The amino acid L-glutamate is the major excitatory neurotransmitter in the central nervous system and activates both ionotropic and metabotropicglutamate receptors. Glutamatergic neurotransmission is involved in most aspects of normal brain function and can be perturbed in many neuropathologic conditions. The metabotropic glutamate receptors are a family of G protein-coupled receptors, that have been divided into 3 groups on the basis of sequence homology, putative signal transduction mechanisms, and pharmacological properties. Group I includes GRM1 and GRM5 and these receptors have been shown to activate phospholipase C. Group II includes GRM2 and GRM3 while Group III includes GRM4, GRM6, GRM7, and GRM8. Group II and III receptors are linked to the inhibition of the cyclic AMP cascade but differ in their agonist selectivities. Alternative splice variants of GRM8 have been described but their full-length nature has not been determined.[2]
Ligands
In addition to the orthosteric site (the site where the endogenous ligand glutamate binds) at least two distinct allostericbinding sites exist on the mGluR5.[3] A respectable number of potent and selective mGluR5 ligands, which also comprise PETradiotracers, has been developed to date.[4] Selective antagonists and negative allosteric modulators of mGluR5 are a particular area of interest for pharmaceutical research, due to their demonstrated anxiolytic, antidepressant and anti-addictive[5][6][7] effects in animal studies and their relatively benign safety profile.[8][9] mGluR5 receptors are also expressed outside the central nervous system, and mGluR5 antagonists have been shown to be hepatoprotective and may also be useful for the treatment of inflammation and neuropathic pain.[10][11] The clinical use of these drugs may be limited by side effects such as amnesia and psychotomimetic symptoms,[12][13][14][15] but these could be an advantage for some indications,[16] or conversely mGluR5 positive modulators may have nootropic effects.[17]
Mice with a knocked out mGluR5 show a lack of cocaine self-administration regardless of dose.[26] This suggested that the receptor may be intimately involved in the rewarding properties of cocaine. However, a later study showed that mGluR5 knockout mice responded the same to cocaine reward as wild type mice demonstrated by a cocaine place-preference paradigm.[27] This evidence taken together shows that mGluR5 may be crucial for drug-related instrumental self-administration learning, but not conditioned associations.
↑Minakami R, Katsuki F, Yamamoto T, Nakamura K, Sugiyama H (March 1994). "Molecular cloning and the functional expression of two isoforms of human metabotropic glutamate receptor subtype 5". Biochemical and Biophysical Research Communications. 199 (3): 1136–43. doi:10.1006/bbrc.1994.1349. PMID7908515.
↑Chen Y, Goudet C, Pin JP, Conn PJ (March 2008). "N-{4-Chloro-2-[(1,3-dioxo-1,3-dihydro-2H-isoindol-2-yl)methyl]phenyl}-2-hydroxybenzamide (CPPHA) acts through a novel site as a positive allosteric modulator of group 1 metabotropic glutamate receptors". Molecular Pharmacology. 73 (3): 909–18. doi:10.1124/mol.107.040097. PMID18056795.
↑Bespalov AY, Dravolina OA, Sukhanov I, Zakharova E, Blokhina E, Zvartau E, Danysz W, van Heeke G, Markou A (2005). "Metabotropic glutamate receptor (mGluR5) antagonist MPEP attenuated cue- and schedule-induced reinstatement of nicotine self-administration behavior in rats". Neuropharmacology. 49 Suppl 1: 167–78. doi:10.1016/j.neuropharm.2005.06.007. PMID16023685.
↑Slassi A, Isaac M, Edwards L, Minidis A, Wensbo D, Mattsson J, Nilsson K, Raboisson P, McLeod D, Stormann TM, Hammerland LG, Johnson E (2005). "Recent advances in non-competitive mGlu5 receptor antagonists and their potential therapeutic applications". Current Topics in Medicinal Chemistry. 5 (9): 897–911. doi:10.2174/1568026054750236. PMID16178734.
↑Gasparini F, Bilbe G, Gomez-Mancilla B, Spooren W (September 2008). "mGluR5 antagonists: discovery, characterization and drug development". Current Opinion in Drug Discovery & Development. 11 (5): 655–65. PMID18729017.
↑Hu Y, Dong L, Sun B, Guillon MA, Burbach LR, Nunn PA, Liu X, Vilenski O, Ford AP, Zhong Y, Rong W (January 2009). "The role of metabotropic glutamate receptor mGlu5 in control of micturition and bladder nociception". Neuroscience Letters. 450 (1): 12–7. doi:10.1016/j.neulet.2008.11.026. PMID19027050.
↑Jesse CR, Wilhelm EA, Bortolatto CF, Savegnago L, Nogueira CW (May 2009). "Selective blockade of mGlu5 metabotropic glutamate receptors is hepatoprotective against fulminant hepatic failure induced by lipopolysaccharide and D-galactosamine in mice". Journal of Applied Toxicology. 29 (4): 323–9. doi:10.1002/jat.1413. PMID19153979.
↑Simonyi A, Schachtman TR, Christoffersen GR (Jul 2005). "The role of metabotropic glutamate receptor 5 in learning and memory processes". Drug News & Perspectives. 18 (6): 353–61. doi:10.1358/dnp.2005.18.6.927927. PMID16247513.
↑Manahan-Vaughan D, Braunewell KH (November 2005). "The metabotropic glutamate receptor, mGluR5, is a key determinant of good and bad spatial learning performance and hippocampal synaptic plasticity". Cerebral Cortex. 15 (11): 1703–13. doi:10.1093/cercor/bhi047. PMID15703249.
↑Palucha A, Pilc A (July 2007). "Metabotropic glutamate receptor ligands as possible anxiolytic and antidepressant drugs". Pharmacology & Therapeutics. 115 (1): 116–47. doi:10.1016/j.pharmthera.2007.04.007. PMID17582504.
↑Christoffersen GR, Simonyi A, Schachtman TR, Clausen B, Clement D, Bjerre VK, Mark LT, Reinholdt M, Schmith-Rasmussen K, Zink LV (August 2008). "MGlu5 antagonism impairs exploration and memory of spatial and non-spatial stimuli in rats". Behavioural Brain Research. 191 (2): 235–45. doi:10.1016/j.bbr.2008.03.032. PMID18471908.
↑Liu F, Grauer S, Kelley C, Navarra R, Graf R, Zhang G, Atkinson PJ, Popiolek M, Wantuch C, Khawaja X, Smith D, Olsen M, Kouranova E, Lai M, Pruthi F, Pulicicchio C, Day M, Gilbert A, Pausch MH, Brandon NJ, Beyer CE, Comery TA, Logue S, Rosenzweig-Lipson S, Marquis KL (December 2008). "ADX47273 [S-(4-fluoro-phenyl)-{3-[3-(4-fluoro-phenyl)-[1,2,4]-oxadiazol-5-yl]-piperidin-1-yl}-methanone]: a novel metabotropic glutamate receptor 5-selective positive allosteric modulator with preclinical antipsychotic-like and procognitive activities". The Journal of Pharmacology and Experimental Therapeutics. 327 (3): 827–39. doi:10.1124/jpet.108.136580. PMID18753411.
↑Zhao Z, Wisnoski DD, O'Brien JA, Lemaire W, Williams DL, Jacobson MA, Wittman M, Ha SN, Schaffhauser H, Sur C, Pettibone DJ, Duggan ME, Conn PJ, Hartman GD, Lindsley CW (March 2007). "Challenges in the development of mGluR5 positive allosteric modulators: the discovery of CPPHA". Bioorganic & Medicinal Chemistry Letters. 17 (5): 1386–91. doi:10.1016/j.bmcl.2006.11.081. PMID17210250.
↑O'Brien JA, Lemaire W, Wittmann M, Jacobson MA, Ha SN, Wisnoski DD, Lindsley CW, Schaffhauser HJ, Rowe B, Sur C, Duggan ME, Pettibone DJ, Conn PJ, Williams DL (May 2004). "A novel selective allosteric modulator potentiates the activity of native metabotropic glutamate receptor subtype 5 in rat forebrain". The Journal of Pharmacology and Experimental Therapeutics. 309 (2): 568–77. doi:10.1124/jpet.103.061747. PMID14747613.
↑Chen Y, Nong Y, Goudet C, Hemstapat K, de Paulis T, Pin JP, Conn PJ (May 2007). "Interaction of novel positive allosteric modulators of metabotropic glutamate receptor 5 with the negative allosteric antagonist site is required for potentiation of receptor responses". Molecular Pharmacology. 71 (5): 1389–98. doi:10.1124/mol.106.032425. PMID17303702.
↑de Paulis T, Hemstapat K, Chen Y, Zhang Y, Saleh S, Alagille D, Baldwin RM, Tamagnan GD, Conn PJ (June 2006). "Substituent effects of N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamides on positive allosteric modulation of the metabotropic glutamate-5 receptor in rat cortical astrocytes". Journal of Medicinal Chemistry. 49 (11): 3332–44. doi:10.1021/jm051252j. PMID16722652.
↑Kinney GG, O'Brien JA, Lemaire W, Burno M, Bickel DJ, Clements MK, Chen TB, Wisnoski DD, Lindsley CW, Tiller PR, Smith S, Jacobson MA, Sur C, Duggan ME, Pettibone DJ, Conn PJ, Williams DL (April 2005). "A novel selective positive allosteric modulator of metabotropic glutamate receptor subtype 5 has in vivo activity and antipsychotic-like effects in rat behavioral models". The Journal of Pharmacology and Experimental Therapeutics. 313 (1): 199–206. doi:10.1124/jpet.104.079244. PMID15608073.
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