Fig. 5. Photomicrographs of pCREB-immunoreactive (IR) cells in the L4–L6 dorsal horn of a normal rat (A  and B ), a rat after partial sciatic nerve ligation (C  and D ) and a rat after partial sciatic nerve ligation and perineural clonidine injection (E  and F ). In (A  and B ), numerous pCREB-IR cells were observed in the dorsal horn of L4–6 spinal cord of the normal rat. The immunoreactivities were restricted to the nuclei of these cells. pCREB-IR cells are particularly more abundant in the superficial laminae than in other laminae. Four weeks after nerve injury, the number of pCREB-IR cells in the ipsilateral dorsal horn (D ) was markedly increased compared with these in the contralateral side (C ). The increase was even more evident in the superficial laminae. Five days after one single injection of clonidine into the injury site of PSNL rats, the number of pCREB-IR cells were dramatically reduced in both ipsilateral (F ) and contralateral (E ) dorsal horn. The reduction was more prominent in the medial half of the dorsal horn. Scale bar = 100 μm.