Ethanol and naloxone differentially upregulate delta opioid receptor gene 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 (DOR) to quantitate the changes in DOR mRNA transcript levels following exposure of NG108-15 cells to ethanol and/or the opioid antagonist, naloxone. Incubation of NG108-15 cells with 200 mM ethanol or 1 microM naloxone, treatments that have previously been shown to upregulate DOR binding, increased DOR mRNA transcript levels 2 to 3 fold. DOR mRNA levels peaked at 24 to 48 h after exposure to either ethanol or naloxone. At 168 h, DOR mRNA levels in NG108-15 cells exposed to naloxone had returned to control (untreated) levels while the levels in ethanol treated cells remained nearly equal to peak values. Exposure to a combination of ethanol plus naloxone for 24 h produced an additive effect, so that 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 hybridization signal produced by each band of the Northern blot. These results demonstrate that each of the DOR transcripts in NG108-15 cells are subject to homologous (naloxone) as well as heterologous (ethanol) upregulation.