Morphine-induced alterations on DNA-binding proteins in developing rat brain.

Endogenous opioids and opiate drugs inhibit nervous system maturation through both direct and indirect mechanisms. Recently much attention has been directed toward changes in the postreceptor events and it has been speculated that the regulation of gene expression may be involved in the development of drug tolerance and dependence. We investigated the changes in the levels of in vitro RNA synthesis in developing rat brain after continuous block of opioid receptors. Repeated naloxone treatment induced increased levels (27-48%) of RNA synthesis during the early postnatal period. Using mobility gel shift assay the presence of octamer binding proteins (Oct-1) and the replication differentiation transcription factor CTF/NF1 in the developing rat brain were studied both after single or repeated morphine and naloxone treatment. Decreased Oct-1 binding activity in brain protein extracts 1 h after morphine application was registered, while opioid antagonist naloxone exerted an opposite effect on this octamer protein following single drug treatment. Repeated administration of morphine or naloxone decreased markedly the DNA-binding affinity of Oct-1. The binding activity of CTF/NF1 changes differently showed higher levels assessed 30-120 min after morphine administration. The opposite trend of the changes in opiate drug and opioid antagonist animals suggests opioid receptor-mediated regulation of Oct-1 and CTF/NF1 transcription factors.