Identification of plasticity‐associated genes regulated by Pavlovian fear conditioning in the lateral amygdala

Abstract

J. Neurochem. (2010) 112, 636–650. Abstract Most recent studies aimed at defining the cellular and molecular mechanisms of Pavlovian fear conditioning have focused on protein kinase signaling pathways and the transcription factor cAMP‐response element binding protein (CREB) that promote fear memory consolidation in the lateral nucleus of the amygdala (LA). Despite this progress, there still remains a paucity of information regarding the genes downstream of CREB that are required for long‐term fear memory formation in the LA. We have adopted a strategy of using microarray technology to initially identify genes induced within the dentate gyrus following in vivo long‐term potentiation (LTP) followed by analysis of whether these same genes are also regulated by fear conditioning within the LA. In the present study, we first identified 34 plasticity‐associated genes that are induced within 30 min following LTP induction utilizing a combination of DNA microarray, qRT‐PCR, and in situ hybridization. To determine whether these genes are also induced in the LA following Pavlovian fear conditioning, we next exposed rats to an auditory fear conditioning protocol or to control conditions that do not support fear learning followed by qRT‐PCR on mRNA from microdissected LA samples. Finally, we asked whether identified genes induced by fear learning in the LA are downstream of the extracellular‐regulated kinase/mitogen‐activated protein kinase signaling cascade. Collectively, our findings reveal a comprehensive list of genes that represent the first wave of transcription following both LTP induction and fear conditioning that largely belong to a class of genes referred to as ‘neuronal activity dependent genes’ that are likely calcium, extracellular‐regulated kinase/mitogen‐activated protein kinase, and CREB‐dependent.

Early growth response gene 1 (Egr-1) is required for new and reactivated fear memories in the lateral amygdala

“…However, Hall and colleagues found equivalent increases in EGR-1 mRNA expression in the LA following exposure to the context alone, suggesting that EGR-1 may not play a selective role in fear learning (Hall et al 2000). This latter pattern of findings is consistent with a recent study that has shown that exposure to a novel context alone can induce robust expression of a variety of genes in the LA (Ploski et al 2010), and suggests that the use of contextual fear conditioning paradigms may be potentially problematic for the study of gene expression following fear learning (Davis et al 2003). In the present series of experiments, we have re-examined the role of EGR-1 in the consolidation of fear memories in the LA using an auditory fear conditioning task.…”

“…In the present series of experiments, we have re-examined the role of EGR-1 in the consolidation of fear memories in the LA using an auditory fear conditioning task. Unlike contextual fear learning tasks, auditory fear conditioning paradigms provide a means to examine training-related changes in gene expression in the absence of those driven by exposure to a novel context (Ploski et al 2010). In our first series of experiments, we asked whether auditory fear conditioning regulates the expression of EGR-1 protein in the LA.…”

“…Interestingly, the amygdala has been shown to be a critical modulator of the formation of contextual memory representations, but only when the context is novel (Huff et al 2005). Accordingly, any study that examines the regulation of genes in the amygdala following contextual fear learning must distinguish between gene expression related to contextual fear learning and that related to context learning and/or novelty alone (Hall et al 2000;Ploski et al 2010). In the present study, we attempted to circumvent these issues by examining the regulation of EGR-1 in the LA following auditory fear conditioning in rats that had been repeatedly exposed to the training context, a procedure that allowed us to examine trainingrelated changes in gene expression in the LA in the absence of those driven by exposure to a novel context (Ploski et al 2010).…”

“…In a second experiment, we examined EGR-1 expression in Paired rats relative to those receiving tone alone ("Tone Alone") or no stimulation ("Naïve"). To rule out the possibility that exposure to the conditioning chamber alone might induce EGR-1 in the LA, rats in this second experiment received extensive habituation to both handling and to the conditioning chamber for 4 d prior to fear conditioning, a procedure that we have previously shown to be useful in significantly reducing novelty-induced gene expression in the LA (Ploski et al 2010). In each of our experiments, EGR-1 labeling was found throughout the dorsal tip of the LA (LAd), ventral portion of the LA (LAv), basal (B), and the central nucleus of the amygdala (CE) (Fig.…”

cAMP Response Element-Binding Protein Is a Primary Hub of Activity-Driven Neuronal Gene Expression

“…sponse to different chemical stimuli presented above, we collected five studies in which different types of stimulations were used, including LTP and chemical stimulation paradigms, for comparison with our data (Hansen et al, 2008;Lemberger et al, 2008;Jancic et al, 2009;Ploski et al, 2010;Ryan et al, 2011). We found that SRF was associated with LTP, kainate, and cocainemediated stimulation, whereas EGR1 was solely linked with cocaine-mediated induction of gene expression.…”