Differential Impact of Social Isolation and Space Radiation on Behavior and Motor Learning in Rats

Abstract

Future missions to Mars will expose astronauts to several physical and psychological challenges, including exposure to space radiation (SR) and periods of social isolation (SI). Each of these stressors, in addition to mission demands, can affect physical and mental health and potentially negatively impact sleep. The effects of inflight stressors may vary with duration and time course, may be additive or compounding, and may vary with individual differences in stress resilience and vulnerability. Determining how individual differences in resilient and vulnerable phenotypes respond to these mission-related stressors and their interactions with sleep will be crucial for understanding and mitigating factors that can impair performance and damage health. Here, we examined the single and compound effects of ground-based analogs of SI and SR on sensorimotor performance on the balance beam (BB) in rats. We also assessed emotional responses during testing on the BB and assessed whether sensorimotor performance and emotion varied with individual differences in stress resiliency using our established animal model in which stress produces different effects on sleep. Results showed differential motor performance and emotion in the BB task between SI and SR, and these varied based on resilient and vulnerable phenotypes. These findings demonstrate that identifying individual responses to stressors that can impact sensorimotor ability and behavior necessary to perform mission-related tasks will be of particular importance for astronauts and future missions. Should similar effects occur in humans, there may be considerable inter-individual variability in the impact that flight stressors have on the mental health of astronauts and their ability to perform mission-related tasks.

Alterations in Blood–Brain Barrier Integrity and Lateral Ventricle Differ in Rats Exposed to Space Radiation and Social Isolation

“…Interestingly, some of the deficits observed in the SR group were marginally rescued in the DFS group. We have also observed a similar effect in some behavioral tasks [17], though the mechanisms are not yet known. Despite this partial rescue, compared to the Control and SI groups, the DFS animals still had a significant reduction in structural integrity.…”

“…BBB dysfunction has been linked to the pathogenesis of multiple neuropsychiatric disorders [16,33,34] and to more severe anxiety symptoms [16,34]. Indeed, the SR and DFS animals in this study exhibited increased BBB damage as well as increased anxiety across multiple behavioral paradigms [17,35]. Elevated anxiety has been previously reported in animals exposed to GCR [4,36].…”

“…Previous studies have shown that SI alone can cause astrocytes to become hyperactive, and this change in astrocyte function by SI has been linked to suppressed memory formation [29]. In our previously published work [17], SI animals experienced blunted learning in sensorimotor tasks, though this was not a chronic impairment. Further investigation into these alterations is required to fully understand the effects of SI on astrocytes.…”

“…Male, outbred, Wistar strain rats (8-9 months old at the time of study, n = 4-5 per group) obtained from Hilltop Lab Animals, Inc. (Scottdale, PA, USA) were used in this study [17]. The rats were either subjected to SI (visual barriers between cages) or individually housed (as a Control group).…”

“…The rats were either subjected to SI (visual barriers between cages) or individually housed (as a Control group). SI began at least eight weeks prior to experimentation and was maintained throughout the study as previously described [17]. Separate groups of rats received a single dose of SR (15 cGy simplified 5-ion galactic cosmic radiation (GCRsim), Brookhaven National Laboratory (BNL); Long Island, NY) and were either individually housed or subjected to SI (dual flight stressors (DFS)).…”