The influence of mecamylamine on ethanol and sucrose self-administration

The role of nicotinic receptors in alcohol consumption

The use of alcohol causes significant morbidity and mortality across the globe. Alcohol use disorder (AUD) is defined by the excessive use of this drug despite a negative impact on the individual's life. While there are currently medications available to treat AUD, they have limited efficacy and several side effects. As such, it is essential to continue to look for novel therapeutics. One target for novel therapeutics is nicotinic acetylcholine receptors (nAChRs). Here we systematically review the literature on the involvement of nAChRs in alcohol consumption. Data from both genetic and pharmacology studies provide evidence that nAChRs modulate alcohol intake. Interestingly, pharmacological modulation of all nAChR subtypes examined can decrease alcohol consumption. The reviewed literature demonstrates that nAChRs should continue to be investigated as novel therapeutics for AUD.

What We Have Gained from Ibogaine: α3β4 Nicotinic Acetylcholine Receptor Inhibitors as Treatments for Substance Use Disorders

For decades, ibogaine─the main psychoactive alkaloid found in Tabernanthe iboga─has been investigated as a possible treatment for substance use disorders (SUDs) due to its purported ability to interrupt the addictive properties of multiple drugs of abuse. Of the numerous pharmacological actions of ibogaine and its derivatives, the inhibition of α3β4 nicotinic acetylcholine receptors (nAChRs), represents a probable mechanism of action for their apparent anti-addictive activity. In this Perspective, we examine several classes of compounds that have been discovered and developed to target α3β4 nAChRs. Specifically, by focusing on compounds that have proven efficacious in pre-clinical models of drug abuse and have been evaluated clinically, we highlight the promising potential of the α3β4 nAChRs as viable targets to treat a wide array of SUDs. Additionally, we discuss the challenges faced by the existing classes of α3β4 nAChR ligands that must be overcome to develop them into therapeutic treatments.

Nicotine' actions on energy balance: Friend or foe?

Obesity has reached pandemic proportions and is associated with severe comorbidities, such as type 2 diabetes mellitus, hepatic and cardiovascular diseases, and certain cancer types. However, the therapeutic options to treat obesity are limited. Extensive epidemiological studies have shown a strong relationship between smoking and body weight, with non-smokers weighing more than smokers at any age. Increased body weight after smoking cessation is a major factor that interferes with their attempts to quit smoking. Numerous controlled studies in both humans and rodents have reported that nicotine, the main bioactive component of tobacco, exerts a marked anorectic action. Furthermore, nicotine is also known to modulate energy expenditure, by regulating the thermogenic activity of brown adipose tissue (BAT) and the browning of white adipose tissue (WAT), as well as glucose homeostasis. Many of these actions occur at central level, by controlling the activity of hypothalamic neuropeptide systems such as proopiomelanocortin (POMC), or energy sensors such as AMP-activated protein kinase (AMPK). However, direct impact of nicotine on metabolic tissues, such as BAT, WAT, liver and pancreas has also been described. Here, we review the actions of nicotine on energy balance. The relevance of this interaction is interesting, because considering the restricted efficiency of obesity treatments, a possible complementary approach may focus on compounds with known pharmacokinetic profile and pharmacological actions, such as nicotine or nicotinic acetylcholine receptors signaling.

The role of nicotinic acetylcholine receptors in alcohol-related behaviors

Alcohol use disorder (AUD) causes an alarming economic and health burden in the United States. Unfortunately, this disease does not exist in isolation; AUD is highly comorbid with nicotine use. Results from both human and animal models demonstrate a genetic correlation between alcohol and nicotine behaviors. These data support the idea of shared genetic and neural mechanisms underlying these behaviors. Nicotine acts directly at nicotinic acetylcholine receptors (nAChR) to have its pharmacological effect. Interestingly, alcohol also acts both directly and indirectly at these receptors. Research utilizing genetically engineered rodents and pharmacological manipulations suggest a role for nAChR in several ethanol behaviors. The current manuscript collates this literature and discusses findings that implicate specific nAChR subunits in ethanol phenotypes. These data suggest future directions for targeting nAChR as novel therapeutics for AUD.

Reduced expression of ethanol sensitization by α3β4 nicotinic acetylcholine receptors in DBA/2J mice

Alcohol use disorder (AUD) is a leading cause of preventable death in the United States, however existing treatments are ineffective and produce aversive side effects such as nausea and fatigue. One potential therapeutic for AUD is the α3β4 nicotinic acetylcholine receptor (nAChR) antagonist 18-methoxycoronaridine (18-MC). Prior work has shown that 18-MC reduces ethanol consumption in rodent models. The present study sought to further examine the therapeutic potential of 18-MC by testing its effects on nonconsummatory behaviors. We examined 2 behavioral measures: ethanol-induced locomotor stimulation, which measures euphoric properties of the drug, and the expression of locomotor sensitization which models neuroadaptations in response to repeated exposure. We tested dose-dependent effects of 18-MC (0, 10, 20 and 30 mg/kg) administration on ethanol stimulation and locomotor sensitization in female and male DBA/2J mice. 18-MC had no effect on acute ethanol-induced stimulation, but the highest dose (30 mg/kg) significantly decreased the expression of locomotor sensitization. Our results support the involvement of α3β4 nAChR in the expression of ethanol-induced locomotor sensitization and suggest that 18-MC may be a therapeutic for AUD. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

UFR2709, a Nicotinic Acetylcholine Receptor Antagonist, Decreases Ethanol Intake in Alcohol-Preferring Rats

Brain nicotinic acetylcholine receptors (nAChRs), a heterogeneous family of pentameric acetylcholine-gated cation channels, have been suggested as molecular targets for the treatment of alcohol abuse and dependence. Here, we examined the effect of the competitive nAChR antagonist UFR2709 on the alcohol consumption of high-alcohol-drinking UChB rats. UChB rats were given free access to ethanol for 24-h periods in a two-bottle free choice paradigm and their ethanol and water intake were measured. The animals were i.p. injected daily for 17 days with a 10, 5, 2.5, or 1 mg/kg dose of UFR2709. Potential confounding motor effects of UFR2709 were assessed by examining the locomotor activity of animals administered the highest dose of UR2709 tested (10 mg/kg i.p.). UFR2709 reduced ethanol consumption and ethanol preference and increased water consumption in a dose-dependent manner. The most effective dose of UFR2709 was 2.5 mg/kg, which induced a 56% reduction in alcohol consumption. Administration of UFR2709 did not affect the weight or locomotor activity of the rats, suggesting that its effects on alcohol consumption and preference were mediated by specific nAChRs.

Erysodine, a competitive antagonist at neuronal nicotinic acetylcholine receptors, decreases ethanol consumption in alcohol-preferring UChB rats

Alcohol abuse is a worldwide health problem with high economic costs to health systems. Emerging evidence suggests that modulation of brain nicotinic acetylcholine receptors (nAChRs) may be a therapeutic target for alcohol dependence. In this work, we assess the effectiveness of four doses of erysodine (1.5, 2.0, 4.0 or 8.0 mg/kg/day, i.p.), a competitive antagonist of nAChRs, on voluntary ethanol consumption behavior in alcohol-preferring UChB rats, administered during three consecutive days. Results show that erysodine administration produces a dose-dependent reduction in ethanol consumption respect to saline injection (control group). The highest doses of erysodine (4 and 8 mg/kg) reduce (45 and 66%, respectively) the ethanol intake during treatment period and first day of post-treatment compared to control group. While, the lowest doses of erysodine (1.5 and 2 mg/kg) only reduce ethanol intake during one day of treatment period. These effective reductions in ethanol intake were 23 and 29% for 1.5 and 2 mg/kg erysodine, respectively. Locomotor activity induced by a high dose of erysodine (10 mg/kg) was similar to those observed with saline injection in control rats, showing that the reduction in ethanol intake was not produced by hypolocomotor effect induced by erysodine. This is the first report showing that erysodine reduces ethanol intake in UChB rats in a dose-dependent manner. Our results highlight the role of nAChRs in the reward effects of ethanol and its modulation as a potentially effective pharmacological alternative for alcohol dependence treatment.

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.

Effects of nicotine on homeostatic and hedonic components of food intake

Chronic tobacco use leads to nicotine addiction that is characterized by exaggerated urges to use the drug despite the accompanying negative health and socioeconomic burdens. Interestingly, nicotine users are found to be leaner than the general population. Review of the existing literature revealed that nicotine affects energy homeostasis and food consumption via altering the activity of neurons containing orexigenic and anorexigenic peptides in the brain. Hypothalamus is one of the critical brain areas that regulates energy balance via the action of these neuropeptides. The equilibrium between these two groups of peptides can be shifted by nicotine leading to decreased food intake and weight loss. The aim of this article is to review the existing literature on the effect of nicotine on food intake and energy homeostasis and report on the changes that nicotine brings about in the level of these peptides and their receptors that may explain changes in food intake and body weight induced by nicotine. Furthermore, we review the effect of nicotine on the hedonic aspect of food intake. Finally, we discuss the involvement of different subtypes of nicotinic acetylcholine receptors in the regulatory action of nicotine on food intake and energy homeostasis.

Re-exposure to nicotine-associated context from adolescence enhances alcohol intake in adulthood

Alcohol and nicotine are the two most commonly-abused substances and are often used together. Nicotine enhances alcohol-drinking behaviors in humans and in animals, and was suggested to enhance the reinforcing properties of other reinforcers. Here, we show that nicotine-associated environment, rather than nicotine itself, enhances alcohol intake in rats. Adolescent rats received repeated intermittent injections of nicotine (0.4 mg/kg, i.p., 5 injections, every 3^rd day) or saline. The injection was paired with their home cage, or with the subsequent alcohol self-administration context. Rats were then trained to self-administer 20% alcohol. Nicotine given in the home cage did not alter subsequent alcohol intake. However, pairing nicotine with the operant chamber during adolescence led to a long-lasting increased alcohol self-administration in adulthood, compared to nicotine pre-treatment in other contexts. This effect persisted 3 months after nicotine cessation, in a relapse test after abstinence. Furthermore, re-exposure to the nicotine-associated context in adult rats led to a decrease in glial cell line-derived neurotrophic factor (Gdnf) mRNA expression in the ventral tegmental area, an effect that leads to increased alcohol consumption, as we have previously reported. Our findings suggest that retrieval of nicotine-associated contextual memories from adolescence may gate alcohol intake in adulthood, with a possible involvement of GDNF.

Medications development for the treatment of alcohol use disorder: insights into the predictive value of animal and human laboratory models

Development of effective treatments for alcohol use disorder (AUD) represents an important public health goal. This review provides a summary of completed preclinical and clinical studies testing pharmacotherapies for the treatment of AUD. We discuss opportunities for improving the translation from preclinical findings to clinical trial outcomes, focusing on the validity and predictive value of animal and human laboratory models of AUD. Specifically, while preclinical studies of medications development have offered important insights into the neurobiology of the disorder and alcohol's molecular targets, limitations include the lack of standardized methods and streamlined processes whereby animal studies can readily inform human studies. Behavioral pharmacology studies provide a less expensive and valuable opportunity to assess the feasibility of a pharmacotherapy prior to initiating larger scale clinical trials by providing insights into the mechanism of the drug, which can then inform recruitment, analyses, and assessments. Summary tables are provided to illustrate the wide range of preclinical, human laboratory, and clinical studies of medications development for alcoholism. Taken together, this review highlights the challenges associated with animal paradigms, human laboratory studies, and clinical trials with the overarching goal of advancing treatment development and highlighting opportunities to bridge the gap between preclinical and clinical research.

The Nicotinic α6-Subunit Selective Antagonist bPiDI Reduces Alcohol Self-Administration in Alcohol-Preferring Rats

Cigarettes and alcohol are the most abused substances in the world and are commonly co-abused. Nicotine primarily acts in the brain on nicotinic acetylcholine receptors (nAChR), which are also a target for alcohol. The alpha6 subunit of nAChR is expressed almost exclusively in the brain reward system and may modulate the rewarding properties of alcohol and nicotine. Recently, N,N-decane-1,10-diyl-bis-3-picolinium diiodide (bPiDI) was synthesized as a selective, brain penetrant α6 subunit antagonist that reduces nicotine self-administration. The current study aimed to examine the effects of bPiDI on alcohol self-administration in inbred alcohol-preferring (iP) rats. Adult, male iP rats were trained to self-administer alcohol or sucrose. Once stable responding was achieved, rats were injected with bPiDI (1, 3 mg/kg, i.p.) and tested for self-administration under fixed and progressive ratio schedules of reinforcement. They subsequently underwent extinction, in which no rewards or cues were presented in the operant chambers. Then, they were injected with bPiDI prior to testing for cue-induced reinstatement of reward seeking. bPiDI (3 mg/kg) significantly reduced alcohol self-administration in both fixed and progressive ratios without any effects on sucrose self-administration or locomotor activity. In contrast, bPiDI (3 mg/kg) did not inhibit cue-induced reinstatement of either alcohol or sucrose seeking. The results support the involvement of α6 containing nAChR in reinforcing effects of alcohol, but not relapse to alcohol-seeking, without any impact on responding for a natural reward or general activity. bPiDI may be a potential lead molecule for a therapeutic strategy to limit nicotine and alcohol consumption.

Neuronal Nicotinic Acetylcholine Receptor Modulators Reduce Sugar Intake

Excess sugar consumption has been shown to contribute directly to weight gain, thus contributing to the growing worldwide obesity epidemic. Interestingly, increased sugar consumption has been shown to repeatedly elevate dopamine levels in the nucleus accumbens (NAc), in the mesolimbic reward pathway of the brain similar to many drugs of abuse. We report that varenicline, an FDA-approved nicotinic acetylcholine receptor (nAChR) partial agonist that modulates dopamine in the mesolimbic reward pathway of the brain, significantly reduces sucrose consumption, especially in a long-term consumption paradigm. Similar results were observed with other nAChR drugs, namely mecamylamine and cytisine. Furthermore, we show that long-term sucrose consumption increases α4β2 * and decreases α6β2* nAChRs in the nucleus accumbens, a key brain region associated with reward. Taken together, our results suggest that nAChR drugs such as varenicline may represent a novel treatment strategy for reducing sugar consumption.

Contribution of NMDA glutamate and nicotinic acetylcholine receptor mechanisms in the discrimination of ethanol-nicotine mixtures

Ethanol and nicotine are commonly coabused drugs, and the incidence of codependence is greater than would be expected on the basis of the summed probability of dependence on each drug alone. Previous findings from our laboratory and others suggest that interactive mechanisms at the level of discriminative stimulus (S(D)) effects may contribute to this coabuse phenomenon. Specifically, ethanol overshadows the nicotine S(D) whereas nicotine potentiates the stimulus salience of ethanol when the two drugs are conditioned as a drug mixture. The goal of the current study was to begin to delineate the pharmacological bases of these ethanol-nicotine interactions. Three groups of C57BL/6J mice were trained to discriminate 0.8 mg/kg nicotine + 0.5 g/kg ethanol (0.8 N + 0.5 E), 0.8 N + 1.0 E, or 0.8 N + 2.0 E. An NMDA receptor antagonist (MK-801) and three nACh receptor ligands were tested for their ability to generalize from or antagonize, respectively, the drug mixtures. MK-801 fully generalized from the 0.8 N + 1.0 E and 0.8 N + 2.0 E mixtures and partially generalized from 0.8 N + 0.5 E. In contrast, nACh receptor ligands had minimal influence in blocking the perception of 0.8 N + 1.0 E and 0.8 N + 2.0 E mixtures, and only mecamylamine partially blocked 0.8 N+0.5 E. Reduced and enhanced contributions of nACh and NMDA receptors, respectively, in the discrimination of ethanol-nicotine mixtures may contribute to the overshadowing and potentiation phenomena observed previously.

Rodent models and mechanisms of voluntary binge-like ethanol consumption: Examples, opportunities, and strategies for preclinical research

Binge ethanol consumption has widespread negative consequences for global public health. Rodent models offer exceptional power to explore the neurobiology underlying and affected by binge-like drinking as well as target potential prevention, intervention, and treatment strategies. An important characteristic of these models is their ability to consistently produce pharmacologically-relevant blood ethanol concentration. This review examines the current available rodent models of voluntary, pre-dependent binge-like ethanol consumption and their utility in various research strategies. Studies have demonstrated that a diverse array of neurotransmitters regulate binge-like drinking, resembling some findings from other drinking models. Furthermore, repeated binge-like drinking recruits neuroadaptive mechanisms in mesolimbocortical reward circuitry. New opportunities that these models offer in the current context of mechanistic research are also discussed.

Microstructural analysis of rat ethanol and water drinking patterns using a modified operant self-administration model

BACKGROUND

Ethanol drinking pattern has emerged as an important factor in the development, maintenance, and health consequences of alcohol use disorders in humans. The goal of these studies was to further our understanding of this important factor through refinement of an operant rodent model of ethanol consumption capable of drinking pattern microstructural analysis. We evaluated measures of total consumption, appetitive behavior, and drinking microstructure for ethanol and water at baseline and assessed alterations induced by two treatments previously shown to significantly alter gross ethanol appetitive and consummatory behaviors in opposing directions.

METHODS

Male Long-Evans rats were trained on an FR1 operant paradigm which allowed for continuous liquid access until an 8 second pause in consumption resulted in termination of liquid access. Total appetitive and consummatory behaviors were assessed in addition to microstructural drinking pattern for both ethanol and water during a five day baseline drinking period, after chronic intermittent ethanol vapor exposure, and following administration of a cannabinoid receptor antagonist SR141716a.

RESULTS

As in previous operant studies, ethanol vapor exposure resulted in increases in ethanol-directed responding, total consumption, and rate of intake. Further, striking differential alterations to ethanol and water bout size, duration, and lick pattern occurred consistent with alterations in hedonic evaluation. Vapor additionally specifically reduced the number of ethanol-directed lever presses which did not result in subsequent consumption. SR141716a administration reversed many of these effects.

CONCLUSIONS

The addition of microstructural analysis to operant self-administration by rodents provides a powerful and translational tool for the detection of specific alterations in ethanol drinking pattern which may enable insights into neural mechanisms underlying specific components of drug consumption.

Enhanced alcohol-seeking behavior by nicotine in the posterior ventral tegmental area of female alcohol-preferring (P) rats: modulation by serotonin-3 and nicotinic cholinergic receptors

RATIONALE

Alcohol and nicotine co-use can reciprocally promote self-administration and drug-craving/drug-seeking behaviors. To date, the neurocircuitry in which nicotine influences ethanol (EtOH) seeking has not been elucidated. Clinical and preclinical research has suggested that the activation of the mesolimbic dopamine system is involved in the promotion of drug seeking. Alcohol, nicotine, and serotonin-3 (5-HT3) receptors interact within the posterior ventral tegmental area (pVTA) to regulate drug reward. Recently, our laboratory has reported that systemic administration of nicotine can promote context-induced EtOH seeking.

OBJECTIVES

The goals of the current study were to (1) determine if microinjections of pharmacologically relevant levels of nicotine into the pVTA would enhance EtOH seeking, (2) determine if coadministration of nicotinic cholinergic receptor antagonist (nACh) or 5-HT3 receptor antagonists would block the ability of nicotine microinjected into the pVTA to promote EtOH seeking, and (3) determine if 5-HT3 receptors in the pVTA can modulate EtOH seeking.

RESULTS

Nicotine (100 and 200 μM) microinjected into the pVTA enhanced EtOH seeking. Coinfusion with 200 μM mecamylamine (nACh antagonist) or 100 and 200 μM zacopride (5-HT3 receptor antagonist) blocked the observed nicotine enhancement of EtOH seeking. The data also indicated that microinjection of 1 μM CPBG (5-HT3 receptor agonist) promotes context-induced EtOH seeking; conversely, microinjection of 100 and 200 μM zacopride alone reduced context-induced EtOH seeking.

CONCLUSIONS

Overall, the results show that nicotine-enhanced EtOH-seeking behavior is modulated by 5-HT3 and nACh receptors within the pVTA and that the 5-HT3 receptor system within pVTA may be a potential pharmacological target to inhibit EtOH-seeking behaviors.

Methamphetamine drinking microstructure in mice bred to drink high or low amounts of methamphetamine

Genetic factors likely influence individual sensitivity to positive and negative effects of methamphetamine (MA) and risk for MA dependence. Genetic influence on MA consumption has been confirmed by selectively breeding mouse lines to consume high (MAHDR) or low (MALDR) amounts of MA, using a two-bottle choice MA drinking (MADR) procedure. Here, we employed a lickometer system to characterize the microstructure of MA (20, 40, and 80mg/l) and water intake in MAHDR and MALDR mice in 4-h limited access sessions, during the initial 4hours of the dark phase of their 12:12h light:dark cycle. Licks at one-minute intervals and total volume consumed were recorded, and bout analysis was performed. MAHDR and MALDR mice consumed similar amounts of MA in mg/kg on the first day of access, but MAHDR mice consumed significantly more MA than MALDR mice during all subsequent sessions. The higher MA intake of MAHDR mice was associated with a larger number of MA bouts, longer bout duration, shorter interbout interval, and shorter latency to the first bout. In a separate 4-h limited access MA drinking study, MALDR and MAHDR mice had similar blood MA levels on the first day MA was offered, but MAHDR mice had higher blood MA levels on all subsequent days, which corresponded with MA intake. These data provide insight into the microstructure of MA intake in an animal model of differential genetic risk for MA consumption, which may be pertinent to MA use patterns relevant to genetic risk for MA dependence.

Potential therapeutic uses of mecamylamine and its stereoisomers

Mecamylamine (3-methylaminoisocamphane hydrochloride) is a nicotinic parasympathetic ganglionic blocker, originally utilized as a therapeutic agent to treat hypertension. Mecamylamine administration produces several deleterious side effects at therapeutically relevant doses. As such, mecamylamine's use as an antihypertensive agent was phased out, except in severe hypertension. Mecamylamine easily traverses the blood-brain barrier to reach the central nervous system (CNS), where it acts as a nicotinic acetylcholine receptor (nAChR) antagonist, inhibiting all known nAChR subtypes. Since nAChRs play a major role in numerous physiological and pathological processes, it is not surprising that mecamylamine has been evaluated for its potential therapeutic effects in a wide variety of CNS disorders, including addiction. Importantly, mecamylamine produces its therapeutic effects on the CNS at doses 3-fold lower than those used to treat hypertension, which diminishes the probability of peripheral side effects. This review focuses on the pharmacological properties of mecamylamine, the differential effects of its stereoisomers, S(+)- and R(-)-mecamylamine, and the potential for effectiveness in treating CNS disorders, including nicotine and alcohol addiction, mood disorders, cognitive impairment and attention deficit hyperactivity disorder.

Interactions between mecamylamine and alcohol in Long-Evans rats: flash-evoked potentials, body temperature, behavior, and blood alcohol concentration

Mecamylamine, a noncompetitive antagonist of nicotinic acetylcholine receptors, has many potential clinical applications, including treating alcohol dependency. However, little is known about the combined effects of mecamylamine and alcohol on visual system electrophysiology. We examined the separate and combined effects of mecamylamine (4.0mg/kg, ip) and alcohol (2.0 g/kg, ip) on flash-evoked potentials (FEPs) recorded from the visual cortex (VC) and superior colliculus (SC) of chronically implanted adult male Long-Evans rats. On separate days, either saline or mecamylamine was given 10 min prior to either saline or ethanol. FEPs were recorded 15 and 30 min after the second injection. In the VC, alcohol significantly decreased the amplitudes of components P23, N29, N39, P89, N143, and P237, but increased P46. N63 amplitude was not significantly altered. In contrast, mecamylamine increased the amplitude of P23, P46, and N63, but reduced the amplitude of N29 and P237. The combination of mecamylamine and alcohol resulted in amplitudes very similar to alcohol alone for components P23, N29, N63, P89, N143, and P237. However, mecamylamine pretreatment reduced the effects of alcohol on components N39 and P46. In the SC, FEP component amplitudes were generally decreased by alcohol but not significantly altered by mecamylamine. Mecamylamine pretreatment did not significantly alter the effects of alcohol on SC amplitudes. Latencies of nearly all components in both structures were significantly increased by all drug treatments, with the greatest increase produced by the combination treatment. Hypothermia was also produced by all drug treatments, with the greatest hypothermia (2.25 °C) produced by the combination treatment, most likely accounting for much of the drug-induced increase in latencies. All drug treatments reduced movement during FEP testing, but later in an open field alcohol increased ambulation while mecamylamine reduced movement. Separate groups of experimentally naïve adult male Holtzman albino and Long-Evans hooded rats were given (ip) either alcohol or mecamylamine plus alcohol. Tail vein samples were taken 30 min later. For both rat strains, blood alcohol concentration in the mecamylamine pretreatment group was significantly less at this time interval by about 50-60 mg/dL, suggesting a mechanism whereby mecamylamine can mitigate some of the acute effects of alcohol (e.g., on VC components N39 and P46).

A genetic animal model of differential sensitivity to methamphetamine reinforcement

Sensitivity to reinforcement from methamphetamine (MA) likely influences risk for MA addiction, and genetic differences are one source of individual variation. Generation of two sets of selectively bred mouse lines for high and low MA drinking has shown that genetic factors influence MA intake, and pronounced differences in sensitivity to rewarding and aversive effects of MA play a significant role. Further validation of these lines as a unique genetic model relevant to MA addiction was obtained using operant methods to study MA reinforcement. High and low MA drinking line mice were used to test the hypotheses that: 1) oral and intracerebroventricular (ICV) MA serve as behavioral reinforcers, and 2) MA exhibits greater reinforcing efficacy in high than low MA drinking mice. Operant responses resulted in access to an MA or non-MA drinking tube or intracranial delivery of MA. Behavioral activation consequent to orally consumed MA was determined. MA available for consumption maintained higher levels of reinforced instrumental responding in high than low MA drinking line mice, and MA intake in the oral operant procedure was greater in high than low MA drinking line mice. Behavioral activation was associated with amount of MA consumed during operant sessions. High line mice delivered more MA via ICV infusion than did low line mice across a range of doses. Thus, genetic risk factors play a critical role in the reinforcing efficacy of MA and the oral self-administration procedure is suitable for delineating genetic contributions to MA reinforcement.

Ivermectin reduces alcohol intake and preference in mice

The high rate of therapeutic failure in the management of alcohol use disorders (AUDs) underscores the urgent need for novel and effective strategies that can deter ethanol consumption. Recent findings from our group showed that ivermectin (IVM), a broad-spectrum anthelmintic with high tolerability and optimal safety profile in humans and animals, antagonized ethanol-mediated inhibition of P2X4 receptors (P2X4Rs) expressed in Xenopus oocytes. This finding prompted us to hypothesize that IVM may reduce alcohol consumption; thus, in the present study we investigated the effects of this agent on several models of alcohol self-administration in male and female C57BL/6 mice. Overall, IVM (1.25-10 mg/kg, intraperitoneal) significantly reduced 24-h alcohol consumption and intermittent limited access (4-h) binge drinking, and operant alcohol self-administration (1-h). The effects on alcohol intake were dose-dependent with the significant reduction in intake at 9 h after administration corresponding to peak IVM concentrations (C(max)) in the brain. IVM also produced a significant reduction in 24-h saccharin consumption, but did not alter operant sucrose self-administration. Taken together, the findings indicate that IVM reduces alcohol intake across several different models of self-administration and suggest that IVM may be useful in the treatment of AUDs.

Acquisition, expression, and reinstatement of ethanol-induced conditioned place preference in mice: effects of exposure to stress and modulation by mecamylamine

Nicotinic acetylcholine receptors mediate some of the rewarding and motivational effects of ethanol, including relapses. Relapses are common in drug addicts during abstinence when exposure to any stressor ensues. However, the role of nicotinic acetylcholine receptors in the ethanol- and stress-induced reinstatement of ethanol-induced conditioned place preference has not yet been explored. Therefore, the present study investigated the influence of mecamylamine, a nicotinic acetylcholine receptors antagonist on acquisition, expression, and reinstatement of ethanol-induced conditioned place preference in adult male Swiss mice. The results revealed that mecamylamine (0.1-10 µg/mouse, intracerebroventricularly) dose dependently prevented the development, expression, and reinstatement of ethanol-induced conditioned place preference. Further, acute treatment with mecamylamine blocked the restraint stress and forced swim stress-induced reinstatement of ethanol-induced conditioned place preference. All of these treatments had no influence on the locomotor activity. Therefore, it is concluded that mecamylamine blocks the acquisition, expression and reinstatement of conditioned reinforcing effects of ethanol without per se reinforcing or aversive influence. This ability of mecamylamine might be a potential advantage in the treatment of alcoholism.

Ethanol drinking-in-the-dark facilitates behavioral sensitization to ethanol in C57BL/6J, BALB/cByJ, but not in mu-opioid receptor deficient CXBK mice

BACKGROUND

Neuroplasticity associated with drug-induced behavioral sensitization has been associated with excessive drug pursuit and consumption characteristic of addiction. Repeated intraperitoneal (ip) injections of ethanol (EtOH) can induce psychomotor sensitization in mice. In terms of its clinical relevance, however, it is important to determine whether this phenomenon can also be produced by voluntary EtOH consumption.

METHODS

The present investigation used a drinking-in-the-dark (DID) methodology to induce high levels of EtOH drinking in mice; EtOH replaces water for 2 or 4h, starting 3h after the beginning of the dark cycle. Animals followed a 3-week DID protocol prior to an evaluation of EtOH-induced locomotor activity (acute and repeated EtOH). For the first week, animals had access to 20% EtOH. On weeks 2 and 3, different concentrations of EtOH (10, 20 or 30%) were used. Three different inbred strains of mice were used: C57BL/6J (B6), BALB/cByJ (BALB), and CXBK. The CXBK mouse line was used because of its reduced expression and functioning of brain mu-opioid receptors, which have been suggested to participate in the development of EtOH-induced sensitization. B6 and BALB mice were used as controls.

RESULTS

B6 and CXBK mice presented comparable levels of EtOH drinking (approx. 3g/kg in 2h), that were higher than those showed by BALB. All animals, regardless of genotype, adjusted volume of EtOH intake to obtain stable g/kg of EtOH across concentrations. Previous EtOH DID produced (B6) or potentiated (BALB) sensitization to EtOH; this effect was not seen in CXBK. Western blot analysis showed a reduced number of mu-opioid receptors in several brain regions of CXBK as compared to that of B6 and BALB mice.

CONCLUSIONS

In summary, here we show that the DID methodology can be used to trigger EtOH-induced neuroplasticity supporting psychomotor sensitization, a process that might require participation of mu-opioid receptors.

Assessment of GABA-B, metabotropic glutamate, and opioid receptor involvement in an animal model of binge drinking

Drinking to intoxication or binge drinking is a hallmark characteristic of alcohol abuse. Although hard to model in rodents, the scheduled high alcohol consumption (SHAC) procedure generates high, stable ethanol intake and blood ethanol concentrations in mice to levels consistent with definitions of binge drinking. The purpose of the present studies was to determine the effects of pharmacological manipulation of the opioidergic, glutamatergic, and γ-aminobutyric acid (GABA)ergic systems on binge drinking with the SHAC procedure. Parallel manipulations were conducted in mice trained in operant self-administration of either sucrose or ethanol. For the SHAC procedure, genetically heterogeneous Withdrawal Seizure Control mice were given varying periods of fluid access, with a 30-min ethanol session every third day (total of seven). Mice were pretreated intraperitoneally with naltrexone (0, 0.6, or 1.25 mg/kg), baclofen (0, 2.5, or 5.0 mg/kg), or 2-methyl-6-(phenylethynyl)-pyridine (MPEP; 0, 3.0, or 10.0 mg/kg) before each ethanol session. For the operant self-administration procedure, separate groups of C57BL/6 mice were trained to complete a single response requirement (16 presses on the active lever) to gain 30 min of access to an ethanol or a sucrose solution. Mice received pretreatments of the same doses of naltrexone, MPEP, or baclofen before the self-administration sessions, with saline injections on intervening days. Naltrexone produced a dose-dependent decrease in binge drinking, and the highest dose also significantly decreased operant self-administration of ethanol and sucrose. Both doses of baclofen significantly decreased binge alcohol consumption, but the higher dose also tended to decrease water intake. The highest dose of baclofen also significantly decreased operant self-administration of sucrose. MPEP (10 mg/kg) significantly decreased binge alcohol consumption and sucrose self-administration. These results indicate that manipulation of the opioidergic, glutamatergic, and GABAergic systems significantly decreased binge drinking.

Varenicline attenuates cue-induced relapse to alcohol, but not nicotine seeking, while reducing inhibitory response control

RATIONALE

Treatment of the most widely abused drugs, nicotine and alcohol, is hampered by high rates of relapse. Varenicline tartrate, an α4β2 nicotinic receptor partial agonist, is currently prescribed as a smoking cessation aid. However, there is emerging evidence that it may also modulate alcohol seeking and cognitive functioning in rats.

OBJECTIVES

As preclinical data on alcohol taking and relapse are limited, we used a self-administration-reinstatement model to evaluate the effects of varenicline on operant responding for alcohol (12%, v/v), intravenous nicotine (40 μg/kg/inf.), sucrose (10%, w/v) and on cue-induced relapse to alcohol and nicotine seeking in rats. At the cognitive level, we assed varenicline's effects on 5-choice serial reaction time task (5-CSRTT) performance with a focus on correct responses (attention) and premature responding (impulsivity), modalities that have previously been associated with addictive behaviour.

RESULTS

Varenicline, at doses of 1.5 and 2.5 mg/kg, reduced alcohol and nicotine self-administration and enhanced operant responding for sucrose. At these doses, varenicline reduced cue-induced relapse to alcohol, but not nicotine seeking. In contrast, at 0.5 mg/kg, varenicline facilitated cue-induced nicotine seeking. Similar to nicotine, varenicline increased premature responding at low doses, but had no effect on any of the other behavioural parameters in the 5-CSRTT.

CONCLUSIONS

Our data indicate that varenicline specifically reduced responding for nicotine and alcohol, but not for natural reinforcers such as sucrose. Interestingly, varenicline strongly attenuated cue-induced relapse to alcohol seeking, but not nicotine seeking. Varenicline may therefore be a promising aid in the treatment of alcohol addiction.

The influence of selection for ethanol withdrawal severity on traits associated with ethanol self-administration and reinforcement

BACKGROUND

Several meta-analyses indicate that there is an inverse genetic correlation between ethanol preference drinking and ethanol withdrawal severity, but limited work has characterized ethanol consumption in 1 genetic animal model, the Withdrawal Seizure-Prone (WSP) and-Resistant (WSR) mouse lines selected for severe or mild ethanol withdrawal, respectively.

METHODS

We determined whether line differences existed in: (i) operant self-administration of ethanol during sucrose fading and under different schedules of reinforcement, followed by extinction and reinstatement of responding with conditioned cues and (ii) home cage drinking of sweetened ethanol and the development of an alcohol deprivation effect (ADE).

RESULTS

Withdrawal Seizure-Prone-1 mice consumed more ethanol than WSR-1 mice under a fixed ratio (FR)-4 schedule as ethanol was faded into the sucrose solution, but this line difference dissipated as the sucrose was faded out to yield an unadulterated 10% v/v ethanol solution. In contrast, WSR-1 mice consumed more ethanol than WSP-1 mice when a schedule was imposed that procedurally separated appetitive and consummatory behaviors. After both lines achieved the extinction criterion, reinstatement was serially evaluated following oral ethanol priming, light cue presentation, and a combination of the 2 cues. The light cue produced maximal reinstatement of responding in WSP-1 mice, whereas the combined cue was required to produce maximal reinstatement of responding in WSR-1 mice. There was no line difference in the home cage consumption of a sweetened ethanol solution over a period of 1 month. Following a 2-week period of abstinence, neither line developed an ADE.

CONCLUSIONS

Although some line differences in ethanol self-administration and reinstatement were identified between WSP-1 and WSR-1 mice, the absence of consistent divergence suggests that the genes underlying these behaviors do not reliably overlap with those that govern withdrawal severity.

Inhibitory influence of mecamylamine on ethanol withdrawal-induced symptoms in C57BL/6J mice

Several reports show the involvement of neuronal nicotinic acetylcholine receptors (nAChRs) in the behavioral effects of ethanol, including ethanol drinking and relapse. Therefore, this study evaluated the effects of mecamylamine, a nAChR antagonist, on ethanol withdrawal signs. Ethanol dependence was induced in C57BL/6J mice by ethanol liquid diet administration. Animals were provided with nutritionally balanced control liquid diet (600 kcal/l) as their sole nutrient source on day 0; from days 1 to 4, 3% v/v of ethanol, followed by 6% v/v of ethanol (from days 5 to 7), and 10% v/v of ethanol (from days 8 to 10) were incorporated into the liquid diet. On day 11, ethanol liquid diet was replaced with nutritionally balanced control liquid diet, and ethanol withdrawal-induced physical signs were recorded. Results showed that acute administration of mecamylamine (1-4 mg/kg, intraperitoneally) dose-dependently attenuated ethanol withdrawal-induced signs, and these effects were comparable with those of diazepam (1-2 mg/kg, intraperitoneally). In addition, chronic administration of mecamylamine into ethanol diet-fed mice markedly attenuated the ethanol withdrawal sign scores, thus supporting the contention that nAChR is involved in ethanol dependence. In conclusion, our results suggest that mecamylamine exhibited inhibitory effects on ethanol withdrawal signs which could be mediated through nAChR.

Inhibitory influence of mecamylamine on the development and the expression of ethanol-induced locomotor sensitization in mice

Several evidences have indicated the involvement of neuronal nicotinic acetylcholine receptors (nAChR) in behavioral effects of drugs of abuse, including ethanol. nAChRs are implicated in ethanol-induced behaviors as well as neurochemical responses to ethanol. Recently, it is demonstrated that mecamylamine, a nAChR antagonist blocks cocaine-, d-amphetamine-, ephedrine-, nicotine-, and methylphenidate-induced psychomotor sensitization. However, no reports are available on its role in ethanol-induced psychomotor sensitization. Therefore, an attempt was made to evaluate its effect on ethanol-induced locomotor sensitization using a model previously described by us. The results revealed that acute administration of mecamylamine (1 and 2mg/kg, i.p.) blocked the acute stimulant effect of ethanol (2.0g/kg, i.p.). In addition, treatment with mecamylamine (0.5-2.0mg/kg, i.p.), 30min prior to the challenge dose of ethanol (2.0g/kg, i.p.) dose dependently attenuated expression of sensitization to locomotor stimulant effect of ethanol. Moreover, administration of mecamylamine (1 and 2mg/kg, i.p.) during development (prior to each ethanol injection on days 1, 4, 7, and 10) blocked acquisition as well as expression (day 15) of sensitization to locomotor stimulant effect of ethanol. Mecamylamine per se did not affect locomotor activity. Further, it also did not influence blood ethanol levels and rotarod performance in mice. These results support the hypothesis that neuroadaptive changes in nAChRs may participate in the development and the expression of ethanol-induced locomotor sensitization.