Comparative effect of dense-and-disperse versus non-repetitive and non-sequential frequencies in electroacupuncture-induced analgesia in a rodent model of peripheral neuropathic pain

Background: Neuropathic pain (NP) is a complex disease that remains challenging to treat. Low-frequency dense-and-disperse (DD) electroacupuncture (EA) has been used as adjuvant therapy for neuropathic pain; however, its analgesic effect decreases as stimulation time increases, or when it is repeatedly used. We hypothesized that a new frequency parameter could improve the effectiveness of EA, and aimed to compare the efficacy and duration of the analgesic effect between classic DD-EA and non-repetitive and non-sequential frequency (random frequency (RF)-EA) in neuropathic rats. Furthermore, the effect of RF-EA at local traditional acupuncture point locations versus auricular vagus nerve stimulation (aVNS) was evaluated. Methods: Male Wistar rats with peripheral neuropathy were subjected to a single session of DD-EA or RF-EA for 20 or 40 min at ST36 + GB34. An additional group of rats was treated with RF-EA for 20 min using aVNS at the appropriate ear point locations. Paw pressure test, von Frey filaments and spontaneous pain scores were evaluated. Sham-operated rats were used as controls. Results: In all, 20 min of RF-EA reversed hyperalgesia (for 24 h) and allodynia (for 8 h), showing a longer analgesic effect than DD-EA. Both RF-EA and DD-EA induced partial inhibition of spontaneous pain for 8 h. Forty minutes of DD-EA did not interfere with the NP phenomena; however, RF-EA induced significant long-term analgesia. aVNS induced an analgesic effect similar to local stimulation. Conclusion: This pilot study shows that RF-EA at both local traditional acupuncture point and auriculotherapy point locations induces long-lasting analgesia in neuropathic rats, and more effectively so than classical DD-EA.