Fig. 6. Quantitative analysis of pCREB-immunoreactive (IR) cells in the dorsal horn of rats with partial sciatic nerve ligation after a perineural injection of saline or clonidine. In (A ) the mean number of pixels in an area occupied by pCREB-IR cells in the ipsilateral dorsal horn was significantly higher than in the contralateral side of PSNL rats receiving perineural saline (*, P < 0.01) and than in the normal dorsal horn (+, P < 0.01). The value was not significantly different between the contralateral dorsal horn of PSNL rats and normal rats. Five days after a single injection of clonidine into the injury site, the mean number of pixels in an area occupied by pCREB-IR cells in both the ipsilateral and contralateral dorsal horn was significantly decreased compared with their respective counterparts in the dorsal horn of PSNL rats with saline injection or with normal rats (+, P < 0.001). In (B ), the mean optical density of an area occupied by pCREB-IR cells in the ipsilateral dorsal horn of PSNL rats with saline injection was not significantly different from the contralateral side. However, the mean optical density of an area occupied by pCREB-IR cells in both ipsilateral and contralateral dorsal horn of PSNL rats with clonidine injection was significantly lower than their respective counterparts in the dorsal horn of rats with saline injection or than normal dorsal horn (+, P < 0.05). Mean ± SEM, n = 4.