Long-Lasting Epigenetic Changes in the Dopamine Transporter in Adult Animals Exposed to Amphetamine during Embryogenesis: Investigating Behavioral Effects

Abstract

The dopamine transporter (DAT) is an integral member of the dopaminergic system and is responsible for the release and reuptake of dopamine from the synaptic space into the dopaminergic neurons. DAT is also the major target of amphetamine (Amph). The effects of Amph on DAT have been intensively studied; however, the mechanisms underlying the long-term effects caused by embryonal exposure to addictive doses of Amph remain largely unexplored. As in mammals, in the nematode C. elegans Amph causes changes in locomotion which are largely mediated by the C. elegans DAT homologue, DAT-1. Here, we show that chronic embryonic exposures to Amph alter the expression of DAT-1 in adult C. elegans via long-lasting epigenetic modifications. These changes are correlated with an enhanced behavioral response to Amph in adult animals. Importantly, pharmacological and genetic intervention directed at preventing the Amph-induced epigenetic modifications occurring during embryogenesis inhibited the long-lasting behavioral effects observed in adult animals. Because many components of the dopaminergic system, as well as epigenetic mechanisms, are highly conserved between C. elegans and mammals, these results could be critical for our understanding of how drugs of abuse initiate predisposition to addiction.

Amphetamine Exposure during Embryogenesis Alters Expression and Function of Tyrosine Hydroxylase and the Vesicular Monoamine Transporter in Adult C. elegans

“…However, when animals were challenged with 0.5 mM Amph for 10 min, we observed significantly increased SWIP in animals exposed to Amph during embryogenesis with respect to animals pre-exposed to control solution (Figure 2c, red and blue circles, respectively). These results confirm our previous reports [12] and resemble recent data showing that mice overexpressing TH exhibited enhanced sensitivity to Amph and elevated striatal DA levels, but no basal hyperdopaminergic behaviors [25,26]. To further investigate the Amph hypersensitivity caused by embryonal exposure to Amph, we quantified cat-2 mRNA in adult animals exposed to Amph during embryogenesis before and after the 10 min of Amph challenge.…”

“…Five H3K9-specific methyltransferases have been identified in mammals [29], and two of them, G9A and SETDB1, have C. elegans homologs, SET-25 and MET-2, respectively [28]. Recently, we showed that pharmacologic and genetic ablation of SET-25 eliminated the long-lasting behavior effects caused by embryonic exposure to Amph [12]. Here, we tested if ablation of the met-2 gene would generate similar results.…”

“…Yet, no study has investigated the mechanisms underlying the long-lasting effects seen after in utero exposure to high concentrations of Meth or Amph. Using C. elegans, we recently demonstrated that adult animals exposed to high concentrations of Amph during embryogenesis exhibit reduced levels of DAT and are hypersensitive to Amph [12]. We also demonstrated that the long-lasting effects caused by Amph are mediated by changes of histone marks at the dat-1 gene.…”

“…To do so, chromatin immune precipitation (ChIP) experiments for two specific histone marks, the histone 3 (H3) lysine 4 (K4) three-methylated (H3K4me3) and H3K9 dimethylated (H3K9me2), were performed. These histone marks were previously shown to be altered by psychostimulants in specific genes of the reward system both in mammals and C. elegans [12,18,19]. There are three alternative transcription start sites (TSSs) for the cat-2 gene.…”

“…Recently, using a DA-dependent behavioral assay named SWIP (Swimming-Induced Paralysis), we showed that exposure to Amph during embryogenesis causes hypersensitivity to Amph in adult C. elegans [12]. SWIP is an easily quantifiable behavior caused by an excess of extracellular DA.…”