Figure 6

Astrocytic hyperactivity and up-regulation of IL-18R in spinal astrocytes induced by SR57227 and fractalkine. A. IL-18R expression in the dorsal horn (a’ and b’) and its colocalization (d’) with GFAP (c’) but not with CD11b (e’) or NeuN (f’), suggesting that IL-18R is only expressed in spinal astrocytes of normal rats. Scale bar=100 μm (a’) and 25 μm (b’-f’). B. SR57227 (10 pmol, i.t.) induced a significant enhancement of GFAP expression in the dorsal horn at 1 h (*, p<0.05, vs. vehicle, n=3 per group), which was suppressed by pretreatment with CX3CR1 Ab (20 μg, n=3) (^#, p<0.05 vs. saline + SR57227). C. Fractalkine (40 ng, i.t., n=4)-induced increases of both GFAP (upper panels) and IL-18R (lower panels) expression were significantly attenuated by pretreatment with CX3CR1 Ab (Ab, 20 μg, i.t., n=3) at 1 h after injection of fractalkine. Scale bar=25 μm. D The levels of IL-18R and GFAP are significantly increased in the dorsal horn at 1 h after fractalkine treatment (40 ng, i.t., n=3) compared with that treated by saline (*, p<0.05, or **, p<0.01, n=3 for each group); such upregulation for GFAP was significantly reduced by pretreatment with CX3CR1 Ab (20 μg, ^#, p<0.05, vs. saline + Fractalkine, n=3 per group); fractalkine-induced increase of IL-18R expression was also attenuated by CX3CR1 Ab (^#, p<0.05, n=3) but did not return to basal expression found in the saline + saline treated group (*, p<0.05). E. Fractalkine-induced increase of GFAP expression in the dorsal horn was partially suppressed by pretreatment with IL-18 Ab (20 μg, i.t.) (*, p<0.05, vs. saline + saline; ^#, p<0.05, vs. saline + fractalkine; n=3 for each group). These data suggest that SR57227 or fractalkine-induced up-regulation of GFAP is mediated by activation of CX3CR1 expression in spinal microglia and of IL-18R in astrocytes.