Influence of a 30-day spaceflight on the structure of motoneurons of the trochlear nerve nucleus in mice

Abstract

During spaceflight and immediately after it, adaptive neuroplastic changes occur in the sensorimotor structures of the central nervous system, which are associated with changes of mainly vestibular and visual signals. It is known that the movement of the eyeball in the vertical direction is carried out by muscles that are innervated by the trochlear nerve (CN IV) and the oculomotor nerve (CN III). To elucidate the cellular processes underlying the atypical vertical nystagmus that occurs under microgravity conditions, it seems necessary to study the state of these nuclei in animals in more detail after prolonged space flights. In this work, we carried out a qualitative and quantitative light-optical and ultrastructural analysis of the nuclei of the trochlear nerve in mice after a 30-day flight on the Bion-M1 biosatellite and followed by a stay for 13-14 hours under the influence of the Earth's gravity after landing. As a result, it was shown that the motoneurons in the nucleus of the trochlear nerve changed their morphology under the influence of microgravity. Cell nuclei of the motoneurons had a more simplified rounded shape than in the control. In addition, the dendrites of these motoneurons significantly reorganized geometry and orientation under microgravity conditions; the number of dendritic branches has been increased to enhance the reduced signal flow. Apparently, to ensure such plastic changes, the number and size of mitochondria in the soma of motoneurons and in axons coming from the vestibular structures increased. In addition, the experimental animals showed an increase in the size of the cisterns of the rough and smooth endoplasmic reticulum in comparison with the control group of animals left on Earth, for which the environmental conditions in the spacecraft were reproduced.Thus, the main role in the adaptation of the trochlear nucleus to microgravity conditions, apparently, belongs to the dendrites of motoneurons, which rearrange their structure and function to enhance the flow of sensory information. These results are useful for the development of new, more effective means to facilitate the stay and work of space travelers in a long spaceflight..

Human cranial bone-derived mesenchymal stem cells cultured under microgravity can improve cerebral infarction in rats

“…Experiments examining changes in mouse brain tissue in actual cosmic space have reported increased dendritic spines of motoneurons, increased number and size of axonal mitochondria, changes in synaptic morphology, and increased synaptic transmission. 23,24 Experiments analyzing changes in bMSCs exposed to an MG environment by spaceflight showed downregulation of cytoskeletal genes and cytoskeleton changes, suggesting that the expression of genes involved in neurogenesis is altered, promoting the activation of neurogenic processes such as nervous system development, differentiating neuron morphogenesis, and increased synaptic transmission. 9,26 Regarding the effect of MG environment on the cytoskeleton, Ulbrich et al and Doty et al reported a decrease in extracellular matrix production in culture experiments with bone and cartilage cells and tumor cells under MG. 27,28 In a parabolic flight experiment, the cytoskeletal systems such as actin and cytokeratin exposed to an MG environment were found to be altered and cells were observed to leave their adherent state, resulting in gene expression changes.…”

“…In recent years, many experiments have been conducted in space, suggesting that an MG environment is a useful tool for cell culture in cell therapy. 9,10,23,24 However, since experiments in space are highly expensive, we used "Gravite," a multi-directional gravity control device developed by our group, to simulate MG. 1,11,25 In vitro experiments showed that genes related to cell proliferation, angiogenesis, neurotrophy, anti-apoptosis, nerve and synapse organization, and cell differentiation inhibition were significantly upregulated in the miRNA-MG group than in the miRNA-1G group. In contrast, genes promoting microtubule and extracellular matrix formation, cell adhesion, cell signaling, and cell differentiation were significantly downregulated in the miRNA-MG group compared with the miRNA-1G group.…”

The mitochondrial proteomic changes of rat hippocampus induced by 28-day simulated microgravity

“…Previously, Mikheeva et al reported that after 30 days flight on the Bion-M1 biosatellite, the number and size of mitochondria in the soma of motoneurons and in axons coming from the vestibular structures increased in mouse [ 22 ]. Tan et al showed that when compared with cells maintained under normal gravity, BL6-10 cells treated with simulating microgravity showed higher mitochondrial content and more abundant cytoplasmic mitochondria, and significantly reduced glycolytic metabolism [ 23 ].…”

Temporal effects of three-dimensional clinostat treatment on bone and serum metabolome in C57BL/J mice: a new method of simulating microgravity effect

“…During long-term space operations 61 , microgravity may affect intracranial physiological functions, such as intracranial pressure, spinal and neurocognitive performance, and brain edema induced by microgravity 92 , resulting in neuro-ocular syndrome 62 . Irina Mikheeva et.al observed 93 that 30-day space ight had a signi cant effect on the structure of motoneurons of the trochlear nerve nucleus in mice. Xiao Wen Mao et.al found that the mice exposure to the space ight environment (Space Shuttle Atlantis, STS-135, 13 day) could induce signi cant changes in protein expression related to neuronal structure and metabolic function.…”