Effects of 15 cGy GCRsim Space Radiation on Conditioned Fear and Stress Responses in Stress Resilient and Vulnerable Rats: Implications for Astronaut Sleep, Health and Mission Performance

The long durations of the proposed NASA Mars missions will expose astronauts to space radiation (SR), which has detrimental effects on brain function that could impair their ability to appropriately cope with any additional unexpected stress they may encounter. Space radiation could also alter stress-related learning and effects may vary with individual differences in stress resilience and vulnerability. Therefore, determining how astronauts may respond to unforeseen mission-related stressors will be crucial for understanding and mitigating factors that would threaten mission success. In this study, we assessed freezing behavior, body temperature [as a measure of stress-induced hyperthermia (SIH)], and sleep quality and duration in rats exposed to radiation and trained in contextual conditioned fear (CF) using footshock stress. We also assessed whether responses differed in stress resilience and vulnerability phenotypes in our established model based on different sleep responses to stress. Space radiation resulted in increased freezing, increased SIH and significant alterations in sleep with some variations in stress resilience and vulnerability rats. Space radiation also reduced extinction of fear-conditioned freezing, SIH, and sleep responses. The data are discussed in the context of the impact of space radiation on stress-induced alterations in emotional learning and its potential impact on astronaut health and mission performance.