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Sunday, 20 November 2011

A Review of the Opioid Receptor System

MOR - Micro Receptor (OP3)

(Ligands: endomorphin, enkephalin, DAMGO)

u1 - analgesia in the brain, euphoria, excitement, psycho-dependence

u2 - analgesia in the spine, sedation, anxiolysis, respiratory depression, constipation, itching, physical dependence, tolerance

u3 - unknown

2 subtypes have been characterized. A 3rd subtype has been theorized based on the analgesia produced by morphine 6-substituted analogues in mu1 and 2 knockout subjects. This third subtype interacts with opioid alkaloid compounds and not opioid peptides; only certain compounds are believed to interact with this subtype - specifically, morphine analogues with C-6 substitutions such as morphine-6-glucuronide, 6-acetylmorphine, heterocodeine, and possibly fentanyl.

KOR - Kappa Receptor (OP2)

(Ligands: dynorphin, enadoline, ketocyclazocine)

spinal analgesia, dysphoria, miosis, sedation, diuresis (increased urination), psychotomimesis, anti-itching, counteraction of mu-agonist effects, anti-addictive effect, dopamine inhibition, mu & dopamine receptor upregulation

At least 2 subtypes of kappa receptor have been characterized. Kappa is the endogenous dynorphin receptor.

DOR - Delta Receptor (OP1)

(Ligands: enkephalin, deltorphin, DPDPE)

anxiolysis, antidepressant properties, respiratory stimulation or depression, upregulation of brain-derived neurotrophic hormone, cardioprotection, potentiation of mu analgesia

2 subtypes of delta receptor have been characterized.

ORL1 - Orphan Receptor, Opioid-Like-Receptor 1 (OP4)

(Ligand: nociceptin)

hyperalgesia (pain), anxiety, counteraction of mu-agonist effects, anorexia or hunger
 
Endogenous receptor for nociceptin, the neurotransmitter implicated in transduction of pain signals.

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