ABA renewal involves enhancements in both GluA2-lacking AMPA receptor activity and GluA1 phosphorylation in the lateral amygdala.

Kyungjoon Park,Justin C Lee,Junuk Lee,Bobae An,Seungbok Lee,Sangho Song,Ingie Hong,Jihye Kim,Hyun Woo Lee,Sukwon Lee,Hyun Kim,Sukwoo Choi,Jeongyeon Kim,Beomjong Song,Sungmo Park,Judith Homberg

doi:10.1371/journal.pone.0100108

Abstract

Fear renewal, the context-specific relapse of fear following fear extinction, is a leading animal model of post-traumatic stress disorders (PTSD) and fear-related disorders. Although fear extinction can diminish fear responses, this effect is restricted to the context where the extinction is carried out, and the extinguished fear strongly relapses when assessed in the original acquisition context (ABA renewal) or in a context distinct from the conditioning and extinction contexts (ABC renewal). We have previously identified Ser831 phosphorylation of GluA1 subunit in the lateral amygdala (LA) as a key molecular mechanism for ABC renewal. However, molecular mechanisms underlying ABA renewal remain to be elucidated. Here, we found that both the excitatory synaptic efficacy and GluA2-lacking AMPAR activity at thalamic input synapses onto the LA (T-LA synapses) were enhanced upon ABA renewal. GluA2-lacking AMPAR activity was also increased during low-threshold potentiation, a potential cellular substrate of renewal, at T-LA synapses. The microinjection of 1-naphtylacetyl-spermine (NASPM), a selective blocker of GluA2-lacking AMPARs, into the LA attenuated ABA renewal, suggesting a critical role of GluA2-lacking AMPARs in ABA renewal. We also found that Ser831 phosphorylation of GluA1 in the LA was increased upon ABA renewal. We developed a short peptide mimicking the Ser831-containing C-tail region of GluA1, which can be phosphorylated upon renewal (GluA1S); thus, the phosphorylated GluA1S may compete with Ser831-phosphorylated GluA1. This GluA1S peptide blocked the low-threshold potentiation when dialyzed into a recorded neuron. The microinjection of a cell-permeable form of GluA1S peptide into the LA attenuated ABA renewal. In support of the GluA1S experiments, a GluA1D peptide (in which the serine at 831 is replaced with a phosphomimetic amino acid, aspartate) attenuated ABA renewal when microinjected into the LA. These findings suggest that enhancements in both the GluA2-lacking AMPAR activity and GluA1 phosphorylation at Ser831 are required for ABA renewal.

Highlights

Fear-related emotional disorders, such as post-traumatic stress disorders (PTSD) and phobia, are clinically challenging to treat because the symptoms strongly relapse even after extensive exposure-based therapy [1,2]
Our findings suggest that similar mechanisms underlie both ABA renewal and ABC renewal; that is, enhancements in both the GluA2-lacking AMPAR activity and GluA1 phosphorylation at Ser831
We have found that GluA2-lacking AMPAR activity is required for renewal, as evidenced by the attenuation of ABA renewal through the microinjection of NASPM into the lateral amygdala (LA)

Summary

Introduction

Fear-related emotional disorders, such as PTSD and phobia, are clinically challenging to treat because the symptoms strongly relapse even after extensive exposure-based therapy [1,2]. The extinguished fear can relapse when the subject is presented with a conditioned stimulus (CS) in the same context in which the fear conditioning was performed (ABA renewal) or in a third context distinct from the context where the fear conditioning or extinction was carried out (ABC renewal). Both ABA and ABC renewal demonstrate the contextdependency of extinction learning, their mechanisms and manifestations have been shown to differ clearly in several aspects [8,9,10,11,12,13,14]. ABA renewal can be important because it is well defined in humans [11], and PTSD patients often experience flashbacks that are triggered by exposure to the contextual aspects of traumatic memories [18]

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Results

Conclusion