Roy R R, Ishihara A, Moran M M, Wade C E, Edgerton V R
Brain Research Institute , University of California Los Angeles, Los Angeles, CA 90095-1761, USA.
Aviat Space Environ Med. 2001 Dec;72(12):1107-12.
Spaceflights of short duration (approximately 2 wk) result in adaptations in the size and/or metabolic properties of a select population of motoneurons located in the lumbosacral region of the rat spinal cord. A decrease in succinate dehydrogenase (SDH, an oxidative marker enzyme) activity of moderately sized (500-800 microm2) motoneurons in the retrodorsolateral region of the spinal cord (L6) has been observed after a 14-d flight.
Our hypothesis was that exposure to short-term hypergravity would result in adaptations in the opposite direction, reflecting a continuum of morphological and biochemical responses in the spinal motoneurons from zero gravity to hypergravity.
Young, male rats were centrifuged at either 1.5 or 2.0 G for 2 wk. The size and SDH activity of a population of motoneurons in the retrodorsolateral region of the spinal cord (L5) were determined and compared with age-matched rats maintained at 1.0 G. The absolute and relative (to body weight) masses of the soleus, gastrocnemius, adductor longus and tibialis anterior muscles were compared among the three groups.
There were no effects of either hypergravity intervention on the motoneuron properties. Rats maintained under hypergravity conditions gained less body mass than rats kept at 1.0 G. For the 1.5 and 2.0 G groups, the muscle absolute mass was smaller and relative mass similar to that observed in the 1.0 G rats, except for the adductor longus. The adductor longus absolute mass was similar to and the relative mass larger in both hypergravity groups than in the 1.0 G group.
Our hypothesis was rejected. The findings suggest that rat motoneurons are more responsive to short-term chronic exposure to spaceflight than to hypergravity conditions.
短期太空飞行（约2周）会导致大鼠脊髓腰段特定运动神经元群体的大小和/或代谢特性发生适应性变化。在14天的飞行后，观察到脊髓后外侧区域（L6）中等大小（500 - 800平方微米）的运动神经元的琥珀酸脱氢酶（SDH，一种氧化标记酶）活性降低。
我们的假设是，暴露于短期超重环境会导致相反方向的适应性变化，这反映了脊髓运动神经元从失重到超重的一系列形态和生化反应。
将年轻雄性大鼠在1.5或2.0 G的离心力下处理2周。测定脊髓后外侧区域（L5）运动神经元群体的大小和SDH活性，并与保持在1.0 G的年龄匹配大鼠进行比较。比较三组比目鱼肌、腓肠肌、长收肌和胫骨前肌的绝对质量和相对质量（相对于体重）。
两种超重干预对运动神经元特性均无影响。处于超重条件下的大鼠体重增加比保持在1.0 G的大鼠少。对于1.5 G和2.0 G组，除长收肌外，肌肉绝对质量较小，相对质量与1.0 G大鼠相似。两个超重组的长收肌绝对质量与1.0 G组相似，相对质量比1.0 G组大。
我们的假设被否定。研究结果表明，大鼠运动神经元对短期慢性太空飞行暴露的反应比对超重条件的反应更敏感。
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