Open Access
The evolution of vertebrate opioid receptors
Craig W Stevens1
Department of Pharmacology and Physiology, Oklahoma State University-Center for Health Sciences, Tulsa, OK, USA.
DOI: 10.2741/3306 Volume 14 Issue 4, pp.1247-1269
Published: 01 January 2009
(This article belongs to the Special Issue regulation and function of opioid receptor genes)

The proteins that mediate the analgesic and other effects of opioid drugs and endogenous opioid peptides are known as opioid receptors. Opioid receptors consist of a family of four closely-related proteins belonging to the large superfamily of G-protein coupled receptors. The three types of opioid receptors shown unequivocally to mediate analgesia in animal models are the mu (MOR), delta (DOR), and kappa (KOR) opioid receptor proteins. The role of the fourth member of the opioid receptor family, the nociceptin or orphanin FQ receptor (ORL), is not as clear as hyperalgesia, analgesia, and no effect was reported after administration of ORL agonists. There are now cDNA sequences for all four types of opioid receptors that are expressed in the brain of six species from three different classes of vertebrates. This review presents a comparative analysis of vertebrate opioid receptors using bioinformatics and data from recent human genome studies. Results indicate that opioid receptors arose by gene duplication, that there is a vector of opioid receptor divergence, and that MOR shows evidence of rapid evolution.

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Craig W Stevens. The evolution of vertebrate opioid receptors. Frontiers in Bioscience-Landmark. 2009. 14(4); 1247-1269.