Double immunostaining of TPH and pCREB in representative DRN tissues. a–c Naïve rat; d–f SNL rat; and g–i SNL+SCS rat. The numbers of TPH-positive serotonergic neurons and pCREB-positive nuclei increased in the DRN region of the SNL+SCS rat compared with the SNL rat (scale bar = 20 μm). j Quantitative summary of pCREB-positive and TPH-positive serotonergic neurons in the DRN of the three groups. The numbers of both neuronal types in the DRN were significantly increased in SNL+SCS rats compared with SNL rats. k Quantitative summary of pCREB-positive serotonergic neurons among the total serotonergic neurons in the DRN. The percentage of pCREB-positive serotonergic neurons was significantly increased in SNL+SCS rats compared with SNL rats. Quantitative data were obtained from three consecutive slices of four rats per group. Data are mean ± SEM; *p < 0.05 and **p < 0.01 by the Tukey–Kramer test.