ABSTRACT
Activation of metabotropic- (mGluRs) or NMDA-type glutamate receptors (NMDARs) each can induce long-term depression (LTD) of synaptic transmission in CA1 hippocampal neurons. These two forms of LTD are triggered by diverse signaling pathways yet both are expressed by the internalization of AMPA-type glutamate receptors (AMPARs). An unanswered question remains as to whether the convergence of the mGluR and NMDAR signaling pathways on AMPAR endocytosis renders these two forms of plasticity functionally equivalent, with both pathways inducing endocytosis of the same population of synaptic AMPARs. We now report evidence that these pathways couple to the endocytosis of distinct populations of AMPARs defined by their mobility in the membrane surface. NMDAR activation enhances removal of surface AMPARs that rapidly cycle into and out of the membrane surface, while activation of mGluRs with DHPG results in the internalization of a non-mobile population of AMPARs. Glutamate Receptor Interacting Proteins 1 and 2 (GRIP1/2) play a key role in defining the non-cycling receptor population. GRIP1/2 knockdown with siRNA increases the proportion of rapidly cycling surface AMPARs and inhibits mGluR- but not NMDAR-mediated AMPAR internalization. Additionally, we find that mGluR activation dissociates surface AMPARs from GRIP1/2 while stimulation of NMDARs elicits the loss of membrane receptors not bound to GRIP1/2. We propose that these two receptor pathways can drive the endocytosis of distinct populations of AMPARs: NMDARs activation induces the endocytosis of rapidly cycling surface AMPARs not directly associated with GRIP1/2 while mGluR activation induces the endocytosis of non-cycling GRIP-bound surface AMPARs.
Subject(s)
Endocytosis/physiology , Receptors, AMPA/metabolism , Receptors, Metabotropic Glutamate/metabolism , Receptors, N-Methyl-D-Aspartate/metabolism , Animals , Carrier Proteins/genetics , Carrier Proteins/metabolism , Cells, Cultured , Hippocampus/cytology , Intercellular Signaling Peptides and Proteins , Intracellular Signaling Peptides and Proteins , Long-Term Synaptic Depression/physiology , Nerve Tissue Proteins/genetics , Nerve Tissue Proteins/metabolism , Neurons/cytology , Neurons/physiology , Patch-Clamp Techniques , RNA, Small Interfering/genetics , RNA, Small Interfering/metabolism , Rats , Rats, Sprague-Dawley , Signal Transduction/physiologyABSTRACT
Visual experience scales down excitatory synapses in the superficial layers of visual cortex in a process that provides an in vivo paradigm of homeostatic synaptic scaling. Experience-induced increases in neural activity rapidly upregulates mRNAs of immediate early genes involved in synaptic plasticity, one of which is Arc (activity-regulated cytoskeleton protein or Arg3.1). Cell biological studies indicate that Arc/Arg3.1 protein functions to recruit endocytic machinery for AMPA receptor internalization, and this action, together with its activity-dependent expression, rationalizes a role for Arc/Arg3.1 in homeostatic synaptic scaling. Here, we investigated the role of Arc/Arg3.1 in homeostatic scaling in vivo by examining experience-dependent development of layer 2/3 neurons in the visual cortex of Arc/Arg3.1 knock-out (KO) mice. Arc/Arg3.1 KOs show minimal changes in basal and developmental regulation of excitatory synaptic strengths but display a profound deficit in homeostatic regulation of excitatory synapses by visual experience. As additional evidence of specificity, we found that the visual experience-induced regulation of inhibitory synapses is normal, although the basal inhibitory synaptic strength is increased in the Arc/Arg3.1 KOs. Our results demonstrate that Arc/Arg3.1 plays a selective role in regulating visual experience-dependent homeostatic plasticity of excitatory synaptic transmission in vivo.
Subject(s)
Cytoskeletal Proteins/metabolism , Nerve Tissue Proteins/metabolism , Neuronal Plasticity/physiology , Neurons/physiology , Photic Stimulation/methods , Synapses/physiology , Visual Cortex/physiology , Age Factors , Analysis of Variance , Animals , Animals, Newborn , Biotinylation/methods , Cytoskeletal Proteins/deficiency , Electric Stimulation/methods , Excitatory Postsynaptic Potentials/drug effects , Excitatory Postsynaptic Potentials/genetics , Excitatory Postsynaptic Potentials/radiation effects , Female , Gene Expression Regulation/genetics , Homeostasis/genetics , In Vitro Techniques , Male , Mice , Mice, Knockout , Nerve Tissue Proteins/deficiency , Neuronal Plasticity/genetics , Patch-Clamp Techniques/methods , Phosphopyruvate Hydratase/metabolism , Receptors, Glutamate/metabolism , Synapses/genetics , Synaptic Transmission/drug effects , Synaptic Transmission/genetics , Synaptic Transmission/physiology , Time Factors , Visual Cortex/cytologyABSTRACT
The activation of NMDA receptors (NMDARs) triggers long-term changes in AMPA receptor-mediated synaptic transmission in the CNS. These long-lasting changes occur via the addition or removal of AMPA receptors (AMPARs) at the synaptic membrane and are mediated by a number of regulatory proteins including the GluR2 AMPAR-interacting proteins n-ethylmaleimide sensitive factor (NSF) and Protein Interacting with C Kinase (PICK1). We have shown that the potent activation of NMDARs drives unclustering of PICK1 and PICK1-GluR2 dissociation in dendrites resulting in increased surface delivery of AMPARs. Here we show that the dispersal of PICK1 is mediated by the actions of NSF. We find that elevated NMDAR signaling leads to the S-nitrosylation of NSF and increased NSF-GluR2 association. Both NMDAR-dependent unclustering of PICK1 and the delivery of surface AMPARs are dependent on release of nitric oxide (NO). Our data suggest that NMDAR activation can drive the surface delivery of AMPARs from a pool of intracellular AMPARs retained by PICK1 through the NO-dependent modification of NSF.