Ethanol-nicotine interactions in long-sleep and short-sleep mice

Mechanisms and genetic factors underlying co-use of nicotine and alcohol or other drugs of abuse

Concurrent use of tobacco and alcohol or psychostimulants represents a major public health concern, with use of one substance influencing consumption of the other. Co-abuse of these drugs leads to substantial negative health outcomes, reduced cessation, and high economic costs, but the underlying mechanisms are poorly understood. Epidemiological data suggest that tobacco use during adolescence plays a particularly significant role. Adolescence is a sensitive period of development marked by major neurobiological maturation of brain regions critical for reward processing, learning and memory, and executive function. Nicotine exposure during this time produces a unique and long-lasting vulnerability to subsequent substance use, likely via actions at cholinergic, dopaminergic, and serotonergic systems. In this review, we discuss recent clinical and preclinical data examining the genetic factors and mechanisms underlying co-use of nicotine and alcohol or cocaine and amphetamines. We evaluate the critical role of nicotinic acetylcholine receptors throughout, and emphasize the dearth of preclinical studies assessing concurrent drug exposure. We stress important age and sex differences in drug responses, and highlight a brief, low-dose nicotine exposure paradigm that may better model early use of tobacco products. The escalating use of e-cigarettes among youth necessitates a closer look at the consequences of early adolescent nicotine exposure on subsequent alcohol and drug abuse.

Varenicline and neuronal nicotinic acetylcholine receptors: a new approach to the treatment of co-occurring alcohol and nicotine addiction?

BACKGROUND AND OBJECTIVES

Alcohol and nicotine dependence are serious public health problems worldwide. They are associated with substantial morbidity and mortality, as well as adverse social effects and increased healthcare costs. Although efficacious treatments are available for these disorders, additional therapeutic options are required to ensure greater treatment utilization. In this paper, we describe the empirical basis on which varenicline, a nicotinic partial agonist approved for smoking cessation, may also have utility in the treatment of alcohol addiction.

METHODS

We sought to identify papers examining nicotine dependence, alcohol dependence, smoking, alcohol, and varenicline for possible inclusion in the present review. We identified over 600 papers through Pubmed/Medline, PsychINFO, and Google Scholar. We found 12 papers taking into consideration the following criteria: original language English, varenicline effect on alcohol consumption.

RESULTS

Animal studies have shown that varenicline reduces alcohol consumption. Two recent studies showed that varenicline also reduces alcohol consumption in humans. Both nicotine and alcohol interact with α4β2 and α3β4 nicotinic acetylcholine (ACh) receptors located in the ventral tegmental area of the brain, inducing dopamine (DA) release at the nucleus accumbens. Varenicline binds to nicotinic ACh receptors, where it has partial agonist effects, producing a moderate and constant level of DA release both in the mesolimbic pathway and in the prefrontal cortex.

CONCLUSIONS AND SCIENTIFIC SIGNIFICANCE

Through these effects, varenicline may reduce alcohol craving, seeking, and consumption, in addition to promoting smoking cessation. Additional studies are needed to confirm the efficacy of varenicline in the treatment of alcohol dependence.

The α5 neuronal nicotinic acetylcholine receptor subunit plays an important role in the sedative effects of ethanol but does not modulate consumption in mice

BACKGROUND

Alcohol use disorders (AUDs) are a major public health problem, and the few treatment options available to those seeking treatment offer only modest success rates. There remains a need to identify novel targets for the treatment of AUDs. The neuronal nicotinic acetylcholine receptors (nAChRs) represent a potential therapeutic target in the brain, as recent human genetic studies have implicated gene variants in the α5 nAChR subunit as high risk factors for developing alcohol dependence.

METHODS

Here, we evaluate the role of the α5* nAChR for ethanol (EtOH)-mediated behaviors using male α5+/+ and α5-/- transgenic mice. We characterized the effect of hypnotic doses of EtOH and investigated drinking behavior using an adapted drinking-in-the-dark (DID) paradigm that has been shown to induce high EtOH consumption in mice.

RESULTS

We found the α5 subunit to be important in mediating the sedative effects of EtOH. The α5-/- mice showed slower recovery from EtOH-induced sleep, as measured by loss of righting reflex. Additionally, the α5-/- mice showed enhanced impairment to EtOH-induced ataxia. We found the initial sensitivity to EtOH and EtOH metabolism to be similar in both α5+/+ and α5-/- mice. Hence, the enhanced sedation is likely due to a difference in the acute tolerance of EtOH in α5-/- mice. However, the α5 subunit did not play a role in EtOH consumption for EtOH concentrations ranging from 5 to 30% using the DID paradigm. Additionally, varenicline was effective in reducing EtOH intake in α5-/- mice.

CONCLUSIONS

Together, our data suggest that the α5 nAChR subunit is important for the sedative effects of EtOH but does not play a role in EtOH consumption in male mice. Varenicline can be a treatment option even when there is loss of function of the α5 nAChR subunit.

Neuronal nicotinic acetylcholine receptors: neuroplastic changes underlying alcohol and nicotine addictions

Addictive drugs can activate systems involved in normal reward-related learning, creating long-lasting memories of the drug's reinforcing effects and the environmental cues surrounding the experience. These memories significantly contribute to the maintenance of compulsive drug use as well as cue-induced relapse which can occur even after long periods of abstinence. Synaptic plasticity is thought to be a prominent molecular mechanism underlying drug-induced learning and memories. Ethanol and nicotine are both widely abused drugs that share a common molecular target in the brain, the neuronal nicotinic acetylcholine receptors (nAChRs). The nAChRs are ligand-gated ion channels that are vastly distributed throughout the brain and play a key role in synaptic neurotransmission. In this review, we will delineate the role of nAChRs in the development of ethanol and nicotine addiction. We will characterize both ethanol and nicotine's effects on nAChR-mediated synaptic transmission and plasticity in several key brain areas that are important for addiction. Finally, we will discuss some of the behavioral outcomes of drug-induced synaptic plasticity in animal models. An understanding of the molecular and cellular changes that occur following administration of ethanol and nicotine will lead to better therapeutic strategies.

The α6 nicotinic acetylcholine receptor subunit influences ethanol-induced sedation

Alcohol and nicotine are often co-used and data from human and animals studies have demonstrated that common genes underlie responses to these two drugs. Recently, the genes that code for the subunits of the nicotinic acetylcholine receptors have been implicated as a common genetic mediator for alcohol and nicotine responses. The mammalian genes that code for the α6 and β3 subunits of the nicotinic acetylcholine receptor (Chrna6 and Chrnb3, respectively) are located adjacent to each other on human and mouse chromosome 8. These subunits have gained attention as potential regulators of drug behaviors because of their expression in the striatum where they have been shown to modulate dopamine release. Human genetic studies have shown that variation in these genes is associated with alcohol phenotypes. In the current experiments, mice lacking the Chrna6 or Chrnb3 gene were tested for three ethanol behaviors: choice ethanol consumption, ataxia, and sedation. Wildtype (WT), heterozygous (HET), and knockout (KO) mice of each strain went through a standard 2-bottle choice drinking paradigm, the balance beam, and the Loss of Righting Reflex (LORR) paradigm. No genotypic effects on any of the 3 behavioral tasks were observed in Chrnb3 animals. While the Chrna6 gene did not significantly influence ethanol consumption (g/kg) or ataxia, mice lacking the α6 subunit took significantly longer to recover their righting reflex than WT animals. These data provide evidence that receptors containing this subunit modulate the sedative effects of ethanol. Further work examining other models of ethanol consumption and behavioral responses to ethanol is needed to fully characterize the role of these receptor subunits in modulating ethanol responses.

Neuronal nicotinic acetylcholine receptors as pharmacotherapeutic targets for the treatment of alcohol use disorders

Alcohol use disorders (AUDs) are complex, and developing effective treatments will require the combination of novel medications and cognitive behavioral therapy approaches. Epidemiological studies have shown there is a high correlation between alcohol consumption and tobacco use, and the prevalence of smoking in alcoholics is as high as 80% compared to about 30% for the general population. Both preclinical and clinical data provide evidence that nicotine administration increases alcohol intake and non-specific nicotinic receptor antagonists reduce alcohol-mediated behaviors. As nicotine interacts specifically with the neuronal nicotinic acetylcholine receptor (nAChR) system, this suggests that nAChRs play an important role in the behavioral effects of alcohol. In this review, we discuss the importance of nAChRs for the treatment of AUDs and argue that the use of FDA approved nAChR ligands, such as varenicline and mecamylamine, approved as smoking cessation aids may prove to be valuable treatments for AUDs. We also address the importance of combining effective medications with behavioral therapy for the treatment of alcohol dependent individuals.

Modulation of ethanol consumption by genetic and pharmacological manipulation of nicotinic acetylcholine receptors in mice

RATIONALE

Alcohol and nicotine are commonly co-abused. Genetic correlations between responses to these drugs have been reported, providing evidence that common genes underlie the response to alcohol and nicotine. Nicotinic acetylcholine receptors (nAChRs) in the mesolimbic dopamine system are important in mediating nicotine response, and several studies suggest that alcohol may also interact with these nAChRs.

OBJECTIVE

The aim of this study was to examine the role of nAChRs containing α7 or β2 subunits in ethanol consumption.

METHODS

A two-bottle choice paradigm was used to determine ethanol consumption in wild-type and nAChR subunit knockout mice. Challenge studies were performed using the α4β2 nAChR partial agonist varenicline.

RESULTS

Mice lacking the β2 subunit consumed a similar amount of ethanol compared to their wild-type siblings in an ethanol-drinking paradigm. In contrast, mice lacking the α7 nAChR receptor subunit consumed significantly less ethanol than wild-type mice but consumed comparable amounts of water, saccharin, and quinine. In C57BL/6J mice, varenicline dose-dependently decreased ethanol consumption with a significant effect of 2 mg/kg, without affecting water or saccharin consumption. This effect of varenicline was not reversed in mice lacking either the α7 or β2 subunit, providing evidence that nAChRs containing one of these subunits are not required for this effect of varenicline.

CONCLUSIONS

This study provides evidence that α7 nAChRs are involved in ethanol consumption and supports the idea that pharmacological manipulation of nAChRs reduces ethanol intake. Additional nAChRs may also be involved in ethanol intake, and there may be functional redundancy in the nicotinic control of alcohol drinking.

The alpha 3 subunit gene of the nicotinic acetylcholine receptor is a candidate gene for ethanol stimulation

Alcohol and nicotine are coabused, and preclinical and clinical data suggest that common genes may influence responses to both drugs. A gene in a region of mouse chromosome 9 that includes a cluster of three nicotinic acetylcholine receptor (nAChR) subunit genes influences the locomotor stimulant response to ethanol. The current studies first used congenic mice to confirm the influential gene on chromosome 9. Congenic F(2) mice were then used to more finely map the location. Gene expression of the three subunit genes was quantified in strains of mice that differ in response to ethanol. Finally, the locomotor response to ethanol was examined in mice heterozygous for a null mutation of the alpha 3 nAChR subunit gene (Chrna3). Congenic data indicate that a gene on chromosome 9, within a 46 cM region that contains the cluster of nAChR subunit genes, accounts for 41% of the genetic variation in the stimulant response to ethanol. Greater expression of Chrna3 was found in whole brain and dissected brain regions relevant to locomotor behavior in mice that were less sensitive to ethanol-induced stimulation compared to mice that were robustly stimulated; the other two nAChR subunit genes in the gene cluster (alpha 5 and beta 4) were not differentially expressed. Locomotor stimulation was not expressed on the genetic background of Chrna3 heterozygous (+/-) and wild-type (+/+) mice; +/- mice were more sensitive than +/+ mice to the locomotor depressant effects of ethanol. Chrna3 is a candidate gene for the acute locomotor stimulant response to ethanol that deserves further examination.

Adolescent and adult rats respond differently to nicotine and alcohol: motor activity and body temperature

Alcohol and nicotine are the most widely abused drugs in the world. The use of these addictive drugs often begins in adolescence, however, little is known about the different impacts of nicotine and alcohol on adolescents versus adults. This study examined both the individual and combined effects of nicotine and alcohol on body temperature and locomotor activity in adolescent and adults rats. Rats were injected with saline (SC) + saline (IP), nicotine (SC) + saline (IP), alcohol (IP) + saline (SC) or alcohol (IP) + nicotine (SC). The dose selected for nicotine was 0.2 mg/kg and for alcohol 2.5 g/kg (16% v/v). For each age/treatment, 10-13 animals were used, with each animal receiving only one treatment. In regards to body temperature, both nicotine and alcohol caused a significant age x drug interaction. The combination of nicotine and alcohol caused greater drop in body temperature in adolescent than in adult rats. Neither of the two drugs, when given alone, caused differential effects in adolescents or adult rats, though both resulted in drop in body temperature. In terms of locomotor activity, the treatment that produced a significantly different effect between adolescents and adults was nicotine alone. Nicotine significantly decreased locomotor activity in adolescent compared to adult rats. These preliminary results suggest that adolescent rats may have an increased sensitivity to nicotine and alcohol, which may consequently impact their initial addiction to these two drugs.

Nicotine-alcohol interactions and cognitive function in rats

Nicotine and ethanol are the most widely abused drugs in the world. They are very often used and abused together. However, little is known about the functional interaction of nicotine and ethanol. The current project studied the interactive effects of nicotine and ethanol on working memory in the eight-arm radial maze. Adult female rats were trained on a radial arm maze for 18 sessions to reach asymptotic levels of choice accuracy. During the maintenance phase of radial arm maze testing, which indexed working memory function, the rats were injected with nicotine (0, 0.15, 0.3, 0.6, and 1.2 mg/kg sc, 20 min before testing) with and without ethanol pretreatment (0 or 1.5 g/kg, 16% v/v ip, 30 min before testing). All animals received the treatments in a counterbalanced order with at least 1 week between treatments. Higher doses of nicotine had a significant interaction with ethanol in terms of radial arm maze choice accuracy. Nicotine plus ethanol coadministration precipitated a significant choice accuracy impairment at doses that when given alone had no effect on performance. At the lower dose range of nicotine, ethanol coadministration eliminated the nicotine-induced memory improvement. No significant effects were seen with either nicotine or ethanol treatment or their interaction on response latency in the radial arm maze. The nicotine-ethanol interactive effects on memory were compared with the interaction of their well-characterized hypothermic effects. Nicotine and alcohol, when injected separately or in combination, induced hypothermia with no significant interactive effect. This study found that ethanol blocked low-dose nicotine-induced memory improvement and precipitated memory impairment with high-dose nicotine treatment. This interaction may be an important consideration for nicotine and ethanol coabuse and the possible therapeutic use of nicotinic drugs for memory dysfunction.

Alcohol tolerance and nicotine cross-tolerance in adolescent mice

The present experiment was designed to evaluate the development of tolerance to alcohol and cross-tolerance to nicotine in adolescent mice. C57BL/6J mice (30-40 days old) were injected IP with alcohol (2.5 g/kg) for 4 consecutive days. A control group received four saline injections. On the test day, all subjects received an alcohol injection. Tolerance to alcohol's hypothermic effect was observed. Mice (male and female) exposed to alcohol for the 4 previous days showed less hypothermic response to an alcohol challenge than animals injected for 4 days with saline and then challenged with alcohol. Tolerance to alcohol's motor incoordinating effects and differences in blood alcohol concentrations were not observed. Thirty days following alcohol treatment, the same mice received a single nicotine injection (1 mg/kg) to assess cross-tolerance. Nicotine's effect on locomotor activity (open field test) and rectal temperature varied as a function of prior adolescent alcohol exposure and gender. Specifically, female mice who had been exposed to alcohol administrations were more resistant to nicotine's effect on locomotion and temperature than saline-treated animals. In summary, these data demonstrate that adolescent mice develop tolerance to some, but not all, alcohol-induced responses, and that female mice are cross-tolerant to nicotine's effects on temperature and activity.

Involvement of nicotinic receptors in alcohol self-administration

BACKGROUND

Alcohol and nicotine, in the form of tobacco, are commonly co-abused. Nicotinic receptors also have been implicated in alcohol action. We designed the present study to examine the possible involvement of nicotinic receptors in alcohol self-administration.

METHODS AND RESULTS

Pretreatment with lower doses (0.1-0.4 mg/kg) of nicotine, administered acutely or chronically, did not affect alcohol consumption, whereas a higher dose (0.8 mg/kg) initially suppressed alcohol consumption but stimulated alcohol consumption on repeated treatment. We observed the same pattern of nicotine effects on alcohol self-administration using an operant procedure. A dose of 0.8 mg/kg of nicotine initially suppressed operant responding for alcohol. Such suppression of alcohol self-administration was more pronounced during the first 20 min of the 60 min operant session. Responding for alcohol in the nicotine treated group, however, was significantly increased above the saline treated group by the 5th day of treatment. Mecamylamine, a noncompetitive nicotinic receptor antagonist, reduced alcohol consumption, whereas dihydro-beta-erythroidine (DHbetaE), a competitive nicotinic receptor antagonist, did not modify alcohol consumption.

CONCLUSIONS

The stimulation of alcohol intake induced by nicotine treatment and the suppression of alcohol intake induced by mecamylamine provide evidence for the involvement of nicotinic receptors in alcohol consumption and/or self-administration. The failure of DHbetaE to reduce alcohol consumption, however, suggests that ethanol-nicotine interaction is mediated by other nicotinic receptor subtypes rather than alpha4beta2 receptor subtype, or that mecamylamine acts through a nonnicotinic mechanism.

The consumption of tobacco, alcohol, and coffee in Caucasian male twins: a multivariate genetic analysis

Despite the fact that epidemiologic studies demonstrate a consistent covariation between the use of tobacco, alcohol, and coffee, most previous behavioral genetic-studies have determined the contribution of genetic and environmental influences as if the consumption of these substances occurred independently of each other. In this study, we used multivariate structural equation modeling to determine the genetic and environmental overlap in the observed correlations between tobacco smoking and alcohol and coffee drinking in 173 monozygotic and 183 dizygotic male twin pairs (M age = 59 years; range = 52-66 years) who participated in a follow-up cardiovascular examination of the National Heart, Lung, and Blood Institute's Twin Study. Consistent with hypothesized psychoneurogenetic predispositions for the joint use of these substances, the most parsimonious model fitting these data identified a common genetic latent factor underlying the observed associations between smoking, alcohol, and coffee use in this cohort. This factor, herein called polysubstance use, underscores the role of genetic influence on the clustering of these behaviors in the same individual.

Alcohol sensitivity and smoking history in men and women

Many studies have found genetic effects to contribute to alcoholism risk in both men and women. Based on preliminary evidence for shared genetic risk between smoking and drinking problems, a reanalysis of alcohol challenge data on 412 Australian twins was performed to explore the possibility that smoking may diminish or moderate the intoxicating effects of alcohol. We found history of smoking to be strongly associated with self-reported intoxication after alcohol challenge in women (women: r = -0.44 +/- 0.08; men: r = -0.21 +/- 0.08), comparable with self-reported average weekly consumption of alcohol, which was more strongly associated in men (women: r = -0.37 +/- 0.07; men: r = -0.54 +/- 0.06). Structural equation model-fitting indicated a strong association between heavy drinking and smoking, but the association between smoking and postalcohol intoxication remained even when the effects of heavy drinking were controlled for. These results prompt the question of whether smoking cigarettes directly influences the transition from moderate to excessive use of alcohol by diminishing feelings of alcohol intoxication.

Selective breeding for initial sensitivity to ethanol

Selective breeding for initial sensitivity to ethanol has been carried out by a number of investigators in order to investigate the mechanisms by which ethanol brings about a myriad of effects on the mammalian central nervous system. In addition the availability of these selectively bred animals provides clues to the causes of the genetic predisposition of humans to alcoholism. Eventually it is envisioned that the synteny between the mouse and human genomes will allow identification of specific genes responsible for acute effects of ethanol in both species as well as clues as to how alcoholism in humans can be better identified, prevented, and treated.

Differential effects of nicotine but not cathinone on motor activity of P and NP rats

The locomotor stimulatory effects of nicotine (0.4 and 0.8 mg/kg) and cathinone (0.5 and 1.0 mg/kg) were assessed in alcohol-preferring (P) and -nonpreferring (NP) rats. Whereas P rats demonstrated enhanced (0.8 mg/kg) or no change (0.4 mg/kg) in spontaneous locomotor activity (SMA) to nicotine, NP animals showed no change (0.4 mg/kg) or depression of activity (0.8 mg/kg). However, following cathinone administration both P and NP rats exhibited an increase in SMA. The above results are discussed in light of the genotypic variations between P/NP rats and the potential mediation of differential neurotransmitter effects in the two lines.

The discriminative stimulus properties of an ethanol-nicotine mixture in rats

Sprague-Dawley rats were trained to discriminate between saline (SAL) and an ethanol-nicotine mixture (0.5 g/kg ethanol plus 0.5 mg/kg nicotine) administered 15 min prior to a 15-min drug discrimination training session under a FR-10 schedule of reinforcement. The mixture dose ratio was adjusted after training to obtain a drug mixture with which both individual drugs contributed about equally to the stimulus control (1.0 g/kg ethanol plus 0.3 mg/kg nicotine). The animals were then retrained for 32 sessions using this new mixture. After training, neither nicotine nor ethanol, when tested singly, engendered > 90% mixture-appropriate responding up to test doses that suppressed responding. Complete generalization occurred when the training doses of either nicotine or ethanol were administered in combination with various doses of the alternate drug element. (+)Nicotine, amphetamine and caffeine engendered dose-dependent increases in responses emitted on the mixture-appropriate lever. Pentobarbital and chloral hydrate only partially generalized to the training mixture. However, depressant/stimulant combinations of chloral hydrate+caffeine and pentobarbital+amphetamine produced complete generalization. The data suggest: (1) drug mixtures are not normally perceived as new entities distinct from their component elements; (2) training dose ratio may influence the characteristics of mixture discriminations; (3) stimulus element saliency may be a factor determining the nature of discriminative control by drug mixture cues; and (4) the ethanol-nicotine cue was most likely based on non-specific depressant/stimulant effects of these drugs.