Objective:To explore the produced-radiation brain damage in simulated solar particle events and to provide evidence for health risk assessment of radiation from manned deep space exploration.Methods:According to the main characteristics of solar particle events, mice were treated with total body irradiation (TBI) with 90 MeV protons in a dose range from 0.1 to 2 Gy, with irradiation dose of 0, 0.1, 0.3, 0.5, 1, 2 Gy, respectively. At 3 and 7 d after irradiation, the behavior of mice was examined using balance beam tests, rotarod tests, and new object recognition tests. Then, the density of dendritic spines and the number of Nissl bodies in the hippocampus were measured using Golgi and Nissl staining. The superoxide dismutase (SOD) activity, malondialdehyde (MDA) content, and neurotransmitter content in brain tissue were detected using the WST-8 method, TBA method, and high pressure liquid chromatography (HPLC), respectively. Besides, cell apoptosis was determined using the TUNEL method, and the dose-response relationship, a function of dose change with damage index, was analyzed using linear and linear square fitting method. Finally, the minimum radiation dose causing a significant change in all indicators of brain damage was determined as the brain damage threshold.Results:Compared to the control group, 1 Gy proton irradiation result ed in a significant decrease in the density of filopod dendritic spines ( t = 1.82, 2.30, P < 0.05) and a significant increase in abnormal Nissl bodies in the CA1 region ( t = 2.44, 3.77, P < 0.05). At 3 and 7 d after irradiation, as well as a significant increase in the DA ( t = 2.52, P<0.05) and Glu contents ( t = 4.04, P < 0.05) on day 7. In contrast, 2 Gy proton irradiation result ed in a decrease in SOD activity on day 3 ( t = 3.44, P < 0.05), and an increase in the MDA content ( t = 1.90, 2.14, P < 0.05), hippocampal cell apoptosis (t = 3.91, 3.54, P < 0.05), and 5-HT levels ( t = 2.81, 2.69, P < 0.05), together with a decrease in climbing time in the rotarod tests ( t = 2.85, 2.64, P<0.05) and propensity to recognize new objects ( t = 2.87, 2.84, P < 0.05) on days 3 and 7. Furthermore, a dose-response relationship was observed in the dose range from 0.1 to 2 Gy ( R2=0.74-0.99). Conclusions:The dose threshold of 90 MeV protons inducing brain damage in mice is inferred to be 1 Gy, and 14 dose-response models are developed, providing a biological basis for organ dose capping and risk assessment of crew experiencing short-term deep space flights.

Objective To explore the effect of bone marrow injury by simulating the radiation from solar particle events in order to address the radiation limit and assess risks during manned deep space exploration.Methods In line with solar particle events(the main component was protons),BALB/c mice(48 mice per group)were irradiated with 90 MeV protons at the doses of 0,0.1,0.3,0.5,1 and 2 Gy.At 3 and 7 days after irradiation.Routine blood counters were employed to detect peripheral blood changes,Giemsa staining was used to detect the ratio of granulocytes to erythrocytes in bone marrow,and flow cytometry was adopted to detect the proportion of bone marrow stem cells,cell subsets and apoptosis before the dose-response relationship and threshold were analyzed.Results In the dose range of 0.1 to 2 Gy,the number of peripheral blood white blood cells and lymphocytes decreased at 3 and 7 days after irradiation and the ratio of granulocytes to erythrocytes in bone marrow and bone marrow cell subsets were abnormal as the dose increased.Seven days after irradiation,the platelet count decreased.The minimum dose that caused significant changes was 0.5 Gy,13 models with dose-response relationships were obtained,and the minimum values of ED25,ED50 and ED63 were 0.25,0.58 and 0.76 Gy,respectively.Conclusion A total of 13 dose-response relationship models of proton-induced bone marrow injury in mice have been obtained,and the dose threshold of proton-induced bone marrow injury ranges from 0.25 to 0.76 Gy.