Induction of thermal pain and inflammation in the foot injection of capsaicin compared with formalin in male rats
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Mohammad.Khajenouri,1,* Masoud Fereidoni,2
1. Department of Biology, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, IRAN
2. Department of Biology, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, IRAN
- Introduction: Stimulation of peripheral pain receptors by chemical and inflammatory agents leads to pain. Injection of formalin as a model of chemical pain causes pain in two stages: neurogenic (direct stimulation of receptors) and inflammatory (due to release of inflammatory agents). Red pepper capsaicin also directly stimulates peripheral pain receptors but may not induce inflammatory pain processes. This study compares the effect of foot injections of different concentrations of capsaicin with formalin.
- Methods: 200 to 250 g male Wistar rats (n = 7) were used. Foot injections of 0.5% formalin and also in three groups of concentrations of 0.20 mg/ lit, 0.10and 0.5capsaicin were performed to induce inflammatory pain and inflammation and changes in pain sensation were recorded within one hour after injection.
- Results: The use of capsaicin solution in a dose-dependent manner reduced the amount of thermal pain at a concentration of 20 mg/lit(P <0.01 **), a concentration of 10 mg/lit (P <0.05 *) but a significant difference at a concentration of 5 mg/lit compared to before injection It did not cause it. Also, only at a concentration of 20 mg/lit we see significant inflammation compared to before the injection (P <0.05 *), which is significantly less than the inflammation caused by formalin (P <0.01 **).
- Conclusion: :Recent research has shown that capsaicin exerts its analgesic (thermal) effect by removing substance P in pain-related sensory fibers by first attaching to the pain receptor and activating this channel.(Painful effect) but then the removal of substance P makes sensory neurons insensitive and analgesic.
- Keywords: Thermal pain, inflammation, rat,Capsaicin
