Opioid receptors (Mu, Kappa, and Delta) (MOR, KOR, DOR)

The opioid receptor system consists of three primary subtypes: the mu (μ), kappa (κ), and delta (δ) receptors, which are members of the G protein-coupled receptor (GPCR) family [1.1.1, 1.3.1]. These receptors are widely distributed throughout the central and peripheral nervous systems, where they play a fundamental role in modulating pain perception, reward processing, and emotional regulation [1.2.1, 1.2.4]. Activation of these receptors by endogenous ligands, such as endorphins and enkephalins, or exogenous drugs like morphine, leads to the inhibition of adenylate cyclase and the modulation of ion channels, effectively reducing neuronal excitability [1.1.2, 1.3.2]. While mu-opioid receptors (MOR) are the primary targets for clinical analgesia, their activation is also linked to euphoria and life-threatening side effects like respiratory depression [1.1.4, 1.2.2]. Kappa-opioid receptors (KOR) are associated with dysphoria and sedation, while delta-opioid receptors (DOR) are increasingly investigated for their potential antidepressant and neuroprotective effects [1.1.3, 1.2.3]. Chronic use of opioid agonists often leads to tolerance, physical dependence, and addiction, making the management of these receptors a central challenge in modern medicine [1.3.1, 1.4.1]. Current research focuses on developing biased agonists and multi-target ligands to achieve effective pain relief with a reduced risk of respiratory failure and abuse [1.2.3].

Other names

MOPKOPDOPOPRM1OPRK1OPRD1Mu-opioid receptorKappa-opioid receptorDelta-opioid receptorOpioid peptide receptors

Drugs targeting these receptors act as agonists, antagonists, or partial agonists to modulate neuronal excitability; they primarily inhibit adenylate cyclase to decrease cAMP levels and regulate ion channels, such as opening potassium channels and closing voltage-gated calcium channels.