Abstract
BACKGROUND Fractalkine is widely expressed throughout the brain and spinal cord, where it can exert effects on pain enhancement and hyperalgesia by activating microglia through CX3C chemokine receptor 1 (CX3CR1), which triggers the release of several pro-inflammatory cytokines in the spinal cord. Fractalkine has also been shown to increase cytosolic calcium ([Ca2+]i) in microglia. MATERIAL AND METHODS Based on the characteristics of CX3CR1, a G protein-coupled receptor, we explored the role of inositol 1,4,5-trisphosphate (IP3) signaling in fractalkine-induced inflammatory response in BV-2 cells in vitro. The effect and the underlying mechanism induced by fractalkine in the brain were observed using a mouse model with intracerebroventricular (i.c.v.) injection of exogenous fractalkine. RESULTS [Ca2+]i was significantly increased and IL-1β and TNF-α levels were higher in the fractalkine-treated cell groups than in the farctalkine+ 2-APB groups. We found that i.c.v. injection of fractalkine significantly increased p-p38MAPK, IL-1β, and TNF-α expression in the brain, while i.c.v. injection of a fractalkine-neutralizing antibody (anti-CX3CR1), trisphosphate receptor (IP3R) antagonist (2-APB), or p38MAPK inhibitor (SB203580) prior to fractalkine addition yielded an effective and reliable anti-allodynia effect, following the reduction of p-p38MAPK, IL-1β, and TNF-α expression. CONCLUSIONS Our results suggest that fractalkine leads to hyperalgesia, and the underlying mechanism may be associated with IP3/p38MAPK-mediated calcium signaling and its phlogogenic properties.