Minocycline Effects on IL-6 Concentration in Macrophage and Microglial Cells in a Rat Model of Neuropathic Pain

Evidence indicates that neuropathic pain pathogenesis is not confined to changes in the activity of neuronal systems but involves interactions between neurons, inflammatory immune and immune-like glial cells. Substances released from immune cells during inflammation play an important role in development and maintenance of neuropathic pain. It has been found that minocycline suppresses the development of neuropathic pain. Here, we evaluated the analgesic effect of minocycline in a chronic constriction injury (CCI) model of neuropathic pain in rat and assessed IL-6 concentration from cultured macrophage and microglia cells. Male Wistar rat (n=6, 150-200 g) were divided into three different groups: 1) CCI+vehicle, 2) sham+vehicle, and 3) CCI+drug. Minocycline (10, 20, and 40 mg/kg) was injected one hour before surgery and continued daily to day 14 post ligation. Von Frey filaments and acetone, as pain behavioral tests, were used for mechanical allodynia and cold allodynia, respectively. Experiments were performed on day 0 (before surgery) and days 1, 3, 5, 7, 10, and 14 post -injury. At day 14, rats were killed and monocyte-derived macrophage from right ventricle and microglia from lumbar part of the spinal cord were isolated and cultured in RPMI and Leibovitz's media, respectively. IL-6 concentration was evaluated in cell culture supernatant after 24 h. Minocycline (10, 20, and 40 mg/kg) attenuated pain behavior, and a decrease in IL-6 concentration was observed in immune cells compared to CCI vehicle-treated animals. Minocycline reduced pain behavior and decreased IL-6 concentration in macrophage and microglial cells.