Regulation of delta opioid receptors by delta9-tetrahydrocannabinol in NG108-15 hybrid cells.
In this study we employed the neuroblastoma x glioma NG 108-15 cell line as a model for investigating the effects of long-term activation of cannabinoid receptors on delta opioid receptor desensitization, down-regulation and gene expression. Exposure of NG 108-15 cells to (-)-delta9-tetrahydrocannabinol (delta9-THC) reduced opioid receptor binding, evaluated in intact cells, by approximately 40-45% in cells exposed for 24 h to 50 and 100 nM delta9-THC and by approximately 25% in cells exposed to 10 nM delta9-THC. Lower doses of delta9-THC (0.1 and 1 nM) or a shorter exposure time to the cannabinoid (6 h) were not effective. Down-regulation of 6 opioid receptors was not observed in cells exposed for 24 h to pertussis toxin (PTX) and then treated for 24 h with 100 nM delta9-THC. In cells that were exposed for 24 h to the cannabinoid, the ability of delta9-THC and of the delta opioid receptor agonist [D-Ser2, Leu5, Thr6]enkephalin to inhibit forskolin-stimulated cAMP accumulation was significantly attenuated. Prolonged exposure of NG 108-15 cells to 100 nM delta9-THC produced a significant elevation of steady-state levels of delta opioid receptor mRNA. This effect was not observed in cells pretreated with PTX. The selective cannabinoid receptor antagonist SR 141716A blocked the effects elicited by delta9-THC on delta opioid receptor desensitization, down-regulation and gene expression; thus indicating that these are mediated via activation of cannabinoid receptors. These data demonstrate the existence, in NG 108-15 cells, of a complex cross-talk between the cannabinoid and opioid receptors on prolonged exposure to delta9-THC triggered by changes in signaling through Gi and/or G0-coupled receptors.
Department of Pharmacology, University of Bologna, Italy.
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Murari
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D000818:Animals; D005576:Colforsin / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D013759:Dronabinol / Q000494:pharmacology*; D004743:Enkephalin, Leucine / Q000031:analogs & derivatives / Q000494:pharmacology; D005910:Glioma / Q000737:chemistry / Q000473:pathology; D051379:Mice; D009447:Neuroblastoma / Q000737:chemistry / Q000473:pathology; D010880:Piperidines / Q000494:pharmacology; D011720:Pyrazoles / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017465:Receptors, Opioid, delta / Q000032:analysis / Q000187:drug effects* / Q000235:genetics; D000077285:Rimonabant; D014407:Tumor Cells, Cultured
D010880:Piperidines; D011720:Pyrazoles; D012333:RNA, Messenger; D017465:Receptors, Opioid, delta; D005576:Colforsin; D004743:Enkephalin, Leucine; C034318:enkephalin, Ser(2), Leu(5), Thr(6)-; D013759:Dronabinol; D000077285:Rimonabant