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GluN2D-containing NMDA receptors-mediate synaptic currents in hippocampal interneurons and pyramidal cells in juvenile mice.

von Engelhardt J, Bocklisch C, Tönges L, Herb A, Mishina M, Monyer H - Front Cell Neurosci (2015)

Bottom Line: In contrast, much less is known about the role of GluN2D, which is expressed at low levels and is downregulated following the second postnatal week.The expression of the transgene was confined to hippocampal interneurons, most of which were parvalbumin- and/or somatostatin-positive.Electrophysiological and morphological analyses showed that GluN2D was present mainly in fast spiking basket and axo-axonic cells.

View Article: PubMed Central - PubMed

Affiliation: Synaptic Signalling and Neurodegeneration, German Cancer Research Center (DKFZ) Heidelberg, Germany ; Synaptic Signalling and Neurodegeneration, German Center for Neurodegenerative Diseases (DZNE) Bonn, Germany.

ABSTRACT
The differential regulation of the two major N-methyl-D-aspartate receptor (NMDAR) subunits GluN2A and GluN2B during development in forebrain pyramidal cells has been thoroughly investigated. In contrast, much less is known about the role of GluN2D, which is expressed at low levels and is downregulated following the second postnatal week. However, it appears that few cells, presumably interneurons, continue to express GluN2D also in juvenile mice. To investigate which hippocampal cell types express this subunit, we generated transgenic mice with EGFP-tagged GluN2D receptors. The expression of the transgene was confined to hippocampal interneurons, most of which were parvalbumin- and/or somatostatin-positive. Electrophysiological and morphological analyses showed that GluN2D was present mainly in fast spiking basket and axo-axonic cells. Based on pharmacological evidence and electrophysiological analysis of GluN2D knockout mice, we conclude that GluN2D-containing NMDARs mediate synaptic currents in hippocampal interneurons of young and juvenile mice and in CA1 pyramidal neurons of newborn mice.

No MeSH data available.


Related in: MedlinePlus

Effects of ifenprodil on NMDAR-mediated EPSCs in GluN2D-EGFP-positive cells. (A) Example traces of NMDAR-mediated EPSCs before and after application of the GluN2B specific antagonist ifenprodil. EPSCs were recorded at a holding potential of +40 mV in CA1 GluN2D-EGFP-positive interneurons in P3-5, P9-12, and P20-25 mice. The quantification of the remaining current after ifenprodil application shows that NMDARs containing other subunits than GluN2B contribute to synaptic currents at all three ages. (B) Example traces of NMDAR-mediated EPSCs before and after ifenprodil application normalized to the peak. The quantification of EPSC τdecay shows that NMDARs with slower decay kinetics (i.e., GluN2D) than that of diheteromeric GluN2B-containing contributed to synaptic currents in GluN2D-EGFP-positive cells in P3-5 and P9-12 mice. The age-dependent decrease of τdecay is consistent with an up-regulation of the “fast” GluN2A subunit. *p < 0.05.
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Figure 6: Effects of ifenprodil on NMDAR-mediated EPSCs in GluN2D-EGFP-positive cells. (A) Example traces of NMDAR-mediated EPSCs before and after application of the GluN2B specific antagonist ifenprodil. EPSCs were recorded at a holding potential of +40 mV in CA1 GluN2D-EGFP-positive interneurons in P3-5, P9-12, and P20-25 mice. The quantification of the remaining current after ifenprodil application shows that NMDARs containing other subunits than GluN2B contribute to synaptic currents at all three ages. (B) Example traces of NMDAR-mediated EPSCs before and after ifenprodil application normalized to the peak. The quantification of EPSC τdecay shows that NMDARs with slower decay kinetics (i.e., GluN2D) than that of diheteromeric GluN2B-containing contributed to synaptic currents in GluN2D-EGFP-positive cells in P3-5 and P9-12 mice. The age-dependent decrease of τdecay is consistent with an up-regulation of the “fast” GluN2A subunit. *p < 0.05.

Mentions: Next we asked if GluN2D receptors contribute to synaptic NMDAR-mediated currents. To this end, EGFP-GluN2D-positive CA1 interneurons were held at a membrane-potential of +40 mV and NMDAR-mediated EPSCs were evoked by Schaffer collateral/commissural fiber stimulation while blocking AMPA receptor- and GABA receptor-mediated currents. GluN2B is the most abundant subunit in hippocampal neurons during the first two postnatal weeks (Monyer et al., 1994). Therefore, to investigate if GluN2D-containing NMDARs mediate synaptic currents, we blocked GluN2B-containing NMDARs with 10 μM of the specific antagonist ifenprodil. This should result in an 80–90% block of dihetromeric GluN1/GluN2B receptors, a negligible block of diheteromeric NMDARs containing any other of the three subunits and most likely a moderate block of triheteromeric GluN2B-containing NMDARs (Mott et al., 1998; Hatton and Paoletti, 2005). NMDAR-mediated current amplitudes were significantly reduced in the presence of ifenprodil to approximately 50% in fluorescent interneurons of all three age groups (Figure 6A, Table 3) consistent with the presence of subunits other than GluN2B in the synapse of EGFP-GluN2D-positive CA1 interneurons. Deactivation time constants (τdecay) of NMDARs comprising different subunits vary considerably (GluN1/GluN2A 4-5 times faster than GluN1/GluN2B; GluN1/GluN2C similar to GluN1/GluN2B; GluN1/GluN2D 6–10 times slower than GluN1/GluN2B) (Monyer et al., 1994; Vicini et al., 1998). Thus, by comparing the τ decay of NMDAR-mediated EPSCs before and after ifenprodil, we could infer the composition of unblocked NMDARs: if EPSCs τdecay decreases, EPSCs should be mediated at least in part by fast GluN2A-containing NMDARs, if τdecay increases, slower GluN2D-containing NMDARs should be involved. Interestingly, ifenprodil significantly increased τdecay of NMDAR-mediated currents in P3-5 and P9-12 mice, indicating that GluN2D subunits contribute to synaptic NMDAR-mediated currents in EGFP-GluN2D-positive CA1 interneurons. In contrast, ifenprodil did not change τdecay in P20-25 animals. τdecay decreased with development from 253 to 177 ms most likely due to the increase in the contribution of fast GluN2A-containing NMDARs (Figure 6B, Table 3).


GluN2D-containing NMDA receptors-mediate synaptic currents in hippocampal interneurons and pyramidal cells in juvenile mice.

von Engelhardt J, Bocklisch C, Tönges L, Herb A, Mishina M, Monyer H - Front Cell Neurosci (2015)

Effects of ifenprodil on NMDAR-mediated EPSCs in GluN2D-EGFP-positive cells. (A) Example traces of NMDAR-mediated EPSCs before and after application of the GluN2B specific antagonist ifenprodil. EPSCs were recorded at a holding potential of +40 mV in CA1 GluN2D-EGFP-positive interneurons in P3-5, P9-12, and P20-25 mice. The quantification of the remaining current after ifenprodil application shows that NMDARs containing other subunits than GluN2B contribute to synaptic currents at all three ages. (B) Example traces of NMDAR-mediated EPSCs before and after ifenprodil application normalized to the peak. The quantification of EPSC τdecay shows that NMDARs with slower decay kinetics (i.e., GluN2D) than that of diheteromeric GluN2B-containing contributed to synaptic currents in GluN2D-EGFP-positive cells in P3-5 and P9-12 mice. The age-dependent decrease of τdecay is consistent with an up-regulation of the “fast” GluN2A subunit. *p < 0.05.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
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Figure 6: Effects of ifenprodil on NMDAR-mediated EPSCs in GluN2D-EGFP-positive cells. (A) Example traces of NMDAR-mediated EPSCs before and after application of the GluN2B specific antagonist ifenprodil. EPSCs were recorded at a holding potential of +40 mV in CA1 GluN2D-EGFP-positive interneurons in P3-5, P9-12, and P20-25 mice. The quantification of the remaining current after ifenprodil application shows that NMDARs containing other subunits than GluN2B contribute to synaptic currents at all three ages. (B) Example traces of NMDAR-mediated EPSCs before and after ifenprodil application normalized to the peak. The quantification of EPSC τdecay shows that NMDARs with slower decay kinetics (i.e., GluN2D) than that of diheteromeric GluN2B-containing contributed to synaptic currents in GluN2D-EGFP-positive cells in P3-5 and P9-12 mice. The age-dependent decrease of τdecay is consistent with an up-regulation of the “fast” GluN2A subunit. *p < 0.05.
Mentions: Next we asked if GluN2D receptors contribute to synaptic NMDAR-mediated currents. To this end, EGFP-GluN2D-positive CA1 interneurons were held at a membrane-potential of +40 mV and NMDAR-mediated EPSCs were evoked by Schaffer collateral/commissural fiber stimulation while blocking AMPA receptor- and GABA receptor-mediated currents. GluN2B is the most abundant subunit in hippocampal neurons during the first two postnatal weeks (Monyer et al., 1994). Therefore, to investigate if GluN2D-containing NMDARs mediate synaptic currents, we blocked GluN2B-containing NMDARs with 10 μM of the specific antagonist ifenprodil. This should result in an 80–90% block of dihetromeric GluN1/GluN2B receptors, a negligible block of diheteromeric NMDARs containing any other of the three subunits and most likely a moderate block of triheteromeric GluN2B-containing NMDARs (Mott et al., 1998; Hatton and Paoletti, 2005). NMDAR-mediated current amplitudes were significantly reduced in the presence of ifenprodil to approximately 50% in fluorescent interneurons of all three age groups (Figure 6A, Table 3) consistent with the presence of subunits other than GluN2B in the synapse of EGFP-GluN2D-positive CA1 interneurons. Deactivation time constants (τdecay) of NMDARs comprising different subunits vary considerably (GluN1/GluN2A 4-5 times faster than GluN1/GluN2B; GluN1/GluN2C similar to GluN1/GluN2B; GluN1/GluN2D 6–10 times slower than GluN1/GluN2B) (Monyer et al., 1994; Vicini et al., 1998). Thus, by comparing the τ decay of NMDAR-mediated EPSCs before and after ifenprodil, we could infer the composition of unblocked NMDARs: if EPSCs τdecay decreases, EPSCs should be mediated at least in part by fast GluN2A-containing NMDARs, if τdecay increases, slower GluN2D-containing NMDARs should be involved. Interestingly, ifenprodil significantly increased τdecay of NMDAR-mediated currents in P3-5 and P9-12 mice, indicating that GluN2D subunits contribute to synaptic NMDAR-mediated currents in EGFP-GluN2D-positive CA1 interneurons. In contrast, ifenprodil did not change τdecay in P20-25 animals. τdecay decreased with development from 253 to 177 ms most likely due to the increase in the contribution of fast GluN2A-containing NMDARs (Figure 6B, Table 3).

Bottom Line: In contrast, much less is known about the role of GluN2D, which is expressed at low levels and is downregulated following the second postnatal week.The expression of the transgene was confined to hippocampal interneurons, most of which were parvalbumin- and/or somatostatin-positive.Electrophysiological and morphological analyses showed that GluN2D was present mainly in fast spiking basket and axo-axonic cells.

View Article: PubMed Central - PubMed

Affiliation: Synaptic Signalling and Neurodegeneration, German Cancer Research Center (DKFZ) Heidelberg, Germany ; Synaptic Signalling and Neurodegeneration, German Center for Neurodegenerative Diseases (DZNE) Bonn, Germany.

ABSTRACT
The differential regulation of the two major N-methyl-D-aspartate receptor (NMDAR) subunits GluN2A and GluN2B during development in forebrain pyramidal cells has been thoroughly investigated. In contrast, much less is known about the role of GluN2D, which is expressed at low levels and is downregulated following the second postnatal week. However, it appears that few cells, presumably interneurons, continue to express GluN2D also in juvenile mice. To investigate which hippocampal cell types express this subunit, we generated transgenic mice with EGFP-tagged GluN2D receptors. The expression of the transgene was confined to hippocampal interneurons, most of which were parvalbumin- and/or somatostatin-positive. Electrophysiological and morphological analyses showed that GluN2D was present mainly in fast spiking basket and axo-axonic cells. Based on pharmacological evidence and electrophysiological analysis of GluN2D knockout mice, we conclude that GluN2D-containing NMDARs mediate synaptic currents in hippocampal interneurons of young and juvenile mice and in CA1 pyramidal neurons of newborn mice.

No MeSH data available.


Related in: MedlinePlus