Deletion of the C-terminal domain of the NR2B subunit alters channel properties and synaptic targeting of N-methyl-D-aspartate receptors in nascent neocortical synapses.
Channel properties and synaptic targeting of N-methyl-D-aspartate (NMDA) receptors determine their importance in synaptic transmission, long-term synaptic plasticity, and developmental reorganization of synaptic circuits. To investigate the involvement of the C-terminal domain of the NR2B subunit in regulating channel properties and synaptic localization, we analyzed gene-targeted mice expressing C-terminally truncated NR2B subunits (NR2B(DeltaC/DeltaC) mice; Sprengel et al. [1998] Cell 92:279-89). Because homozygous NR2B(DeltaC/DeltaC) mice die perinatally, we studied embryonic neocortical neurons differentiating in culture. At early stages in vitro, neurons predominantly expressed NR1/NR2B receptors, as shown by the NR2B subunit-specific antagonist ifenprodil. At these nascent synapses, NMDA excitatory postsynaptic currents (EPSCs) in neurons from NR2B(DeltaC/DeltaC) mice showed a strong-amplitude reduction to 20% of control, but AMPA EPSCs were unaltered. Analysis of the MK-801 block of NMDA receptor-mediated whole-cell currents revealed a decreased peak open probability of NMDA receptor channels (to about 60%) in neurons from NR2B(DeltaC/DeltaC) mice, although their single channel conductance was unchanged. To study effects on synaptic targeting, we determined the fraction of synaptically localized NMDA receptors relative to the whole-cell NMDA receptor population. In neurons from NR2B(DeltaC/DeltaC) mice, the synaptic NMDA receptor fraction was drastically reduced, suggesting that the C-terminal domain of the NR2B subunit plays a major role in synaptic targeting of NMDA receptors at nascent synapses. With increasing time in culture, the reduction in NMDA EPSCs in neurons from NR2B(DeltaC/DeltaC) mice diminished. This is explained by the expression of additional NMDA receptor subtypes containing NR2A subunits at more mature synapses.
Lehrstuhl für Zellphysiologie, Ruhr-Universität Bochum, Bochum, Germany.
Ralf
R
Mohrmann
Georg
G
Köhr
Hanns
H
Hatt
Rolf
R
Sprengel
Kurt
K
Gottmann
D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects / Q000235:genetics*; D004558:Electric Stimulation; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000235:genetics; D005260:Female; D005333:Fetus; D017353:Gene Deletion; D018390:Gene Targeting; D018698:Glutamic Acid / Q000378:metabolism / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation / Q000187:drug effects / Q000235:genetics*; D019579:Neocortex / Q000166:cytology / Q000196:embryology* / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010880:Piperidines / Q000494:pharmacology; D011247:Pregnancy; D017434:Protein Structure, Tertiary / Q000187:drug effects / Q000235:genetics*; D018091:Receptors, AMPA / Q000187:drug effects / Q000378:metabolism; D016194:Receptors, N-Methyl-D-Aspartate / Q000737:chemistry* / Q000187:drug effects / Q000235:genetics; D013569:Synapses / Q000187:drug effects / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology
D018691:Excitatory Amino Acid Antagonists; C121001:NR2B NMDA receptor; D010880:Piperidines; D018091:Receptors, AMPA; D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid; D013779:Tetrodotoxin; C010739:ifenprodil