MICROGRAVITY EFFECTS ON NEUROMUSCULAR DEVELOPMENT

描述：本研究的目的是了解 微重力的发展，成熟和维护， 包括人类在内的陆生哺乳动物的神经肌肉系统。的 拟议的研究将使用大鼠作为模型，并将探索广泛的 一种假设，即需要重力相关的承重 出生后对于运动神经元的正常神经肌肉发育， 神经肌肉接头和反重力肌纤维类型 比目鱼肌，而不是指长伸肌， 非承重肌肉幼鼠（3-5日龄）将暴露于 微重力14-21天。一组飞行动物将被杀死 在接近使命结束时飞行，另一组将返回 在处理组织之前将其暴露于地球重力下1个月。 平行的地面控制组将在正常和 后肢悬吊卸载（HSU）大鼠。三个预测将是 在这些研究中测试。首先，大脑的神经肌肉系统 在微重力条件下，大鼠幼仔的比目鱼肌将无法正常发育 而EDL的开发将不受影响地进行。该分析 将确定微重力是否会破坏运动神经元的成熟， 是否会有正常的多神经支配的消除， 肌纤维，以及肌纤维类型是否正常分化 比目鱼肌和趾长伸肌都会出现第二，影响 后肢悬吊减负荷的神经肌肉发育（in 地面研究）和微重力可能类似。但他们可能不 由于在后肢悬挂中增加了变量， 研究，不应该是一个问题，在太空飞行（隔离， 母亲和哺乳中断，体温变化等）。 第三，研究了幼年大鼠比目鱼肌神经肌肉系统的异常， 微重力不会通过后期暴露于 负重，而EDL将继续正常成熟。动物 返回地球并在重力暴露后1个月进行处理， 分析了这些研究中的总体分析将涉及处理 腰脊髓、比目鱼肌和趾长伸肌组织化学染色， 免疫细胞化学、原位杂交、凝胶电泳和 电镜逆行标记将用于识别 比目鱼肌和趾长伸肌运动神经元。神经肌肉系统分析 发展将包括评估运动神经元的成熟， 两个肌肉群（使用体大小，细胞色素氧化酶（CO）活性， CO mRNA水平和胆碱乙酰转移酶（CHAT）活性）， 消除运动终板的多神经元神经支配，和 肌纤维类型的分化（使用肌球蛋白同种型，和 信息、肌原纤维ATP酶活性和CO活性和信息）。 据预测，微重力将导致新生儿持续性 属性和/或比目鱼肌异常的发展，但不是 EDL，并返回动物到地球重力预计不会 反向诱导异常。预计这些结果 将对饲养正常动物（包括 人类）在太空微重力环境中，但另外将 进一步加深了我们对负重活动重要性的理解 对于地球上个体的运动系统发展来说。

DESCRIPTION: The goal of this study is to understand the influence of microgravity on the development, maturation, and maintenance of the neuromuscular system of terrestrial mammals, including humans. The proposed studies will use rats as a model and will explore the broad hypothesis stating that gravity-associated weightbearing is required postnatally for normal neuromuscular development of motoneurons, neuromuscular junctions, and muscle fiber types of the antigravity soleus muscle, but not for that of the extensor digitorum longus, a nonweightbearing muscle. Rat pups (3-5 days old) will be exposed to microgravity for 14-21 days. One group of flight animals will be killed inflight near the end of the mission, and another group will be returned to terrestrial gravity for 1 month before tissues are processed. Parallel groups of ground controls will be conducted on normal and hindlimb suspended unloaded (HSU) rats. Three predictions will be tested in these studies. Firstly, that the neuromuscular system of the soleus will not develop normally in the rat pups exposed to microgravity whereas the EDL development will proceed uncompromised. This analysis will establish whether microgravity disrupts maturation of motoneurons, whether there will be normal elimination of multiple innervation of muscle fibers, and whether normal differentiation of muscle fiber types in the soleus and EDL will occur. Secondly, that the effects on neuromuscular development of unloading by hindlimb suspension (in ground-based study) and microgravity may be similar. But they may not be identical since there are added variables in the hindlimb suspension study that should not be a problem in space flight (isolation from mother and disruption of suckling, body temperature changes, etc). Thirdly, the aberrant soleus neuromuscular system of rat pups raised in microgravity will not be restored to normality by late exposure to weight bearing whereas the EDL will continue normal maturation. Animals returned to earth and processed 1 month after gravity exposure will be analyzed. Overall analysis in these studies will involve processing of the lumbar spinal cords and soleus and EDL muscles using histochemistry, immuno-cytochemistry, in situ hybridization, gel electrophoresis, and electron microscopy. Retrograde labelling will be employed to identify soleus and EDL motoneurons. Analysis of the neuromuscular system development will include assessing maturation of the motoneurons of the two muscle groups (using somal size, cytochrome oxidase (CO) activity, CO mRNA levels, and choline acetyltransferase (CHAT) activity), elimination of polyneuronal innervation of motor endplates, and differentiation of muscle fiber types (using myosin protein isoforms, and messages, myofibrillar ATPase activity, and CO activity and message). It is predicted that microgravity will cause persistence of neonatal attributes and/or the development of anomalies in the soleus but not the EDL, and returning animals to terrestrial gravity is not predicted to reverse induced abnormalities. It is anticipated that these results will raise important implications for rearing normal animals (including humans) in the microgravity environment of space, but additionally will further our understanding of the importance of weightbearing activity for motor system development of individuals on Earth.