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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 of wildtype mice. (A) Example traces of NMDAR-mediated EPSCs before and after application of ifenprodil. EPSCs were recorded in CA1 pyramidal cells in P3-5, P9-12, and P20-25 wildtype 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. The decrease of blocking efficiency speaks for a developmental reduction in the proportional contribution of diheteromeric GluN2B-containing NMDARs. (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 than that of diheteromeric GluN2B-containing NMDARs contribute to synaptic currents in pyramidal cells in P3-5 mice. In contrast, ifenprodil decreases τdecay in P9-12 and P20-25 mice, indicating that GluN2A-containing NMDARs contribute to synaptic currents. *p < 0.05, **p < 0.01.
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Figure 7: Effects of ifenprodil on NMDAR-mediated EPSCs in pyramidal cells of wildtype mice. (A) Example traces of NMDAR-mediated EPSCs before and after application of ifenprodil. EPSCs were recorded in CA1 pyramidal cells in P3-5, P9-12, and P20-25 wildtype 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. The decrease of blocking efficiency speaks for a developmental reduction in the proportional contribution of diheteromeric GluN2B-containing NMDARs. (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 than that of diheteromeric GluN2B-containing NMDARs contribute to synaptic currents in pyramidal cells in P3-5 mice. In contrast, ifenprodil decreases τdecay in P9-12 and P20-25 mice, indicating that GluN2A-containing NMDARs contribute to synaptic currents. *p < 0.05, **p < 0.01.

Mentions: We did not detect fluorescence in pyramidal cells in EGFP-GluN2D mice. However, several studies indicated that GluN2D is expressed in CA1 pyramidal and granule cells especially of young mice (Scherzer et al., 1998; Kirson et al., 1999; Hrabetova et al., 2000; Lozovaya et al., 2004; Harney et al., 2008). It is possible that EGFP-GluN2D expression is very faint in pyramidal cells of transgenic mice, or that all fusion-protein is transported into dendrites. In both cases pyramidal cells would appear non-fluorescent in spite of EGFP-GluN2D expression. On the other hand, BAC-transgenic mice sometimes display false-negative expression (Meyer et al., 2002; von Engelhardt et al., 2007). Hence we cannot take recourse to EGFP-GluN2D mice to help us identify pyramidal cells that might potentially express GluN2D. We used wildtype mice to investigate if GluN2D-containing NMDARs contribute to synaptic currents in pyramidal cells. The τdecay decreased with development from 312 ms in P3-5 mice to 241 ms in P20-25 mice, consistent with the developmental upregulation of GluN2A. As expected, there was also a developmental decrease in the blocking efficiency of ifenprodil (Figure 7A, Table 3). Ifenprodil significantly increased the τdecay in P3-5 mice, while there was a significant decrease in P9-11 and P20-25 mice (Figure 7B, Table 3), providing indirect evidence that slow GluN2D-containing NMDARs may contribute to synaptic currents in young 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 of wildtype mice. (A) Example traces of NMDAR-mediated EPSCs before and after application of ifenprodil. EPSCs were recorded in CA1 pyramidal cells in P3-5, P9-12, and P20-25 wildtype 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. The decrease of blocking efficiency speaks for a developmental reduction in the proportional contribution of diheteromeric GluN2B-containing NMDARs. (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 than that of diheteromeric GluN2B-containing NMDARs contribute to synaptic currents in pyramidal cells in P3-5 mice. In contrast, ifenprodil decreases τdecay in P9-12 and P20-25 mice, indicating that GluN2A-containing NMDARs contribute to synaptic currents. *p < 0.05, **p < 0.01.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 7: Effects of ifenprodil on NMDAR-mediated EPSCs in pyramidal cells of wildtype mice. (A) Example traces of NMDAR-mediated EPSCs before and after application of ifenprodil. EPSCs were recorded in CA1 pyramidal cells in P3-5, P9-12, and P20-25 wildtype 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. The decrease of blocking efficiency speaks for a developmental reduction in the proportional contribution of diheteromeric GluN2B-containing NMDARs. (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 than that of diheteromeric GluN2B-containing NMDARs contribute to synaptic currents in pyramidal cells in P3-5 mice. In contrast, ifenprodil decreases τdecay in P9-12 and P20-25 mice, indicating that GluN2A-containing NMDARs contribute to synaptic currents. *p < 0.05, **p < 0.01.
Mentions: We did not detect fluorescence in pyramidal cells in EGFP-GluN2D mice. However, several studies indicated that GluN2D is expressed in CA1 pyramidal and granule cells especially of young mice (Scherzer et al., 1998; Kirson et al., 1999; Hrabetova et al., 2000; Lozovaya et al., 2004; Harney et al., 2008). It is possible that EGFP-GluN2D expression is very faint in pyramidal cells of transgenic mice, or that all fusion-protein is transported into dendrites. In both cases pyramidal cells would appear non-fluorescent in spite of EGFP-GluN2D expression. On the other hand, BAC-transgenic mice sometimes display false-negative expression (Meyer et al., 2002; von Engelhardt et al., 2007). Hence we cannot take recourse to EGFP-GluN2D mice to help us identify pyramidal cells that might potentially express GluN2D. We used wildtype mice to investigate if GluN2D-containing NMDARs contribute to synaptic currents in pyramidal cells. The τdecay decreased with development from 312 ms in P3-5 mice to 241 ms in P20-25 mice, consistent with the developmental upregulation of GluN2A. As expected, there was also a developmental decrease in the blocking efficiency of ifenprodil (Figure 7A, Table 3). Ifenprodil significantly increased the τdecay in P3-5 mice, while there was a significant decrease in P9-11 and P20-25 mice (Figure 7B, Table 3), providing indirect evidence that slow GluN2D-containing NMDARs may contribute to synaptic currents in young 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