Microglia are involve in pain related behaviors during the acute and chronic phase of arthritis inflammation

Background: Pain is one of the main protests of inflammatory diseases, hence, understanding the mechanisms which involved in the induction and persistence of pain is essential. Microglia is a contributing factor in the onset and maintenance of inflammation. Increased microglial activation increases the level of central pro-inflammatory cytokines and the development of central sensitization following inflammation. The aim of this study was evaluated the relation of spinal microglia activity with pain related behaviors during Complete Freund’s adjuvant (CFA)-induced inflammation. Materials and Methods: Inflammation caused by subcutaneous injection of Complete Freund’s adjuvant (CFA) in a single dose to the animal’s right hind paw. The edema and hyperalgesia caused by inflammation, respectively, were measured by Plethysmometer and Radiant Heat, on days 0, 7, 14, and 21. Spinal Iba-1 protein expression was detected by Western blotting. Minocycline hydrochloride (Sigma, U.S.A) was administered intraperitoneal at a dose of 40 mg/kg daily. Results: Our study findings indicated that CFA injection to the right hind paw of rats increased paw volume and hyperalgesia significantly during different stages of study, while Minocycline treatment significantly reduced paw volume and hyperalgesia. CFA injection into the right hind paw of the rat increases the expression of molecules ionized calcium binding adaptor molecule-1 (Iba-1) on different days of study, while Minocycline administration reduced spinal Iba-1 expression significantly compared to the CFA group. Conclusion: The results of this study indicated significant roles of microglia activation in deterioration of pain related behaviors during different stages of CFA-induced inflammation. The steady injection of Minocycline (as a microglia inhibitor) could reduce the inflammatory symptoms.