Journal of Addiction Research & Therapy
Open Access

Abstract

E pigenetic regulation of neuronal pathways has been shown to regulate the transcriptome and modify behavioral outcomes in response to abused drugs such as ethanol. It was shown that rats display an anxiolytic response after acute ethanol exposure, whereas a subsequent second exposure produces rapid tolerance to this effect. Here it was investigated whether epigenetic regulation at the level of DNA methylation and histone acetylation of the synaptic plasticity associated genes, activity- regulated cytoskeleton-associated protein (Arc) and brain-derived neurotrophic factor (BDNF) play a role in mediating these responses. The effects of one (1g/kg intraperitoneal) and two doses of ethanol (1g/kg; 24h apart) on anxiety-like behaviors in adult male Sprague-Dawley rats were measured. It was found that a single ethanol exposure produced anxiolytic behavioral effects whereas two doses of ethanol normalized the anxiety-like behavior back to control levels indicating tolerance to the effect. In the amygdala one dose of ethanol decreased DNA Methyltransferase (DNMT) activity which correlated with decreased 5-Methylcytosine (5mc) levels within specific promoter regions of BDNF (Exons I & IV) and Arc as measured using the MethylMiner protocol followed by quantitative real-time PCR. There were also increased acetylated-H3 (AcH3 K9-14) levels in these same regions as measured by Chromatin immunoprecipitation (ChIP) assays. Additionally BDNF and Arc mRNA and protein levels were found to be increased, which substantiate the above epigenetic findings. Following two doses of ethanol (tolerance group), it was observed that amygdaloid DNMT activity and corresponding 5mc levels at the promoters of BDNF (Exons I & IV) and Arc decreased in the tolerance group. On the other hand AcH3 levels at the promoters of BDNF (Exons I & IV) and Arc normalized to control levels and this also resulted in the normalization of mRNA and protein levels of BDNF and Arc. In order to establish BDNFs role in the tolerance phenotype, central amygdaloid infusion of BDNF was performed in rats that received two doses of ethanol. Interestingly central amygdaloid infusion of BDNF was able to circumvent the tolerant phenotype and cause anxiolytic effects following two doses of ethanol, thus mimicking the behavioral phenotype of rats that received one dose. Acute ethanol leads to epigenetic changes at the promoters of BDNF and Arc genes, decreased DNA methylation and increased histone H3 acetylation, resulting in increased mRNA and protein levels of BDNF and Arc, thereby regulating synaptic plasticity leading to the anxiolytic response. Interestingly in the tolerance group, normalization of histone acetylation, rather than DNA methylation, could be operative in normalizing mRNA and protein levels, which leads to the development of rapid tolerance to anxiolytic effects of ethanol. Increasing BDNF through CeA exogenous infusion is able to abolish the tolerance phenotype leading to anxiolytic effects. This study has revealed the importance of epigenetic signaling pathways in the amygdala that presumably play a role in regulating tolerance to anxiolytic-like effects following acute ethanol exposure.

Biography

Harish R Krishnan obtained his MD from Stanley Medical College in Chennai, India and his PhD in Neuroscience from the University of Texas at Austin in Austin, Texas. He is currently a Postdoctoral Fellow at the Department of Psychiatry, University of Illinois, Chicago, Illinois where using genome-wide approaches in pre- clinical rat models he studies the molecular etiology of alcoholism