Visualizing synaptic plasticity in vivo by large-scale imaging of endogenous AMPA receptors.
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ABSTRACT:
SUBMITTER: Graves AR
PROVIDER: S-EPMC8616579 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:During NMDA receptor-mediated long-term potentiation (LTP), synapses are strengthened by trafficking AMPA receptors to the synapse through a calcium-dependent kinase cascade following activation of NMDA receptors. This process results in a long-lasting increase in synaptic strength that is thought to be a cellular mechanism for learning and memory. Over the past 20 years, many signaling pathways have been shown to be involved in the induction and maintenance of LTP including the MAPK cascade. However, the crucial link between NMDA receptors and the signaling cascades involved in AMPA receptor trafficking during LTP remains elusive. In this study, we aimed to identify and characterize NMDA receptor signaling proteins that link NMDA receptor activation to downstream signaling pathways that lead to trafficking of AMPA receptors. We have identified a novel NMDA receptor interacting signaling protein, AGAP3. AGAP3 contains multiple signaling domains, a GTPase-like domain, a pleckstrin homology domain, and an ArfGAP domain, and exists as a component of the NMDA receptor complex. In addition, we found that AGAP3 regulates NMDA receptor-mediated Ras/ERK and Arf6 signaling pathways during chemically induced LTP in rat primary neuronal cultures. Finally, knocking down AGAP3 expression leads to occlusion of AMPA receptor trafficking during chemically induced LTP. Together, AGAP3 is an essential signaling component of the NMDA receptor complex that links NMDA receptor activation to AMPA receptor trafficking.
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Project description:Regulation of AMPA receptor (AMPAR) membrane trafficking is critical for synaptic plasticity, as well as for learning and memory. However, the mechanisms of AMPAR trafficking in vivo remain elusive. Using in vivo two-photon microscopy in the mouse somatosensory barrel cortex, we found that acute whisker stimulation led to a significant increase in the intensity of surface AMPAR GluA1 subunit (sGluA1) in both spines and dendritic shafts and a small increase in spine size relative to prestimulation values. Interestingly, the initial spine properties biased spine changes following whisker stimulation. Changes in spine sGluA1 intensity were positively correlated with changes in spine size and dendritic shaft sGluA1 intensity following whisker stimulation. The increase in spine sGluA1 intensity evoked by whisker stimulation was NMDA receptor dependent and long lasting, similar to major forms of synaptic plasticity in the brain. In this study we were able to observe experience-dependent AMPAR trafficking in real time and characterize, in vivo, a major form of synaptic plasticity in the brain.
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Project description:Sensory experience, and the lack thereof, can alter the function of excitatory synapses in the primary sensory cortices. Recent evidence suggests that changes in sensory experience can regulate the synaptic level of Ca(2+)-permeable AMPA receptors (CP-AMPARs). However, the molecular mechanisms underlying such a process have not been determined. We found that binocular visual deprivation, which is a well-established in vivo model to produce multiplicative synaptic scaling in visual cortex of juvenile rodents, is accompanied by an increase in the phosphorylation of AMPAR GluR1 (or GluA1) subunit at the serine 845 (S845) site and the appearance of CP-AMPARs at synapses. To address the role of GluR1-S845 in visual deprivation-induced homeostatic synaptic plasticity, we used mice lacking key phosphorylation sites on the GluR1 subunit. We found that mice specifically lacking the GluR1-S845 site (GluR1-S845A mutants), which is a substrate of cAMP-dependent kinase (PKA), show abnormal basal excitatory synaptic transmission and lack visual deprivation-induced homeostatic synaptic plasticity. We also found evidence that increasing GluR1-S845 phosphorylation alone is not sufficient to produce normal multiplicative synaptic scaling. Our study provides concrete evidence that a GluR1 dependent mechanism, especially S845 phosphorylation, is a necessary pre-requisite step for in vivo homeostatic synaptic plasticity.
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