Genome-wide DNA hydroxymethylation identifies potassium channels in the nucleus accumbens as discriminators of methamphetamine addiction and abstinence

Abstract

Epigenetic consequences of exposure to psychostimulants are substantial but the relationship of these changes to compulsive drug taking and abstinence is not clear. Here, we used a paradigm that helped to segregate rats that reduce or stop their methamphetamine (METH) intake (nonaddicted) from those that continue to take the drug compulsively (addicted) in the presence of footshocks. We used that model to investigate potential alterations in global DNA hydroxymethylation in the nucleus accumbens (NAc) because neuroplastic changes in the NAc may participate in the development and maintenance of drug-taking behaviors. We found that METH-addicted rats did indeed show differential DNA hydroxymethylation in comparison with both control and nonaddicted rats. Nonaddicted rats also showed differences from control rats. Differential DNA hydroxymethylation observed in addicted rats occurred mostly at intergenic sites located on long and short interspersed elements. Interestingly, differentially hydroxymethylated regions in genes encoding voltage (Kv1.1, Kv1.2, Kvb1 and Kv2.2)-and calcium (Kcnma1, Kcnn1 and Kcnn2)-gated potassium channels observed in the NAc of nonaddicted rats were accompanied by increased mRNA levels of these potassium channels when compared with mRNA expression in METH-addicted rats. These observations indicate that changes in differentially hydroxymethylated regions and increased expression of specific potassium channels in the NAc may promote abstinence from drug-taking behaviors. Thus, activation of specific subclasses of voltage-and/or calcium-gated potassium channels may provide an important approach to the beneficial treatment for METH addiction.

Increased expression of proenkephalin and prodynorphin mRNAs in the nucleus accumbens of compulsive methamphetamine taking rats

“…However, our methamphetamine data are consistent with results of studies that we have run so far, in which we found that 40–50% of the rats are resistant to footshocks15. The differences may be related to the fact that we used methamphetamine while the others used cocaine5455.…”

“…These ideas are consistent with the demonstration that rats that had undergone a 2 h/day methamphetamine self-administration procedure exhibited increased baseline glutamate levels in the NAc after one day of withdrawal40. Since we used a longer access (9 h/day) to methamphetamine self-administration in our experiments1541, it is conceivable that rats in the present study might show even greater changes in baseline glutamate levels in the NAc. Although these ideas will need to be tested further, they are consistent with the accumulated evidence that glutamate systems do play important roles in addiction42.…”

“…We anesthetized rats with ketamine and xylazine (50 and 5 mg/kg, i.p., respectively) and inserted silastic catheters into the jugular veins, as described previously1541. We attached the catheters to a modified 22-gauge cannula that was mounted to their skulls with dental cement.…”

“…We performed the training procedure for methamphetamine self-administration according to previously described protocol1541. On the first day of training, we brought rats to the self-administration room and chronically housed them in self-administration chambers.…”

“…The present study was thus carried out to identify transcriptional changes in the NAc of rats that showed two divergent phenotypes while receiving contingent footshocks during methamphetamine self-administration15. One group of animals continued to compulsively press a lever to receive the drug (shock-resistant) whereas another reduced their drug intake (shock-sensitive).…”