Bruce L L, Fritzsch B
Creighton University, Department of Biomedical Sciences, Omaha, NE 68178, USA.
J Gravit Physiol. 1997 Jul;4(2):P59-62.
Existing experimental embryological data suggests that the vestibular system initially develops in a very rigid and genetically controlled manner. Nevertheless, gravity appears to be a critical factor in the normal development of the vestibular system that monitors position with respect to gravity (saccule and utricle). In fact several studies have shown that prenatal exposure to microgravity causes temporary deficits in gravity-dependent righting behaviors, and prolonged exposure to hypergravity from conception to weaning causes permanent deficits in gravity-dependent righting behaviors. Data on hypergravity and microgravity exposure suggest some changes in the otolith formation during development, in particular the size although these changes may actually vary with the species involved. In adults exposed to microgravity there is a change in the synaptic density in the optic sensory epithelia suggesting that some adaptation may occur there. However, effects have also been reported in the brainstem. Several studies have shown synaptic changes in the lateral vestibular nucleus and in the nodulus of the cerebellum after neonatal exposure to hypergravity. We report here that synaptogenesis in the medial vestibular nucleus is retarded in developing rat embryos that were exposed to microgravity from gestation days 9 to 19.
现有的实验胚胎学数据表明，前庭系统最初以一种非常严格且受基因控制的方式发育。然而，重力似乎是前庭系统正常发育的关键因素，前庭系统负责监测相对于重力的位置（球囊和椭圆囊）。事实上，多项研究表明，产前暴露于微重力环境会导致依赖重力的翻正行为出现暂时缺陷，而从受孕到断奶长期暴露于超重力环境会导致依赖重力的翻正行为出现永久性缺陷。关于超重力和微重力暴露的数据表明，发育过程中耳石形成会发生一些变化，特别是大小，尽管这些变化实际上可能因所涉及的物种而异。在暴露于微重力环境的成年个体中，视觉感觉上皮的突触密度会发生变化，这表明那里可能会发生一些适应性变化。然而，脑干中也有相关影响的报道。多项研究表明，新生动物暴露于超重力环境后，外侧前庭核和小脑小结会出现突触变化。我们在此报告，在妊娠第9天至19天暴露于微重力环境的发育中大鼠胚胎中，内侧前庭核的突触发生受到抑制。
