[Effect of Electroacupuncture on Intracellular Calcium Ion Concentration and Expression of Calcium/Calmodulin Dependent Protein Kinase Ⅱ in Lumbar Spinal Cord in Rats with Neuropathic Pain].

OBJECTIVE: To observe the changes of intracellular calcium ([Ca2＋ ]i) concentration and expression of calcium/calmodulin dependent protein kinaseⅡ (CaMKⅡ) in spinal dorsal horn neurons of spared nerve injury (SNI) rats, so as to explore its mechanisms underlying improvement of neuropathic pain.

METHODS: One hundred and ten SD rats were randomly divided into 5 groups: sham control, model, EA, AP-5 and L-NAME groups. The sham group underwent only 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 "Weizhong" (BL 40) and "Huantiao" (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, and the calcium fluorescence intensity (shown by Fluo-3/AM calcium fluorescence indicator) of the superficial layer of the lumbar spinal cord (L 4－L 6) was measured by immunohistochemical staining and the expression of spinal cord (L 4－L 6) CaMK Ⅱ protein was detected by Western blot (WB).

RESULTS: After modeling, the mechanical pain threshold was significantly decreased on day 10 and 16 after operation in comparison with the sham operation group and baseline data of pre-operation in each group ( P <0.01), and remarkably increased in the EA, AP-5 and L-NAME groups relevant to the model group on day 16 ( P <0.01, P <0.05), while the effect of EA was significantly superior to that of AP-5 and L-NAME groups ( P <0.05), suggesting a reduction of EA analgesia after administration of AP-5 and L-NAME. The concentration of intracellular [Ca2＋ ]i was significantly higher in the model group than in the sham group, and considerably lower in the EA, AP-5 and L-NAME groups than in the model group ( P <0.01, P <0.05). Moreover, the expression level of CaMKⅡ shown by WB and immunohistochemical staining was significantly higher in the model group than in the sham group ( P <0.05) and obviously lower in the EA group (not the AP-5 and L-NAME groups) than in the model group on day 16 after the intervention ( P <0.05). It suggests an involvement of glutamate NMDA receptor and NMDAR-NOS/NO signaling in the analgesic effect and CaMKⅡ expression down-regulation of EA.

CONCLUSIONS: EA can ease pain in rats with neuropathic pain, which is closely related to its effect in reducing the calcium concentration and the expression of CaMKⅡ in the lumbar spinal cord, possibly mediated by glutamate NMDA receptor and NMDAR-NOS/NO signaling.