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

Jakob Von Engelhardt,Masayoshi Mishina,Lars Tã¶Nges,Anne Herb,Hannah Monyer,Christina Bocklisch

doi:10.3389/fncel.2015.00095

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.

Highlights

N-methyl-D-aspartate (NMDA) receptors are heteromers comprising two GluN1 and two GluN2 (Seeburg, 1993; Laube et al, 1998) or NR3 subunits (Ciabarra et al, 1995; Nishi et al, 2001)
EGFP-GluN2D is Expressed in Hippocampal Interneurons To identify GluN2D-expressing neurons in acute brain slices, we generated BAC transgenic mice that express the fusion protein EGFP and GluN2D (EGFP-GluN2D) under the control of the GluN2D promoter (Figure S1)
EGFP-GluN2D-positive cells had an interneuron identity as indicated by the localization of their cell body, electrophysiological properties, and neurite feature/arborization (Freund and Buzsaki, 1996; McBain and Fisahn, 2001; Klausberger and Somogyi, 2008). This is in accordance with a previous investigation that showed GluN2D mRNA expression in interneurons in the hippocampus of adult rats (Standaert et al, 1996)

Summary

Introduction

N-methyl-D-aspartate (NMDA) receptors are heteromers comprising two GluN1 and two GluN2 (Seeburg, 1993; Laube et al, 1998) or NR3 subunits (Ciabarra et al, 1995; Nishi et al, 2001). The composition of NMDARs influences functional properties such as kinetics, block by Mg2+ions, agonist affinity and modulation by polyamines (Monyer et al, 1994; Sheng et al, 1994; Williams, 1995; Vicini et al, 1998). Recombinant receptors that contain GluN2A subunits display fast, GluN2B or GluN2C intermediate and GluN2D substantially slower decay kinetics (Monyer et al, 1994; Vicini et al, 1998). The four GluN2 subunits differ in their developmental and regional mRNA expression profile (Watanabe et al, 1992; Monyer et al, 1994). GluN2B and GluN2D are present during embryonic development, whereas GluN2A and GluN2C expression commences after birth. GluN2A and GluN2B display a strong expression in the cortex and hippocampus and GluN2C in the cerebellum of adult rodents. GluN2D expression is high during the first postnatal weeks especially in the diencephalon, brainstem (e.g., substantia nigra), Frontiers in Cellular Neuroscience | www.frontiersin.org von Engelhardt et al

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