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More than a normal neurotransmitter The molecular mechanisms underlying the persistence of addiction remain largely unclear. Lepack et al. found that, with cocaine exposure, there is an intracellular accumulation of dopamine in neurons of a brain region called the ventral tegmental area (see the Perspective by Girault). Dopamine associates with chromatin to initiate a previously unknown form of epigenetic regulation called dopaminylation. This modification has an impact on ventral tegmental area function and, consequently, on dopaminergic action potentials. The result is aberrant dopamine signaling in the ventral striatum during periods of drug seeking. Science , this issue p. 197 ; see also p. 134

Proteasomal-regulated chromatin remodeler mediates cocaine relapse during abstinence., Neuroadaptations in the nucleus accumbens (NAc) underlie cue-induced cocaine craving that intensifies (“incubates”) during abstinence and is believed to contribute to persistent relapse vulnerability. Changes in gene expression often govern perpetual behavioral abnormalities, but epigenetic plasticity during prolonged abstinence from drug exposure is poorly understood. We examined how E3 ubiquitin ligase TRIM3 dysregulates chromatin remodeler INO80 to mediate cocaine craving during prolonged abstinence. We found that INO80 expression increased in the NAc on abstinence day 30 (AD30) but not on AD1 following cocaine self-administration. Furthermore, TRIM3, which mediates degradation of INO80, was reduced on AD30, along with TRIM3-INO80 interaction. Viral-mediated gene transfer of INO80 or TRIM3 governed cocaine craving during prolonged abstinence. Lastly, chromatin immunoprecipitation followed by massively parallel DNA sequencing identified INO80-mediated transcriptional regulation of predicted pathways associated with cocaine plasticity. Together, these results demonstrate a novel ubiquitin-proteasomal-epigenetic mechanism by which TRIM3-INO80 mediates cocaine craving during prolonged abstinence.