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Repeated Ethanol Exposure Alters DNA Methylation Status and Dynorphin/Kappa-Opioid Receptor Expression in Nucleus Accumbens of Alcohol-Preferring AA Rats.

ABSTRACT: Growing evidence suggests that epigenetic mechanisms, such as DNA methylation and demethylation, and histone modifications, are involved in the development of alcohol and drug addiction. However, studies of alcohol use disorder (AUD) that are focused on epigenetic DNA modifications and gene expression changes remain conflicting. Our aim was to study the effect of repeated ethanol consumption on epigenetic regulatory enzymes such as DNA methyltransferase and demethylase enzymes and whether those changes affected dynorphin/kappa-opioid receptor system in the Nucleus Accumbens (NAc). Two groups of male alcohol-preferring Alko Alcohol (AA) rats, rats which are selectively bred for high voluntary alcohol consumption and one group of male Wistar rats were used. The first group of AA rats had access to alcohol (10% ethanol solution) for 90 min on Mondays, Wednesdays and Fridays over a period of 3 weeks to establish a stable baseline of ethanol intake (AA-ethanol). The second group of AA rats (AA-water) and the Wistar rats (Wistar-water) were provided with water. Using qPCR, we found that voluntary alcohol drinking increased Dnmt1, -3a, and -3b mRNA levels and did not affect Tet family transcripts in the AA-ethanol group when compared with AA- and Wistar-water rats. DNMT and TET enzymatic activity measurements showed similar results to qPCR, where DNMT activity was increased in AA-ethanol group compared with AA-water and Wistar-water groups, with no statistically significant difference between groups in TET enzyme activity. In line with previous data, we found an increased percentage of global DNA methylation and hydroxymethylation in the AA-ethanol group compared with control rats. Finally, we investigated changes of selected candidate genes from dynorphin/kappa-opioid receptor system (Pdyn, Kor) and Dnmt3a genes that might be important in AUD-related behaviour. Our gene expression and promoter methylation analysis revealed a significant increase in the mRNA levels of Pdyn, Kor, and Dnmt3a in the AA-ethanol group, however, these changes can only be partially associate with the aberrant DNA methylation in promoter areas of the selected candidate genes. Thus, our findings suggest that the aberrant DNA methylation is rather one of the several mechanisms involved in gene expression regulation in AA rat model.

SUBMITTER: Niinep K

PROVIDER: S-EPMC8652212 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundChronic ethanol exposure reduces dopamine transmission in the nucleus accumbens, which may contribute to the negative affective symptoms associated with ethanol withdrawal. Kappa opioid receptors have been implicated in withdrawal-induced excessive drinking and anxiety-like behaviors and are known to inhibit dopamine release in the nucleus accumbens. The effects of chronic ethanol exposure on kappa opioid receptor-mediated changes in dopamine transmission at the level of the dopamine terminal and withdrawal-related behaviors were examined.MethodsFive weeks of chronic intermittent ethanol exposure in male C57BL/6 mice were used to examine the role of kappa opioid receptors in chronic ethanol-induced increases in ethanol intake and marble burying, a measure of anxiety/compulsive-like behavior. Drinking and marble burying were evaluated before and after chronic intermittent ethanol exposure, with and without kappa opioid receptor blockade by nor-binaltorphimine (10mg/kg i.p.). Functional alterations in kappa opioid receptors were assessed using fast scan cyclic voltammetry in brain slices containing the nucleus accumbens.ResultsChronic intermittent ethanol-exposed mice showed increased ethanol drinking and marble burying compared with controls, which was attenuated with kappa opioid receptor blockade. Chronic intermittent ethanol-induced increases in behavior were replicated with kappa opioid receptor activation in naïve mice. Fast scan cyclic voltammetry revealed that chronic intermittent ethanol reduced accumbal dopamine release and increased uptake rates, promoting a hypodopaminergic state of this region. Kappa opioid receptor activation with U50,488H concentration-dependently decreased dopamine release in both groups; however, this effect was greater in chronic intermittent ethanol-treated mice, indicating kappa opioid receptor supersensitivity in this group.ConclusionsThese data suggest that the chronic intermittent ethanol-induced increase in ethanol intake and anxiety/compulsive-like behaviors may be driven by greater kappa opioid receptor sensitivity and a hypodopaminergic state of the nucleus accumbens.

Project description:This study investigated changes in gene expression associated with ethanol drinking in adult male P rats under the following conditions for 8 weeks: continuous access (24 hr/day, 7 days/week), multiple scheduled access (three 1-hr sessions during the dark cycle/day, 5 days/week) and ethanol-naive (water). The objective of this study was to investigate changes in gene expression associated with ethanol drinking. Adult male alcohol-preferring (P) rats were given Ethanol in their home-cages under continuous access (CA; 24 hr/day, 7 days/week) or multiple scheduled access (MSA; three 1-hr sessions during the dark cycle/day, 5 days/week) conditions for 8 weeks. A third group was ethanol-naÃÂ¯ve (W group). Average ethanol intakes, across the 8 weeks, for the CA and MSA groups were approximately 9.5 and 6.5 g/kg/day, respectively. Fifteen hr after the last ethanol drinking episode, rats were euthanized, the brains rapidly extracted, and the nucleus accumbens (ACB) dissected. RNA was extracted and purified for microarray analysis. The only significant differences, overall, were between the CA and W groups (p < 0.01; Storey false discovery rate = 0.15); there were 374 significant differences in unique named genes between these 2 groups. There were 20 significant Gene Ontology (GO) biological processes categories, which included Ã¢ÂÂnegative regulation of protein kinase activityÃ¢ÂÂ, Ã¢ÂÂanti-apoptosisÃ¢ÂÂ, and Ã¢ÂÂregulation of G-protein-coupled receptor protein signaling pathwayÃ¢ÂÂ. IngenuityÃÂ® analysis indicated a network of transcription factors, involving oncogenes (Fos, Jun, Junb had higher expression levels in the ACB of the CA than W group), suggesting increased neuronal activity in the CA group. There were 13 genes (Hspa5, Stom, Lcn7, Tceb3, Cdc42, Rap1ga1, Ece1, Dhrs3, Plod1, Kif1b, Nmnat1, Srpr, Esam) significantly different between the CA and W groups located within both mouse and rat ethanol QTLs, suggesting that these genes may contribute to ethanol drinking behavior. In conclusion, the robust differences in gene expression found between the CA and W groups, but not observed between the MSA and W groups, may be a result of the higher daily ethanol intakes of the CA group, and/or its initial ethanol withdrawal. Experiment Overall Design: 10 samples each of control, continuous ethanol and limited access ethanol

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Repeated Ethanol Exposure Alters DNA Methylation Status and Dynorphin/Kappa-Opioid Receptor Expression in Nucleus Accumbens of Alcohol-Preferring AA Rats.

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