Molecular mechanisms underlying alcohol-drinking behaviours

cAMP-Fyn signaling in the dorsomedial striatum direct pathway drives excessive alcohol use

Fyn kinase in the dorsomedial striatum (DMS) of rodents plays a central role in mechanisms underlying excessive alcohol intake. The DMS is comprised of medium spiny neurons (MSNs) that project directly (dMSNs) or indirectly (iMSNs) to the substantia nigra. Here, we examined the cell-type specificity of Fyn's actions in alcohol use. First, we knocked down Fyn selectively in DMS dMSNs or iMSNs of mice and measured the level of alcohol consumption. We found that downregulation of Fyn in dMSNs, but not in iMSNs, reduces excessive alcohol but not saccharin intake. D1Rs are coupled to Gαs/olf, which activate cAMP signaling. To examine whether Fyn's actions are mediated through cAMP signaling, DMS dMSNs were infected with GαsDREADD, and the activation of Fyn signaling was measured following CNO treatment. We found that remote stimulation of cAMP signaling in DMS dMSNs activates Fyn and promotes the phosphorylation of the Fyn substrate, GluN2B. In contract, remote activation of GαsDREADD in DLS dMSNs did not alter Fyn signaling. We then tested whether activation of GαsDREADD in DMS dMSNs or iMSNs alters alcohol intake and observed that CNO-dependent activation of GαsDREADD in DMS dMSNs but not iMSNs increases alcohol but not saccharin intake. Finally, we examined the contribution of Fyn to GαsDREADD-dependent increase in alcohol intake, and found that systemic administration of the Fyn inhibitor, AZD0503 blocks GαsDREADD-dependent increase in alcohol consumption. Our results suggest that the cAMP-Fyn axis in the DMS dMSNs is a molecular transducer of mechanisms underlying the development of excessive alcohol consumption.

Alcohol consumption is associated with widespread changes in blood DNA methylation: Analysis of cross-sectional and longitudinal data

DNA methylation may be one of the mechanisms by which alcohol consumption is associated with the risk of disease. We conducted a large-scale, cross-sectional, genome-wide DNA methylation association study of alcohol consumption and a longitudinal analysis of repeated measurements taken several years apart. Using the Illumina HumanMethylation450 BeadChip, DNA methylation was measured in blood samples from 5606 Melbourne Collaborative Cohort Study (MCCS) participants. For 1088 of them, these measures were repeated using blood samples collected a median of 11 years later. Associations between alcohol intake and blood DNA methylation were assessed using linear mixed-effects regression models. Independent data from the London Life Sciences Prospective Population (LOLIPOP) (N = 4042) and Cooperative Health Research in the Augsburg Region (KORA) (N = 1662) cohorts were used to replicate associations discovered in the MCCS. Cross-sectional analyses identified 1414 CpGs associated with alcohol intake at P < 10-7 , 1243 of which had not been reported previously. Of these novel associations, 1078 were replicated (P < .05) using LOLIPOP and KORA data. Using the MCCS data, we also replicated 403 of 518 previously reported associations. Interaction analyses suggested that associations were stronger for women, non-smokers, and participants genetically predisposed to consume less alcohol. Of the 1414 CpGs, 530 were differentially methylated (P < .05) in former compared with current drinkers. Longitudinal associations between the change in alcohol intake and the change in methylation were observed for 513 of the 1414 cross-sectional associations. Our study indicates that alcohol intake is associated with widespread changes in DNA methylation across the genome. Longitudinal analyses showed that the methylation status of alcohol-associated CpGs may change with alcohol consumption changes in adulthood.

Network preservation reveals shared and unique biological processes associated with chronic alcohol abuse in NAc and PFC

Chronic alcohol abuse has been linked to the disruption of executive function and allostatic conditioning of reward response dysregulation in the mesocorticolimbic pathway (MCL). Here, we analyzed genome-wide mRNA and miRNA expression from matched cases with alcohol dependence (AD) and controls (n = 35) via gene network analysis to identify unique and shared biological processes dysregulated in the prefrontal cortex (PFC) and nucleus accumbens (NAc). We further investigated potential mRNA/miRNA interactions at the network and individual gene expression levels to identify the neurobiological mechanisms underlying AD in the brain. By using genotyped and imputed SNP data, we identified expression quantitative trait loci (eQTL) uncovering potential genetic regulatory elements for gene networks associated with AD. At a Bonferroni corrected p≤0.05, we identified significant mRNA (NAc = 6; PFC = 3) and miRNA (NAc = 3; PFC = 2) AD modules. The gene-set enrichment analyses revealed modules preserved between PFC and NAc to be enriched for immune response processes, whereas genes involved in cellular morphogenesis/localization and cilia-based cell projection were enriched in NAc modules only. At a Bonferroni corrected p≤0.05, we identified significant mRNA/miRNA network module correlations (NAc = 6; PFC = 4), which at an individual transcript level implicated miR-449a/b as potential regulators for cellular morphogenesis/localization in NAc. Finally, we identified eQTLs (NAc: mRNA = 37, miRNA = 9; PFC: mRNA = 17, miRNA = 16) which potentially mediate alcohol's effect in a brain region-specific manner. Our study highlights the neurotoxic effects of chronic alcohol abuse as well as brain region specific molecular changes that may impact the development of alcohol addiction.

Synthesis and biological analysis of anti-addiction effect and hepatotoxicity of tow baclofen analogues complexed with β-Cyclodextrin

AIM AND OBJECTIVE

The excessive consumption of alcohol and the installation of a dependence is, in most cases, facilitated by favorable psychological factors which trigger and maintain the behavior of consumption. Examples more frequently encountered in individuals having difficulty with alcohol are in particular: one or more anxiety disorders, deficits in the capacities to manage stress and anxiety. The main objective of this work was study in vivo the anti-addiction effect and hepatotoxicity of tow baclofen analogues complexed with β-Cyclodextrin (βCD) on an alcohol-dependent rat model.

MATERIALS AND METHODS

The synthesis of two analogues ABF1 and ABF2 close to baclofen was reported. The structural determination of the two compounds was confirmed by NMR and IR analysis. The complexation of analogues with βCyclodextrin (βCD) was performed in water at room temperature (25 °C). The interactions of ABF with β-Cyclodextrin, and the stability constant (Ka) of the inclusion complex formed between them were investigated by using UV-visible spectroscopy. The biological effects of baclofen and the two analogues on alcohol dependence were studied in wistar rats. The anti-addiction effect of the analogues was tested by measuring the alcohol intake and the variation of the animal behaviour. The toxicity of the compounds was also analysed on liver injury markers.

RESULTS

The amino-3-phenylbutanoic acid (ABF1) and 3,4,5-trihydroxy-N-(methyl-2-acetate) benzamide (ABF2) were synthesized. The complexation of both analogues of baclofen (BF) with β-cyclodextrin (βCD) (ABF- βCD) was realized and confirmed by the stability constant of the inclusion complex (Ka) and Job's method. The evaluation of anti-addiction activity in vivo showed that ABF1-βCD inhibits the consumption of alcohol at the doses equivalent to those of baclofen. Both baclofen analogues have shown an anxiolytic effect. Regarding the toxicity of the two compounds, our results showed that ABF1-βCD has less toxic effect than baclofen, it reduces the activity of ALT and AST enzymes. Histologically ABF1-βCD has no effect on structure of the liver in addition and has a protective effect against lesions alcohol-induced liver disease.

CONCLUSION

Therefore, it can be suggested that ABF1 analogue combined with β-Cyclodextrin can be used as a treatment for alcohol dependence. Further clinical works are needed to confirm its effectiveness.

Growth Factors and Alcohol Use Disorder

Neurotrophic growth factors were originally characterized for their support in neuronal differentiation, outgrowth, and survival during development. However, it has been acknowledged that they also play a vital role in the adult brain. Abnormalities in growth factors have been implicated in a variety of neurological and psychiatric disorders, including alcohol use disorder (AUD). This work focuses on the interaction between alcohol and growth factors. We review literature suggesting that several growth factors play a unique role in the regulation of alcohol consumption, and that breakdown in these growth factor systems is linked to the development of AUD. Specifically, we focus on the brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), fibroblast growth factor 2 (FGF2), and insulin growth factor 1 (IGF-1). We also review the literature on the potential role of midkine (MDK) and pleiotrophin (PTN) and their receptor, anaplastic lymphoma kinase (ALK), in AUD. We show that alcohol alters the expression of these growth factors or their receptors in brain regions previously implicated in addiction, and that manipulations on these growth factors and their downstream signaling can affect alcohol-drinking behaviors in animal models. We conclude that there is a need for translational and clinical research to assess the therapeutic potential of new pharmacotherapies targeting these systems.

Investigating the link between serum concentrations of brain-derived neurotrophic factor and behavioral measures in anxious alcohol-dependent individuals

Brain-derived neurotrophic factor (BDNF) plays a role in different neurophysiological processes, including those involved in alcohol- and anxiety-related behaviors. Preclinical and clinical studies indicate that chronic excessive alcohol use leads to a downregulation of BDNF production in the periphery and in the brain. In addition, a decrease in BDNF concentrations in the blood has been reported to be associated with increased anxiety levels. Non-treatment-seeking alcohol-dependent individuals with high trait anxiety were studied to assess whether serum BDNF concentrations may be linked to self-reported levels of alcohol drinking, anxiety, and other behavioral measures. Participants had a current diagnosis of alcohol dependence, high trait anxiety score, and were not seeking treatment for alcohol dependence or anxiety. A fasting blood sample was collected from each participant and serum BDNF was measured using an enzyme-linked immunosorbent assay (ELISA). Behavioral data were collected on the same day, including measures of alcohol drinking, craving, dependence severity, and anxiety. Bivariate correlations were run between BDNF levels and behavioral measures. Serum BDNF concentrations were negatively correlated with average drinks per drinking days (r = -0.41, p = 0.02) and positively correlated with obsessive-compulsive drinking scale (r = 0.48, p = 0.007) and state-trait anxiety inventory (r = 0.52, p = 0.003) scores. These findings shed light on the possible role of the BDNF system in the neurobiology of alcohol- and anxiety-related behaviors.

CUX2, BRAP and ALDH2 are associated with metabolic traits in people with excessive alcohol consumption

Molecular mechanisms that prompt or mitigate excessive alcohol consumption could be partly explained by metabolic shifts. This genome-wide association study aims to identify the susceptibility gene loci for excessive alcohol consumption by jointly measuring weekly alcohol consumption and γ-GT levels. We analysed the Taiwan Biobank data of 18,363 Taiwanese people, including 1945 with excessive alcohol use. We found that one or two copies of the G allele in rs671 (ALDH2) increased the risk of excessive alcohol consumption, while one or two copies of the C allele in rs3782886 (BRAP) reduced the risk of excessive alcohol consumption. To minimize the influence of extensive regional linkage disequilibrium, we used the ridge regression. The ridge coefficients of rs7398833, rs671 and rs3782886 were unchanged across different values of the shrinkage parameter. The three variants corresponded to posttranscriptional activity, including cut-like homeobox 2 (a protein coded by CUX2), Glu504Lys of acetaldehyde dehydrogenase 2 (a protein encoded by ALDH2) and Glu4Gly of BRCA1-associated protein (a protein encoded by BRAP). We found that Glu504Lys of ALDH2 and Glu4Gly of BRAP are involved in the negative regulation of excessive alcohol consumption. The mechanism underlying the γ-GT-catalytic metabolic reaction in excessive alcohol consumption is associated with ALDH2, BRAP and CUX2. Further study is needed to clarify the roles of ALDH2, BRAP and CUX2 in the liver–brain endocrine axis connecting metabolic shifts with excessive alcohol consumption.

Flying Together: Drosophila as a Tool to Understand the Genetics of Human Alcoholism

Alcohol use disorder (AUD) exacts an immense toll on individuals, families, and society. Genetic factors determine up to 60% of an individual's risk of developing problematic alcohol habits. Effective AUD prevention and treatment requires knowledge of the genes that predispose people to alcoholism, play a role in alcohol responses, and/or contribute to the development of addiction. As a highly tractable and translatable genetic and behavioral model organism, Drosophila melanogaster has proven valuable to uncover important genes and mechanistic pathways that have obvious orthologs in humans and that help explain the complexities of addiction. Vinegar flies exhibit remarkably strong face and mechanistic validity as a model for AUDs, permitting many advancements in the quest to understand human genetic involvement in this disease. These advancements occur via approaches that essentially fall into one of two categories: (1) discovering candidate genes via human genome-wide association studies (GWAS), transcriptomics on post-mortem tissue from AUD patients, or relevant physiological connections, then using reverse genetics in flies to validate candidate genes' roles and investigate their molecular function in the context of alcohol. (2) Utilizing flies to discover candidate genes through unbiased screens, GWAS, quantitative trait locus analyses, transcriptomics, or single-gene studies, then validating their translational role in human genetic surveys. In this review, we highlight the utility of Drosophila as a model for alcoholism by surveying recent advances in our understanding of human AUDs that resulted from these various approaches. We summarize the genes that are conserved in alcohol-related function between humans and flies. We also provide insight into some advantages and limitations of these approaches. Overall, this review demonstrates how Drosophila have and can be used to answer important genetic questions about alcohol addiction.

Choosing the Optimal Brain Target for Neuromodulation Therapies as Alcohol Addiction Progresses—Insights From Pre-Clinical Studies

Purpose of the Review

Development of addiction involves a transition from reward-driven to habitual behavior, mediated by neuroplastic changes. Based on preclinical findings, this article article reviews the current knowledge on the use of neuromodulation therapies to target alcohol addiction and essentially reduce relapse.

Recent Findings

To date, only a limited number of preclinical studies have investigated the use of neuromodulation in alcohol addiction, with the focus being on targeting the brain reward system. However, as addiction develops, additional circuits are recruited. Therefore, a differential setup may be required when seeking to alter the chronic alcohol-dependent brain, as opposed to treating earlier phases of alcohol addiction.

Summary

To promote enduring relapse prevention, the choice of brain target should match the stage of the disorder. Further studies are needed to investigate which brain areas should be targeted by neuromodulating strategies, in order to sufficiently alter the behavior and pathophysiology as alcohol addiction progresses.

7,8-Dihydroxyflavone Attenuates Alcohol-Related Behavior in Rat Models of Alcohol Consumption via TrkB in the Ventral Tegmental Area

Alcohol use disorder (AUD) is a ubiquitous substance use disorder in the world, of which neural mechanisms remain unclear. Alcohol consumption induces neuro-adaptations in the dopaminergic system originating from the ventral tegmental area (VTA), an important brain region for the reward function in AUD. Endogenous brain-derived neurotrophic factor (BDNF)-TrkB implicated in the development of neuroplasticity, including long-term potentiation of GABAergic synapses (LTP _GABA ). We previously found that ethanol blocks LTP _GABA in the VTA, either in vivo or in vitro. 7,8-dihydroflavone (7,8-DHF), a BDNF-mimicking small compound, was recently found to penetrate the blood-brain barrier to mimic the biological role of BDNF-TrkB. In this study, we demonstrate that repeated ethanol consumption (including intermittent and continuous ethanol exposure) results in low expression of BDNF in rat VTA. The amount of ethanol intake enhances significantly in rats with intermittent ethanol exposure after 72 h abstinence. Withdrawal signs emerge in rats with continuous ethanol exposure within 3 days after abstinence. Using behavioral tests, intraperitoneal injection of 7,8-DHF can reduce excessive ethanol consumption and preference as well as withdrawal signs in rats with repeated ethanol exposure. Interestingly, microinjection of K252a, an antagonist of TrkB, into the VTA blocks the effects of 7,8-DHF on ethanol-related behaviors. Furthermore, direct microinjection of BDNF into the VTA mimics the effect of 7,8-DHF on ethanol related behaviors. Taken together, 7,8-DHF attenuates alcohol-related behaviors in rats undergoing alcohol consumption via TrkB in the VTA. Our findings suggest BDNF-TrkB in VTA is a part of regulating signals for opposing neural adaptations in AUD, and 7,8-DHF may serve as a potential candidate for treating alcoholism.

Alcohol Causes Lasting Differential Transcription in Drosophila Mushroom Body Neurons

Repeated alcohol experiences can produce long-lasting memories for sensory cues associated with intoxication. These memories can problematically trigger relapse in individuals recovering from alcohol use disorder (AUD). The molecular mechanisms by which ethanol changes memories to become long-lasting and inflexible remain unclear. New methods to analyze gene expression within precise neuronal cell types can provide further insight toward AUD prevention and treatment. Here, we used genetic tools in Drosophila melanogaster to investigate the lasting consequences of ethanol on transcription in memory-encoding neurons. Drosophila rely on mushroom body (MB) neurons to make associative memories, including memories of ethanol-associated sensory cues. Differential expression analyses revealed that distinct transcripts, but not genes, in the MB were associated with experiencing ethanol alone compared to forming a memory of an odor cue associated with ethanol. Adult MB-specific knockdown of spliceosome-associated proteins demonstrated the necessity of RNA-processing in ethanol memory formation. These findings highlight the dynamic, context-specific regulation of transcription in cue-encoding neurons, and the lasting effect of ethanol on transcript usage during memory formation.

Alcohol consumption alters Gdnf promoter methylation and expression in rats

Alcohol use disorder is one of the most disabling diseases worldwide. Glial-cell derived neurotrophic factor (Gdnf) shows promising results concerning the inhibition of alcohol consumption in rodent models. We investigated the epigenetic regulation of Gdnf following ethanol consumption and withdrawal in a rat model. 32 Wistar rats underwent 7 weeks of intermittent access to alcohol in a 2-bottle choice (IA2BC). Whole blood, Nucleus Accumbens (NAc) and Ventral Tegmental Area (VTA) were collected immediately after the last 24 h of an alcohol-drinking session (alcohol group, AG) or 24 h after withdrawal (withdrawal group, WG). MRNA levels were measured using real-time quantitative PCR. Bisulfite-conversion of DNA and capillary sequencing was used to determine methylation levels of the core promoter (CP) and the negative regulatory element (NRE). The CP of the AG in the NAc was significantly less methylated compared to controls (p < 0.05). In the NAc, mRNA expression was significantly higher in the WG (p < 0.05). In the WG, mRNA expression levels in the VTA were significantly lower (p < 0.05) and showed significantly less methylation in the NRE in the VTA (p < 0.001) and the NAc (p < 0.01) compared to controls. Changes in the cerebral mRNA expression correspond to alterations in DNA methylation of the Gdnf promoter in a rodent model. Our results hold clinical relevance since differences in Gdnf mRNA expression and DNA methylation could be a target for pharmacological interventions.

Brain-wide functional architecture remodeling by alcohol dependence and abstinence

Alcohol abuse and alcohol dependence are key factors in the development of alcohol use disorder, which is a pervasive societal problem with substantial economic, medical, and psychiatric consequences. Although our understanding of the neurocircuitry that underlies alcohol use has improved, novel brain regions that are involved in alcohol use and novel biomarkers of alcohol use need to be identified. The present study used a single-cell whole-brain imaging approach to 1) assess whether abstinence from alcohol in an animal model of alcohol dependence alters the functional architecture of brain activity and modularity, 2) validate our current knowledge of the neurocircuitry of alcohol abstinence, and 3) discover brain regions that may be involved in alcohol use. Alcohol abstinence resulted in the whole-brain reorganization of functional architecture in mice and a pronounced decrease in modularity that was not observed in nondependent moderate drinkers. Structuring of the alcohol abstinence network revealed three major brain modules: 1) extended amygdala module, 2) midbrain striatal module, and 3) cortico-hippocampo-thalamic module, reminiscent of the three-stage theory. Many hub brain regions that control this network were identified, including several that have been previously overlooked in alcohol research. These results identify brain targets for future research and demonstrate that alcohol use and dependence remodel brain-wide functional architecture to decrease modularity. Further studies are needed to determine whether the changes in coactivation and modularity that are associated with alcohol abstinence are causal features of alcohol dependence or a consequence of excessive drinking and alcohol exposure.

Neurochemical Evidence of Preclinical and Clinical Reports on Target-Based Therapy in Alcohol Used Disorder

Alcohol use disorder (AUD) is a chronic relapsing disorder, which enforces a person to compulsively seek alcohol, restricting control over alcohol intake leads to emergence of an undesired emotional state during abstinence. There are recent advances for better understanding of neurocircuitry involved in the pathophysiology of AUD. Alcohol interaction with neuronal membrane proteins results in changes in neuronal circuits. It is also linked with the potential medication and their clinical validation concerning their pharmacological targets for alcoholic abstinence. This review covers research work from the past few decades on the therapeutic advances on treatment of alcohol dependence; further detailing the fundamental neurochemical mechanisms after alcohol administration. It also covers interaction of alcohol with GABAergic, glutaminergic, dopaminergic, serotonergic and opioid systems. This review further elaborated the neurobiology of noradrenergic, cholinergic and cannabinoid systems and their interaction with AUD. Elaborative information of potential drug targets under current exploration for AUD treatment with their mechanisms are reported here along with clinical outcomes and the associated side effects.

GPCR and Alcohol-Related Behaviors in Genetically Modified Mice

G protein-coupled receptors (GPCRs) constitute the largest class of cell surface signaling receptors and regulate major neurobiological processes. Accordingly, GPCRs represent primary targets for the treatment of brain disorders. Several human genetic polymorphisms affecting GPCRs have been associated to different components of alcohol use disorder (AUD). Moreover, GPCRs have been reported to contribute to several features of alcohol-related behaviors in animal models. Besides traditional pharmacological tools, genetic-based approaches mostly aimed at deleting GPCR genes provided substantial information on how key GPCRs drive alcohol-related behaviors. In this review, we summarize the alcohol phenotypes that ensue from genetic manipulation, in particular gene deletion, of key GPCRs in rodents. We focused on GPCRs that belong to fundamental neuronal systems that have been shown as potential targets for the development of AUD treatment. Data are reviewed with particular emphasis on alcohol reward, seeking, and consumption which are behaviors that capture essential aspects of AUD. Literature survey indicates that in most cases, there is still a gap in defining the intracellular transducers and the functional crosstalk of GPCRs as well as the neuronal populations in which their signaling regulates alcohol actions. Further, the implication of only a few orphan GPCRs has been so far investigated in animal models. Combining advanced pharmacological technologies with more specific genetically modified animals and behavioral preclinical models is likely necessary to deepen our understanding in how GPCR signaling contributes to AUD and for drug discovery.

mTORC1 in the orbitofrontal cortex promotes habitual alcohol seeking

The mechanistic target of rapamycin complex 1 (mTORC1) plays an important role in dendritic translation and in learning and memory. We previously showed that heavy alcohol use activates mTORC1 in the orbitofrontal cortex (OFC) of rodents (Laguesse et al., 2017a). Here, we set out to determine the consequences of alcohol-dependent mTORC1 activation in the OFC. We found that inhibition of mTORC1 activity in the OFC attenuates alcohol seeking and restores sensitivity to outcome devaluation in rats that habitually seek alcohol. In contrast, habitual responding for sucrose was unaltered by mTORC1 inhibition, suggesting that mTORC1’s role in habitual behavior is specific to alcohol. We further show that inhibition of GluN2B in the OFC attenuates alcohol-dependent mTORC1 activation, alcohol seeking and habitual responding for alcohol. Together, these data suggest that the GluN2B/mTORC1 axis in the OFC drives alcohol seeking and habit.

Sex and Individual Differences in Alcohol Intake Are Associated with Differences in Ketamine Self-Administration Behaviors and Nucleus Accumbens Dendritic Spine Density

Clinical and preclinical studies have shown that ketamine, an NMDA receptor antagonist, has promising therapeutic value for the treatment of alcohol use disorder (AUD). However, the maintenance of remission will ultimately require repeated infusions of ketamine, which may lead to abuse potential and may hinder its therapeutic benefits. It is therefore crucial to assess the effects of repeated treatments with ketamine on alcohol intake. Accordingly, this study aimed to examine in both sexes how individual differences in alcohol intake alter ketamine self-administration and how ketamine self-administration will alter subsequent alcohol-drinking behaviors. Male and female rats intermittently drank alcohol or water for 10 weeks and were divided into high- or low-alcohol intake groups prior to ketamine self-administration. Rats self-administered ketamine under fixed and progressive ratio schedules of reinforcement from week 4 to 7, and the incubation of ketamine craving was examined from week 8 to 10. To investigate structural plasticity in a brain region involved in reward, nucleus accumbens dendritic spine morphology was examined. Our results show that high alcohol intake in male rats attenuated ketamine self-administration, whereas in female rats high alcohol intake enhanced motivation to self-administer ketamine. Ketamine reduced alcohol intake in high-alcohol male rats but increased it in low-alcohol female rats. Incubation of ketamine craving developed in all groups except low-alcohol females. Three weeks of abstinence from ketamine was associated with increased mushroom spines in all groups except the high-alcohol male group. Overall, these data suggest that ketamine as a treatment for AUD may benefit male subjects, but not female subjects, and warrants further investigation before use as a therapeutic agent.

The grey future: Overgenerality of emotional future thinking in alcohol-use disorders

BACKGROUND

While previous research has highlighted the overgenerality of future thinking in alcohol-use disorders (AUD), the emotional characteristics of future thinking were not taken into account. We therefore evaluated the ability to retrieve episodic (i.e., events that happened at a particular place and time and lasted for a day or less) emotional future events in AUD.

METHODS

We invited 36 participants with AUD and 40 control participants to imagine positive, negative and neutral future scenarios and analyzed these scenarios regarding their episodic characteristics (i.e., the ability of participants to imagine future events situated in time and space enriched with phenomenological details).

RESULTS

Analysis demonstrated lower episodic positive, negative and neutral future thinking in participants with AUD than in control participants. Participants with AUD also demonstrated lower episodic positive and negative future thinking compared to episodic neutral future thinking. Interestingly, high depression scores were associated with overgenerality of neutral, positive, and negative future thinking in AUD participants.

CONCLUSIONS

These findings demonstrate overgenerality of both positive and negative future thinking in AUD. This overgenerality may represent an avoidance strategy in which individuals with AUD may try to avoid the hopelessness and/or conflicts that may be activated when constructing future scenarios.

Inhibition of FGF Receptor-1 Suppresses Alcohol Consumption: Role of PI3 Kinase Signaling in Dorsomedial Striatum

Excessive alcohol intake leads to mesostriatal neuroadaptations, and to addiction phenotypes. We recently found in rodents that alcohol increases fibroblast growth factor 2 (FGF2) expression in the dorsomedial striatum (DMS), which promotes alcohol consumption. Here, we show that systemic or intra-DMS blockade of the FGF2 receptor, FGF receptor-1 (FGFR1), suppresses alcohol consumption, and that the effects of FGF2-FGFR1 on alcohol drinking are mediated via the phosphoinositide 3 kinase (PI3K) signaling pathway. Specifically, we found that sub-chronic alcohol treatment (7 d × 2.5 g/kg, i.p.) increased Fgfr1 mRNA expression in the dorsal hippocampus and dorsal striatum. However, prolonged and excessive voluntary alcohol consumption in a two-bottle choice procedure increased Fgfr1 expression selectively in DMS. Importantly, systemic administration of the FGFR1 inhibitor PD173074 to mice, as well as its infusion into the DMS of rats, decreased alcohol consumption and preference, with no effects on natural reward consumption. Finally, inhibition of the PI3K, but not of the mitogen-activated protein kinase (MAPK) signaling pathway, blocked the effects of FGF2 on alcohol intake and preference. Our results suggest that activation of FGFR1 by FGF2 in the DMS leads to activation of the PI3K signaling pathway, which promotes excessive alcohol consumption, and that inhibition of FGFR1 may provide a novel therapeutic target for alcohol use disorder.SIGNIFICANCE STATEMENT Long-term alcohol consumption causes neuroadaptations in the mesostriatal reward system, leading to addiction-related behaviors. We recently showed that alcohol upregulates the expression of fibroblast growth factor 2 (FGF2) in dorsomedial striatum (DMS) or rats and mice, and in turn, FGF2 increases alcohol consumption. Here, we show that long-term alcohol intake also increases the expression of the FGF2 receptor, FGFR1 in the DMS. Importantly, inhibition of FGFR1 activity by a selective receptor antagonist reduces alcohol drinking, when given systemically or directly into the DMS. We further show that the effects of FGF2-FGFR1 on alcohol drinking are mediated via activation of the PI3K intracellular signaling pathway, providing an insight on the mechanism for this effect.

Mammalian target of rapamycin complex 1 and its downstream effector collapsin response mediator protein-2 drive reinstatement of alcohol reward seeking

Alcohol use disorder is a chronic relapsing disease. Maintaining abstinence represents a major challenge for alcohol-dependent patients. Yet the molecular underpinnings of alcohol relapse remain poorly understood. In the present study, we investigated the potential role of the mammalian target of rapamycin complex 1 (mTORC1) in relapse to alcohol-seeking behavior by using the reinstatement of a previously extinguished alcohol conditioned place preference (CPP) response as a surrogate relapse paradigm. We found that mTORC1 is activated in the nucleus accumbens shell following alcohol priming-induced reinstatement of alcohol place preference. We further report that the selective mTORC1 inhibitor, rapamycin, abolishes reinstatement of alcohol place preference. Activation of mTORC1 initiates the translation of synaptic proteins, and we observed that reinstatement of alcohol CPP is associated with increased protein levels of one of mTORC1's downstream targets, collapsin response mediator protein-2 (CRMP2), in the nucleus accumbens. Importantly, the level of mTORC1 activation and CRMP2 expression positively correlate with the CPP score during reinstatement. Finally, we found that systemic administration of the CRMP2 inhibitor, lacosamide, attenuates alcohol priming-induced reinstatement of CPP. Together, our results reveal that mTORC1 and its downstream target, CRMP2, contribute to mechanisms underlying reinstatement of alcohol reward seeking. Our results could have important implications for the treatment of relapse to alcohol use and position the Food and Drug Administration approved drugs, rapamycin and lacosamide, for the treatment of alcohol use disorder.

Amygdala Arginine Vasopressin Modulates Chronic Ethanol Withdrawal Anxiety-Like Behavior in the Social Interaction Task

BACKGROUND

Chronic ethanol (EtOH) exposure induces neurobehavioral maladaptations in the brain though the precise changes have not been fully explored. The central nucleus of the amygdala (CEA) regulates anxiety-like behavior induced by withdrawal from chronic intermittent EtOH (CIE) exposure, and the arginine vasopressin (AVP) system within the CEA regulates many anxiety-like behaviors. Thus, adaptations occur in the CEA AVP system due to chronic EtOH exposure, which lead to anxiety-like behaviors in rats.

METHODS

Chronic exposure to a low-dose EtOH (4.5% wt/vol) induces anxiety-like behavior in rats. Wistar or Sprague Dawley rats were exposed to a modified CIE or CIE, while intra-CEA microinjections of AVP or a V1b receptor antagonist were used to elicit or block withdrawal-induced anxiety. Additionally, AVP microinjections into the CEA were given 24 hours following 15 days of continuous high-dose EtOH (7% wt/vol), a time period when rats no longer express anxiety. Chemogenetics was also used to activate the basolateral amygdala (BLA) or deactivate the dorsal periaqueductal gray=(dm/dlPAG) therefore PAG=periaqueductal gray to elicit or block withdrawal-induced anxiety.

RESULTS

AVP microinjected into the CEA in lieu of exposure to the first 2 cycles of CIE was sufficient to induce anxiety-like behavior in these commonly used rat strains. The V1b receptor antagonist, but not an oxytocin receptor agonist, into the CEA during the first 2 withdrawal cycles suppressed anxiety. However, activation of the BLA in lieu of exposure to the first 2 cycles of CIE was insufficient to induce anxiety-like behavior. AVP microinjection into the CEA 24 hours into withdrawal reelicited anxiety-like behavior, and deactivation of the dm/dlPAG reduced this effect of CEA AVP.

CONCLUSIONS

Taken together, this study demonstrates a role of CEA AVP and a CEA-dm/dlPAG circuit in the development of anxiety induced by CIE. Such information is valuable for identifying novel therapeutic targets for alcohol- and anxiety-associated disorders.

Novel Adenosine Analog, N6-(4-Hydroxybenzyl)-Adenosine, Dampens Alcohol Drinking and Seeking Behaviors

Adenosine signaling is associated with ethanol-related behaviors. We previously found that adenosine A_2A receptor (A_2AR) activation dampens ethanol drinking behaviors in equilibrative nucleoside transporter 1 (ENT1) knockout mice, and A_2AR inhibition augments reward-seeking behavior in wild-type mice. The novel adenosine analog N6-(4-hydroxybenzyl)-adenosine (NHBA), which is isolated from the rhizomes of Gastrodia elata, activates A_2AR and inhibits ENT1. Here, we examined the effects of NHBA on ethanol drinking in the two-bottle choice test and operant ethanol seeking behaviors. We selected mice exhibiting high ethanol drinking behavior in the two-bottle choice test. NHBA (0.1 mg/kg, i.p.) reduced ethanol drinking behavior in a limited-access 3-hour drinking session in high-consumption ethanol drinking mice, and NHBA (0.1 mg/kg, i.p.) did not alter locomotor activity in the open-field test. Operant conditioning with 10% ethanol and 10% sucrose (10E10S) reward increased zone entries and time spent in the ethanol zone, while NHBA (0.1 mg/kg, i.p.) dampened ethanol zone preference in the Y-maze. Furthermore, NHBA (0.1 mg/kg, i.p.) devalued 10E10S and 10% ethanol (10E) reward after operant conditioning with 10E10S and 10E. Taken together, NHBA through A_2AR activation and ENT1 modulation may dampen ethanol drinking and seeking behaviors, suggesting that NHBA is a potential therapeutic agent for treating alcohol use disorder. SIGNIFICANCE STATEMENT: Our work highlights that A_2AR activation and ENT1 inhibition by a novel adenosine analog isolated from Gastrodia elata, N6-(4-hydroxybenzyl)-adenosine, decreases ethanol drinking and seeking behaviors. We suggest that NHBA is a potential therapeutic agent to treat alcohol use disorder.

Cross-Species Co-analysis of Prefrontal Cortex Chronic Ethanol Transcriptome Responses in Mice and Monkeys

Despite recent extensive genomic and genetic studies on behavioral responses to ethanol, relatively few new therapeutic targets for the treatment of alcohol use disorder have been validated. Here, we describe a cross-species genomic approach focused on identifying gene networks associated with chronic ethanol consumption. To identify brain mechanisms underlying a chronic ethanol consumption phenotype highly relevant to human alcohol use disorder, and to elucidate potential future therapeutic targets, we conducted a genomic study in a non-human primate model of chronic open-access ethanol consumption. Microarray analysis of RNA expression in anterior cingulate and subgenual cortices from rhesus macaques was performed across multiple cohorts of animals. Gene networks correlating with ethanol consumption or showing enrichment for ethanol-regulated genes were identified, as were major ethanol-related hub genes within these networks. A subsequent consensus module analysis was used to co-analyze monkey data with expression data from a chronic intermittent ethanol vapor-exposure and consumption model in C57BL/6J mice. Ethanol-related gene networks conserved between primates and rodents were enriched for genes involved in discrete biological functions, including; myelination, synaptic transmission, chromatin modification, Golgi apparatus function, translation, cellular respiration, and RNA processing. The myelin-related network, in particular, showed strong correlations with ethanol consumption behavior and displayed marked network reorganization between control and ethanol-drinking animals. Further bioinformatics analysis revealed that these networks also showed highly significant overlap with other ethanol-regulated gene sets. Altogether, these studies provide robust primate and rodent cross-species validation of gene networks associated with chronic ethanol consumption. Our results also suggest potential novel focal points for future therapeutic interventions in alcohol use disorder.

Nicotine and alcohol: the role of midbrain dopaminergic neurons in drug reinforcement

Nicotine and alcohol addiction are leading causes of preventable death worldwide and continue to constitute a huge socio-economic burden. Both nicotine and alcohol perturb the brain's mesocorticolimbic system. Dopamine (DA) neurons projecting from the ventral tegmental area (VTA) to multiple downstream structures, including the nucleus accumbens, prefrontal cortex, and amygdala, are highly involved in the maintenance of healthy brain function. VTA DA neurons play a crucial role in associative learning and reinforcement. Nicotine and alcohol usurp these functions, promoting reinforcement of drug taking behaviors. In this review, we will first describe how nicotine and alcohol individually affect VTA DA neurons by examining how drug exposure alters the heterogeneous VTA microcircuit and network-wide projections. We will also examine how coadministration or previous exposure to nicotine or alcohol may augment the reinforcing effects of the other. Additionally, this review briefly summarizes the role of VTA DA neurons in nicotine, alcohol, and their synergistic effects in reinforcement and also addresses the remaining questions related to the circuit-function specificity of the dopaminergic system in mediating nicotine/alcohol reinforcement and comorbidity.

Indirect Medium Spiny Neurons in the Dorsomedial Striatum Regulate Ethanol-Containing Conditioned Reward Seeking

Adenosine 2A receptor (A_2AR)-containing indirect medium spiny neurons (iMSNs) in the dorsomedial striatum (DMS) contribute to reward-seeking behaviors. However, those roles for ethanol-seeking behaviors remain unknown. To investigate ethanol-seeking behaviors, we used an ethanol-containing reward (10% ethanol and 10% sucrose solution; 10E10S). Upon conditioning with 10E10S, mice that initially only preferred 10% sucrose, not 10E10S, showed a stronger preference for 10E10S. Then, we investigated whether the manipulation of the DMS-external globus pallidus (GPe) iMSNs circuit alters the ethanol-containing reward (10E10S) seeking behaviors using the combination of pharmacologic and optogenetic approaches. DMS A_2AR activation dampened operant conditioning-induced ethanol-containing reward, whereas A_2AR antagonist abolished the effects of the A_2AR agonist and restored ethanol-containing reward-seeking. Moreover, pre-ethanol exposure potentiated the A_2AR-dependent reward-seeking. Interestingly, mice exhibiting ethanol-containing reward-seeking showed the reduction of the DMS iMSNs activity, suggesting that disinhibiting iMSNs decreases reward-seeking behaviors. In addition, we found that A_2AR activation reversed iMSNs neural activity in the DMS. Similarly, optogenetic stimulation of the DMS-GPe iMSNs reduced ethanol-containing reward-seeking, whereas optogenetic inhibition of the DMS-GPe iMSNs reversed this change. Together, our study demonstrates that DMS A_2AR and iMSNs regulate ethanol-containing reward-seeking behaviors.SIGNIFICANCE STATEMENT Our findings highlight the mechanisms of how operant conditioning develops the preference of ethanol-containing conditioned reward. Mice exhibiting ethanol-containing reward-seeking showed a reduction of the indirect medium spiny neuronal activity in the dorsomedial striatum. Pharmacological activation of adenosine A_2A receptor (A_2AR) or optogenetic activation of indirect medium spiny neurons dampened operant conditioned ethanol-containing reward-seeking, whereas inhibiting this neuronal activity restored ethanol-containing reward-seeking. Furthermore, repeated intermittent ethanol exposure potentiated A_2AR-dependent reward-seeking. Therefore, our finding suggests that A_2AR-containing indirect medium spiny neuronal activation reduces ethanol-containing reward-seeking, which may provide a potential therapeutic target for alcohol use disorder.

Protein Translation and Psychiatric Disorders

Although historically research has focused on transcription as the central governor of protein expression, protein translation is now increasingly being recognized as a major factor for determining protein levels within cells. The central nervous system relies on efficient updating of the protein landscape. Thus, coordinated regulation of mRNA localization, initiation, or termination of translation is essential for proper brain function. In particular, dendritic protein synthesis plays a key role in synaptic plasticity underlying learning and memory as well as cognitive processes. Increasing evidence suggests that impaired mRNA translation is a common feature found in numerous psychiatric disorders. In this review, we describe how malfunction of translation contributes to development of psychiatric diseases, including schizophrenia, major depression, bipolar disorder, and addiction.

Silencing synaptic MicroRNA-411 reduces voluntary alcohol consumption in mice

Chronic alcohol consumption alters the levels of microRNAs and mRNAs in the brain, but the specific microRNAs and processes that target mRNAs to affect cellular function and behavior are not known. We examined the in vivo manipulation of previously identified alcohol-responsive microRNAs as potential targets to reduce alcohol consumption. Silencing of miR-411 by infusing antagomiR-411 into the prefrontal cortex of female C57BL/6J mice reduced alcohol consumption and preference, without altering total fluid consumption, saccharin consumption, or anxiety-related behaviors. AntagomiR-411 reduced alcohol consumption when given to mice exposed to a chronic alcohol drinking paradigm but did not affect the acquisition of consumption in mice without a history of alcohol exposure, suggesting that antagomiR-411 has a neuroadaptive, alcohol-dependent effect. AntagomiR-411 decreased the levels of miR-411, as well as the association of immunoprecipitated miR-411 with Argonaute2; and, it increased levels of Faah and Ppard mRNAs. Moreover, antagomiR-411 increased the neuronal expression of glutamate receptor AMPA-2 protein, a known alcohol target and a predicted target of miR-411. These results suggest that alcohol and miR-411 function in a homeostatic manner to regulate synaptic mRNA and protein, thus reversing alcohol-related neuroadaptations and reducing chronic alcohol consumption.

Perineurial Barrier Glia Physically Respond to Alcohol in an Akap200-Dependent Manner to Promote Tolerance

Ethanol is the most common drug of abuse. It exerts its behavioral effects by acting on widespread neural circuits; however, its impact on glial cells is less understood. We show that Drosophila perineurial glia are critical for ethanol tolerance, a simple form of behavioral plasticity. The perineurial glia form the continuous outer cellular layer of the blood-brain barrier and are the interface between the brain and the circulation. Ethanol tolerance development requires the A kinase anchoring protein Akap200 specifically in perineurial glia. Akap200 tightly coordinates protein kinase A, actin, and calcium signaling at the membrane to control tolerance. Furthermore, ethanol causes a structural remodeling of the actin cytoskeleton and perineurial membrane topology in an Akap200-dependent manner, without disrupting classical barrier functions. Our findings reveal an active molecular signaling process in the cells at the blood-brain interface that permits a form of behavioral plasticity induced by ethanol.

PCSK9 is Increased in Cerebrospinal Fluid of Individuals With Alcohol Use Disorder

BACKGROUND

Recent studies have shown that alcohol use affects the regulation and expression of proprotein convertase subtilisin/kexin 9 (PCSK9). While a major role of PCSK9 in hepatic function and lipid regulation has been clearly established, other pleiotropic effects remain poorly understood. Existing research suggests a positive association between PCSK9 expression in the brain and psychopathology, with increased levels of PCSK9 in the cerebrospinal fluid (CSF) of individuals with dementia and epigenetic modifications of PCSK9 associated with alcohol use disorder (AUD). In this study, we hypothesized that chronic alcohol use would increase PCSK9 expression in CSF.

METHODS

PCSK9 levels in CSF were measured in individuals with AUD (n = 42) admitted to an inpatient rehabilitation program and controls (n = 25). CSF samples in AUD were assessed at 2 time points, at day 5 and day 21 after admission. Furthermore, plasma samples were collected and measured from the individuals with AUD.

RESULTS

PCSK9 in CSF was significantly increased in the AUD group at day 5 and day 21 compared to the controls (p < 0.0001). Plasma PCSK9 levels were correlated positively with CSF PCSK9 levels in AUD (p = 0.0493).

CONCLUSIONS

Our data suggest that PCSK9 is elevated in the CSF of individuals with AUD, which may indicate a potential role of PCSK9 in AUD. Additional studies are necessary to further elucidate the functions of PCSK9 in the brain.

Reduced Alcohol Seeking and Withdrawal Symptoms in Mice Lacking the BDNF Receptor SorCS2

Alcohol use disorder (AUD) is characterized by repetitive and uncontrolled intake of alcohol with severe consequences for affected individuals, their families and society as a whole. Numerous studies have implicated brain-derived neurotrophic factor (BDNF) activity in the neurobiology underlying AUD. The BDNF signaling mechanism is complex and depends on two receptor systems, TrkB and p75NTR, which appear to have opposite effects on alcohol seeking behavior in animal models. We recently discovered that the sortilin-related receptor SorCS2 forms complexes with both TrkB and p75NTR and is important for BDNF activity in the developing and adult CNS. Moreover, the SORCS2 gene was recently identified as the top association signal for severity of alcohol withdrawal symptoms. Hence, we speculated that SorCS2 deficient mice would have an altered response to alcohol. The role of SorCS2 in the acute and adapted response to alcohol was therefore investigated by comparing SorCS2 knockout (Sorcs2^-/- ) mice to wild type (WT) mice in three paradigms modeling alcohol sensitivity and consumption; alcohol-induced conditioned place preference, two-bottle choice test as well as the behavioral response to alcohol withdrawal. We found that, when compared to the WT mice, (I) Sorcs2^-/- mice displayed complete lack of alcohol-induced place preference, (II) when given free choice between water and alcohol, Sorcs2^-/- mice consumed less alcohol, and (III) Sorcs2^-/- mice showed no handling-induced convulsion in response to alcohol withdrawal following extended alcohol exposure. Taken together, these results show that lack of the alcohol withdrawal risk gene Sorcs2 results in abnormal behavioral response to alcohol in mice. Consequently, SorCS2 may play an important role in the molecular pathways underlying AUD and complications associated with alcohol withdrawal.

GDNF and alcohol use disorder

Glial cell line-derived neurotrophic factor (GDNF) has been extensively studied for its role in the development and maintenance of the midbrain dopaminergic system, although evidence suggests that GDNF also plays a role in drug and alcohol addiction. This review focuses on the unique actions of GDNF in the mechanisms that prevent the transition from recreational alcohol use to abuse. Specifically, we describe studies in rodents suggesting that alcohol acutely increases GDNF expression in the ventral tegmental area, which enables the activation of the mitogen-activated protein kinase signaling pathway and the gating of alcohol intake. We further provide evidence to suggest that GDNF acts in the ventral tegmental area via both nongenomic and genomic mechanisms to suppress alcohol consumption. In addition, we describe findings indicating that when this endogenous protective pathway becomes dysregulated, alcohol intake levels escalate. Finally, we describe the potential use of GDNF inducers as a novel therapeutic approach to treat alcohol use disorder.

Advances in behavioral animal models of alcohol use disorder

Alcohol use disorder (AUD) is a multifaceted neuropsychiatric disease that combines behavioral, psychosocial, and neurobiological aspects. Over the previous decade, animal models have advanced in modeling the major psychological constructs that characterize AUD. These advances pave the road for more sophisticated behavioral models that capture addiction-related aspects, such as alcohol craving, compulsive seeking and intake, dependence, and relapse. In this review, we survey the recent progress in behavioral animal modeling of five aspects of AUD: alcohol consumption, dependence, and seeking; compulsivity in alcohol intake despite adverse outcomes; vulnerability and resilience factors in alcohol addiction; relapse despite treatment; and relapse prevention by manipulating alcohol-associated memory reconsolidation. These advances represent a general attempt to grasp the complexity and multidimensional nature of AUD, and to focus on behavioral characteristics that better reflect and model this disorder.

The use of chemogenetic approaches in alcohol use disorder research and treatment

Several novel techniques were developed recently to explore neural circuit mechanisms of neuropsychiatric disorders. These techniques include the Designer Receptors Exclusively Activated by Designer Drugs (DREADD)-based chemogenetic tools, which represent valuable platforms for selective and non-invasive control of neural activity with a high degree of spatial resolution. Among all variants, Gq- and Gi-DREADDs are widely used by neuroscientists to dissect out the circuitry and cellular signals. This review is focused on strategies to access a specific neuronal population or circuit using the DREADD technique and summarizes the current knowledge of the DREADDs' application in alcohol use disorder research and therapeutics.

Activity-dependent neuroprotective protein (ADNP) is an alcohol-responsive gene and negative regulator of alcohol consumption in female mice

Neuroadaptations in the brain reward system caused by excessive alcohol intake, lead to drinking escalation and alcohol use disorder phenotypes. Activity-dependent neuroprotective protein (ADNP) is crucial for brain development, and is implicated in neural plasticity in adulthood. Here, we discovered that alcohol exposure regulates Adnp expression in the mesolimbic system, and that Adnp keeps alcohol drinking in moderation, in a sex-dependent manner. Specifically, Sub-chronic alcohol treatment (2.5 g/kg/day for 7 days) increased Adnp mRNA levels in the dorsal hippocampus in both sexes, and in the nucleus accumbens of female mice, 24 h after the last alcohol injection. Long-term voluntary consumption of excessive alcohol quantities (~10-15 g/kg/24 h, 5 weeks) increased Adnp mRNA in the hippocampus of male mice immediately after an alcohol-drinking session, but the level returned to baseline after 24 h of withdrawal. In contrast, excessive alcohol consumption in females led to long-lasting reduction in hippocampal Adnp expression. We further tested the regulatory role of Adnp in alcohol consumption, using the Adnp haploinsufficient mouse model. We found that Adnp haploinsufficient female mice showed higher alcohol consumption and preference, compared to Adnp intact females, whereas no genotype difference was observed in males. Importantly, daily intranasal administration of the ADNP-snippet drug candidate NAP normalized alcohol consumption in Adnp haploinsufficient females. Finally, female Adnp haploinsufficient mice showed a sharp increase in alcohol intake after abstinence, suggesting that Adnp protects against relapse in females. The current data suggest that ADNP is a potential novel biomarker and negative regulator of alcohol-drinking behaviors.

Defining the place of habit in substance use disorders

It has long been suggested that alcohol or substance use disorders could emerge from the progressive development and dominance of drug habits. Like habits, drug-related behaviors are often triggered by drug-associated cues. Like habits, addictive behaviors are strong, rigid and "hard to break". Like habits, these behaviors are insensitive to their outcome and persist despite negative consequences. "Pathological habit" thus appears as a good candidate to explain the transition to compulsive drug use. However, drug use could also be considered as a goal-directed choice, driven by the expectation of drug outcomes. For example, drug addicts may engage in drug-seeking behaviors because they view the drug as more valuable than available alternatives. Substance use disorders therefore may not be all about habit, nor fully intentional, and could be considered as resulting from an imbalance between goal-directed and habitual control. The main objective of this review is to disentangle the relative contribution of habit formation and impairment of goal-directed behavior in this unbalanced control of addictive behaviors. Although deficits in goal-directed behavior have been demonstrated in alcohol and substance use disorders, reliable demonstration of abnormal habit formation has been curtailed by the paucity of paradigms designed to assess habit as a positive result. Refining our animal and human model of habit is therefore required to precisely define the place of habit in substance use disorders and develop appropriate and adapted neurobehavioral treatments.

Intranasal erythropoietin ameliorates neurological function impairments and neural pathology in mice with chronic alcoholism by regulating autophagy‑related Nrf2 degradation

The neurological disorders and neural pathology brought about by chronic alcoholism are difficult to be reversed. Increasing evidence highlights the protective roles of erythropoietin (EPO) in neurodegenerative diseases and injuries of the central nervous system. In the present study, we investigated the therapeutic effects of EPO on the neurological function deficits and neural pathology caused by chronic alcoholism and the regulatory mechanisms. Using the canonical mouse model of chronic alcohol exposure designed to mimic the repeated cycles of heavy abuse typical of chronic alcoholism, it was found that EPO delivered via intranasal route effectively restored the alcohol-impaired motor cooperation in rotarod and beam walk tests, reversed alcoholic cognitive and emotional alterations in the novel location recognition task and open-filed test, and rescued alcohol-disrupted nervous conduction in the somatosensory-evoked potential (SSEP) test. Consistently, the intranasally administered EPO promoted the remyelination and synapse formation in chronic alcohol-affected neocortex and hippocampus as evidenced by immunofluorescence staining and transmission electron microscopy. Additionally, we discovered that the exogenous rhEPO, which entered the cerebrum through intranasal route, activated the erythropoietin receptor (EPOR) and the downstream ERKs and PI3K/AKT signaling, and suppressed autophagy-related degradation of nuclear factor, erythroid 2-like 2 (Nrf2). Furthermore, the intranasal EPO-exerted neuroprotection was almost abolished when the specific Nrf2 antagonist ATRA was administered intraperitoneally prior to intranasal EPO treatment. Collectively, our data demonstrated the repairing potential of EPO for the neurological disorders and neural pathology caused by chronic alcoholism, and identified the Nrf2 activity as the key mechanism mediating the protective effects of EPO.

Ethanol-induced enhancement of inhibitory synaptic transmission in the rat spinal substantia gelatinosa

Recent studies have shown that ethanol produces a widespread modulation of neuronal activity in the central nervous system. It is not fully understood, however, how ethanol changes nociceptive transmission. We investigated acute effects of ethanol on synaptic transmission in the substantia gelatinosa (lamina II of the spinal dorsal horn) and mechanical responses in the spinal dorsal horn. In substantia gelatinosa neurons, bath application of ethanol at low concentration (10 mM) did not change the frequency and amplitude of spontaneous inhibitory postsynaptic currents. At medium to high concentrations (20–100 mM), however, ethanol elicited a barrage of large amplitude spontaneous inhibitory postsynaptic currents. In the presence of tetrodotoxin, such enhancement of spontaneous inhibitory postsynaptic currents was not detected. In addition, ethanol (20–100 mM) increased the frequency of spontaneous discharge of vesicular GABA transporter-Venus-labeled neurons and suppressed the mechanical nociceptive response in wide-dynamic range neurons in the spinal dorsal horn. The present results suggest that ethanol may reduce nociceptive information transfer in the spinal dorsal horn by enhancement of inhibitory GABAergic and glycinergic synaptic transmission.

Acute alcohol administration dampens central extended amygdala reactivity

Alcohol use is common, imposes a staggering burden on public health, and often resists treatment. The central extended amygdala (EAc)—including the bed nucleus of the stria terminalis (BST) and the central nucleus of the amygdala (Ce)—plays a key role in prominent neuroscientific models of alcohol drinking, but the relevance of these regions to acute alcohol consumption in humans remains poorly understood. Using a single-blind, randomized-groups design, multiband fMRI data were acquired from 49 social drinkers while they performed a well-established emotional faces paradigm after consuming either alcohol or placebo. Relative to placebo, alcohol significantly dampened reactivity to emotional faces in the BST. To rigorously assess potential regional differences in activation, data were extracted from unbiased, anatomically predefined regions of interest. Analyses revealed similar levels of dampening in the BST and Ce. In short, alcohol transiently reduces reactivity to emotional faces and it does so similarly across the two major divisions of the human EAc. These observations reinforce the translational relevance of addiction models derived from preclinical work in rodents and provide new insights into the neural systems most relevant to the consumption of alcohol and to the initial development of alcohol abuse in humans.

Alcohol consumption is positively associated with fasting serum ghrelin in non-dependent adults: Results from the population-based LIFE-Adult-Study

BACKGROUND

Animal experiments and studies in alcohol dependent patients indicate that ghrelin signaling in the brain is causally involved in the regulation of alcohol reward and intake. Increasing ghrelin levels enhances alcohol craving and intake, blocking ghrelin receptors abolishes these effects. If ghrelin is also involved in non-dependent alcohol consumption in humans, though, remains unknown. The aim was therefore to investigate the relationship between ghrelin serum levels and alcohol consumption in a large population-based sample.

METHODS

Total ghrelin was determined after an overnight fast in 1666 subjects participating in a population-based cross-sectional study ('LIFE') including 10,000 adults. 1521 subjects were included in this analysis. Alcohol consumption was assessed using a food frequency questionnaire (FFQ). Multiple linear regression analyses and extreme group comparisons testing for statistical differences of alcohol consumption between the highest and lowest quartile according to ghrelin levels were performed.

RESULTS

Alcohol consumption was positively associated with serum ghrelin; total sample: β = 0.003, p = 0.002; men: β = 0.005, p = 0.023; women: β = 0.002, p = 0.007, adjusted for age, BMI and smoking status. Mean alcohol consumption in men/women belonging to the highest quartile of serum ghrelin levels (men: 21.5 (21.1) g/day; women: 7.5 (11.4) g/day) was considerably higher than in those belonging to the lowest quartile (men: 16.5 (19.3) g/day p < 0.002; women: 4.59 (10.7) g/day p = 0.0001).

CONCLUSION

This is the first study showing that alcohol consumption is positively associated with serum ghrelin in a population-based sample. The study provides an initial indication that ghrelin is also involved in the regulation of alcohol consumption in non-dependent subjects.

Dynamic changes in gene expression and alternative splicing mediate the response to acute alcohol exposure in Drosophila melanogaster

Environmental changes typically cause rapid gene expression responses in the exposed organisms, including changes in the representation of gene isoforms with different functions or properties. Identifying the genes that respond to environmental change, including in genotype-specific ways, is an important step in treating the undesirable physiological effects of stress, such as exposure to toxins or ethanol. Ethanol is a unique environmental stress in that chronic exposure results in permanent physiological changes and the development of alcohol use disorders. Drosophila is a classic model for deciphering the mechanisms of the response to alcohol exposure, as it meets the criteria for the development of alcohol use disorders, and has similar physiological underpinnings with vertebrates. Because many studies on the response to ethanol have relied on a priori candidate genes, broad surveys of gene expression and splicing are required and have been investigated here. Further, we expose Drosophila to ethanol in an environment that is genetically, socially, and ecologically relevant. Both expression and splicing differences, inasmuch as they can be decomposed, contribute to the response to ethanol in Drosophila melanogaster. However, we find that while D. melanogaster responds to ethanol, there is very little genetic variation in how it responds to ethanol. In addition, the response to alcohol over time is dynamic, suggesting that incorporating time into studies on the response to the environment is important.

On the safety of repeated ketamine infusions for the treatment of depression: Effects of sex and developmental periods

In this review, we will discuss the safety of repeated treatments with ketamine for patients with treatment-resistant depression (TRD), a condition in which patients with major depression do not show any clinical improvements following treatments with at least two antidepressant drugs. We will discuss the effects of these treatments in both sexes at different developmental periods. Numerous small clinical studies have shown that a single, low-dose ketamine infusion can rapidly alleviate depressive symptoms and thoughts of suicidality in patients with TRD, and these effects can last for about one week. Interestingly, the antidepressant effects of ketamine can be prolonged with intermittent, repeated infusion regimens and produce more robust therapeutic effects when compared to a single infusion. The safety of such repeated treatments with ketamine has not been thoroughly investigated. Although more studies are needed, some clinical and preclinical reports indicated that repeated infusions of low doses of ketamine may have addictive properties, and suggested that adolescent and adult female subjects may be more sensitive to ketamine's addictive effects. Additionally, during ketamine infusions, many TRD patients report hallucinations and feelings of dissociation and depersonalization, and therefore the effects of repeated treatments of ketamine on cognition must be further examined. Some clinical reports indicated that, compared to women, men are more sensitive to the psychomimetic effects of ketamine. Preclinical studies extended these findings to both adolescent and adult male rodents and showed that male rodents at both developmental periods are more sensitive to ketamine's cognitive-altering effects. Accordingly, in this review we shall focus our discussion on the potential addictive and cognitive-impairing effects of repeated ketamine infusions in both sexes at two important developmental periods: adolescence and adulthood. Although more work about the safety of ketamine is warranted, we hope this review will bring some answers about the safety of treating TRD with repeated ketamine infusions.

Metabotropic Glutamate Receptors in Alcohol Use Disorder: Physiology, Plasticity, and Promising Pharmacotherapies

Developing efficacious treatments for alcohol use disorder (AUD) has proven difficult. The insidious nature of the disease necessitates a deep understanding of its underlying biology as well as innovative approaches to ameliorate ethanol-related pathophysiology. Excessive ethanol seeking and relapse are generated by long-term changes to membrane properties, synaptic physiology, and plasticity throughout the limbic system and associated brain structures. Each of these factors can be modulated by metabotropic glutamate (mGlu) receptors, a diverse set of G protein-coupled receptors highly expressed throughout the central nervous system. Here, we discuss how different components of the mGlu receptor family modulate neurotransmission in the limbic system and other brain regions involved in AUD etiology. We then describe how these processes are dysregulated following ethanol exposure and speculate about how mGlu receptor modulation might restore such pathophysiological changes. To that end, we detail the current understanding of the behavioral pharmacology of mGlu receptor-directed drug-like molecules in animal models of AUD. Together, this review highlights the prominent position of the mGlu receptor system in the pathophysiology of AUD and provides encouragement that several classes of mGlu receptor modulators may be translated as viable treatment options.

The role of fibroblast growth factor 2 in drug addiction

Fibroblast growth factor 2 (FGF2) is a member of the FGF-family, which consists of 22 members, with four known FGF receptors (five in humans). Over the last 30 years, FGF2 has been extensively studied for its role in cell proliferation, differentiation, growth, survival and angiogenesis during development, as well as for its role in adult neurogenesis and regenerative plasticity. Over the past decade, FGF2 has been implicated in learning and memory, as well as in several neuropsychiatric disorders, including anxiety, stress, depression and drug addiction. In this review, we present accumulating evidence indicating the involvement of FGF2 in neuroadaptations caused by drugs of abuse, namely, amphetamine, cocaine, nicotine and alcohol. Moreover, evidence suggests that FGF2 is a positive regulator of alcohol and drug-related behaviors. Thus, although additional studies are yet required, we suggest that reducing FGF2 activity may provide a novel therapeutic approach for substance use disorders.

Methylomic profiling and replication implicates deregulation of PCSK9 in alcohol use disorder

Alcohol use disorder (AUD) is a common and chronic disorder with substantial effects on personal and public health. The underlying pathophysiology is poorly understood but strong evidence suggests significant roles of both genetic and epigenetic components. Given that alcohol affects many organ systems, we performed a cross-tissue and cross-phenotypic analysis of genome-wide methylomic variation in AUD using samples from 3 discovery, 4 replication, and 2 translational cohorts. We identified a differentially methylated region in the promoter of the proprotein convertase subtilisin/kexin 9 (PCSK9) gene that was associated with disease phenotypes. Biological validation showed that PCSK9 promoter methylation is conserved across tissues and positively correlated with expression. Replication in AUD datasets confirmed PCSK9 hypomethylation and a translational mouse model of AUD showed that alcohol exposure leads to PCSK9 downregulation. PCSK9 is primarily expressed in the liver and regulates low-density lipoprotein cholesterol (LDL-C). Our finding of alcohol-induced epigenetic regulation of PCSK9 represents one of the underlying mechanisms between the well-known effects of alcohol on lipid metabolism and cardiovascular risk, with light alcohol use generally being protective while chronic heavy use has detrimental health outcomes.

Role of Dorsal Striatum Histone Deacetylase 5 in Incubation of Methamphetamine Craving

BACKGROUND

Methamphetamine (meth) seeking progressively increases after withdrawal (incubation of meth craving). We previously demonstrated an association between histone deacetylase 5 (HDAC5) gene expression in the rat dorsal striatum and incubation of meth craving. Here we used viral constructs to study the causal role of dorsal striatum HDAC5 in this incubation.

METHODS

In experiment 1 (overexpression), we injected an adeno-associated virus bilaterally into dorsal striatum to express either green fluorescent protein (control) or a mutant form of HDAC5, which strongly localized to the nucleus. After training rats to self-administer meth (10 days, 9 hours/day), we tested the rats for relapse to meth seeking on withdrawal days 2 and 30. In experiment 2 (knockdown), we injected an adeno-associated virus bilaterally into the dorsal striatum to express a short hairpin RNA either against luciferase (control) or against HDAC5. After training rats to self-administer meth, we tested the rats for relapse on withdrawal days 2 and 30. We also measured gene expression of other HDACs and potential HDAC5 downstream targets.

RESULTS

We found that HDAC5 overexpression in dorsal striatum increased meth seeking on withdrawal day 30 but not day 2. In contrast, HDAC5 knockdown in the dorsal striatum decreased meth seeking on withdrawal day 30 but not on day 2; this manipulation also altered other HDACs (Hdac1 and Hdac4) and potential HDAC5 targets (Gnb4 and Suv39h1).

CONCLUSIONS

Results demonstrate a novel role of dorsal striatum HDAC5 in incubation of meth craving. These findings also set up future work to identify HDAC5 targets that mediate this incubation.

Increased Alcohol Seeking in Mice Lacking Gpr88 Involves Dysfunctional Mesocorticolimbic Networks

BACKGOUND

Alcohol use disorder (AUD) is devastating and poorly treated, and innovative targets are actively sought for prevention and treatment. The orphan G protein-coupled receptor GPR88 is enriched in mesocorticolimbic pathways, and Gpr88 knockout mice show hyperactivity and risk-taking behavior, but a potential role for this receptor in drug abuse has not been examined.

METHODS

We tested Gpr88 knockout mice for alcohol-drinking and -seeking behaviors. To gain system-level understanding of their alcohol endophenotype, we also analyzed whole-brain functional connectivity in naïve mice using resting-state functional magnetic resonance imaging.

RESULTS

Gpr88 knockout mice showed increased voluntary alcohol drinking at both moderate and excessive levels, with intact alcohol sedation and metabolism. Mutant mice also showed increased operant responding and motivation for alcohol, while food and chocolate operant self-administration were unchanged. Alcohol place conditioning and alcohol-induced dopamine release in the nucleus accumbens were decreased, suggesting reduced alcohol reward in mutant mice that may partly explain enhanced alcohol drinking. Seed-based voxelwise functional connectivity analysis revealed significant remodeling of mesocorticolimbic centers, whose hallmark was predominant weakening of prefrontal cortex, ventral tegmental area, and amygdala connectional patterns. Also, effective connectivity from the ventral tegmental area to the nucleus accumbens and amygdala was reduced.

CONCLUSIONS

Gpr88 deletion disrupts executive, reward, and emotional networks in a configuration that reduces alcohol reward and promotes alcohol seeking and drinking. The functional connectivity signature is reminiscent of alterations observed in individuals at risk for AUD. The Gpr88 gene, therefore, may represent a vulnerability/resilience factor for AUD, and a potential drug target for AUD treatment.

Adolescent alcohol exposure epigenetically regulates CREB signaling in the adult amygdala

Binge alcohol drinking in adolescence leads to increased risk for alcohol use and other psychiatric disorders in adulthood. The transcription factor cAMP-response element binding (CREB) protein is involved in the neuronal response to adult ethanol exposure, but its role in the enduring effects of adolescent alcohol exposure in adulthood is unknown. We exposed male rats to adolescent intermittent ethanol (AIE) or saline (AIS) during post-natal days 28-41 and evaluated the epigenetic regulation of CREB dynamics in the adult amygdala. A subset of these adult rats was exposed to an acute ethanol challenge. AIE decreased CREB, phosphorylated CREB, CREB-binding protein (CBP) and p300 protein levels in adult amygdaloid brain structures. AIE exposure also causes deficits in Creb1, Cbp, and p300 mRNA expression in the amygdala of AIE adult rats which are normalized after acute ethanol exposure. Interestingly, occupancy of acetylated histone H3K9/14 proteins at specific locations in the Creb1, Cbp, and p300 gene promoter regions was decreased in the amygdala of AIE adult rats and was normalized by acute ethanol exposure. These results suggest that AIE exposure epigenetically reduces CREB and other related transcriptional activators in the amygdala in adulthood that may be associated with the behavioral effects of adolescent alcohol exposure.

Systemic and Intra-Habenular Activation of the Orphan G Protein-Coupled Receptor GPR139 Decreases Compulsive-Like Alcohol Drinking and Hyperalgesia in Alcohol-Dependent Rats

GPR139 is an orphan G protein-coupled receptor (GPCR) that is expressed mainly in the brain, with the highest expression in the medial habenula. The modulation of GPR139 receptor function has been hypothesized to be beneficial in the treatment of some mental disorders, but behavioral studies have not yet provided causal evidence of the role of GPR139 in brain dysfunction. Because of the high expression of GPR139 in the habenula, a critical brain region in addiction, we hypothesized that GPR139 may play role in alcohol dependence. Thus, we tested the effect of GPR139 receptor activation using the selective, brain-penetrant receptor agonist JNJ-63533054 on addiction-like behaviors in alcohol-dependent male rats. Systemic administration of JNJ-63533054 (30 mg/kg but not 10 mg/kg, p.o.) reversed the escalation of alcohol self-administration in alcohol-dependent rats, without affecting water or saccharin intake in dependent rats or alcohol intake in nondependent rats. Moreover, systemic JNJ-63533054 administration decreased withdrawal-induced hyperalgesia, without affecting somatic signs of alcohol withdrawal. Further analysis demonstrated that JNJ-63533054 was effective only in a subgroup of dependent rats that exhibited compulsive-like alcohol drinking. Finally, site-specific microinjection of JNJ-63533054 in the habenula but not interpeduncular nucleus (IPN) reduced both alcohol self-administration and withdrawal-induced hyperalgesia in dependent rats. These results provide robust preclinical evidence that GPR139 receptor activation reverses key addiction-like behaviors in dependent animals, suggest that GPR139 may be a novel target for the treatment of alcohol use disorder, and demonstrate that GPR139 is functionally relevant in regulating mammalian behavior.