μ-Opioid Receptor / mu-Opioid Receptor


What is μ-Opioid Receptor (mu-Opioid Receptor)?

MOR or μ-opioid receptor is a type of Opioid Receptor which has a very close affinity for ‘Enkephalins’ (pentapeptide) and ‘Beta-endorphin’ (opioid nucleotide). However, it exhibits a very low affinity for ‘Dynorphins’ (a type of opioid peptide). The gene OPRM1 also expresses this type of opioid receptor in vertebrates. MOR or μ-opioid receptor plays a very significant role in the body, serving as a target for pain relievers and even contributing to drug abuse treatment. Besides, the μ-opioid receptor is essentially a ‘7 multispanning integral protein’, which you will usually find in the dorsal root ganglion cells and peripheral nerve. To learn more about MOR here is presenting the following article explaining all the basic facts you need to know about it.


How does a μ-Opioid Receptor Act to Resolve Pain?

Firstly, you need to know that MOR or μ-opioid receptor is a G-protein coupled receptor (GPCR), which stimulates the Gi alpha subunit, which blocks adenylate cyclase activity to lower cAMP levels. It binds with extraneous opiate drugs (morphine) and endogenous opiate peptide neurotransmitters (endorphins). They then bind as ligands to disrupt pain signalling with the endogenous and especially exogenous opioids producing a very powerful physiological response to reduce pain sensations in the body. The most important regulatory proteins that play a major role in MOR or μ-opioid receptors include the arrestin beta two and the beta arrestins arrestin beta. The activation of MOR, in simple words, impacts dendritic spines depending upon the agonist.


What are Some of The Major Subtypes of MOR or μ-Opioid Receptors?

MOR or μ-opioid receptor is available in essentially five types. They are as follows:

zeta (ζ) or ZOR

Delta or DOR

Kappa K or KOR

mu or MOR

Nociceptin Receptor

OGFr was discovered and given the name zeta (ζ). Moreover, you will find that none of these receptors share common properties.


List of MOR or μ-Opioid Receptor Antagonists:

There are several MOR or μ-opioid receptor inverse agonists or antagonists available in the market today that you need to know. Usually, many bind to the Kappa K or KOR receptor or Delta or DOR receptor and serve by stimulating either the central or peripheral nervous system. These include the following:








Most of the MOR or μ-opioid receptor types are non-selective; they either act by inhibiting several mu or MOR type receptors while activating KOR types. Moreover, these days due to advancements in scientific research, there is a significant development in the production of antagonists that are highly selective to one among the four receptors. They are as follows:


J-113 397




Adverse Side-Effects of MOR or μ-Opioid Receptor Antagonist Drugs:

Like many other synthetic drugs, MOR or μ-opioid receptor antagonist drugs, when used to relieve pain, can often trigger quite a few serious side effects. They are as follows:

Feeling of sedation


Respiratory depression



Dependence/ Withdrawal


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