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A hallmark of addiction is the ability of drugs of abuse to trigger relapse after periods of prolonged abstinence. Here, we describe an epigenetic mechanism whereby chronic cocaine exposure causes lasting chromatin and downstream transcriptional modifications in the nucleus accumbens (NAc), a critical brain region controlling motivation. We link prolonged withdrawal from cocaine to the depletion of the histone variant H2A.Z, coupled with increased genome accessibility and latent priming of gene transcription, in D1 dopamine receptor-expressing medium spiny neurons (D1 MSNs) that relate to aberrant gene expression upon drug relapse. The histone chaperone ANP32E removes H2A.Z from chromatin, and we demonstrate that D1 MSN-selective Anp32e knockdown prevents cocaine-induced H2A.Z depletion and blocks cocaine's rewarding actions. By contrast, very different effects of cocaine exposure, withdrawal, and relapse were found for D2 MSNs. These findings establish histone variant exchange as an important mechanism and clinical target engaged by drugs of abuse to corrupt brain function and behavior.

Background: Cholinergic interneurons (ChINs) in the nucleus accumbens (NAc) play critical roles in processing information related to reward. However, the contribution of ChINs to the emergence of addiction-like behaviors and its underlying molecular mechanisms remain elusive., Methods: We employed cocaine self-administration to identify two mouse subpopulations: susceptible and resilient to cocaine seeking. We compared the subpopulations for physiological responses with single-unit recording of NAc ChINs, and for gene expression levels with RNA sequencing of ChINs sorted using fluorescence-activated cell sorting. To provide evidence for a causal relationship, we manipulated the expression level of dopamine D 2 receptor (DRD2) in ChINs in a cell type-specific manner. Using optogenetic activation combined with a double whole-cell recording, the effect of ChIN-specific DRD2 manipulation on each synaptic input was assessed in NAc medium spiny neurons in a pathway-specific manner., Results: Susceptible mice showed higher levels of nosepoke responses under a progressive ratio schedule, and impairment in extinction and punishment procedures. DRD2 was highly abundant in the NAc ChINs of susceptible mice. Elevated abundance of DRD2 in NAc ChINs was sufficient and necessary to express high cocaine motivation, putatively through reduction of ChIN activity during cocaine exposure. DRD2 overexpression in ChINs mimicked cocaine-induced effects on the dendritic spine density and the ratios of excitatory inputs between two distinct medium spiny neuron cell types, while DRD2 depletion precluded cocaine-induced synaptic plasticity., Conclusions: These findings provide a molecular mechanism for dopaminergic control of NAc ChINs that can control the susceptibility to cocaine-seeking behavior., (Copyright © 2020 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.)

The role of somatostatin interneurons in nucleus accumbens (NAc), a key brain reward region, remains poorly understood due to the fact that these cells account for < 1% of NAc neurons. Here, we use optogenetics, electrophysiology, and RNA-sequencing to characterize the transcriptome and functioning of NAc somatostatin interneurons after repeated exposure to cocaine. We find that the activity of somatostatin interneurons regulates behavioral responses to cocaine, with repeated cocaine reducing the excitability of these neurons. Repeated cocaine also induces transcriptome-wide changes in gene expression within NAc somatostatin interneurons. We identify the JUND transcription factor as a key regulator of cocaine action and confirmed, by use of viral-mediated gene transfer, that JUND activity in somatostatin interneurons influences behavioral responses to cocaine. Our results identify alterations in NAc induced by cocaine in a sparse population of somatostatin interneurons, and illustrate the value of studying brain diseases using cell type-specific whole transcriptome RNA-sequencing.