SP-CTA stimulates the production of the immediate early gene c-Fos in dorsal horn neurons. Sections from the same animals as in figure 4 were used for immunohistochemistry with antibodies to c-Fos. The sections were prepared as previously described. The c-Fos labels as dark staining nuclei. The arrow points to an example of a c-Fos positive nucleus. The approximate locations of lamina I, III and V are indicated. These data indicate that c-Fos expression is stimulated by SP-CTA.