Elemene Emulsion Injection Administration Reduces Neuropathic Pain by Inhibiting Astrocytic NDRG2 Expression within Spinal Dorsal Horn

Objective To investigate the mechanisms underlying elemene-induced analgesia in rats with spared nerve injury (SNI). Methods Sixty-five rats were equally divided into 5 groups using a random number table: naive group, sham group, SNI group, SNI + elemene (40 mg·kg −1 ·d −1 ) group and naive + elemene (40 mg·kg −1 ·d −1 ) group. An SNI rat model was established and the intervention were given respectively for 14 consecutive days. Von Frey filament tests and elevated plus-maze (EPM) tests were used to evaluate the effect of elemene on the mechanical threshold and anxiety, respectively. Immunoblotting and immunostaining were used to measure the expression of glial fibrillary acidic protein (GFAP) and NMYC downstream-regulated gene 2 (NDRG2) within the lumbar spinal dorsal horn (SDH). Results The SNI rat model exhibited a significant decrease in paw withdrawal threshold and exploratory behaviour in the EPM ( P <0.05). Consecutive administration of elemene alleviated SNI-induced mechanical allodynia and anxiety in rats ( P <0.05). Immunohistochemical data showed that elemene decreased SNI-induced upregulation of NDRG2 within the SDH ( P <0.05). Double immunofluorescent staining data further showed that elemene decreased SNI-induced upregulation of the number of GFAP immunoreactive (-ir), NDRG-ir, and GFAP/NDRG2 double-labelled cells within the SDH ( P <0.05). Immunoblotting data showed that elemene decreased SNI-induced upregulation of GFAP and NDRG2 within the SDH ( P <0.05). Conclusion Elemene possibly alleviated neuropathic pain by downregulating the expression of NDRG2 in spinal astrocytes in a rat model of SNI.