Exposure to interplanetary or space environment has been observed to affect all system of human physiology and anatomy. In this article, the authors have summarized the neurologic compromise expected or encountered from space exposure, the extreme foreign environmental pressure to affect the human species. The negative effects from the radiation of space and micronegativity have been discussed. Exposure to the ionizing radiation fields in space can cause progressive and debilitating effects on the brain such as on cognition including memory, attention, learning , cognitive flexibility, depression and other behavioral disorders leading to changes in CNS microvascular beds, reduction in the structural complexity of neurons and persistent neuroinflammation. Hippocampal and cortical neurons of entorhinal cortex and prefrontal cortex exhibit significant decrease in dendritic complexity, dendritic spine density and immature spine morphologies as well as impaired neurotransmission as a result of multiple pathologies persisting long after exposure. Gene expression changes derived from radiation-induced neuroepigenetic aberrations could elicit several alterations in synaptic protein levels (e.g., disruption in post-synaptic density protein-95) and contribute to the neuroinflammation (e.g, increased number of activated microglia). Studies where experimental mice were exposed to space relevant doses of cosmic radiation have shown increased presence of beta-amyloid and dense fibrillary proteins within the cerebrum. Disruption of CNS functionality may vary depending on radiation quality disparities.
Following up research on long-duration ISS crew members discovered ophthalmologic changes that NASA has termed "vision impairment and intracranial pressure." Moreover, microgravity was suspected to trigger a number of cardiovascular reactions that raised intracranial and intraocular pressures. The vestibular side effects of space and weightlessness can lead to poor balance and proprioceptive properties as well as impairment of blood pressure, heart rate and many more serious downstream effects. Observation of jerk nystagmus, rebound nystagmus and oscillation are observed in the astronauts and cosmonauts following prolonged space-flight.
Furthermore cytoarchitecture of cells has been seen to be impacted by gravitational effects, which results in cytoskeletal fiber shortening, disarray, disruptions in DNA replication, RNA transcription, and protein transport. Experiments have shown that gravitational influences can selectively contribute to differential preferences of stem cells. Microgravitation related decrease in presence of pyruvate dehydrogenase and synuclein beta results in increased oxidative stress and increased evidence of abnormal protein aggregation respectively. Experiments have shown that microgravity related loss of gray matter and white matter tracts can limit the astronaut’s judgment and memory function. After landing of Mars, the atmosphere, terrain and day/night cycle of Mars can interrupt the cognition, performance and circadian rhythm of the space traveller. In addition, the changes in intestinal flora/gut microbiome can have dramatic effects on gastrointestinal physiology with secondary effects on all the organ systems including the CNS.
Reference:
Jandial, R., Hoshide, R., Waters, J. D., & Limoli, C. L. (2018). Space-brain: The negative effects of space exposure on the central nervous system. Surgical neurology international, 9, 9. https://doi.org/10.4103/sni.sni_250_17
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