Both c-Fos and prodynorphin mRNA and peptide increase unilaterally in nociceptive-specific neurons in the lumbar rat spinal cord during chronic hindpaw inflammation. To study the mechanisms underlying prodynorphin gene expression, we examined transcription factors and their interactions at the CRE/AP-1-like site, DYNCRE3, found in the prodynorphin gene promoter. CREB repressed while c-Fos and c-Jun activated transcription through the DYNCRE3 site in transient co-transfections in PC12 cells. Following inflammation of the rat hindpaw, immunostaining demonstrated a bilateral increase in phosphorylated CREB (P-CREB)-positive neurons in the spinal cord. Gel supershift studies showed that spinal cord extracts contained CREB, P-CREB, and phosphorylated c-Jun (P-c-Jun) proteins that bound to the DYNCRE3 site. We propose a model in which inflammation-induced phosphorylation of CREB relieves CREB repression at the DYNCRE3 site, P-CREB binds to the c-Fos promoter, and Fos/Fra, P-CREB, and P-c-Jun interact at the DYNCRE3 site to activate prodynorphin gene transcription.