title: What happens to your brain on the way to Mars.
abstract: As NASA prepares for the first manned spaceflight to Mars, questions have surfaced concerning the potential for increased risks associated with exposure to the spectrum of highly energetic nuclei that comprise galactic cosmic rays. Animal models have revealed an unexpected sensitivity of mature neurons in the brain to charged particles found in space. Astronaut autonomy during long-term space travel is particularly critical as is the need to properly manage planned and unanticipated events, activities that could be compromised by accumulating particle traversals through the brain. Using mice subjected to space-relevant fluences of charged particles, we show significant cortical- and hippocampal-based performance decrements 6 weeks after acute exposure. Animals manifesting cognitive decrements exhibited marked and persistent radiation-induced reductions in dendritic complexity and spine density along medial prefrontal cortical neurons known to mediate neurotransmission specifically interrogated by our behavioral tasks. Significant increases in postsynaptic density protein 95 (PSD-95) revealed major radiation-induced alterations in synaptic integrity. Impaired behavioral performance of individual animals correlated significantly with reduced spine density and trended with increased synaptic puncta, thereby providing quantitative measures of risk for developing cognitive decrements. Our data indicate an unexpected and unique susceptibility of the central nervous system to space radiation exposure, and argue that the underlying radiation sensitivity of delicate neuronal structure may well predispose astronauts to unintended mission-critical performance decrements and/or longer-term neurocognitive sequelae.
authors.affiliation: Department of Radiation Oncology, University of California, Irvine, Irvine, CA 92697-2695, USA.
authors.forename: Vipan K
authors.initials: VK
authors.lastname: Parihar
authors.affiliation: Department of Radiation Oncology, University of California, Irvine, Irvine, CA 92697-2695, USA.
authors.forename: Barrett
authors.initials: B
authors.lastname: Allen
authors.affiliation: Department of Radiation Oncology, University of California, Irvine, Irvine, CA 92697-2695, USA.
authors.forename: Katherine K
authors.initials: KK
authors.lastname: Tran
authors.affiliation: Department of Radiation Oncology, University of California, Irvine, Irvine, CA 92697-2695, USA.
authors.forename: Trisha G
authors.initials: TG
authors.lastname: Macaraeg
authors.affiliation: Department of Radiation Oncology, University of California, Irvine, Irvine, CA 92697-2695, USA.
authors.forename: Esther M
authors.initials: EM
authors.lastname: Chu
authors.affiliation: Department of Radiation Oncology, University of California, Irvine, Irvine, CA 92697-2695, USA.
authors.forename: Stephanie F
authors.initials: SF
authors.lastname: Kwok
authors.affiliation: Department of Radiation Oncology, University of California, Irvine, Irvine, CA 92697-2695, USA.
authors.forename: Nicole N
authors.initials: NN
authors.lastname: Chmielewski
authors.affiliation: Department of Radiation Oncology, University of California, Irvine, Irvine, CA 92697-2695, USA.
authors.forename: Brianna M
authors.initials: BM
authors.lastname: Craver
authors.affiliation: Department of Radiation Oncology, University of California, Irvine, Irvine, CA 92697-2695, USA.
authors.forename: Janet E
authors.initials: JE
authors.lastname: Baulch
authors.affiliation: Department of Radiation Oncology, University of California, Irvine, Irvine, CA 92697-2695, USA.
authors.forename: Munjal M
authors.initials: MM
authors.lastname: Acharya
authors.affiliation: Department of Health Physics and Diagnostic Sciences, University of Nevada, Las Vegas, Las Vegas, NV 89154, USA.
authors.forename: Francis A
authors.initials: FA
authors.lastname: Cucinotta
authors.affiliation: Department of Radiation Oncology, University of California, Irvine, Irvine, CA 92697-2695, USA.
authors.forename: Charles L
authors.initials: CL
authors.lastname: Limoli