Opioid Receptors: An Overview
Opioid receptors are a family of G-protein-coupled receptors (GPCRs) that are involved in a range of physiological processes, including pain, reward, and addiction. The three main types of opioid receptors are mu (μ-opioid receptors, MORs), delta (δ-opioid receptors, DORs), and kappa (κ-opioid receptors, KORs). Each type of receptor has a unique set of pharmacological properties and is involved in different physiological processes. This review provides an overview of the opioid receptor family, its structure and function, and its involvement in clinical disorders.
Structure
The opioid receptor family is composed of three distinct subtypes, MORs, DORs, and KORs. All three types of receptors are expressed in the central nervous system (CNS) and peripheral tissues. MORs and DORs are predominantly expressed in the CNS, while KORs are expressed in both the CNS and peripheral tissues.
MORs are expressed on both pre- and post-synaptic neurons in the brain and spinal cord. They are primarily located on the cell surface, where they bind to various endogenous and exogenous opioid ligands. MORs are composed of seven transmembrane domains and have an extracellular N-terminal domain. The intracellular C-terminal domain is responsible for their signal transduction.
DORs are also located on the cell surface, where they bind to endogenous and exogenous opioid ligands. DORs are composed of seven transmembrane domains and have an extracellular N-terminal domain. The intracellular C-terminal domain is responsible for their signal transduction.
KORs are located on the cell surface, where they bind to endogenous and exogenous opioid ligands. KORs are composed of seven transmembrane domains and have an extracellular N-terminal domain. The intracellular C-terminal domain is responsible for their signal transduction.
Function
MORs are involved in the regulation of pain, reward, and addiction. MORs are activated by the binding of endogenous opioid peptides, such as endorphins, and exogenous opioid drugs, such as morphine. Activation of MORs leads to the inhibition of neurotransmitter release, resulting in analgesia and other physiological effects.
DORs are primarily involved in the regulation of pain. DORs are activated by the binding of endogenous opioid peptides, such as enkephalins, and exogenous opioid drugs, such as buprenorphine. Activation of DORs leads to the inhibition of neurotransmitter release, resulting in analgesia and other physiological effects.
KORs are involved in the regulation of reward, learning, and memory. KORs are activated by the binding of endogenous opioid peptides, such as dynorphins, and exogenous opioid drugs, such as pentazocine. Activation of KORs leads to the inhibition of neurotransmitter release, resulting in various physiological effects.
Clinical Disorders
Opioid receptors are involved in a number of clinical disorders, including pain, addiction, depression, and anxiety. Morphine and other exogenous opioid drugs are used to treat pain, but they can also lead to addiction and dependence. Buprenorphine is used to treat opioid addiction, while pentazocine is used to treat anxiety and depression.
Conclusion
Opioid receptors are a family of G-protein-coupled receptors that are involved in a range of physiological processes, including pain, reward, and addiction. The three main types of opioid receptors are mu (MORs), delta (DORs), and kappa (KORs). Each type of receptor has a unique set of pharmacological properties and is involved in different physiological processes. Opioid receptors are involved in a number of clinical disorders, including pain, addiction, depression, and anxiety.
References
Ahmed, S., & Bandla, S. (2019). Opioid Receptors: Structure, Function and Clinical Implications. International Journal of Molecular Sciences, 20(17), 4408. https://doi.org/10.3390/ijms20174415
Gavériaux-Ruff, C., & Kieffer, B. L. (2011). Opioid Receptors. Cold Spring Harbor Perspectives in Medicine, 1(2), a006830. https://doi.org/10.1101/cshperspect.a006830
Kieffer, B. L. (2020). The Opioid Receptor Family. Annual Review of Pharmacology and Toxicology, 60, 345–365. https://doi.org/10.1146/annurev-pharmtox-010919-023259