Exposure to chronic, low dose radiation — the conditions present in deep space — causes neural and behavioral impairments in mice, researchers report in eNeuro.
These results highlight the pressing need to develop safety measures to protect the brain from radiation during deep space missions as astronauts prepare to travel to Mars.
Radiation is known to disrupt signaling among other processes in the brain.
However, previous experiments used short-term, higher dose-rate exposures of radiation, which does not accurately reflect the conditions in space.
To investigate how deep space travel could affect the nervous system, Charles Limoli and colleagues at the University of California, Irvine, Stanford University, Colorado State University and the Eastern Virginia School of Medicine exposed mice to chronic, low dose radiation for six months.
They found that the radiation exposure impaired cellular signaling in the hippocampus and prefrontal cortex, resulting in learning and memory impairments.
They also observed increased anxiety behaviors, indicating that the radiation also impacted the amygdala.
Radiation exposure alters the electrophysiological properties of neurons in the hippocampus. The image is credited to Acharya et al., eNeuro 2019.
The researchers predict that during a deep space mission approximately one in five astronauts would experience anxiety-like behavior and one in three would experience certain levels of memory impairments.
Additionally, the astronauts may struggle with decision-making.
The exploration of space presents countless challenges to the ingenuity of humankind. Vast distances separate our planet from those within and beyond our solar system and necessitate further advances in engineering to minimize the deep space travel time and in biology to ameliorate as many of the adverse effects of prolonged space travel as possible.
While many threats to the success of such extraterrestrial missions have been popularized in the media and entertainment industries, one area that has not received such attention are the human health risks associated with cosmic radiation exposure.
Charged particles that represent the GCR are a component of cosmic radiation that is deflected from the surface of the Earth by its protective magnetosphere.
Due to their high energy, multiple charged particle species can penetrate the hull of a spacecraft and tissues of the body depositing a trail of dense ionizations along particle trajectories3.
In the body, the ionization events resulting from these interactions damage a variety of critical molecular targets, producing complex lesions that compromise cellular repair processes and protract the recovery of irradiated tissues.
Recovery from cosmic radiation injury is further confounded by secondary ionizations caused by delta rays that emanate from primary particle tracks, considerably increasing the range and amount of cellular damage4,5.
NASA and international space agencies have recognized the potential health concerns associated with cosmic radiation exposure6, and based on recent evidence derived from rodent models have an increased awareness of the potential neurocognitive complications that could compromise mission critical activities or long term cognitive health7.
Despite our long-standing knowledge that patients subjected to cranial radiotherapy for the control of brain malignancies develop severe and progressive cognitive deficits8,9, the total doses and radiation types used in the clinic differ significantly from those encountered in space.
Compelling evidence has now demonstrated the adverse effects of space-relevant fluences of charged particles on cognition7,10,11,12,13,14,15, and our studies, have linked functional behavioral decrements to the erosion of neuronal structure and synaptic integrity in specific regions of the brain7,16.
Importantly, these changes were found to persist 6 weeks following acute exposure of rodents to charged particles, and showed little or no signs of recovery, regeneration or repair7.
Here, we extend our studies longer term and show convincingly that very low doses of charged particles can compromise cognitive performance at not only 12, but 24 weeks after acute exposure, effects that are associated with reductions in dendritic complexity, changes in synaptic protein levels and elevations in neuroinflammation.
Calli McMurray – SfN
The image is credited to Acharya et al., eNeuro 2019.
Original Research: Closed access
“New concerns for neurocognitive function during deep space exposures to chronic, low dose rate, neutron radiation”. M. M. Acharya, J. E. Baulch, P. M. Klein, A. A. D. Baddour, L. A. Apodaca, E.A. Kramár, L. Alikhani, C. Garcia, M. C. Angulo, R. S. Batra, C. M. Fallgren, T. B. Borak, C. E. L. Stark, M. A. Wood, R. A. Britten, I. Soltesz and C. L. Limoli.
Nature Biomedical Engineering. doi:10.1523/ENEURO.0094-19.20191