Analgesic effect of α-terpineol on neuropathic pain induced by chronic constriction injury in rat sciatic nerve: Involvement of spinal microglial cells and inflammatory cytokines

Neuropathic pain is a prevalent and debilitating neurological disorder. Ample evidence indicates that microglial cells and inflammatory cytokines are involved in the pathogenesis of neuropathic pain. Alpha-terpineol is a monoterpenoid alcohol with inhibitory effect on inflammatory cytokines. The main purpose of this study was to evaluate the effect of α-terpineol on neuropathic pain in rats. Chronic constriction injury (CCI) model was utilized to induce neuropathic pain in male Wistar rats. The rats were randomly divided into control, sham, α-terpineol, and gabapentin groups. Normal saline, α-terpineol (25, 50, and 100 mg/kg), and gabapentin (100 mg/kg) were administered intraperitoneally in the above-mentioned groups once daily for 14 days post-CCI. Behavioral tests, including Von Frey, acetone, and Hargreaves were used to assess mechanical allodynia, cold allodynia, and hyperalgesia in rats. Iba1 immunostaining and ELISA procedures were used to assess the activation of microglial cells and inflammatory cytokines level. The results showed that α-terpineol (50 and 100 mg/kg) significantly attenuated mechanical allodynia, cold allodynia, and hyperalgesia in the neuropathic rats. The analgesic effect of α-terpineol (100 mg/kg) was comparable with that of gabapentin as a standard antineuropathic pain drug. In addition, α-terpineol (25, 50 and 100 mg/kg) significantly decreased the number of Iba1-positive cells and diminished the concentration of IL-1β and TNF-α in the spinal tissue. It was ultimately attained that α-terpineol attenuates neuropathic pain through the suppression of the microglial cells and reduction of inflammatory cytokine levels in the spinal cord of rats.