Adaptive Problem Solving in Female Rats Exposed to Space Radiation
Abstract
Introduction: The upcoming long-duration missions to the Moon and Mars will pose significant challenges to the physical and mental health of astronauts compared to the ISS missions. Astronauts will be exposed to spaceflight stressors, including space radiation (SR), which have been demonstrated to impact CNS functionality. A growing body of evidence from ground-based rodent studies, including the Associative Recognition Memory and Interference Touchscreen (ARMIT) test, indicates that even low doses of SR can impair various cognitive functions. The ARMIT was designed to determine if adaptive problem solving are affected by changing associative cues presented over multiple learning sessions under time constraints to obtain a reward. However, astronauts travelling to deep space will be exposed to double the radiation during their journey to and from their destination. This study aims to replicate the ARMIT in rats subjected to doubled doses of GCRSim irradiation to assess whether an additional dose of radiation impacts on executive function, working memory, and long-term memory.
Methods: The doubly irradiated rats were part of a subset previously exposed to a low dose (10 cGy) cocktail of 6 ions simulating the galactic cosmic ray spectrum (GCRSim). These rats were initially screened on an attentional set shifting (ATSET) task to provide a measure of executive function and had participated in a separate study on risk taking propensity (RTP). After their second irradiation, the rats underwent gradual training for the ARMIT task. They were first familiarized with the C1.1 configuration for seven consecutive days, to ensure that the rats have a strong memory of the location of these holes. Thereafter the rats are then presented sequentially with the C.1.1; followed by C.1.2; then C.1.3. If a rat fails to correctly chose the rewarded hole in C.1.1 or C.1.2, the chamber light is switched on (aversive stimuli) during a 20 s time-out period, the chamber light is then switched off and the sequence restarts at the C.1.1 stage. The rats are presented with the C.1.1 to C.1.3 transition task for three consecutive days.
Results: This study determined that GCRSim exposed rats tend to pick the incorrect choice more often when transitioned to the C1.2 format than the sham rats. There was no statistical difference in C1.3 tasks. However, this may be due to the low number of successfully completed C1.2 trials. Additionally, an analysis of the response time revealed that the doubly irradiated rats took significantly longer to make a selection than did the shams, suggesting a SR-induced loss of processing speed.
Conclusion: This study provides preliminary data that doubly irradiated GCRSim rats show a trend in performance decrements in the complex ARMIT task as compared to the sham rats. These irradiated rats exhibit a decline in processing speed, similar to what was observed in the RTP test, which may contribute to their diminished ability to adapt to new formats of the ARMIT.