Acute treatment with NOR-BNI increases prodynorphin mrna levels in arcuate nucleus

The effects of a single dose of opioid receptor antagonists on mRNA levels of proDynorphin (proDYN) and proOpiomelanocortin (POMC) were examined. Male Sprague-Dawley rats received one ICV injection of either saline, 50 nmoles norbinaltorphimine (NorBNI) or 50 nmoles B-funaltrexamine (B-FNA) and were sacrificed 24 h post-injection. Food was withheld during the 24 h period. In the arcuate nucleus (ARC), proDYN mRNA levels were elevated 180% above saline levels (P=0. 016) following Nor-BNI, but were unaffected by B-FNA (P=0. 33). ARC POMC mRNA levels were slightly elevated above saline levels following Nor-BNI (P=0. 075), but were unaffected by B-FNA (P=0. 598). Levels of proDYN and POMC mRNA were not significantly affected by either Nor-BNI or B-FNA in caudate putamen, hippocampus or nucleus of the solitary tract (Tit P> 0. 05). This suggests that regional differences exist for the ability of a single injection of the opioid receptor antagonist NorBNI to increase opioid peptide mRNA levels and that Nor-BNI has an effect on the precursor molecule for proDYN and perhaps POMC in the ARC.