Addiction Biology

Co-occurrence of substance use disorders (SUD) and aggressive behaviour in the same individual has been frequently described. As dopamine (DA) and serotonin (5-HT) are key neurotransmitters for both phenotypes, we explored the genetic contribution of these pathways to SUD, aggressive behaviour and related behavioural traits. Here, we tested the association of 275 dopaminergic genes and 176 serotonergic genes with these phenotypes by performing gene-based, gene-set and transcriptome-wide association studies (TWAS) in 11 genome-wide association studies (GWAS) datasets on SUD (alcohol, cocaine, cannabis, opioids and a multivariate analysis of three drugs of abuse), aggressive behaviour (disruptive behaviour and antisocial behaviour) and related behaviours (irritability, neuroticism, risk taking and anxiety). At the gene-wide level, 68 DA and 27 5-HT genes were found to be associated with at least one GWAS on SUD or related behaviour. Among them, six genes had a pleiotropic effect, being associated with at least three phenotypes: ADH1C, ARNTL, CHRNA3, HPRT1, HTR1B and DRD2, the latter with five. Additionally, we found nominal associations between the DA gene sets and antisocial behaviour, opioid use disorder, SUD, irritability and neuroticism, and between the 5-HT-core gene set and neuroticism. Gene expression correlates in brain were also found for 19 genes, highlighting the association for CHRNA3 and CELSR3 with OUD, SUD and irritability and CELSR3 also with neuroticism. Our study shows a pleiotropic contribution of dopaminergic and serotonergic genes to addiction, aggression and related behaviours, highlighting a special role for DA genes, which could explain, in part, the co-occurrence of these phenotypes.

IntroductionTobacco smoking is a major health burden worldwide, especially in populations suffering from other substance use disorders (SUDs). Several smoking phenotypes have been associated with single nucleotide polymorphisms (SNPs) of nicotinic acetylcholine receptors (nAChRs). Yet, little is known about the genetics of tobacco smoking in populations with other SUDs, particularly regarding gene-gene interactions and pleiotropy, which are likely involved in the polygenic architecture of SUDs. Thus, we undertook a candidate pathway association study of nAChR-related genes and smoking phenotypes in a sample of SUD patients.\n\nMethods493 patients with genetically-verified Caucasian ancestry were characterized extensively regarding patterns of tobacco smoking, other SUDs, and 83 SNPs from the nicotinic pathway, encompassing all brain nAChR subunits and metabolic/chaperone/trafficking proteins. Single-SNP, gene-based and SNP x SNP interactions analyses were performed to investigate associations with relevant tobacco smoking phenotypes. This included Bayesian analyses to detect pleiotropy, and adjustment on clinical and sociodemographic confounders.\n\nResultsAfter multiple adjustment, we found independent associations between CHRNA3 rs8040868 and a higher number of cigarettes per day (CPD), and between RIC3 rs11826236 and a lower age at smoking initiation. Two SNP x SNP interactions were associated with age at onset (AAO) of daily smoking. There was pleiotropy regarding three SNPs in CHRNA3 (CPD, AAO daily smoking), ACHE (CPD, HSI) and CHRNB4 (CPD, both AAOs).\n\nDiscussionDespite limitations, the present study shows that the genetics of tobacco smoking in SUD patients are both distinct and partially shared across smoking phenotypes, and involve metabolic and chaperone effectors of the nicotinic pathway.

Increases in drug consumption over time, also known as escalation, is a key behavioral component of substance use disorder (SUD) that is related to potential harm to users, such as overdose. Studying escalation also allows researchers to investigate the transition from casual drug use to more SUD-like drug use. Understanding the neurobiological systems that drive this transition will inform therapeutic treatments in the aim to prevent increases in drug use and the development of SUD. The kappa opioid receptor (KOR) system is typically known for its role in negative affect, which is commonly found in SUD as well. Furthermore, the KOR system has also been implicated in drug use and importantly, modulating the negative effects of drug use. However, the specific neuronal subpopulation expressing KOR involved has not been identified. Here, we first demonstrated that pharmacologically inhibiting KOR in the nucleus accumbens core (NAcC), as a whole, blocks cocaine escalation under long-access self-administration conditions. We then demonstrated that KOR expressed on ventral tegmental area (VTA) neurons but not NAcC neurons is sufficient for blocking cocaine escalation by utilizing a novel virally-mediated CRISPR-SaCas9 knock-out of the oprk1 gene. Together, this suggests that activation of KOR on VTA terminals in the NAcC drives the transition to the SUD-like phenotype of escalation of cocaine consumption.

Animal models indicate that the endocannabinoid system (ECS) plays a modulatory role in stress and reward processing, both crucially impaired in addictive disorders. Preclinical findings showed endocannabinoid-modulated synaptic plasticity in reward brain networks linked to the metabotropic-glutamate-5 receptor (mGluR5), contributing to drug-reinforcing effects and drug-seeking behavior. Although animal models postulate a link between ECS and cocaine addiction, human translational studies are lacking. Here, we tested previous preclinical findings by investigating plasma endocannabinoids (eCBs) anandamide (AEA), 2-arachidonoylglycerol (2-AG), and the related N-acylethanolamines (NAEs) palmitoylethanolamide (PEA) and oleoylethanolamide (OEA), including their interaction with cerebral mGluR5, in chronic cocaine users (CU). We compared basal plasma concentrations between chronic CU (N=103; 69 recreational CU and 34 dependent CU) and stimulant-naive healthy controls (N=92). Follow-up basal eCB/NAE plasma levels after 12 months were used for reliability and stability check (CU: N=33; controls: N=43). In an additional analysis using 11C-ABP688 positron emission tomography (PET) in a male subsample (CU: N=18; controls: N=16), we investigated the relationships between eCBs/NAEs and mGluR5 density in the brain. We found higher 2-AG plasma levels in dependent CU compared to controls and recreational CU. 2-AG levels were stable over time across all groups. In the PET-subsample, a positive association between 2-AG and mGluR5 brain density only in CU was found. Our results corroborate animal findings suggesting an alteration of the ECS in cocaine dependence and an association between peripheral 2-AG levels and cerebral mGluR5 in humans. Therefore, the ECS might be a promising pharmaco-therapeutic target for novel treatments of cocaine dependence.

ObjectivesWe aimed to determine whether chronic nicotine use, alcohol consumption, and gambling alters brain glucose metabolism. MethodsWe retrospectively analyzed data from 473 healthy men who participated in health checkups at Samsung Changwon Hospital Health Promotion Center during 2013 (baseline) and 2018 (follow-up). The health checks included a brain 18F-fluorodeoxyglucose positron emission tomography (PET), a questionnaire of tobacco use, the Alcohol Use Disorders Identification Test (AUDIT; Korean version), and the Problem Gambling Severity Index (PGSI). From brain PET scans, the mean uptake in regions-of-interest was scaled to the mean global cortical uptake by each individual, defining the standardized uptake value ratio. We established a model for tobacco use, AUDIT, and PGSI with regional SUVR as a dependent variable and tobacco use, AUDIT, and PGSI as predictors adjusted for age using Bayesian hierarchical modelling. Bayesian models were estimated using four Markov chains, each of which had 4,000 iterations including 1,000 warm-ups, thus totaling 12,000 post-warmup samples. The sampling parameters were slightly modified to facilitate convergence (max tree depth = 20). All data were analyzed using R (The R Foundation for Statistical Computing, Vienna, Austria). ResultsThis study included 131 healthy males (mean age at baseline and follow-up: 43.0 {+/-} 3.4, 48.1 {+/-} 3.3 years, respectively). Tobacco use was negatively associated with glucose metabolism in the caudate, thalamus, cingulate, and frontal lobe, and positively associated with the cerebellum, whereas AUDIT or PGSI were not associated. ConclusionTobacco use was associated with altered brain glucose metabolism in the caudate, thalamus, cingulate, frontal lobe, and the cerebellum. However, neither hazardous alcohol consumption, nor problem gambling showed any association with brain glucose metabolism. Our findings might provide new insights into the neural mechanisms of chronic nicotine use.

Opioid Use Disorder (OUD) and opioid-related deaths remain a major public health concern in the United States. Both environmental and genetic factors influence risk for OUD. We previously identified Hnrnph1 as a quantitative trait gene underlying the stimulant, rewarding, and reinforcing properties of methamphetamine. Prior work demonstrates that hnRNP H1, the RNA-binding protein encoded by Hnrnph1, post-transcriptionally regulates Oprm1 (mu opioid receptor gene) - the primary molecular target for the therapeutic and addictive properties of opioids. Because genetic variants can exert pleiotropic effects on behaviors induced by multiple drugs of abuse, in the current study, we tested the hypothesis that Hnrnph1 mutants would show reduced behavioral sensitivity to the mu opioid receptor agonist fentanyl. Hnrnph1 mutants showed reduced sensitivity to fentanyl-induced locomotor activity, along with a female-specific reduction in, and a male-specific induction of, locomotor sensitization following three, daily injections (0.2 mg/kg, i.p.). Hnrnph1 mutants also required a higher dose of fentanyl to exhibit opioid reward as measured via conditioned place preference. Male Hnrnph1 mutants showed reduced fentanyl reinforcement. Hnrnph1 mutants also showed reduced sucrose motivation, suggesting a reward deficit. No genotypic differences were observed in baseline thermal nociception, fentanyl-induced antinociception, physical or negative affective signs of opioid dependence, or in sensorimotor gating. In the context of our prior work, these findings suggest that Hnrnph1 dysfunction exerts a selective role in reducing the addiction liability to drugs of abuse (opioids and psychostimulants), which could provide new biological pathways to improve their therapeutic profiles.

Addiction to nicotine and alcohol continues to be a leading cause of death and loss of productivity as measured in disability-adjusted life years. Polymorphisms in the nicotinic acetylcholine receptor subunit 5 (CHRNA5) have been identified as risk factors associated with nicotine dependence in human genetic studies and rodent models. Whether the chrna5 function is independently relevant to phenotypes associated with disorders comorbid with substance use, and if genetic factors influence subsequent outcomes when exposure to psychoactive substances happens at an early age, are questions of interest. We generated a stable mutant line in zebrafish using the CRISPR-Cas9 technique. We found that the chrna5 mutant fish exhibit an increased acute preference to both nicotine and alcohol in the Self-Administration Zebrafish Assay (SAZA). When subjected to multi-day exposures to either, chrna5 mutants exhibited greater behavioural change, but reduced transcriptomic changes compared to WT siblings, suggesting an impaired homeostatic regulation following drug exposure. Further, chrna5 mutants exhibited drug-independent changes in appetite and circadian rhythms, suggesting a genetic predisposition to disorders often comorbid with substance dependence. We expect these results to give new insights into the operation of genes whose normal function modulates vulnerability to multi-substance use and comorbid disorders.

Recent studies have drawn the attention to the link between Alcohol Use Disorder (AUD) and the presence of pain. Indeed, the correct management of pain in patients with a previous history of AUD has been reported to decrease the risk of relapse in alcohol drinking, suggesting that in this prone population, pain may increase the vulnerability to relapse. Previous data in male rats revealed that inflammatory pain desensitizes mu opioid receptors (MORs) in the ventral tegmental area (VTA) and increases intake of high doses of heroine. Due to the relevant role of MORs in alcohol effects, we hypothesize that pain may also alter alcohol reinforcing properties and therefore affect alcohol relapse in male rats. Our microdialysis studies show that the presence of inflammatory pain blunted the increase of extracellular dopamine levels in the Nucleus Accumbens induced by 1.5g/kg of ethanol (s.c.). Moreover, we also revealed that the administration of 52 nmol of ethanol into the VTA failed to induce place preference only in inflammatory pain-suffering animals, and a higher dose (70nmol) was necessary to reverse this effect. Finally, we evaluated the effect of inflammatory pain on the alcohol deprivation effect (ADE) in long-term ethanol-experienced male rats. After four cycles of free ethanol intake and abstinence periods, inflammatory pain induced ADE without affecting its magnitude. These intriguing data reveals the impact of pain on neurochemical and behavioral effects following alcohol administration but also underscore the necessity of finding an appropriate paradigm to determine the long-term behavioral consequences.

Chronic psychostimulant use can cause long lasting changes to neural and cognitive function that persist even after long periods of abstinence. As cocaine users transition from drug use to abstinence, a parallel transition from hyperactivity to hypoactivity has been found in orbitofrontal-striatal glucose metabolism, and striatal D2/D3 receptor activity. Targeting these changes pharmacologically, using highly selective dopamine D3 receptor (D3R) antagonists and partial agonists, has shown significant promise in reducing drug-taking, and attenuating relapse in animal models of cocaine and opioid use disorder. However, much less attention has been focused on treating inflexible and potentially maladaptive non-drug behaviors following chronic psychostimulant use. Here we tested the selective D3R antagonist VK4-116 as a treatment for the long-term behavioral inflexibility in abstinent male and female rats with a prior history of chronic cocaine use. Rats were first trained to self-administer cocaine (0.75 mg/kg/reinforcer) or a sucrose liquid (10%, .04 mL/reinforcer) for 2 weeks (FR1 schedule, max 60 reinforcers in 3 hrs/ day), followed by 4 weeks of abstinence. Cognitive and behavioral flexibilities were then assessed using a sensory preconditioning (SPC) learning paradigm. Rats were given an VK4-116 (15 mg/kg, i.p.) or vehicle 30 mins prior to each SPC training session, thus creating four drug-treatment groups: sucrose-vehicle, sucrose-VK4-116, cocaine-vehicle, cocaine-VK4-116. The control groups (sucrose-vehicle, sucrose-VK4-116) demonstrated significant evidence of flexible SPC behavior, whereas cocaine use (cocaine-vehicle) disrupted SPC behavior. Remarkably, the D3R antagonist VK4-116 mitigated this cocaine deficit in the cocaine-VK4-116 group, demonstrating flexible SPC to levels comparable to the control groups. These preclinical findings demonstrate that highly selective dopamine D3R antagonists, particularly VK4-116, show significant promise as a pharmacological treatment for the long-term negative behavioral consequences of cocaine use disorder.

Relapse to cocaine use after abstinence remains a significant challenge for treating cocaine use disorder. While the mechanisms of relapse are still under investigation, adaptations in mesolimbic dopamine systems may contribute to cocaine craving and propensity for relapse. Current pharmacological treatments targeting dopamine systems are often intolerable and may have abuse potential. Therefore, identifying novel pharmacological targets for cocaine use disorder is crucial. The hypocretin/orexin system has been shown to regulate cocaine-associated behavior and dopamine transmission. Our previous studies indicated that the hypocretin receptor 1 antagonist, RTIOX-276, reduced motivation for cocaine and attenuated dopamine responses to cocaine. Importantly, the effects of RTIOX-276 on dopamine transmission persisted for at least 24 hours, suggesting lasting effects of hypocretin receptor antagonism. Here, we hypothesized that a single RTIOX-276 treatment would reduce motivation for cocaine and normalize dopamine transmission after abstinence. Rats were pre-assessed for cocaine consumption and motivation using a within-session threshold schedule before intermittent access exposure to cocaine. Rats were subsequently treated with RTIOX-276 on the first day of a 7-day abstinence period, after which they were reassessed for cocaine consumption and motivation or examined for dopamine transmission using fast-scan cyclic voltammetry in nucleus accumbens core slices. We found that a single treatment with RTIOX-276 on the first day of abstinence reduced motivation for cocaine and normalized aberrant dopamine uptake observed following intermittent access to cocaine. These findings suggest that hypocretin receptor 1 may be a viable target for reducing motivation for cocaine through alterations in dopamine transmission in the nucleus accumbens.

A major problem in treating opioid use disorder is persistence of craving after protracted abstinence. This has been modeled in rodents using the incubation of craving model, in which cue-induced drug seeking increases over the first weeks of abstinence from drug self-administration and then remains high for an extended period. Incubation has been reported for several opioids, including oxycodone, but little is known about underlying synaptic plasticity. In contrast, it is well established that incubation of cocaine and methamphetamine craving depends on strengthening of glutamate synapses in the nucleus accumbens (NAc) through incorporation of calcium-permeable AMPARs (CP-AMPARs). CP-AMPARs have higher conductance than the calcium-impermeable AMPARs that mediate NAc excitatory transmission in drug-naive animals, as well as other distinct properties. Here we examined AMPAR transmission in medium spiny neurons (MSN) of NAc core and shell subregions in rats during forced abstinence from extended-access oxycodone self-administration. In early abstinence (prior to incubation), CP-AMPAR levels were low. After 17-33 days of abstinence (when incubation is stably plateaued), CP-AMPAR levels were significantly elevated in both subregions. These results explain the prior demonstration that infusion of a selective CP-AMPAR antagonist into NAc core or shell subregions prevents expression of oxycodone incubation. Then, using transgenic rats, we found CP-AMPAR upregulation on both D1 and D2 receptor-expressing MSN, which contrasts with selective upregulation on D1 MSN after cocaine and methamphetamine incubation. Overall, our results demonstrate a common role for CP-AMPAR upregulation in psychostimulant and oxycodone incubation, albeit with differences in MSN subtype-specificity.

BackgroundCocaine use disorder (CUD) is a major public health crisis with detrimental individual and societal effects. The specific genes mediating CUD remain largely unknown. MethodsWe conducted a genome-wide association study (GWAS) using outbred N/NIH Heterogeneous Stock (HS; n = 836, female = 415, male = 421) rats. We examined multiple CUD-related phenotypes that captured acquisition of self-administration, escalation of intake, and compulsive-like responding. ResultsConsistent with the existing literature, these traits were phenotypically and genetically correlated and exhibited modest heritability (h2 = 0.07 - 0.16). We identified six genome-wide significant associations. One locus on chromosome 19 was associated with the variable time between cocaine infusions (post infusion interval) and contains several carboxylesterase genes that are orthologous to the human CES1 gene; notably, carboxylesterases metabolize cocaine. Three non-synonymous coding variants in the genes Ces1c and Ces1d were in perfect linkage disequilibrium with this locus, suggesting that one or more of them might be the causal SNP. The other 5 loci also contained promising coding and expression variants, including Trak2, a gene previously associated with CUD in human GWAS and Slc10a7, Plcl1, and Satb2 which have been associated with alcohol and tobacco use disorder. ConclusionsThis is the largest genetic study of cocaine self-administration ever conducted in any species. Our results replicate previous loci associated with CUD in humans and provide several novel biological insights including the potential of pharmacological strategies targeting carboxylesterases for the treatment of CUD.

A minority of healthy individuals (poor decision-makers, PD) exhibit a combination of behavioral traits reminiscent, at least in part, of addiction and predicting poor decision-making (DM), namely motor impulsivity, inflexibility, risk-taking, and higher motivation in Wistar Han rats. Two behavioral features, motivation and working memory (WM), play a role in DM capacities although the precise relationship is not entirely known. Additionally, we previously reported that neurotransmitters e.g., dopamine - modulation was tightly linked to the PD phenotype. The goal of the study was to investigate the detailed motivational functions in PD individuals including saccharin intake, reward-seeking or incentive behaviors under different internal states i.e., food-deprived or ad libitum. Maze-based spatial WM was also evaluated. Moreover, two inbred strains of rats, Lewis and Fisher 344 (F344) rats, known for modeling vulnerability to drug addiction and affected by substantial variations in the mesolimbic dopaminergic pathway, were run in the DM task (Rat Gambling Task, RGT). PD Wistar Han rats displayed higher saccharin intake levels and a drastic increased reward-seeking behavior on a fixed schedule. PD were more sensitive to the internal state in responding to saccharin delivery in fixed but not in progressive schedules. A few relationships were found within motivational functions, and with DM, that is a positive correlation between saccharin intake and reward-seeking behavior, and a negative correlation between saccharin intake and DM. PD were significantly not impaired in WM. Lewis and F344 rats displayed improved performance early in the task (exploration) and a higher proportion of PD was observed in Lewis as compared to F344 rats. Altogether, these findings complete the preclinical panel of behavioral functions that relate to poor DM and extend a presumed role of dopamine in such processes.

Background: Substance use disorders (SUDs), including alcohol and drug dependence, and smoking, pose a public health threat with their high prevalence and comorbidity with other diseases, and contribution to mortality. SUDs are highly correlated, and their genetic background is shared to some degree. Objectives: We aimed to investigate the genetic associations of previously reported loci for a wide range of SUDs in an unstudied Ukrainian population. Methods: We collected data from 595 individuals (339 women, 253 men), including 321 participants from two rehab centres. Based on clinical review and questionnaire data we defined drug dependence, alcohol dependence, alcohol abuse, binge drinking, smoking, opiate, amphetamine, cannabis, and hallucinogen use, along with several intermediary alcohol use and smoking variables considering the amount of use and the level of dependence. We genotyped COMT-rs4680, ADH1B-ADH1C-rs1789891, and HTR2A-rs6313, and applied logistic and ordered logistic regression assuming an additive inheritance model, controlling for the recruitment group, other substance uses, age, and sex, in the association analyses. Results: We replicate (P<0.05) the associations at COMT-rs4680 with smoking status (OR[95% CI]=1.56[1.01-2.41], P=0.047) and heaviness (1.37[1.04-1.80], P=0.026), and at ADH1B-ADH1C-rs1789891 and HTR2A-rs6313 with alcohol dependence (1.69[1.03-2.76], P=0.038 and 0.66[0.47-0.92, P=0.016], respectively). Furthermore, we provide evidence for an association at HTR2A-rs6313 with hallucinogen use (0.58[0.35-0.98], P=0.040). Conclusion: In this study on multiple SUDs we shed light on the genetic background of SUDs in Ukrainians and provide further evidence that variation at COMT is mainly associated with smoking, at ADH1B-ADH1C with alcohol-related variables, whereas HTR2A is a more general SUD-associated locus.

Addiction is viewed as maladaptive glutamate-mediated neuroplasticity that is regulated, in part, by calcium-permeable AMPA receptor (CP-AMPAR) activity. However, the contribution of CP-AMPARs to alcohol-seeking behavior remains to be elucidated. We evaluated CP-AMPAR activity in the basolateral amygdala (BLA) as a potential target of alcohol that also regulates alcohol self-administration in C57BL/6J mice. Operant self-administration of sweetened alcohol increased spontaneous EPSC frequency in BLA neurons that project to the nucleus accumbens as compared to behavior-matched sucrose controls indicating an alcohol-specific upregulation of synaptic activity. Bath application of the CP-AMPAR antagonist NASPM decreased evoked EPSC amplitude only in alcohol self-administering mice indicating alcohol-induced synaptic insertion of CP-AMPARs in BLA projection neurons. Moreover, NASPM infusion in the BLA dose-dependently decreased the rate of operant alcohol self-administration providing direct evidence for CP-AMPAR regulation of alcohol reinforcement. Since most CP-AMPARs are GluA1-containing, we asked if alcohol alters the activation state of GluA1-containing AMPARs. Immunocytochemistry results showed elevated GluA1-S831 phosphorylation in the BLA of alcohol as compared to sucrose mice. To investigate mechanistic regulation of alcohol self-administration by GluA1-containing AMPARs, we evaluated the necessity of GluA1 trafficking using a TET-ON AAV encoding a dominant-negative GluA1 c-terminus (GluA1ct) that blocks activity-dependent synaptic delivery of native GluA1-containing AMPARs. GluA1ct expression in the BLA reduced alcohol self-administration with no effect on sucrose controls. These results show that CP-AMPAR activity and GluA1 trafficking in the BLA mechanistically regulate the reinforcing effects of sweetened alcohol. Pharmacotherapeutic targeting these mechanisms of maladaptive neuroplasticity may aid medical management of alcohol use disorder.

Tobacco use disorder is a chronic condition characterized by compulsive nicotine use and withdrawal symptoms after smoking cessation. Smoking is the leading preventable cause of morbidity and mortality worldwide. Smoking cessation leads to anhedonia, which is an inability to experience pleasure from previously enjoyed activities and is caused by dysregulation of the brains reward and stress systems. It is also a key withdrawal symptom that contributes to relapse to smoking after a period of abstinence. To better understand the development of anhedonia, we investigated its onset and time course in rats that self-administered nicotine. Rats were implanted with intracranial self-stimulation (ICSS) electrodes to assess reward function and intravenous catheters for nicotine self-administration. Elevations in ICSS brain reward thresholds reflect decreased sensitivity to rewarding electrical stimuli, indicating anhedonia. The rats self-administered 0.06 mg/kg of nicotine intermittently, three days per week, for seven weeks. Brain reward thresholds were determined once a week 24 h after nicotine self-administration during weeks 1 to 3, and at 12, 24, and 48 h during weeks 4, 5, and 7. Elevations in brain reward thresholds were not observed during the first four weeks of nicotine self-administration. However, the brain reward thresholds were elevated in both weeks 5 and 7 at least 12 h after nicotine self-administration, indicating that anhedonia emerges gradually and then persists. As withdrawal severity gradually increases, smoking cessation may become more challenging. Therefore, behavioral or pharmacological interventions soon after smoking initiation are critical to prevent the development of a tobacco use disorder. HighlightsO_LIIntermittent long-access nicotine self-administration leads to dependence in rats. C_LIO_LICessation of nicotine intake increased reward thresholds after 5 and 7 weeks. C_LIO_LIAnhedonia emerged after 5 weeks of long-access nicotine self-administration. C_LIO_LIBrain reward thresholds increased during spontaneous and precipitated withdrawal. C_LIO_LIResponse latencies increased during both spontaneous and precipitated withdrawal. C_LI

The endocannabinoid system is prominently implicated in the control of cocaine reinforcement due to its relevant role in synaptic plasticity and neurotransmitter modulation in the mesocorticolimbic system. The inhibition of fatty acid amide hydrolase (FAAH), and the resulting increase in anandamide and other N-acylethanolamines, represents a promising strategy for reducing drug seeking. In the present study, we aimed to assess the effects of the FAAH inhibitor URB597 (1 mg/kg) on crucial features of cocaine addictive-like behaviour in mice. Therefore, we tested the effects of URB597 on acquisition of cocaine (0.6 mg/kg/inf) self-administration, compulsive-like cocaine intake and cue-induced drug-seeking behaviour during withdrawal. URB597 reduced cocaine intake under conditioned punishment while having no impact on acquisition. This result was associated to increased cannabinoid receptor 1 gene expression in the ventral striatum and medium spiny neurons activation in the nucleus accumbens shell. Moreover, URB597 reduced cue-induced drug-seeking behaviour during prolonged abstinence and prevented the withdrawal-induced increase in FAAH gene expression in the ventral striatum. In this case, URB597 decreased activation of medium spiny neurons in the nucleus accumbens core. Our findings evidence the prominent role of endocannabinoids in the development of cocaine addictive-like behaviours and support the potential of FAAH inhibition as a therapeutical target for the treatment of cocaine addiction.

The insular cortex has been identified as a promising target in brain-based therapies for Tobacco Use Disorder, and has three major sub-regions (ventral anterior, dorsal anterior, and posterior) that serve distinct functional networks. How these subregions and associated networks contribute to nicotine dependence has not been well understood, and therefore was the subject of this study. Forty-seven individuals (24 women; 18-45 years old) who smoked cigarettes daily rated their dependence using the Fagerstrom Test for Nicotine Dependence (FTND), abstained from smoking overnight (~12 h), and underwent resting-state functional MRI. Correlations between dependence and resting-state functional connectivity (RSFC) of the major insular sub-regions were evaluated using whole-brain-corrected voxel-wise analyses and post-hoc region-of-interest (ROI) analyses. Dependence was analyzed both as a unitary (FTND total score) and bivariate construct - two FTND factors ("morning smoking" and "daytime smoking"). Dependence was negatively correlated with connectivity of both the right dorsal and left ventral anterior insula with the left precuneus, and with connectivity of the left posterior insula to the left putamen. In post-hoc analyses, dependence correlated negatively with connectivity between all anterior insula subregions and the left precuneus, and with bilateral posterior insula connectivity with the left posterior putamen. The latter finding was driven by "daytime smoking". These results suggest an anterior-posterior distinction in functional insular networks associated with different dimensions of nicotine dependence, with greater dependence linked to weaker connectivity. They may inform therapeutic approaches involving brain stimulation that may elicit differential clinical outcomes depending on the insular subnetwork targeted.

RationaleThe development and progression of alcohol use disorder (AUD) is widely viewed as maladaptive neuroplasticity. The transmembrane alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR) regulatory protein {gamma}8 (TARP {gamma}-8) is a molecular mechanism of neuroplasticity that has not been evaluated in AUD or other addictions. ObjectiveTo address this gap in knowledge, we evaluated the mechanistic role of TARP {gamma}-8 bound AMPAR activity in the basolateral amygdala (BLA) and ventral CA3 hippocampus (vHPC) in the positive reinforcing effects of alcohol, which drive repetitive alcohol use throughout the course of AUD, in C57BL/6J mice. These brain regions were selected because they exhibit high levels of TARP {gamma}-8 expression and send glutamate projections to the nucleus accumbens (NAc), which is a key nucleus in the brain reward pathway. Methods and ResultsSite-specific pharmacological inhibition of AMPARs bound to TARP {gamma}-8 in the BLA via bilateral infusion of the selective negative modulator JNJ-55511118 significantly decreased operant alcohol self-administration with no effect on sucrose self-administration in behavior-matched controls. Temporal analysis showed that reduction of alcohol-reinforced responding occurred >25 min after the onset of responding, consistent with a blunting of the positive reinforcing effects of alcohol in the absence of nonspecific behavioral effects. In contrast, inhibition of TARP {gamma}-8 bound AMPARs in the vHPC selectively decreased sucrose self-administration with no effect on alcohol. ConclusionsThis study reveals a novel brain region-specific role of TARP {gamma}-8 bound AMPARs as a molecular mechanism of the positive reinforcing effects of alcohol and non-drug rewards.

BackgroundThe mesolimbic dopamine system plays a central role in motivating behavior. In alcohol use disorder (AUD), this system is thought to be dysfunctional, leading to hyperreactivity to alcohol-related cues. In contrast, evidence on how individuals with AUD respond to alcohol-unrelated reward cues is inconclusive, and the motivation for social rewards has not yet been investigated. MethodsTo address this gap, 36 individuals with AUD and 34 healthy controls performed an incentive delay task to assess social reward anticipation with a monetary and a non-reward control condition while undergoing functional magnetic resonance imaging. The ventral striatum was defined as region of interest because of its central role in neuronal circuits for motivation. ResultsNeither behavioral nor neuroimaging data provided any evidence of reduced motivation for social or monetary rewards in AUD. Exploratory whole-brain analyses only revealed stronger activation in the occipital/cuneal cortex in individuals with AUD than in healthy controls across all trials. ConclusionTogether, these results suggest that sensitivity to social reward cues is not fundamentally impaired in AUD. Furthermore, they imply that motivational changes related to the substance do not generally alter the reward potential of alcohol-unrelated domains in AUD, opening perspectives for social-behavioral treatments for this disorder.