Exploring The Role Of Aquaporin-4 In The Remifentanil-induced Hyperalgesia In Mice

Objective: This study aims to observe the change of mice's thermal and mechanical pain threshold following intraoperative analgesia with remifentanil, detect the distribution of AQP-4 in mice's lumbar spinal cord and then investigate the unique impact of AQP-4 on remifentanil-induced hyperalgesia including the change of the expression of GLT-1 and Cx43.Methods: In order to recognize whether intraoperative analgesia with remifentanil would induce hyperalgesia,24 healthy male CD1 mice were randomly divided into four groups. Group C: continuous subcutaneous inject saline; group I: had a plantar incision during subcutaneous inject saline; group R: continuous subcutaneous inject remifentanil; group R+I: had a plantar incision during subcutaneous inject remifentanil. Then we evaluate the remifentanil-induced pain behaviours by measuring thermal and mechanical pain threshold in a mouse hind paw of different groups at a day before modeling and the six hour, the first day, the second day, the seventh day after modeling. The distribution of AQP-4 in mice's lumbar spinal cord was determined by immunohistochemistry assay. Protein expression of AQP-4 in group R at different time and in different groups at the second day after modeling was determined by Western blotting. To figure out the mechanical that AQP-4 participated in remifentanil-induced hyperalgesia, we explored the expression of GLT-1 and Cx43 in Lumbar segment of spinal cord by Western blotting.Results: Basic mechanical and thermal pain threshold of the mice in different groups had no difference(P > 0.05). Compared with the LPWTL and L50%MWT measured at the day before modeling, in addition to the group C, the LPWTL and L50%MWT of the rest of the group were significantly decreased(P < 0.05)at the first day, the second day and the seventh day after modeling, and it's most clear at the second day. Besides, compared with the group C, the LPWTL and L50%MWT in group I, group R and group R + I were droped at the first day and the second day after modeling. To the mice's right paw, In addition to the group I, the change of the RPWTL and R50 % MWT of the rest of the groups were similar with the left paw. The immunohistochemical results showed that AQP-4 was concentrated in laminae I and II of the spinal cord, and it also obvious expresses near the spinal central canal. Western blot detected that at the second day after model establishment, the expression of the protein AQP-4 was higher than the day before modeling, and still higher at the seventh day. On the second day after model establishment, the expression of AQP-4 in group I, group R and group R+I significantly increased by comparing with group C, while the expression of GLT 1 were significantly decreased(P < 0.05); In addition, compared with group I, the expression of AQP-4 in group R+I was higher too, but the expression of GLT-1 was droped; the expression of protein GLT-1 in each group was in contrast to the AQP-4. And the change of the expression of protein Cx43 is also different from AQP-4. There is no distinction among different groups in the term of the expression level of Cx43.Conclusion: Intraoperative analgesia with remifentanil could induce postoperative mechanical and thermal pain threshold decreased, which was named hyperalgesia. It was the most obvious on the the second day after modeling. AQP-4 might participate in remifentanil-induced postoperative hyperalgesia and might work together with the GLT-1.