Abstract
Exposure to drugs of abuse produces robust transcriptional and epigenetic reorganization within brain reward circuits that outlives the direct effects of the drug and may contribute to addiction. DNA methylation is a covalent epigenetic modification that is altered following stimulant exposure and is critical for behavioral and physiological adaptations to drugs of abuse. Although activity-related loss of DNA methylation requires the Gadd45 (Growth arrest and DNA-damage-inducible) gene family, very little is known about how this family regulates activity within the nucleus accumbens or behavioral responses to drugs of abuse. Here, we combined genome-wide transcriptional profiling, pharmacological manipulations, electrophysiological measurements, and CRISPR tools with traditional knockout and behavioral approaches in rodent model systems to dissect the role of Gadd45b in dopamine-dependent epigenetic regulation and cocaine reward. We show that acute cocaine administration induces rapid upregulation of Gadd45b mRNA in the rat nucleus accumbens, and that knockout or site-specific CRISPR/Cas9 gene knockdown of Gadd45b blocks cocaine conditioned place preference. In vitro, dopamine treatment in primary striatal neurons increases Gadd45b mRNA expression through a dopamine receptor type 1 (DRD1)-dependent mechanism. Moreover, shRNA-induced Gadd45b knockdown decreases expression of genes involved in psychostimulant addiction, blocks induction of immediate early genes by DRD1 stimulation, and prevents DRD1-mediated changes in DNA methylation. Finally, we demonstrate that Gadd45b knockdown decreases striatal neuron action potential burst duration in vitro, without altering other electrophysiological characteristics. These results suggest that striatal Gadd45b functions as a dopamine-induced gene that is necessary for cocaine reward memory and DRD1-mediated transcriptional activity.
Highlights
Addiction is an increasingly prevalent problem in the United States, associated with progressively higher rates of morbidity and mortality
Using a primary rat striatal neuron culture system, we demonstrate that DA-induced increases in Gadd45b require DRD1 activation, mitogen-activated protein kinase (MEK) signaling, and cAMP response element binding protein (CREB)
Gadd45b is induced by acute cocaine and cocaine-paired contexts To examine the effects of cocaine on Gadd45b expression in vivo, we collected nucleus accumbens (NAc) tissue of adult naive male rats at 1 hr and 24 hr following treatment with either cocaine (10 mg/kg, i.p.; n = 11) or saline (n = 12)
Summary
Addiction is an increasingly prevalent problem in the United States, associated with progressively higher rates of morbidity and mortality. Experience with drugs of abuse results in significant transcriptional and epigenetic alterations in the nucleus accumbens (NAc) that support both synaptic and behavioral plasticity, outlasting the direct effects of the drug and contributing to the development of addiction [1,2,3,4]. Despite their various mechanisms of action, one common feature of many drugs of abuse is that they act upon the mesocorticolimbic dopamine (DA) system, which includes the ventral tegmental area (VTA), the NAc, and the prefrontal cortex [2, 5]. Intra-cranial delivery of the DNA methylation inhibitor RG108 resulted in enhanced cocaine conditioned place preference (CPP)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
