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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.


Morphology and firing pattern of GluN2D-EGFP-positive cells in P3-5 transgenic mice. (A–D) Reconstruction of four EGFP-GluN2D-positive cells (P3) with voltage responses to hyperpolarizing and depolarizing current injections. (E,F) Reconstruction of two EGFP-GluN2D-positive cells (P5) with voltage responses to hyperpolarizing and depolarizing current injections. Localization of cell body, dendritic and axonal arbors indicate that the two neurons may be an immature basket (upper) and an immature axo-axonic cell. The image of part of the axon in the stratum pyramidale of the lower cell (see dashed box in reconstruction) shows vertical rows of boutons (parallel to axon initial segments), typical for axo-axonic cells. SO, Stratum oriens; SP, stratum pyramidale; SR, stratum radiatum; SLM, stratum lacunosum-moleculare.
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Figure 3: Morphology and firing pattern of GluN2D-EGFP-positive cells in P3-5 transgenic mice. (A–D) Reconstruction of four EGFP-GluN2D-positive cells (P3) with voltage responses to hyperpolarizing and depolarizing current injections. (E,F) Reconstruction of two EGFP-GluN2D-positive cells (P5) with voltage responses to hyperpolarizing and depolarizing current injections. Localization of cell body, dendritic and axonal arbors indicate that the two neurons may be an immature basket (upper) and an immature axo-axonic cell. The image of part of the axon in the stratum pyramidale of the lower cell (see dashed box in reconstruction) shows vertical rows of boutons (parallel to axon initial segments), typical for axo-axonic cells. SO, Stratum oriens; SP, stratum pyramidale; SR, stratum radiatum; SLM, stratum lacunosum-moleculare.

Mentions: While recording, we filled EGFP-GluN2D-positive cells with biocytin to obtain information about their morphology. The cell body of most filled neurons was located in the stratum pyramidale and the stratum oriens. Only few cells were located in the stratum radiatum. The dendritic and axonal arbor of EGFP-GluN2D-positive cells was diverse as expected from the different interneuronal marker proteins that they expressed. Dendrites of most cells were spine-free, with only some cells exhibiting a few spine-like protrusions. Axons usually had many boutons. Many filled cells could not be classified because they were stained too weakly or the axon was severed. Thirty two cells could be classified based on the localization of their dendritic and axonal arbor (Freund and Buzsaki, 1996; Klausberger and Somogyi, 2008). The majority had the morphology of soma targeting interneurons with basal and apical dendritic arbors in stratum oriens and stratum radiatum, respectively, and the main part of the axonal arbor in stratum pyramidale. Fifty percent of these cells resembled classical “pyramidal-shaped basket cells.” Most of them had the cell body in the stratum pyramidale, few in the lower stratum oriens. The dendritic arbor was reminiscent of that of pyramidal cells (i.e., a prominent dendrite that runs toward the stratum radiatum where it arborizes and a shorter dendritic arbor in the stratum oriens) (Figures 3–5) (Freund and Buzsaki, 1996). Most of the remaining interneurons with the main portion of the axon arbor in the stratum pyramidale (i.e., presumptive basket cells) had the cell body also in the stratum pyramidale, but had dendritic arbors different from that of pyramidal-shaped basket cells (e.g., little or no dendrites in stratum radiatum). Some neurons in slices of young mice (P5 and P9) had the appearance of immature basket cells with shorter dendritic arbors (Figures 3, 4). Four neurons resembled axo-axonic (chandelier) cells based on their axonal arbor in stratum pyramidale and lower stratum oriens with vertical rows of boutons (parallel to axon initial segments of pyramidal cells, Figures 3–5). Two of these cells had a rather immature appearance. Finally, two immature neurons in slices of P3 mice might be trilaminar and bistratified cells (or immature basket cells). A classification of biocytin-filled immature neurons based on morphology cannot be done with absolute certainty (Figures 3, 4).


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)

Morphology and firing pattern of GluN2D-EGFP-positive cells in P3-5 transgenic mice. (A–D) Reconstruction of four EGFP-GluN2D-positive cells (P3) with voltage responses to hyperpolarizing and depolarizing current injections. (E,F) Reconstruction of two EGFP-GluN2D-positive cells (P5) with voltage responses to hyperpolarizing and depolarizing current injections. Localization of cell body, dendritic and axonal arbors indicate that the two neurons may be an immature basket (upper) and an immature axo-axonic cell. The image of part of the axon in the stratum pyramidale of the lower cell (see dashed box in reconstruction) shows vertical rows of boutons (parallel to axon initial segments), typical for axo-axonic cells. SO, Stratum oriens; SP, stratum pyramidale; SR, stratum radiatum; SLM, stratum lacunosum-moleculare.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: Morphology and firing pattern of GluN2D-EGFP-positive cells in P3-5 transgenic mice. (A–D) Reconstruction of four EGFP-GluN2D-positive cells (P3) with voltage responses to hyperpolarizing and depolarizing current injections. (E,F) Reconstruction of two EGFP-GluN2D-positive cells (P5) with voltage responses to hyperpolarizing and depolarizing current injections. Localization of cell body, dendritic and axonal arbors indicate that the two neurons may be an immature basket (upper) and an immature axo-axonic cell. The image of part of the axon in the stratum pyramidale of the lower cell (see dashed box in reconstruction) shows vertical rows of boutons (parallel to axon initial segments), typical for axo-axonic cells. SO, Stratum oriens; SP, stratum pyramidale; SR, stratum radiatum; SLM, stratum lacunosum-moleculare.
Mentions: While recording, we filled EGFP-GluN2D-positive cells with biocytin to obtain information about their morphology. The cell body of most filled neurons was located in the stratum pyramidale and the stratum oriens. Only few cells were located in the stratum radiatum. The dendritic and axonal arbor of EGFP-GluN2D-positive cells was diverse as expected from the different interneuronal marker proteins that they expressed. Dendrites of most cells were spine-free, with only some cells exhibiting a few spine-like protrusions. Axons usually had many boutons. Many filled cells could not be classified because they were stained too weakly or the axon was severed. Thirty two cells could be classified based on the localization of their dendritic and axonal arbor (Freund and Buzsaki, 1996; Klausberger and Somogyi, 2008). The majority had the morphology of soma targeting interneurons with basal and apical dendritic arbors in stratum oriens and stratum radiatum, respectively, and the main part of the axonal arbor in stratum pyramidale. Fifty percent of these cells resembled classical “pyramidal-shaped basket cells.” Most of them had the cell body in the stratum pyramidale, few in the lower stratum oriens. The dendritic arbor was reminiscent of that of pyramidal cells (i.e., a prominent dendrite that runs toward the stratum radiatum where it arborizes and a shorter dendritic arbor in the stratum oriens) (Figures 3–5) (Freund and Buzsaki, 1996). Most of the remaining interneurons with the main portion of the axon arbor in the stratum pyramidale (i.e., presumptive basket cells) had the cell body also in the stratum pyramidale, but had dendritic arbors different from that of pyramidal-shaped basket cells (e.g., little or no dendrites in stratum radiatum). Some neurons in slices of young mice (P5 and P9) had the appearance of immature basket cells with shorter dendritic arbors (Figures 3, 4). Four neurons resembled axo-axonic (chandelier) cells based on their axonal arbor in stratum pyramidale and lower stratum oriens with vertical rows of boutons (parallel to axon initial segments of pyramidal cells, Figures 3–5). Two of these cells had a rather immature appearance. Finally, two immature neurons in slices of P3 mice might be trilaminar and bistratified cells (or immature basket cells). A classification of biocytin-filled immature neurons based on morphology cannot be done with absolute certainty (Figures 3, 4).

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.