Table_1_NAIAD-2020: Characteristics of Motor Evoked Potentials After 3-Day Exposure to Dry Immersion in Women.DOCX

As female astronauts participate in space flight more and more frequently, there is a demand for research on how the female body adapts to the microgravity environment. In particular, there is very little research on how the neuromuscular system reacts to gravitational unloading in women. We aimed to estimate changes in motor evoked potentials (MEPs) in the lower leg muscles in women after 3-day exposure to Dry Immersion (DI), which is one of the most widely used ground models of microgravity. Six healthy female volunteers (mean age 30.17 ± 5.5 years) with a natural menstrual cycle participated in this experiment. MEPs were recorded from the gastrocnemius and soleus muscles twice before DI, on the day of DI completion, and 3 days after DI, during the recovery period. To evoke motor responses, transcranial and trans-spinal magnetic stimulation was applied. We showed that changes in MEP characteristics after DI exposure were different depending on the stimulation site, but were similar for both muscles. For trans-spinal stimulation, MEP thresholds decreased compared to baseline values, and amplitudes, on the contrary, increased, resembling the phenomenon of hypogravitational hyperreflexia. This finding is in line with data observed in other experiments on both male and female participants. MEPs to transcranial stimulation had an opposing dynamic, which may have resulted from the small group size and large inter-subject variability, or from hormonal fluctuations during the menstrual cycle. Central motor conduction time remained unchanged, suggesting that pyramidal tract conductibility was not affected by DI exposure. More research is needed to explore the underlying mechanisms.

随着女性宇航员参与太空飞行的频次日益增加，针对女性身体如何适应微重力环境开展研究的需求愈发迫切。目前针对女性神经肌肉系统如何应对重力卸载的相关研究仍十分匮乏。本研究旨在评估女性受试者在为期3天的干燥卧床（Dry Immersion, DI）——这一目前应用最广泛的微重力地面模拟模型之一——暴露后，小腿肌肉运动诱发电位（Motor Evoked Potentials, MEPs）的变化情况。本实验共招募6名月经周期自然规律的健康女性志愿者，平均年龄为30.17±5.5岁。分别在干燥卧床干预前、干预结束当日及干预后恢复期的第3天，从腓肠肌和比目鱼肌中采集运动诱发电位数据，每个时间点采集两次。本次实验采用经颅磁刺激与经脊髓磁刺激来诱发运动反应。研究结果显示，干燥卧床暴露后运动诱发电位特征的变化因刺激位点不同而存在差异，但在两块肌肉中表现出相似的变化趋势。对于经脊髓磁刺激，运动诱发电位阈值较基线水平有所降低，而波幅则相反出现升高，这与低重力反射亢进现象相符。这一结果与此前针对男性及女性受试者开展的其他实验所得数据一致。经颅磁刺激对应的运动诱发电位则呈现出相反的变化趋势，这一现象可能源于样本量较小、受试者间差异较大，或是月经周期内的激素波动所致。中枢运动传导时间未发生明显变化，提示干燥卧床暴露并未影响锥体束的传导功能。未来仍需开展更多研究以探索其潜在机制。