Effects of gravity changes on CNS : molecular mechanisms of impaired spatial learning

大多数宇航员在暴露于失重状态后都会经历空间定向障碍，这表明在空间认知过程中，恒定的重力被用作稳定的外部参考。我们试图阐明恒定重力在空间学习中的作用，采用径向臂迷宫实验，将大鼠安置在由离心装置产生的超重力环境中。雄性Wistar大鼠在空间学习任务前保持2G线性加速2周，持续10天。对照大鼠被放置在离离心装置较近的地方，但不暴露在超重力环境中。空间学习是通过准确性和再入率来评估的，再入率分别是正确进入手臂的比率和进入他们已经访问过的手臂的比率。运动活动以每分钟进入次数测量。还测量了动物每分钟吃下的诱饵数量。结果表明，大鼠的空间学习精度明显低于对照组，再入速度明显高于对照组，表明动物在空间学习中使用恒定的重力作为稳定的外部参考。然而，这些差异在5天后消失，这表明HG大鼠比对照组更快地学习空间任务。HG大鼠的运动活动更高，每分钟的诱饵数量在HG和对照组之间没有差异。综上所述，如果空间认知所必需的感觉信号受到重力变化的干扰，动物可以通过增加运动活动来补充其他感觉信号，如本体感受和运动感知复制信号。研究了超重力负荷对长期植入颈静脉导管大鼠下丘脑-垂体轴（HPA轴）的影响。血浆ACTH和皮质酮水平分别在超重负荷1小时前、刚负荷后、1小时后和3小时后测定。这两种激素在负荷后和负荷后一小时均有所增加，但在负荷后3小时恢复到基础水平。负荷后血浆ACTH的下降（恢复）速度比皮质酮更快，这可能是因为皮质酮的变化可能是ACTH变化的下游。在长期的超重力负荷（2周）中，皮质酮升高至少一周，但ACTH未升高，但在负荷2周后，两种激素均恢复到控制水平，提示ACTH反应具有较短的时间常量，并能快速适应超重力负荷。结果表明，超重力作用激活了大鼠的下丘脑轴，并参与了空间导航功能障碍的学习和恢复。少

Most astronauts experience spatial disorientation after exposure to weightlessness, indicating that constant gravity is utilized as a stable external reference during spatial cognition. We attempted to elucidate the role of constant gravity in spatial learning using a radial arm maze test on rats housed in a hypergravity environment (HG) produced by a centrifuge device. Male Wistar rats were kept in 2G linear acceleration for two weeks before the spatial learning task, which lasted for ten days. The control rats were placed close to the centrifuge device but not exposed to hypergravity. Spatial learning was evaluated by the accuracy and the re-entry rate, which were the rate of correct arm entries and the rate of entries into the arms that they had already visited, respectively. Locomotor activity was measured by number of entries per minute. The number of baits the animal took per minute was also measured. The results showed that accuracy was significantly inferior and the re-entry ra … More te was significantly higher in the HG rats than in the controls, suggesting that animals use a constant gravity as a stable external reference in spatial learning. However, these differences disappeared at five days later, indicating that the HG rats learned the spatial task more rapidly than the controls. Locomotor activity was higher in the HG rats and there was no difference in number of baits per minute between the HG and control animals. In conclusion, if one sensory cue necessary for spatial cognition is disturbed by gravity change, animals can subsidize with other sensory cues such as proprioceptive and motor efference copy signals through increased locomotor activities.Effects of hypergravity load on hypothalamus-pituitary axis (HPA axis) were investigated in rats with chronically implanted canula in the cervical vein. Plasma ACTH and corticosterone levels were measured pre-, just after, 1 hour after, and 3 hours after the hypergravity load for one hour. Both hormones were increased just after and one hour after the load, however, their levels returned to the basal level 3 hours after the load. Decrease (recovery) of plasma ACTH after the load was more rapid in ACTH than corticosterone, probably because changes in corticosterone may be the downstream of ACTH changes. During the long term load (2 weeks) of hypergravity, corticosterone but not ACTH was increased at least for one week, however, both hormones returned to the control level 2 weeks after the load, suggesting that ACTH response has a short time constant and adapted to the hyoergravity load quickly. It is demonstrated that HPA axis was activated by hypergravity load and was involved in a better learning and recovery of impaired spatial navigation induced by the gravity changes. Less