Peripheral injection of CGRP induces a sustained increase in expression of neuronal c-Fos in spinal trigeminal nucleus. (A) An image (40×) of a section of spinal cord 4 mm from the obex stained with the nuclear dye DAPI is shown. The white box represents the area encompassing the spinomedullary junction (Vc/C1-C2) transition zone. (B) Sections of spinal cord within the Vc/C1-2 region of the spinal trigeminal nucleus were obtained from control animals (CON), animals 2 hours post CGRP injections, or animals 24 hours post CGRP injection. Images of spinal cord tissues stained for c-Fos are shown in the top panels. Magnification bar = 50 μm. The same sections costained for c-Fos and DAPI are displayed in the bottom panels. (C) The average fold change ± SEM of c-Fos staining intensity from control values is reported (n = 3 independent experiments). * P < 0.05 when compared to control values.