Environment-specific expression of the immediate-early gene Arc in hippocampal neuronal ensembles

Abstract

We used fluorescent in-situ hybridization and confocal microscopy to monitor the subcellular distribution of the immediate-early gene Arc. Arc RNA appeared in discrete intranuclear foci within minutes of neuronal activation and subsequently disappeared from the nucleus and accumulated in the cytoplasm by 30 minutes. The time course of nuclear versus cytoplasmic Arc RNA accumulation was distinct, and could therefore be used to infer the activity history of individual neurons at two times. Following sequential exposure of rats to two different environments or to the same environment twice, the proportion of CA1 neurons with cytoplasmic, nuclear or overlapping Arc expression profiles matched predictions derived from ensemble neurophysiological recordings of hippocampal neuronal ensembles. Arc gene induction is thus specifically linked to neural encoding processes.

Mapping neuronal activation and the influence of adrenergic signaling during contextual memory retrieval

“…These properties allow one to determine the recent activation history of a neuron at two distinct times, referred to as cellular compartment analysis of temporal activity by FISH (catFISH) (Guzowski et al 1999(Guzowski et al , 2001. Arc catFISH has been used to examine activation of hippocampal pyramidal neurons in identical and distinct contexts (Guzowski et al 1999), generating results supported by electrophysiologic recordings (Kubie and Ranck 1983;Thompson and Best 1990;Wilson and McNaughton 1993).One goal of this study was to determine whether Arc catFISH would identify neurons uniquely activated as a result of exposure to a salient versus neutral context (the former resulting in the retrieval of a contextual fear memory). If it could, activation of these neurons would likely reflect a variety of processes related to contextual fear, including retrieval of the contextual fear memory, increased arousal or fear following retrieval, or conditioned responses generated by fear, such as freezing.…”

“…Basal expression of Arc is very low in most neurons. However, transcription is rapidly induced by neuronal activation, and FISH to Arc reveals two small, intense intranuclear foci within 2 min of activation (Guzowski et al 1999). By ∼20 min the nuclear signal has disappeared and perinuclear cytoplasmic labeling is transiently observed before disappearing due to dendritic transport of Arc mRNA (Steward et al 1998).…”

“…Our analysis included the hippocampus for several reasons. First, induction of Arc occurs readily in hippocampal pyramidal neurons following a change in context (Guzowski et al 1999). Second, the hippocampus is critical for contextual memory storage and discrimination of contexts during memory retrieval Phillips and LeDoux 1992;Holt and Maren 1999).…”

“…By ∼20 min the nuclear signal has disappeared and perinuclear cytoplasmic labeling is transiently observed before disappearing due to dendritic transport of Arc mRNA (Steward et al 1998). These properties allow one to determine the recent activation history of a neuron at two distinct times, referred to as cellular compartment analysis of temporal activity by FISH (catFISH) (Guzowski et al 1999(Guzowski et al , 2001. Arc catFISH has been used to examine activation of hippocampal pyramidal neurons in identical and distinct contexts (Guzowski et al 1999), generating results supported by electrophysiologic recordings (Kubie and Ranck 1983;Thompson and Best 1990;Wilson and McNaughton 1993).…”

Differential activation of extracellular signal-regulated kinase 1 and a related complex in neuronal nuclei

“…We also find another p-ERK and 14-3-3 reactive band at 70 kDa in the cytosol, but it remains undetermined whether this represents an incomplete version of PERC-160, or whether it serves a unique cytosolic function. Importantly, scaffolding can serve to increase the speed of signaling, a critical feature if ERKs are to regulate genes such as arc, which can be detected as early as 2 minutes after stimulation (Guzowski et al 1999;Waltereit et al 2001). This association would certainly not be without trade-offs, however, in that scaffolding ERK to its nuclear substrates and/or upstream activators in such a 1:1:1 ratio would restrict any amplification processes (Kolch 2005) (Fig.…”