Heroin self-administration: II. CNS gene expression following withdrawal and cue-induced drug-seeking behavior

Abstract

In the accompanying paper, we described incubation of heroin-seeking behavior in rats following 14 days of abstinence. To gain an understanding of genomic changes that accompany this behavioral observation, we measured the expression of genes previously reported to respond to drugs of abuse. Specifically, after 1 or 14 days of abstinence, mRNA expression was measured for 11 genes in the medial prefrontal cortex (mPFC) and nucleus accumbens (NAc) immediately following a single 90 min extinction session. Additionally, the role of contingency was examined in control rats that received yoked, response-independent heroin administration. Gene expression was quantified by real-time quantitative PCR. Expression of five genes (Arc, EGR1, EGR2, Fos, and Homer1b/c) was changed in the mPFC. EGR1 and EGR2 expression was increased following the 90 min extinction session in a contingency-specific manner and this increase persisted through the 14 days of abstinence. Fos expression was also increased after 1 and 14 days of abstinence, but at 14 days this increase was response-independent (i.e., it occurred in both the rats with a history of heroin self-administration and in the yoked controls). Arc expression increased following the extinction session only in rats with a history of heroin self-administration and only when tested following 1, but not 14, days of abstinence. Homer 1 b/c decreased after 14 days of enforced abstinence in rats that received non-contingent heroin. Expression of only a single gene (EGR2) was increased in the NAc. These data demonstrate that behavioral incubation is coincident with altered levels of specific transcripts and that this response is contingently-specific. Moreover, EGR1 and EGR2 are specifically upregulated in self-administering rats following extinction and this finding persists through 14 days of abstinence, suggesting that these genes are particularly associated with the incubation phenomenon. These latter observations of persistent changes in gene expression following abstinence may reflect molecular correlates of relapse liability.

The NK1 Receptor Antagonist L822429 Reduces Heroin Reinforcement

“…These results are in line with previous studies demonstrating differential neuroadaptations in rats receiving heroin in a response-contingent vs -non-contingent manner (Kuntz et al, 2008;Jacobs et al, 2004;Jacobs et al, 2005), and these data may have particular importance for addiction and pain management fields, respectively. Interestingly, we also found that increases in NAc TacR1 mRNA following repeated (moderate dose) heroin was reduced following non-contingent, escalated-dose heroin exposure, possibly reflecting tolerance-associated changes in the NK1 receptor system.…”

Using c-fos to study neuronal ensembles in corticostriatal circuitry of addiction

“…Even when drug is not onboard, contextual cues and discrete cues previously paired with drug self-administration activate many of the same prefrontal cortex and striatal areas during reinstatement of lever pressing (Bastle et al, 2012; Bossert et al, 2011; Cruz et al, 2014; Fanous et al, 2012; Fanous et al, 2013; Hamlin et al, 2008; Kufahl et al, 2009; Mahler and Aston-Jones, 2012; Neisewander et al, 2000; Shalev et al, 2003; Zavala et al, 2007; Zhou et al, 2013) or exposure to the paired context alone without lever responding (Doherty et al, 2013). Perhaps due to higher variability, in situ hybridization and quantitative PCR assays for c-fos mRNA identify activation of only a subset of these same brain areas (Celentano et al, 2009; Daunais et al, 1993; Daunais et al, 1995; Hearing et al, 2008a; Hearing et al, 2008b; Koya et al, 2006; Kuntz et al, 2008; Kuzmin and Johansson, 1999). Overall, cellular imaging studies indicate that c-fos mRNA and Fos protein are expressed within sparsely distributed neurons in many of the same prefrontal cortex and nucleus accumbens regions shown with in vivo electrophysiology studies using similar drug and cue conditions in drug self-administration and relapse models.…”

A Role For The Prefrontal Cortex In Heroin-Seeking After Forced Abstinence By Adult Male Rats But Not Adolescents

“…Stimulus-induced neural activity can be visualized with the immediate early gene product, Fos (Harlan and Garcia, 1998). Fos expression in the context of drug self-administration predicts neural plasticity (Nestler, 2001), and context-or cue-induced reinstatement of heroinseeking in adult rats elevates mPFC c-fos mRNA (Koya et al, 2006;Kuntz et al, 2008). Thus, the aim of the present study was to test the hypothesis that the extent of mPFC activation during a 1-h heroin-seeking test after forced abstinence from heroin self-administration would be lower among rats that self-administered heroin as adolescents compared with adults.…”