Objective:To investigate the protective effect and mechanisms of umbilical cord tissue transplantation on radiation-induced learning and memory impairment in rats.Methods:Sixty SD rats were randomly divided into three groups with 20 in each group: control group, model group (whole brain X-ray irradiation, dose 20 Gy) and treatment group (whole brain X-ray irradiation, dose 20 Gy + umbilical cord tissue transplantation). The changes of body mass were observed, and the learning and memory of rats were observed by water maze test on the 14th and 28th day after irradiation, the neuron state of hippocampus was observed by HE staining, and the expressions of NF-κB pathway related proteins and IL-6 in hippocampus were detected by Western blot.Descriptive analysis and hypothesis testing were processed by SPSS 17.0.Results:(1) On the 28th day, the escaping latency in the water maze experiment of the treatment group was significantly higher than that of the control group and lower than that of the model group (control group: (11.77±3.02) s, model group: (23.75±3.27)s, treatment group: (18.49±2.32)s; t=3.940, -2.943, both P<0.05); the number of crossing platform in the treatment group was significantly lower than that in the control group and higher than that in the model group (control group: (7.20±0.84), model group (3.60±1.14 ), treatment group (5.00±1.00); t=-3.773, 2.064, both P<0.05). (2)HE staining showed that the neurons in the control group were arranged orderly and the cytoplasm was transparent.The neurons in the model group were arranged disorderly and the contraction of the cell body was triangular or irregular.The number of neurons in the treatment group was less than that in the model group. (3) On the 14th day, the relative expression of TLR4 in the treatment group was significantly higher than that in the control group and lower than that in the model group (control group: (0.69±0.03), model group: (1.06±0.11), treatment group: (0.90±0.04); t=7.275, -2.368, both P<0.05). The relative expression of NF-κB p65 in the treatment group was significantly higher than that in the control group and lower than that in the model group (control group: (1.67±0.12), model group: (2.08 ±0.06), treatment group: (1.93±0.08); t=3.236, -2.684, both P<0.05). The relative expression of IL-6 in the treatment group was significantly higher than that in the control group and lower than that in the model group (control group: (0.77±0.08), model group: (1.12±0.07), treatment group: (0.95±0.06); t=3.274, -3.495, both P<0.05). The relative expression of Bcl-2 / Bax in the treatment group was significantly lower than that in the control group and higher than that in the model group (control group: (1.40±0.52), model group: (0.48±0.06), treatment group: (0.72±0.0 3); t=-2.263, 6.350, both P<0.05). The expression trend of IL-6 and Bcl-2 / Bax protein on the 28th day was the same as that on the 14th day. Conclusion:Cord tissue transplantation can improve the learning and memory impairment caused by radiotherapy, which may be related with the inhibition of inflammation caused by radiotherapy.