title: Tonic facilitation of glutamate release by glycine binding sites on presynaptic NR2B-containing NMDA autoreceptors in the rat visual cortex.
abstract: We have previously shown that glycine binding sites on presynaptic NMDA receptors (NMDA-Rs) can tonically regulate glutamate release in the rat visual cortex. In the present study, we investigated the subunit composition of these presynaptic NMDA-Rs. We recorded miniature a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated excitatory postsynaptic currents (mEPSCs) using whole-cell voltage clamp in layer II/III pyramidal neurons of the rat visual cortex with the open-channel NMDA receptor blocker, MK-801, in the recording pipette. We found that the frequency of mEPSCs is significantly reduced by 7-chloro-kynurenic acid (7-Cl KYNA) an NMDA-R glycine binding site antagonist, and glycine reverses this effect. Using a specific antagonist for NR2B-NMDA-Rs, Ro 25-6981 [(alphaR,betaS)-alpha-(4-hydroxyphenyl)-beta-methyl-4-(phenylmethyl)-1-piperidinepropanol hydrochloride], instead of 7-Cl KYNA, we found that the frequency of mEPSCs is also significantly reduced but glycine cannot reverse this effect. Moreover, Zn(2+), an NR2A-NMDA-R antagonist, did not affect mEPSC frequency. These results suggest that presynaptic NR2B-containing NMDA-Rs are located in layer II/III pyramidal neurons of the rat visual cortex, and that the glycine binding site of these type NMDA-Rs tonically regulates glutamate release.
authors.affiliation: Department of Physiology, School of Medicine, Xi'an Jiaotong University, Zhuque Dajie 205, Xi'an 710061, PR China.
authors.forename: Yan-Hai
authors.initials: YH
authors.lastname: Li
authors.forename: Tai-Zhen
authors.initials: TZ
authors.lastname: Han
authors.forename: Kai
authors.initials: K
authors.lastname: Meng
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001665:Binding Sites / Q000187:drug effects / Q000502:physiology; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004347:Drug Interactions; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D018698:Glutamic Acid / Q000378:metabolism*; D005998:Glycine / Q000494:pharmacology*; D066298:In Vitro Techniques; D007736:Kynurenic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010636:Phenols / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D014793:Visual Cortex / Q000166:cytology*
chemical_list: D018691:Excitatory Amino Acid Antagonists; C121001:NR2B NMDA receptor; D010636:Phenols; D010880:Piperidines; D016194:Receptors, N-Methyl-D-Aspartate; C109643:Ro 25-6981; C084485:7-chlorothiokynurenic acid; D018698:Glutamic Acid; D016291:Dizocilpine Maleate; D007736:Kynurenic Acid; D005998:Glycine