Observation on the analgesic effect of repeated electroacupuncture and its relation to the expression of synaptophysin in rat's hippocampus and hypothalamus

Objective:To observe the cumulative analgesic effect of repeated electroacupuneture(EA) and its relation to the expressions of synaptophysin(SYN) in rats' hippocampus and hypothalamus tissues in chronic constrictive injury(CCI) and post ovariectomy(OVX) rats'.Method:A total of 70 Wistar rats were randomized into control,CCI,CCI+EA 2 days,CCI+EA 2 weeks,OVX+CCI,OVX+CCI+EA 2 days and OVX+CCI+EA 2 weeks groups,with 10 rats in each group.For rats of the latest 3 groups,subcutaneous injection of D-galactose was given once daily for 7 weeks.Morris water maze test was conducted to evaluate the rats' memory-learning ability.Chronic pain model was established by ligating the left sciatic nerve with a piece of catgut.EA(2/15Hz,1-2 mA) was applied to bilateral "Zusanli"(ST 36)-"Yanglingquan"(GB 34),for 30min,once daily for 2d,2 weeks respectively.Result:Compared with control group,hyperalgesia score(HAS) increased significantly after CCI.HAS in CCI+EA 2weeks group was markedly lower than those in CCI and CCI+EA 2d groups(P0.05),suggesting a cumulative analgesic effect after EA 2 weeks.In comparison with OVX+CCI+EA 2 weeks group,HAS in OVX+CCI+EA 2 weeks group was significantly higher(P0.05),suggesting an attenuation of the analgesic effect after OVX.SYN immunoreaction positive product integral grey values(IGV) in rats' hippocampal CA1 area and hypothalamic PVN in CCI+EA 2 weeks group were significantly lower(upregulation of expression) than those in CCI group(P0.05).SYN IGV of CA1 and hypothalamus in OVX+CCI+EA 2 weeks group were significantly lower than those in OVX+CCI group(P 0.05) but obviously higher than those in CCI+EA 2 weeks group(P0.05).Conclusion:Repeated EA(2 weeks) could provide an accumulative analgesic effect in both CCI and CCI+OVX rats,which were closely related to the upregulation of SYN expression.OVX+D-galactose administration may weaken the cumulative effect of EA.