Lack of increased immediate early gene expression in rats reinstating cocaine-seeking behavior to discrete sensory cues.

Matthew D Riedy,Kristen A Keefe

doi:10.1371/journal.pone.0072883

Abstract

Drug-seeking behavior elicited by drug-associated cues contributes to relapse in addiction; however, whether relapse elicited by drug-associated conditioned reinforcers (CR) versus discriminative stimuli (DS) involves distinct or overlapping neuronal populations is unknown. To address this question, we developed a novel cocaine self-administration and cue-induced reinstatement paradigm that exposed the same rats to distinct cocaine-associated CR and DS. Rats were trained to self-administer cocaine in separate sessions. In one, a DS signaled cocaine availability; in the other, cocaine delivery was paired with a different CR. After extinction training and reinstatement testing, where both cues were presented in separate sessions, rats were sacrificed and processed for cellular analysis of temporal activity by fluorescent in situ hybridization (CatFISH) for activity regulated cytoskeleton-associated protein (Arc) mRNA and for radioactive in situ hybridization for Arc and zif268 mRNAs. CatFISH did not reveal significant changes in Arc mRNA expression. Similar results were obtained with radioactive in situ hybridization. We have shown that while rats reinstate drug seeking in response to temporally discrete presentations of distinct drug-associated cues, such reinstatement is not associated with increased transcriptional activation of Arc or zif268 mRNAs, suggesting that expression of these genes may not be necessary for cue-induced reinstatement of drug-seeking behavior.

Highlights

Drug addiction is defined as uncontrollable, compulsive drug seeking and use in the face of negative consequences
EXP rats that did not meet this criterion during both stimulus-exposure segments of the reinstatement test were excluded from the subsequent gene expression analysis
Planned comparisons via Bonferroni-corrected student’s t-tests revealed significant increases in active- vs. inactive-lever pressing for the EXP group during both the conditioned reinforcers (CR) (DF56 t9.0, p,0.01) and Discriminative stimuli (DS) (DF56 t3.4, p,0.01) exposure segments of the reinstatement test session

Summary

Introduction

Drug addiction is defined as uncontrollable, compulsive drug seeking and use in the face of negative consequences (http://www. nida.nih.gov/PublishedArticles/Essence.html). Understanding the neural mechanisms that encode drug-cuebehavior associations during initial drug use and how subsequent exposure to drug-associated stimuli influences brain activity and behavior is critical for designing successful interventions for drug addiction and relapse. There are likely similarities and differences in the neural circuits underlying drug-seeking and drug-taking behavior mediated by exposure to CRs and DS [2]. Prior studies investigating the neural substrates of CR-maintained drug-seeking behavior using lesion and pharmacological approaches have produced substantial evidence for a neural circuit involving the basolateral amygdala (BLA) [8,9], prefrontal cortex (PFC) [8,10,11], nucleus accumbens core (NAc) [12], hypothalamus [13], and ventral tegmental area (VTA) [14] in mediating the ability of CRs to maintain drug-seeking behavior [15]. With the exception of the BLA, the extent to which different brain regions are activated by CRs maintaining drug-seeking behavior is not clear

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