Despite persistent public health initiatives, many women continue to smoke during pregnancy. Since maternal smoking has been linked to persisting sex-dependent neurobehavioral deficits in offspring, some consider nicotine to be a safer alternative to tobacco during pregnancy, and the use of electronic nicotine delivery systems is on the rise. We presently show, however, that sustained exposure to low doses of nicotine during fetal development, approximating plasma levels seen clinically with the nicotine patch, produces substantial changes in developing corticostriatal dopamine systems in adolescence. Briefly, pregnant dams were implanted on gestational day 4 with an osmotic minipump that delivered either saline (GS) or nicotine (3 mg/kg/day) (GN) for two weeks. At birth, pups were cross-fostered with treatment naïve dams and were handled daily. Biochemical analyses, signaling assays, and behavioral responses to cocaine were assessed on postnatal day 32, representative of adolescence in the rodent. GN treatment had both sex-dependent and sex-independent effects on prefrontal dopamine systems, altering Catechol-O-methyl transferase (COMT)-dependent dopamine turnover in males and norepinephrine transporter (NET) binding expression in both sexes. GN enhanced cocaine-induced locomotor activity in females, concomitant with GN-induced reductions in striatal dopamine transporter (DAT) binding. GN enhanced ventral striatal D2-like receptor expression and G-protein coupling, while altering the roles of D2 and D3 receptors in cocaine-induced behaviors. These data show that low-dose prenatal nicotine treatment sex-dependently alters corticostriatal dopamine system development, which may underlie clinical deficits seen in adolescents exposed to tobacco or nicotine in utero.

Cross-species translational approaches to human genomic analyses are lacking. The present study uses an integrative framework to investigate how genes associated with nicotine use in model organisms contribute to the genetic architecture of human tobacco consumption. First, we created a model organism geneset by collecting results from five animal models of nicotine exposure (RNA expression changes in brain) and then tested the relevance of these genes and flanking genetic variation using genetic data from human cigarettes per day (UK BioBank N = 123,844; all European Ancestry). We tested three hypotheses: (1) DNA variation in, or around, the 'model organism geneset' will contribute to the heritability to human tobacco consumption, (2) that the model organism genes will be enriched for genes associated with human tobacco consumption, and (3) that a polygenic score based off our model organism geneset will predict tobacco consumption in the AddHealth sample (N = 1667; all European Ancestry). Our results suggested that: (1) model organism genes accounted for ~5-36% of the observed SNP-heritability in human tobacco consumption (enrichment: 1.60-31.45), (2) model organism genes, but not negative control genes, were enriched for the gene-based associations (MAGMA, H-MAGMA, SMultiXcan) for human cigarettes per day, and (3) polygenic scores based on our model organism geneset predicted cigarettes per day in an independent sample. Altogether, these findings highlight the advantages of using multiple species evidence to isolate genetic factors to better understand the etiological complexity of tobacco and other nicotine consumption.

Smoking influences body weight such that smokers weigh less than non-smokers and smoking cessation often leads to weight increase. The relationship between body weight and smoking is partly explained by the effect of nicotine on appetite and metabolism. However, the brain reward system is involved in the control of the intake of both food and tobacco. We evaluated the effect of single-nucleotide polymorphisms (SNPs) affecting body mass index (BMI) on smoking behavior, and tested the 32 SNPs identified in a meta-analysis for association with two smoking phenotypes, smoking initiation (SI) and the number of cigarettes smoked per day (CPD) in an Icelandic sample (N=34,216 smokers). Combined according to their effect on BMI, the SNPs correlate with both SI (r=0.019, P=0.00054) and CPD (r=0.032, P=8.0 × 10(-7)). These findings replicate in a second large data set (N=127,274, thereof 76,242 smokers) for both SI (P=1.2 × 10(-5)) and CPD (P=9.3 × 10(-5)). Notably, the variant most strongly associated with BMI (rs1558902-A in FTO) did not associate with smoking behavior. The association with smoking behavior is not due to the effect of the SNPs on BMI. Our results strongly point to a common biological basis of the regulation of our appetite for tobacco and food, and thus the vulnerability to nicotine addiction and obesity.

It has been proposed that vulnerability to nicotine addiction is moderated by variation at the μ-opioid receptor locus (OPRM1), but results from human studies vary and prospective studies based on genotype are lacking. We have developed a humanized mouse model of the most common functional OPRM1 polymorphism rs1799971_A>G (A118G). Here we use this model system together with a cohort of German youth to examine the role of the OPRM1 A118G variation on nicotine reward. Nicotine reinforcement was examined in the humanized mouse model using i.v. self-administration. Male (n=17) and female (n=26) mice homozygous either for the major human A allele (AA) or the minor G allele (GG) underwent eight daily 2 h sessions of nicotine self-administration. Furthermore, male (n=104) and female (n=118) subjects homozygous for the A allele or carrying the G allele from the Mannheim Study of Children at Risk were evaluated for pleasurable and unpleasant experiences during their initial smoking experience. A significant sex-by-genotype effect was observed for nicotine self-administration. Male 118GG mice demonstrated higher nicotine intake than male 118AA mice, suggesting increased nicotine reinforcement. In contrast, there was no genotype effect in female mice. Human male G allele carriers reported increased pleasurable effects from their first smoking experience, as compared to male homozygous A, female G and female homozygous A allele carriers. The 118G allele appears to confer greater sensitivity to nicotine reinforcement in males, but not females.

The majority of smokers relapse even after successfully quitting because of the craving to smoking after unexpectedly re-exposed to smoking-related cues. This conditioned craving is mediated by reward memories that are frequently experienced and stubbornly resistant to treatment. Reconsolidation theory posits that well-consolidated memories are destabilized after retrieval, and this process renders memories labile and vulnerable to amnestic intervention. This study tests the retrieval reconsolidation procedure to decrease nicotine craving among people who smoke. In this study, 52 male smokers received a single dose of propranolol (n = 27) or placebo (n = 25) before the reactivation of nicotine-associated memories to impair the reconsolidation process. Craving for smoking and neural activity in response to smoking-related cues served as primary outcomes. Functional magnetic resonance imaging was performed during the memory reconsolidation process. The disruption of reconsolidation by propranolol decreased craving for smoking. Reactivity of the postcentral gyrus in response to smoking-related cues also decreased in the propranolol group after the reconsolidation manipulation. Functional connectivity between the hippocampus and striatum was higher during memory reconsolidation in the propranolol group. Furthermore, the increase in coupling between the hippocampus and striatum positively correlated with the decrease in craving after the reconsolidation manipulation in the propranolol group. Propranolol administration before memory reactivation disrupted the reconsolidation of smoking-related memories in smokers by mediating brain regions that are involved in memory and reward processing. These findings demonstrate the noradrenergic regulation of memory reconsolidation in humans and suggest that adjunct propranolol administration can facilitate the treatment of nicotine dependence. The present study was pre-registered at ClinicalTrials.gov (registration no. ChiCTR1900024412).

We conducted a 1000 Genomes-imputed genome-wide association study (GWAS) meta-analysis for nicotine dependence, defined by the Fagerström Test for Nicotine Dependence in 17 074 ever smokers from five European-ancestry samples. We followed up novel variants in 7469 ever smokers from five independent European-ancestry samples. We identified genome-wide significant association in the alpha-4 nicotinic receptor subunit (CHRNA4) gene on chromosome 20q13: lowest P=8.0 × 10(-9) across all the samples for rs2273500-C (frequency=0.15; odds ratio=1.12 and 95% confidence interval=1.08-1.17 for severe vs mild dependence). rs2273500-C, a splice site acceptor variant resulting in an alternate CHRNA4 transcript predicted to be targeted for nonsense-mediated decay, was associated with decreased CHRNA4 expression in physiologically normal human brains (lowest P=7.3 × 10(-4)). Importantly, rs2273500-C was associated with increased lung cancer risk (N=28 998, odds ratio=1.06 and 95% confidence interval=1.00-1.12), likely through its effect on smoking, as rs2273500-C was no longer associated with lung cancer after adjustment for smoking. Using criteria for smoking behavior that encompass more than the single 'cigarettes per day' item, we identified a common CHRNA4 variant with important regulatory properties that contributes to nicotine dependence and smoking-related consequences.

Myelination defects in the central nervous system (CNS) are associated with various psychiatric disorders, including drug addiction. As these disorders are often observed in individuals prenatally exposed to cigarette smoking, we tested the hypothesis that such exposure impairs central myelination in adolescence, an important period of brain development and the peak age of onset of psychiatric disorders. Pregnant Sprague Dawley rats were treated with nicotine (3 mg kg(-1) per day; gestational nicotine (GN)) or gestational saline via osmotic mini pumps from gestational days 4-18. Both male and female offsprings were killed on postnatal day 35 or 36, and three limbic brain regions, the prefrontal cortex (PFC), caudate putamen and nucleus accumbens, were removed for measurement of gene expression and determination of morphological changes using quantitative real-time PCR (qRT-PCR) array, western blotting and immunohistochemical staining. GN altered myelin gene expression at both the mRNA and protein levels, with striking sex differences. Aberrant expression of myelin-related transcription and trophic factors was seen in GN animals, which correlated highly with the alterations in the myelin gene expression. These correlations suggest that these factors contribute to GN-induced alterations in myelin gene expression and also indicate abnormal function of oligodendrocytes (OLGs), the myelin-producing cells in the CNS. It is unlikely that these changes are attributable solely to an alteration in the number of OLGs, as the cell number was changed only in the PFC of GN males. Together, our findings suggest that abnormal brain myelination underlies various psychiatric disorders and drug abuse associated with prenatal exposure to cigarette smoke.

The significant heterogeneity in smoking behavior among smokers, coupled with the inconsistent efficacy of approved smoking cessation therapies, supports the presence of individual variations in the mechanisms underlying smoking. This emphasizes the need to shift from standardized to personalized smoking cessation therapies. However, informed precision medicine demands precision fundamental research. Tobacco smoking is influenced and sustained by diverse psychopharmacological interactions between nicotine and environmental stimuli. In the classical experimental rodent model for studying tobacco dependence, namely intravenous self-administration of nicotine, seeking behavior is reinforced by the combined delivery of nicotine and a discrete cue (nicotine+cue). Whether self-administration behavior is driven by the same psychopharmacological mechanisms across individual rats remains unknown and unexplored. To address this, we employed behavioral pharmacology and unbiased cluster analysis to investigate individual differences in the mechanisms supporting classical intravenous nicotine self-administration (0.04 mg/kg/infusion) in male outbred Sprague-Dawley rats. Our analysis identified two clusters: one subset of rats sought nicotine primarily for its reinforcing effects, while the second subset sought nicotine to enhance the reinforcing effects of the discrete cue. Varenicline (1 mg/kg i.p.) reduced seeking behavior in the former group, whereas it tended to increase in the latter group. Crucially, despite this fundamental qualitative difference revealed by behavioral manipulation, the two clusters exhibited quantitatively identical nicotine+cue self-administration behavior. The traditional application of rodent models to study the reinforcing and addictive effects of nicotine may mask individual variability in the underlying motivational mechanisms. Accounting for this variability could significantly enhance the predictive validity of translational research.

Smoking cessation leads to a dysphoric state and this increases the risk for relapse. Animal studies indicate that the dysphoric state associated with nicotine withdrawal is at least partly mediated by an increase in corticotropin-releasing factor (CRF) release in the central nucleus of the amygdala (CeA). In the present study, we investigated whether a sustained overexpression of CRF in the CeA affects the dysphoric-like state associated with nicotine withdrawal. To study brain reward function, rats were prepared with intracranial self-stimulation (ICSS) electrodes in the medial forebrain bundle. An adeno-associated virus (AAV, pseudotype 2/5) was used to overexpress CRF or green fluorescent protein (GFP, control) in the CeA and minipumps were used to induce nicotine dependence. The AAV2/5-CRF vector induced a 40% increase in CRF protein and mRNA levels in the CeA. Administration of the nicotinic receptor antagonist mecamylamine (precipitated withdrawal) or nicotine pump removal (spontaneous withdrawal) led to elevations in ICSS thresholds. Elevations in ICSS thresholds are indicative of a dysphoric-like state. The overexpression of CRF did not affect baseline ICSS thresholds but diminished the elevations in ICSS thresholds associated with precipitated and spontaneous nicotine withdrawal. The real-time reverse transcriptase (RT)-PCR analysis showed that the overexpression of CRF led to a decrease in CRF1 mRNA levels and an increase in CRF2 mRNA levels in the CeA. In conclusion, the overexpression of CRF in the CeA diminishes the dysphoric-like state associated with nicotine withdrawal and this might be driven by neuroadaptive changes in CRF1 and CRF2 receptor gene expression.

Variants in serotonergic genes are implicated in nicotine dependence (ND) in subjects of European and African origin, but their involvement with smoking in Asians is largely unknown. Moreover, mechanisms underlying the ND risk-associated single-nucleotide polymorphisms (SNPs) in these genes are rarely investigated. The Fagerström Test for Nicotine Dependence (FTND) score was used to assess ND in 2616 male Chinese Han smokers. Both association and interaction analysis were used to examine the association of variants in the serotonergic genes with FTND. Further, expression and methylation quantitative trait loci (cis-mQTL) analysis was employed to determine the association of individual SNPs with the extent of methylation of each CpG locus. Individual SNP-based association analysis revealed that rs1176744 in HTR3B was marginally associated with FTND (p = 0.042). Haplotype-based association analysis found that one major haplotype, T-T-A-G, formed by SNPs rs3758987-rs4938056-rs1176744-rs2276305, located in the 5' region of HTR3B, showed a significant association with FTND (p = 0.00025). Further, a significant genetic interactive effect affecting ND was detected among SNPs rs10160548 in HTR3A, and rs3758987, rs2276305, and rs1672717 in HTR3B (p = 0.0074). Finally, we found four CpG sites (CpG_4543549, CpG_4543464, CpG_4543682, and CpG_4546888) to be significantly associated with three cis-mQTL SNPs (i.e., rs3758987, rs4938056, and rs1176744) located in our detected haplotype within HTR3B. In sum, we showed SNP rs1176744 (Tyr129Ser) to be associated with ND. Together with the SNPs rs3758987 and rs4938056 in HTR3B, they formed a major haplotype, which had significant association with ND. We further showed these SNPs contribute to ND through four methylated sites in HTR3B. All these findings suggest that variants in the serotonergic system play an important role in ND in the Chinese Han population. More importantly, these findings demonstrated that the involvement of this system in ND is through gene-by-gene interaction and methylation.

Smoking and major depression frequently co-occur, at least in part due to shared genetic risk. However, the nature of the shared genetic basis is poorly understood. To detect genetic risk variants for comorbid nicotine dependence (ND) and major depression (MD), we conducted genome-wide association study (GWAS) in two samples of African-American participants (Yale-Penn 1 and 2) using linear mixed model, followed by meta-analysis. 3724 nicotine-exposed subjects were analyzed: 2596 from Yale-Penn-1 and 1128 from Yale-Penn-2. Continuous measures (Fagerström Test for Nicotine Dependence (FTND) scores and DSM-IV MD criteria) rather than disorder status were used to maximize the power of the GWAS. Genotypes were ascertained using the Illumina HumanOmni1-Quad array (Yale-Penn-1 sample) or the Illumina HumanCore Exome array (Yale-Penn-2 sample), followed by imputation based on the 1000 Genomes reference panel. An intronic variant at the GRIA4 locus, rs68081839, was significantly associated with ND-MD comorbidity (β = 0.69 [95% CI, 0.43-0.89], P = 1.53 × 10-8). GRIA4 encodes an AMPA-sensitive glutamate receptor that mediates fast excitatory synaptic transmission and neuroplasticity. Conditional analyses revealed that the association was explained jointly by both traits. Enrichment analysis showed that the top risk genes and genes co-expressed with GRIA4 are enriched in cell adhesion, calcium ion binding, and synapses. They also have enriched expression in the brain and they have been implicated in the risk for other neuropsychiatric disorders. Further research is needed to determine the replicability of these findings and to identify the biological mechanisms through which genetic risk for each condition is conveyed.

Nicotine dependence (ND) is a worldwide health problem. Numerous genetic studies have demonstrated a significant association of variants in nicotinic acetylcholine receptors (nAChRs) with smoking behaviors. However, most of these studies enrolled only subjects of European or African ancestry. In addition, although an increasing body of evidence implies a causal connection of single-nucleotide polymorphisms (SNPs) and epigenetic regulation of gene expression, few studies of this issue have been reported. In this study, we performed both association and interaction analysis for 67 SNPs in CHRNA3-A5, CHRNA7, CHRNB2, and CHRNB4 with ND in a Chinese Han population (N = 5055). We further analyzed cis-mQTL for the three most significant SNPs and 5580 potential methylation loci within these target gene regions. Our results indicated that the SNPs rs1948 and rs7178270 in CHRNB4 and rs3743075 in CHRNA3 were significantly associated with the Fagerström Test for Nicotine Dependence (FTND) score (p = 6.6 × 10-5; p = 2.0 × 10-4, and p = 7.0 × 10-4, respectively). Haplotype-based association analysis revealed that two major haplotypes, T-G and C-A, formed by rs3743075-rs3743074 in CHRNA3, and other two major haplotypes, A-G-C and G-C-C, formed by rs1948-rs7178270-rs17487223 in CHRNB4, were significantly associated with the FTND score (p ≤ 8.0 × 10-4). Further, we found evidence for the presence of significant interaction among variants within CHRNA3/B4/A5, CHRNA4/B2/A5, and CHRNA7 in affecting ND, with corresponding p values of 5.8 × 10-6, 8.0 × 10-5, and 0.012, respectively. Finally, we identified two CpG sites (CpG_2975 and CpG_3007) in CHRNA3 that are significantly associated with three cis-mQTL SNPs (rs1948, rs7178270, rs3743075) in the CHRNA5/A3/B4 cluster (p ≤ 1.9 × 10-6), which formed four significant CpG-SNP pairs in our sample. Together, we revealed at least three novel SNPs in CHRNA3 and CHRNB4 to be significantly associated with the FTND score. Further, we showed that these significant variants contribute to ND via two methylated sites, and we demonstrated significant interaction affecting ND among variants in CHRNA5/A3/B4, CHRNA7, and CHRNA4/B2/A5. In sum, these findings provide robust evidence that SNPs in nAChR genes convey a risk of ND in the Chinese Han population.

While polygenic risk scores (PRS) have been shown to predict many diseases and risk factors, the potential of genomic prediction in harm caused by alcohol use has not yet been extensively studied. Here, we built a novel polygenic risk score of 1.1 million variants for alcohol consumption and studied its predictive capacity in 96,499 participants from the FinnGen study and 39,695 participants from prospective cohorts with detailed baseline data and up to 25 years of follow-up time. A 1 SD increase in the PRS was associated with 11.2 g (=0.93 drinks) higher weekly alcohol consumption (CI = 9.85-12.58 g, p = 2.3 × 10-58). The PRS was associated with alcohol-related morbidity (4785 incident events) and the risk estimate between the highest and lowest quintiles of the PRS was 1.83 (95% CI = 1.66-2.01, p = 1.6 × 10-36). When adjusted for self-reported alcohol consumption, education, marital status, and gamma-glutamyl transferase blood levels in 28,639 participants with comprehensive baseline data from prospective cohorts, the risk estimate between the highest and lowest quintiles of the PRS was 1.58 (CI = 1.26-1.99, p = 8.2 × 10-5). The PRS was also associated with all-cause mortality with a risk estimate of 1.33 between the highest and lowest quintiles (CI = 1.20-1.47, p = 4.5 × 10-8) in the adjusted model. In conclusion, the PRS for alcohol consumption independently associates for both alcohol-related morbidity and all-cause mortality. Together, these findings underline the importance of heritable factors in alcohol-related health burden while highlighting how measured genetic risk for an important behavioral risk factor can be used to predict related health outcomes.

Genome-wide association studies (GWAS) identify genetic variants associated with a trait, regardless of how those variants are associated with the outcome. Characterizing whether variants for psychiatric outcomes operate via specific versus general pathways provides more informative measures of genetic risk. In the current analysis, we used multivariate GWAS to tease apart variants associated with problematic alcohol use (ALCP-total) through either a shared risk for externalizing (EXT) or a problematic alcohol use-specific risk (ALCP-specific). SNPs associated with ALCP-specific were primarily related to alcohol metabolism. Genetic correlations showed ALCP-specific was predominantly associated with alcohol use and other forms of psychopathology, but not other forms of substance use. Polygenic scores for ALCP-total were associated with multiple forms of substance use, but polygenic scores for ALCP-specific were only associated with alcohol phenotypes. Polygenic scores for both ALCP-specific and EXT show different patterns of associations with alcohol misuse across development. Our results demonstrate that focusing on both shared and specific risk can better characterize pathways of risk for substance use disorders. Parsing risk pathways will become increasingly relevant as genetic information is incorporated into clinical practice.

Understanding molecular processes that link comorbid traits such as addictions and mental disorders can provide novel therapeutic targets. Neuregulin signaling pathway (NSP) has previously been implicated in schizophrenia, a neurodevelopmental disorder with high comorbidity to smoking. Using a Finnish twin family sample, we have previously detected association between nicotine dependence and ERBB4 (a neuregulin receptor), and linkage for smoking initiation at the ERBB4 locus on 2q33. Further, Neuregulin3 has recently been shown to associate with nicotine withdrawal in a behavioral mouse model. In this study, we scrutinized association and linkage between 15 036 common, low frequency and rare genetic variants in 10 NSP genes and phenotypes encompassing smoking and alcohol use. Using the Finnish twin family sample (N=1998 from 740 families), we detected 66 variants (representing 23 LD blocks) significantly associated (false discovery rate P<0.05) with smoking initiation, nicotine dependence and nicotine withdrawal. We comprehensively annotated the associated variants using expression (eQTL) and methylation quantitative trait loci (meQTL) analyses in a Finnish population sample. Among the 66 variants, we identified 25 eQTLs (in NRG1 and ERBB4), 22 meQTLs (in NRG3, ERBB4 and PSENEN), a missense variant in NRG1 (rs113317778) and a splicing disruption variant in ERBB4 (rs13385826). Majority of the QTLs in blood were replicated in silico using publicly available databases, with additional QTLs observed in brain. In conclusion, our results support the involvement of NSP in smoking behavior but not in alcohol use and abuse, and disclose functional potential for 56 of the 66 associated single-nucleotide polymorphism.

Smoking is partly attributed to alterations of reward processing. However, findings on the neurobiological mechanisms that underlie smoking-related and smoking-unrelated reward processing in smokers have been inconsistent. Neuroimaging experiments that used functional magnetic resonance imaging (fMRI) and reported brain responses to smoking-related cues and nonsmoking reward-related cues in smokers and healthy controls as coordinates in a standard anatomic reference space were identified by searching the PubMed, Embase, and Web of Science databases up to December 2018. Three meta-analyses were performed using random-effect nonparametric statistics with Seed-based d Mapping software, with brain activity contrast from individual studies as the input. The striatum showed higher activation in response to smoking-related cues compared with neutral cues in 816 smokers from 28 studies and lower activation in response to nonsmoking reward-related cues in 275 smokers compared with 271 healthy control individuals from 13 studies. The relative reactivity of the putamen to smoking-related cues increased in 108 smokers compared with 107 healthy controls from seven studies. Meta-regression showed that smokers with a greater severity of nicotine dependence exhibited less engagement of the striatum in response to both smoking-related cues and nonsmoking reward-related cues. The present results reveal the disruption of reward system function in smokers and provide new insights into diverging theories of addiction. With the escalation of nicotine dependence, nicotine appears to exert dynamic effects on reward processing, based on incentive sensitization theory and reward deficiency syndrome theory.

Despite the benefits associated with longer buprenorphine treatment duration (i.e., >180 days) (BTD) for opioid use disorder (OUD), retention remains poor. Research on the impact of co-occurring psychiatric issues on BTD has yielded mixed results. It is also unknown whether the genetic risk in the form of polygenic scores (PGS) for OUD and other comorbid conditions, including problematic alcohol use (PAU) are associated with BTD. We tested the association between somatic and psychiatric comorbidities and long BTD and determined whether PGS for OUD-related conditions was associated with BTD. The study included 6686 individuals with a buprenorphine prescription that lasted for less than 6 months (short-BTD) and 1282 individuals with a buprenorphine prescription that lasted for at least 6 months (long-BTD). Recorded diagnosis of substance addiction and disorders (Odds Ratio (95% CI) = 22.14 (21.88-22.41), P = 2.8 × 10-116), tobacco use disorder (OR (95% CI) = 23.4 (23.13-23.68), P = 4.5 × 10-111), and bipolar disorder (OR(95% CI) = 9.70 (9.48-9.92), P = 1.3 × 10-91), among others, were associated with longer BTD. The PGS of OUD and several OUD co-morbid conditions were associated with any buprenorphine prescription. A higher PGS for OUD (OR per SD increase in PGS (95%CI) = 1.43(1.16-1.77), P = 0.0009), loneliness (OR(95% CI) = 1.39(1.13-1.72), P = 0.002), problematic alcohol use (OR(95%CI) = 1.47(1.19-1.83), P = 0.0004), and externalizing disorders (OR(95%CI) = 1.52(1.23 to 1.89), P = 0.0001) was significantly associated with long-BTD. Associations between BTD and the PGS of depression, chronic pain, nicotine dependence, cannabis use disorder, and bipolar disorder did not survive correction for multiple testing. Longer BTD is associated with diagnoses of psychiatric and somatic conditions in the EHR, as is the genetic score for OUD, loneliness, problematic alcohol use, and externalizing disorders.

Elevated drug-cue elicited brain activity is one of the most widely cited, transdiagnostically relevant traits of substance dependent populations. These populations, however, are typically studied in isolation. The goal of this study was to prospectively investigate the spatial topography of drug-cue reactivity in a large set of individuals dependent on either cocaine, alcohol, or nicotine. Functional MRI data was acquired from 156 substance dependent individuals (55 cocaine, 53 alcohol, and 48 nicotine) as they performed a standardized drug-cue exposure task. Clusters of significant activation to drug-cues relative to neutral cues ('hot spots') were isolated for each individual. K-means clustering was used to classify the spatial topography of the hotspots in the data set. The percentage of hotspots that would be reached at several distances (2-5 cm) of transcranial magnetic stimulation (TMS) were calculated. One hundred and three participants had at least one cluster of significant frontal cortex activity (66%). K-means revealed 3 distinct clusters within the medial prefrontal cortex (MPFC), left inferior frontal gyrus/insula, right premotor cortex. For the group as a whole (and for alcohol users and nicotine users independently), medial prefrontal cortex (BA 10) was the location of the greatest number of hotspots. The frontal pole was cortical location closest to the largest percentage of hotspots. While there is individual variability in the location of the cue-elicited 'hot spot' these data demonstrate that elevated BOLD signal to drug cues in the MPFC may be a transdiagnostic endophenotype of addiction which may also be a fruitful neuromodulation target.

Alcohol dependence (AD) frequently co-occurs with major depressive disorder (MDD). While this comorbidity is associated with an increase in disease burden, worse treatment outcomes, and greater economic costs, the underlying neurobiology remains poorly understood. A recent large-scale GWAS of MDD has identified a locus in the TMEM161B-MEF2C region (rs10514299) as a novel risk variant; however, the biological relevance of this variant has not yet been studied. Given previous reports of disrupted reward processing in both AD and MDD, we hypothesized that rs10514299 would be associated with differences in striatal BOLD responses during reward/loss anticipation in AD. DNA samples from 45 recently detoxified patients with AD and 45 healthy controls (HC) were genotyped for rs10514299. Participants performed the Monetary Incentive Delay task in a 3-Tesla MRI scanner. Effects of rs10514299 on striatal activation during anticipation of high/low reward/loss were investigated. Furthermore, we examined associations between rs10514299 and lifetime AD diagnosis in two independent clinical samples [NIAAA: n = 1858 (1123 cases, 735 controls); SAGE: n = 3838 (1848 cases, 1990 controls)], as well as its association with depression severity in a subsample of individuals with a lifetime AD diagnosis (n = 953). Patients carrying the T allele showed significantly greater putamen activation during anticipation of high reward (p = 0.014), low reward (at trend-level; p = 0.081), high loss (p = 0.024), and low loss (p = 0.046) compared to HCs. Association analyses in the NIAAA sample showed a trend-level relationship between rs10514299 and a lifetime AD diagnosis in the European American subgroup (odds ratio = 0.82, p = 0.09). This finding was not replicated in the SAGE sample. In the NIAAA sample, the T allele was significantly associated with greater depression symptom severity in individuals with a lifetime AD diagnosis (β = 1.25, p = 0.02); this association was driven by the African American ancestry subgroup (β = 2.11, p = 0.008). We show for the first time that the previously identified MDD risk variant rs10514299 in TMEM161B-MEF2C predicts neuronal correlates of reward processing in an AD phenotype, possibly explaining part of the shared pathophysiology and comorbidity between the disorders.

G protein-coupled receptor 55 (GPR55) has been thought to be a putative cannabinoid receptor. However, little is known about its functional role in cannabinoid action and substance use disorders. Here we report that GPR55 is predominantly found in glutamate neurons in the brain, and its activation reduces self-administration of cocaine and nicotine in rats and mice. Using RNAscope in situ hybridization, GPR55 mRNA was identified in cortical vesicular glutamate transporter 1 (VgluT1)-positive and subcortical VgluT2-positive glutamate neurons, with no detection in midbrain dopamine (DA) neurons. Immunohistochemistry detected a GPR55-like signal in both wildtype and GPR55-knockout mice, suggesting non-specific staining. However, analysis using a fluorescent CB1/GPR55 ligand (T1117) in CB1-knockout mice confirmed GPR55 binding in glutamate neurons, not in midbrain DA neurons. Systemic administration of the GPR55 agonist O-1602 didnt impact ∆9-THC-induced analgesia, hypothermia and catalepsy, but significantly mitigated cocaine-enhanced brain-stimulation reward caused by optogenetic activation of midbrain DA neurons. O-1602 alone failed to alter extracellar DA, but elevated extracellular glutamate, in the nucleus accumbens. In addition, O-1602 also demonstrated inhibitory effects on cocaine or nicotine self-administration under low fixed-ratio and/or progressive-ratio reinforcement schedules in rats and wildtype mice, with no such effects observed in GPR55-knockout mice. Together, these findings suggest that GPR55 activation may functionally modulate drug-taking and drug-seeking behavior possibly via a glutamate-dependent mechanism, and therefore, GPR55 deserves further study as a new therapeutic target for treating substance use disorders.