Astroglial mechanisms for inflammatory pain

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DESCRIPTION (provided by applicant): Tissue injury-induced inflammatory pain is characterized by mechanical allodynia and heat hyperalgesia that are mediated by distinct mechanisms. In particular, persistent pain is characterized by mechanical allodynia. Our incomplete understanding of how mechanical allodynia is maintained hinders the effective treatment of chronic pain. Current pain research focuses primarily on neuronal cells and neural networks. Less is known about the importance of glial cells and the glial network, in particular the astroglial network in chronic pain conditions. The overall goal of this application is to investigate the role of spinal astrocytes and astroglial network in regulating mechanical allodynia during persistent inflammatory pain. Our strategy is to target signaling molecules that are specifically expressed and induced in spinal astrocytes after tissue injury. c-Jun N-terminal kinase (INK) is a member of MAP kinase family. Our pilot studies have shown that (a) CFA inflammation induces JNK activation exclusively in spinal astrocytes, (b) a peptide INK inhibitor blocks maintenance phase of mechanical allodynia without affecting heat hyperalgesia, and (c) the astroglial gap junction protein connexin-43 (Cx43) is upregulated by inflammation and a gap junction blocker suppresses mechanical allodynia but not heat hyperalgesia. Our central hypothesis is that JNK is a critical signaling molecule in spinal astrocytes, and that persistent JNK activation by inflammation makes important contribution to the maintenance of mechanical allodynia via an astroglial network. This hypothesis will be tested using the methods of behavioral testing, immunohistochemistry, in situ hybridization, Western blotting, and a kinase assay. Cellular localization of signaling molecules will be examined by double staining of immunofluorescence and double staining of fluorescence in situ hybridization and immunofluorescence. We will use the CFA inflammation model to accomplish the following three specific aims: (1) to establish that inflammation induces persistent JNK activation in spinal astrocytes and that this activation is essential for the maintenance of mechanical allodynia, (2) to define the importance of Cx43-mediated spinal astroglial network for persistent mechanical allodynia, and (3) to explore molecular and cellular mechanisms by which spinal JNK and the astroglial network regulate mechanical allodynia. These proposed studies will (a) identify novel molecular and cellular mechanisms underlying the maintenance of mechanical allodynia, (b) document important roles of spinal astrocytes and the glial network for chronic pain, and (c) reveal spinal JNK pathway as a new target for the treatment of chronic pain.