Suppression of activity-regulated cytoskeleton-associated gene expression in the dorsal striatum attenuates extinction of cocaine-seeking

Abstract

The caudate putamen (CPu) has been implicated in habit learning and neuroadaptive changes that mediate the compulsive nature of drug-seeking following chronic cocaine self-administration. Re-exposure to an operant chamber previously associated with cocaine, but not yoked-saline, increases activity-regulated cytoskeleton-associated (Arc) gene mRNA expression within the dorsolateral (dl) CPu following prolonged abstinence. In this study, we tested the hypothesis that antisense gene knockdown of Arc within the dlCPu would alter cocaine-seeking. Initial studies showed that a single infusion of Arc antisense oligodeoxynucleotide (ODN) into the dlCPu significantly attenuated the induction of Arc mRNA and Arc protein by a single cocaine exposure (20 mg/kg i.p.) compared to scrambled-ODN-infused controls. In cocaine self-administering rats, infusion of Arc antisense ODN into the dlCPu 3 h prior to a test of context-driven drug-seeking significantly attenuated Arc protein induction, but failed to alter responding during testing, suggesting striatal Arc does not facilitate context-induced drug-seeking following prolonged abstinence. However, Arc antisense ODN infusion blunted the decrease in responding during subsequent 1-h extinction tests 24 and 48 h later. Following re-exposure to a cocaine-paired context, surface expression of the AMPA-type glutamate receptor GluR1 was significantly reduced whereas GluR2 was significantly increased in the dlCPu, independent of Arc antisense ODN infusion. Together, these findings indicate an important role for Arc in neuroadaptations within brain regions responsible for drug-seeking after abstinence and direct attention to changes occurring within striatal circuitry that are necessary to break down the habitual behaviour that leads to relapse.

Fig 1

Schematic representation of the experimental paradigms used in Experiments 1-5.

Fig 2

Intra-dlCPu infusion of AS-ODN suppresses acute cocaine-induced Arc mRNA and protein. (a) Representative coronal hemi-sections and (b) quantitative analysis of the integrated density of the arc mRNA hybridization signal in the dlCPu (left) and dmCPu (right). (c) Top: Representative subsections of immunoblots illustrating Arc and calnexin bands in the dlCPu (left) and dmCPu (right) from each group. Bottom: Quantitative analysis of Arc protein levels in the dlCPu (left) and dmCPu (right) 2 h following acute cocaine injection. ^$p<.51 vs. SAL-SC; *p<.05 vs COC-AS; ^#p<.05 cocaine vs. saline. ID = Integrated Density; CNCX= Calnexin. SAL = saline; COC = cocaine; SC = S-ODN; AS = AS-ODN.

Fig 3

Intra-dlCPu AS-ODN infusion suppresses Arc protein induced by re-exposure to a cocaine-paired context following abstinence, but fails to alter drug-seeking behavior. (a) Active and inactive lever responding averaged over the last 3 d of 2 h self-administration sessions and (b) during a 1 h context re-exposure test following prolonged abstinence. (c) Top: Representative subsection of an immunoblot illustrating Arc and calnexin bands in the dlCPu from each group. Bottom: Quantitative analysis of Arc protein in the dlCPu (Experiment 3) following a 1 h context test. (d) Top: Representative subsection of an immunoblot illustrating biotinylated GluR1 and total GluR1 bands in the dlCPu from each group. Bottom: Ratio of surface/total GluR1 in the dlCPu following a 1 h context test. (e) Top: Representative immunoblot illustrating biotinylated GluR2 and total GluR2 bands in the dlCPu from each group. Bottom: Ratio of surface/total GluR2 expression in the dCPu following a 1 h context test. (f) A control image shows the specificity of the biotinylation assay. No band can be detected for the cytoplasmic-rich protein AGS1 in the biotinylated fraction in representative immunoblot of each treatment group. ^$p<.05 vs. SAL-SC; ^{^}p<.05 vs. SAL-AS; *p<.05, vs. COC-AS;. ^#p<.05, cocaine vs. saline; SAL = saline; COC = cocaine; SC = SC-ODN; AS = AS-ODN; AGS1= activator of g-protein signaling 1; CNCX= Calnexin.

Fig 4

Intra-dlCPu Arc AS-ODN infusion prior to context-driven relapse attenuates extinction of cocaine-seeking behavior during subsequent context exposures. (a) Active and inactive lever pressing during a 1 h context test (left) and extinction day 2 (right; Experiment 4). (b) Active lever responses with the 1 h context test (left) and extinction day 2 (right) represented in 15 min time bins. (c) Active and inactive lever responding during a 1 h context test and subsequent extinction days (Experiment 5). ^#p<.05, cocaine vs saline; ^{^}p<.05, COC-AS vs. SAL-AS; ^@p<.05, COC-AS vs. COC-SC; ^$p<.05 COC-SC vs. SAL-SC. SAL = saline; COC = cocaine; SC = S-ODN; AS = AS-ODN.