Opioid binds MOR Opioid dissociates from MOR PathwayStep5811 PathwayStep5821 PathwayStep5789 PathwayStep5796 PathwayStep5797 DARPP-32 events G-protein mediated events G-protein activation Opioid Signalling Authored: Le Novere, N, Jassal, B, 2004-03-31 12:22:05 Edited: Schmidt, EE, 0000-00-00 00:00:00 Opioids are chemical substances similar to opiates, the active substances found in opium (morphine, codeine etc.). Opioid action is mediated by the receptors for endogenous opioids; peptides such as the enkephalins, the endorphins or the dynorphins. Opioids possess powerful analgesic and sedative effects, and are widely used as pain-killers. Their main side-effect is the rapid establishment of a strong addiction. Opioids receptors are G-protein coupled receptors (GPCR). There are four classes of receptors: mu (MOR), kappa (KOR) and delta (DOR), and the nociceptin receptor (NOP). Pubmed16612131 Pubmed9218123 Pubmed9422713 Reactome Database ID Release 43111885 Reactome, http://www.reactome.org ReactomeREACT_15295 Reviewed: Castagnoli, L, 2008-11-06 12:55:54