CBP in the nucleus accumbens regulates cocaine-induced histone acetylation and is critical for cocaine-associated behaviors

Abstract

Cocaine exposure triggers molecular events that lead to long-lasting changes in brain structure and function. These changes can lead to the development of persistent and robust behavioral adaptations that characterize addiction. Recent evidence suggests the regulation of transcription via chromatin modification, such as histone acetylation, has an important role in the development of addictive behavior. Histone acetylation is regulated by histone acetyltransferases (HATs), which acetylate histones and promote transcription, and histone deacetylases (HDACs), which remove acetyl groups and silence transcription. Studies have demonstrated that HDACs may negatively regulate cocaine-induced behaviors, but very little is known about the role of specific HATs in long-lasting drug-induced plasticity. The histone acetyltransferase CREB-binding protein (CBP) mediates transcriptional activation by recruiting basal transcription machinery and acetylating histones. CBP is a critically important chromatin-modifying enzyme involved in regulating gene expression required for long-term plasticity and memory. However, the role of CBP in cocaine-induced behaviors remains largely unknown. We examined the role of CBP in drug-induced plasticity using CBP-FLOX genetically modified mice in combination with adeno-associated virus expressing Cre-recombinase to generate focal homozygous deletions of Cbp in the nucleus accumbens (NAc). A complete loss of CBP in NAc neurons results in decreased histone acetylation and significantly altered c-fos expression in response to cocaine. Furthermore, the deletion of CBP in the NAc correlates with significant impairments in cocaine sensitivity and context-cocaine associated memory. This is the first study to demonstrate a definitive role for CBP in modulating gene expression that may subserve drug-seeking behaviors.

Figure 1.

AAV2/1-Cre infusion in Cbp^flox/flox mice results in a complete focal deletion of CBP restricted to nucleus accumbens. A, Representative images [4× (left) and 20× (right) magnification of the regions boxed in white] showing CBP immunoreactivity in nucleus accumbens of AAV2/1-Cre-infused Cbp^+/+ and Cbp^flox/flox mice. CBP labeling is found throughout striatum, except in the AAV2/1-Cre infusion site of Cbp^flox/flox mice. B, Deletion of CBP in AAV2/1-Cre infused Cbp^flox/flox mice is confined to nucleus accumbens, spreading +1.20 to +0.70 mm AP from bregma.

Figure 2.

Homozygous deletion of Cbp disrupts histone acetylation induced in the nucleus accumbens by cocaine treatment. Nucleus accumbens sections from Cbp^+/+ and Cbp^flox/flox mice infused with AAV2/1-Cre were immunolabeled, and optical density of 20× magnification images of infusion site (CBP deletion confirmed by immunolabeling in Cbp^+/+ and Cbp^flox/flox mice) was quantified. A, Acetylation of H3K14 increases with acute cocaine and increases further with chronic cocaine in Cbp^+/+ mice, but H3K14Ac does not increase in Cbp^flox/flox mice in response to cocaine. B, Acetylation of H2BK12 increases with acute and chronic cocaine but is significantly reduced in Cbp^flox/flox mice. C, Acetylation of H4K12 is reduced with acute and chronic cocaine treatment but is not different between Cbp^+/+ and Cbp^flox/flox mice. D, Dimethylation of H3K9 is reduced by acute cocaine and further reduced with chronic treatment in both Cbp^+/+ and Cbp^flox/flox mice. ^†Significantly different from saline; *significantly different from Cbp^+/+ mice; p < 0.05.

Figure 3.

Cocaine-induced c-fos expression is regulated by CBP and altered in response to cocaine in the absence of CBP. ChIP was performed on ventral striata of saline and cocaine-treated wild-type mice with anti-acetylated H3 (AcH3) (A) or anti-CBP (B) antibodies and levels of c-fos promoter in the IPs were measured by quantitative PCR. A, Acetylation on the c-fos promoter increases 1 h after acute and chronic cocaine treatment in wild-type mice, with a more robust effect by acute treatment. B, Cocaine exposure leads to the recruitment of CBP to the c-fos promoter, with a more robust effect by acute cocaine. C, Acute cocaine induces c-fos expression and chronic cocaine desensitizes c-fos expression in Cbp^+/+ mice. In Cbp^flox/flox mice, basal c-fos expression is unaltered, but acute cocaine fails to induce c-fos expression. Furthermore, c-fos expression is deregulated with chronic cocaine in Cbp^flox/flox mice. *Significantly different from saline, p < 0.05; ^†significantly different between genotype, p < 0.05.

Figure 4.

Focal homozygous deletion of CBP in nucleus accumbens disrupts locomotor activating effects of cocaine. A, Baseline locomotion in response to saline on (days 1–4) is similar between Cbp^+/+ and Cbp^flox/flox mice, but behavioral response to an acute cocaine injection (day 5) is impaired. B, Cbp^+/+ mice show increased locomotor activity in response to chronic cocaine (days 1–5) compared to chronic saline (days 1–5) treatment, but Cbp^flox/flox mice have reduced sensitivity to chronic cocaine. *Significantly different between genotype, p < 0.05.

Figure 5.

Nucleus accumbens deletion of CBP impairs cocaine reward. No initial preference for either context across all groups. Following conditioned place preference (CPP) training, Cbp^+/+ mice infused with AAV2/1-Cre and sham-treated Cbp^flox/flox mice exhibited a preference for the cocaine-paired context. However, intranucleus accumbens AAV2/1-Cre-infused Cbp^flox/flox mice did not form a preference for the cocaine-paired context. Data presented as difference in time spent in cocaine-paired versus saline-paired context during initial and final preference tests. *Significantly different between groups, p < 0.05.