Yamasaki M, Shimizu T, Katahira K, Waki H, Nagayama T, O-Ishi H, Katsuda S, Miyake M, Miyamoto Y, Wago H, Okouchi T, Matsumoto S
Department of Physiology, Fukushima Medical University School of Medicine, 1 Hikari-ga-oka, Fukushima 960-1295, Japan.
Neuroscience. 2004;128(4):819-29. doi: 10.1016/j.neuroscience.2004.07.022.
Hydrostatic pressure gradients due to the gravitational force in blood vessels disappear under conditions of microgravity during spaceflight, and the ability of the baroreceptor reflex to control arterial pressure and blood distribution may be altered. We hypothesized, on the basis of the results obtained in our previous experiments using the head-down tilt method in rats and rabbits, that the range of increase in arterial pressure caused by animal behavior narrows under conditions of microgravity, affecting the development of high-threshold unmyelinated fibers in the rat aortic nerve which sends signals from baroreceptors located in the aortic wall to the reflex center. We verified this hypothesis using 9-day-old rat neonates housed with their dams for 16 days on the space shuttle Columbia in outer space (STS-90, Neurolab Mission). Age-matched neonatal rats with the dams remained on the ground as controls. After breeding was carried out in the three experimental groups (FLT, spaceflight; AGC, asynchronous ground control; VIV, vivarium ground control), specimens of the 25-day-old rats were excised and five left aortic nerves in each group were examined by electron microscopy. The number of aortic unmyelinated fibers was significantly less in the FLT group than in each ground control (mean+/-S.D.; 139+/-37 in the FLT, 207+/-36 in the AGC, 283+/-121 in the VIV; P<0.05), which may be related to the weakness of the baroreceptor reflex under conditions of microgravity in space. This result may contribute to understanding of the several cardiovascular issues which occur under microgravity and after reexposure to gravity in human.
在太空飞行的微重力条件下，血管中由于重力产生的静水压力梯度消失，压力感受器反射控制动脉血压和血液分布的能力可能会改变。基于我们之前使用大鼠和兔子头低位倾斜法所获得的实验结果，我们推测，在微重力条件下，动物行为引起的动脉血压升高范围变窄，这会影响大鼠主动脉神经中高阈值无髓纤维的发育，该神经将位于主动脉壁的压力感受器发出的信号传递至反射中枢。我们利用9日龄的新生大鼠，在太空梭哥伦比亚号上于外层空间（STS - 90，神经实验室任务）与它们的母鼠一起饲养16天，验证了这一假设。与实验大鼠年龄匹配的新生大鼠及其母鼠留在地面作为对照。在三个实验组（FLT，太空飞行组；AGC，异步地面对照组；VIV，饲养室地面对照组）完成繁育后，切除25日龄大鼠的样本，每组取五条左主动脉神经进行电子显微镜检查。FLT组主动脉无髓纤维的数量显著少于各地面对照组（平均值±标准差；FLT组为139±37，AGC组为207±36，VIV组为283±121；P<0.05），这可能与太空微重力条件下压力感受器反射减弱有关。这一结果可能有助于理解人类在微重力条件下以及重新暴露于重力环境后出现的一些心血管问题。
