Aim: To investigate the effects of complete Freund's adjuvant (CFA) on inflammatory hyperalgesia and morphological change of the coexsistence of interleukin-1 beta (IL-1β) and type I IL-1 receptor (IL-1RI) in neurons and glia cells of rat dorsal root ganglion (DRG).
Methods: The pain-related parameters and the expression of IL-1RI and IL-1β positive neurons and glia cells of DRG in normal saline (NS) and adjuvant-induced arthritic (AA) group were examined with pain behavior assessment methods and immunohistochemical assay, respectively.
Results: Five hours, 1 d, and 2 d after intra-articular injection of 50 μL CFA, tactile hyperalgesia induced by CFA was observed in the foot flexion and extension scores of the ipsilateral hindpaw of AA group. Three days after injection, the distribution of IL-1RI/IL-1β double-stained coexisted neurons and glia cells were observed in ipsilateral DRG of both groups. The number of IL-1β positive neurons, IL-1RI positive neurons, IL-1β/IL-1RI double-stained neurons, and IL-1RI positive glia cells in ipsilateral DRG of the AA group were higher than that of NS group (P < 0.05 or P < 0.01).
Conclusion: The coexsistence of IL-1β and IL-1RI in neurons and nonneuronal cells suggests an as yet unknown autocrine and/or paracrine function of IL-1β in the DRG. The function was enhanced in articular arthritis induced by CFA and could play an important role in hyperalgesia under inflammatory conditions.