Abstract
Astronauts on interplanetary missions - such as to Mars - will be exposed to space radiation, a spectrum of highly-charged, fast-moving particles that includes 56Fe and 28Si. Earth-based preclinical studies show space radiation decreases rodent performance in low- and some high-level cognitive tasks. Given astronaut use of touchscreen platforms during training and space flight and given the ability of rodent touchscreen tasks to assess functional integrity of brain circuits and multiple cognitive domains in a non-aversive way, here we exposed 6-month-old C57BL/6J male mice to whole-body space radiation and subsequently assessed them on a touchscreen battery. Relative to Sham treatment, 56Fe irradiation did not overtly change performance on tasks of visual discrimination, reversal learning, rule-based, or object-spatial paired associates learning, suggesting preserved functional integrity of supporting brain circuits. Surprisingly, 56Fe irradiation improved performance on a dentate gyrus-reliant pattern separation task; irradiated mice learned faster and were more accurate than controls. Improved pattern separation performance did not appear to be touchscreen-, radiation particle-, or neurogenesis-dependent, as 56Fe and 28Si irradiation led to faster context discrimination in a non-touchscreen task and 56Fe decreased new dentate gyrus neurons relative to Sham. These data urge revisitation of the broadly-held view that space radiation is detrimental to cognition.
Highlights
Astronauts on interplanetary missions - such as to Mars - will be exposed to space radiation, a spectrum of highly-charged, fast-moving particles that includes 56Fe and 28Si
Given the power of touchscreen testing, it is surprising that it is not known how whole body exposure of mature rodents to HZE particles influences performance on a battery of rodent touchscreen tests. This is notable as the touchscreen platform permits analysis of many higher cognitive functions - such as pattern separation - which are part of the astronaut’s mission-critical skill set yet which have not been preclinically assessed for their sensitivity to space radiation
To address these major knowledge gaps, mature C57BL/6J male mice received either Sham irradiation (IRR) or whole body 56Fe particle IRR and were assessed on a battery of touchscreen cognitive tasks to assess complex learning, cognitive flexibility, visuospatial learning, and stimulus-response habit learning[39,41,42,43]. This touchscreen battery revealed an unexpected finding: improved pattern separation in 56Fe IRR vs. Sham mice. To assess whether this improvement was dependent on touchscreen testing or on 56Fe IRR, we assessed separate cohorts of 56Fe IRR vs. Sham mice for pattern separation performance in a non-touchscreen task, contextual discrimination fear conditioning (CDFC), and assessed the impact of 28Si IRR vs. Sham on CDFC
Summary
Astronauts on interplanetary missions - such as to Mars - will be exposed to space radiation, a spectrum of highly-charged, fast-moving particles that includes 56Fe and 28Si. Given the power of touchscreen testing, it is surprising that it is not known how whole body exposure of mature rodents to HZE particles influences performance on a battery of rodent touchscreen tests This is notable as the touchscreen platform permits analysis of many higher cognitive functions - such as pattern separation - which are part of the astronaut’s mission-critical skill set yet which have not been preclinically assessed for their sensitivity to space radiation. To address these major knowledge gaps, mature C57BL/6J male mice received either Sham irradiation (IRR) or whole body 56Fe particle IRR and were assessed on a battery of touchscreen cognitive tasks to assess complex learning, cognitive flexibility, visuospatial learning, and stimulus-response habit learning[39,41,42,43]. These data show whole body exposure to HZE particles is not detrimental to high level cognition in mature mice and enhances performance in certain mission-critical tasks, such as pattern separation
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