To investigate the alteration of the expression of cysteine-dependent aspartate-specific proteases-9 (caspase-9) in the condylar cartilage of tempromadibualr joint (TMJ) of rats.

The 48 male SD rats were randomly divided into 6 groups with random table method: blank control (CON) group (1, 5, and 9 weeks) and psychological stress (PS) group (1, 5, and 9 weeks) , the rats were treated by chronic unpredicted mild stress (CUMS) except those in the control group. After corresponding weeks of CUMS treatment, the open filed test and sucrose preference were performed to assess the depression state, the data were analyzed with repeated measures analysis of variance, then the rats were killed and the immunohistochemical staining as well as western blot were applied to detect the expression of caspase-9 in condylar. The data between CON group and PS group of the same time were processed by two independent sample t test.

Compared with CON group, PS group had showed less distance movement (t= 8.676, P = 0.011) and less time spent in center (t = 5.091, P = 0.041) in the open field test and short of sucrose preference (t = 10.150, P<0.001) starting from the first week. Besides, edema and releases of collagen fiber in the condylar surface were observed in PS 1-week group. In PS 5-week group, the results also shown collagen fiber loosen, fracture of cracks in the condyle. In PS 9-week group, the cells in condylar decreased significantly, appearing the "blank" area without cells. The variation of expression on Caspase-9 in PS group, which were significantly higher than that in CON group at the same time (P<0.001) .

The CUMS can lead to SD rats changing behaviors and taking less surcose, and high expression of caspase-9 were shown in condylar cartilage of the stressed rats, which may be one of the mechanisams of TMJ damage induced by CUMS.