H3 antagonist

An H₃-receptor antagonist is a classification of drugs used to block the action of histamine on the Histamine H3 receptor. Unlike the H₁ and H₂ receptors which have primarily peripheral actions, but cause sedation if they are blocked in the brain, H₃ receptors are primarily found in the brain and are inhibitory autoreceptors located on histaminergic nerve terminals, which modulate the release of histamine. Histamine release in the brain triggers secondary release of excitatory neurotransmitters such as glutamate and acetylcholine via stimulation of H₁ receptors in the cerebral cortex. Consequently unlike the H₁ antagonist antihistamines which are sedating, H₃ antagonists have stimulant and nootropic effects, and are being researched as potential drugs for the treatment of neurodegenerative conditions such as Alzheimer's disease.

Examples of selective H₃ antagonists include clobenpropit,cite journal |author=Yoneyama H, Shimoda A, Araki L, "et al" |title=Efficient approaches to S-alkyl-N-alkylisothioureas: syntheses of histamine H3 antagonist clobenpropit and its analogues |journal=J. Org. Chem. |volume=73 |issue=6 |pages=2096–104 |year=2008 |month=March |pmid=18278935 |doi=10.1021/jo702181x |url=http://dx.doi.org/10.1021/jo702181x] ABT-239,cite journal | author = Fox GB, Esbenshade TA, Pan JB, Radek RJ, Krueger KM, Yao BB, Browman KE, Buckley MJ, Ballard ME, Komater VA, Miner H, Zhang M, Faghih R, Rueter LE, Bitner RS, Drescher KU, Wetter J, Marsh K, Lemaire M, Porsolt RD, Bennani YL, Sullivan JP, Cowart MD, Decker MW, Hancock AA | title = Pharmacological properties of ABT-239 [4-(2-{2- [(2R)-2-Methylpyrrolidinyl] ethyl}-benzofuran-5-yl)benzonitrile] : II. Neurophysiological characterization and broad preclinical efficacy in cognition and schizophrenia of a potent and selective histamine H₃ receptor antagonist | journal = J. Pharmacol. Exp. Ther. | volume = 313 | issue = 1 | pages = 176–90 | year = 2005 | pmid = 15608077 | doi = 10.1124/jpet.104.078402 | issn = ] ciproxifan,cite journal | author = LLigneau X, Lin J, Vanni-Mercier G, Jouvet M, Muir JL, Ganellin CR, Stark H, Elz S, Schunack W, Schwartz J | title = Neurochemical and behavioral effects of ciproxifan, a potent histamine H₃-receptor antagonist | journal = J. Pharmacol. Exp. Ther. | volume = 287 | issue = 2 | pages = 658–66 | year = 1998 | month = November | pmid = 9808693 | doi = 10.1016/j.bcp.2007.01.002 | url = | issn = ] and A-349,821. [Esbenshade TA, Fox GB, Krueger KM, Baranowski JL, Miller TR, Kang CH, Denny LI, Witte DG, Yao BB, Pan JB, Faghih R, Bennani YL, Williams M, Hancock AA. Pharmacological and behavioral properties of A-349821, a selective and potent human histamine H3 receptor antagonist. "Biochemical Pharmacology". 2004 Sep 1;68(5):933-45. PMID 15294456]

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