Precipitated morphine withdrawal stimulates multiple activator protein-1 signaling pathways in rat brain.

Morphine dependence is a long lasting form of neuronal plasticity. Naloxone-precipitated morphine withdrawal, a model of opioid dependence, induces brain region-specific changes in activator protein-1 (AP-1) transcription factor gene expression. Rapid increases in c-fos, fos-B, jun-B, and c-jun mRNA levels accompany withdrawal, with the relative level of induction correlating with the severity of physical dependence. Altered patterns of c-fos mRNA expression were limited to neuronal circuits mediating stress responses, motivation, and cognition. AP-1 DNA-binding activity and dimer composition also exhibited regulation after withdrawal, presumably as a result of both transcriptional and post-translational events. Thus, morphine dependence results in the alteration of diverse, brain region-specific, signal transcription pathways involving AP-1 transcription factors.