title: Age dependency of inhibition of alpha7 nicotinic receptors and tonically active N-methyl-D-aspartate receptors by endogenously produced kynurenic acid in the brain.
abstract: In the mouse hippocampus normal levels of kynurenic acid (KYNA), a neuroactive metabolite synthesized in astrocytes primarily by kynurenine aminotransferase II (KAT II)-catalyzed transamination of L-kynurenine, maintain a degree of tonic inhibition of α7 nicotinic acetylcholine receptors (nAChRs). The present in vitro study was designed to test the hypothesis that α7 nAChR activity decreases when endogenous production of KYNA increases. Incubation (2-7 h) of rat hippocampal slices with kynurenine (200 μM) resulted in continuous de novo synthesis of KYNA. Kynurenine conversion to KYNA was significantly decreased by the KAT II inhibitor (S)-(-)-9-(4-aminopiperazine-1-yl)-8-fluoro-3-methyl-6-oxo-2,3,5,6-tetrahydro-4H-1-oxa-3a-azaphenalene-5carboxylic acid (BFF122) (100 μM) and was more effective in slices from postweaned than preweaned rats. Incubation of slices from postweaned rats with kynurenine inhibited α7 nAChRs and extrasynaptic N-methyl-D-aspartate receptors (NMDARs) on CA1 stratum radiatum interneurons. These effects were attenuated by BFF122 and mimicked by exogenously applied KYNA (200 μM). Exposure of human cerebral cortical slices to kynurenine also inhibited α7 nAChRs. The α7 nAChR sensitivity to KYNA is age-dependent, because neither endogenously produced nor exogenously applied KYNA inhibited α7 nAChRs in slices from preweaned rats. In these slices, kynurenine-derived KYNA also failed to inhibit extrasynaptic NMDARs, which could, however, be inhibited by exogenously applied KYNA. In slices from preweaned and postweaned rats, glutamatergic synaptic currents were not affected by endogenously produced KYNA, but were inhibited by exogenously applied KYNA. These results suggest that in the mature brain α7 nAChRs and extrasynaptic NMDARs are in close apposition to KYNA release sites and, thereby, readily accessible to inhibition by endogenously produced KYNA.
authors.affiliation: Department of Pharmacology and Experimental Therapeutics, University of Maryland School of Medicine, 10 S. Pine St., Baltimore, MD 21201, USA.
authors.forename: Manickavasagom
authors.initials: M
authors.lastname: Alkondon
authors.forename: Edna F R
authors.initials: EF
authors.lastname: Pereira
authors.forename: Howard M
authors.initials: HM
authors.lastname: Eisenberg
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Kajii
authors.forename: Robert
authors.initials: R
authors.lastname: Schwarcz
authors.forename: Edson X
authors.initials: EX
authors.lastname: Albuquerque
mesh_terms: D000328:Adult; D000375:Aging; D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D002794:Choline / Q000494:pharmacology; D005260:Female; D058787:GABA-A Receptor Antagonists / Q000494:pharmacology; D006624:Hippocampus / Q000187:drug effects* / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D007395:Interneurons / Q000187:drug effects* / Q000502:physiology; D007736:Kynurenic Acid / Q000378:metabolism*; D007737:Kynurenine / Q000378:metabolism*; D008297:Male; D018733:Nicotinic Antagonists / Q000494:pharmacology; D018697:Nootropic Agents / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011247:Pregnancy; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000378:metabolism*; D064569:alpha7 Nicotinic Acetylcholine Receptor
chemical_list: C579167:Chrna7 protein, human; C579166:Chrna7 protein, mouse; C579165:Chrna7 protein, rat; D058787:GABA-A Receptor Antagonists; D018733:Nicotinic Antagonists; D018697:Nootropic Agents; D016194:Receptors, N-Methyl-D-Aspartate; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor; D007737:Kynurenine; D007736:Kynurenic Acid; D002794:Choline; D001640:Bicuculline