Effects of Ginkgo Biloba Extract EGb-761 on Neuropathic Pain in Mice: Involvement of Opioid System.

Neuropathic pain is considered as one of the most difficult types of pain to manage with conventional analgesics. EGb-761 is extracted from leaves of Ginkgo biloba and has analgesia and anti-inflammatory properties. This study aimed to examine the effect of EGb-761 on chronic constriction injury (CCI)-induced neuropathic pain behaviors, including thermal hyperalgesia and mechanical allodynia, and to explore the possible mechanisms underlying this action. To this end, CCI mice were intraperitoneally injected with EGb-761 (10, 20, 40, and 80 mg/kg), and thermal hyperalgesia, mechanical allodynia, cytokines, and mu-opioid receptor expression were measured. Results showed that EGb-761 attenuated thermal hyperalgesia and mechanical allodynia dose-dependently and the best delivery time window was from day 7 to day 14 after CCI. Additionally, EGb-761 treatment significantly decreased pro-inflammatory cytokines and enhanced mu opioid receptor (MOR) expression in the sciatic nerve. Moreover, the opioid antagonist naloxone prevented the effect of EGb-761 on thermal hyperalgesia and mechanical allodynia but did not influence the effect of EGb-761 on inflammatory cytokines. In conclusion, this study suggests that the potential of EGb-761 as a new analgesic for neuropathic pain treatment, and opioid system may be involved in the EGb-761-induced attenuation of thermal hyperalgesia and mechanical allodynia.