BRG1 in the Nucleus Accumbens Regulates Cocaine-Seeking Behavior

Abstract

Background Drug addiction is defined as a chronic disease characterized by compulsive drug seeking and episodes of relapse despite prolonged periods of drug abstinence. Neurobiological adaptations, including transcriptional and epigenetic alterations in the nucleus accumbens, are thought to contribute to this life-long disease state. We previously demonstrated that transcription factor SMAD3 is increased following seven days of withdrawal from cocaine self-administration. However, it is still unknown which additional factors participate in the process of chromatin remodeling and facilitate the binding of SMAD3 to promoter regions of target genes. Here we examined the possible interaction of BRG1—also known as SMARCA4, an ATPase-containing chromatin remodeler—and SMAD3 in response to cocaine exposure. Methods The expression of BRG1, as well as its binding to SMAD3 and target gene promoter regions, was evaluated in the nucleus accumbens and dorsal striatum of rats using Western blotting, co-immunoprecipitation, and chromatin immunoprecipitation techniques, respectively, following withdrawal from cocaine self-administration. Rats were assessed for cocaine-seeking behaviors following either intra-accumbal injections of the BRG1 inhibitor PFI3 or viral-mediated overexpression of BRG1. Results Following withdrawal from cocaine self-administration, BRG1 expression and complex formation with SMAD3 are increased in the nucleus accumbens, resulting in increased binding of BRG1 to the promoter regions of Ctnnb1, Mef2d, and Dbn1. Intra-accumbal infusion of PFI3 attenuated, while viral overexpression of Brg1 enhanced, cocaine-reinstatement behavior. Conclusion BRG1 is a key mediator of the SMAD3-dependent regulation of cellular and behavioral plasticity mediating cocaine seeking following a period of withdrawal.

E3 Ubiquitin-Protein Ligase SMURF1 in the Nucleus Accumbens Mediates Cocaine Seeking

“…Our sample sizes are similar to those reported in previous publications (32,33,43). All statistical analyses were performed using Prism (GraphPad Software, La Jolla, CA).…”

“…Jugular catheterization and self-administration were conducted as previously described (31–33). Catheters were flushed daily with 0.2 mL of a solution of enrofloxacin (4 mg/mL) in heparinized saline (50 IU/mL in 0.9% sterile saline) to preserve catheter patency.…”

“…Tissue collection and immunoblotting were performed as previously described (32,33) (see Supplement). …”

“…Bilateral guide cannula implantation and microinjections were carried out as previously described (32,33), with minor modifications. On WD1 following cocaine self-administration, guide cannulas (C235G-2.4; Plastics One, Roanoke, VA) aimed at the coordinates (from bregma) anterior–posterior, +1.8, medial– lateral, +1.2, and dorsal–ventral, −6.5 (35) were implanted and fixed to the skull by an acrylic resin and stainless-steel screws.…”

“…Quantitative chromatin immunoprecipitation (ChIP) was performed for Runt-related transcript factor 2 (RUNX2) as previously described (32,33), with minor modifications. Four NAc punches from 2 rats were pooled together for each sample ( n = 6 samples for saline and n = 5 samples for cocaine group).…”