title: Glycine binding sites of presynaptic NMDA receptors may tonically regulate glutamate release in the rat visual cortex.
abstract: In the CNS, activation of N-methyl-D-aspartate receptor (NMDA-R) glycine binding sites is a prerequisite for activation of postsynaptic NMDA-Rs by the excitatory neurotransmitter glutamate. Here we provide electrophysiological evidence that the glycine binding sites of presynaptic NMDA-Rs regulate glutamate release in layer II/III pyramidal neurons of the rat visual cortex. Specifically, our results reveal that the frequency of miniature excitatory postsynaptic currents is significantly reduced by 7-chloro-kynurenic acid (7-Cl KYNA), a NMDA-R glycine binding site antagonist, and glycine or D-serine reverses this effect. Similar results are obtained when the open-channel NMDA receptor blocker, MK-801, is included in the recording pipette. Our data indicate that the glycine binding site of postsynaptic NMDA-Rs is not saturated. Moreover, they suggest that presynaptic NMDA-Rs are located in layer II/III pyramidal neurons of the rat visual cortex and that the glycine binding site of presynaptic NMDA-Rs tonically regulates glutamate release.
authors.affiliation: Dept. of Physiology, School of Medicine, Xi'an Jiaotong University, Zhuque Dajie 205, Xi'an, Shaanxi 710061, PR China.
authors.forename: Yan-Hai
authors.initials: YH
authors.lastname: Li
authors.forename: Tai-Zhen
authors.initials: TZ
authors.lastname: Han
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000187:drug effects / Q000502:physiology; D001667:Binding, Competitive / Q000187:drug effects / Q000502:physiology; D016291:Dizocilpine Maleate / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D018698:Glutamic Acid / Q000378:metabolism*; D005998:Glycine / Q000378:metabolism* / Q000494:pharmacology; D007736:Kynurenic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D009924:Organ Culture Techniques; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D017966:Pyramidal Cells / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D009435:Synaptic Transmission / Q000502:physiology*; D014793:Visual Cortex / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D018691:Excitatory Amino Acid Antagonists; D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid; D016291:Dizocilpine Maleate; D007736:Kynurenic Acid; C057013:7-chlorokynurenic acid; D005998:Glycine