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Voltage-independent GluN2A-type NMDA receptor Ca 2+ signaling promotes audiogenic seizures, attentional and cognitive deficits in mice. Commun Biol 2021; 4:59. [PMID: 33420383 PMCID: PMC7794508 DOI: 10.1038/s42003-020-01538-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2020] [Accepted: 11/20/2020] [Indexed: 12/21/2022] Open
Abstract
The NMDA receptor-mediated Ca2+ signaling during simultaneous pre- and postsynaptic activity is critically involved in synaptic plasticity and thus has a key role in the nervous system. In GRIN2-variant patients alterations of this coincidence detection provoked complex clinical phenotypes, ranging from reduced muscle strength to epileptic seizures and intellectual disability. By using our gene-targeted mouse line (Grin2aN615S), we show that voltage-independent glutamate-gated signaling of GluN2A-containing NMDA receptors is associated with NMDAR-dependent audiogenic seizures due to hyperexcitable midbrain circuits. In contrast, the NMDAR antagonist MK-801-induced c-Fos expression is reduced in the hippocampus. Likewise, the synchronization of theta- and gamma oscillatory activity is lowered during exploration, demonstrating reduced hippocampal activity. This is associated with exploratory hyperactivity and aberrantly increased and dysregulated levels of attention that can interfere with associative learning, in particular when relevant cues and reward outcomes are disconnected in space and time. Together, our findings provide (i) experimental evidence that the inherent voltage-dependent Ca2+ signaling of NMDA receptors is essential for maintaining appropriate responses to sensory stimuli and (ii) a mechanistic explanation for the neurological manifestations seen in the NMDAR-related human disorders with GRIN2 variant-meidiated intellectual disability and focal epilepsy. Ilaria Bertocchi et al. use a mouse model of Grin2a dysfunction to show that activity-independent NMDA receptors are involved in audiogenic seizure generation. Their results suggest a role for NMDA receptors in maintaining an appropriate response to sensory stimuli and a potential mechanism for disease phenotypes in epilepsy patients with GRIN2A mutations.
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Ballesteros JJ, Buschler A, Köhr G, Manahan-Vaughan D. Afferent Input Selects NMDA Receptor Subtype to Determine the Persistency of Hippocampal LTP in Freely Behaving Mice. Front Synaptic Neurosci 2016; 8:33. [PMID: 27818632 PMCID: PMC5073893 DOI: 10.3389/fnsyn.2016.00033] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2016] [Accepted: 09/26/2016] [Indexed: 01/07/2023] Open
Abstract
The glutamatergic N-methyl-D-aspartate receptor (NMDAR) is critically involved in many forms of hippocampus-dependent memory that may be enabled by synaptic plasticity. Behavioral studies with NMDAR antagonists and NMDAR subunit (GluN2) mutants revealed distinct contributions from GluN2A- and GluN2B-containing NMDARs to rapidly and slowly acquired memory performance. Furthermore, studies of synaptic plasticity, in genetically modified mice in vitro, suggest that GluN2A and GluN2B may contribute in different ways to the induction and longevity of synaptic plasticity. In contrast to the hippocampal slice preparation, in behaving mice, the afferent frequencies that induce synaptic plasticity are very restricted and specific. In fact, it is the stimulus pattern and not variations in afferent frequency that determine the longevity of long-term potentiation (LTP) in vivo. Here, we explored the contribution of GluN2A and GluN2B to LTP of differing magnitudes and persistence in freely behaving mice. We applied differing high-frequency stimulation (HFS) patterns at 100 Hz to the hippocampal CA1 region, to induce NMDAR-dependent LTP in wild-type (WT) mice, that endured for <1 h (early (E)-LTP), (LTP, 2–4 h) or >24 h (late (L)-LTP). In GluN2A-knockout (KO) mice, E-LTP (HFS, 50 pulses) was significantly reduced in magnitude and duration, whereas LTP (HFS, 2 × 50 pulses) and L-LTP (HFS, 4 × 50 pulses) were unaffected compared to responses in WT animals. By contrast, pharmacological antagonism of GluN2B in WT had no effect on E-LTP but significantly prevented LTP. E-LTP and LTP were significantly impaired by GluN2B antagonism in GluN2A-KO mice. These data indicate that the pattern of afferent stimulation is decisive for the recruitment of distinct GluN2A and GluN2B signaling pathways that in turn determine the persistency of hippocampal LTP. Whereas brief bursts of patterned stimulation preferentially recruit GluN2A and lead to weak and short-lived forms of LTP, prolonged, more intense, afferent activation recruits GluN2B and leads to robust and persistent LTP. These unique signal-response properties of GluN2A and GluN2B enable qualitative differentiation of information encoding in hippocampal synapses.
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Affiliation(s)
- Jesús J Ballesteros
- Department of Neurophysiology, Medical Faculty, Ruhr University Bochum Bochum, Germany
| | - Arne Buschler
- Department of Neurophysiology, Medical Faculty, Ruhr University Bochum Bochum, Germany
| | - Georg Köhr
- Max Planck Institute for Medical Research Heidelberg, Germany
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Berlin S, Szobota S, Reiner A, Carroll EC, Kienzler MA, Guyon A, Xiao T, Trauner D, Isacoff EY. A family of photoswitchable NMDA receptors. eLife 2016; 5. [PMID: 26929991 PMCID: PMC4786437 DOI: 10.7554/elife.12040] [Citation(s) in RCA: 60] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2015] [Accepted: 01/31/2016] [Indexed: 02/07/2023] Open
Abstract
NMDA receptors, which regulate synaptic strength and are implicated in learning and memory, consist of several subtypes with distinct subunit compositions and functional properties. To enable spatiotemporally defined, rapid and reproducible manipulation of function of specific subtypes, we engineered a set of photoswitchable GluN subunits ('LiGluNs'). Photo-agonism of GluN2A or GluN2B elicits an excitatory drive to hippocampal neurons that can be shaped in time to mimic synaptic activation. Photo-agonism of GluN2A at single dendritic spines evokes spine-specific calcium elevation and expansion, the morphological correlate of LTP. Photo-antagonism of GluN2A alone, or in combination with photo-antagonism of GluN1a, reversibly blocks excitatory synaptic currents, prevents the induction of long-term potentiation and prevents spine expansion. In addition, photo-antagonism in vivo disrupts synaptic pruning of developing retino-tectal projections in larval zebrafish. By providing precise and rapidly reversible optical control of NMDA receptor subtypes, LiGluNs should help unravel the contribution of specific NMDA receptors to synaptic transmission, integration and plasticity.
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Affiliation(s)
- Shai Berlin
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States
| | - Stephanie Szobota
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States
| | - Andreas Reiner
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States
| | - Elizabeth C Carroll
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States
| | - Michael A Kienzler
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States
| | - Alice Guyon
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.,Institut de Pharmacologie Moléculaire et Cellulaire, Université de Nice Sophia Antipolis, Nice, France
| | - Tong Xiao
- Department of Chemistry, University of California, Berkeley, Berkeley, United States
| | - Dirk Trauner
- Department of Chemistry, Center of Integrated Protein Science, University of Munich, Munich, Germany
| | - Ehud Y Isacoff
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.,Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, United States.,Physical Bioscience Division, Lawrence Berkeley National Laboratory, Berkeley, United States
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Attiori Essis S, Laurier-Laurin ME, Pépin É, Cyr M, Massicotte G. GluN2B-containing NMDA receptors are upregulated in plasma membranes by the sphingosine-1-phosphate analog FTY720P. Brain Res 2015; 1624:349-358. [PMID: 26260438 DOI: 10.1016/j.brainres.2015.07.055] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2015] [Revised: 07/28/2015] [Accepted: 07/30/2015] [Indexed: 11/29/2022]
Abstract
Sphingosine-1-phosphate (S1P) is a ceramide derivative serving not only as a regulator of immune properties but also as a modulator of brain functions. To better understand the mechanism underlying the effects of S1P on brain functions, we investigated the potential impact of S1P receptor (S1PR) activation on NMDA receptor subunits. We used acute rat hippocampal slices as a model system, and determined the effects of the active phosphorylated S1P analog, fingolimod (FTY720P) on various NMDA receptors. Treatment with FTY720P significantly increased phosphorylation of GluN2B-containing NMDA receptors at Tyr1472. This effect appears rather specific, as treatment with FTY720P did not modify GluN2B-Tyr1336, GluN2B-Ser1480, GluN2A-Tyr1325 or GluN1-Ser897 phosphorylation. Pre-treatment of hippocampal slices with the compounds W146 and PP1 indicated that FTY720P-induced GluN2B phosphorylation at Tyr1472 epitopes was dependent on activation of S1PR subunit 1 (S1PR1) and Src/Fyn kinase, respectively. Cell surface biotinylation experiments indicated that FTY720P-induced GluN2B phosphorylation at Tyr1472 was also associated with increased levels of GluN1 and GluN2B subunits on membrane surface, whereas no change was observed for GluN2A subunits. We finally demonstrate that FTY720P is inclined to favor Tau and Fyn accumulation on plasma membranes. These results suggest that activation of S1PR1 by FTY720P enhances GluN2B receptor phosphorylation in rat hippocampal slices, resulting in increased levels of GluN1 and GluN2B receptor subunits in neuronal membranes through a mechanism probably involving Fyn and Tau.
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Affiliation(s)
- Suzanne Attiori Essis
- Département de biologie médicale, Université du Québec à Trois-Rivières, Trois-Rivières, Québec, Canada G9A 5H7
| | - Marie-Elaine Laurier-Laurin
- Département de biologie médicale, Université du Québec à Trois-Rivières, Trois-Rivières, Québec, Canada G9A 5H7
| | - Élise Pépin
- Département de biologie médicale, Université du Québec à Trois-Rivières, Trois-Rivières, Québec, Canada G9A 5H7
| | - Michel Cyr
- Département de biologie médicale, Université du Québec à Trois-Rivières, Trois-Rivières, Québec, Canada G9A 5H7
| | - Guy Massicotte
- Département de biologie médicale, Université du Québec à Trois-Rivières, Trois-Rivières, Québec, Canada G9A 5H7.
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Melatonin attenuates dexamethasone-induced spatial memory impairment and dexamethasone-induced reduction of synaptic protein expressions in the mouse brain. Neurochem Int 2013; 63:482-91. [DOI: 10.1016/j.neuint.2013.08.011] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2013] [Revised: 07/31/2013] [Accepted: 08/08/2013] [Indexed: 11/19/2022]
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Anisuzzaman ASM, Uwada J, Masuoka T, Yoshiki H, Nishio M, Ikegaya Y, Takahashi N, Matsuki N, Fujibayashi Y, Yonekura Y, Momiyama T, Muramatsu I. Novel contribution of cell surface and intracellular M1-muscarinic acetylcholine receptors to synaptic plasticity in hippocampus. J Neurochem 2013; 126:360-71. [DOI: 10.1111/jnc.12306] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2013] [Revised: 04/30/2013] [Accepted: 05/14/2013] [Indexed: 01/08/2023]
Affiliation(s)
- Abu Syed Md Anisuzzaman
- Division of Pharmacology; Department of Biochemistry and Bioinformative Sciences; School of Medicine; University of Fukui; Eiheiji Japan
| | - Junsuke Uwada
- Division of Pharmacology; Department of Biochemistry and Bioinformative Sciences; School of Medicine; University of Fukui; Eiheiji Japan
- Organization for Life Science Advancement Programs; University of Fukui; Eiheiji Japan
| | - Takayoshi Masuoka
- Department of Pharmacology; School of Medicine; Kanazawa Medical University; Uchinada Japan
| | - Hatsumi Yoshiki
- Division of Pharmacology; Department of Biochemistry and Bioinformative Sciences; School of Medicine; University of Fukui; Eiheiji Japan
| | - Matomo Nishio
- Department of Pharmacology; School of Medicine; Kanazawa Medical University; Uchinada Japan
| | - Yuji Ikegaya
- Laboratory of Chemical Pharmacology; Graduate School of Pharmaceutical Sciences; The University of Tokyo; Hongo Bunkyo-ku Japan
| | - Naoya Takahashi
- Laboratory of Chemical Pharmacology; Graduate School of Pharmaceutical Sciences; The University of Tokyo; Hongo Bunkyo-ku Japan
| | - Norio Matsuki
- Laboratory of Chemical Pharmacology; Graduate School of Pharmaceutical Sciences; The University of Tokyo; Hongo Bunkyo-ku Japan
| | | | | | - Toshihiko Momiyama
- Department of Pharmacology; Jikei University School of Medicine; Minato-ku Japan
| | - Ikunobu Muramatsu
- Division of Pharmacology; Department of Biochemistry and Bioinformative Sciences; School of Medicine; University of Fukui; Eiheiji Japan
- Organization for Life Science Advancement Programs; University of Fukui; Eiheiji Japan
- Child Development Research Center; Graduate School of Medicine; University of Fukui; Eiheiji Japan
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Astori S, Pawlak V, Köhr G. Spike-timing-dependent plasticity in hippocampal CA3 neurons. J Physiol 2010; 588:4475-88. [PMID: 20876200 DOI: 10.1113/jphysiol.2010.198366] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Synaptic plasticity of different inputs converging onto CA3 pyramidal neurons is central to theories of hippocampal function. The mossy fibre (MF) input to these neurons is thought to exhibit plasticity that is in nearly all aspects fundamentally different from plasticity in other brain regions: in particular, when induced by high frequency presynaptic stimulation, plasticity at these synapses is independent of NMDA receptor (NMDAR) activation and presynaptically expressed. Here, we show that different stimulation protocols that depend on the close timing of MF activity and postsynaptic spikes induce bidirectional plasticity in CA3 neurons in 3-week-old rats. Long-term potentiation (LTP) is observed when an excitatory postsynaptic potential (EPSP), evoked by MF stimulation, precedes a single postsynaptic action potential (AP) or a brief AP burst by 10 ms. Instead, timing-dependent long-term depression (LTD) requires the pairing of a single AP to an EPSP with a delay of 30 ms. The pairing of APs to synaptic activity is required for plasticity induction, since the application of unpaired APs or EPSPs did not alter synaptic strength. Furthermore, our results demonstrate that both timing-dependent LTP and LTD critically depend on the activation of NMDARs. Specifically blocking postsynaptic NMDARs prevents plasticity, demonstrating that NMDARs important to spike-timing-dependent plasticity in CA3 neurons are required at postsynaptic sites. In summary, this study shows that the close timing of APs to MF excitatory synaptic input can alter synaptic efficacy in CA3 neurons in a bidirectional manner.
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Affiliation(s)
- S Astori
- Department of Molecular Neurobiology, Max-Planck-Institute for Medical Research, 69120 Heidelberg, Germany
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Chen PE, Errington ML, Kneussel M, Chen G, Annala AJ, Rudhard YH, Rast GF, Specht CG, Tigaret CM, Nassar MA, Morris RGM, Bliss TVP, Schoepfer R. Behavioral deficits and subregion-specific suppression of LTP in mice expressing a population of mutant NMDA receptors throughout the hippocampus. Learn Mem 2009; 16:635-44. [PMID: 19794189 DOI: 10.1101/lm.1316909] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The NMDA receptor (NMDAR) subunit GluN1 is an obligatory component of NMDARs without a known functional homolog and is expressed in almost every neuronal cell type. The NMDAR system is a coincidence detector with critical roles in spatial learning and synaptic plasticity. Its coincidence detection property is crucial for the induction of hippocampal long-term potentiation (LTP). We have generated a mutant mouse model expressing a hypomorph of the Grin1(N598R) allele, which leads to a minority (about 10%) of coincidence detection-impaired NMDARs. Surprisingly, these animals revealed specific functional changes in the dentate gyrus (DG) of the hippocampal formation. Early LTP was expressed normally in area CA1 in vivo, but was completely suppressed at perforant path-granule cell synapses in the DG. In addition, there was a pronounced reduction in the amplitude of the evoked population spike in the DG. These specific changes were accompanied by behavioral impairments in spatial recognition, spatial learning, reversal learning, and retention. Our data show that minor changes in GluN1-dependent NMDAR physiology can cause dramatic consequences in synaptic signaling in a subregion-specific fashion despite the nonredundant nature of the GluN1 gene and its global expression.
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Affiliation(s)
- Philip E Chen
- Laboratory for Molecular Pharmacology, University College London, London WC1E 6BT, United Kingdom.
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Peddie CJ, Davies HA, Colyer FM, Stewart MG, Rodríguez JJ. Colocalisation of serotonin2A receptors with the glutamate receptor subunits NR1 and GluR2 in the dentate gyrus: an ultrastructural study of a modulatory role. Exp Neurol 2008; 211:561-73. [PMID: 18439999 DOI: 10.1016/j.expneurol.2008.03.003] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2008] [Revised: 03/03/2008] [Accepted: 03/06/2008] [Indexed: 11/24/2022]
Abstract
The serotonin(2A) receptor (5-HT(2A)R) is implicated in many neurological disorders and has a role in cognitive processes, reliant upon hippocampal glutamate receptors. Recent studies show that 5-HT(2A)R agonists and/or antagonists can influence cognitive function, suggesting a critical hippocampal role for these receptors, yet their cellular and subcellular distribution within this region has not been comprehensively analysed. Here, we have conducted an electron microscopic examination of 5-HT(2A)R distribution with the glutamate N-methyl-D-aspartate (NMDA) and amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid (AMPA) receptor subunits NR1 and GluR2 in the hippocampal dentate gyrus (DG) in order to investigate whether 5-HT(2A)R location is compatible with a modulatory role over NMDA and/or AMPA receptor mediated neurotransmission. Of 5-HT(2A)R positive profiles, 56% were dendrites and 16% were dendritic spines. Labelling was both cytoplasmic and membranous. Spinous labelling was more frequently membranous at peri- and extra-synaptic sites, though was also associated with synaptic specialisations. Profiles displaying colocalisation of immunoreactivity for 5-HT(2A)Rs with NR1 or GluR2 were predominantly dendrites, representing 11% and 8% of 5-HT(2A)R positive profiles, respectively. Additionally, 12% of 5-HT(2A)R labelled profiles also displayed immunoreactivity for gamma-aminobutyric acid (GABA). These data indicate most 5-HT(2A)Rs are expressed on granule cell projections, with a smaller subpopulation expressed on GABAergic interneurons.
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Affiliation(s)
- C J Peddie
- Department of Life Sciences, The Open University, Milton Keynes, MK7 6AA, UK.
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Trasande CA, Ramirez JM. Activity deprivation leads to seizures in hippocampal slice cultures: is epilepsy the consequence of homeostatic plasticity? J Clin Neurophysiol 2007; 24:154-64. [PMID: 17414971 DOI: 10.1097/wnp.0b013e318033787f] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
SUMMARY Neural networks operate robustly despite destabilizing factors, ranging from gene product turnover to circuit refinement, throughout life. Maintaining functional robustness of neuronal networks critically depends upon forms of homeostatic plasticity including synaptic scaling. Synaptic strength and intrinsic excitability have been shown to "scale" (up or down) in response to altered ambient activity levels, and this has led to the general idea that homeostatic plasticity operates along a continuum. After 48 hours of activity deprivation, cultured hippocampal networks exhibited a homeostatic-type reconfiguration that was discrete: a switch from spontaneous spiking to oscillatory bursting. Blockade of fast glutamatergic and GABAergic transmission abolished spontaneous network bursting, but the majority of neurons exhibited intrinsic bursting in response to current injection, which was not the case in control tissue. This de novo intrinsic bursting could be blocked by cadmium chloride, suggesting that this bursting involves calcium mechanisms. Immunohistochemistry confirmed that activity-deprived slice cultures exhibited a widespread upregulation of voltage-dependent calcium channels compared with controls. Calcium imaging studies from activity-deprived slices demonstrated that spontaneous bursting was not a local behavior, but rather a global, synchronous phenomenon, reminiscent of seizure activity. These data suggest that the input/output transformation of individual neurons undergoing homeostatic remodeling is more complex than simple scaling. Network consequences of this transformation include network destabilization of epileptic proportions. Spontaneous activity plays a critical role in actively maintaining homeostatic balance in networks, which is lost after activity deprivation.
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Affiliation(s)
- Caitlin Aptowicz Trasande
- Committee on Neurobiology, Department of Organismal Biology and Anatomy, The University of Chicago, Chicago, Illinois, USA.
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Berberich S, Punnakkal P, Jensen V, Pawlak V, Seeburg PH, Hvalby Ø, Köhr G. Lack of NMDA receptor subtype selectivity for hippocampal long-term potentiation. J Neurosci 2006; 25:6907-10. [PMID: 16033900 PMCID: PMC6725356 DOI: 10.1523/jneurosci.1905-05.2005] [Citation(s) in RCA: 252] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
NMDA receptor (NMDAR) 2A (NR2A)- and NR2B-type NMDARs coexist in synapses of CA1 pyramidal cells. Recent studies using pharmacological blockade of NMDAR subtypes proposed that the NR2A type is responsible for inducing long-term potentiation (LTP), whereas the NR2B type induces long-term depression (LTD). This contrasts with the finding in genetically modified mice that NR2B-type NMDARs induce LTP when NR2A signaling is absent or impaired, although compensatory mechanisms might have contributed to this result. We therefore assessed the contribution of the two NMDAR subtypes to LTP in mouse hippocampal slices by different induction protocols and in the presence of NMDAR antagonists, including the NR2A-type blocker NVP-AAM077, for which an optimal concentration for subtype selectivity was determined on recombinant and native NMDARs. Partial blockade of NMDA EPSCs by 40%, either by preferentially antagonizing NR2A- or NR2B-type NMDARs or by the nonselective antagonist D-AP-5, did not impair LTP, demonstrating that hippocampal LTP induction can be generated by either NMDAR subtype.
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Affiliation(s)
- Sven Berberich
- Department of Molecular Neurobiology, Max-Planck-Institute for Medical Research, D-69120 Heidelberg, Germany
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