Effect of SNL on 5-HT immunoreactivity (5-HT-ir) in the superficial dorsal horn of the spinal cord. A–C, SNL significantly decreased the density of 5HT-immunoreactive varicosities at all spinal levels examined. A, Segment C2; B, segment T2; C, segment L4 (*p < 0.05; two-way ANOVA). D, Images of 5-HT immunoreactivity in superficial dorsal horn of rats receiving sham surgery or SNL. Note reduced 5-HT immunoreactivity in SNL image. Box in inset denotes area from which images were obtained.