Abstract
A limitation of simulated space radiation studies is that radiation exposure is not the only environmental challenge astronauts face during missions. Therefore, we characterized behavioral and cognitive performance of male WAG/Rij rats 3 months after sham-irradiation or total body irradiation with a simplified 5-ion mixed beam exposure in the absence or presence of simulated weightlessness using hindlimb unloading (HU) alone. Six months following behavioral and cognitive testing or 9 months following sham-irradiation or total body irradiation, plasma and brain tissues (hippocampus and cortex) were processed to determine whether the behavioral and cognitive effects were associated with long-term alterations in metabolic pathways in plasma and brain. Sham HU, but not irradiated HU, rats were impaired in spatial habituation learning. Rats irradiated with 1.5 Gy showed increased depressive-like behaviors. This was seen in the absence but not presence of HU. Thus, HU has differential effects in sham-irradiated and irradiated animals and specific behavioral measures are associated with plasma levels of distinct metabolites 6 months later. The combined effects of HU and radiation on metabolic pathways in plasma and brain illustrate the complex interaction of environmental stressors and highlights the importance of assessing these interactions.
Highlights
The space environment consists of multiple charged particles that may impact brain function during and after exploratory missions
When activity levels were analyzed for two subsequent days in the open field (Figure 2A), there was no main effect of radiation (Figure 2C) or hindlimb unloading (HU), or a radiation × HU interaction (Figure 2D)
The activity was lower in the T than A trials in sham-irradiated animals (t = 2.095, p = 0.0484, 2-tailed) without HU and there was a trend toward the activity being lower in the T than A trials in rats irradiated with 1.5 Gy of simGCRsim alone (t = 1.948, p = 0.0774, 2tailed)
Summary
The space environment consists of multiple charged particles that may impact brain function during and after exploratory missions. Various studies have reported effects of limited types of simulated space radiation on brain function in mice (Raber et al, 2015; Impey et al, 2016; Raber et al, 2016; Acharya et al, 2019; Raber et al, 2019; Torres et al, 2019) and rats (Rabin et al, 2015; Britten et al, 2017; Mange et al, 2018). Space radiation and microgravity might interact in their effects on brain function
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