[Effect of Electroacupuncture Intervention on Expression of Pain Sensory and Affective Proce- Ssing-related µ-opioid Receptor, Etc. in the Amygdala in Chronic Neuropathy Pain Rats]

Objective: To observe the effect of electroacupuncture (EA) on expression of pain sensory and affective processing-related µ-opioid receptor (MOR), glutamatergic AMPA receptor subunit GIuA 1, extracellular signal-regulated kinase (ERK 1/2), cAMP response element binding protein(CREB) in the amygdala in chronic constrictive injury (CC) + negative affection(NA) rats, so as to reveal its mechanism underlying pain relief.

Methods: A total of 32 male Wistar rats were randomized into normal control, model, EA, and anesthesia+ EA (AEA) groups (n = 8 in each group). The neuropathic pain NA model was established by ligation of the left sciatic nerve and repeated electrical stimulation of the paw-bottom in the pain-paired compartment. EA was applied to bilateral "Zusanli" (ST 36) and "Yanglingquan" (GB 34) for 30 min, once daily for 7 days. Thermal pain threshold (paw withdrawl latency, PWL) of the bilateral paws was measured by using a Tail-Flick Unit. The expression levels of MOR and p-CREB in the central amygdala (CeA) and those of MOR, GluA 1, p-ERK 1/2 and p-CREB in the right amygdala area were determined using immunofluorescence and Western blot, respectively.

Results: in comparison with the normal group, PWL difference (PWLD) values of the model group were significantly increased (P < 0.001), and the time spent in the CPA-paired. compartment was considerably decreased (P < 0.001). After EA, the PWLD levels of both EA and AEA groups were apparently decreased (P < 0.05), showing a pain relief; and the time spent in the CPA-paired compartment was apparently increased in the EA group (P < 0.05) , rather than in the AEA group (P > 0.05). Additionally , compared to the normal group, the expression level of MOR protein in the amygdala was remarkably increased (P < 0.05) and those of GIuA 1, p-ERK 2 and p-CREB proteins were apparently decreased (P < 0.05). After EA intervention for 7 days, the expression levels of these four proteins in the EA group, and those of MOR, p-ERK 2 and p-CREB in the AEA group were significantly up-regulated (P < 0.001, P < 0.01, P < 0.05). The expression level of GIuA 1 was significantly higher in the EA group than in the AEA group (P < 0.05).

Conclusion: Repeated EA stimulation of ST 36-GB 34 has a definite effect in relieving both sensation and affection dimensions of pain in NA rats, which may be related to its effect in up-regulating the expression of GIuA 1 in the amygdala, but the effects of MOR, p-ERK 2 and p-CREB need being researched further.