skip to main content

Title: Rapid exchange of synaptic and extrasynaptic NMDA receptors in hippocampal CA1 neurons
N-methyl-d-aspartate receptors (NMDARs) are fundamental coincidence detectors of synaptic activity necessary for the induction of synaptic plasticity and synapse stability. Adjusting NMDAR synaptic content, whether by receptor insertion or lateral diffusion between extrasynaptic and synaptic compartments, could play a substantial role defining the characteristics of the NMDAR-mediated excitatory postsynaptic current (EPSC), which in turn would mediate the ability of the synapse to undergo plasticity. Lateral NMDAR movement has been observed in dissociated neurons; however, it is currently unclear whether NMDARs are capable of lateral surface diffusion in hippocampal slices, a more physiologically relevant environment. To test for lateral mobility in rat hippocampal slices, we rapidly blocked synaptic NMDARs using MK-801, a use-dependent and irreversible NMDAR blocker. Following a 5-min washout period, we observed a strong recovery of NMDAR-mediated responses. The degree of the observed recovery was proportional to the amount of induced blockade, independent of levels of intracellular calcium, and mediated primarily by GluN2B-containing NMDA receptors. These results indicate that lateral diffusion of NMDARs could be a mechanism by which synapses rapidly adjust parameters to fine-tune synaptic plasticity. NEW & NOTEWORTHY N-methyl-d-aspartate-type glutamate receptors (NMDARs) have always been considered stable components of synapses. We show that in rat hippocampal slices synaptic NMDARs are in constant exchange with extrasynaptic receptors. This exchange of receptors is mediated primarily by NMDA receptors containing GluN2B, a subunit necessary to undergo synaptic plasticity. Thus this lateral movement of synaptic receptors allows synapses to rapidly regulate the total number of synaptic NMDARs with potential consequences for synaptic plasticity.  more » « less
Award ID(s):
Author(s) / Creator(s):
Date Published:
Journal Name:
Journal of Neurophysiology
Page Range / eLocation ID:
1004 to 1014
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Severe voluntary food restriction is the defining symptom of anorexia nervosa (AN), but anxiety and excessive exercise are maladaptive symptoms that contribute significantly to the severity of AN and which individuals with AN have difficulty suppressing. We hypothesized that the excitability of hippocampal pyramidal neurons, known to contribute to anxiety, leads to the maladaptive behavior of excessive exercise. Conversely, since glutamate transporter GLT‐1 dampens the excitability of hippocampal pyramidal neurons through the uptake of ambient glutamate and suppression of the GluN2B‐subunit containing NMDA receptors (GluN2B‐NMDARs), GLT‐1 may contribute toward dampening excessive exercise. This hypothesis was tested using the mouse model of AN, called activity‐based anorexia (ABA), whereby food restriction evokes the maladaptive behavior of excessive wheel running (food restriction‐evoked running, FRER). We tested whether individual differences in ABA vulnerability of mice, quantified based on FRER, correlated with individual differences in the levels of GLT‐1 at excitatory synapses of the hippocampus. Electron microscopic immunocytochemistry (EM‐ICC) was used to quantify GLT‐1 levels at the excitatory synapses of the hippocampus. The FRER seen in individual mice varied more than 10‐fold, and Pearson correlation analyses revealed a strong negative correlation (p = .02) between FRER and GLT‐1 levels at the axon terminals of excitatory synapses and at the surrounding astrocytic plasma membranes. Moreover, synaptic levels of GluN2B‐NMDARs correlated strongly with GLT‐1 levels at perisynaptic astrocytic plasma membranes. There is at present no accepted pharmacotherapy for AN, and little is known about the etiology of this deadly illness. Current findings suggest that drugs increasing GLT‐1 expression may reduce AN severity through the reduction of GluN2B‐NMDAR activity.

    more » « less
  2. Key points

    The angiotensin AT1 receptor expression and protein kinase C (PKC)‐mediated NMDA receptor phosphorylation levels in the hypothalamus are increased in a rat genetic model of hypertension.

    Blocking AT1 receptors or PKC activity normalizes the increased pre‐ and postsynaptic NMDA receptor activity of hypothalamic presympathetic neurons in hypertensive animals.

    Inhibition of AT1 receptor–PKC activity in the hypothalamus reduces arterial blood pressure and sympathetic nerve discharges in hypertensive animals.

    AT1 receptors in the hypothalamus are endogenously activated to sustain NMDA receptor hyperactivity and elevated sympathetic outflow via PKC in hypertension.


    Increased synapticN‐methyl‐d‐aspartate receptor (NMDAR) activity in the hypothalamic paraventricular nucleus (PVN) plays a major role in elevated sympathetic output in hypertension. Although exogenous angiotensin II (AngII) can increase NMDAR activity in the PVN, whether endogenous AT1 receptor–protein kinase C (PKC) activity mediates the augmented NMDAR activity of PVN presympathetic neurons in hypertension is unclear. Here we show that blocking AT1 receptors with losartan or inhibiting PKC with chelerythrine significantly decreased the frequency of NMDAR‐mediated miniature excitatory postsynaptic currents (mEPSCs) and the amplitude of puff NMDA currents of retrogradely labelled spinally projecting PVN neurons in spontaneously hypertensive rats (SHRs). Also, treatment with chelerythrine abrogated the potentiating effect of AngII on mEPSCs and puff NMDA currents of labelled PVN neurons in SHRs. In contrast, neither losartan nor chelerythrine had any effect on mEPSCs or puff NMDA currents in labelled PVN neurons in Wistar–Kyoto (WKY) rats. Furthermore, levels of AT1 receptor mRNA and PKC‐mediated NMDAR phosphorylation in the PVN were significantly higher in SHRs than in WKY rats. In addition, microinjection of losartan or chelerythrine into the PVN substantially reduced blood pressure and renal sympathetic nerve discharges in SHRs but not in WKY rats. Chelerythrine blocked sympathoexcitatory responses to AngII microinjected into the PVN. Our findings suggest that endogenous AT1 receptor–PKC activity is essential for presynaptic and postsynaptic NMDAR hyperactivity of PVN presympathetic neurons and for the augmented sympathetic outflow in hypertension. This information advances our mechanistic understanding of the interplay between angiotensinergic and glutamatergic excitatory inputs in hypertension.

    more » « less
  3. Abstract Open science badges

    This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. More information about the Open Practices badges can be found at

    more » « less
  4. It is well established that, during neural circuit development, glutamatergic synapses become strengthened via NMDA receptor (NMDAR)-dependent upregulation of AMPA receptor (AMPAR)-mediated currents. In addition, however, it is known that the neuromodulator serotonin is present throughout most regions of the vertebrate brain while synapses are forming and being shaped by activity-dependent processes. This suggests that serotonin may modulate or contribute to these processes. Here, we investigate the role of serotonin in the developing retinotectal projection of theXenopustadpole. We altered endogenous serotonin transmission in stage 48/49 (∼10–21 days postfertilization)Xenopustadpoles and then carried out a set of whole-cell electrophysiological recordings from tectal neurons to assess retinotectal synaptic transmission. Because tadpole sex is indeterminate at these early stages of development, experimental groups were composed of randomly chosen tadpoles. We found that pharmacologically enhancing and reducing serotonin transmission for 24 h up- and downregulates, respectively, AMPAR-mediated currents at individual retinotectal synapses. Inhibiting 5-HT2receptors also significantly weakened AMPAR-mediated currents and abolished the synapse strengthening effect seen with enhanced serotonin transmission, indicating a 5-HT2receptor–dependent effect. We also determine that the serotonin-dependent upregulation of synaptic AMPAR currents was mediated via an NMDAR-independent, PI3K-dependent mechanism. Altogether, these findings indicate that serotonin regulates AMPAR currents at developing synapses independent of NMDA transmission, which may explain its role as an enabler of activity-dependent plasticity.

    more » « less
  5. The NMDA receptor (NMDAR) is inhibited by synaptically released zinc. This inhibition is thought to be the result of zinc diffusion across the synaptic cleft and subsequent binding to the extracellular domain of the NMDAR. However, this model fails to incorporate the observed association of the highly zinc-sensitive NMDAR subunit GluN2A with the postsynaptic zinc transporter ZnT1, which moves intracellular zinc to the extracellular space. Here, we report that disruption of ZnT1-GluN2A association by a cell-permeant peptide strongly reduced NMDAR inhibition by synaptic zinc in mouse dorsal cochlear nucleus synapses. Moreover, synaptic zinc inhibition of NMDARs required postsynaptic intracellular zinc, suggesting that cytoplasmic zinc is transported by ZnT1 to the extracellular space in close proximity to the NMDAR. These results challenge a decades-old dogma on how zinc inhibits synaptic NMDARs and demonstrate that presynaptic release and a postsynaptic transporter organize zinc into distinct microdomains to modulate NMDAR neurotransmission. 
    more » « less