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Objective To study the morphological changes of soleus muscle spindle and electrical activity of neurons in Red Nucleus(RN) of the rat after 2 weeks' simulated weightlessness, and to reveal the interaction between proprioceptive inputs of muscle spindles and reciprocal alterations in RN under simulated weightlessness. Methods Twenty female rats were exposed to weightlessness simulated by tail-suspension for 14 days (SW-14d). Body weight(200-220g) matched female rats were control group(Con). The morphological changes in isolated muscle spindle of soleus muscle, the discharges of red nucleus neurons were observed after 14d tail-suspensions by silver staining and extracellular recording respectively. Results Compared with control group ,the nerve ending of muscle spindle in SW-14d was distorted, degenerated and dissolved; the diameters of intrafusal fibers and capsule in equatorial region of soleus muscle spindles were diminished(P＜0.05). The spontaneous cell activity and discharge of RN neurons (spikes/s) induced by afferent firing from muscle spindles after injection of succinylcholine were reduced after 2 weeks' simulated weightlessness respectively (18.44±5.96 vs. 10.19±6.88, 32.50±8.08 vs. 16.86±5.97, P＜0.01). Conclusion The degeneration of muscle spindle induced by simulated weightlessness may be one of the causes that led to alterations in discharges of RN.
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Objective To observe the changes of diameter of intrafusal fibers and capsule at equatorial region of rat soleus muscle spindle caused by hindlimb-unloading.Method Tail-suspended female rats were used as the model of hindlimb-unloading,all rats were randomly divided into 4 groups according to body weight.The four groups were exposed to tail-suspension for: 7 d,14 d,28 d and 0 d,respectively.The diameter of intrafusal fibers and capsule of single muscle spindle was measured and analyzed.Result The diameter of intrafual fibers,including nuclear-bag fibers and nuclear-chain fibers, were reduced slightly in both 7 d group and 28 d group and obviously reduced in 14 d group.The capsule diameter at equatorial region was obviously reduced in 7 d group.Conclusion Hindlimb-unloading can obviously reduce the diameters of intrafusal fibers and capsule at equatorial region of rat soleus muscle spindle.
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Objective To investigate changes induced by hindlimb unloading in morphology of nerve endings in soleus muscle spindles.Method Hindlimb unloading model was simulated by tail suspension in female rats.Fast silver-staining was used to observe morphology of nerve endings of single muscle spindle in 7 d,14 d,21 d and 28 d tail-suspended and control rats.Result Nerve endings of muscle spindles in control rats were intact and clear,and there was no obvious abnormality in single soleus muscle spindle of 7 d tail-suspended rats.Slight fragmentation of nerve endings was observed in Equatorial Region of soleus muscle spindle in 14 d tail-suspended rats,while reduction in density and disruption of nerve endings were observed in soleus muscle spindle in 21 d tail-suspended rats.Serious degeneration and distortion of nerve endings were found in soleus muscle spindle in 28 d tail-suspended rats.Conclusion Hindlimb-unloading can induce time-related changes in morphology of nerve endings of muscle spindle in rats soleus muscle.
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Objective: To study the morphological changes of soleus muscle spindle and electrical activity of neurons in Red Nucleus(RN) of the rat after 2 weeks' simulated weightlessness, and to reveal the interaction between proprioceptive inputs of muscle spindles and reciprocal alterations in RN under simulated weightlessness. Methods: Twenty female rats were exposed to weightlessness simulated by tail-suspension for 14 days (SW-14d). Body weight(200 -220 g) matched female rats were control group (Con). The morphological changes in isolated muscle spindle of soleus muscle, the discharges of red nucleus neurons were observed after 14d tail-suspensions by silver staining and extracellular recording respectively. Results: Compared with control group, the nerve ending of muscle spindle in SW-14d was distorted, degenerated and dissolved; the diameters of intrafusal fibers and capsule in equatorial region of soleus muscle spindles were diminished(P<0.05). The spontaneous cell activity and discharge of RN neurons (spikes/ s) induced by afferent firing from muscle spindles after injection of succinylcholine were reduced after 2 weeks' simulated weightlessness respectively (18.44±5.96 vs. 10.19±6.88, 32.50±8.08 vs. 16.86±5.97, P<0.01). Conclusion: The degeneration of muscle spindle induced by simulated weightlessness may be one of the causes that led to alterations in discharges of RN.
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Objective To study counteracting effects of high frequency vibration on simulated weightlessness-induced atrophy of soleus muscles in rats. Methods Female Sprague-Dawley (SD) rats were assigned randomly to one of the three groups: simultaneous control (CON), simulated weightlessness (SUS), and SUS plus high frequency vibration (SUS+HFV). Soleus muscles were examined 7 days later. Sections were treated with adenosinetriphosphatase (ATPase) stain. The cross-sectional areas (CSA) of fibers, the relative proportion of types I and II were measured using Leica image analysis system. Results Compared with those of CON, the wet weight /body of soleus and the cross-sectional areas (CSA) of type I/II fibers in SUS were significantly reduced. The relative proportion of type I fibers in SUS was reduced and type II fibers increased. In SUS+HFV group, the wet weight/body of soleus and the cross-sectional areas (CSA) of type I/II fibers recovered completely. The relative proportion of type I/II fibers recovered completely. Conclusion The present study demonstrates that HFV is effective in counteracting the muscle atrophy induced by simulated weightlessness.