Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, Pushchino, Moscow Region 142290 Russia.
Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, Pushchino, Moscow Region 142290 Russia.
Brain Res. 2022 Nov 15;1795:148077. doi: 10.1016/j.brainres.2022.148077. Epub 2022 Sep 9.
The negative effect of hypogravity on the human organism is manifested to a greater extent after the astronauts return to the conditions of habitual gravity. In this work, to elucidate the causes underlying atypical nystagmus, arising after the flight, we studied structural changes in the motoneurons of the trochlear nerve after a 7-day readaptation of mice to the conditions of Earth's gravity. It is known, that motoneurons of the trochlear nerve innervate the muscle that controls the movement of the eyes in the vertical direction. We showed that the number of axodendritic synapses and some other morphological parameters of motoneurons changed by microgravity can return to their original state in 7 days. However, according to some parameters, motoneurons retain a "memory" of the action of microgravity and do not completely restore the structure. The volume of the soma, the shape of the nuclei, the number and orientation of dendrites do not return to pre-flight parameters. The number of dendrites after 7 days of adaptation remained increased, and the proportion of dendrites in the ventrolateral direction became 2.5 times greater than in motoneurons after space flight. The increased number of mitochondria after space flight became even more significant after readaptation. Microgravity-induced plastic changes retain to some extent "memory traces" after readaptation to Earth's gravity. It can be assumed that the restoration of the function of the trochlear nuclei (overcoming nystagmus) is carried out not only by reversible restoration of the structure of neurons, but partially using those mechanisms that are formed in weightlessness.
微重力对人体的负面影响在宇航员返回惯常重力环境后表现得更为明显。在这项工作中，为了阐明飞行后出现非典型眼球震颤的原因，我们研究了在小鼠适应地球重力环境的 7 天后，滑车神经运动神经元的结构变化。已知滑车神经运动神经元支配控制眼球垂直运动的肌肉。我们表明，由微重力引起的轴突树突突触数量和运动神经元的一些其他形态参数可以在 7 天内恢复到原来的状态。然而，根据一些参数，运动神经元保留了微重力作用的“记忆”，并且结构并未完全恢复。胞体体积、核形状、树突数量和方向都没有恢复到飞行前的参数。适应 7 天后的树突数量仍然增加，并且在飞行后的运动神经元中，侧向方向的树突比例增加了 2.5 倍。飞行后线粒体数量的增加在适应后变得更加显著。微重力诱导的可塑性变化在适应地球重力后在一定程度上保留了“记忆痕迹”。可以假设，滑车核（克服眼球震颤）功能的恢复不仅通过神经元结构的可逆恢复来进行，而且部分通过在失重状态下形成的那些机制来进行。
