DNA Methylation Status of Tyrosine Hydroxylase Gene in the Locus Ceruleus of rats During Abstinence from Morphine

Background: Repeated use of addictive drugs such as morphine, promotes alterations in gene expression that underly addiction as well as compensatory neuroadaptations. Epigenetic mechanisms, including histone modification and DNA methylation are implicated in stimulant-induced gene expression and addiction behavior. The expression of TH gene is known to be regulated in the locus coeruleus (LC) during morphine exposure and drugabstinence. Upregulation of TH expression would be expected to increase the synthesis of dopamine and norepinephrine and is believed to contribute to particular withdrawal symptoms. We investigated correlation between regulation of tyrosine hydroxylase (TH) expression and the methylation level of the TH promoter in chronic morphine treatment and morphine withdrawal. Material and Methods: In this study, morphine dependence was induced in male rats by rising doses of morphine (10 to 50 mg/kg i.p) twice per day for 11 days and then they were decapitated at 3 different time points. LC tissues were dissected and the DNA was extracted. After modification of DNA, promoter methylation of TH gene in the samples was analyzed by methylation by methylation specific PCR (MS-PCR). Result: MS-PCR analysis at the TH promoter (-75 / +111) showed no difference between methylation status in morphine abstinence groups and chronic morphine treatment. Our data also showed that methylation status did not change around the TH gene promoter in the LC of case and control groups. Conclusion: In our experiment, there were no correlation between methylation status and TH gene expression at different time points after cessation of chronic morphine administration.