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.