Cosmic radiation exposure and persistent cognitive dysfunction.

Vipan K Parihar,Chongshan Caressi,Richard A Britten,Charles L Limoli,Barrett D Allen,Janet E Baulch,Nicole N Chmielewski,Katherine K Tran,Stephanie Kwok,Esther Chu,Munjal M Acharya,Erich Giedzinski

doi:10.1038/srep34774

Abstract

The Mars mission will result in an inevitable exposure to cosmic radiation that has been shown to cause cognitive impairments in rodent models, and possibly in astronauts engaged in deep space travel. Of particular concern is the potential for cosmic radiation exposure to compromise critical decision making during normal operations or under emergency conditions in deep space. Rodents exposed to cosmic radiation exhibit persistent hippocampal and cortical based performance decrements using six independent behavioral tasks administered between separate cohorts 12 and 24 weeks after irradiation. Radiation-induced impairments in spatial, episodic and recognition memory were temporally coincident with deficits in executive function and reduced rates of fear extinction and elevated anxiety. Irradiation caused significant reductions in dendritic complexity, spine density and altered spine morphology along medial prefrontal cortical neurons known to mediate neurotransmission interrogated by our behavioral tasks. Cosmic radiation also disrupted synaptic integrity and increased neuroinflammation that persisted more than 6 months after exposure. Behavioral deficits for individual animals correlated significantly with reduced spine density and increased synaptic puncta, providing quantitative measures of risk for developing cognitive impairment. Our data provide additional evidence that deep space travel poses a real and unique threat to the integrity of neural circuits in the brain.

Highlights

Longer term and show convincingly that very low doses of charged particles can compromise cognitive performance at 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
Multiple comparison testing showed that exposure to 30 cGy 48Ti significantly reduced recognition memory (P = 0.03), while 5 cGy 48Ti or 16O and 30 cGy 16O had no effect on memory retention (Fig. 1a)
Individual analysis showed that 48Ti 30 cGy irradiation impaired object in place (OiP) memory (P < 0.004), while 5 cGy 48Ti or 16O and 30 cGy 16O again had no effect on spatial memory function

Summary

Introduction

Longer term and show convincingly that very low doses of charged particles can compromise cognitive performance at 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. The inability of these irradiated animals to react to novelty after exposure to space relevant doses of cosmic radiation demonstrates the persistence of cognitive decrements in learning and memory.

Results

Conclusion