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  • Title: Potent indole- and quinoline-containing N-methyl-D-aspartate antagonists acting at the strychnine-insensitive glycine binding site.
    Author: Baron BM, Harrison BL, McDonald IA, Meldrum BS, Palfreyman MG, Salituro FG, Siegel BW, Slone AL, Turner JP, White HS.
    Journal: J Pharmacol Exp Ther; 1992 Sep; 262(3):947-56. PubMed ID: 1388205.
    Abstract:
    The N-methyl-D-aspartate (NMDA)-preferring glutamate receptor subtype possesses, in addition to the recognition site for glutamate, a binding site for glycine. We report here on the pharmacological properties of 3-(4,6-dichloro-2-carboxyindol-3-yl)-propionic acid (MDL 29,951) and 4-carboxymethylamino-5,7-dichloroquinoline-2-carboxylic acid (MDL 100,748), two novel glycine antagonists of NMDA receptor activation in vitro and in vivo. We have measured in parallel the effects of two previously described glycine antagonists, 7-chlorokynurenic acid and 5,7-dichlorokynurenic acid. All were potent inhibitors of [3H]glycine binding. Ki values (microM) were 0.36 (7-chlorokynurenic acid), 0.08 (5,7-dichlorokynurenic acid), 0.07 (MDL 100,748) and 0.14 (MDL 29,951). MDL 100,748 and MDL 29,951 were approximately 2000-fold selective for the glycine binding site relative to the glutamate recognition sites. All four compounds completely inhibited the use-dependent binding of [3H]N-[1-(2-thienyl) cyclohexyl]-piperidine and were noncompetitive, glycine-reversible inhibitors of both NMDA-induced biochemical and electrophysiological responses in brain slice preparations. A competitive interaction with the glycine binding site was also evident in that MDL 29,951 and MDL 100,748 produced parallel rightward shifts in the glycine requirement for demonstration of NMDA-stimulated elevations in cytosolic calcium in cultured neuronal preparations. The glycine antagonists were potent anticonvulsants after their i.c.v. administration to audiogenic seizure-susceptible DBA/2J mice. Because the compounds chosen encompass a variety of chemical structures, the results indicate that glycine is required for NMDA receptor activation and that bioavailable glycine antagonists may form the basis of a novel therapy for epilepsy.
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