Effects of electroacupuncture at "Futu" (LI 18), etc. on expression of spinal 5-HT 1 AR mRNA, 5-HT 2 AR mRNA and protein in rats with neck incision pain
Objective: To observe the effect of electroacupuncture (EA) at bilateral "Futu" (LI 18), etc. on the expression of 5-HT 1 A receptor (R) mRNA, 5-HT2 AR mRNA and protein in the spinal cord of rats with neck incision pain, so as to explore its underlying mechanism in relieving incision pain.
Methods: A total of 48 Wistar rats were randomly divided into control, model (incision pain), Futu (LI 18), Hegu (LI 4)-Neiguan (PC 6, LI 4-PC 6), Zusanli (ST 36)-Yanglingquan (GB 34) cervical cord (ST 36-GB 34 C) and lumbar cord (ST 36-GB 34 L) groups. A 1.5 cm longitudinal incision was made in the middle of the neck under Isoflurane inhalation anesthesia. Pain threshold (PT) was measured using radiant heat. EA (1-2 mA, 2 Hz/15 Hz) was applied to bilateral LI 18, LI 4-PC 6, ST 36-GB 34 for 30 min. The expression of 5-HT 1 AR mRNA, 5-HT 2 AR mRNA and protein in the cervical spinal cord (C1-C4) tissue, and 5-HT 1 AR mRNA and 5-HT 2 AR mRNA in the lumbar cord (L1- L3) were detected with Real-time PCR and Western blot analysis, respectively.
Results: After the operation, the thermal PT was shortened obviously In comparison with pre-operation (P < 0.05). Compared with post-operation, the PT values were increased markedly in the LI 18 group and LI 4-PC 6 group (P < 0.05), rather than in the ST 36-GB 34 group (P > 0.05). The expression levels of 5-HT 1 AR mRNA, 5-HT 2 AR mRNA and 5-HT 2 AR protein in the cervical cord of the model group were increased significantly compared with those of the control group (P < 0.05). In comparison with the model group, the expression level of 5-HT 1 AR mRNA was down-regulated considerably in the LI 18 and LI 4-PC 6 groups (P < 0.05), and those of spinal 5-HT 2 AR mRNA and protein were up-regulated significantly in the LI 18 and LI 4-PC 6 groups (P < 0.05). No significant changes were found in the expression of 5-HT 1 AR mRNA and 5-HT 2 AR mRNA in the ST 36-GB 34 C group in comparison with the model group (P > 0.05). The expression levels of 5-HT 1 AR mRNA and 5-HT 2 AR mRNA in the ST 36-GB 34 L group were significantly lower than those of the ST 36-GB 34 C group (P < 0.05).
Conclusions: EA of LI 18 and LI 4-PC 6 can significantly suppress pain reaction of neck incision in the rat, which is closely associated with its effects in down-regulating the expression of 5-HT 1 AR mRNA and in up-regulating 5-HT 2 AR mRNA and 5-HT 2 AR protein in the cervical spinal cord.