ABSTRACT
Aim To investigate the role and mecha-nism of exchange protein directly activated by cAMP (Epac) protein in the paraventricular nucleus(PVN) of the hypothalamus in the development of inflammatory pain in rats. Methods Adult SD male rats were cho-sen to establish the model of inflammatory pain through subcutaneous injection of complete Freund's adjuvant(CFA) on the center of left hind foot. Western blot was used to detect the changes of the expression of Ep-ac protein. Thermal withdrawal latency(TWL) was ob-served after the PVN injecting 8p-CPT-2′-O-Me-cAMP (8p-CPT),the agonist of Epac. Then activated down-stream MEK1/2 protein of Epac in PVN was detected using Western blot when the potency was the strongest.Results ① Compared with normal saline(control group),TWL decreased significantly on d 1, d 3, d 5, d 7,d 9 on the ipsilateral foot of CFA group rats(P<0.01),whereas it returned to normal level in d 13;the paw mechanical withdrawal threshold(PMWT) de-creased significantly on d 6,d 8,d 10,d 12 and d 14 (P<0.05);②Compared with the control,the Epac1 protein in CFA group rats began to decrease from d 3, and significantly decreased on d 3 and d 9(P<0.05), however the expression of Epac2 had no significant change, meanwhile p-MEK1/2 protein decreased sig-nificantly on d 3(P<0.05);③Compared with micro-injection of saline into the PVN(Saline group), the heat hyperalgesia of 20 min and 1h decreased signifi-cantly and TWL increased significantly after PVN ad-ministration of 8p-CPT(8p-CPT group)(P <0.05);paraventricular nucleus p-MEK1/2 protein expression increased significantly in 30 min(P <0.05) and re-covered to normal level 2 h after administration. Con-clusion The Epac1-MEK1/2 signaling pathway in the paraventricular nucleus of the hypothalamus may be in-volved in the development of chronic inflammatory pain induced by CFA.