Fig. 1.

Articular inflammation drives secondary mechanical allodynia, glio-vascular activation and microglia reactivity in the spinal cord. Tibiofemoral joint diameter (a), weight borne on the ipsilateral hind paw (b), ipsilateral mechanical stimulus withdrawal threshold (c) and contralateral mechanical stimulus (d) withdrawal threshold after intra-articular CFA (single dose, 100 μg), n = 9 (CFA), n = 4 (non-inflamed controls). Immunoreactivity of GFAP and CD11b antibodies in the dorsal horn 8 and 11 days following induction of inflammatory arthritis (e-l). Representative images (e,g,k) showing the increase in GFAP (red) and CD11b (green) immunoreactivity in the dorsal horn in (e-f) non-inflamed control, (g-j) day eight and (k-l) day 11 following induction of articular inflammation with CFA (nuclei- blue). High magnification imaging revealed microvessels, identified by strings of flat (longitudinal) or curved (cross-sectional) nuclei (blue), surrounded by GFAP⁺ astrocytic end-feet (red, arrowhead) and associated with CD11b⁺ cells (green, arrows) at day eight (h,i). 2D image following z-stack reconstruction showing a CD11b⁺ cell with a cellular projection within the vessel lumen (j). Wide spread dorsal horn CD11b⁺ microglia-like staining within the dorsal horn parenchyma by day 11 (k-l). Representative images showing ICAM-1 expression in the dorsal horn of non-inflamed controls (m-r) and CFA-treated animals on day 8 (n) and 11 (m). ICAM-1⁺ microvessel fragments (p) were observed throughout the dorsal horn. ICAM-1⁺ immunoreactivity was associated with CD31⁺ vessels (q) and vessels wrapped in GFAP⁺ astrocytic end-feet (r). Statistical analysis: two-way repeated measures analysis of variance + Dunnett’s multiple comparisons test. CFA + vehicle vs. respective baseline: ***p,<0.001, ****p < 0.0001. Group size = 8–9. Data displayed as mean ± SD. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)