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The Roles of Opioid Receptors and agonists in health and disease Conditions

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Author(s): A.O. Ibegbu | I. Mullaney | L. Fyfe | D. MacBean

Journal: British Journal of Pharmacology and Toxicology
ISSN 2044-2459

Volume: 2;
Issue: 2;
Start page: 84;
Date: 2011;
Original page

Keywords: Opioid Receptors | G-protein coupled receptors | Opioid agonists | Opioid Antagonists | Mu Opioid | Kappa Opioid | Delta Opioid

ABSTRACT
Opioid receptors are found in the central nervous system (CNS) and are classified as mu (µ), kappa (κ), delta (δ) and sigma (σ) opioid receptors. Opioid receptors belong to the large family of G protein coupled receptors (GPCRs), and have diverse and important physiological roles. Opioid receptors are not uniformly distributed in the CNS and are found in areas concerned with pain, with the highest concentration in the cerebral cortex, followed by the amygdala, septum, thalamus, hypothalamus, midbrain and spinal cord. Activated delta opioid receptors are coupled to Gi1 while activated mu opioid receptors are coupled to Gi3 in neuroblastoma cells. Mu opioid receptors are activated by mu receptor agonists and are coupled through the Gαi1 and GαoA. Both mu and kappa opioid receptors are coupled via both Gi and Gz and opioid receptors are important targets for thousands of pharmacological agents. GPCRs typically require activation by agonists for their signalling activity to be initiated but some of the GPCRs may display basal or spontaneous signalling activity in the absence of an agonist. The stimulation of these receptors triggers analgesic effects and affects the function of the nervous system, gastrointestinal tract and other body systems. Hundreds of analogs of opioid peptides have been synthesized in an effort to make the compounds more active, selective, and resistant to biodegradation than the endogenous ligands. All these modifications resulted in obtaining very selective agonists and antagonists with high affinity at mu-, delta-, and kappa-opioid receptors, which are useful in further studies on the pharmacology of opioid receptors in a mammalian organism.
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