Opioid receptors characteristics

Detailed characterization of opioid receptors began in 1992 with the identification and cloning of the OPl (delta) receptor, followed by subsequent identification and cloning of OP2 (kappa) and OP3 (mu) receptors. All of these receptors are G-coupled proteins that have seven transmembrane domains and share 60% of structural homology. In 1994, a new receptor subtype was identified and was originally given the name opioid receptor like-1 (ORL-1). This subtype has typical opioid receptor characteristics, such as a G-coupled... 

Bleich A, Gelkopf M, Weizman T, et al Benzodiazepine abuse in a methadone maintenance treatment clinic in Israel characteristics and a pharmacotherapeutic approach. Isr J Psychiatry Relat Sci 39 104-112, 2002 Bohn LM, Gainetdinov RR, Lin FT, et al Mu-opioid receptor desensitization by beta-arrestin-2 determines morphine tolerance but not dependence. Nature 408 720— 723, 2000... 

Tolerance and dependence are characteristic of repeated administration of opioid drugs, which limits their use in treatment. It has been proposed that tolerance results from desensitization of opioid receptors and altered... 

Opioids are compounds that bind one or more of the many different opioid receptors in the body. Opioids act primarily on the central nervous system. The selectivity of a given opioid for the various opioid receptors determines its characteristic activity. While many opioids are powerful analgesics, opioids often cause physical dependence and have tolerance issues. Sedation and decreased rate of breathing are also side effects associated with opioids. Despite their problems, opioids are generally the drug of choice for treating severe, acute pain. 

Suzuki T, Funada M, Narita M, Misawa M, Nagase H (1993) Morphine-induced place preference in the CXBK mouse characteristics of p. opioid receptor subtypes. Brain Res 602 45-52... 

Belief in the existence of yet another variety of opioid receptor, designated e, is gaining ground.(228,240) This species was originally postulated to account for the unique characteristics of opioid receptors in the rat vas deferens.<229) /VEndorphin is a potent agonist in this tissue, but its effects do not appear to be mediated at /a-, k-, or 5-sites. Specific benzomorphan sites in rat brain membranes have been described that also do not seem to be of the /c-variety/230 and since /3h-endorphin is likewise a potent ligand for these sites,<231) they may well correspond to the putative e-receptors. 

The biological activity of epibatidine has not been studied in any detail because of the minute quantities available from the frog Epipedobates tricolor. Its presence as a trace alkaloid and its chromatographic purification were based on the Straub tail response that epibatidine causes in mice. The Straub tail response is characteristic of opiate alkaloids however, unlike that caused by morphine and other opiates, the response caused by epibatidine was not reversed by the opiate antagonist naloxone (765). Epibatidine proved to be a potent analgetic, being manyfold more potent than morphine in the hot plate analgetic assay (765). Epibatidine had very low affinity for opioid receptors (765). 

Spetea M, Toth F, Schiitz J, Otvos F, Toth G, Benyhe S, Borsodi A, Schmidhammer H (2003) Binding characteristics of [3H] 14-methoxymetopon, a high affinity p-opioid receptor agonist. Eur J Neurosci 18 290-295... 

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