Effect of Electroacupuncture of "Weizhong" (BL 40) and "Huantiao" (GB 30) on cAMP-PKA-CREB Signaling of Spinal Cord in Rats with Neuropathic Pain

Abstract

We have demonstrated that electroacupuncture (EA) of "Weizhong" (BL 40) and "Huantiao" (GB 30) could evidently relieve mechanical hyperalgesia in spared nerve injury (SNI) rats. The present study was designed to observe the effect of EA on levels of cAMP, and protein kinase A (PKA) and cAMP response element binding protein (CREB) in the lumbar spinal cord of the same pain model rats, so as to explore its mechanisms underlying improvement of neuropathic pain. One hundred male SD rats were randomly divided into 5 groups: sham operation, model, EA, AP-5 and L-NAME groups (n＝20 in each group). The sham operation group underwent a simple separation of the sciatic nerve but without ligation and abscission. The neuropathic pain model was established by abscission of the right tibial and common peroneal nerve. EA (2 Hz, 1－3 mA) was applied to right BL 40 and GB 30 for 30 min, once a day for 7 days, starting from day 11 after surgery. For rats of the AP-5 and L-NAME groups, AP-5 (a competitive antagonist for NMDA receptor, 0.7 mg•kg－1•d－1) and L-NAME (a non-selective antagonist for nitric oxide synthase, NOS, 60 mg•kg－1•d－1) were respectively administrated by intraperitoneal injection, once daily for 7 days. The mechanical pain threshold was measured, the cAMP content of spinal cord (L 4－L 6) was determined by radioimmunoassay, and the expression of PKA, p-PKA and CREB proteins of spinal cord (L 4－L 6) was detected by Western blot. The content of cAMP and the expression levels of PKA, p-PKA and CREB were significantly higher in the model group than in the sham operation group (P<0.01), and considerably lower in the EA group than in the model group (P<0.01, P<0.05). Compared to the model group, the expression levels of PKA and p-PKA were significantly decreased in the AP-5 and L-NAME groups (P<0.01, P<0.05). Compared to the EA group, the content of cAMP and the expression levels of CREB were significantly higher (P<0.05), and the expression of p-PKA was significantly lower in the AP-5 and L-NAME groups (P<0.05)．. EA intervention-induced down-regulation of cAMP, PKA and CREB levels in the lumbar spinal cord may contribute to its analgesic effect in neuropathic pain rats, suggesting an involvement of reduction of cAMP/PKA/CREB signaling of spinal cord in EA analgesia.