Ketamine

The rats were anesthetized via an intraperitoneal injection of 100 mg/kg ketamine + 8 mg/kg xylazine (Sangon Biotech, Shanghai, China) (21 (link)), and underwent surgery following deep anesthesia. The Control group received no treatment. In the Injury group, the left Achilles tendons of the rats were located by palpation, and incision and dissection were used to expose the Achilles tendon tissues. Thereafter, the tissue was dissected from the middle of Achilles tendon, prior to the skin being sutured and disinfected. In the S100A9 group, 0.5 mL of 1 mg/mL rhS100A9 solution was injected subcutaneously into the Achilles tendon in the left foot of each rat. In the S100A9 + Paquinimod group, 0.25 mL of 1 mg/mL rhS100A9 solution (Abcam, Shanghai, China) and 0.25 mL of 1 mg/mL Paquinimod solution (MedChemExpress Co., Ltd., Shanghai, China) were injected subcutaneously into the Achilles tendon in the left foot of each rat (Figure 1) (19 (link),22 (link),23 (link)).

The SCI model was generated as described previously (Ravikumar et al., 2005). The rats were anesthetized with an intraperitoneal injection of sodium pentobarbital (50 mg/kg; Sigma-Aldrich, St. Louis, MO, USA) and a mixture of ketamine (44 mg/kg; Sangon Biotech, Shanghai, China), atropine (0.02633 mg/kg; Sintong Chemical Industrial Co., Taoyuan, Taiwan, China) and xylazine (5 mg/kg; Sangon Biotech, Shanghai, China). The T₈ and T₉ vertebral peduncles were removed by laminectomy. After that, the moderate contusion injury was performed by a modified Allen's weight drop apparatus (10 g weight at 50 mm, 10 g × 50 mm) on the exposed spinal cord. For the control rats, the same laminectomy was performed, but without SCI. The success of the compression can be confirmed by the spasm of the tail, the retraction-like flutter of legs and delayed paralysis.