Expression of nitric oxide synthase (NOS) isoforms in dorsal horns of control and monoarthritic rats. (a) Right dorsal horn; (b) left dorsal horn. Monoarthritis was induced by intra-articular injection of complete Freund's adjuvant (CFA) into the right tibio-tarsal joint; control rats received the vehicle of CFA. The expression of NOS isoforms was determined 4 weeks later. Bar graphs show the expression of the neuronal (nNOS), inducible (iNOS) and endothelial (eNOS) isoforms in standardized units (means ± SEM); below each bar graph a representative example of immunodot blotting is shown. Only nNOS was expressed in control rats. In monoarthritic rats the expression of the three NOS isoforms was found to be increased bilaterally (*p < 0.05 compared with control; Kruskal–Wallis test).