Neuroimmune response and sleep studies after whole body irradiation with high-LET particles

in order to investigate the biological effects of galactic rays on astronaut cerebral functions after space flight, mice were exposed to different heavy ions (HZE) in whole-body conditions at doses comparable to the galactic flux: C-12, O-16 and Ne-20 (95 MeV/u, at 42-76 mGy). Animals were also exposed to 42 mGy of Co-60 radiation for comparison with HZE. The neuroimmune response, evaluated by interleukin-I (IL-1) measurement, showed that this cytokine was produced 3 h after irradiation by O-16 or Co-60. In contrast, neither C-12 (56.7 mGy) nor Ne-20 (76 mGy) induced IL-1 production. However, immunohistochemical staining of C-12-irradiated mouse brain tissue showed 2 months later a marked inflammatory reaction in the hippocampus and a diffuse response in parenchyma. Sleep studies were realized before and after exposure to 42 mGy of O-16 and 76 mGy of Ne-20: only the Ne-20 radiation displayed a small effect. A slight decrease in paradoxical sleep, corresponding to a reduction in the number of episodes of paradoxical sleep, was manifested between 8 and 22 days after exposure. Exposure to C-12 and O-16 induced no changes either in cellularity of spleen or thymus, or in caspase 3 activity (as much as four months after irradiation). Taken together, these data indicate that the CNS could be sensitive to heavy ions and that responses to HZE impact depend on the nature of the particle, the dose threshold and the time delay to develop biological processes. Differences in responses to different HZE highlight the complex biological phenomena to which astronauts are submitted during space flight. (C) 2009 COSPAR. Published by Elsevier Ltd. All rights reserved.