Effect of the activation of P2X7 receptor on D-serine release in ventrolateral periaqueductal gray in rats with bone cancer pain / 医学研究生学报

ABSTRACT

Objective　The activation of P2X7 receptor in ventrolateral periaqueductal gray (vlPAG) is involved in the formation and maintenance of bone cancer pain (BCP). This study will establish a rat model of BCP and observe the effect of the activation of P2X7 receptor in vlPAG on D-serine level through brain microdialysis combined with ELISA.　Methods　Forty-two female SD rats were divided into four groups by random number table normal control group (n=12), sham group (n=12), BCP group (n=12) and P2X7 receptor antagonist group (n= 6). The model of metastatic BCP in the tibias of the rats was established in the BCP group, and 20μL of RPMI-1640 medium cell suspension containing SHZ-88 breast cancer cells was injected (1×107 cancer cells/0.5 mL). The sham group was injected with treated cancer cells of the same volume (SHZ-88 breast cancer cells were kept in boiling water at 90 ℃ for 20 min), and the rest of the operation was the same as the BCP group. The normal control group received no treatment. The P2X7 receptor antagonist group was treated the same as the BCP group, except that the P2X7 receptor-specific antagonist A-438079 was added to the perfusion solution. The thermal pain threshold and mechanical pain threshold were detected at the same time in the normal control group, the sham group and the BCP group. The positive expression of P2X7 receptor in vlPAG of rats was detected by immunohistochemistry in each group in 21 days. The changes of D-serine in vlPAG dialysate were detected by ELISA in each group.　Results　The mechanical pain threshold and thermal pain threshold of the rats in BCP group on Day 5, 7, 10, 14, 18 and 21 were lower than those of the normal control group and sham group (P<0.01). The positive expression of P2X7 was scattered in vlPAG in normal control group and sham group. The number of P2X7 receptor positive cells in the BCP group was significantly higher than that in the control group and sham group (P<0.01). The content of D-serine in vlPAG of the rats in BCP group [(220.28±63.38)ng/mL] was significantly higher than that in the control group [(148.09±46.89)ng/mL] and the sham group [(147.32±51.44)ng/mL] (P<0.05). The content of D-serine in vlPAG [(134.20±41.77)ng/mL] in P2X7 receptor antagonist group was significantly lower than that in BCP group (P<0.05).　Conclusion　The activation of the P2X7 receptor in ventrolateral periaqueductal gray promotes D-serine release and participates in the mechanisms of BCP in rats .