Histone acetylation in the nucleus accumbens shell modulates ethanol-induced locomotor activity in DBA/2J mice

Epigenetic Effects of Addictive Drugs in the Nucleus Accumbens

Substance use induces long-lasting behavioral changes and drug craving. Increasing evidence suggests that epigenetic gene regulation contributes to the development and expression of these long-lasting behavioral alterations. Here we systematically review extensive evidence from rodent models of drug-induced changes in epigenetic regulation and epigenetic regulator proteins. We focus on histone acetylation and histone methylation in a brain region important for drug-related behaviors: the nucleus accumbens. We also discuss how experimentally altering these epigenetic regulators via systemically administered compounds or nucleus accumbens-specific manipulations demonstrate the importance of these proteins in the behavioral effects of drugs and suggest potential therapeutic value to treat people with substance use disorder. Finally, we discuss limitations and future directions for the field of epigenetic studies in the behavioral effects of addictive drugs and suggest how to use these insights to develop efficacious treatments.

Chronic alcohol exposure reduces acetylated histones in the sleep-wake regulatory brain regions to cause insomnia during withdrawal

BACKGROUND

Alcohol use disorder (AUD) develops after chronic and heavy use of alcohol. Insomnia, a hallmark of AUD, plays a crucial role in the development of AUD. However, the causal mechanisms are unknown. Since chronic alcohol reduces acetylated histones and disrupts the epigenome, we hypothesized that chronic alcohol exposure will reduce acetylated histones in wake-promoting regions of the brain to cause insomnia during alcohol withdrawal.

METHODS

Adult male C57BL/6J mice, surgically instrumented for electrophysiological monitoring of sleep-wakefulness, were exposed to chronic alcohol (6.8%) consumption using Lieber-DeCarli liquid diet. Three experiments were performed. First, the effect of chronic alcohol consumption was examined on sleep-wakefulness during 7 days of withdrawal. Second, the expression of acetylated histones, H3 lysine 14 (AcH3K14), was examined in two major sleep-wake regulatory brain regions: basal forebrain (BF) and lateral hypothalamus (LH) of the brain by using western blotting. Next, blockade of histone deacetylase, via systemic administration of TSA was examined on alcohol-induced changes in sleep-wakefulness.

RESULTS

Alcoholic mice displayed a significant reduction in the quality and quantity of NREM sleep coupled with a significant increase in wakefulness that lasted for several days during alcohol withdrawal. In addition, alcoholic mice displayed a significant reduction in the expression of AcH3K14 in both BF and LH. Systemic administration of TSA significantly attenuated insomnia and improved the quality and quantity of sleep during alcohol withdrawal.

CONCLUSIONS

Based on our results, we suggest that a causal relationship exists between reduced histone acetylation and insomnia during alcohol withdrawal.

Brain STAT5 Modulates Long-Term Metabolic and Epigenetic Changes Induced by Pregnancy and Lactation in Female Mice

Several metabolic and behavioral adaptations that emerge during pregnancy remain present after weaning. Thus, reproductive experience causes long-lasting metabolic programming, particularly in the brain. However, the isolate effects of pregnancy or lactation and the molecular mechanisms involved in these long-term modifications are currently unknown. In the current study, we investigated the role of brain signal transducer and activator of transcription-5 (STAT5), a key transcription factor recruited by hormones highly secreted during gestation or lactation, for the long-term adaptations induced by reproductive experience. In control mice, pregnancy followed by lactation led to increased body adiposity and reduced ambulatory activity later in life. Additionally, pregnancy+lactation induced long-term epigenetic modifications in the brain: we observed upregulation in hypothalamic expression of histone deacetylases and reduced numbers of neurons with histone H3 acetylation in the paraventricular, arcuate, and ventromedial nuclei. Remarkably, brain-specific STAT5 ablation prevented all metabolic and epigenetic changes observed in reproductively experienced control female mice. Nonetheless, brain-specific STAT5 knockout (KO) mice that had the experience of pregnancy but did not lactate showed increased body weight and reduced energy expenditure later in life, whereas pregnancy KO and pregnancy+lactation KO mice exhibited improved insulin sensitivity compared with virgin KO mice. In summary, lactation is necessary for the long-lasting metabolic effects observed in reproductively experienced female mice. In addition, epigenetic mechanisms involving histone acetylation in neuronal populations related to energy balance regulation are possibly associated with these long-term consequences. Finally, our findings highlighted the key role played by brain STAT5 signaling for the chronic metabolic and epigenetic changes induced by pregnancy and lactation.

Histone deacetylase inhibition differentially attenuates cue-induced reinstatement: An interaction of environment and acH3K9 expression in the dorsal striatum

Substance use disorder is driven by complex gene-environment interactions. Epigenetic histone regulation is a significant contributor to several behavioral phenotypes of drug abuse. The primary epigenetic mechanisms that drive drug taking and drug seeking are still being investigated, and it is unclear how environmental conditions alter epigenetic histone acetylation to change behaviors geared toward drug reward. This study examined the effects of environmental condition on amphetamine self-administration, and whether drug-taking and drug-seeking behaviors could be influenced through inhibition of an epigenetic regulator, histone deacetylase (HDAC). Male rats reared for 30 days in enriched (EC), isolated (IC), or standard conditions (SC) prior to amphetamine (0.03, 0.05, 0.1 mg/kg/infusion, IV) self-administration, extinction, and reinstatement sessions. The HDAC inhibitor, Trichostatin A (TsA; 0.3 mg/kg, IV), was injected 30 min prior to operant sessions. After amphetamine-induced reinstatement (0.25 mg/kg, subcutaneous [s.c.]), tissue was extracted for Western blot analyses of acetylated histone H3 lysine 9 (acH3K9) in the nucleus accumbens (NAc) and dorsal striatum (DSt). While TsA did not significantly affect amphetamine self-administration or extinction, TsA decreased cue-, but not drug-induced reinstatement in IC rats only. In the DSt, but not in the NAc, IC rats exhibited significantly less acH3K9 expression than EC and SC rats, irrespective of TsA treatment. HDAC inhibition decreases cue-induced reinstatement of amphetamine seeking in IC rats. While IC rats exhibit less acH3K9 expression in the DSt, future studies are needed to elucidate the critical epigenetic factors that drive substance abuse, particularly in vulnerable populations. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Effects of histone deacetylase inhibitor sodium butyrate on heroin seeking behavior in the nucleus accumbens in rats

Histone acetylation and other modifications of the chromatin are important regulators of gene expression and may contribute to drug-induced behaviors and neuroplasticity. Inhibition of histone deacetylases (HDAC) activity results in the change of some drug-induced behaviors，however, relatively little is known about the effects of HDAC inhibitors on heroin-seeking behavior. In the present study, male rats were trained to self-administer heroin under a FR1 schedule for consecutive 14 days, followed by 14 daily 2h extinction session in the operant chamber. After training, the heroin priming (250μg/kg) was introduced for the reinstatement of heroin-seeking behavior. Pretreatment with sodium butyrate (NaB) (200 or 400mg/kg, i.p.), an inhibitor of HDAC, failed to affect heroin self-administration. Additionally，systemic administration of NaB (400mg/kg, i.p.)increased significantly the reinstatement of heroin-seeking induced by heroin priming when NaB administered 12h, but not 6h before the reinstatement test. The same effect was observed after the intracerebroventricular injection of NaB (5μL, 100μg/μL). Moreover, the levels of histone H3 acetylation at lysine 18（H3K18）and H4 acetylation at lysine 5 or lysine 8（H4K5 or H4K8）in the accumbens nucleus core and shell were remarkably increased during the reinstatement and were further strengthened after intracerebroventricular injection of NaB. These results demonstrated that activation of histone acetylation may be involved in the heroin-seeking behavior, and identifying these epigenetic changes will be critical in proposing a novel pharmacological strategy for treating heroin addiction.

Repeated vapor ethanol exposure induces transient histone modifications in the brain that are modified by genotype and brain region

Background: Emerging research implicates ethanol (EtOH)-induced epigenetic modifications in regulating gene expression and EtOH consumption. However, consensus on specific epigenetic modifications induced by EtOH has not yet emerged, making it challenging to identify mechanisms and develop targeted treatments. We hypothesized that chronic intermittent EtOH (CIE) induces persistent changes in histone modifications across the cerebral cortex (CCx), nucleus accumbens (NAc), and prefrontal cortex (PFC), and that these histone modifications are altered in a knock-in mouse strain with altered sensitivity to EtOH.

Methods: C57BL/6J (B6) mice and α1SHLA knockin mice on a B6 background were exposed to 16 h of vapor EtOH or room air followed by 8 h of room air for 4 consecutive days and sacrificed at multiple time points up to 72 h following exposure. Histone modifications were assessed using Western blot and dot blot. RT-qPCR was used to study expression of chromatin modifying enzymes in NAc and PFC.

Results: In NAc, CIE significantly increased acetylation of histone subunit H3 at lysine 9 (H3K9ac) but not lysine 14 (H3K14ac) or lysine 27 (H3K27ac). In PFC, CIE significantly increased H3K9ac but not H3K14 or H3K27ac. There were no significant changes at 8 or 72 h after EtOH exposure in either NAc or PFC. CIE was also associated with increased expression of Kat2b, Kat5, and Tet1 in NAc but not PFC. In CCx, CIE had a significant effect on levels of H3K18ac; there was also a significant effect of the α1SHLA mutation on levels of H3K27me3, H3K14ac, and H3K18ac as well as a trend for H3S10pK14ac.

Conclusions: The EtOH-induced histone modifications observed were transient and varied significantly between brain regions. A genetic mutation that altered sensitivity to EtOH was associated with altered induction of histone modifications during CIE. These results have implications for studying EtOH-induced histone modifications and EtOH sensitivity.