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会出现空间定向障碍，这表明在空间认知过程中，恒定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对大鼠在超重力环境（HG）的离心装置产生的。雄性Wistar大鼠在2G线性加速度下保持2周后进行空间学习任务，持续10天。对照组大鼠被放置在离离心装置很近的地方，但没有暴露在超重力下。空间学习的准确性和再进入率，这是正确的手臂进入率和进入率，他们已经访问过，分别评估。自发活动通过每分钟进入的次数来测量。还测量了动物每分钟服用的诱饵数量。结果表明，准确性明显较差， ...更多信息 TE在HG大鼠中显著高于对照组，表明动物在空间学习中使用恒定重力作为稳定的外部参考。然而，这些差异在五天后消失，表明HG大鼠学习空间任务比对照组更快。HG大鼠的自发活动更高，HG和对照动物之间每分钟的诱饵数没有差异。总之，如果空间认知所必需的感觉线索被重力改变干扰，动物可以通过增加运动活动来补充其他感觉线索，如本体感受和运动传出复制信号。在超重力负荷1小时前、后、1小时后和3小时后测量血浆ACTH和皮质酮水平。两种激素在负荷后即刻和负荷后1小时增加，然而，它们的水平在负荷后3小时恢复到基础水平。负荷后血浆促肾上腺皮质激素的下降（恢复）比皮质酮更快，这可能是因为皮质酮的变化可能是促肾上腺皮质激素变化的下游。在超重力长期负荷（2周）过程中，皮质酮至少在1周内升高，而ACTH无明显变化，但在2周后两种激素均恢复到对照水平，表明ACTH反应时间常数短，对超重力负荷的适应快。结果表明，超重力负荷激活HPA轴，并参与了更好的学习和恢复由重力变化引起的受损的空间导航。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