1.Interleukin-20 (IL-20) is a proinflammatory cytokine belonging to the IL-10 family. IL-20 is produced by activated keratinocytes and monocytes and transmits an intracellular signal through two distinct cell-surface receptor complexes on keratinocytes and other epithelial cells. IL-20 regulates proliferation and differentiation of keratinocytes during inflammation, particularly inflammation associated with the skin. It is also involved in the pathogenesis of osteoporosis and is a new target to treat this disease. However, little data demonstrated its role on pain. Meanwhile, IL-10 was involved many pain models and suppresses IL-10 expression also reduce pain in animal models. In this sub-project, Our preliminary data demonstrated increase of IL-20 after morphine administration. Therefore, the investigators will explore the role of IL-20 in pain management.