[Effects of electroacupuncture at "Futu"(LI 18), etc. on pain threshold and cervico-spinal mGlu receptor 5/cAmp/CREB signaling in rats with neck incision pain].

Objective: To observe the effect of electroacupuncture (EA) at "Futu" (LI 18),etc. on the pain threshold and expression of metabotropic glutamate receptor subtype 5 (mGluR 5), cyclic adenosine monophosphate (cAMP), mitogen-activated protein kinase (MAPK), cAMP responsive element binding protein (CREB) genes in the cervico-spinal dorsal region in rats with neck incision pain so as to analyze its underlying analgesic mechanism in performing thyroid surgery.

Methods: Forty male Wistar rats were randomly divided into control, model, Futu (LI 18), Hegu (LI 4)-Neiguan (PC 6), Zusanli (ST 36)-Yanglingquan (GB 34) groups, with 8 cases in each group. Neck-incision pain model was established by making a longitudinal incision along the midline of the neck under anesthesia (isoflurane) except rats in the control group. EA(2 Hz/15 Hz, 1-2 mA) was applied to bilateral LI 18, LI 4-PC 6 and ST 36-GB 34 for 30 min, 4 h, 24 h and 48 h after modeling, respectively. The thermal pain threshold was detected before modeling, and before and after each treatment. After removing the ventral part, the spinal tissue of the cervical 1 -4 segments was collected for detecting the expression of mGluR 5, cAMP, MAPK, CREB genes by using quantitative real-time-PCR technique.

Results: In comparison with the control group, the pain threshold of the model group was decreased obviously (P<0.05). Compared with the model group, the pain thresholds of the LI 18 and LI 4-PC 6 groups were upregulated markedly after treatment (P<0.05). No significant differences were found between the LI 18 and LI 4-PC 6 groups, and between the model and ST 36-GB 34 groups in pain thresholds (P>0.05). Compared with the control group, the expression le-vels of mGluR 5 mRNA, cAMP mRNA and CREB mRNA in the cervico-spinal cord were upregulated significantly in the model group (P<0.05). While in comparison with the model group, cervico-spinal cAMP mRNA, and CREB mRNA were down-regulated markedly (P<0.05) and mGluR 5 mRNA was down-regulated moderately (P>0.05) in the LI 18 group, rather than in the LI 4-PC 6 and ST 36-GB 34 groups (P>0.05).

Conclusion: EA-LI 18 can significantly suppress neck incision pain induced pain reaction, which may be closely associated with its functions in down-regulating expression levels of intracellular cAMP mRNA and CREB mRNA in the cervico-spinal cord.