Figure 2

Rostrocaudal distribution of Fos-immunoreactive (Fos-ir) neurons after two conditioning noxious stimulations. Fos-ir neurons were identified at the L2 (A, C, E, G) and L5 (B, D, F, H) spinal dorsal horn at 90 min after the E20 and Fm20 stimulations. The groups shown in the figure are: the E20 (A, B), E50 (C, D), Fm20 (E, F), and control groups (G, H). Fos-ir neurons were few in the control and E20 rats at all segments (A, B, G, H). Formalin (Fm20) and supramaximal electrical (E50) stimulation induced Fos expression in L2 and L5 superficial laminae (C-F). In comparison, E50-induced Fos-ir neurons were densely distributed at the medial one-third of the L2 superficial dorsal horn (C), whereas Fm20-induced expression was relatively loosely distributed in the superficial dorsal horns (E). Scale bar = 100 μm.