Role of increasing serum tumor necrosis factor on hyperalgesia and edema variation during different stages of adjuvant- induced arthritis in male rats

 Introduction: Tumor necrosis factor α (TNF-α) is a potent cytokine that exerts pleiotropic functions in inflammatory symptoms. With regarding to the important role of TNFα in hyperalgesia and edema induction via intra-cellular signaling pathways, we aimed to investigate the role of increasing serum TNF-α on hyperalgesia and edema and spinal mu opioid receptor (mOR) expression variation during different stages of Complete Freound Adjuvant- induced arthritis in male rats. Materials and Methods: Mono-arthritis was induced by CFA and then inflammatory symptoms (hyperalgesia and edema) were assessed on day 0, 3,7th, 14 and 21 following CFAinduction. In addition, anti-TNF-α was daily administered for 21 days for all different experimental groups. Spinal mOR expression were detected by western blotting.  Results: Our results showed that anti-TNFα administration in AA group resulted in decrease of paw volume and hyperalgesia until day 14, whereas, those symptoms were increased on day 21 following CFAinduction. Our study stated that anti- TNFα antibody administration causes a significant decreasing in spinal mOR protein expression on days 14 and 21 of the study. Conclusion: This study confirmed the time-dependent and bi-directional effects of serum TNF-α levsel on CFA-induced hyperalgesia, which it can say, a portion of these effects might be mediated via spinal mOR expression variation.