title: Morphine-Induced mu-opioid receptor desensitization.
abstract: Morphine has been widely accepted as the opioid agonist that sustains signaling because it does not cause receptor desensitization or internalization. This notion has led to the hypothesis that long-term morphine treatment initiates downstream adaptations that underlie tolerance and dependence. This study uses whole-cell recordings from neurons in the locus ceruleus to measure the potassium current induced by morphine. The results show that morphine does cause short-term desensitization. The desensitization induced by morphine was slower and smaller then that induced by [MET](5)-enkephalin (ME). After a brief application of a saturating concentration of ME, the current induced by morphine was smaller, and desensitization was not observed. In tissue taken from morphine-treated animals, the peak current induced by morphine was the same as in untreated animals, but morphine-induced desensitization was facilitated. The results suggest that morphine, like other agonists, can initiate receptor desensitization to decrease signaling.
authors: Vollum Institute, Oregon Health Sciences University, Portland, OR 97239, USA.
authors: Vu C
authors: VC
authors: Dang
authors: John T
authors: JT
authors: Williams
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D004361:Drug Tolerance; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D015221:Potassium Channels / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017450:Receptors, Opioid, mu / Q000037:antagonists & inhibitors*
chemical_list: D000701:Analgesics, Opioid; D015221:Potassium Channels; D017450:Receptors, Opioid, mu; D009020:Morphine