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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 pyramidal cells and stratum oriens interneurons in P3-5 grin2d−/− mice. (A) Example traces of NMDAR-mediated EPSCs before and after application of the GluN2B specific antagonist ifenprodil. EPSCs were recorded in CA1 stratum oriens interneurons and CA1 pyramidal cells of P3-5 grin2d−/− mice. The quantification of the remaining current after ifenprodil application is shown on the right. (B) Example traces of NMDAR-mediated EPSCs before and after ifenprodil application normalized to the peak. The quantification shows that ifenprodil does not alter τdecay of EPSC in interneurons and decreases τdecay of EPSC in pyramidal cells, suggesting that slow GluN2D subunits do not contribute to synaptic NMDARs in P3-5 grin2d−/− mice, in contrast to their contribution in EGFP-GluN2D, PV-EGFP, and wildtype mice. **p < 0.01.
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Figure 9: Effects of ifenprodil on NMDAR-mediated EPSCs in pyramidal cells and stratum oriens interneurons in P3-5 grin2d−/− mice. (A) Example traces of NMDAR-mediated EPSCs before and after application of the GluN2B specific antagonist ifenprodil. EPSCs were recorded in CA1 stratum oriens interneurons and CA1 pyramidal cells of P3-5 grin2d−/− mice. The quantification of the remaining current after ifenprodil application is shown on the right. (B) Example traces of NMDAR-mediated EPSCs before and after ifenprodil application normalized to the peak. The quantification shows that ifenprodil does not alter τdecay of EPSC in interneurons and decreases τdecay of EPSC in pyramidal cells, suggesting that slow GluN2D subunits do not contribute to synaptic NMDARs in P3-5 grin2d−/− mice, in contrast to their contribution in EGFP-GluN2D, PV-EGFP, and wildtype mice. **p < 0.01.

Mentions: The ifenprodil-mediated increase in τdecay indicates that NMDAR subunits with slower kinetics than GluN2B subunits are present in the synapse of interneurons and pyramidal cells of young mice. If GluN2D subunits contribute to synaptic currents in hippocampal interneurons and pyramidal cells, we would expect that the ifenprodil-mediated increase in τdecay is absent in mice lacking the GluN2D subunit (i.e., grin2d−/− mice). Since the increase in τdecay was most pronounced in P3-5 mice, we analyzed NMDAR-mediated EPSCs in lower stratum oriens interneurons and pyramidal cells of P3-5 grin2d−/− mice. Ifenprodil significantly blocked NMDAR-mediated EPSCs in both cell types (Figure 9A, Table 3). In fact, ifenprodil was more efficient in blocking NMDAR-mediated EPSCs in interneurons of grin2d−/− than in interneurons of EGFP-GluN2D mice (remaining current 25 vs. 45 %). Considering that 10 μM ifenprodil blocks 80–90% of diheteromeric GluN2B-containing NMDARs, these results indicate that there are almost purely GluN1/GluN2B heteromeric NMDARs in interneuron synapses of grin2d−/− mice. Consistently, ifenprodil did not affect τdecay of NMDAR-mediated EPSCs in interneurons (Figure 9B, Table 3), in contrast to the ifenprodil mediated τdecay increase in EGFP-GluN2D-positive and in PV-positive interneurons. Ifenprodil decreased the τdecay of NMDAR-mediated EPSCs in pyramidal cells in grin2d−/− mice (Figure 9B, Table 3), in stark contrast to the increase in wildtype mice. The fact that NMDAR-mediated EPSCs decayed even faster after blocking GluN2B-containing NMDARs indicates that fast GluN2A subunits are already expressed in synapses of pyramidal cells at an age of P3-5 old mice. In conclusion, these results are consistent with the loss of synaptic GluN2D-containing NMDARs in interneurons and pyramidal cells of grin2d−/− mice.


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 pyramidal cells and stratum oriens interneurons in P3-5 grin2d−/− mice. (A) Example traces of NMDAR-mediated EPSCs before and after application of the GluN2B specific antagonist ifenprodil. EPSCs were recorded in CA1 stratum oriens interneurons and CA1 pyramidal cells of P3-5 grin2d−/− mice. The quantification of the remaining current after ifenprodil application is shown on the right. (B) Example traces of NMDAR-mediated EPSCs before and after ifenprodil application normalized to the peak. The quantification shows that ifenprodil does not alter τdecay of EPSC in interneurons and decreases τdecay of EPSC in pyramidal cells, suggesting that slow GluN2D subunits do not contribute to synaptic NMDARs in P3-5 grin2d−/− mice, in contrast to their contribution in EGFP-GluN2D, PV-EGFP, and wildtype mice. **p < 0.01.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4373385&req=5

Figure 9: Effects of ifenprodil on NMDAR-mediated EPSCs in pyramidal cells and stratum oriens interneurons in P3-5 grin2d−/− mice. (A) Example traces of NMDAR-mediated EPSCs before and after application of the GluN2B specific antagonist ifenprodil. EPSCs were recorded in CA1 stratum oriens interneurons and CA1 pyramidal cells of P3-5 grin2d−/− mice. The quantification of the remaining current after ifenprodil application is shown on the right. (B) Example traces of NMDAR-mediated EPSCs before and after ifenprodil application normalized to the peak. The quantification shows that ifenprodil does not alter τdecay of EPSC in interneurons and decreases τdecay of EPSC in pyramidal cells, suggesting that slow GluN2D subunits do not contribute to synaptic NMDARs in P3-5 grin2d−/− mice, in contrast to their contribution in EGFP-GluN2D, PV-EGFP, and wildtype mice. **p < 0.01.
Mentions: The ifenprodil-mediated increase in τdecay indicates that NMDAR subunits with slower kinetics than GluN2B subunits are present in the synapse of interneurons and pyramidal cells of young mice. If GluN2D subunits contribute to synaptic currents in hippocampal interneurons and pyramidal cells, we would expect that the ifenprodil-mediated increase in τdecay is absent in mice lacking the GluN2D subunit (i.e., grin2d−/− mice). Since the increase in τdecay was most pronounced in P3-5 mice, we analyzed NMDAR-mediated EPSCs in lower stratum oriens interneurons and pyramidal cells of P3-5 grin2d−/− mice. Ifenprodil significantly blocked NMDAR-mediated EPSCs in both cell types (Figure 9A, Table 3). In fact, ifenprodil was more efficient in blocking NMDAR-mediated EPSCs in interneurons of grin2d−/− than in interneurons of EGFP-GluN2D mice (remaining current 25 vs. 45 %). Considering that 10 μM ifenprodil blocks 80–90% of diheteromeric GluN2B-containing NMDARs, these results indicate that there are almost purely GluN1/GluN2B heteromeric NMDARs in interneuron synapses of grin2d−/− mice. Consistently, ifenprodil did not affect τdecay of NMDAR-mediated EPSCs in interneurons (Figure 9B, Table 3), in contrast to the ifenprodil mediated τdecay increase in EGFP-GluN2D-positive and in PV-positive interneurons. Ifenprodil decreased the τdecay of NMDAR-mediated EPSCs in pyramidal cells in grin2d−/− mice (Figure 9B, Table 3), in stark contrast to the increase in wildtype mice. The fact that NMDAR-mediated EPSCs decayed even faster after blocking GluN2B-containing NMDARs indicates that fast GluN2A subunits are already expressed in synapses of pyramidal cells at an age of P3-5 old mice. In conclusion, these results are consistent with the loss of synaptic GluN2D-containing NMDARs in interneurons and pyramidal cells of grin2d−/− mice.

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