[Influence of simulated weightlessness on the morphology of nerve endings of muscle spindle in rat soleus muscle].

OBJECTIVE: To study changes in structure and innervation of soleus muscle spindle in rats induced by simulated weightlessness. METHOD: Weightlessness was simulated by tail suspension in female rats. The technique of Fawosky's Staining was used to detect the morphology of nerve endings of soleus muscle spindle in 7 d, 14 d, 21 d tail-suspended and control rats. RESULT: The intrafusal muscle fibers were regular and nerve endings were intact and clear in the soleus spindles of control rats. No obvious change was observed in muscle spindles of 7 d tail-suspended rats. Intrafusal muscle fibers became irregular, with rough and vague nerve endings in 14 d tail-suspended rats. The distinct retrograde change of muscle spindles and nerve endings were observed in 21 d tail-suspended rats. Degeneration and rupture were found in nerve endings, which made it unclear and pale in staining. CONCLUSION: Simulated weightlessness could induce time-related changes in structure and innervation of soleus muscle spindle in rats.