246 research outputs found

    Intense Synaptic Activity Enhances Temporal Resolution in Spinal Motoneurons

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    In neurons, spike timing is determined by integration of synaptic potentials in delicate concert with intrinsic properties. Although the integration time is functionally crucial, it remains elusive during network activity. While mechanisms of rapid processing are well documented in sensory systems, agility in motor systems has received little attention. Here we analyze how intense synaptic activity affects integration time in spinal motoneurons during functional motor activity and report a 10-fold decrease. As a result, action potentials can only be predicted from the membrane potential within 10 ms of their occurrence and detected for less than 10 ms after their occurrence. Being shorter than the average inter-spike interval, the AHP has little effect on integration time and spike timing, which instead is entirely determined by fluctuations in membrane potential caused by the barrage of inhibitory and excitatory synaptic activity. By shortening the effective integration time, this intense synaptic input may serve to facilitate the generation of rapid changes in movements

    A Conditioning Lesion Provides Selective Protection in a Rat Model of Amyotrophic Lateral Sclerosis

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    Amyotrophic Lateral Sclerosis (ALS) is neurodegenerative disease characterized by muscle weakness and atrophy due to progressive motoneuron loss. The death of motoneuron is preceded by the failure of neuromuscular junctions (NMJs) and axonal retraction. Thus, to develop an effective ALS therapy you must simultaneously preserve motoneuron somas, motor axons and NMJs. A conditioning lesion has the potential to accomplish this since it has been shown to enhance neuronal survival and recovery from trauma in a variety of contexts. rats that received a conditioning lesion was delayed and less severe. These improvements in motor function corresponded to greater motoneuron survival, reduced motor axonopathy, and enhanced NMJ maintenance at disease end-stage. Furthermore, the increased NMJ maintenance was selective for muscle compartments innervated by the most resilient (slow) motoneuron subtypes, but was absent in muscle compartments innervated by the most vulnerable (fast fatigable) motoneuron subtypes.These findings support the development of strategies aimed at mimicking the conditioning lesion effect to treat ALS as well as underlined the importance of considering the heterogeneity of motoneuron sub-types when evaluating prospective ALS therapeutics

    Changes in antagonist muscles' coactivation in response to strength training in older women.

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    Background. The purpose of this study was to assess changes in neuromuscular function of the plantarflexor and dorsiflexor muscles after 1 year of strength training of these muscles in elderly women. Twelve participants were assigned to a training (74.2 \ub1 3.1 years) group and eight to a nontraining group (73.6 \ub1 4.3 years). Methods. Isometric maximum voluntary contractions (MVC) and muscle activation based on surface electromyography (EMG) were recorded before and after the 12-month training program at six different joint angles. Results. After training (in the training group), (a) plantarflexion (PF) MVC increased on average by 14.4% (p < .05) across ankle joint angles from -20\ub0 dorsiflexion (DF) to +30\ub0 PF, (b) DF MVC decreased by 5.7% (p < .05), (c) PF EMG root mean square increased on average by 22.3% (p < .05), and (d) PF antagonists' coactivation increased on average by 7.5% across the tested joint angles. No changes were observed in the nontraining group. Conclusions. The present results show a significant increase in antagonist muscle coactivation with strength training in older women. The hypothesis is put forward that with a training-induced gain in agonist muscles' torque, stabilization of the ankle joint by increasing antagonist coactivation is needed because of a changed ratio of maximal PF torque to maximal DF torque. Copyright 2007 by The Gerontological Society of America

    Wars, Presidents and Popularity: The Political Cost(s) of War Re-Examined

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    Extensive research demonstrates that war casualties depress incumbent popularity. The present study argues that analyses of the political costs of warfare should also account for the financial toll of wars since a) financial costs of wars are substantial, b) these costs are publicly observed and understood and c) fiscal policy affects incumbents' approval ratings. Empirical evidence based on US data for the 1948-2008 period supports this theoretical claim: pecuniary costs of warfare either directly affect presidential popularity (e.g., in the Korean War) or their inclusion affects the predicted political cost of war casualties (e.g., in the Korean and Iraq/Afghanistan Wars). Interestingly, the adverse effect of war-spending is strongest under favourable economic conditions (i.e. low unemployment).Umfangreiche Forschungen zeigen, dass Kriegsopfer der Popularität des Amtsinhabers schaden. Die vorliegende Studie liefert Argumente dafür, dass Analysen der politischen Kosten der Kriegsführung in die Berechnung der finanziellen Kriegsausgaben miteinbezogen werden sollten, da a) die finanziellen Kosten von Kriegen beträchtlich sind, b) diese Kosten von der Öffentlichkeit wahrgenommen und verstanden werden, c) Fiskalpolitik die Umfragewerte des Amtsinhabers beeinflusst. Basierend auf US-Daten über den Zeitraum 1948-2008 wird dieser theoretische Anspruch empirisch unterstützt: pekuniäre Kosten der Kriegsführung haben entweder direkt eine Auswirkung auf die Popularität des Präsidenten (z. B. Koreakrieg) oder deren Einbeziehung beeinflusst die vorhergesagten politischen Kosten durch Kriegsopfer (z. B. Korea- und Irak/-Afghanistankrieg). Interessanterweise sind die negativen Auswirkungen der Kriegsausgaben am stärksten, wenn die wirtschaftlichen Bedingungen günstig (d.h. niedrige Arbeitslosigkeit) sind
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