Abstract: Objective: To observe the effect of hypothalamus pituitary adrenal axis(HPA) disorder on the depression-like behavior and the expression of Caspase-3 protein in hippocampus tissue of the spinal cord injury(SCI) rats, and to explore its possible mechanism. Methods: A total of 40 male SD rats were rardomly divided into normal group (12 rats), sham model group (12 rats) and SCI group (16 rats). The SCI model was made by using self-made impactor. Open field test was used to detect the total distance of locomotor activities, sucrose preference test was used to detect the percentages of sucrose preference, forced swimming test was used to detect the immobility time of forced swimming, and ELISA method was used to detect the serum adrenocorticotropic hormone(ACTH) and corticosterone(CORT) levels of the rats in various groups. Results: The Open field test results showed that there was a significant difference in the total distances of locomotor activities of the rats between various groups at different time points (F=23.950, P=0.000); the sucrose preference of showed that there was a significant difference in the percentages of sucrose preference of the rats between various groups at different time points (F=11.99, P=0.001); compared with the baseline time point, the difference of percentages of sucrose preference of the rats in various groups on the 9th and 33rd days were increased(P<0.01);compared wtih sham model group,the percentages of sucrose preference of the rats in SCI group were significantly decreased(P<0.05).The forced swimming test results showed that the differences of immobility time of forced swimming of the rats in various groups had a statistically significant difference(F=104.281, P=0.000) at different time points, and there was a interaction between time and groups(F=58.036, P=0.000). The ELISA results showed that there was a significant difference in the serum CORT level of the rats between various groups at different time points(F=22.869, P=0.000), and there was a interaction between time and groups (F=7.753, P=0.000). There was a significant difference in the serum ACTH levels of the rats between various groups at different time points(F=36.598, P=0.000), and there was a interaction between time and groups (F=6.452, P=0.000). The expression levels of Caspase-3 protein in hippocampus tissue of the rats in various groups had a statistically significant difference (F=169.937, P=0.000); compared with normal group and sham model group, the level of Caspase-3 protein in hippocampus tissue of the rats in SCI group had a statistically significant difference (P<0.01). Conclusion: The hyperfunction of HPA axis in the SCI rats leads to the increase of Caspase-3 protein expression in hippocampus tissue, which leads to the depression-like behavior in the SCI rats, thus reducing the negative feedback regulation function of HPA axis and promoting the occurrence and development of depression of the SCI rats.

Key words: spinal cord injury, depression, hypothalamic-pituitary-adrenal, Caspase-3