title: Sustained saturating level of glycine induces changes in NR2B-containing-NMDA receptor localization in the CA1 region of the hippocampus.
abstract: Post-synaptic actions of glycine are terminated by specialized transporters. There are two genes encoding glycine transporters, GlyT1 and GlyT2. Glycine acts as a co-agonist at N-methyl-d-aspartate glutamatergic receptors (NMDARs). Blockage of GlyT1 enhances NMDAR function by controlling ambient glycine concentrations. Using whole-cell patch-clamp recordings of acute hippocampal slices, we investigated NMDAR kinetics of CA1 pyramidal neurons of mice expressing 50% of GlyT1 (GlyT1+/-). In this study, we report that the glycine modulatory site of the NMDAR at CA1 synapses is saturated in GlyT1+/- but not in wild-type (WT) mice. We also found that the effect of ifenprodil, a highly selective NR2B-containing-NMDAR antagonist, is significantly reduced at CA1 synapses in GlyT1+/- compared to WT mice while immunoblotting experiments do not show significant differences for NR1, NR2A-B-C-D subunits in both types of mice, suggesting alteration in NR2B-containing-NMDAR localization under a state of chronic saturating level of endogenous glycine. Using a pharmacological approach with MK-801 and DL-TBOA, we discriminated synaptic vis-à-vis extra-synaptic NMDARs. We found that NR2B-containing-NMDARs are expressed at a higher level in the extra-synaptic area of CA1 pyramidal neurons from GlyT1+/- compared to WT mice. Our results demonstrate that chronic saturating level of glycine induces significant changes in NMDAR localization and kinetic. Therefore, results from our study should help to gain a better understanding of the role of glycine in pathological conditions.
authors.affiliation: Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada.
authors.forename: Yukio
authors.initials: Y
authors.lastname: Imamura
authors.forename: Chun-Lei
authors.initials: CL
authors.lastname: Ma
authors.forename: Mohan
authors.initials: M
authors.lastname: Pabba
authors.forename: Richard
authors.initials: R
authors.lastname: Bergeron
mesh_terms: D000818:Animals; D056547:CA1 Region, Hippocampal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D023902:Chromosome Pairing / Q000187:drug effects / Q000502:physiology; D005998:Glycine / Q000008:administration & dosage* / Q000378:metabolism / Q000502:physiology*; D050487:Glycine Plasma Membrane Transport Proteins / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D016194:Receptors, N-Methyl-D-Aspartate / Q000819:agonists* / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000378:metabolism
chemical_list: D050487:Glycine Plasma Membrane Transport Proteins; C121001:NR2B NMDA receptor; D016194:Receptors, N-Methyl-D-Aspartate; D005998:Glycine