The treatment of alcoholism requires the proper management of ethanol withdrawal symptoms, such as anxiety, to prevent further alcohol use and abuse. In this study, we investigated the potential role of brain chromatin remodeling, caused by histone modifications, in alcoholism. We found that the anxiolytic effects produced by acute alcohol were associated with a decrease in histone deacetylase (HDAC) activity and increases in acetylation of histones (H3 and H4), levels of CREB (cAMP-responsive element binding) binding protein (CBP), and neuropeptide Y (NPY) expression in the amygdaloid brain regions of rats. However, the anxiety-like behaviors during withdrawal after chronic alcohol exposure were associated with an increase in HDAC activity and decreases in acetylation of H3 and H4, and levels of both CBP and NPY in the amygdala. Blocking the observed increase in HDAC activity during alcohol withdrawal with the HDAC inhibitor, trichostatin A, rescued the deficits in H3 and H4 acetylation and NPY expression (mRNA and protein levels) in the amygdala (central and medial nucleus of amygdala) and prevented the development of alcohol withdrawal-related anxiety in rats as measured by the elevated plus maze and light/dark box exploration tests. These results reveal a novel role for amygdaloid chromatin remodeling in the process of alcohol addiction and further suggest that HDAC inhibitors may be potential therapeutic agents in treating alcohol withdrawal symptoms.

Binge drinking is common during adolescence and can lead to the development of psychiatric disorders, including alcoholism in adulthood. Here, the role and persistent effects of histone modifications during adolescent intermittent ethanol (AIE) exposure in the development of anxiety and alcoholism in adulthood were investigated. Rats received intermittent ethanol exposure during post-natal days 28-41, and anxiety-like behaviors were measured after 1 and 24 hrs of the last AIE. The effects of AIE on anxiety-like and alcohol-drinking behaviors in adulthood were measured with or without treatment with the histone deacetylase (HDAC) inhibitor, trichostatin A (TSA). Amygdaloid brain regions were collected to measure HDAC activity, global and gene-specific histone H3 acetylation, expression of brain-derived neurotrophic factor (BDNF) and activity-regulated cytoskeleton-associated (Arc) protein and dendritic spine density (DSD). Adolescent rats displayed anxiety-like behaviors after 24 hrs, but not 1 hr, of last AIE with a concomitant increase in nuclear and cytosolic amygdaloid HDAC activity and HDAC2 and HDAC4 levels leading to deficits in histone (H3-K9) acetylation in the central (CeA) and medial (MeA), but not in basolateral nucleus of amygdala (BLA). Interestingly, some of AIE-induced epigenetic changes such as, increased nuclear HDAC activity, HDAC2 expression, decreased global histone acetylation persisted in adulthood. In addition, AIE decreased BDNF exon I, IV and Arc promoter specific histone H3 acetylation that was associated with decreased BDNF, Arc expression and DSD in the CeA and MeA during adulthood. AIE also induced anxiety-like behaviors and enhanced ethanol intake in adulthood, which was attenuated by TSA treatment via normalization of deficits in histone H3 acetylation of BDNF and Arc genes. These novel results indicate that AIE induces long-lasting effects on histone modifications and deficits in synaptic events in the amygdala, which are associated with anxiety-like and alcohol drinking behaviors in adulthood.

Background Epigenetic mechanisms have been implicated in psychiatric disorders, including alcohol dependence. However, the epigenetic basis and role of specific histone deacetylase (HDAC) isoforms in the genetic predisposition to anxiety and alcoholism is unknown. Methods We measured amygdaloid HDAC activity, levels of HDAC isoforms and histone H3 acetylation in selectively-bred alcohol-preferring (P) and -nonpreferring (NP) rats. We employed HDAC2 siRNA infusion into the central nucleus of amygdala (CeA) of P rats to determine the causal role of HDAC2 in anxiety-like and alcohol-drinking behaviors. Chromatin immunoprecipitation analysis was performed to examine the histone acetylation status of brain-derived neurotrophic factor (BDNF) and activity-regulated cytoskeleton associated protein (Arc) genes. Golgi-Cox staining was performed to measure dendritic spine density. Results We found that P rats innately display higher nuclear HDAC activity and HDAC2, but not HDAC 1, 3, 4, 5, and 6 protein levels, and lower acetylation of H3-K9, but not H3-K14, in the CeA and medial nucleus of amygdala (MeA) compared with NP rats. Acute ethanol exposure decreased amygdaloid HDAC activity and HDAC2 protein levels, increased global and gene (BDNF and Arc)-specific histone acetylation and attenuated anxiety-like behaviors in P rats, but had no effects in NP rats. HDAC2 knockdown in the CeA attenuated anxiety-like behaviors and voluntary alcohol, but not sucrose, consumption in P rats and increased histone acetylation of BDNF and Arc with a resultant increase in protein levels that correlated with increased dendritic spine density. Conclusions These novel data demonstrate the role of HDAC2-mediated epigenetic mechanisms in anxiety and alcoholism.

The immediate early gene, activity-regulated cytoskeleton-associated protein (Arc), has been implicated in synaptic plasticity. However, the role of Arc in alcoholism is unknown. Here, we report that the anxiolytic effects of acute ethanol were associated with increased brain-derived neurotrophic factor (BDNF) and tyrosine kinase B (trkB) expression, increased phosphorylation of extracellular signalregulated kinases 1/2 (Erk1/2), Elk-1, and cAMP responsive element-binding protein (CREB), increased Arc expression, and increased dendritic spine density (DSD) in both the central amygdala (CeA) and medial amygdala (MeA) but not in the basolateral amygdala (BLA) of rats. Conversely, the anxiogenic effects of withdrawal after long-term ethanol exposure were associated with decreased BDNF and trkB expression, decreased phosphorylation of Erk1/2, Elk-1, and CREB, decreased Arc expression, and decreased DSD in both the CeA and MeA but not in the BLA of rats. We also showed that BDNF infusion into the CeA normalized phosphorylation of Erk1/2, Elk-1, and CREB, and normalized Arc expression, thereby protecting against the onset of ethanol withdrawal-related anxiety. We further demonstrated that arresting Arc expression in the CeA decreased DSD, thereby increasing anxiety-like and alcohol-drinking behaviors in control rats. These results revealed that BDNF-Arc signaling and the associated DSD in the CeA, and possibly in the MeA, may be involved in the molecular processes of alcohol dependence and comorbidity of anxiety and alcohol-drinking behaviors.