ETHANOL AND NALOXONE DIFFERENTIALLY UP-REGULATE DELTA-OPIOID RECEPTORGENE-EXPRESSION IN NEUROBLASTOMA HYBRID (NG108-15) CELLS

We have used a sensitive solution hybridization assay with a riboprobe transcribed from the coding sequence of the delta opioid receptor (DO R) to quantitate the changes in DOR mRNA transcript levels following e xposure of NG108-15 cells to ethanol and/or the opioid antagonist, nal oxone. Incubation of NG108-15 cells with 200 mM ethanol or 1 mu M nalo xone, treatments that have previously been shown to upregulate DOR bin ding, increased DOR mRNA transcript levels 2 to 3 fold. DOR mRNA level s peaked at 24 to 48 h after exposure to either ethanol or naloxone. A t 168 h, DOR mRNA levels in NG108-15 cells exposed to naloxone had ret urned to control (untreated) levels while the levels in ethanol treate d cells remained nearly equal to peak values. Exposure to a combinatio n of ethanol plus naloxone for 24 h produced an additive effect, so th at DOR mRNA transcripts were increased 3 fold. Northern blot analysis identified six DOR transcript bands ranging in size from 8.7 to 2.1 kb . The above treatments increased each of the six bands proportionately , so that no difference was observed in the fraction of the total hybr idization signal produced by each band of the Northern blot. These res ults demonstrate that each of the DOR transcripts in NG108-15 cells ar e subject to homologous (naloxone) as well as heterologous (ethanol) u pregulation.