Abstract
Future long-duration space missions will involve travel outside of the Earth’s magnetosphere protection and will result in astronauts being exposed to high energy and charge (HZE) ions and protons. Exposure to this type of radiation can result in damage to the central nervous system and deficits in numerous cognitive domains that can jeopardize mission success. Social processing is a cognitive domain that is important for people living and working in groups, such as astronauts, but it has received little attention in terms of HZE ion exposure. In the current study, we assessed the effects of whole-body oxygen ion (16O; 1000 MeV/n) exposure (1 or 10 cGy) on social odor recognition memory in male Long-Evans rats at one and six months following exposure. Radiation exposure did not affect rats’ preferences for a novel social odor experienced during Habituation at either time point. However, rats exposed to 10 cGy displayed short and long-term deficits in 24-h social recognition. In contrast, rats exposed to 1 cGy only displayed long-term deficits in 24-h social recognition. While an age-related decrease in Ki67+ staining (a marker of cell proliferation) was found in the subventricular zone, it was unaffected by radiation exposure. At one month following exposure, plasma KC/GRO (CXCL1) levels were elevated in the 1 cGy rats, but not in the 10 cGy rats, suggesting that peripheral levels of this cytokine could be associated with intact social recognition at earlier time points following radiation exposure. These results have important implications for long-duration missions and demonstrate that behaviors related to social processing could be negatively affected by HZE ion exposure.
Highlights
In the near future, astronauts will spend more prolonged periods in space, venturing to the moon and Mars
While we showed no radiation-induced change in Ki67+ staining in the subventricular zone (SVZ) at six months, Krukowski and colleagues [8] showed a significant correlation between social recognition memory and plasma immune cell levels, which the authors suggested as a possible biomarker of deficits in social processing
The goals of this study were to (1) determine if these lower doses of 16O ions result in shortand/or long-term deficits in social recognition, (2) determine if a threshold dose of 16O ions exists for inducing social recognition deficits, (3) determine if these changes are associated with alterations in cell proliferation in the SVZ at an earlier time point, and (4) assess changes in inflammatory cytokines that could be used as potential biomarkers indicative of deficits in social processing
Summary
Astronauts will spend more prolonged periods in space, venturing to the moon and Mars. Current spacecraft provide limited protection from GCR exposure, which includes alpha particles, high energy, charge (HZE) particles, and protons [2] Exposure to these particles has already been shown to have deleterious effects on animals’ central nervous system (CNS), and could result in impaired neurobehavioral performances in humans, jeopardizing astronaut health and mission success [3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]. Decreased preference for the first novel odor on the latter Recognition Test, experienced during Habituation 24-h earlier, is indicative of a social recognition memory deficit
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