Project description:After exposure to drugs of abuse, the reward circuit can experience persistent changes that are thought to underlie relapse behavior. These changes can be epigenetic in nature, and here we identify an epigenetic regulator of memory processes, nuclear orphan receptor subfamily4 groupA member2 (NR4A2 aka NURR1), as necessary for relapse to cocaine-seeking behavior. Nr4a2 is an epigenetically regulated immediate early gene and transcription factor that is highly expressed in the medial habenula (MHb). Despite the well-studied contributions of the MHb to nicotine-associated behaviors, the MHb is not classically included in reward circuits. Therefore, the role of MHb NR4A2 in cocaine-seeking and relapse behavior remains largely unknown. This is a key open question as NR4A2 is a powerful regulator of memory processes dependent on epigenetic mechanisms. In this study, we examined the role of MHb NR4A2 in cued reinstatement of cocaine self-administration in mice, and found that over-expressing a dominant negative form of Nr4a2 (Nurr2c) in the MHb results in a near complete block of relapse-like behavior. We used single-nucleus transcriptomics to characterize the molecular cascade following the manipulation of Nr4a2, revealing changes in transcriptional networks related to addiction, neuroplasticity, and glutamatergic signaling. Together, these results place the MHb in the reward circuit as a pivotal regulator of relapse behavior and demonstrate the importance of NR4A2 as a key mechanism driving relapse behavior in the MHb.
Project description:Abstract Background Psychostimulant use disorder is a major public health issue, and despite the scope of the problem there are currently no FDA approved treatments. There would be tremendous utility in development of a treatment that could help patients both achieve and maintain abstinence. Previous work from our group has identified granulocyte-colony stimulating factor (G-CSF) as a neuroactive cytokine that alters behavioral response to cocaine, increases synaptic dopamine release, and enhances cognitive flexibility. Here, we investigate the role of G-CSF in affecting extinction and reinstatement of cocaine-seeking and perform detailed characterization of its proteomic effects in multiple limbic substructures. Methods Sprague-Dawley rats were injected with PBS or G-CSF during (1) extinction or (2) abstinence from cocaine self-administration, and drug seeking behavior was measured. Quantitative assessment of changes in the proteomic landscape in the nucleus accumbens (NAc) and medial prefrontal cortex (mPFC) were performed via data-independent acquisition (DIA) mass spectrometry analysis. Results Administration of G-CSF during extinction accelerated the rate of extinction, and administration during abstinence attenuated cue-induced cocaine-seeking. Analysis of global protein expression demonstrated that G-CSF regulated proteins primarily in mPFC that are critical to glutamate signaling and synapse maintenance. Conclusion Taken together, these findings support G-CSF as a viable translational research target with the potential to reduce drug craving or seeking behaviors. Importantly, recombinant G-CSF exists as an FDA-approved medication which may facilitate rapid clinical translation. Additionally, using cutting-edge multi-region discovery proteomics analyses, these studies identify a novel mechanism underlying G-CSF effects on behavioral plasticity.
Project description:Drug overdose deaths involving cocaine have skyrocketed, an outcome attributable in part to the lack of FDA-approved medications for the treatment of cocaine use disorder (CUD), highlighting the need to identify new pharmacotherapeutic targets. Vulnerability to cocaine-associated environmental contexts and stimuli serves as a risk factor for relapse in CUD recovery, with individual differences evident in the motivational aspects of these cues. The medial prefrontal cortex (mPFC) provides top-down control of striatal circuitry to regulate the incentive-motivational properties of cocaine-associated stimuli. Clinical and preclinical studies have identified genetic variations that impact the degree of executive restraint over drug-motivated behaviors, and we designed the present study to employ next-generation sequencing to identify specific genes associated with heightened cue-evoked cocaine-seeking in the mPFC of male, outbred rats. Rats were trained to stably self-administer cocaine, and baseline cue-reinforced cocaine-seeking was established. Rats were phenotyped as either high cue (HC) or low cue (LC) responders based upon lever pressing for previously associated cocaine cues and allowed 10 days of abstinence in their home cages prior to mPFC collection for RNA-sequencing. The expression of 309 genes in the mPFC was significantly different in HC vs. LC rats. Functional gene enrichment analyses identified ten biological processes that were overrepresented in the mPFC of HC vs. LC rats. The present study identifies distinctions in mPFC mRNA transcripts that characterizes individual differences in relapse-like behavior and provides prioritized candidates (i.e., Htr2c, Adora2a, Drd2) for future pharmacotherapeutics aimed to help maintain abstinence in CUD.
Project description:After intarvenouse catheter surgery, nicotine self-administration using an operant self-administration chamber, was conducted for 44 days with various doses of nicotine solution. Age-matched mice were used for control. After the self-administration, the Lateral Habenual (LHb) and the Medial Habenula (MHb) of the mouse brain were collected. We used microarrays to detail the mRNA expression profile of the Lateral Habenual (LHb) and the Medial Habenula (MHb) after the nicotine self-administration.
Project description:Enduring patterns of epigenomic and transcriptional plasticity within the mesolimbic dopamine system contribute importantly to persistent behavioral adaptations that characterize substance use disorders (SUD). While drug addiction has long been thought of as a disorder of dopamine (DA) neurotransmission, therapeutic interventions targeting receptor mediated DA-signaling have not yet resulted in efficacious treatments. Our laboratory recently identified a non-canonical, neurotransmission-independent signaling moiety for DA in brain, termed dopaminylation, whereby DA itself acts as a donor source for the establishment of post-translational modifications (PTM) on substrate proteins (e.g., histone H3 at glutamine 5; H3Q5dop). In our previous studies, we demonstrated that H3Q5dop plays a critical role in the regulation of neuronal transcription and, when perturbed within monoaminergic neurons of the ventral tegmental area (VTA), critically contribute to pathological states, including relapse vulnerability to both psychostimulants (e.g., cocaine) and opiates (e.g., heroin). Importantly, H3Q5dop is also observed throughout the mesolimbic DA reward pathway (e.g., in nucleus accumbens/NAc and medial prefrontal cortex/mPFC, which receive DA input from VTA). As such, we investigated whether H3Q5dop may similarly be altered in its expression in response to drugs of abuse in these non-dopamine-producing regions. In rats undergoing extended abstinence from cocaine self-administration (SA), we observed both acute and prolonged accumulation of H3Q5dop in NAc, but not mPFC. Attenuation of H3Q5dop in NAc during drug abstinence reduced cocaine-seeking and affected cocaine-induced gene expression programs associated with altered dopamine signaling and neuronal function. These findings thus establish H3Q5dop in NAc, but not mPFC, as an important mediator of cocaine-induced behavioral and transcriptional plasticity during extended cocaine abstinence.
Project description:Cocaine use disorder represents a public health crisis with no FDA-approved medications for its treatment. A growing body of research has detailed the important connections between the brain and the resident population of bacteria in the gut, the gut microbiome in psychiatric disease models. Acute depletion of gut bacteria results in enhanced reward in a mouse cocaine place preference model, and repletion of bacterially-derived short-chain fatty acid (SCFA) metabolites reverses this effect. However, the role of the gut microbiome and its metabolites in modulating cocaine-seeking behavior after prolonged abstinence is unknown. Given that relapse prevention is the most clinically challenging issue in treating substance use disorders, studies examining the effects of microbiome manipulations in relapse-relevant models are critical. Here, Sprague-Dawley rats received either untreated water or antibiotics to deplete the gut microbiome and its metabolites. Rats were trained to self-administer cocaine and subjected to either within-session threshold testing to evaluate motivation for cocaine or 21 days of abstinence followed by a cue-induced cocaine-seeking task to model relapse behavior. Microbiome depletion did not affect cocaine acquisition on an FR1 schedule. However, microbiome-depleted subjects exhibited significantly enhanced motivation for low dose cocaine on a within-session threshold task. Similarly, microbiome depletion increased cue-induced cocaine-seeking following prolonged abstinence. In the absence of a normal microbiome, repletion of bacterially-derived SCFA metabolites reversed the behavioral and transcriptional changes associated with microbiome depletion. These findings suggest that gut bacteria, via their metabolites, are key regulators of drug-seeking behaviors, positioning the microbiome as a potential translational research target.
Project description:MicroRNAs are “master regulators” of gene expression. To investigate microRNAs involved in the incentive motivation for cocaine elicited by exposure to cocaine-associated cues, we conducted NanoString nCounter analyses of microRNA expression in the nucleus accumbens shell of male rats that had been tested for cue reactivity in a previous study. These rats had been trained to self-administer cocaine while living in isolate housing, then during a subsequent 21-day forced abstinence period they either stayed under isolate housing or switched to environmental enrichment (EE), as this EE intervention is known to decrease cocaine seeking. This allowed us to create groups of “high” and “low” cocaine seekers using a median split of cocaine-seeking behavior. We conducted a differential expression analysis across these two groups that identified 33 miRNAs that were differentially altered in the nucleus accumbens shell. Predicted mRNA targets of these microRNAs are implicated in synaptic plasticity and neuronal signaling. Some of these microRNAs have previously been implicated in substance use disorders, while others are predicted to target large numbers of cocaine-related genes. Of the 33 differentially expressed microRNAs, 8 were specifically downregulated in the low-seeking group and another set of 8 had expression levels that were significantly correlated with cocaine-seeking. These findings suggest that processes involved in cocaine-seeking behavior may alter, or be altered by, multiple microRNAs. Further research examining the mechanisms involved in these microRNA changes and their effects on signaling may reveal novel therapeutic targets for attenuating drug craving.
Project description:Vulnerability to relapse during periods of attempted abstinence from cocaine use is hypothesized to result from rewiring of brain reward circuitries, particularly ventral tegmental area (VTA) dopamine neurons. How cocaine exposures act on midbrain dopamine neurons to precipitate addiction-relevant changes in gene expression is unclear. We found that histone H3 glutamine 5 dopaminylation (H3Q5dop) plays a critical role in cocaine-induced transcriptional plasticity in midbrain. Rats undergoing withdrawal from cocaine showed an accumulation of H3Q5dop in VTA. By reducing H3Q5dop in VTA during withdrawal, we reversed cocaine-mediated gene expression changes, attenuated cue-induced dopamine release in nucleus accumbens and reduced cocaine-seeking behavior. These findings establish a neurotransmission-independent role for nuclear dopamine in relapse-related transcriptional plasticity in VTA.
Project description:After intarvenouse catheter surgery, nicotine self-administration using an operant self-administration chamber, was conducted for 44 days with various doses of nicotine solution. Age-matched mice were used for control. After the self-administration, the Lateral Habenual (LHb) and the Medial Habenula (MHb) of the mouse brain were collected.