San–Yong Niu, Che–Hui Kuo, Eiichi Taira, Osamu Muraoka,
Yasuyuki Irie, Ye–Hua Gan, Eunju Do and Naomasa Miki*
Department of Pharmacology, Osaka University School of Medicine, A–6, 2–2 Yamadaoka, Suita, Osaka 565–0871, Japan
*To whom correspondence should be addressed.
Abstract: Chronic administration of morphine is known to decrease the levels of neurofilaments (NFs) in the ventral tegmental area. We ligated a promoter region of the mouse 68–KDa neurofilament (NF–68) gene to the pGL3–enhancer vector containing a luciferase gene, transfected it into SK–N–SH cells and then analyzed transcriptional activity in the cells treated with agonists or antagonists of opiate receptors. The activity of the NF–68 promoter was suppressed by naloxone about 55% at 10-5M and 30% at 10-7M at 48h, but suppressed not by morphine. Naltrexone at 10-5M suppressed the promoter activity about 20%, but levallorphan, DAMGO, DPDPE and U50488 did not. The inhibition by naloxone was dose–dependent and not reversed by morphine. The inhibitory effect of naloxone was not observed in N18TG–2 cells and PC12 cells. Experiments with various deletion mutants revealed that a region responsible for naloxone suppression spans from -328 to -101 in the gene. These results suggest that naloxone has the ability to suppress transcriptional activity in some neurons.
Keywords: Naloxone, Morphine, Promoter, Neurofilament, SK–N–SH cell