Rodenas-Ruano, A. | bioRxiv Science

bioRxiv2026

GluN2D-containing NMDA receptors regulate dentate gyrus function by facilitating granule cell activity and mediating synaptic plasticity

N-Methyl-D-aspartate ionotropic glutamate receptors (NMDARs) are crucial for synaptic transmission, long-term plasticity, neuronal activity, and cognition. Consistent with these functions, NMDAR dysfunction is linked to several brain disorders, including Alzheimers disease, autism, schizophrenia, and depression. NMDARs are tetrameric complexes composed of two essential GluN1 subunits and two distinct GluN2 subunits (GluN2A-D) that define their functional characteristics. Although the roles of GluN2A and GluN2B, which are highly expressed in the brain, have been extensively studied, much less is known about GluN2D in brain function. Using selective GluN2D antagonists in the mature rodent brain and a conditional GluN2D knockout model, we assessed the role of GluN2D-containing NMDARs in dentate granule cells (GCs). We found that these receptors are tonically active, primarily extrasynaptic, and facilitate GC action-potential firing. Additionally, physiologically relevant presynaptic and postsynaptic activity patterns induced strong long-term potentiation of NMDAR-mediated transmission at medial perforant path synaptic inputs. This plasticity was likely driven by lateral diffusion of GluN2D and supported by non-canonical glutamate delta-1 (GluD1) receptors. Finally, removing GluN2D from excitatory cells in the dentate gyrus impaired spatial memory. Overall, our findings demonstrate that GluN2D-containing NMDARs are vital for hippocampal function, likely by modulating GC activity and mediating NMDAR synaptic plasticity. TEASERGluN2D-containing NMDA receptors control dentate gyrus function by regulating neuronal firing and synaptic plasticity

neuroscience↗

bioRxiv2022

Heterosynaptic NMDA Receptor Plasticity in Hippocampal Dentate Granule Cells

The dentate gyrus is a key relay station that controls information transfer from the entorhinal cortex to the hippocampus proper. This process heavily relies on dendritic integration by dentate granule cells (GCs) of excitatory synaptic inputs from medial and lateral entorhinal cortex via medial and lateral perforant paths (MPP and LPP, respectively). N-methyl-D-aspartate receptors (NMDARs) can contribute significantly to the integrative properties of neurons. While early studies reported that excitatory inputs from entorhinal cortex onto GCs can undergo activity-dependent long-term plasticity of NMDAR-mediated transmission, the input-specificity of this plasticity along the dendritic axis remains unknown. Here, we examined the NMDAR plasticity rules at MPP-GC and LPP-GC synapses using physiologically relevant patterns of stimulation in acute rat hippocampal slices. We found that MPP-GC, but not LPP-GC synapses, expressed homosynaptic NMDAR-LTP. In addition, induction of NMDAR-LTP at MPP-GC synapses heterosynaptically potentiated distal LPP-GC NMDAR plasticity. The same stimulation protocol induced homosynaptic -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR)-LTP at MPP-GC but heterosynaptic AMPAR-LTD at distal LPP synapses, demonstrating that NMDAR and AMPAR are governed by different plasticity rules. Remarkably, heterosynaptic but not homosynaptic NMDAR-LTP required Ca2+ release from intracellular, ryanodine-dependent Ca2+ stores. Lastly, the induction and maintenance of both homo- and heterosynaptic NMDAR-LTP were blocked by GluN2D antagonism, suggesting the recruitment of GluN2D-containing receptors to the synapse. Our findings uncover a mechanism by which distinct inputs to the dentate gyrus may interact functionally and contribute to hippocampal-dependent memory formation. Significance StatementNMDARs are key players in synaptic plasticity. In addition to their classical role as coincidence detectors and triggers of AMPAR plasticity, there is compelling evidence that NMDARs can undergo activity-dependent plasticity independent of AMPAR plasticity. However, whether NMDAR-plasticity is expressed heterosynaptically remains unclear. Here, in the dentate gyrus of the hippocampus, we show that the induction of burst timing-dependent LTP of NMDAR-mediated transmission at proximal medial perforant path synapses is accompanied by heterosynaptic NMDAR-LTP at lateral perforant path synapses. These findings provide the first evidence for heterosynaptic NMDAR plasticity, which may have important consequences on the dendritic integration of functionally distinct excitatory inputs by dentate granule cells.

neuroscience↗