| Background: A lot of clinical date and animal experiments show that inactivation, immobilization or muscle unloading all can lead to obvious disuse atrophy in skeletal muscles. Therefore, one of the most important and urgent issues is finding efficient ways and methods to solve this problem that the mechanism of disused muscle atrophy in clinical medicine, sports medicine, rehabilitation medicine and space medicine Nevertheless, few researches have focused on this field, and the relation between muscle spindle of hibernating animals and muscle disused is almost blank.In the long-term evolution, many animals developed a series of survival strategy to adapt the rigorous environment;the hibernation is an adaptation for many rodents to cold, food deficiency, et al. Daurian ground squirrel {citellus dauricus) is one of this kind of rodents. During 5 to 6 month-long hibernation, their skeletal muscle is no doubt disused, when arousing, the animal did not exhibit distinct skeletal muscle atrophy symptom, such as difficulty or even incapability of walking. So, under the condition of muscle disuse or hibernation, what happened in skeletal muscles of these animals? Whether there is muscle atrophy happened?Objective: Study changes in morphological structure of intrafusal and extrafusal, and biochemistry metabolism under such a condition as muscle disused (tail-suspended or hibernation) about soleus of ground squirrels, and then compared with that of tail suspended rats. Finally, we would like to provide novel experiment data to find new idea for protecting and treating disuse atrophy.Methods:(1) Establishe the disuse muscle model by tail-suspension;(2) Observe each group ofmicrostructure in intrafusal and extrafusal fibers in SOL by microscope;(3) Measure the soleus muscle (SOL) fiber cross-sectional area (CSA) by image analysis software;(4) Detect activities of intrafusal and extrafusa fibers in SOL by the way of Ca2+-myosin ATPase (mATPase), then analyze the proportion of type I and type II fibers;(5) Detect the immunity reactivity in SOL fibers of ground squirrels to monoclonal antibody MY32 during in-hibernating and post-hibernating period by immunity histochemistry technology. Result:(1) Primarily did some ecological observation about this research at different activated stages, collected some video documents, and finished the field collection of ground squirrels. Achieved the goals of the domination and hibernation in the laboratory;(2) Established disuse muscle model of ground squirrel for the first time, by using tail-suspension technique.(3) Observed the effect of tail-suspended on the SOL morphology of ground squirrels.For rats, compared with the control group, SOL wet weight in 14d's tail-suspended group showed a significant difference as well as CSA. The average of SOL wet weight to body wet weight decreased significantly (PO.001), so did CSA of type I and type II fiber (PO.05);the muscle fiber assumed triangle or irregular polygon, the fascicle gap increased;spindle cystic obviously devious, the structure became fuzzy, even dissolution, destruction, break, the diameter of intrafusal SOL muscle fibers remarkably reduced, structure slurred;Above changes were not remarkable in ground squirrel SOL. The result indicated that, short-term tail-suspension may lead SOL atrophy of rats';such phenomenon didn't occurre in ground squirrel SOL.(4) Observed the effect of tail-suspension on myosin ATPase activities in intrafusal and extrafusa fibers in soleus muscle of ground squirrel.After 14d tail-suspension, the intrafusal and extrafusa fibers in SOL of rat both showed significantly higher activities of mATPase as compared with that of the control.The proportion of type I fibers decreased, while that of type II fibers increased, PO.001. For ground squirrels, the activities of mATPase in intrafusal and extrafusa fibers also increased significantly after 14d tail-suspension. The proportion of type I fibers decreased significantly, meanwhile, that of the type II fibers increased, PO.05.(5) Observed the impact of the hibernation on body weight, SOL wet weight and myosin heavy chain (MHC) expression level in ground squirrel SOL fibers.The descending rate of body weight in ground squirrel increased obviously along with the hibernation period, the SOL wet weight in hibernation period was steady, but the SOL wet weight to body weight increased gradually. It may be lie in the fact that fat proportion dropped during the hibernation period, while body mass conservated. Compared with ground squirrels in the post-hibernating stage, the MHC II expression level in SOL fibers decreased in those in the in-hibernating period, in addition, the MHC I expression level increased. In SOL, the proportion of type I fibers increased, while that of type II fibers decreased. Conclusion:(1) The Daurian ground squirrel can be successfully raised and completed hibernation, reproduction under laboratory conditions;(2) Tail-suspended model for ground squirrel is an ideal model to investigate influence on sketel muscle in hibernation animal under disuse condition.(3) For rats, the 14d tail-suspension may contribute to evident muscle atrophy, the metabolic type in SOL transforms significantly from type I to type II;For ground squirrel, the 14d tail-suspension show inconspicuous muscle atrophy. But the metabolic type in SOL transforms significantly from type I to type II.(4) During hibernation period, the wet weight of ground squirrel SOL is stable, the body weight obviously drops along with the hibernation time, the ratio of SOL wet weight to body weight increase gradually;The proportion of type I fibers increase , while that of type II fibers decrease. This kind of transformation will reverse after arousing.
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