Objective     To investigate the changes of dopamine-β-hydroxylase (DBH) and activator protein 2-α (AP-2α) expression in spinal cord under the condition of stress or pain stimulation

so as to explore the mechanism for changes of noradrenergic (NA) neurons in the spinal cord of rat pain model.      Methods     Immunohistochemical staining

double immunofluorescent staining

Western blotting and computing-image analysis system were used to detect the changes of DBH/AP-2α expression in the spinal cord of formalin-induced rat pain model.      Results     A small number of DBH-positive neurons were sparsely distributed in the ventral horn of the normal spinal cord

while in the formalin-treated group

much more darkly-stained DBH-positive neurons appeared primarily in the ventral horn

intermediate zone

and the dorsal horn

which reached the highest level on day 3 after formalin-injection. The grey value and number of DBH-positive neurons on day 7 after injection began to decrease

but still higher than that in the control group. Compared with control group

the number of noradrenergic neurons in spinal cord of formalin-treated rat was increased significantly

which was also confirmed by Western blotting. Double immunofluorescent staining showed that DBH and AP-2α co-existed in the cells of the spinal cord. The changes of AP-2α expression were similarly to that of DBH in the spinal cord of rat pain model.      Conclusion     Our results indicated that some non-noradrenergic neurons with different chemical properties might convert into noradrenergic neurons under pain stimulation; noradrenaline may be involved in the formalin-induced pain and behavior regulation; As one of transcription factors

AP-2α may promote the DBH synthesis.