Effects of 16O charged-particle irradiation on cognition, hippocampal morphology and mutagenesis in female mice.

The effects of radiation in space on human cognition are a growing concern for NASA scientists and astronauts as the possibility for long-duration missions to Mars becomes more tangible. Oxygen (16O) radiation is of utmost interest considering that astronauts will interact with this radiation frequently. 16O radiation is a class of galactic cosmic ray (GCR) radiation and also present within spacecrafts. Whole-body exposure to high linear energy transfer (LET) radiation has been shown to affect hippocampal-dependent cognition. To assess the effects of high-LET radiation, we gave 6-month-old female C57BL/6 mice whole-body exposure to 16O at 0.25 or 0.1 Gy at NASA's Space Radiation Laboratory. Three months following irradiation, animals were tested for cognitive performance using the Y-maze and Novel Object Recognition paradigms. Our behavioral data shows that 16O radiation significantly impairs object memory but not spatial memory. Also, dendritic morphology characterized by the Sholl analysis showed that 16O radiation significantly decreased dendritic branch points, ends, length, and complexity in 0.1 Gy and 0.25 Gy dosages. Finally, we found no significant effect of radiation on single nucleotide polymorphisms in hippocampal genes related to oxidative stress, inflammation, and immediate early genes. Our data suggest exposure to heavy ion 16O radiation modulates hippocampal neurons and induces behavioral deficits at a time point of three months after exposure in female mice.