the lumbar paraspinal muscles is poorly understood even in healthy individuals. For example, studies probing trunk muscle representations with transcranial magnetic stimulation (TMS) in humans have mainly focused on a single region: the primary motor cortex (M1). However, evidence suggests the major involvement of other neural circuits such as the supplementary motor area (SMA). Depending on the direction of the electrical current used (posterior-anterior [PA] vs. antero-posterior [AP]), TMS could activate different neural circuits that might be differently involved in trunk muscle control. It has been suggested that the circuits recruited by the AP current may reflect the action of premotor structures (premotor and SMA) on the M1. The general objective of the thesis is to explore, using neurophysiological techniques (TMS and stretch reflex (SR)), the functioning of different neural circuits involved in the motor control of lumbar paraspinal muscles in healthy individuals. Methods: A systematic review of the literature was conducted to systematically examine studies of the neural control of lumbar muscles in humans tested by TMS. Then, TMS was used in two studies to measure the corticospinal excitability of lumbar spinal erector spinae (LES) muscles. In Study 2, the effect of different TMS current directions (PA- vs. AP-TMS) on the measurement of corticomotor control of the LES muscles and on the mapping of the cortical representation of the LES muscles were performed during a static postural maintenance task in healthy individuals. In Study 3, the excitability of PA- and AP-TMS neural circuits as well as spinal excitability via the stretch reflex were tested during the preparation and execution of postural and voluntary LES muscle tasks. MEPs and SR were measured at several time intervals before the execution of a pelvic tilt (voluntary activation of the lumbar muscles) and a bilateral shoulder flexion (postural activation of the lumbar muscles). Results: The results obtained in Study 1 suggest bilateral projections from each M1 to a lumbar muscle and the presence of intracortical inhibitory and excitatory circuits in M1. In Study 2, the use of AP-TMS current resulted in a later response latency, greater inhibition with a paired pulses stimulation protocol, and a higher motor threshold than with PA-TMS current. The results of Study 3 revealed (i) in the postural task, a higher modulation of corticospinal and motoneuronal excitability during execution than during motor preparation, regardless of the direction of the current and (ii) in the voluntary task, a modulation of corticospinal excitability that was present only with the AP-TMS current. Conclusion: Knowledge of the neural structures underlying motor control of lumbar paraspinal muscles is greatly influenced by neurophysiological studies of motor control of distal muscles (e.g., hand). However, the results of the thesis support the existence of differences between the motor control of the lumbar paraspinal muscles and the distal muscles, notably through a greater contribution of bilateral descending pathways. Furthermore, the results support the existence of two underlying neuronal circuits of LES muscle motor control recruited by PA- and AP-TMS currents. These circuits also appear to contribute differently to LES motor control depending on the type of task being performed (postural or voluntary) in healthy individuals. Future studies are needed to explore whether these circuits are active differently in the presence of experimental (e.g., electrical stimulation) and clinical (e.g., low back pain) pain.

Nitrate is a progenitor of nitric oxide found in high concentrations in diets rich in fruits and vegetables, such as the Mediterranean. Following enterosalivary circulation, nitrate is converted by salivary bacteria to nitrite and then nitric oxide. Nitrite is a bioactive metabolite of nitric oxide hypothesised to play a role in several metabolic pathways. We explored the effect of nitrate and nitrite in skeletal muscle metabolism and mitochondrial function in mice and humans. Our aims were to assess whether the mouse model is appropriate for use to ascertain the effects of nitrate supplementation, to determine whether these effects are nitrate or nitrite dependent and to investigate whether 7 days nitrate supplementation with nitrate in humans affects metabolism and mitochondrial function. Nitrate supplementation in the mouse, increased plasma nitrate concentration but did not elicit any changes in skeletal muscle metabolism or mitochondrial function at rest. Nitrite supplementation increased plasma nitrate and nitrite concentrations and achieved an increase in metabolic efficiency manifested as a reduction in complex I-linked leak respiration at rest. Nitrate supplementation in humans for 7 days increased plasma nitrate but not nitrite concentration. Skeletal muscle metabolism and mitochondrial function after nitrate did not differ from the placebo. However, blood perfusion of muscles consisting predominantly of type I fibres was increased. Our work suggested that nitrate metabolism is similar between mice and humans and the mouse could be a good model to investigate the effects of nitrate supplementation on skeletal muscle metabolism. This work also suggests that increases in plasma nitrite concentration may be responsible for the changes observed in mitochondrial efficiency. Finally, nitrate supplementation in humans did not elicit any metabolic changes. Deliberate nitrate supplementation in order to increase performance requires further research and any recommendations on increased consumption of nitrates for this purpose may not be accurate.

published_or_final_version / Zoology / Master / Master of Science

published_or_final_version / Zoology / Master / Master of Science

No description available.

The tail-cast suspension system was used as a ground-based model of weightlessness to study the effects of reduced weight-bearing (unloading) and attendant atrophy on carbohydrate metabolism in the rat soleus muscle. Changes in glycogen metabolism during unloading were biphasic. The initial phase, which took place during the first 24 hours, was characterized by increased glycogen concentrations, the result of decreased glycogenolysis. This glycogen accumulation in turn decreased the glycogen synthase activity ratio. These alterations were maintained thereafter. A similar glycogen increase was seen in the soleus unloaded by hypogravity. A rapid decline in glucose uptake also occurred during this initial phase of unloading, both in the absence and presence of insulin. During the second phase of this unloading response, beyond 24 hours, there was an increase in the sensitivity of the soleus to insulin for glucose uptake that coincided with the onset of muscle atrophy. However, this increased insulin sensitivity was not seen for glycogen synthesis, indicating differential regulation of these two processes by insulin. The enhanced insulin sensitivity likely resulted from an increase in the binding capacity for the hormone, resulting from no increased turnover of the insulin receptor during unloading. Additionally, the onset of increased insulin sensitivity coincided with a return to normal of basal glucose uptake, despite the continued unloading. When the 3-day unloaded soleus was reloaded, carbohydrate metabolism returned to normal after a triphasic response. Within two hours, the glycogen concentration decreased below control levels, due to increased glycogenolysis. During the second phase of reloading, from two to 24 hours, glycogen accumulated dramatically due to an enhanced capacity of the muscle for glycogenesis. Insulin sensitivity returned to normal by 24 hours of reloading. In the final phase, beyond 24 hours, glycogen decreased to control values. An uncoupling of the inverse relationship between glycogen and the activity ratio of glycogen synthase was seen beyond four hours of reloading. These effects of unloading and reloading were not due to systemic factors, as the extensor digitorum longus was unaffected. It is apparent that the unloaded soleus is a potent model with which to study the individual factors that regulate carbohydrate metabolism in skeletal muscle.

The investigation of motor-unit fatigability in reduced-animal models has been dominated by a single fatigue test, one fatigue index, and an emphasis on changes in the magnitude of (usually peak) force. Although the standard fatigue test has been reported to elicit changes in the dynamic phases of an isometric tetanus, this has not been systematically studied in single motor units. Furthermore, changes in the profile of individual tetani during the fatigue test have led some investigators to suggest that other force parameters (i.e., integrated force) or fatigue indices may provide additional information about motor-unit performance during the test. The purposes of this project were to: (1) evaluate the time courses of a variety of force parameters characterizing both the magnitude of force and the dynamic aspects of force during a 4-min fatigue test of functionally isolated cat, tibialis posterior motor units; and (2) determine if motor units could be classified into the conventional motor-unit types based on these new parameters. There was considerable variability in the average time course of the magnitude of force during the fatigue test. The variability within the type FR and F(int) motor-unit groups resulted in several units whose characteristics bordered those which, by definition, separate unit types. The classification of these units depended on the force parameter and fatigue index used to quantify their fatigability. The time course of the magnitude of force also revealed differences in the behavior of potentiating and non-potentiating groups. There were many differences between motor-unit types in terms of dynamic-force parameters before, during and after the fatigue test. Comparison of initial and 2-min values revealed a preferential effect of stimulation on force development in type S and FR units (i.e., increased rate) and on force decay in type F(int) and FF units (i.e., prolonged duration and decreased rate). The time courses of these effects further revealed qualitative differences between different combinations of motor-unit types. Groups of units (or lack thereof) revealed by dynamic-force parameters were compared to conventional motor-unit types by discriminant analysis. The results were not always consistent with conventional types.

No description available.