Target For Alcohol Use Disorder Research Articles

Pharmacological GHSR (ghrelin receptor) blockade reduces alcohol binge-like drinking in male and female mice

Ghrelin is a peptide that is produced by endocrine cells that are primarily localized in the stomach. Ghrelin receptors (GHSR) are expressed in the brain and periphery. Preclinical and clinical studies support a role for ghrelin in alcohol drinking and seeking. The GHSR has been suggested to be a potential pharmacotherapeutic target for alcohol use disorder (AUD). However, the role of the ghrelin system and its potential modulation by biological sex on binge-like drinking has not been comprehensively investigated. The present study tested six GHSR antagonists in an alcohol binge-like drinking procedure in male and female mice. Systemic administration of the GHSR antagonists JMV2959, PF-5190457, PF-6870961, and HM-04 reduced alcohol intake in both male and female mice. YIL-781 decreased intake in males, and LEAP2 (likely peripherally restricted) did not reduce intake in mice of either sex. We also administered LEAP2 and JMV2959 intracerebroventricularly to investigate whether the effects of GHSR blockade on alcohol intake are mediated by central receptors. The central administration of LEAP2 and JMV2959 decreased alcohol intake, particularly in high-drinking animals. Finally, in a preliminary experiment, an anti-ghrelin vaccine was examined for its potential effect on binge-like drinking and had no effect. In all experiments, there was a lack of meaningful sex differences. These findings suggest that central GHSR mediates binge-like alcohol intake. These data reveal novel pharmacological compounds with translational potential in the treatment of AUD and provide further evidence of the GHSR as a potential treatment target for AUD.

Role of prefrontal cortex Gsk3b as a new therapeutic target for alcohol use disorder

Role of prefrontal cortex Gsk3b as a new therapeutic target for alcohol use disorder

A critical review of effects on ethanol intake of the dynorphin/kappa opioid receptor system in the extended amygdala: From inhibition to stimulation.

The dynorphin (DYN)/kappa opioid receptor (KOR) system has increasingly been investigated as a possible pharmacotherapeutic target for alcohol use disorder, but findings on the direction of its effects have been mixed. Activation of KORs by DYN has been shown to elicit dysphoric effects, and the DYN/KOR system has canonically been considered particularly important in driving alcohol intake through negative reinforcement in dependent states. However, this review also highlights its activity in opposing the positive reinforcement that drives alcohol intake at earlier stages. Both DYN and KORs are concentrated in the extended amygdala, a set of interconnected regions that includes the bed nucleus of the stria terminalis, central nucleus of the amygdala, and nucleus accumbens shell. This review focuses on the role of the DYN/KOR system in the extended amygdala in ethanol use. It begins by examining the effects of ethanol on the expression of DYN/KOR in the extended amygdala, expression of DYN/KOR in alcohol-preferring and alcohol-avoiding animals, and the effects of knocking out DYN/KOR genes on ethanol intake. Then, it examines the effects on ethanol use in both dependent and nondependent states from systemic pharmacological manipulations of DYN/KOR and from specific manipulation of this system in regions of the extended amygdala. We propose that greater expression and binding of DYN/KOR, by reducing the positive reinforcement that drives early stages of intake, initially acts to prevent the escalation of ethanol drinking. However, prolonged, binge-like, or intermittent ethanol intake enhances levels of DYN/KOR in the extended amygdala such that the system ultimately facilitates the negative reinforcement that drives later stages of ethanol drinking. This review highlights the potential of the DYN/KOR system as a target that can affect different outcomes across different stages of ethanol drinking and the development of alcohol use disorder.

Ethanol-Induced Suppression of G Protein–Gated Inwardly Rectifying K+–Dependent Signaling in the Basal Amygdala

BackgroundThe basolateral amygdala (BLA) regulates mood and associative learning and has been linked to the development and persistence of alcohol use disorder. The GABABR (gamma-aminobutyric acid B receptor) is a promising therapeutic target for alcohol use disorder, and previous work suggests that exposure to ethanol and other drugs can alter neuronal GABABR-dependent signaling. The effect of ethanol on GABABR-dependent signaling in the BLA is unknown. MethodsGABABR-dependent signaling in the mouse BLA was examined using slice electrophysiology following repeated ethanol exposure. Neuron-specific viral genetic manipulations were then used to understand the relevance of ethanol-induced neuroadaptations in the basal amygdala subregion (BA) to mood-related behavior. ResultsThe somatodendritic inhibitory effect of GABABR activation on principal neurons in the basal but not the lateral subregion of the BLA was diminished following ethanol exposure. This adaptation was attributable to the suppression of GIRK (G protein–gated inwardly rectifying K+) channel activity and was mirrored by a redistribution of GABABR and GIRK channels from the surface membrane to internal sites. While GIRK1 and GIRK2 subunits are critical for GIRK channel formation in BA principal neurons, GIRK3 is necessary for the ethanol-induced neuroadaptation. Viral suppression of GIRK channel activity in BA principal neurons from ethanol-naïve mice recapitulated some mood-related behaviors observed in C57BL/6J mice during ethanol withdrawal. ConclusionsThe ethanol-induced suppression of GIRK-dependent signaling in BA principal neurons contributes to some of the mood-related behaviors associated with ethanol withdrawal in mice. Approaches designed to prevent this neuroadaptation and/or strengthen GIRK-dependent signaling may prove useful for the treatment of alcohol use disorder.

RGS6 negatively regulates inhibitory G protein signaling in dopamine neurons and positively regulates binge-like alcohol consumption in mice.

Drugs of abuse, including alcohol, increase dopamine in the mesocorticolimbic system via actions on dopamine neurons in the ventral tegmental area (VTA). Increased dopamine transmission can activate inhibitory G protein signalling pathways in VTA dopamine neurons, including those controlled by GABAB and D2 receptors. Members of the R7 subfamily of regulator of G protein signalling (RGS) proteins can regulate inhibitory G protein signalling, but their influence on VTA dopamine neurons is unclear. Here, we investigated the influence of RGS6, an R7 RGS family memberthat has been implicated in the regulation of alcohol consumption in mice, on inhibitory G protein signalling in VTA dopamine neurons. We used molecular, electrophysiological and genetic approaches to probe the impact of RGS6 on inhibitory G protein signalling in VTA dopamine neurons and on binge-like alcohol consumption in mice. RGS6 is expressed in adult mouse VTA dopamine neurons and it modulates inhibitory G protein signalling in a receptor-dependent manner, tempering D2 receptor-induced somatodendritic currents and accelerating deactivation of synaptically evoked GABAB receptor-dependent responses. RGS6-/- mice exhibit diminished binge-like alcohol consumption, a phenotype replicated in female (but not male) mice lacking RGS6 selectively in VTA dopamine neurons. RGS6 negatively regulates GABAB - and D2 receptor-dependent inhibitory G protein signalling pathways in mouse VTA dopamine neurons and exerts a sex-dependent positive influence on binge-like alcohol consumption in adult mice. As such, RGS6 may represent a new diagnostic and/or therapeutic target for alcohol use disorder.

The GPR88 agonist RTI-13951-33 reduces alcohol drinking and seeking in mice.

GPR88 is an orphan G‐protein‐coupled receptor that is considered a potential target to treat neuropsychiatric disorders, including addiction. Most knowledge about GPR88 function stems from knockout mouse studies, and in vivo pharmacology is still scarce. Here we examine the effects of the novel brain‐penetrant agonist RTI‐13951‐33 on several alcohol‐related behaviours in the mouse. In the intermittent‐access‐two‐bottle‐choice paradigm, the compound reduced excessive voluntary alcohol drinking, while water drinking was intact. This was observed for C57BL/6 mice, as well as for control but not Gpr88 knockout mice, demonstrating efficacy and specificity of the drug in vivo. In the drinking‐in‐the‐dark paradigm, RTI‐13951‐33 also reduced binge‐like drinking behaviour for control but not Gpr88 knockout mice, confirming the alcohol consumption‐reducing effect and in vivo specificity of the drug. When C57BL/6 mice were trained for alcohol self‐administration, RTI‐13951‐33 decreased the number of nose‐pokes over a 4‐h session and reduced the number of licks and bursts of licks, suggesting reduced motivation to obtain alcohol. Finally, RTI‐13951‐33 did not induce any place preference or aversion but reduced the expression of conditioned place preference to alcohol, indicative of a reduction of alcohol‐reward seeking. Altogether, data show that RTI‐13951‐33 limits alcohol intake under distinct conditions that require consummatory behaviour, operant response or association with contextual cues. RTI‐13951‐33 therefore is a promising lead compound to evaluate GPR88 as a therapeutic target for alcohol use disorders. More broadly, RTI‐13951‐33 represents a unique tool to better understand GPR88 function, disentangle receptor roles in development from those in the adult and perhaps address other neuropsychiatric disorders.

Differential association between the GLP1R gene variants and brain functional connectivity according to the severity of alcohol use

Growing evidence suggests that the glucagon-like peptide-1 (GLP-1) system is involved in mechanisms underlying alcohol seeking and consumption. Accordingly, the GLP-1 receptor (GLP-1R) has begun to be studied as a potential pharmacotherapeutic target for alcohol use disorder (AUD). The aim of this study was to investigate the association between genetic variation at the GLP-1R and brain functional connectivity, according to the severity of alcohol use. Participants were 181 individuals categorized as high-risk (n = 96) and low-risk (n = 85) alcohol use, according to their AUD identification test (AUDIT) score. Two uncommon single nucleotide polymorphisms (SNPs), rs6923761 and rs1042044, were selected a priori for this study because they encode amino-acid substitutions with putative functional consequences on GLP-1R activity. Genotype groups were based on the presence of the variant allele for each of the two GLP-1R SNPs of interest [rs6923761: AA + AG (n = 65), GG (n = 116); rs1042044: AA + AC (n = 114), CC (n = 67)]. Resting-state functional MRI data were acquired for 10 min and independent component (IC) analysis was conducted. Multivariate analyses of covariance (MANCOVA) examined the interaction between GLP-1R genotype group and AUDIT group on within- and between-network connectivity. For rs6923761, three ICs showed significant genotype × AUDIT interaction effects on within-network connectivity: two were mapped onto the anterior salience network and one was mapped onto the visuospatial network. For rs1042044, four ICs showed significant interaction effects on within-network connectivity: three were mapped onto the dorsal default mode network and one was mapped onto the basal ganglia network. For both SNPs, post-hoc analyses showed that in the group carrying the variant allele, high versus low AUDIT was associated with stronger within-network connectivity. No significant effects on between-network connectivity were found. In conclusion, genetic variation at the GLP-1R was differentially associated with brain functional connectivity in individuals with low versus high severity of alcohol use. Significant findings in the salience and default mode networks are particularly relevant, given their role in the neurobiology of AUD and addictive behaviors.

Epigenome-Wide Association Study of Alcohol Consumption in N=8161 Individuals and Relevance to Alcohol Use Disorder Pathophysiology

Growing evidence suggests that alcohol consumption is strongly associated with alterations in DNA methylation. Identification of alcohol-associated methylomic variation might provide novel insights into pathophysiology and novel treatment targets for alcohol use disorder (AUD).

Gene knockdown of HCN2 ion channels in the ventral tegmental area reduces ethanol consumption in alcohol preferring rats

ABSTRACT Background: Hyperpolarization-Activated Cyclic Nucleotide-Gated (HCN) ionic channels are known to play a key role in the control of neuron excitability and have been proposed as a molecular target of ethanol. Previous studies in rats have shown that gene-induced overexpression of the HCN2 channel in the ventral tegmental area (VTA) increases the rewarding effects of ethanol and its intake by the animals. Objective: The aim of this work was to study the effects of VTA HCN2 gene knockdown in the voluntary ethanol consumption of alcohol-preferring UChB rats. Methods: Two lentiviral vectors were generated; LV-siRNA-HCN2, coding for a siRNA that elicited >95% reduction of HCN2 protein levels in vitro, and a control vector coding for a scrambled siRNA sequence. Female UChB naïve rats (n = 14) were microinjected into the VTA with LV-siRNA-HCN2 or the scrambled control vector (n = 11). Four days after, animals were given a daily free access to 10% ethanol and water for 10 days. Results: Rats treated with the LV-siRNA-HCN2 vector showed a ~ 70% reduction (p < .001) in their ethanol preference and ethanol intake compared to control animals. No changes were observed in the total fluid intake of both groups. HCN2 levels in the VTA were measured by Western blot showing a reduction of 40% (p < .05) in the rats injected with LV-siRNA-HCN2, compared to control animals. Conclusion: These results show that knockdown of HCN2 ionic channels in the VTA of UChB rats markedly reduces their voluntary ethanol intake, supporting the idea that HCN2 channels may constitute a therapeutic target for alcohol use disorders.

The GABAB receptor positive allosteric modulator ASP8062 reduces operant alcohol self-administration in male and female Sprague Dawley rats.

Pre-clinical evidence implicates the GABAergic system in mediating the reinforcing effects of alcohol and offers a therapeutic target for alcohol use disorder (AUD). The orthosteric GABAB receptor agonist baclofen decreases alcohol self-administration in animals and alcohol use in humans; however side effects limit its utility. Pre-clinical evidence shows positive allosteric GABAB receptor modulators also decrease alcohol self-administration without untoward side effects. We assessed the impact of the novel GABAB-positive allosteric modulator ASP8062 and baclofen on operant alcohol self-administration and their potential non-specific effects. The effects of ASP8062 (1 - 10mg/kg, PO) and baclofen (0.3 - 3mg/kg, IP) were evaluated in male and female rats lever pressing for alcohol (10%, w/v) under a fixed ratio 2 schedule of reinforcement. On the fourth consecutive day of vehicle, ASP8062 or baclofen administration, active and inactive lever presses, reinforcers earned, head entries, and estimated alcohol consumed were analyzed. Locomotor activity was assessed in separate groups of rats following dosing. Both ASP8062 and baclofen decreased alcohol self-administration and amount consumed (g/kg) in male and female rats. ASP8062 decreased operant alcohol self-administration to a greater extent in male rats, whereas baclofen was more efficacious in female rats. ASP8062 did not alter locomotor activity in either sex, whereas baclofen (3.0mg/kg) decreased activity in male rats yet (1.0mg/kg) increased activity in female rats. ASP8062 decreases alcohol reinforcement like baclofen but without non-specific effects which are influenced by sex. Results support further development of ASP8062 as a potential treatment for AUD in humans.

Neuroendocrine Response to Exogenous Ghrelin Administration, Combined With Alcohol, in Heavy-Drinking Individuals: Findings From a Randomized, Double-Blind, Placebo-Controlled Human Laboratory Study.

Accumulating evidence has established a role for the orexigenic hormone ghrelin in alcohol-seeking behaviors. Accordingly, the ghrelin system may represent a potential pharmacotherapeutic target for alcohol use disorder. Ghrelin modulates several neuroendocrine pathways, such as appetitive, metabolic, and stress-related hormones, which are particularly relevant in the context of alcohol use. The goal of the present study was to provide a comprehensive assessment of neuroendocrine response to exogenous ghrelin administration, combined with alcohol, in heavy-drinking individuals. This was a randomized, crossover, double-blind, placebo-controlled human laboratory study, which included 2 experimental alcohol administration paradigms: i.v. alcohol self-administration and i.v. alcohol clamp. Each paradigm consisted of 2 counterbalanced sessions of i.v. ghrelin or placebo administration. Repeated blood samples were collected during each session, and peripheral concentrations of the following hormones were measured: leptin, glucagon-like peptide-1, pancreatic polypeptide, gastric inhibitory peptide, insulin, insulin-like growth factor-1, cortisol, prolactin, and aldosterone. Despite some statistical differences, findings were consistent across the 2 alcohol administration paradigms: i.v. ghrelin, compared to placebo, increased blood concentrations of glucagon-like peptide-1, pancreatic polypeptide, cortisol, and prolactin, both acutely and during the whole session. Lower levels of leptin and higher levels of aldosterone were also found during the ghrelin vs placebo session. These findings, gathered from a clinically relevant sample of heavy-drinking individuals with alcohol use disorder, provide a deeper insight into the complex interplay between ghrelin and appetitive, metabolic, and stress-related neuroendocrine pathways in the context of alcohol use.

Are non-abstinent reductions in World Health Organization drinking risk level a valid treatment target for alcohol use disorders in adolescents with ADHD?

IntroductionAbstinence from drinking represents the primary treatment target for alcohol use disorders (AUD) in youth, but few adolescents who engage in problematic drinking seek treatment. A reduction in World Health Organization (WHO) drinking risk level has been established as valid and reliable non-abstinent treatment target for AUD in adults but remains unstudied in youth. MethodsThe present study used data from the NIDA-CTN-0028 trial to examine associations between reductions in WHO drinking risk level and changes in global functioning and attention-deficit hyperactivity disorder (ADHD) symptoms during treatment in a sample of adolescents (ages 13–18 years) with ADHD and comorbid substance use disorder (SUD) (n = 297, 61% with AUD) receiving a 16-week intervention that combined ADHD pharmacotherapy (OROS-methylphenidate vs. placebo) and drug-focused cognitive-behavioral therapy. ResultsShifts in drinking risk level during treatment were highly variable in adolescents treated for ADHD/SUD, and influenced by AUD diagnostic status. In the total sample, 15% of participants had a 2-level or greater reduction in WHO drinking risk level, with 59% and 24% showing no change or an increase in risk-level during treatment respectively. Achieving at least a 2-level change in WHO drinking risk level during treatment was associated with greater reduction in ADHD symptoms and better functional outcomes. ConclusionsThese findings parallel the adult AUD literature and provide preliminary support for the use 2-level reductions in WHO risk levels for alcohol use as a clinically valid non-abstinent treatment outcome for youth with ADHD and comorbid AUD.

A Population Pharmacokinetic Analysis of PF-5190457, a Novel Ghrelin Receptor Inverse Agonist in Healthy Volunteers and in Heavy Alcohol Drinkers.

The ghrelin receptor (GHS-R1a) is a potential target for alcohol use disorders. PF-5190457 is the first inverse agonist of GHS-R1a to progress to clinical development with potential to treat alcohol use disorder. We present a population pharmacokinetic model for PF-5190457 in non-heavy (alcohol consumption status = 0) and heavy alcohol drinkers (alcohol consumption status = 1), and identify relevant factors that can influence its pharmacokinetics. Plasma concentration-time data from non-heavy (n = 35) and heavy drinkers (n = 12) were pooled for the population pharmacokinetic model development. The influence of various covariates including alcohol consumption status was evaluated. The accuracy, precision, and robustness of the model were also evaluated using bootstrapping and visual predictive checks. A two-compartment model best described the pharmacokinetics of PF-5190457. The apparent volume of distribution of 44.5 L, apparent clearance of 72.0 L/h, apparent peripheral volume of distribution of 271 L, apparent distributional clearance of 28.7 L/h, and first-order absorption rate constant of 0.27/h were accurate and precise. The apparent volume of distribution was 3.8-fold higher (169 L) in heavy drinkers, and correlated with a lower maximum plasma concentration in heavy drinkers compared with non-heavy drinkers at the same dose; and a corresponding reduced incidence of somnolence in heavy drinkers at doses > 50mg. This work provides an accurate, precise, and robust two-compartment model that describes the pharmacokinetics of PF-5190457 and suggests a possible link of PF-5190457 pharmacokinetics with somnolence. ClinicalTrials.gov identifier numbers NCT01247896 and NCT02039349.

SLC Neurotransmitter Transporters as Therapeutic Targets for Alcohol Use Disorder: A Narrative Review.

Alcohol use disorder (AUD) is 1 of the most prevalent of all substance use disorders and contributes significantly to global disease burden. Despite its prevalence, <10% of individuals with AUD receive treatment. A significant barrier to receiving treatment is a lack of effective pharmacotherapies. While 3 medications have been approved by the FDA for AUD (disulfiram, acamprosate, naltrexone), their efficacy remains low. Furthermore, a number of undesirable side effects associated with these drugs further reduce patient compliance. Thus, research into new effective pharmacotherapies for AUD is warranted. Due to their involvement in regulating synaptic neurotransmitter levels, solute carrier (SLC) transporters could be targeted for developing effective treatment strategies for AUD. Indeed, a number of studies have shown beneficial reductions in alcohol consumption through the use of drugs that target transporters of dopamine, serotonin, glutamate, glycine, and GABA. The purpose of this narrative review is to summarize preclinical and clinical studies from the last 2 decades targeting SLC neurotransmitter transporters for the treatment of AUD. Limitations, as well as future directions for expanding this field, are also discussed.

Acetylcholine Muscarinic M4 Receptors as a Therapeutic Target for Alcohol Use Disorder: Converging Evidence From Humans and Rodents

BackgroundAlcohol use disorder (AUD) is a major socioeconomic burden on society, and current pharmacotherapeutic treatment options are inadequate. Aberrant alcohol use and seeking alters frontostriatal function. MethodsWe performed genome-wide RNA sequencing and subsequent quantitative polymerase chain reaction and receptor binding validation in the caudate–putamen of human AUD samples to identify potential therapeutic targets. We then back-translated our top candidate targets into a rodent model of long-term alcohol consumption to assess concordance of molecular adaptations in the rat striatum. Finally, we adopted rat behavioral models of alcohol intake and seeking to validate a potential therapeutic target. ResultsWe found that G protein–coupled receptors were the top canonical pathway differentially regulated in individuals with AUD. The M4 muscarinic acetylcholine receptor (mAChR) was downregulated at the gene and protein levels in the putamen, but not in the caudate, of AUD samples. We found concordant downregulation of the M4 mAChR, specifically on dopamine D1 receptor–expressing medium spiny neurons in the rat dorsolateral striatum. Systemic administration of the selective M4 mAChR positive allosteric modulator, VU0467154, reduced home cage and operant alcohol self-administration, motivation to obtain alcohol, and cue-induced reinstatement of alcohol seeking in rats. Local microinjections of VU0467154 in the rat dorsolateral striatum reduced alcohol self-administration and cue-induced reinstatement of alcohol seeking. ConclusionsCollectively, these results identify the M4 mAChR as a potential therapeutic target for the treatment of AUD and the D1 receptor–positive medium spiny neurons in the dorsolateral striatum as a key site mediating the actions of M4 mAChR in relation to alcohol consumption and seeking.

Lower brain fatty acid amide hydrolase in treatment-seeking patients with alcohol use disorder: a positron emission tomography study with [C-11]CURB.

The endocannabinoid enzyme, fatty acid amide hydrolase (FAAH), has been proposed as a therapeutic target for alcohol use disorder (AUD) and co-morbid psychiatric illnesses. Investigating this target in the living human brain and its relationship to clinical outcome is a critical step of informed drug development. Our objective was to establish whether brain FAAH levels are low in individuals with AUD and related to drinking behavior. In this pilot study, treatment-seeking patients with AUD completed two PET scans with the FAAH radiotracer [C-11]CURB after 3-7 days (n = 14) and 2-4 weeks (n = 9) of monitored abstinence. Healthy controls (n = 25) completed one scan. FAAH genetic polymorphism (rs324420) and blood concentrations of anandamide and other N-acylethanolamines metabolized by FAAH were determined and AUD symptoms assessed. In AUD, brain FAAH levels were globally lower than controls during early abstinence (F(1,36) = 5.447; p = 0.025)) and FAAH substrates (anandamide, oleoylethanolamide, and N-docosahexaenoylethanolamide) were significantly elevated (30-67%). No significant differences in FAAH or FAAH substrates were noted after 2-4 weeks abstinence. FAAH levels negatively correlated with drinks per week (r = -0.57, p = 0.032) and plasma concentrations of the three FAAH substrates (r > 0.57; p < 0.04)). Our findings suggest that early abstinence from alcohol in AUD is associated with transiently low brain FAAH levels, which are inversely related to heavier alcohol use and elevated plasma levels of FAAH substrates. Whether low FAAH is an adaptive beneficial response to chronic alcohol is unknown. Therapeutic strategies focusing on FAAH inhibition should consider the possibility that low FAAH during early abstinence may be related to drinking.

Cannabinoids and the Microbiota-Gut-Brain Axis: Emerging Effects of Cannabidiol and Potential Applications to Alcohol Use Disorders.

The endocannabinoid system (ECS) has emerged in recent years as a potential treatment target for alcohol use disorders (AUD). In particular, the nonpsychoactive cannabinoid cannabidiol (CBD) has shown preclinical promise in ameliorating numerous clinical symptoms of AUD. There are several proposed mechanism(s) through which cannabinoids (and CBD in particular) may confer beneficial effects in the context of AUD. First, CBD may directly impact specific brain mechanisms underlying AUD to influence alcohol consumption and the clinical features of AUD. Second, CBD may influence AUD symptoms through its actions across the digestive, immune, and central nervous systems, collectively known as the microbiota-gut-brain axis (MGBA). Notably, emerging work suggests that alcohol and cannabinoids exert opposing effects on the MGBA. Alcohol is linked to immune dysfunction (e.g., chronic systemic inflammation in the brain and periphery) as well as disturbances in gut microbial species (microbiota) and increased intestinal permeability. These MGBA disruptions have been associated with AUD symptoms such as craving and impaired cognitive control. Conversely, existing preclinical data suggest that cannabinoids may confer beneficial effects on the gastrointestinal and immune system, such as reducing intestinal permeability, regulating gut bacteria, and reducing inflammation. Thus, cannabinoids may exert AUD harm-reduction effects, at least in part, through their beneficial actions across the MGBA. This review will provide a brief introduction to the ECS and the MGBA, discuss the effects of cannabinoids (particularly CBD) and alcohol in the brain, gut, and immune system (i.e., across the MGBA), and put forth a theoretical framework to inform future research questions.

Receptor Tyrosine Kinases as Therapeutic Targets for Alcohol Use Disorder.

The receptor tyrosine kinases (RTKs) are a large family of proteins that transduce extracellular signals to the inside of the cell to ultimately affect important cellular functions such as cell proliferation, survival, apoptosis, differentiation, and migration. They are expressed in the nervous system and can regulate behavior through modulation of neuronal and glial function. As a result, RTKs are implicated in neurodegenerative and psychiatric disorders such as depression and addiction. Evidence has emerged that 5 RTKs (tropomyosin-related kinase B (TrkB), RET proto-oncogene (RET), anaplastic lymphoma kinase (ALK), fibroblast growth factor receptor (FGFR), and epidermal growth factor receptor (EGFR)) modulate alcohol drinking and other behaviors related to alcohol addiction. RTKs are considered highly "druggable" targets and small-molecule inhibitors of RTKs have been developed for the treatment of various conditions, particularly cancer. These kinases are therefore attractive targets for the development of new pharmacotherapies to treat alcohol use disorder (AUD). This review will examine the preclinical evidence describing TrkB, RET, ALK, FGFR, and EGFR modulation of alcohol drinking and other behaviors relevant to alcohol abuse.

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

Adenosine 2A receptor (A2AR)-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 A2AR activation dampened operant conditioning-induced ethanol-containing reward, whereas A2AR antagonist abolished the effects of the A2AR agonist and restored ethanol-containing reward-seeking. Moreover, pre-ethanol exposure potentiated the A2AR-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 A2AR 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 A2AR 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 A2A receptor (A2AR) 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 A2AR-dependent reward-seeking. Therefore, our finding suggests that A2AR-containing indirect medium spiny neuronal activation reduces ethanol-containing reward-seeking, which may provide a potential therapeutic target for alcohol use disorder.

Glucagon-like peptide-1 receptors within the nucleus of the solitary tract regulate alcohol-mediated behaviors in rodents

The ability of glucagon-like peptide-1 (GLP-1) to reduce food intake involves activation of GLP-1 receptors (GLP-1R) in the nucleus of the solitary tract (NTS). It has also been demonstrated that systemic administration of GLP-1R agonists attenuates alcohol-mediated behaviors via, to date, unknown mechanisms. Therefore, we evaluated the effects of NTS-GLP-1R activation by exendin-4 (Ex4) on alcohol-induced locomotor stimulation, accumbal dopamine release and memory of alcohol reward in the conditioned place preference (CPP) model in mice. Moreover, the ability of Ex4 infusion into the NTS on alcohol intake was explored in rats. Ex4 into the NTS inhibits the acute effects of alcohol as measured by alcohol-induced locomotor stimulation, accumbal dopamine release and the memory consolidation of alcohol reward in the CPP paradigm. In addition, NTS-Ex4 dose-dependently decreases alcohol intake in rats consuming alcohol for 12 weeks. Pharmacological suppression of GLP-1R in the NTS prevents the ability of systemic Ex4 to block the alcohol-induced locomotor stimulation in mice. These data add a functional role of GLP-1R within the NTS, involving alcohol-related behaviors. In addition, they may provide insight into the GLP-1R containing brain areas that modulate the ability of GLP-1R agonists to reduce alcohol reinforcement. Collectively, this further supports GLP-1R as potential treatment targets for alcohol use disorder.