The μ-opioid receptors (using the Greek letter mu, abbreviated MOR) are a class of opioid receptors with a high affinity for enkephalins and beta-endorphin, but a low affinity for dynorphins. They are also referred to as μ(mu)-opioid peptide (MOP) receptors. The prototypical μ-opioid receptor agonist is morphine, the primary psychoactive alkaloid in opium and for which the receptor was named, with mu being the first letter of Morpheus, the compound's namesake in the original Greek. It is an inhibitory G-protein coupled receptor that activates the Gi alpha subunit, inhibiting adenylate cyclase activity, lowering cAMP levels.
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Opioid receptor in the context of Kappa-opioid receptor
The κ-opioid receptor or kappa opioid receptor, abbreviated KOR or KOP for its ligand ketazocine, is a G protein-coupled receptor that in humans is encoded by the OPRK1 gene. The KOR is coupled to the G protein Gi/G0 and is among related receptors that bind opioid-like compounds in the brain and are responsible for mediating the effects of these compounds. These include altering nociception, mood, reward system, and motor control.
KOR is one of the two opioid receptors that bind dynorphin opioid peptides as the primary endogenous ligands, the other being newly deorphanized GPR139 receptor. In addition, oxytocin was found to be a positive allosteric modulator of KOR, and a variety of natural alkaloids, terpenes and synthetic ligands bind to the receptor.
Opioid receptor in the context of Ibogaine
Ibogaine is a psychoactive indole alkaloid derived from plants such as Tabernanthe iboga, characterized by hallucinogenic and oneirogenic effects. Traditionally used by Central African foragers, it has undergone controversial research for the treatment of substance use disorders. Ibogaine exhibits complex pharmacology by interacting with multiple neurotransmitter systems, notably affecting opioid, serotonin, sigma, and NMDA receptors, while its metabolite noribogaine primarily acts as a serotonin reuptake inhibitor and κ-opioid receptor agonist.
The psychoactivity of the root bark of the iboga tree, T. iboga, one of the plants from which ibogaine is extracted, was first discovered by forager tribes in Central Africa, who passed the knowledge to the Bwiti tribe of Gabon. It was first documented in the 19th century for its spiritual use, later isolated and synthesized for its psychoactive properties, briefly marketed in Europe as a stimulant, and ultimately researched—and often controversial—for its potential in treating addiction despite being classified as a controlled substance.