NMDA Receptor-Dependent Synaptic Potentiation via APPL1 Signaling Is Required for the Accessibility of a Prefrontal Neuronal Assembly in Retrieving Fear Extinction.

BACKGROUND: The ventromedial prefrontal cortex has been viewed as a locus for storage and recall of extinction memory. However, the synaptic and cellular mechanisms underlying these processes remain elusive. METHODS: We combined transgenic mice, electrophysiological recording, activity-dependent cell labeling, and chemogenetic manipulation to analyze the role of adaptor protein APPL1 in the ventromedial prefrontal cortex in fear extinction retrieval. RESULTS: We found that both constitutive and conditional APPL1 knockout decreased NMDA receptor (NMDAR) function in the ventromedial prefrontal cortex and impaired fear extinction retrieval. Moreover, APPL1 undergoes nuclear translocation during extinction retrieval. Blocking APPL1 nucleocytoplasmic translocation reduced NMDAR currents and disrupted extinction retrieval. We also identified a prefrontal neuronal ensemble that is both necessary and sufficient for the storage of extinction memory. Inducible APPL1 knockout in this ensemble abolished NMDAR-dependent synaptic potentiation and disrupted extinction retrieval, while chemogenetic activation of this ensemble simultaneously rescued the impaired behaviors. CONCLUSIONS: Our results indicate that a prefrontal neuronal ensemble stores extinction memory, and APPL1 signaling supports these neurons in retrieving extinction memory by controlling NMDAR-dependent potentiation.