Neuronal nicotinic acetylcholine receptors: common molecular substrates of nicotine and alcohol dependence

Nicotinic α7 receptors on cholinergic neurons in the striatum mediate cocaine-reinforcement, but not food reward

The neurotransmitter acetylcholine has since long been implicated in reward learning and drug addiction. However, the role of specific cholinergic receptor subtypes on different neuronal populations remain elusive. Here, we studied the function of nicotinic acetylcholinergic alpha 7 receptors (α7 nAChRs) in cocaine and food-enforced behaviors. We found that global deletion of α7 nAChRs in mice attenuates cocaine seeking in a Pavlovian conditioned place preference paradigm and decreases operant responding to cocaine in a runway task and in self-administration, without influencing responding to palatable food. This effect can be attributed to alpha 7 receptor signaling in the striatum, as selective deletion of striatal α7 nAChRs using a viral vector approach resulted in a similar decrease in cocaine-preference as that of global deletion. To investigate which type of striatal neurons are responsible for this effect, we selectively targeted Cholinergic (ChAT-expressing) neurons and dopamine D1-receptor (D1R) expressing neurons. Mice with conditional deletion of α7 nAChRs in ChAT-neurons (α7 nAChR-ChATCre) exhibited decreased cocaine place preference and intact place preference for food, while α7 nAChR-D1RCre mice had no changes in reward learning to neither food nor cocaine. Cocaine induction of striatal immediate early gene expression of cFos, FosB, Arc and EGR2 was blocked in α7 nAChR-ChATCre mice, demonstrating the importance of α7 nAChRs on cholinergic neurons for striatal neuronal activity changes. Collectively, our findings show that α7 nAChRs on cholinergic interneurons in the striatum are pivotal for learning processes related to cocaine, but not food reward.

Reduced brain network segregation in alcohol use disorder: Associations with neurocognition

The human brain consists of functionally segregated networks, characterized by strong connections among regions belonging to the same network and weak connections between those of different networks. Alcohol use disorder (AUD) is associated with premature brain aging and neurocognitive impairments. Given the link between decreased brain network segregation and age-related cognitive decline, we hypothesized lower brain segregation in patients with AUD than healthy controls (HCs). Thirty AUD patients (9 females, 21 males) and 61 HCs (35 females, 26 males) underwent resting-state functional MRI (rs-fMRI), whose data were processed to assess segregation within the brain sensorimotor and association networks. We found that, compared to HCs, AUD patients had significantly lower segregation in both brain networks as well as poorer performance on a spatial working memory task. In the HC group, brain network segregation correlated negatively with age and positively with spatial working memory. Our findings suggest reduced brain network segregation in individuals with AUD that may contribute to cognitive impairment and is consistent with premature brain aging in this population.

Distinct Chrna5 mutations link excessive alcohol use to types I/II vulnerability profiles and IPN GABAergic neurons

Genome wide association and animal studies have implicated genetic variations in CHRNΑ5, encoding the α5 subunit-containing nicotinic acetylcholine receptors (α5*nAChRs), as a risk factor for developing alcohol use disorders (AUDs). To understand how α5*nAChR mutations may influence alcohol (EtOH) drinking behavior, we used a two-bottle choice procedure with intermittent access to alcohol in male and female transgenic mice expressing either the highly frequent human single nucleotide polymorphism (α5SNP/rs16969968) or a deletion of the Chrna5 gene (α5KO). AUDs-related preconsommatory traits (anxiety, sensation-seeking and impulsivity) were assessed with a battery of relevant tasks (elevated-plus maze, novel place preference and step-down inhibitory avoidance). The implication of the α5-expressing IPN GABAergic neurons in AUDs and related behavioral traits was verified using neurospecific lentiviral (LV)-induced reexpression of the α5 subunit in α5KOxGAD-Cre mice. Both α5SNP and α5KO mice showed over-consumption of EtOH, but displayed opposite vulnerability profiles consistent with Cloninger's subtypes of human AUDs. α5SNP mice showed Type I-like characteristics, i.e., high anxiety, novelty avoidance, whereas α5KOs exhibited Type II-like features such as low anxiety and high impulsivity. LV re-expression of the α5 subunit in IPN GABAergic neurons restored the control of EtOH intake and improved the impulsive phenotype. We demonstrate that the SNP (rs16969968) or null mutation of Chrna5 result in increased volitional EtOH consumption but opposite effects on anxiety, novelty-seeking and impulsive-like behaviors that match Cloninger type I and II of AUDs, including sex-related variations. IPN GABAergic neurons expressing α5*nAChRs play a key role in limiting both EtOH drinking and motor impulsivity.

Cholinergic mu-opioid receptor deletion alters reward preference and aversion-resistance

The endogenous opioid system has been implicated in alcohol consumption and preference in both humans and animals. The mu opioid receptor (MOR) is expressed on multiple cells in the striatum, however little is known about the contributions of specific MOR populations to alcohol drinking behaviors. The current study used mice with a genetic deletion of MOR in cholinergic cells (ChAT-Cre/Oprm1fl/fl) to examine the role of MORs expressed in cholinergic interneurons (CINs) in home cage self-administration paradigms. Male and female ChAT-Cre/Oprm1fl/fl mice were generated and heterozygous Cre+ (knockout) and Cre- (control) mice were tested for alcohol consumption in two drinking paradigms: limited access "Drinking in the Dark" and intermittent access. Quinine was added to the drinking bottles in the DID experiment to test aversion-resistant, "compulsive" drinking. Nicotine and sucrose drinking were also assessed so comparisons could be made with other rewarding substances. Cholinergic MOR deletion did not influence consumption or preference for ethanol (EtOH) in either drinking task. Differences were observed in aversion-resistance in males with Cre + mice tolerating lower concentrations of quinine than Cre-. In contrast to EtOH, preference for nicotine was reduced following cholinergic MOR deletion while sucrose consumption and preference was increased in Cre+ (vs. Cre-) females. Locomotor activity was also greater in females following the deletion. These results suggest that cholinergic MORs participate in preference for rewarding substances. Further, while they are not required for consumption of alcohol alone, cholinergic MORs may influence the tendency to drink despite negative consequences.

Toxicity evaluation of neonicotinoids to earthworm (Eisenia fetida) behaviors by a novel locomotion tracking assay

Pesticides are substances used for controlling, preventing, and repelling pests in agriculture. Among them, neonicotinoids have become the fastest-growing class of insecticides because of their efficiency in targeting pests. They work by strongly binding to nicotinic acetylcholine receptors (nAChRs) in the central nervous system of insects, leading to receptor blockage, paralysis, and death. Despite their selectivity for insects, these substances may be hazardous to non-target creatures, including earthworms. Although earthworms may be invasive in some regions like north America, they contribute to the development of soil structure, water management, nutrient cycling, pollution remediation, and cultural services, positively impacting the environment, particularly in the soil ecosystem. Thus, this study aimed to develop a novel earthworm behavior assay since behavior is a sensitive marker for toxicity assay, and demonstrated its application in evaluating the toxicity of various neonicotinoids. Here, we exposed Eisenia fetida to 1 and 10 ppb of eight neonicotinoids (acetamiprid, clothianidin, dinotefuran, imidacloprid, nitenpyram pestanal, thiacloprid, thiametoxam, and sulfoxaflor) for 3 days to observe their behavior toxicities. Overall, all of the neonicotinoids decreased their locomotion, showed by a reduction of average speed by 24.94-68.63% and increment in freezing time movement ratio by 1.51-4.25 times, and altered their movement orientation and complexity, indicated by the decrement in the fractal dimension value by 24-70%. Moreover, some of the neonicotinoids, which were acetamiprid, dinotefuran, imidacloprid, nitenpyram, and sulfoxaflor, could even alter their exploratory behaviors, which was shown by the increment in the time spent in the center area value by 6.94-12.99 times. Furthermore, based on the PCA and heatmap clustering results, thiametoxam was found as the neonicotinoid that possessed the least pronounced behavior toxicity effects among the tested pesticides since these neonicotinoid-treated groups in both concentrations were grouped in the same major cluster with the control group. Finally, molecular docking was also conducted to examine neonicotinoids' possible binding mechanism to Acetylcholine Binding Protein (AChBP), which is responsible for neurotransmission. The molecular docking result confirmed that each of the neonicotinoids has a relatively high binding energy with AChBP, with the lowest binding energy was possessed by thiametoxam, which consistent with its relatively low behavior toxicities. Thus, these molecular docking results might hint at the possible mechanism behind the observed behavior alterations. To sum up, the present study demonstrated that all of the neonicotinoids altered the earthworm behaviors which might be due to their ability to bind with some specific neurotransmitters and the current findings give insights into the toxicities of neonicotinoids to the environment, especially animals in a soil ecosystem.

Expression pattern of nicotinic acetylcholine receptor subunit transcripts in neurons and astrocytes in the ventral tegmental area and locus coeruleus

Acetylcholine is the endogenous agonist for the neuronal nicotinic acetylcholine receptor (nAChR) system, which is involved in attention, memory, affective behaviours and substance use disorders. Brain nAChRs are highly diverse with 11 different subunits that can form multiple receptor subtypes, each with distinct receptor and pharmacological properties. Different neuronal cell types can also express different nAChR subtypes, resulting in highly complex cholinergic signalling. Identifying which nAChR subunit transcripts are expressed in cell types can provide an indication of which nAChR combinations are possible and which receptor subtypes may be most pharmacologically relevant to target. In addition to differences in expression across cell types, nAChRs also undergo changes in expression levels from adolescence to adulthood. In this study, we used fluorescent in situ hybridization to identify and quantify the expression of α4, α5, α6, β2 and β3 nAChR subunit transcripts in dopaminergic, GABAergic, glutamatergic and noradrenergic neurons and astrocytes in the ventral tegmental area (VTA) and locus coeruleus (LC) in adult and adolescent, male and female C57BL/6J mice. There were distinct differences in the pattern of nAChR subunit transcript expression between the two brain regions. LC noradrenergic neurons had high prevalence of α6, β2 and β3 expression, with very low expression of α4, suggesting the α6(non-α4)β2β3 receptor as a main subtype in these neurons. VTA astrocytes from adult mice showed greater prevalence of α5, α6, β2 and β3 transcript compared with adolescent mice. These data highlight the complex nAChR expression patterns across brain region and cell type.

Cholinergic mu-opioid receptor deletion alters reward preference and aversion-resistance

Heavy alcohol use and binge drinking are important contributors to alcohol use disorder (AUD). The endogenous opioid system has been implicated in alcohol consumption and preference in both humans and animals. The mu opioid receptor (MOR) is expressed on multiple cells in the striatum, however little is known about the contributions of specific MOR populations to alcohol drinking behaviors. The current study used mice with a genetic deletion of MOR in cholinergic cells (ChAT-Cre/Oprm1fl/fl) to examine the role of MORs expressed in cholinergic interneurons (CINs) in home cage self-administration paradigms. Male and female ChAT-Cre/Oprm1fl/fl mice were generated and heterozygous Cre+ (knockout) and Cre- (control) mice were tested for alcohol and nicotine consumption. In Experiment 1, binge-like and quinine-resistant drinking was tested using 15% ethanol (EtOH) in a two-bottle, limited-access Drinking in the Dark paradigm. Experiment 2 involved a six-week intermittent access paradigm in which mice received 20% EtOH, nicotine, and then a combination of the two drugs. Experiment 3 assessed locomotor activity, sucrose preference, and quinine sensitivity. Deleting MORs in cholinergic cells did not alter consumption of EtOH in Experiment 1 or 2. In Experiment 1, the MOR deletion resulted in greater consumption of quinine-adulterated EtOH in male Cre+ mice (vs. Cre-). In Experiment 2, Cre+ mice demonstrated a significantly lower preference for nicotine but did not differ from Cre- mice in nicotine or nicotine + EtOH consumption. Overall fluid consumption was also heightened in the Cre+ mice. In Experiment 3, Cre+ females were found to have greater locomotor activity and preference for sucrose vs. Cre- mice. These data suggest that cholinergic MORs are not required for EtOH, drinking behaviors but may contribute to aversion resistant EtOH drinking in a sex-dependent manner.

Nicotine Abuse and Neurodegeneration: Novel Pharmacogenetic Targets to Aid Quitting and Reduce the Risk of Dementia

Nicotine dependence has deleterious neurological impacts. Previous studies found an association between cigarette smoking and accelerating age-related thinning of the brain's cortex and subsequent cognitive decline. Smoking is considered the third most common risk factor for dementia, which prompted the inclusion of smoking cessation in dementia prevention strategies. Traditional pharmacologic options for smoking cessation include nicotine transdermal patches, bupropion and varenicline. However, based on smokers' genetic makeup, pharmacogenetics can be used to develop novel therapies to replace these traditional approaches. Genetic variability of cytochrome P450 2A6 has a major impact on smokers' behavior and their response to quitting therapies. Gene polymorphism in nicotinic acetylcholine receptor subunits also has a great influence on the ability to quit smoking. In addition, polymorphism of certain nicotinic acetylcholine receptors was found to affect the risk of dementia and the impact of tobacco smoking on the development of Alzheimer's disease. Nicotine dependence involves the activation of pleasure response through the stimulation of dopamine release. Central dopamine receptors, catechol-o-methyltransferase and the dopamine transporter protein, regulate synaptic dopamine levels. The genes of these molecules are potential targets for novel smoking cessation drugs. Pharmacogenetic studies of smoking cessation also investigated other molecules, such as ANKK1 and dopamine-beta-hydroxylase (DBH). In this perspective article, we aim to highlight the promising role of pharmacogenetics in the development of effective drugs for smoking cessation, which can increase the success rate of smoking quitting plans and ultimately reduce the incidence of neurodegeneration and dementia.

Individual differences in response to alcohol and nicotine in zebrafish: Gene expression and behavior

Alcohol and nicotine are psychoactive substances responsible for serious health consequences. Although the biological mechanisms of alcohol and nicotine have been studied extensively, individual differences in the response to these drugs have received little attention. Here we evaluated gene expression and behavior of bold and shy individuals after acute exposure to alcohol and nicotine. For this, zebrafish were classified as bold and shy individuals based on emergence tests, and then fish were exposed to 0.00, 0.10, and 0.50% alcohol or 0.00, 1.00, and 5.00 mg/L nicotine and their anxiety-like and locomotor behavior was observed. After behavioral assessment, brain mRNA expression (ache, bdnf, gaba1, gad1b, th1, and tph1) was evaluated. Locomotion patterns differed between profiles depending on alcohol and nicotine concentration. Anxiety increased in shy fish and decreased in bold fish after exposure to both drugs. Alcohol exposure induced an increase in tph1 mRNA expression in bold fish, while bdnf mRNA expression was increased in shy fish. Nicotine increased ache, bdnf, and tph1 mRNA levels in both profiles, but at higher levels in bold fish. Based on our research, we found that alcohol induces anxiogenic effects in both bold and shy zebrafish. Additionally, shy individuals exposed to a low concentration of nicotine exhibited stronger anxiety-like responses than their bold counterparts. These findings further support the validity of using zebrafish as a dependable tool for studying the effects of drugs and uncovering the underlying mechanisms associated with individual variations.

Reduction of nicotine and ethanol intake in alcohol-preferring (UChB) female rats by the α4β2 nicotinic acetylcholine receptor partial agonists 5-bromocytisine and cytisine

RATIONALE

Neuronal nicotinic acetylcholine receptors (nAChRs) are implicated in the reinforcing effects of nicotine and ethanol. Previous studies have shown that cytisine and its 5-bromo derivative are partial agonists at the α4β2 nAChRs and that the parent molecule cytisine is effective in reducing both nicotine- and ethanol-self-administration in rats. However, whether 5-bromocytisine affects nicotine or ethanol self-administration was unknown.

OBJECTIVES

The present study compared the effects of 5-bromocytisine and cytisine on nicotine self-administration and further assessed the effect of daily drug injection on voluntary ethanol consumption in alcohol-preferring female rats. Animals were administered a 1.5mg/kg i.p. dose of 5-bromocytisine or cytisine every day for 15-16 days.

RESULTS

The initial efficacy of 5-bromocytisine and cytisine in reducing nicotine intake was similar (-80%) while for voluntary ethanol intake 5-bromocytisine was a superior inhibitor over cytisine (-78% and -40% respectively). The efficacy of cytisine began to diminish after 10 days of daily administration, which was attributed to tolerance development to its inhibitory effects both on nicotine and ethanol self-administration. Tolerance did not develop for 5-bromocytisine.

CONCLUSION

5-Bromocytisine, a weaker α4β2 nAChR partial agonist than cytisine, also produces a sustained inhibition of both nicotine and ethanol self-administration, and unlike cytisine, it does not develop tolerance.

Advice for smokers in smoking cessation clinic: a review

Background

Tobacco dependence has become a global public health concern. We chose to investigate the modifiable factors and motivations during the period of smoking cessation based on the mechanism of nicotine addiction.

Methods

We selected emotion, sleep, alcohol, caffeine beverages, mental activities after dinner, exercise and CYP2A6 genotype as influencing factors, and provided corresponding recommendations for smokers based on these factors. Based on these characteristics, we reviewed literature and summarized the relationship between these factors and nicotine dependence or smoking.

Results

Different emotion, sleep deficiency, caffeine intake, alcohol consumption, mental activities after dinner, physical exercises and CYP2A6 genotype have an effect on daily smoking and nicotine dependence.

Conclusion

These suggestions related literature-derived factors may increase the success rate of smoking cessation.

Binge alcohol drinking alters the differential control of cholinergic interneurons over nucleus accumbens D1 and D2 medium spiny neurons

Animals studies support the notion that striatal cholinergic interneurons (ChIs) play a central role in basal ganglia function by regulating associative learning, reward processing, and motor control. In the nucleus accumbens (NAc), a brain region that mediates rewarding properties of substance abuse, acetylcholine regulates glutamatergic, dopaminergic, and GABAergic neurotransmission in naïve mice. However, it is unclear how ChIs orchestrate the control of these neurotransmitters/modulators to determine the synaptic excitability of medium spiny neurons (MSNs), the only projecting neurons that translate accumbens electrical activity into behavior. Also unknown is the impact of binge alcohol drinking on the regulation of dopamine D1- and D2 receptor-expressing MSNs (D1- and D2-MSNs, respectively) by ChIs. To investigate this question, we optogenetically stimulated ChIs while recording evoked and spontaneous excitatory postsynaptic currents (sEPSCs) in nucleus accumbens core D1- and D2-MSN of ChAT.ChR2.eYFPxDrd1.tdtomato mice. In alcohol-naïve mice, we found that stimulating NAc ChIs decreased sEPSCs frequency in both D1- and D2-MSNs, presumably through a presynaptic mechanism. Interestingly, ChI stimulation decreased MSN synaptic excitability through different mechanisms in D1- vs. D2-MSNs. While decrease of ChI-mediated sEPSCs frequency in D1-MSNs was mediated by dopamine, the same effect in D2-MSNs resulted from a direct control of glutamate release by ChIs. Interestingly, after 2 weeks of binge alcohol drinking, optogenetic stimulation of ChIs enhanced glutamate release in D1-MSNs, while its effect on D2-MSNs remained unchanged. Taken together, these data suggest that cholinergic interneurons could be a key target for regulation of NAc circuitry and for alcohol consumption.

β2* nicotinic acetylcholine receptor subtypes mediate nicotine-induced enhancement of Pavlovian conditioned responding to an alcohol cue

Nicotine enhances Pavlovian conditioned responses to reward-associated cues. We investigated through which nicotinic acetylcholine receptor (nAChR) subtypes nicotine acts to produce this behavioral effect to an alcohol-associated cue. Male Long-Evans rats with freely available food and water were first accustomed to drinking 15% ethanol in their home cages using an intermittent access, two-bottle choice procedure. Then the rats were given 15 Pavlovian conditioning sessions in which a 15-s audiovisual conditioned stimulus (CS) predicted the delivery of 0.2 ml of ethanol, the unconditioned stimulus (US). Each session contained 12 CS-US trials. A control group received explicitly unpaired presentations of the CS and US. We measured Pavlovian conditioned approach to the site of US delivery during presentations of the CS, accounting for pre-CS baseline activity. Before each conditioning session, rats were injected subcutaneously with nicotine (0.4 mg/kg) or saline (1 ml/kg). During nAChR antagonist test sessions, rats were first injected systemically with the β2*-selective nAChR antagonist dihydro-beta-erythroidine (DHβE; 3 mg/kg) or the α7-selective nAChR antagonist methyllycaconitine (MLA; 6 mg/kg), followed by their assigned nicotine or saline injection before assessing their conditioned response to the alcohol-associated cue. Consistent with previous reports, nicotine enhanced the Pavlovian conditioned response to the alcohol-paired cue. DHβE attenuated this enhancement, whereas MLA did not. These results suggest that nicotine acts via β2*, but not α7, nAChRs to amplify Pavlovian conditioned responding to an alcohol cue. These findings contribute to a growing literature that identifies nAChRs as potential targets for pharmacological treatment of co-morbid alcohol and tobacco use disorders.

Targeting prefrontal cortex GABAergic microcircuits for the treatment of alcohol use disorder

Developing novel treatments for alcohol use disorders (AUDs) is of paramount importance for improving patient outcomes and alleviating the suffering related to the disease. A better understanding of the molecular and neurocircuit mechanisms through which alcohol alters brain function will be instrumental in the rational development of new efficacious treatments. Clinical studies have consistently associated the prefrontal cortex (PFC) function with symptoms of AUDs. Population-level analyses have linked the PFC structure and function with heavy drinking and/or AUD diagnosis. Thus, targeting specific PFC cell types and neural circuits holds promise for the development of new treatments. Here, we overview the tremendous diversity in the form and function of inhibitory neuron subtypes within PFC and describe their therapeutic potential. We then summarize AUD population genetics studies, clinical neurophysiology findings, and translational neuroscience discoveries. This study collectively suggests that changes in fast transmission through PFC inhibitory microcircuits are a central component of the neurobiological effects of ethanol and the core symptoms of AUDs. Finally, we submit that there is a significant and timely need to examine sex as a biological variable and human postmortem brain tissue to maximize the efforts in translating findings to new clinical treatments.

UFR2709, an Antagonist of Nicotinic Acetylcholine Receptors, Delays the Acquisition and Reduces Long-Term Ethanol Intake in Alcohol-Preferring UChB Bibulous Rats

Alcoholism is a worldwide public health problem with high economic cost and which affects health and social behavior. It is estimated that alcoholism kills 3 million people globally, while in Chile it is responsible for around 9 thousand deaths per year. Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels expressed in the central nervous system, and they were suggested to modulate the ethanol mechanism involved in abuse and dependence. Previous work demonstrated a short-term treatment with UFR2709, a nAChRs antagonist, which reduced ethanol intake using a two-bottle free-choice paradigm in University of Chile bibulous (UChB) rats. Here, we present evidence of the UFR2709 efficacy in reducing the acquisition and long-term ethanol consumption. Our results show that UFR2709 (2.5 mg/kg i.p.) reduces the seek behavior and ethanol intake, even when the drug administration was stopped, and induced a reduction in the overall ethanol intake by around 55%. Using naïve UChB bibulous rats, we demonstrate that UFR2709 could delay and reduce the genetically adaptive impulse to seek and drink ethanol and prevent its excessive intake.

The incentive amplifying effects of nicotine: Roles in alcohol seeking and consumption

Nicotine has a unique profile among drugs of abuse. To the noninitiated user, nicotine has powerful aversive effects and its relatively weak euphorigenic effects undergo rapid tolerance. Despite this, nicotine is commonly abused despite negative heath consequences, and nicotine users have enormous difficulty quitting. Further, nicotine is one of the most commonly co-abused substances, in that it is often taken in combination with other drugs. One explanation of this polydrug use is that nicotine has multiple appetitive and consummatory conditioning effects. For example, nicotine is a reinforcement enhancer in that it can potently increase the incentive value of other stimuli, including those surrounding drugs of abuse such as alcohol. In addition, nicotine also has a unique profile of neurobiological effects that alter regulation of alcohol intake and interoception. This review discusses the psychological and biological mechanisms surrounding nicotine's appetitive conditioning and consummatory effects, particularly its interactions with alcohol.

Effect of Combination Treatment With Varenicline and Nicotine Patch on Smoking Cessation Among Smokers Who Drink Heavily: A Randomized Clinical Trial

IMPORTANCE

The concurrent use of both tobacco and alcohol causes substantial disease and early mortality, and smokers who drink heavily tend to be less successful in smoking cessation than smokers who do not. Although varenicline combined with nicotine replacement therapy for smoking cessation has been examined among smokers who do not drink heavily, this combination treatment has not yet been examined among smokers who drink heavily.

OBJECTIVE

To determine whether combined treatment with varenicline tartrate and nicotine patch improves continuous abstinence from cigarette smoking among smokers who drink heavily.

DESIGN, SETTING, AND PARTICIPANTS

This double-blind, placebo-controlled, superiority randomized clinical trial evaluated combined treatment with varenicline and nicotine patch compared with placebo and nicotine patch for smoking cessation (primary outcome) and drinking behavior (secondary outcome) among smokers who drink heavily. The clinical trial was conducted at 2 outpatient sites in Chicago, Illinois, with enrollment from March 26, 2018, to February 14, 2020. The 122 participants were recruited from the community via social media and public transit advertisements and equally randomized to the 2 treatment groups, which were stratified by sex and smoking behavior. Eligible participants smoked between 5 and 30 cigarettes per day and drank heavily (>14 drinks per week for men or >7 drinks per week for women and ≥1 heavy drinking day [defined as >5 drinks per occasion for men or >4 drinks per occasion for women] per month for the past year) and had a desire to quit smoking.

INTERVENTIONS

Varenicline tartrate, 1.0 mg, twice daily or matching placebo pills twice daily for 12 weeks. Nicotine patch at manufacturer-recommended doses for 10 weeks and brief individual smoking cessation counseling the week before the quit date and on the quit date.

MAIN OUTCOMES AND MEASURES

The primary outcome was self-reported continuous cigarette abstinence through weeks 9 to 12; abstinence was biochemically confirmed at the week 12 study visit. Secondary outcomes were the frequency of weekly drinking and weekly heavy drinking during the study period.

RESULTS

Among 122 participants (mean [SD] age, 44.0 [12.4] years; 67 men [54.9%]), 61 were randomly assigned to receive combined treatment with varenicline and nicotine patch (varenicline group), and 61 were randomly assigned to receive placebo and nicotine patch (placebo group). A total of 54 participants (44.3%) self-identified as Black, 56 (45.9%) as White, and 12 (9.8%) as other races (including American Indian or Alaska Native, Asian, >1 race, and unspecified race). A total of 8 participants (6.6%) self-identified as Hispanic and 114 (93.4%) as non-Hispanic ethnicity. Study retention to 12 weeks was 89%. The intention-to-treat analyses showed higher smoking cessation rates during weeks 9 to 12 in the varenicline group vs the placebo group (27 participants [44.3%] vs 17 participants [27.9%]; odds ratio, 2.20; 95% CI, 1.01-4.80; P = .047) and lower likelihood of relapse throughout treatment in the varenicline group relative to the placebo group (hazard ratio, 0.62; 95% CI, 0.40-0.96; P = .03). Both treatments were well tolerated; however, compared with participants in the placebo group, those in the varenicline group experienced more adverse effects, with 5 participants in the varenicline group discontinuing medication due to adverse effects.

CONCLUSIONS AND RELEVANCE

In this study, combined treatment with varenicline and nicotine patch was more effective than placebo and nicotine patch for smoking cessation among smokers who drink heavily. The combination treatment had no effect on alcohol consumption, with both groups showing significant reductions. Combination treatment with varenicline and nicotine patch may be a viable option for smokers who drink heavily.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02859142.

The effect of varenicline on smoking and drinking outcomes among Black and White adults with alcohol use disorder and co-occurring cigarette smoking: A secondary analysis of two clinical trials

INTRODUCTION

Varenicline is an FDA-approved medication for smoking cessation and has demonstrated promise in reducing alcohol use. This study sought to compare the efficacy of varenicline in reducing smoking and drinking among Black and White people seeking alcohol treatment.

METHODS

Linear mixed modeling was conducted using data from two multi-site placebo-controlled randomized clinical trials examining the effects of varenicline for treatment of Alcohol Use Disorder (AUD; O'Malley et al., 2018; Litten et al., 2013) among Black and White adults with AUD and co-occurring cigarette smoking. The primary analyses were conducted in a sample of 117 adults (O'Malley trial: 29.1% female, 55.2% Black), and replicated in an independent sample of 73 adults (Litten trial: 23.3% female, 45.2% Black).

RESULTS

Black participants smoked fewer cigarettes per day compared to White participants (O'Malley trial: F_1,116 = 8.95, p = .003; Litten trial: F_1,68.9 = 4.74p = .03). Linear mixed models revealed a marginal effect of varenicline on reducing cigarettes smoked per day regardless of race in the O'Malley trial (F_1,109 = 3.34, p = .07), which was replicated in the Litten trial (F_1,67.1 = 20.77p < .0001). Participants reduced the number of drinks consumed regardless of treatment condition or race in both trials (O'Malley trial: F_1,98 = 131.69, p < .0001; Litten trial:F_1,69 = 60.36, p < .0001).

CONCLUSIONS

Our adjusted model findings suggest varenicline reduced smoking among Black and White people with AUD and co-occurring cigarette smoking. However, these findings should be replicated in a larger sample.

Sex Differences in the Nicotinic Acetylcholine Receptor System of Rodents: Impacts on Nicotine and Alcohol Reward Behaviors

Alcohol and nicotine are the two most widely used and misused drugs around the world, and co-consumption of both substances is highly prevalent. Multiple lines of evidence show a profound effect of sex in many aspects of alcohol and nicotine reward, with women having more difficulty quitting smoking and showing a faster progression toward developing alcohol use disorder compared with men. Both alcohol and nicotine require neuronal nicotinic acetylcholine receptors (nAChRs) to elicit rewarding effects within the mesolimbic system, representing a shared molecular pathway that likely contributes to the frequent comorbidity of alcohol and nicotine dependence. However, the majority of preclinical studies on the mechanisms of alcohol and nicotine reward behaviors utilize only male rodents, and thus our understanding of alcohol and nicotine neuropharmacology relies heavily on male data. As preclinical research informs the development and refinement of therapies to help patients reduce drug consumption, it is critical to understand the way biological sex and sex hormones influence the rewarding properties of alcohol and nicotine. In this review, we summarize what is known about sex differences in rodent models of alcohol and nicotine reward behaviors with a focus on neuronal nAChRs, highlighting exciting areas for future research. Additionally, we discuss the way circulating sex hormones may interact with neuronal nAChRs to influence reward-related behavior.

Smoking reduction is associated with lower alcohol consumption and depressive symptoms among young adults over one year

BACKGROUND

This secondary analysis examined whether smoking reduction among young adults participating in a Facebook-based smoking cessation intervention study was associated with corresponding reductions in alcohol consumption and depressive symptoms.

METHODS

Participants were young adults who smoked and engaged in heavy episodic drinking (HED). Alcohol consumption (AUDIT-C, days of HED), depressive symptoms (PHQ-2), and past-month cigarettes per day (CPD) were self-reported at baseline and 12 months (N = 150). Linear regression estimated the relationship between the mean change in CPD and mean changes in alcohol consumption and depressive symptoms.

RESULTS

CPD, alcohol consumption, and depressive symptoms decreased significantly between baseline and 12 months. The adjusted mean reduction in CPD was significantly associated with mean reductions in AUDIT-C (Beta [β] = 0.09, 95 % confidence interval [CI] = 0.04-0.14), days of HED (β = 0.17, 95 % CI = 0.04-0.29) and PHQ-2 (β = 0.05, 95 % CI = 0.01-0.08). Smoking abstinence (n = 48) was associated with a significantly larger mean reduction in AUDIT-C compared to a ≥50 % reduction (n = 45) (-2.9 vs -1.7 points, p = 0.03) or <50 % reduction in CPD (n = 57) (-2.9 vs -1.1 points, p < 0.01). The mean reduction in AUDIT-C did not differ between a ≥50 % reduction and <50 % reduction in CPD (-1.7 vs.-1.1 points, p = 0.18). Mean reductions in days of HED and the PHQ-2 did not differ according to the level of reduction in CPD.

CONCLUSION

Smoking reduction was associated with reductions in alcohol consumption and depressive symptoms. Reductions appeared to be greater for those who achieved abstinence compared to a reduction in smoking.

Effects of adolescent substance use disorders on central cholinergic function

Adolescence is a transitional period between childhood and adulthood, in which the individual undergoes significant cognitive, behavioral, physical, emotional, and social developmental changes. During this period, adolescents engage in experimentation and risky behaviors such as licit and illicit drug use. Adolescents' high vulnerability to abuse drugs and natural reinforcers leads to greater risk for developing substance use disorders (SUDs) during adulthood. Accumulating evidence indicates that the use and abuse of licit and illicit drugs during adolescence and emerging adulthood can disrupt the cholinergic system and its processes. This review will focus on the effects of peri-adolescent nicotine and/or alcohol use, or exposure, on the cholinergic system during adulthood from preclinical and clinical studies. This review further explores potential cholinergic agents and pharmacological manipulations to counteract peri-adolescent nicotine and/or alcohol abuse.

Structure, Dynamics, and Ligand Recognition of Human-Specific CHRFAM7A (Dupα7) Nicotinic Receptor Linked to Neuropsychiatric Disorders

Cholinergic α7 nicotinic receptors encoded by the CHRNA7 gene are ligand-gated ion channels directly related to memory and immunomodulation. Exons 5-7 in CHRNA7 can be duplicated and fused to exons A-E of FAR7a, resulting in a hybrid gene known as CHRFAM7A, unique to humans. Its product, denoted herein as Dupα7, is a truncated subunit where the N-terminal 146 residues of the ligand binding domain of the α7 receptor have been replaced by 27 residues from FAM7. Dupα7 negatively affects the functioning of α7 receptors associated with neurological disorders, including Alzheimer's diseases and schizophrenia. However, the stoichiometry for the α7 nicotinic receptor containing dupα7 monomers remains unknown. In this work, we developed computational models of all possible combinations of wild-type α7 and dupα7 pentamers and evaluated their stability via atomistic molecular dynamics and coarse-grain simulations. We assessed the effect of dupα7 subunits on the Ca2+ conductance using free energy calculations. We showed that receptors comprising of four or more dupα7 subunits are not stable enough to constitute a functional ion channel. We also showed that models with dupα7/α7 interfaces are more stable and are less detrimental for the ion conductance in comparison to dupα7/dupα7 interfaces. Based on these models, we used protein-protein docking to evaluate how such interfaces would interact with an antagonist, α-bungarotoxin, and amyloid Aβ42. Our findings show that the optimal stoichiometry of dupα7/α7 functional pentamers should be no more than three dupα7 monomers, in favour of a dupα7/α7 interface in comparison to a homodimer dupα7/dupα7 interface. We also showed that receptors bearing dupα7 subunits are less sensitive to Aβ42 effects, which may shed light on the translational gap reported for strategies focused on nicotinic receptors in 'Alzheimer's disease research.

Nicotine: A Targeted Therapy for Epilepsy Due to nAChR Gene Variants

OBJECTIVE

Genetic variants of the neuronal nicotinic acetylcholine receptor (nAChR) cause autosomal dominant sleep-related hypermotor epilepsy. Approximately 30% of autosomal dominant sleep-related hypermotor epilepsy patients are medically intractable. In preclinical models, pathogenic nAChR variants cause a gain of function mutation with sensitivity to acetylcholine antagonists and agonists. Nicotine modifies the activity of nAChRs and can be used as targeted therapy.

METHODS

We reviewed next-generation sequencing epilepsy panels from a single laboratory (GeneDx) from patients at Children's Medical Center Dallas between 2011 and 2015 and identified patients with nAChR variants. Retrospective review of records included variant details, medical history, neuroimaging findings, and treatment history.

RESULTS

Twenty-one patients were identified. Four patients were prescribed nicotine patches for intractable seizures. Three of 4 patients had a clinical response, with >50% seizure reduction.

CONCLUSIONS

Treatment with a nicotine patch can be an effective therapy in epilepsy patients with nAChR gene variants. We propose consideration of transdermal nicotine treatment in intractable epilepsy with known nAChR variants as an experimental therapy. Further clinical trials are needed to fully define therapeutic effects.

Multidimensional Intersection of Nicotine, Gene Expression, and Behavior

The cholinergic system plays a crucial role in nervous system function with important effects on developmental processes, cognition, attention, motivation, reward, learning, and memory. Nicotine, the reinforcing component of tobacco and e-cigarettes, directly acts on the cholinergic system by targeting nicotinic acetylcholine receptors (nAChRs) in the brain. Activation of nAChRs leads to a multitude of immediate and long-lasting effects in specific cellular populations, thereby affecting the addictive properties of the drug. In addition to the direct actions of nicotine in binding to and opening nAChRs, the subsequent activation of circuits and downstream signaling cascades leads to a wide range of changes in gene expression, which can subsequently alter further behavioral expression. In this review, we provide an overview of the actions of nicotine that lead to changes in gene expression and further highlight evidence supporting how these changes can often be bidirectional, thereby inducing subsequent changes in behaviors associated with further drug intake.

Nicotinic Receptors in the Brainstem Ascending Arousal System in SIDS With Analysis of Pre-natal Exposures to Maternal Smoking and Alcohol in High-Risk Populations of the Safe Passage Study

Pre-natal exposures to nicotine and alcohol are known risk factors for sudden infant death syndrome (SIDS), the leading cause of post-neonatal infant mortality. Here, we present data on nicotinic receptor binding, as determined by 125I-epibatidine receptor autoradiography, in the brainstems of infants dying of SIDS and of other known causes of death collected from the Safe Passage Study, a prospective, multicenter study with clinical sites in Cape Town, South Africa and 5 United States sites, including 2 American Indian Reservations. We examined 15 pons and medulla regions related to cardiovascular control and arousal in infants dying of SIDS (n = 12) and infants dying from known causes (n = 20, 10 pre-discharge from time of birth, 10 post-discharge). Overall, there was a developmental decrease in 125I-epibatidine binding with increasing postconceptional age in 5 medullary sites [raphe obscurus, gigantocellularis, paragigantocellularis, centralis, and dorsal accessory olive (p = 0.0002-0.03)], three of which are nuclei containing serotonin cells. Comparing SIDS with post-discharge known cause of death (post-KCOD) controls, we found significant decreased binding in SIDS in the nucleus pontis oralis (p = 0.02), a critical component of the cholinergic ascending arousal system of the rostral pons (post-KCOD, 12.1 ± 0.9 fmol/mg and SIDS, 9.1 ± 0.78 fmol/mg). In addition, we found an effect of maternal smoking in SIDS (n = 11) combined with post-KCOD controls (n = 8) on the raphe obscurus (p = 0.01), gigantocellularis (p = 0.02), and the paragigantocellularis (p = 0.002), three medullary sites found in this study to have decreased binding with age and found in previous studies to have abnormal indices of serotonin neurotransmission in SIDS infants. At these sites, 125I-epibatidine binding increased with increasing cigarettes per week. We found no effect of maternal drinking on 125I-epibatidine binding at any site measured. Taken together, these data support changes in nicotinic receptor binding related to development, cause of death, and exposure to maternal cigarette smoking. These data present new evidence in a prospective study supporting the roles of developmental factors, as well as adverse exposure on nicotinic receptors, in serotonergic nuclei of the rostral medulla-a finding that highlights the interwoven and complex relationship between acetylcholine (via nicotinic receptors) and serotonergic neurotransmission in the medulla.

Enhancement of alcohol aversion by the nicotinic acetylcholine receptor drug sazetidine-A

The prevalence of alcohol use disorders (AUDs) has steadily increased in the United States over the last 30 years. Alcohol acts on multiple receptor systems including the nicotinic acetylcholine receptors (nAChRs), which are known to mediate alcohol consumption and reward. We previously reported that the preclinical drug sazetidine-A, a nAChR agonist and desensitizer, reduces alcohol consumption without affecting nicotine consumption in C57BL/6J mice. Here, we found that sazetidine-A enhances the expression of alcohol aversion without affecting the expression or acquisition of conditioned alcohol reward in C57BL/6J mice. Microinjection of sazetidine-A into the ventral midbrain targeting the ventral tegmental area (VTA) reduced binge alcohol consumption, implicating this region in mediating the effects of sazetidine-A. Furthermore, the sazetidine-A-induced reduction in alcohol consumption was mediated by non-α4 containing nAChRs, as sazetidine-A reduced binge alcohol consumption in both α4 knock-out and wild-type mice. Finally, we found that in mice pretreated with sazetidine-A, alcohol induced Fos transcript in Th-, but not Gad2-expressing neurons in the VTA as measured by increased Fos transcript expression. In summary, we find that sazetidine-A enhances the expression of alcohol aversion, which may underlie the reduction in alcohol consumption induced by sazetidine-A. Elucidating the identity of non-α4 nAChRs in alcohol aversion mechanisms will provide a better understanding the complex role of nAChRs in alcohol addiction and potentially reveal novel drug targets to treat AUDs.

Binding properties to nicotinic acetylcholine receptors can explain differential toxicity of neonicotinoid insecticides in Chironomidae

Neonicotinoids are neuroactive insecticides commonly detected in freshwater ecosystems. Recent studies have indicated that these compounds are markedly toxic to Chironomidae, a widespread family of ecologically important aquatic insects. However, despite their sensitivity, the pharmacological mechanisms driving neonicotinoid toxicity have yet to be characterized in these insect species. Here, we used a combination of saturation and competition binding studies to characterize neonicotinoid binding properties to nicotinic acetylcholine receptors (nAChR) in two different Chironomidae (Chironomus riparius and Chironomus dilutus) at two different life stages (larval and adult). Using radiolabeled imidacloprid ([³H]-IMI), we characterized and compared receptor density (B_max), imidacloprid binding affinity (K_D), and receptor binding affinity (K_i) to three different neonicotinoid competitors (imidacloprid, clothianidin, and thiamethoxam). We then compared receptor density and binding affinity parameters derived for Chironomidae to data previously generated for other dipterans and agricultural pests. We found that there were limited differences in neonicotinoid binding between C. riparius and C. dilutus, with both organisms demonstrating high affinities for imidacloprid (K_D = 0.22-0.87 nM) and high receptor densities (B_max = 0.92-6.53 pmol/mg). However, there were significant differences between life-stages, with larvae expressing higher densities of nicotinic acetylcholine receptors and higher imidacloprid affinities than adults. Moreover, there were compound-specific differences in receptor affinity, with larval stages displaying relative affinities (K_i) that generally correlated with acute neonicotinoid toxicity (e.g. clothianidin ≥ imidacloprid >>> thiamethoxam). Finally, compared to other dipterans and agricultural pests, Chironomidae display very high densities of high affinity nicotinic acetylcholine receptors, which likely contribute to their sensitivity. Results indicated that receptor-level differences in neonicotinoid binding may be responsible for ecotoxicological differences amongst distinct insect species, and they likely play a role in life stage-, and compound-level toxicity differences previously observed for Chironomidae. Overall, this study highlights the value of understanding the toxicological mechanisms of action of neonicotinoids in sensitive, non-target aquatic insects, to better predict adverse effects associated with unintentional neonicotinoid exposure.

Neuroprotective Effect of Curcumin on the Nigrostriatal Pathway in a 6-Hydroxydopmine-Induced Rat Model of Parkinson's Disease is Mediated by α7-Nicotinic Receptors

Parkinson’s disease (PD) is a common neurodegenerative disorder, characterized by selective degeneration of dopaminergic nigrostriatal neurons. Most of the existing pharmacological approaches in PD consider replenishing striatal dopamine. It has been reported that activation of the cholinergic system has neuroprotective effects on dopaminergic neurons, and human α7-nicotinic acetylcholine receptor (α7-nAChR) stimulation may offer a potential therapeutic approach in PD. Our recent in-vitro studies demonstrated that curcumin causes significant potentiation of the function of α7-nAChRs expressed in Xenopus oocytes. In this study, we conducted in vivo experiments to assess the role of the α7-nAChR on the protective effects of curcumin in an animal model of PD. Intra-striatal injection of 6-hydroxydopmine (6-OHDA) was used to induce Parkinsonism in rats. Our results demonstrated that intragastric curcumin treatment (200 mg/kg) significantly improved the abnormal motor behavior and offered neuroprotection against the reduction of dopaminergic neurons, as determined by tyrosine hydroxylase (TH) immunoreactivity in the substantia nigra and caudoputamen. The intraperitoneal administration of the α7-nAChR-selective antagonist methyllycaconitine (1 µg/kg) reversed the neuroprotective effects of curcumin in terms of both animal behavior and TH immunoreactivity. In conclusion, this study demonstrates that curcumin has a neuroprotective effect in a 6-hydroxydopmine (6-OHDA) rat model of PD via an α7-nAChR-mediated mechanism.

Understanding the neurobiological effects of drug abuse: Lessons from zebrafish models

Drug abuse and brain disorders related to drug comsumption are public health problems with harmful individual and social consequences. The identification of therapeutic targets and precise pharmacological treatments to these neuropsychiatric conditions associated with drug abuse are urgently needed. Understanding the link between neurobiological mechanisms and behavior is a key aspect of elucidating drug abuse-related targets. Due to various molecular, biochemical, pharmacological, and physiological features, the zebrafish (Danio rerio) has been considered a suitable vertebrate for modeling complex processes involved in drug abuse responses. In this review, we discuss how the zebrafish has been successfully used for modeling neurobehavioral phenotypes related to drug abuse and review the effects of opioids, cannabinoids, alcohol, nicotine, and psychedelic drugs on the central nervous system (CNS). Moreover, we summarize recent advances in zebrafish-based studies and outline potential advantages and limitations of the existing zebrafish models to explore the neurochemical bases of drug abuse and addiction. Finally, we discuss how the use of zebrafish models may present fruitful approaches to provide valuable clinically translatable data.

Probing the Manipulated Neurochemical Drive in Alcohol Addiction and Novel Therapeutic Advancements

Alcohol addiction is one of the highly prevalent neurological disorders and a major threat to public health in the 21st century. Alcohol addiction affects people from all age groups and often leads to other serious comorbidities. The pathophysiology of alcohol addiction involves imbalance between the excitatory and inhibitory neurotransmitters in the brain. These changes occur in various regions of the brain including reward circuit such as the ventral tegmental area (VTA), nucleus accumbens (NAc), and prefrontal cortex. In this review, we have discussed several neurochemical circuitries which get manipulated and maladapted during alcohol addiction. To date there is no effective therapeutic intervention in clinics devoid of side effects that can successfully treat the patients suffering from alcohol addiction. Understanding the neurobiological intricacies of alcohol addiction is critical for the development of novel anti-addiction therapeutics. Apart from this, we have also discussed the recent therapeutic milestones for the management of alcohol addiction including vasopressin receptors, corticotrophin-releasing factor, GABA receptors, glucocorticoid receptors, brain stimulation and mindfulness-oriented recovery enhancement.

Behavioral and Molecular Basis of Cholinergic Modulation of Pain: Focus on Nicotinic Acetylcholine Receptors

Nicotinic acetylcholine receptors (nAChRs) have emerged as a novel therapeutic strategy for pain and inflammatory disorders. In particular, α4β2∗, α7, and α9α10 nAChR subtypes have been investigated as potential targets to treat pain. The nAChRs are distributed on the pain transmission pathways, including central and peripheral nervous systems and immune cells as well. Several agonists for α4β2∗ nAChR subtypes have been investigated in multiple animal pain models with promising results. However, studies in human indicated a narrow therapeutic window for α4β2∗ agonists. Furthermore, animal studies suggest that using agonists for α7 nAChR subtype and antagonists for α9α10 nAChR subtypes are potential novel therapies for chronic pain management, including inflammatory and neuropathic pain. More recently, alternative nAChRs ligands such as positive allosteric modulators and silent agonists have shown potential to develop into new treatments for chronic pain.

Nicotinic Receptors Underlying Nicotine Dependence: Evidence from Transgenic Mouse Models

Nicotine underlies the reinforcing properties of tobacco cigarettes and e-cigarettes. After inhalation and absorption, nicotine binds to various nicotinic acetylcholine receptor (nAChR) subtypes localized on the pre- and postsynaptic membranes of cells, which subsequently leads to the modulation of cellular function and neurotransmitter signaling. In this chapter, we begin by briefly reviewing the current understanding of nicotine's actions on nAChRs and highlight considerations regarding nAChR subtype localization and pharmacodynamics. Thereafter, we discuss the seminal discoveries derived from genetically modified mouse models, which have greatly contributed to our understanding of nicotine's effects on the reward-related mesolimbic pathway and the aversion-related habenulo-interpeduncular pathway. Thereafter, emerging areas of research focusing on modulation of nAChR expression and/or function are considered. Taken together, these discoveries have provided a foundational understanding of various genetic, neurobiological, and behavioral factors underlying the motivation to use nicotine and related dependence processes, which are thereby advancing drug discovery efforts to promote long-term abstinence.

Nutritional Contingency Reduces Alcohol Drinking by Altering Central Neurotransmitter Receptor Gene Expression in Rats

We have previously shown that 6 weeks of intermittent high-fat diet (Int-HFD) pre-exposure significantly reduced alcohol drinking in rats, providing preliminary evidence of the effectiveness of a dietary intervention in reducing alcohol intake. However, the functional framework and underlying neurobiological mechanisms of such dietary intervention are unknown. Here, we examined the impact of Int-HFD pre-exposure duration on alcohol drinking, plasma feeding peptides, and central neurotransmitter receptors gene expression. Male Long Evans rats (n = 6-7/group) received no pre-exposure, 1 or 2 weeks pre-exposure to Int-HFD and alcohol drinking (two-bottle choice) was evaluated. We observed HFD pre-exposure-dependent decrease in alcohol drinking, with a significant decrease observed following 2 weeks of Int-HFD pre-exposure. No significant between-group differences in plasma feeding peptides (i.e., ghrelin, leptin, insulin) were detected. A PCR array revealed that the expression of several neurotransmitter receptors was significantly (p < 0.05 and ≥2-fold) altered in the striatum and ventral tegmental area compared to controls. These data suggest that pre-exposure to a palatable diet is critical to reduce alcohol drinking in rats, possibly through genetic alterations in the brain reward circuitry. Importantly, the present study is a step forward in identifying the critical framework needed to evaluate the therapeutic potential of nutritional contingency in the management of alcoholism.

Effects of chronic alcohol consumption and withdrawal on the cholinergic neurons of the pedunculopontine and laterodorsal tegmental nuclei of the rat: An unbiased stereological study

The brain cholinergic system comprises two main recognized subdivisions, the basal forebrain and the brainstem cholinergic systems. The effects of chronic alcohol consumption on the basal forebrain cholinergic nuclei have been investigated extensively, but there is only one study that has examined those effects on the brainstem cholinergic nuclei. The last one comprises the pedunculopontine tegmental (PPT) and the laterodorsal tegmental (LDT) nuclei, which are known to give origin to the main cholinergic projection to the ventral tegmental area, a key brain region of the neural circuit, the mesocorticolimbic system, that mediates several behavioral and physiological processes, including reward. In the present study, we have examined, using stereological methods, the effects of chronic alcohol consumption (6 months) and subsequent withdrawal (2 months) on the total number and size of PPT and LDT choline acetyltransferase (ChAT)-immunoreactive neurons. The total number of PPT and LDT ChAT-immunoreactive neurons was unchanged in ethanol-treated and withdrawn rats. However, ChAT-immunoreactive neurons were significantly hypertrophied in ethanol-treated rats, an alteration that did not revert 2 months after ethanol withdrawal. These results show that prolonged exposure to ethanol leads to long-lasting, and potentially irreversible, cytoarchitectonic and neurochemical alterations in the brainstem cholinergic nuclei. These alterations suggest that the alcohol-induced changes in the brainstem cholinergic nuclei might play a role in the mechanisms underlying the development of addictive behavior to alcohol.

Longitudinal Findings from a Randomized Clinical Trial of Varenicline for Alcohol Use Disorder with Comorbid Cigarette Smoking

BACKGROUND

This study is the first to examine longitudinal posttreatment outcomes of a placebo-controlled trial of varenicline for alcohol use disorder (AUD) with comorbid cigarette smoking.

METHODS

Participants were 131 adults (n = 39 female) seeking alcohol treatment in a randomized, double-blind, parallel group, placebo-controlled, 16-week multisite trial of varenicline combined with medical management (MM). Timeline follow-back assessments of alcohol and smoking behavior were conducted at the end of treatment (4 months), with follow-ups at 6, 9, and 12 months. Outcomes were percentage of heavy drinking days (PHDD), percent of participants with no heavy drinking days (NHDD), cotinine-confirmed prolonged smoking abstinence (PA), and good clinical outcome on either NHDD or PA.

RESULTS

Treatment improvements were maintained posttreatment. For the sample overall, PHDD or NHDD did not differ significantly by treatment condition (ps > 0.13), but varenicline produced higher rates of PA versus placebo at 4, 9, and 12 months (p < 0.05). Significant differences were observed by sex: Males had higher rates of NHDD with varenicline (28.9%) versus placebo (6.4%) at the end of treatment (p = 0.004), and these effects were maintained at 12 months (varenicline: 40.0% vs. placebo: 19.2%, p = 0.03). Higher rates of PA were seen for varenicline in both males (8.9%) and females (21.1%) versus placebo (males/females: 0%) at the end of treatment (p = 0.05), and this effect was maintained at 12 months for females (varenicline: 21.1% vs. placebo, 0.0%, p = 0.05).

CONCLUSIONS

Varenicline treatment combined with MM appears to have enduring benefits for patients with co-occurring AUD and cigarette smoking, and these effects may differ by sex.

Insights Into Nicotinic Receptor Signaling in Nicotine Addiction: Implications for Prevention and Treatment

BACKGROUND

Nicotinic acetylcholine receptors (nAChRs) belong to the Cys-loop ligandgated ion-channel (LGIC) superfamily, which also includes the GABA, glycine, and serotonin receptors. Many nAChR subunits have been identified and shown to be involved in signal transduction on binding to them of either the neurotransmitter acetylcholine or exogenous ligands such as nicotine. The nAChRs are pentameric assemblies of homologous subunits surrounding a central pore that gates cation flux, and they are expressed at neuromuscular junctions throughout the nervous system.

METHODS AND RESULTS

Because different nAChR subunits assemble into a variety of pharmacologically distinct receptor subtypes, and different nAChRs are implicated in various physiological functions and pathophysiological conditions, nAChRs represent potential molecular targets for drug addiction and medical therapeutic research. This review intends to provide insights into recent advances in nAChR signaling, considering the subtypes and subunits of nAChRs and their roles in nicotinic cholinergic systems, including structure, diversity, functional allosteric modulation, targeted knockout mutations, and rare variations of specific subunits, and the potency and functional effects of mutations by focusing on their effects on nicotine addiction (NA) and smoking cessation (SC). Furthermore, we review the possible mechanisms of action of nAChRs in NA and SC based on our current knowledge.

CONCLUSION

Understanding these cellular and molecular mechanisms will lead to better translational and therapeutic operations and outcomes for the prevention and treatment of NA and other drug addictions, as well as chronic diseases, such as Alzheimer's and Parkinson's. Finally, we put forward some suggestions and recommendations for therapy and treatment of NA and other chronic diseases.

Pilot investigation: randomized-controlled analog trial for alcohol and tobacco smoking co-addiction using contingency management

Contingency management (CM) is associated with decreases in off-target drug and alcohol use during primary target treatment. The primary hypothesis for this trial was that targeting alcohol use or tobacco smoking would yield increased abstinence in the opposite, nontargeted drug. We used a 2 [CM vs. noncontingent control (NC) for alcohol]×2 (CM vs. NC for smoking tobacco) factorial design, with alcohol intake (through urinary ethyl glucuronide) and tobacco smoking (through urinary cotinine) as the primary outcomes. Thirty-four heavy-drinking smokers were randomized into one of four groups, wherein they received CM, or equivalent NC reinforcement, for alcohol abstinence, smoking abstinence, both drugs, or neither drug. The CM for alcohol and tobacco group had only two participants and therefore was not included in analysis. Compared with the NC for alcohol and tobacco smoking group, both the CM for the tobacco smoking group [odds ratio (OR)=12.03; 95% confidence interval (CI): 1.50-96.31] and the CM for the alcohol group (OR=37.55; 95% CI: 4.86-290.17) submitted significantly more tobacco-abstinent urinalyses. Similarly, compared with the NC for the alcohol and tobacco group, both the CM for smoking (OR=2.57; 95% CI: 1.00-6.60) and the CM for alcohol groups (OR=3.96; 95% CI: 1.47-10.62) submitted significantly more alcohol-abstinent urinalyses. These data indicate cross-over effects of CM on indirect treatment targets. Although this is a pilot investigation, it could help to inform the design of novel treatments for alcohol and tobacco co-addiction.

Gene editing vectors for studying nicotinic acetylcholine receptors in cholinergic transmission

Nicotinic acetylcholine receptors (nAChRs), prototype members of the cys-loop ligand-gated ion channel family, are key mediators of cholinergic transmission in the central nervous system. Despite their importance, technical gaps exist in our ability to dissect the function of individual subunits in the brain. To overcome these barriers, we designed CRISPR/Cas9 small guide RNA sequences (sgRNAs) for the production of loss-of-function alleles in mouse nAChR genes. These sgRNAs were validated in vitro via deep sequencing. We subsequently targeted candidate nAChR genes in vivo by creating herpes simplex virus (HSV) vectors delivering sgRNAs and Cas9 expression to mouse brain. The production of loss-of-function insertions or deletions (indels) by these 'all-in-one' HSV vectors was confirmed using brain slice patch clamp electrophysiology coupled with pharmacological analysis. Next, we developed a scheme for cell type-specific gene editing in mouse brain. Knockin mice expressing Cas9 in a Cre-dependent manner were validated using viral microinjections and genetic crosses to common Cre-driver mouse lines. We subsequently confirmed functional Cas9 activity by targeting the ubiquitous neuronal protein, NeuN, using adeno-associated virus (AAV) delivery of sgRNAs. Finally, the mouse β2 nAChR gene was successfully targeted in dopamine transporter (DAT)-positive neurons via CRISPR/Cas9. The sgRNA sequences and viral vectors, including our scheme for Cre-dependent gene editing, should be generally useful to the scientific research community. These tools could lead to new discoveries related to the function of nAChRs in neurotransmission and behavioral processes.

Differential regulation of alcohol taking and seeking by antagonism at α4β2 and α3β4 nAChRs

RATIONALE

Alcoholism is a serious public health problem throughout the world. Current pharmacotherapies for the treatment of this disorder are poorly effective. Preclinical and clinical findings point to nicotinic acetylcholine receptors (nAChRs) as a promising target for the development of novel and effective medications. Assuage Pharmaceuticals, in collaboration with Torrey Pines Institute for Molecular Studies, has discovered a new class of potent and selective α4β2 nAChR antagonists.

OBJECTIVE

Here, it was hypothesized that α4β2 nAChR antagonism is a viable approach for treatment of alcohol use disorders.

RESULTS

When tested in rats, one lead compound, AP-202, attenuated both operant alcohol and nicotine self-administration in a paradigm in which the two reinforcers were concurrently available. The conotoxin TP2212-59, a selective α3β4 nAChR antagonist, was only effective in reducing nicotine self-administration. AP-202 also reduced alcohol but not food responding when alcohol was presented as the only reinforcer, whereas the commercially available α4β2 nAChR antagonist dihydro-β-erythroidine failed to alter alcohol self-administration. AP-202 did not block relapse-like behavior induced by previously alcohol-associated stimuli or yohimbine stress. In a reinstatement paradigm, in which alcohol seeking was triggered by a nicotine challenge, a behavior successfully inhibited by the nonselective nAChR antagonist mecamylamine, AP-202 was not effective, while pretreatment with TP2212-59 abolished nicotine-induced reinstatement of alcohol seeking.

CONCLUSIONS

These findings suggest differential roles for α4β2 and α3β4 nAChR on alcohol taking and seeking with selective blockade of α4β2 nAChR being more implicated in modulating alcohol taking while selective blockade of α3β4 nAChR is involved in nicotine-induced alcohol seeking.

The nicotinic receptor drug sazetidine-A reduces alcohol consumption in mice without affecting concurrent nicotine consumption

Alcohol and nicotine addiction are frequently co-morbid. The nicotinic acetylcholine receptors (nAChRs) are critical for both alcohol and nicotine addiction mechanisms, since nAChR drugs that reduce nicotine consumption have been shown to also reduce alcohol consumption. Sazetidine-A, a pre-clinical nAChR drug with agonist and desensitizing effects at α4β2 and α7 nAChRs, has been reported to reduce alcohol consumption and nicotine self-administration in rats when administered at high doses. However, this effect has not been replicated in mice. In this study, we examined the effect of sazetidine-A on alcohol and nicotine consumption in male and female mice utilizing voluntary oral consumption procedures previously developed in our lab. We found that sazetidine-A (1 mg/kg, i.p) reduced overnight alcohol consumption, but did not affect nicotine consumption when presented either alone or concurrently with alcohol. Sazetidine-A did not reduce water or saccharin consumption at any dose tested. In a chronic co-consumption experiment in which either alcohol or nicotine was re-introduced after one week of forced abstinence, sazetidine-A attenuated post-abstinence consumption of alcohol but not nicotine. Sazetidine-A also significantly reduced alcohol consumption in an acute, binge drinking-in-the-dark procedure. Finally, we tested the effect of sazetidine-A on alcohol withdrawal, and found that sazetidine-A significantly reduced handling-induced convulsions during alcohol withdrawal. Collectively, these data suggest a novel role for the nAChR targets of sazetidine-A in specifically mediating alcohol consumption, separate from the involvement of nAChRs in mediating nicotine consumption. Delineation of this pathway may provide insight into novel therapies for the treatment of alcohol use disorders.

Effect of Varenicline Combined With Medical Management on Alcohol Use Disorder With Comorbid Cigarette Smoking: A Randomized Clinical Trial

IMPORTANCE

Individuals with alcohol use disorder have high rates of cigarette smoking. Varenicline tartrate, an approved treatment for smoking cessation, may reduce both drinking and smoking.

OBJECTIVES

To test the efficacy of varenicline with medical management for patients with alcohol use disorder and comorbid smoking seeking alcohol treatment, and to evaluate the secondary effects on smoking abstinence.

DESIGN, SETTING, AND PARTICIPANTS

This phase 2, randomized, double-blind, parallel group, placebo-controlled trial was conducted at 2 outpatient clinics from September 19, 2012, to August 31, 2015. Eligible participants met alcohol-dependence criteria and reported heavy drinking (≥5 drinks for men and ≥4 drinks for women) 2 or more times per week and smoking 2 or more times per week; 131 participants were randomized to either varenicline or placebo stratified by sex and site. All analyses were of the intention-to-treat type. Data analysis was conducted from February 5, 2016, to September 29, 2017.

INTERVENTIONS

Varenicline tartrate, 1 mg twice daily, and matching placebo pills for 16 weeks. Medical management emphasized medication adherence for 4 weeks followed by support for changing drinking.

MAIN OUTCOMES AND MEASURES

Percentage of heavy drinking days (PHDD) weeks 9 to 16, no heavy drinking days (NHDD) weeks 9 to 16, and prolonged smoking abstinence weeks 13 to 16.

RESULTS

Of 131 participants, 39 (29.8%) were women and 92 (70.2%) were men, the mean (SD) age was 42.7 (11.7) years, and the race/ethnicity self-identified by most respondents was black (69 [52.7%]). Sixty-four participants were randomized to receive varenicline, and 67 to receive placebo. Mean change in PHDD between varenicline and placebo across sex and site was not significantly different. However, a significant treatment by sex by time interaction for PHDD (F1,106 = 4.66; P = .03) revealed that varenicline compared with placebo resulted in a larger decrease in log-transformed PHDD in men (least square [LS] mean difference in change from baseline, 0.54; 95% CI, -0.09 to 1.18; P = .09; Cohen d = 0.45) but a smaller decrease in women (LS mean difference, -0.69; 95% CI, -1.63 to 0.25; P = .15; Cohen d = -0.53). Thirteen of 45 men (29%) had NHDD taking varenicline compared with 3 of 47 men (6%) taking placebo (Cohen h = 0.64; 95% CI, 0.22-1.03), whereas 1 of 19 women (5%) had NHDD compared with 5 of 20 women (25%) taking placebo (Cohen h = -0.60; 95% CI, -1.21 to 0.04). Taking varenicline, 8 of 64 participants (13%) achieved prolonged smoking abstinence; no one (0 of 67) quit smoking taking placebo (P = .003; Cohen h = 0.72; 95% CI, 0.38-1.07).

CONCLUSIONS AND RELEVANCE

Varenicline with medical management resulted in decreased heavy drinking among men and increased smoking abstinence in the overall sample. Varenicline could be considered to promote improvements in men with these dual behavioral health risks.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT01553136.

Nicotinic acetylcholine receptors (nAChRs) are expressed in Trpm5 positive taste receptor cells (TRCs)

Nicotine evokes chorda tympani (CT) taste nerve responses and an aversive behavior in Trpm5 knockout (KO) mice. The agonists and antagonists of nicotinic acetylcholine receptors (nAChRs) modulate neural and behavioral responses to nicotine in wildtype (WT) mice, Trpm5 KO mice and rats. This indicates that nicotine evokes bitter taste by activating a Trpm5-dependent pathway and a Trpm5-independent but nAChR-dependent pathway. Rat CT responses to ethanol are also partially inhibited by nAChR blockers, mecamylamine and dihydro-β-erythroidine. This indicates that a component of the bitter taste of ethanol is also nAChR-dependent. However, at present the expression and localization of nAChR subunits has not been investigated in detail in taste receptor cells (TRCs). To this end, in situ hybridization, immunohistochemistry and q-RT-PCR techniques were utilized to localize nAChR subunits in fungiform and circumvallate TRCs in WT mice, Trpm5-GFP transgenic mice, nAChR KO mice, and rats. The expression of mRNAs for α7, β2 and β4 nAChR subunits was observed in a subset of rat and WT mouse circumvallate and fungiform TRCs. Specific α3, α4, α7, β2, and β4 antibodies localized to a subset of WT mouse circumvallate and fungiform TRCs. In Trpm5-GFP mice α3, α4, α7, and β4 antibody binding was observed in a subset of Trpm5-positive circumvallate TRCs. Giving nicotine (100 μg/ml) in drinking water to WT mice for 3 weeks differentially increased the expression of α3, α4, α5, α6, α7, β2 and β4 mRNAs in circumvallate TRCs to varying degrees. Giving ethanol (5%) in drinking water to WT mice induced an increase in the expression of α5 and β4 mRNAs in circumvallate TRCs with a significant decrease in the expression of α3, α6 and β2 mRNAs. We conclude that nAChR subunits are expressed in Trpm5-positive TRCs and their expression levels are differentially altered by chronic oral exposure to nicotine and ethanol.

Alcohol and the Brain: Neuronal Molecular Targets, Synapses, and Circuits

Ethanol is one of the most commonly abused drugs. Although environmental and genetic factors contribute to the etiology of alcohol use disorders, it is ethanol's actions in the brain that explain (1) acute ethanol-related behavioral changes, such as stimulant followed by depressant effects, and (2) chronic changes in behavior, including escalated use, tolerance, compulsive seeking, and dependence. Our knowledge of ethanol use and abuse thus relies on understanding its effects on the brain. Scientists have employed both bottom-up and top-down approaches, building from molecular targets to behavioral analyses and vice versa, respectively. This review highlights current progress in the field, focusing on recent and emerging molecular, cellular, and circuit effects of the drug that impact ethanol-related behaviors. The focus of the field is now on pinpointing which molecular effects in specific neurons within a brain region contribute to behavioral changes across the course of acute and chronic ethanol exposure.

Effects of Nicotine on Alcohol Drinking in Female Mice Selectively Bred for High or Low Alcohol Preference

BACKGROUND

Studies show that repeated nicotine use associates with high alcohol consumption in humans and that nicotine exposure sometimes increases alcohol consumption in animal models. However, the relative roles of genetic predisposition to high alcohol consumption, the alcohol drinking patterns, and the timing of nicotine exposure both with respect to alcohol drinking and developmental stage remain unclear. The studies here manipulated all these variables, using mice selectively bred for differences in free-choice (FC) alcohol consumption to elucidate the role of genetics and nicotine exposure in alcohol consumption behaviors.

METHODS

In Experiments 1 and 2, we assessed the effects of repeated nicotine (0, 0.5, or 1.5 mg/kg) injections immediately before binge-like (drinking-in-the-dark; Experiment 1) or during FC alcohol access (Experiment 2) on these alcohol drinking behaviors (immediately after injections and during re-exposure to alcohol access 14 days later) in adult high- (HAP2) and low-alcohol-preferring (LAP2) female mice (co-exposure model). In Experiments 3 and 4, we assessed the effects of repeated nicotine (0, 0.5, or 1.5 mg/kg) injections 14 days prior to binge-like and FC alcohol access on these alcohol drinking behaviors in adolescent HAP2 and LAP2 female mice (Experiment 3) or adult HAP2 female mice (Experiment 4).

RESULTS

In Experiment 1, we found that repeated nicotine (0.5 and 1.5 mg/kg) and alcohol co-exposure significantly increased binge-like drinking behavior in HAP2 but not LAP2 mice during the re-exposure phase after a 14-day abstinence period. In Experiment 2, 1.5 mg/kg nicotine injections significantly reduced FC alcohol intake and preference in the third hour postinjection in HAP2 but not LAP2 mice. No significant effects of nicotine treatment on binge-like or FC alcohol drinking were observed in Experiments 3 and 4.

CONCLUSIONS

These results show that the temporal parameters of nicotine and alcohol exposure, pattern of alcohol access, and genetic predisposition for alcohol preference influence nicotine's effects on alcohol consumption. These findings in selectively bred mice suggest that humans with a genetic history of alcohol use disorders may be more vulnerable to develop nicotine and alcohol co-use disorders.

Overdominant Effect of a CHRNA4 Polymorphism on Cingulo-Opercular Network Activity and Cognitive Control

The nicotinic system plays an important role in cognitive control and is implicated in several neuropsychiatric conditions. However, the contributions of genetic variability in this system to individuals' cognitive control abilities are poorly understood and the brain processes that mediate such genetic contributions remain largely unidentified. In this first large-scale neuroimaging genetics study of the human nicotinic receptor system (two cohorts, males and females, fMRI total N = 1586, behavioral total N = 3650), we investigated a common polymorphism of the high-affinity nicotinic receptor α4β2 (rs1044396 on the CHRNA4 gene) previously implicated in behavioral and nicotine-related studies (albeit with inconsistent major/minor allele impacts). Based on our prior neuroimaging findings, we expected this polymorphism to affect neural activity in the cingulo-opercular (CO) network involved in core cognitive control processes including maintenance of alertness. Consistent across the cohorts, all cortical areas of the CO network showed higher activity in heterozygotes compared with both types of homozygotes during cognitive engagement. This inverted U-shaped relation reflects an overdominant effect; that is, allelic interaction (cumulative evidence p = 1.33 * 10-5). Furthermore, heterozygotes performed more accurately in behavioral tasks that primarily depend on sustained alertness. No effects were observed for haplotypes of the surrounding CHRNA4 region, supporting a true overdominant effect at rs1044396. As a possible mechanism, we observed that this polymorphism is an expression quantitative trait locus modulating CHRNA4 expression levels. This is the first report of overdominance in the nicotinic system. These findings connect CHRNA4 genotype, CO network activation, and sustained alertness, providing insights into how genetics shapes individuals' cognitive control abilities.SIGNIFICANCE STATEMENT The nicotinic acetylcholine system plays a central role in neuromodulatory regulation of cognitive control processes and is dysregulated in several neuropsychiatric disorders. Despite this functional importance, no large-scale neuroimaging genetics studies have targeted the contributions of genetic variability in this system to human brain activity. Here, we show the impact of a common polymorphism of the high-affinity nicotinic receptor α4β2 that is consistent across brain activity and behavior in two large human cohorts. We report a hitherto unknown overdominant effect (allelic interaction) at this locus, where the heterozygotes show higher activity in the cingulo-opercular network underlying alertness maintenance and higher behavioral alertness performance than both homozygous groups. This gene-brain-behavior relationship informs about the biological basis of interindividual differences in cognitive control.

Effect of single-nucleotide polymorphisms in ADH1B, ADH4, ADH1C, OPRM1, DRD2, BDNF, and ALDH2 genes on alcohol dependence in a Caucasian population

Alcohol is a frequently used addictive substance worldwide. Aim of this study is to determine the frequency distribution of SNPs within ADH1B,ADH4,ADH1C,ALDH2, BDNF,OPRM1, and DRD2 genes in a southeastern European Caucasian population from Greece. For this purpose samples of 1276 volunteers were analyzed after deidentification and anonymization. The allele distribution of the examined polymorphisms in the present Greek population cohort was as follows: rs1229984 (ADH1B): GG(wt) = 64.14%, GA = 29.86%, AA = 4.00%; rs1693482 (ADH1C): CC(wt) = 57.45%, CT = 36.76%, TT = 5.80%; rs1799971 (OPRM1): AA(wt) = 72.43%, AG = 28.72%, GG = 1.89%; rs1800497 (DRD2): CC(wt) = 70.84%, CT = 27.18%, TT = 1.98%; rs1800759 (ADH4): CC(wt) = 34.25%, CA = 48.12%, AA = 17.63%; rs6265 (BDNF): GG(wt) = 65.99%, GA = 31.02%, AA = 2.99%; and rs671 (ALDH2): GG(wt) = 99.84% GA = 0.16%, AA = 0.00%. Mutant rs1229984 allele A was ~6.5× more frequent in the Greek than in the European population. Mutant rs1693482 allele T was ~1.7× more frequent in the European than in the Greek population. Mutant alleles for polymorphisms rs1800759 and rs1799971 show similar frequencies in both northern and southern Europeans. One rs671 mutant A allele was detected in the Greek population (0.08%). The mutant rs1800497 allele T was ~1.2× more frequent in the European than in the Greek population and the mutant rs6265 allele A was ~1.1× more frequent in the European than in the Greek population. An alcohol addiction‐specific algorithm was generated (TGS) that may predict alcohol addiction prevalence in a population. According to our findings, the analyzed Southeastern population may differ genetically from north Europeans due to influences from neighboring Asian and African populations and a calculated TGS score >50 indicates individuals with low susceptibility to develop alcohol addiction.

The crystal structure of Ac-AChBP in complex with α-conotoxin LvIA reveals the mechanism of its selectivity towards different nAChR subtypes

The α3* nAChRs, which are considered to be promising drug targets for problems such as pain, addiction, cardiovascular function, cognitive disorders etc., are found throughout the central and peripheral nervous system. The α-conotoxin (α-CTx) LvIA has been identified as the most selective inhibitor of α3β2 nAChRs known to date, and it can distinguish the α3β2 nAChR subtype from the α6/α3β2β3 and α3β4 nAChR subtypes. However, the mechanism of its selectivity towards α3β2, α6/α3β2β3, and α3β4 nAChRs remains elusive. Here we report the co-crystal structure of LvIA in complex with Aplysia californica acetylcholine binding protein (Ac-AChBP) at a resolution of 3.4 Å. Based on the structure of this complex, together with homology modeling based on other nAChR subtypes and binding affinity assays, we conclude that Asp-11 of LvIA plays an important role in the selectivity of LvIA towards α3β2 and α3/α6β2β3 nAChRs by making a salt bridge with Lys-155 of the rat α3 subunit. Asn-9 lies within a hydrophobic pocket that is formed by Met-36, Thr-59, and Phe-119 of the rat β2 subunit in the α3β2 nAChR model, revealing the reason for its more potent selectivity towards the α3β2 nAChR subtype. These results provide molecular insights that can be used to design ligands that selectively target α3β2 nAChRs, with significant implications for the design of new therapeutic α-CTxs.

No evidence of a role of the β4 subunit of the nicotinic acetylcholine receptor in alcohol-related behaviors

Background

Nicotinic acetylcholine receptors have gained attention in the last several years as mediators of alcohol-related behaviors. The genes that code for the α5, α3, and β4 subunits (Chrna5, Chrna3, and Chrnb4, respectively) map adjacent to each other on human chromosome 15/mouse chromosome 9. Genetic variants in this region have been associated with alcohol phenotypes and mice that overexpress these three subunits have reduced ethanol intake. In the present experiments, we examined the role of the Chrnb4 gene in three ethanol behaviors: consumption, ataxia, and sedation. Wildtype, heterozygous, and knockout mice were tested for ethanol consumption with a 2-bottle choice procedure and the drinking-in-the-dark paradigm. Ethanol-induced ataxia was measured with the balance beam and dowel test. Finally, the sedative effects of ethanol were measured with the loss of righting reflex paradigm.

Results

We observed no significant genotypic effects on any of the ethanol behaviors examined, suggesting that the β4 subunit is not involved in mediating these responses.

Conclusions

While we found no evidence for the involvement of the β4 subunit in ethanol responses, it is possible that this subunit modulates other behaviors not tested and further work should address this before completely ruling out its involvement.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-017-2470-7) contains supplementary material, which is available to authorized users.