[Effects of intrathecal injection of IRF8 SiRNA on pain threshold and activation of spinal cord microglia in rats with postoperative persistent pain].

Objective: To investigate the effects of intrathecal injection of IRF8 SiRNA on the pain threshold and activation of spinal cord microglia in rats with postoperative persistent pain. Methods: One hundred and twenty male Sprague-Dawley rats were randomly divided into sham group (SH, n=12), SMIR group (SM, n=48), SMIR + DEPC group (SD, n=12) and SMIR + irf8 SiRNA group (SS, n=48). In the SM group, the persistent postsurgical pain(PPsP) model was established according to the skin/muscle incision and retraction (SMIR), and the SH group was only incised without retracted. The SD group and SS group received intrathecal catheterization one week before SMIR, the SS group was injected with 20 µl of IRF8 SiRNA solution (dissolved in DEPC-treated water, 150 pmol) intrathecally on the 5th and 6th day after SMIR, and the SD group was injected with the same amount of DEPC-treated water. The paw withdrawal threshold (PWT) of each group was measured and recorded before SMIR and on the 1st, 3rd, 7th, 12th, 22nd and 33rd days after SMIR. Western blot was used to detect the expression of Iba-1 in the dorsal horn of spinal cord on the 12th days after SMIR, and the saphenous nerves in the SH group and SM group were collected to observe their ultrastructural changes under electron microscope. The flow cytometry was used to detect the activation of microglia in spinal cord dorsal horn before SMIR and on the 1st, 3rd, 7th, 12th, 22nd and 33rd days after SMIR in the SM group and SS group. Results: Compared with D0, the PWT of SM group was decreased on the 1th to 22nd day after SMIR (P＜0.05 or P＜0.01), and returned to normal level on the 33rd day after SMIR (P＞ 0.05). Compared with the SH group, the PWT of the SM group was decreased on the 1th to 22nd day after SMIR (P＜0.05 or P＜ 0.01). However, compared with the SD group, the PWT of the SS group was increased on the 7th to 22nd day after SMIR (P＜0.05 or P＜0.01). Compared with SH group, the PWT of SS group was decreased on the 7th to 22nd day after SMIR (P＜0.05 or P＜0.01). The average thickness of saphenous nerve myelin was (377.0 3±69.60) nm in the SH group and (369.50±73.26) nm in the SM group, and there was no significant difference between the two groups (P＞0.05). Compared with the SH group, the expression level of Iba-1 was increased significantly (P＜0.01) in the SM group. Compared with the SD group, the expression of Iba-1 was inhibited (P＜0.05) in the SS group, and compared with the SH group, the expression of Iba-1 was also statistically different (P＜0.05) in the SS group, while the expression of Iba-1 was not statistically significant between the SM group and the SD group (P＞0.05). Compared with D0, the activation ratio of microglia was increased significantly on the 3rd to 22nd day after SMIR (P＜0.01) in the SM group , while the activation of microglia reached a peak on 3rd day after SMIR (P＜0.01) in the SS group. After intrathecal administration, the activation rate of microglia in the spinal dorsal horn of the SS group was decreased significantly, and compared with the SM group, it was decreased significantly on the 7th to 12th day after SMIR (P＜0.01). Conclusion: The significant and persistent mechanical hyperalgesia in PPsP induced by SMIR was caused non-obvious peripheral nerve injury, which may be mediated by the activation of microglia in the dorsal horn of the spinal cord. IRF8 SiRNA administrated by intrathecal injection could inhibit the activation of microglia and reverse SMIR-induced hyperalgesia.

[A new design puncture needle and a device of microcatheter protection for lumbar intrathecal catheterization in rats].

Objective: To introduce a new design needle and a device of microcatheter protection for lumbar intrathecal catheterization in rats,and evaluate its feasibility and effectiveness.Methods: Sixty pathogen-free adult male Sprogue-Dawley rats were randomly divided into two groups(n=30 in each group), the control group (group C) and the modification group(group M). The traditional puncture device, 20G needle, was used in the group C without extemal shielding protection. The new design puncture needle and the microinjection cock were used in the group M. All rats were assessed for motor function on postoperative. The motor function was evaluated 1 day afteroperation. Lidocaine was injected in the catheter at 1st,3rd,7th,14th,21st day post-catheterization, methylene blue was injected in intrathecal at 30th day after operation, and the catheter location was observed. The paw withdrawal threshold(PWT) was measured at 1st,3rd,7th,14th,21st,30th day after operation, open-field test was tested at preoperative and one week postoperative for the purpose of evaluating the autonomous behavior of rats. Results: About motor function:level Ⅰ 75.9%,level Ⅱ 20.7%,level Ⅲ 3.4% in group C, and level Ⅰ 96.7%,level Ⅱ 3.3% in group M, Compared with group C,group M had higher percentage of the level Ⅰ in motor function (P＜0.05);Lidocaine test and methylen blue location showed that each one case of catheter was removed on the 14th and 21st day after intubation in group C, and total four cases were removed till the 30th day, while all catheters were in normal location in group M. There was significant difference between two groups in protection of the extemal portion of catheter(P＜0.05); The time of intrathecal injection in group M was only 1 minute, and it spent more than 3 minutes in group C. Compared with group C,the time of intrathecal injection is significantly shorter in group M(P＜0.01);PWT was reduced to the lowest on the third day after catheterization, and there was significant difference compared with preoperative(P＜0.05), PWT recovered on the 7th day and there were no significant difference between two groups; Compared with preoperative, there was no significant difference in the parameters of the group M in the open field test, neither between two groups. Conclusion: The new design puncture needle by its less injury and higher efficiency can be used in intrathecal catheterization. The microinjection cock is reliable and convenient for repeat injection with a perfect protection function of the external portion of catheter, meanwhile it has no impact on rats' autonomous behavior so that it is worthy of further promoting.