Krasnov I B
Institute of Biomedical Problems, Moscow, Russia.
Adv Space Biol Med. 1994;4:85-110.
This review shows that morphological studies of the central, peripheral and autonomic nervous system of animals exposed to altered gravity yield data which are extremely significant for our understanding of the mechanisms of adaptation of the nervous system, and of the mammalian organism as a whole, to increased and decreased loading. Neuromorphological studies, correlating structure and function, indicate a decreased activity in weightlessness for spinal ganglia neurons and motoneurons of the spinal cord, as well as the neurons of the hypothalamic nuclei producing arginine vasopressin and growth hormone releasing factor. Structural changes of the somatosensory cortex and spinal ganglia suggest a decreased afferent flow to the somatosensory cortex in microgravity. The results characterize the mechanisms of structural adaptation to a decreased afferent flow in microgravity by the neurons in the hemisphere cortex and brain stem nuclei. There is also morphological evidence for an increased sensitivity of the otolith apparatus and for the development of a hyponoradrenergic syndrome in weightlessness. These studies have shown that both microgravity and the simulation of microgravity effects by tail suspension-induced structural changes in the large neurons of lumbar spinal ganglia and motoneurons of the lumbar spinal cord, which occur under conditions of nerve cell hypoactivity. The structural changes, and consequently the development of neuron hypoactivity, are expressed more extensively after microgravity than after tail suspension for the same length of time. The influence of microgravity and hypergravity on animals is expressed by opposing changes in nervous tissue structure in the spinal ganglia, spinal cord, and nodulus of cerebellar vermis. These changes indicate neuron hypoactivity under microgravity and neuron hyperactivity under 2 G. Morphological assessment of the functional state of other structures of the brain under hypergravity will require further study. Can all structural changes which occur in nerve tissue under microgravity or under hypergravity be explained on the basis of increased or decreased activity of its structural elements? The presently available data regarding the correlation of structure and functional state of cells in brain and spinal cord suggest an affirmative answer. Ultrastructural studies of the nodular cortex of the cerebellum in rats after different duration spaceflights provide what appears to be a convincing example. However, it should be pointed out that the criteria for the morphological assessment of the functional state of single nerve cells will certainly be different from those for groups of neurons connected in a nerve cell network.(ABSTRACT TRUNCATED AT 400 WORDS)
本综述表明，对处于改变重力环境下的动物的中枢、外周和自主神经系统进行形态学研究所得出的数据，对于我们理解神经系统以及整个哺乳动物机体适应负荷增加和减少的机制极为重要。将结构与功能相关联的神经形态学研究表明，在失重状态下，脊髓神经节神经元、脊髓运动神经元以及产生精氨酸加压素和生长激素释放因子的下丘脑核神经元的活性降低。体感皮层和脊髓神经节的结构变化表明，在微重力环境下，流向体感皮层的传入信息流减少。这些结果描述了半球皮层和脑干核中的神经元在微重力环境下对传入信息流减少进行结构适应的机制。也有形态学证据表明，在失重状态下耳石器官的敏感性增加以及出现低去甲肾上腺素能综合征。这些研究表明，微重力以及通过尾部悬吊模拟微重力效应，都会导致腰脊髓神经节的大神经元和腰脊髓运动神经元发生结构变化，这些变化发生在神经细胞活动不足的情况下。在相同时长下，微重力作用后结构变化以及由此导致的神经元活动不足的发展，比尾部悬吊后更为广泛。微重力和超重对动物的影响表现为脊髓神经节、脊髓和小脑蚓部小结的神经组织结构出现相反的变化。这些变化表明，在微重力环境下神经元活动不足，而在2G重力环境下神经元活动过度。超重状态下对大脑其他结构功能状态的形态学评估还需要进一步研究。在微重力或超重状态下神经组织中发生的所有结构变化，能否基于其结构元件活性的增加或减少来解释呢？目前关于大脑和脊髓中细胞结构与功能状态相关性的现有数据给出了肯定的答案。对经历不同时长太空飞行的大鼠小脑小结皮层进行的超微结构研究似乎提供了一个有说服力的例子。然而，应该指出的是，对单个神经细胞功能状态进行形态学评估的标准肯定与神经细胞网络中相连神经元群体的评估标准不同。（摘要截选至400词）
