Application of unrestrained conscious rats with acute inflammatory ankle pain to study of acupuncture analgesia

Abstract

To compare the analgesic effect of manual acupuncture(MA) stimulation of "Zusanli" (ST36) in rats with inflammatory pain under unrestrained conscious, restrained and general anesthesia conditions, so as to explore the applicability of unrestrained conscious model in the evaluation of acupuncture analgesia effect. Male SD rats were divided into 5 groups: blank control (n=9), pain model (n=7), unrestrained conscious conditions+MA (n=6), restrained conditions+MA (n=6), and general anesthesia (GA)+MA(n=6). The acute pain model was established by injection of complete Freund's adjuvant (CFA) into the left ankle joint 48 h ahead of acupuncture. Subsequently, a single 20 min session of MA was applied to the left ST36. The mechanical and thermal pain thresholds (MPT and TPT) were determined before and after injection of CFA, and after MA stimulation. In order to evaluate the autonomic behavior activities, rats were randomly divided into blank control (n=11), pain model (n=11) and conscious-unrestrained conditions +MA (n=12) groups. The rats' exploratory movements were assessed by open field tests. Both MPT and TPT were significantly decreased after injection of CFA in the model group relevant to the blank control group (P<0.001), and significantly higher in the three MA groups than in the model group (P<0.001). Comparison among the three MA groups showed that both MPT and TPT were significantly higher in the conscious unrestrained conditions+MA group than in the restrained conditions+MA and GA+MA groups (P<0.05, P<0.01). Open filed tests showed that the total moving distance in the open field and wall climbing times were significantly lower in the model group than in the blank control group (P<0.01), and the wall climbing times were obviously more in the unstrained conditions+MA group than in the model group (P<0.05). The central area resistance time was significantly shorter in the model group than in the control group (P<0.05), and was moderately increased after MA despite no evident significance (P>0.05). No significant changes were found in the total moving distance after MA and in the central area moving distance after modeling and MA (P>0.05). MA has a better therapeutic effect in relieving pain and pain-induced depression-like behavior in conscious unrestrained rats than in restrained and GA rats, implying a higher applicability of unrestrained conscious pain model to the assessment of acupuncture analgesia.