Walton Kerry D, Benavides Louis, Singh Neeraj, Hatoum Nagi
Department of Physiology and Neuroscience, 550 First Avenue, New York, NY 10016, USA.
J Physiol. 2005 Jun 1;565(Pt 2):609-26. doi: 10.1113/jphysiol.2004.074393. Epub 2005 Mar 10.
The postnatal development of sensory systems has been shown in studies over the last four decades to be influenced by experience during critical periods of development. We report here that similar experience-dependent development can be observed in the swimming behaviour of young rats reared from postnatal day 14 (P14) to P30 in the reduced gravitational field of low earth orbit. Animals flown in space when placed in the water on the day of landing maintained their head and forelimbs in a balanced posture. However, until the animals began to swim, their hindquarters showed little lateral postural control resulting in rotation about the longitudinal axis (60 degrees+/-4 deg). Such results suggest an 'unlinking' of postural control of the forequarters from the hindquarters in the early hours after landing. Similar instability seen in animals age-matched to the day of launch (97+/-7 deg) and in ground control animals (9+/-3 deg) was corrected within one or two rotations, even in the absence of swimming. Animals flown in space began to swim sooner after being placed in the water, and the duration of swimming strokes was shorter than in control animals. Motion analysis revealed a difference in the swimming style on landing day. In flight animals, the knee joint was more flexed throughout the stroke, there was a narrower range of movement, and the linear velocity of the tip of the foot was faster throughout most of the stroke than in age-matched control animals. Thus, posture in the water as well as swimming speed and style were altered in the animals flown in space. Some of these characteristics persisted for as long as the animals were followed (30 days). These included the short pre-swimming interval and short stroke duration in flight animals. These findings clearly show that an altered gravitational field influences the postnatal development of motor function. The nature of the differences between animals reared in space for 16 days and those remaining on the ground reflects an adaptation of the flight animals to the microgravity environment. The data suggest that the most fundamental of these adaptations is a resetting of the basic motor rhythm to a higher frequency.
在过去四十年的研究中已表明，感觉系统的产后发育会受到发育关键期内经验的影响。我们在此报告，在低地球轨道的低重力场中从出生后第14天（P14）饲养至P30的幼鼠的游泳行为中，可观察到类似的经验依赖性发育。在着陆当天放入水中时，在太空中飞行过的动物能保持其头部和前肢处于平衡姿势。然而，在动物开始游泳之前，它们的后躯几乎没有横向姿势控制，导致围绕纵轴旋转（60度±4度）。这些结果表明，着陆后早期前躯的姿势控制与后躯“脱钩”。在与发射当天年龄匹配的动物（97±7度）和地面对照动物（9±3度）中看到的类似不稳定性，即使在没有游泳的情况下，也能在一两次旋转内得到纠正。在太空中飞行过的动物放入水中后更快开始游泳，且游泳划水的持续时间比对照动物短。运动分析揭示了着陆当天游泳方式的差异。在飞行过的动物中，整个划水过程中膝关节弯曲得更厉害，运动范围更窄，并且在大多数划水过程中，脚尖的线速度比年龄匹配的对照动物更快。因此，在太空中飞行过的动物在水中的姿势以及游泳速度和方式都发生了改变。其中一些特征在对动物进行跟踪的整个期间（30天）都持续存在。这些特征包括飞行过的动物游泳前间隔时间短和划水持续时间短。这些发现清楚地表明，重力场的改变会影响运动功能的产后发育。在太空中饲养16天的动物与留在地面上的动物之间差异的性质反映了飞行过的动物对微重力环境的适应。数据表明，这些适应中最基本的是将基本运动节律重置为更高频率。
