Intrathecal administration of SP-CTA A. NK1 expressing neurons in the dorsal horn take up SP-CTA. Three rats received intrathecal injections of 10 μg SP-CTA. One hour following the injections the animals were euthanized and the spinal cords were removed and labeled for NK1 (green) and CTA (red) using immunohistochemistry. Cells co-labeled for NK1 and CTA appear yellow to orange. These data indicated that SP-CTA was taken up by the NK1 receptor expressing neurons. B. Activation of dorsal horn neurons by SP-CTA. Rats (N = 6 per treatment group) received intrathecal injections of SP-CTA (50 μg), CTA (50 μg) or Saline (20 μl). The animals were allowed to recover for 24 hours. The animals were euthanized and perfused as described in the methods section. The spinal cords were removed and prepared for immunohistochemistry using an antibody to pCREB, a secondary antibody coupled to HRP and diaminobenzidine. Phosphorylated CREB is visible as dark staining nuclei. The arrow points to an example of pCREB expressing nuclei. The approximate locations of lamina I, III and V are indicated. These data indicate that CREB phosphorylation is stimulated by SP-CTA, but not CTA alone.