Change in NGF content in the L4 DRG, L4 SpN and ScN after L5 spinal nerve ligation (closed circles) and after sham operation (open circles). NGF content was measured by ELISA, and the values of the ipsilateral side are presented as mean ± SEM (%) of the contralateral side (n = 4 independent experiments). *p < 0.05 versus naive control (N) by one-way ANOVA followed by Fisher's PLSD.