Chronic pain is a major health issue affecting 20% of the population and reducing quality of life measures and incurring a large health care related cost for society. In this thesis we investigate the role of non-neuronal cells of the spinal cord in regulating both the onset of acute inflammatory pain and the maintenance of chronic inflammatory pain. We demonstrate that a two-week peripheral inflammation as produced by the K/BxN serum transfer arthritis model results in chronic mechanical hypersensitivity as measured by von Frey hairs with changes in the ATF3 transcription factor of the dorsal root ganglia, a characteristic of neuropathic pain, in addition to spinal non-neuronal cell activation. The transition to a chronic mechanical hypersensitivity is further demonstrated by knockout and antagonist treatments to be spinal toll-like receptor 4 dependent. By LC/MS/MS lipid spinal cord analysis this is shown to be critical in production of the anti-inflammatory/ anti-nociceptive arachidonic acid metabolite 15d-PGJ₂ which is lost during K/BxN serum transfer arthritis. Additional studies utilizing the carrageenan model, wherein an inflammatory stimulant is injected into the hindpaw resulting in inflammation concurrent with thermal hyperalgesia and tactile allodynia, were conducted to investigate endogenous compounds released from non-neuronal cells during initiation of pain-like behavior. Here we demonstrate that the catalytically active form of matrix metalloproteinase 3 is released spinally and will induce an enzymatically mediated, microglia specific, release of tumor necrosis factor. Intrathecal antagonist blockade of MMP activity attenuates the onset of thermal and tactile hypersensitivity suggesting a role for these enzymes in the initial stages of peripheral inflammation induced pain -like behavior. This thesis reveals the crucial role of non-neuronal cells related factors in mediating both acute peripheral inflammation and chronic inflammation induced pain-like behavior utilizing multiple animal inflammation models and converging biochemical and molecular biological techniques

Persistent pain after resolution of clinically appreciable signs of arthritis poses a therapeutic challenge, and immunosuppressive therapies do not meet this medical need. To investigate this conversion to persistent pain, we utilized the K/BxN serum transfer arthritis model, which has persistent mechanical hypersensitivity despite the resolution of visible inflammation. Toll-like receptor (TLR) 4 has been implicated as a potential therapeutic target in neuropathic and other pain models. We compared the relative courses of serum transfer arthritis and mechanical hypersensitivity in wild type (WT) and Tlr4(-/-) mice. K/BxN serum transfer induced similar joint swelling and inflammation from days 4-22 in WT and Tlr4(-/-) mice. Unlike WT mice, Tlr4(-/-) mice displayed a significant reversal in mechanical hypersensitivity and diminished appearance of glial activation markers after resolution of peripheral inflammation. Intrathecal (IT) delivery of a TLR4 antagonist, lipopolysaccharide Rhodobacter sphaeroides (LPS-RS; 10 μg), on days 6, 9, and 12 abrogated the transition to persistent mechanical hypersensitivity in WT arthritic mice, while later administration had no impact. We utilized a lipidomics liquid chromatography tandem mass spectrometry methodology to determine spinal cord profiles of bioactive lipid species after early LPS-RS treatment compared to vehicle-treated control animals. WT arthritic mice had reduced spinal levels of the anti-inflammatory prostaglandin 15-deoxy-Δ(12,14)-PGJ(2) (15d-PGJ(2)) on day 6, compared to IT LPS-RS-treated mice. Direct IT application of 15d-PGJ(2) (0.5 μg) on day 6 improved mechanical hypersensitivity in arthritic mice within 15 min. Hence, TLR4 signaling altered spinal bioactive lipid profiles in the serum transfer model and played a critical role in the transition from acute to chronic postinflammatory mechanical hypersensitivity.