Age as a factor in the responsiveness of the organism to the disruption of cognitive performance by exposure to HZE particles differing in LET

Authors: RABIN, BERNARD - University Of Maryland; CARRIHILL-KNOLL, KIRSTY - University Of Maryland; BARTON, KERI - University Of Maryland; Miller, Marshall; Shukitt-Hale, Barbara

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 11/5/2016
Publication Date: 1/23/2017
Citation: Rabin, B.M., Carrihill-Knoll, K., Barton, K., Miller, M.G., Shukitt Hale, B. 2017. Age as a factor in the responsiveness of the organism to the disruption of cognitive performance by exposure to HZE particles differing in LET. [Abstract]. NASA Human Research Program Investigators' Workshop, Program #17172.

Interpretive Summary:

Technical Abstract: INTRODUCTION Previous research has shown that the dose of 56Fe particles needed to disrupt cognitive performance decreases as the age at which the subject is irradiated increases. It remains to be established whether a similar relationship would be observed with lower Linear energy transfer (LET) particles. This issue arises because astronauts are likely to be middle-aged and exposure to HZE particles causes accelerated aging. Also, a significant proportion of the radiation dose to which astronauts are likely to be exposed is composed of lower LET particles (4He and 1H), so it is important to know the impact that exposure to these particles has on cognition. METHODS In the first series of experiments, 11- and 15-month old F-344 rats obtained from the National Institute of Aging and 2-month old F-344 rats obtained from Taconic Farms were given head-only exposures to 48Ti particles (500 MeV/n; 1, 10 cGy) or 16-O particles (1000 MeV/n; 0.1, 0.5 cGy). For the second series of experiments 7-week old F-344 rats were obtained from Charles River and maintained at the University of Maryland Baltimore County (UMBC) until shipped to Brookhaven National Laboratory (BNL) at 11 and 16 months of age. Two-month old control rats were obtained from Charles River and shipped directly to BNL by the supplier. All rats were given head only exposure to 4He particles (1000 MeV/n; 0.01, 0.05, 0.10 cGy. Control rats (0 cGy) were taken to the NASA Space Radiation Laboratory (NSRL) and placed into restraining tubes, but not exposed. Following irradiation, all rats were shipped to UMBC and tested for performance on the elevated plus-maze (baseline anxiety) and operant responding on an ascending fixed-ratio schedule (motivation to work for reinforcement and responsiveness to changes in environmental contingencies). The animals that were aged at UMBC were tested twice on the operant task before being shipped to BNL. RESULTS The results indicated that exposing older animals to 48Ti particles, similar to exposure to 56Fe particles, disrupted performance in the elevated plus-maze and the operant task at a lower dose than was required to disrupt performance of younger subjects. A similar age-dependent effect was not observed following exposure to 16-O or 4He particles. DISCUSSION The reasons for the failure to observe an age-dependent change in the threshold dose of lower LET particles are not certain. It is possible that there is a floor effect, i.e., that a specific minimum dose is needed to affect cognitive performance, and because the doses of 16-O and 4He particles needed to affect cognitive performance in young subjects are already so low, a further decrease in dose results in a dose that falls below a critical threshold level. Nonetheless, these results may have implications for some astronauts who may be at a greater risk for cosmic ray-induced disruption of cognitive performance than currently anticipated.