title: Functional selectivity at the μ-opioid receptor: implications for understanding opioid analgesia and tolerance.
abstract: Opioids are the most effective analgesic drugs for the management of moderate or severe pain, yet their clinical use is often limited because of the onset of adverse side effects. Drugs in this class produce most of their physiological effects through activation of the μ opioid receptor; however, an increasing number of studies demonstrate that different opioids, while presumably acting at this single receptor, can activate distinct downstream responses, a phenomenon termed functional selectivity. Functional selectivity of receptor-mediated events can manifest as a function of the drug used, the cellular or neuronal environment examined, or the signaling or behavioral measure recorded. This review summarizes both in vitro and in vivo work demonstrating functional selectivity at the μ opioid receptor in terms of G protein coupling, receptor phosphorylation, interactions with β-arrestins, receptor desensitization, internalization and signaling, and details on how these differences may relate to the progression of analgesic tolerance after their extended use.
authors.affiliation: Molecular Therapeutics and Neuroscience, The Scripps Research Institute, Jupiter, Florida, USA.
authors.forename: Kirsten M
authors.initials: KM
authors.lastname: Raehal
authors.forename: Cullen L
authors.initials: CL
authors.lastname: Schmid
authors.forename: Chad E
authors.initials: CE
authors.lastname: Groer
authors.forename: Laura M
authors.initials: LM
authors.lastname: Bohn
mesh_terms: D000700:Analgesics / Q000494:pharmacology* / Q000627:therapeutic use; D000701:Analgesics, Opioid / Q000494:pharmacology* / Q000627:therapeutic use; D004361:Drug Tolerance; D020555:GTP-Binding Protein Regulators / Q000187:drug effects / Q000502:physiology; D006801:Humans; D010146:Pain / Q000188:drug therapy* / Q000503:physiopathology; D017450:Receptors, Opioid, mu / Q000502:physiology*
chemical_list: D000700:Analgesics; D000701:Analgesics, Opioid; D020555:GTP-Binding Protein Regulators; D017450:Receptors, Opioid, mu