Cumulating evidence has demonstrated that μ opioid receptor (MOR) agonists promote
spinal glial activation, lead to synthesis and release of proinflammatory cytokines and
chemokines, and contribute to opioid-induced hyperalgesia and development of opioid
tolerance and dependence. However, whether these MOR agonists directly or indirectly act
on spinal cord astrocytes and microglial cells in vivo is unclear. In the present study, by
combining the techniques of in-situ hybridization of MOR mRNA with immunohistochemistry …