Nicotine discrimination and self-administration in humans as a function of smoking status

Human Abuse Liability Assessment of Tobacco and Nicotine Products: Approaches for Meeting Current Regulatory Recommendations

Many regulatory bodies now recommend that tobacco product manufacturers provide information regarding new tobacco products' abuse liability to inform regulatory authorization of currently marketed tobacco products or new product applications (including premarket tobacco product applications in the United States). In addition, the US Food and Drug Administration (FDA) recommends including this information as part of modified risk tobacco product applications. Regulators, including FDA, and many public health officials and researchers consider abuse liability assessment a model which predicts the likelihood that the use of the tobacco product would result in addiction and be used repeatedly or even sporadically resulting in undesirable effects. Abuse liability of a new, potentially reduced harm product can also inform its ability to substitute completely for more harmful tobacco products. While many methods exist, no standard tobacco product abuse liability assessment has been established. The purpose of this review is to provide background information and practical recommendations for human abuse liability testing methods to meet tobacco regulatory needs. A combination of nicotine test product pharmacokinetic, subjective effect and/or behavioral response, and physiological response data relative to comparator products with known abuse liability satisfies some regulatory requirements. Implications: This review provides a practical inspection of the current, international regulatory recommendations for abuse liability assessment of tobacco and regulatory review of such information within the United States and also recommends study designs and methods for abuse liability testing of tobacco products based on scientific and regulatory knowledge. Given that tobacco product abuse liability testing is of increasing interest to regulatory bodies globally, especially with the emergence of novel tobacco products, this timely work provides background and functional recommendations for tobacco product abuse liability testing.

Transitioning From Cigarettes to Electronic Cigarettes Increases Alcohol Consumption

OBJECTIVE

Electronic cigarettes (e-cigs) are a nicotine delivery device that have recently been linked to alcohol use. Many individuals that smoke cigarettes transition to e-cigs as an alternative to cigarette use, despite potential negative health effects of e-cigs. No research to date has examined how former smokers that have transitioned to e-cigs differ from former smokers that do not use e-cigs, particularly in relation to alcohol use. Further, no research has examined how former smokers that use e-cigs regularly or socially may differ in alcohol consumption.

METHOD

Using an online community dwelling sample (Former smokers N = 198, mean age = 34.70, SD = 11.45, 56.1% female, 78.3% Caucasian, 37.9% e-cig users), the present study assessed smoking status and alcohol use, with the latter assessed using a timeline followback calendar and the alcohol use disorder identification test (AUDIT).

RESULTS

In all former smokers, total drinks (b = 4.01, p = 0.02) and average drinks per drinking day (b = 0.61, p =.01) were both related to e-cig use status, with e-cig users reporting higher alcohol consumption. Among e-cig using former smokers, social users, but not regular users, showed positive relationships with AUDIT scores, b = 1.90, p =.02, total drinks, b = 9.12, p <.001, average drinks, b = 0.98, p =.006, and hazardous drinking status, OR = 3.21, p =.01.

CONCLUSIONS

Findings suggest that: (1) former smokers who use e-cigs may have a potential for higher alcohol use; and (2) those who use e-cigs socially may be at heightened risk for hazardous patterns of alcohol consumption. This should be taken into consideration by healthcare providers.

Combined expectancies of alcohol and e-cigarette use relate to higher alcohol use

Electronic cigarettes (e-cigs) were created to approximate the look, feel, and experience of using a cigarette. Since cigarette and alcohol use co-occur, we hypothesized that e-cig and alcohol use also co-occur, likely due to shared positive drug expectations. Using self-report data from two independent samples of community-dwelling alcohol using adults, the present study: (1) modified the Nicotine and Other Substance Interaction Expectancy Questionnaire (NOSIE) to assess expectancies of combined e-cig and alcohol use (i.e. the individuals perceived likelihood of using e-cigs and alcohol together; NOSIE-ER); and (2) examined the relationships among e-cig use, expectancies, and alcohol use across e-cig use status. In the first sample (N=692, mean age=32.6, SD=9.74, 50.7% female, 82.2% Caucasian), exploratory factor analysis suggested the presence of two factors: (1) alcohol use leads to e-cig use (Scale 1; α=0.85); and (2) e-cig use leads to alcohol use (Scale 2; α=0.91). In the second sample (N=714, mean age=34.1, SD=10.89, 47.8% female, 75.6% Caucasian), confirmatory factor analysis supported this factor structure (χ(2)=47.00, p<0.01, df=19; RMSEA=0.08, 90% CI=0.05-0.11; TLI=0.99; CFI=0.99). Compared to non e-cig users, e-cig users had significantly higher problematic alcohol use in both samples (b's=0.09 to 0.14, p's<.05). Expectancies of combined e-cig and alcohol use were significantly related to problematic alcohol use (b's=-0.92 to 0.26, p's<.05). In sum, e-cig use is related to alcohol use and expectancies of combined e-cig and alcohol use; consequently, reshaping of beliefs about needs or desires to co-use could be a prime point of intervention.

Nicotine reinforcement in never-smokers

RATIONALE

Global tobacco-related mortality dwarfs that of all other drugs. Nicotine is believed to be the primary agent responsible for tobacco use and addiction. However, nicotine is a relatively weak and inconsistent reinforcer in nonhumans and nicotine reinforcement has not been demonstrated in never-smokers.

OBJECTIVES

This study investigated the discriminative, subjective, and reinforcing effects of nicotine in never-smokers.

METHODS

Eighteen never-smokers (< 50 lifetime nicotine exposures) participated in a double-blind study. During a drug discrimination phase, volunteers ingested oral nicotine and placebo capsules (quasi-random order) at least 2 h apart and rated subjective effects repeatedly for 2 h after ingestion in daily sessions. Blocks of 10 sessions were continued until significant discrimination was achieved (p ≤ 0.05, binomial test; ≥ 8 of 10). Following discrimination, nicotine choice was tested by having volunteers choose which capsule set to ingest on each daily session. Successive blocks of 10 sessions were conducted until choice for nicotine or placebo met significance within each volunteer (≥ 8 of 10 sessions).

RESULTS

All 18 volunteers significantly discriminated nicotine from placebo; the lowest dose discriminated ranged from 1.0 to 4.0 mg/70 kg. Nine volunteers significantly chose nicotine (choosers) and nine significantly chose placebo (nicotine avoiders). The choosers reported predominately positive nicotine subjective effects (e.g., alert/attentive, good effects, liking), while avoiders tended to report negative effects (e.g., dizzy, upset stomach, disliking). Both choosers and avoiders attributed their choice to the qualitative nature of drug effects.

CONCLUSIONS

These results provide the first evidence that nicotine can function as a reinforcer in some never-smokers.

A hierarchical instrumental decision theory of nicotine dependence

It is important to characterize the learning processes governing tobacco-seeking in order to understand how best to treat this behavior. Most drug learning theories have adopted a Pavlovian framework wherein the conditioned response is the main motivational process. We favor instead a hierarchical instrumental decision account, wherein expectations about the instrumental contingency between voluntary tobacco-seeking and the receipt of nicotine reward determines the probability of executing this behavior. To support this view, we review titration and nicotine discrimination research showing that internal signals for deprivation/satiation modulate expectations about the current incentive value of smoking, thereby modulating the propensity of this behavior. We also review research on cue-reactivity which has shown that external smoking cues modulate expectations about the probability of the tobacco-seeking response being effective, thereby modulating the propensity of this behavior. Economic decision theory is then considered to elucidate how expectations about the value and probability of response-nicotine contingency are integrated to form an overall utility estimate for that option for comparison with qualitatively different, nonsubstitute reinforcers, to determine response selection. As an applied test for this hierarchical instrumental decision framework, we consider how well it accounts for individual liability to smoking uptake and perseveration, pharmacotherapy, cue-extinction therapies, and plain packaging. We conclude that the hierarchical instrumental account is successful in reconciling this broad range of phenomenon precisely because it accepts that multiple diverse sources of internal and external information must be integrated to shape the decision to smoke.

Developing and validating a human laboratory model to screen medications for smoking cessation

INTRODUCTION

To facilitate translational work in medications development for smoking cessation, we have developed a human laboratory analogue of smoking lapse behavior. Our paradigm models 2 critical features of smoking lapse: the ability to resist the first cigarette and subsequent ad libitum smoking. In this paper we present the results of 2 studies designed to develop and validate the effect of nicotine deprivation on smoking lapse behavior.

METHODS

Study 1 (n = 30) was designed to develop the model parameters by examining varying levels of nicotine deprivation (1, 6, and 18 hr; within-subject) and identifying optimum levels of monetary reinforcement to provide while modeling the ability to resist smoking. Study 2 was designed to validate the model by screening smoking cessation medications with known clinical efficacy. Subjects (n = 62) were randomized to either varenicline 2 mg/day, bupropion 300 mg/day, or placebo, and we then modeled their ability to resist smoking and subsequent ad libitum smoking.

RESULTS

In Study 1, increasing levels of nicotine deprivation and decreasing levels of monetary reinforcement decreased the ability to resist smoking. In Study 2, the lapse model was found to be sensitive to medication effects among smokers who demonstrated a pattern of heavy, uninterrupted, and automated smoking (i.e., smoked within 5 min of waking). Ratings of craving, mood, withdrawal, and subjective cigarette effects are presented as secondary outcomes with results mirroring clinical findings.

CONCLUSIONS

Our smoking lapse model demonstrates promise as a translational tool to screen novel smoking cessation medications. Next steps in this line of research will focus on evaluating predictive validity.

If the data contradict the theory, throw out the data: Nicotine addiction in the 2010 report of the Surgeon General

The reports of US Surgeon General on smoking are considered the authoritative statement on the scientific state of the art in this field. The previous report on nicotine addiction published in 1988 is one of the most cited references in scientific articles on smoking and often the only citation provided for specific statements of facts regarding nicotine addiction. In this commentary we review the chapter on nicotine addiction presented in the recent report of the Surgeon General. We show that the nicotine addiction model presented in this chapter, which closely resembles its 22 years old predecessor, could only be sustained by systematically ignoring all contradictory evidence. As a result, the present SG's chapter on nicotine addiction, which purportedly "documents how nicotine compares with heroin and cocaine in its hold on users and its effects on the brain," is remarkably biased and misleading.

Nicotine reduction revisited: science and future directions

Regulation of nicotine levels in cigarettes and other tobacco products is now possible with the passage of the Family Smoking Prevention and Tobacco Control Act (FSPTCA) in 2009, giving the US Food and Drug Administration (FDA) authority to regulate tobacco products, and with Articles 9-11 of the WHO Framework Convention on Tobacco Control. Both regulatory approaches allow establishing product standards for tobacco constituents, including nicotine. The FSPTCA does not allow nicotine levels to be decreased to zero, although the FDA has the authority to reduce nicotine yields to very low, presumably non-addicting levels. The proposal to reduce levels of nicotine to a level that is non-addicting was originally suggested in 1994. Reduction of nicotine in tobacco products could potentially have a profound impact on reducing tobacco-related morbidity and mortality. To examine this issue, two meetings were convened in the US with non-tobacco-industry scientists of varied disciplines, tobacco control policymakers and representatives of government agencies. This article provides an overview of the current science in the area of reduced nicotine content cigarettes and key conclusions and recommendations for research and policy that emerged from the deliberations of the meeting members.

Subjective effects of transdermal nicotine among nonsmokers

The subjective experience of nicotine, which may be influenced by personality traits as well as environmental factors, may be important for understanding the factors associated with the initiation and maintenance of nicotine dependence. The present study examined the effects of 7 mg transdermal nicotine among a relatively large sample (n = 91; 44 women) of college-aged nonsmokers. Using a placebo controlled, double-blind, within-subjects design, nicotine's effects were examined at rest and again after participants completed a sustained attention task. Sex and personality factors (Behavioral Inhibition and Behavioral Approach; BIS/BAS Scales; Carver & White, 1994) were examined as potential moderators. Overall, the effects of nicotine were generally modest and unpleasant. In the context of the cognitive task, nicotine increased nausea and negative affect but reduced fatigue, relative to placebo. In contrast, effects of nicotine during the initial 4 hr of patch administration, in which participants were in their natural environments, were moderated by individual differences in behavioral approach. Neither behavioral inhibition nor gender reliably moderated any subjective effects of nicotine. The present work suggests transdermal nicotine exerts only modest, mostly negative effects among nonsmokers. Future work should examine both contextual and personality moderators in large samples of participants who are exposed to nicotine through multiple routes of administration.

Abuse liability assessment of tobacco products including potential reduced exposure products

The harm produced by tobacco products is a result of frequent use of a highly toxic product. Reducing the adverse public health impact of tobacco products might be most effectively achieved by reducing the likelihood of their use and the toxicity of the products. Products that retain some characteristics of cigarettes but have been altered with the intention of reducing toxicity have been referred to as modified risk tobacco products or potential reduced exposure products (MRTP/PREP). Evaluation of their content, emission, and toxicity is discussed in other articles in this special issue. Here, we discuss the methodology that has been used to examine the likelihood of abuse or addiction. Abuse liability assessment (ALA) methodology has been used by the Food and Drug Administration (FDA) and other drug regulatory agencies world-wide for decades to assess the risks posed by a wide variety of pharmacologically active substances. ALA is routinely required among other evaluations of safety during the pre-market assessment of new drugs, and is continually adapted to meet the challenges posed by new drug classes and drug formulations. In the 2009 law giving FDA regulation over tobacco products, FDA is now required to evaluate new tobacco products including MRTP/PREPs to determine their risk for abuse and toxicity at the population level. This article describes the traditional tools and methods of ALA that can be used to evaluate new tobacco and nicotine products including MRTP/PREPs. Such ALA data could contribute to the scientific foundation on which future public policy decisions are based.

Measures for assessing subjective effects of potential reduced-exposure products

Potential reduced-exposure products (PREP) may reduce toxicant exposure and thereby may possibly reduce health risks associated with conventional tobacco use. However, lessened health risk to the individual or harm to the population through the use of PREPs is unknown. Research is being conducted to evaluate the possible health effects associated with PREP use. As part of this evaluation, it is critical to provide sound measures of subjective responses to PREPs to determine the use and the abuse potential of a product, that is, the likelihood that the product will lead to addiction. The goal of this paper is to conduct a systematic review of scales that have been used to measure the subjective responses to PREPs and examine their characteristics. In this article, scales are identified and the items on the scales are described. Scales are also examined to determine whether they are sensitive in testing PREPs. Furthermore, scales to assess PREPs are recommended to investigators. Where no scales exist, items that may be critical for the development and validation of new scales are identified.

Alcohol-induced increases in smoking behavior for nicotinized and denicotinized cigarettes in men and women

INTRODUCTION

Alcohol has been shown to increase smoking urges and smoking behavior. However, alcohol's effects on specific components of smoking behavior for nicotine versus non-nicotine factors and potential sex differences in this response have not been investigated.

METHODS

Forty-two young male and female non-dependent, heavy social drinking smokers participated in two double-blind laboratory sessions. They were randomized to either an alcohol (0.8 g/kg; n = 29) or placebo (n = 13) beverage pre-administration group. After beverage consumption, they were assessed for smoking urges and then given the opportunity to smoke cigarettes which were either all nicotinized (0.6 mg/cigarette) or denicotinized (< or =0.05 mg/cigarette) over a 3-h period; smoking behavior was quantified by a smoking topography device. Subjects took standardized puffs of the session's cigarette both before and after beverage administration to provide a reference when making future smoking choices.

RESULTS

Alcohol, compared with placebo beverage, increased both men's and women's smoking urge, as well as subjective ratings of smoking reference puffs for either nicotinized or denicotinized cigarettes. In terms of smoking choice behavior, regardless of cigarette type, alcohol (>placebo) increased men's smoking behavior, including puff count, volume, and duration. In contrast, for women, smoking topography measures did not differ between alcohol and placebo conditions.

DISCUSSION

In summary regardless of nicotine content, in men, alcohol increased smoking urge and behavior, whereas in women, alcohol increased smoking urge but did not increase smoking behavior. These results indicate that the mechanisms underlying co-use of alcohol and tobacco in women may be more complex than in men.

Discriminative stimulus effects of nicotine in humans

Behavioral discrimination procedures clearly demonstrate that nicotine elicits interoceptive stimulus effects in humans that are malleable by various pharmacological manipulations as well as by some behavioral manipulations. The parameters of nicotine discrimination and both chronic and acute factors that may alter discrimination behavior are addressed in this chapter, which emphasizes research by the author involving nicotine delivered by nasal spray. Human discrimination of nicotine is centrally mediated, as the central and peripheral nicotine antagonist mecamylamine blocks discrimination but the peripheral antagonist trimethaphan does not. The threshold dose for discrimination of nicotine via spray appears to be very low in smokers as well as nonsmokers. Because smoked tobacco delivers nicotine more rapidly than spray, the threshold dose of nicotine via smoking is probably even lower. In terms of individual differences, smokers may become tolerant to the discriminative stimulus effects of higher nicotine doses but not of low doses. Men may be more sensitive than women to nicotine's discriminative stimulus effects, consistent with other research suggesting that nicotine is more reinforcing in men than in women. Other potential individual differences in nicotine discrimination have not been clearly tested, but may include genetics, obesity, and dependence on other drugs. Acute environmental factors that alter nicotine discrimination include the specific training and testing conditions, pointing to the need for careful control over such conditions during research. Other factors, such as concurrent acute use of alcohol or caffeine, do not appear to alter nicotine discrimination, suggesting that changes in nicotine discrimination are not likely explanations for the association of smoking behavior with use of those drugs. Concurrent physical activity also does not appear to alter nicotine discrimination, indicating that results from studies of discrimination in subjects at quiet rest, the standard approach in this research, generalize well to discrimination in subjects engaged in various activities, as often occurs in the natural environment. Future research should more clearly examine the potential role of nicotine's discriminative stimulus effects in nicotine reinforcement and determine the generalizability of these findings to nicotine delivered by other means, particularly tobacco smoking.

Developing human laboratory models of smoking lapse behavior for medication screening

Use of human laboratory analogues of smoking behavior can provide an efficient, cost-effective mechanistic evaluation of a medication signal on smoking behavior, with the result of facilitating translational work in medications development. Although a number of human laboratory models exist to investigate various aspects of smoking behavior and nicotine dependence phenomena, none have yet modeled smoking lapse behavior. The first instance of smoking during a quit attempt (i.e. smoking lapse) is highly predictive of relapse and represents an important target for medications development. Focusing on an abstinence outcome is critical for medication screening as the US Food and Drug Administration approval for cessation medications is contingent on demonstrating effects on smoking abstinence. This paper outlines a three-stage process for the development of a smoking lapse model for the purpose of medication screening. The smoking lapse paradigm models two critical features of lapse behavior: the ability to resist the first cigarette and subsequent ad libitum smoking. Within the context of the model, smokers are first exposed to known precipitants of smoking relapse (e.g. nicotine deprivation, alcohol, stress), and then presented their preferred brand of cigarettes. Their ability to resist smoking is then modeled and once smokers 'give in' and decide to smoke, they participate in a tobacco self-administration session. Ongoing and completed work developing and validating these models for the purpose of medication screening is discussed.

Effects of nicotine in experimental animals and humans: an update on addictive properties

Tobacco use through cigarette smoking is the leading preventable cause of death in the developed world. Nicotine, a psychoactive component of tobacco, appears to play a major role in tobacco dependence, but the reinforcing effects of nicotine have often been difficult to demonstrate directly in controlled studies with laboratory animals or human subjects. Here we update our earlier review published in Psychopharmacology (Berl) in 2006 on findings obtained with various procedures developed to study dependence-related behavioral effects of nicotine in experimental animals and humans. Results obtained with drug self-administration, conditioned place preference, subjective reports of nicotine effects and nicotine discrimination indicate that nicotine can function as an effective reinforcer of drug-seeking and drug-taking behavior both in experimental animals and humans under appropriate conditions. Interruption of chronic nicotine exposure produces ratings of drug withdrawal and withdrawal symptoms that may contribute to relapse. Difficulties encountered in demonstrating reinforcing effects of nicotine under some conditions, relative to other drugs of abuse, may be due to weaker primary reinforcing effects of nicotine, to aversive effects produced by nicotine, or to a more critical contribution of environmental stimuli to the maintenance of drug-seeking and drug-taking behavior with nicotine than with other drugs of abuse. Several recent reports suggest that other chemical substances inhaled along with nicotine in tobacco smoke may play a role in sustaining smoking behavior. However, conflicting results have been obtained with mice and rats and these findings have not yet been validated in nonhuman primates or human subjects. Taken together, these findings suggest that nicotine acts as a typical drug of abuse in experimental animals and humans in appropriate situations.

Variability in initial nicotine sensitivity due to sex, history of other drug use, and parental smoking

Initial sensitivity to nicotine's effects during early exposure to tobacco may relate to dependence vulnerability. We examined the association of initial nicotine sensitivity with individual difference factors of sex, other drug use history (i.e. cross-tolerance or cross-sensitization), and parental smoking status in young adult nonsmokers (N=131). Participants engaged in 4 sessions, the first 3 to assess the dose-response effects of nasal spray nicotine (0, 5, 10 microg/kg) on rewarding, mood, physiological, sensory processing, and performance effects, and the fourth to assess nicotine reinforcement using a choice procedure. Men had greater initial sensitivity than women to some self-reported effects of nicotine related to reward and incentive salience and to impairment in sensory processing, but men and women did not differ on most other effects. Prior marijuana use was associated with greater nicotine reward, nicotine reinforcement was greater in men versus women among those with prior marijuana use, and having parents who smoked was related to increased incentive salience. However, history of other drug use and parental smoking were not otherwise associated with initial nicotine sensitivity. These findings warrant replication with other methods of nicotine administration, especially cigarette smoking, and in more diverse samples of subjects naïve to nicotine. Yet, they suggest that sex differences in initial sensitivity to nicotine reward occur before the onset of dependence. They also suggest that parental smoking may not increase risk of nicotine dependence in offspring by altering initial nicotine sensitivity, and that cross-tolerance between other drugs and nicotine may not be robust in humans.

Cigarette abstinence impairs memory and metacognition despite administration of 2 mg nicotine gum

The authors assessed the effects of cigarette abstinence (nonabstinent vs. minimum 8 hours abstinent) and nicotine gum (0 mg vs. 2 mg nicotine) on sustained attention, free recall, and metacognition using a within-subjects design. Moderate smokers (10 women and 22 men) received one training session followed by four test sessions on consecutive days. Nicotine gum improved sustained attention in both abstinent and nonabstinent states, but had no significant effect on predicted or actual recall levels. Cigarette abstinence significantly impaired free recall and reduced the magnitude of participants' predictions of their own performance. In addition, participants were significantly more overconfident about their future memory when abstinent. Thus, nicotine gum can improve smokers' performance in basic aspects of cognition (e.g., sustained attention) but may not alleviate the detrimental effects of cigarette abstinence on higher-level processes such memory and metacognition.

Sex differences in the relationship between alcohol-associated smoking urge and behavior: a pilot study

This study examined sex differences in alcohol-associated smoking urge and smoking patterns to elucidate factors contributing to the co-use of alcohol and cigarettes. Participants were 39 (22M, 17F) binge-drinking tobacco chippers. Although men and women showed similar alcohol-smoking patterns and similar alcohol-induced smoking urges, a positive association between these factors was observed only in men. The lack of relationship in women suggests that co-use of these substances may be due to exteroceptive factors beyond the pharmacological effects of alcohol potentiating smoking urge.

Dose-related enhancement of mood and cognition in smokers administered nicotine nasal spray

The discovery of the role of nicotinic receptors in attention and memory has led to the testing of nicotinic analogs as cognitive enhancing agents in patient populations. Empirical information about nicotine's ability to enhance elements of attention and memory in normal individuals might guide development of therapeutic uses of nicotine in cognitively impaired populations. The purpose of this study was to determine the effect of nicotine on continuous attention, working memory, and computational processing in tobacco-deprived and nondeprived smokers. A total of 28 smokers (14 men, 14 women) participated in a double-blind, placebo-controlled, within-subject study, in which they were overnight (12 h) tobacco deprived at one session and smoked ad libitum before the other session. At each session, participants received 0, 1, and 2 mg nicotine via nasal spray in random order at 90 min intervals. Before and after each dose, a battery of cognitive, subjective, and physiological measures was administered, and blood samples were taken for plasma nicotine concentration. Overnight tobacco deprivation resulted in impaired functioning on all cognitive tests and increased self-reports of tobacco craving and negative mood; nicotine normalized these deficits. In the nondeprived condition, nicotine enhanced performance on the continuous performance test (CPT) and an arithmetic test in a dose-related manner, but had no effect on working memory. In general, women were more sensitive than men to the subjective effects of nicotine. These results provide an unequivocal determination that nicotine enhanced attentional and computational abilities in nondeprived smokers and suggest these cognitive domains as substrates for novel therapeutic indications.

Modeling the effect of alcohol on smoking lapse behavior

OBJECTIVE

The primary aim of this project was to examine the role of alcohol use in smoking lapse behavior, as alcohol consumption is a known risk factor for poor smoking cessation outcomes.

MATERIALS AND METHODS

We have developed a novel human laboratory model to examine two primary aspects of alcohol-mediated tobacco relapse: (1) Does alcohol facilitate the initiation of the first cigarette? (2) Once the first cigarette is initiated, does alcohol facilitate subsequent smoking? Using a within-subject design, 16 daily smokers who were also heavy social drinkers received a priming drink (0.03 g/dl or taste-masked placebo) and then had the option of initiating a tobacco self-administration session or delaying initiation by 5-min increments for up to 50 min in exchange for monetary reinforcement. Subsequently, the tobacco self-administration session consisted of a 1-h period in which subjects could choose to smoke their preferred brand of cigarettes using a smoking topography system or receive monetary reinforcement for cigarettes not smoked. Alcohol craving, tobacco craving, subjective reactivity to alcohol, and nicotine withdrawal were assessed as secondary outcomes.

RESULTS

Results demonstrated that after consuming the alcohol beverage, subjects were less able to resist the first cigarette and initiated their smoking sessions sooner, and smoked more cigarettes compared to the placebo beverage. These findings have implications for smoking cessation in alcohol drinkers and model development to assess smoking lapse behavior.

Nicotine as a typical drug of abuse in experimental animals and humans

RATIONALE AND BACKGROUND

Tobacco use through cigarette smoking is the leading preventable cause of death in the developed world. Nicotine, a psychoactive component of tobacco, appears to play a major role in tobacco dependence, but reinforcing effects of nicotine often are difficult to demonstrate directly in controlled laboratory studies with animal or human subjects.

OBJECTIVE

To review the major findings obtained with various procedures developed to study dependence-related behavioral effects of nicotine in experimental animals and humans, i.e., drug self-administration, conditioned place preference, subjective reports of nicotine effects and nicotine discrimination, withdrawal signs, and ratings of drug withdrawal.

RESULTS

Nicotine can function as an effective reinforcer of drug-seeking and drug-taking behavior both in experimental animals and humans under appropriate conditions. Interruption of chronic nicotine exposure produces withdrawal symptoms that may contribute to relapse. Difficulties encountered in demonstrating reinforcing effects of nicotine under some conditions, relative to other drugs of abuse, may be due to weaker primary reinforcing effects of nicotine or to a more critical contribution of environmental stimuli to the maintenance of drug-seeking and drug-taking behavior with nicotine than with other drugs of abuse. Further experiments are also needed to delineate the role other chemical substances inhaled along with nicotine in tobacco smoke play in sustaining smoking behavior.

CONCLUSION

Nicotine acts as a typical drug of abuse in experimental animals and humans.

Does nicotine do what we think it does? A meta-analytic review of the subjective effects of nicotine in nasal spray and intravenous studies with smokers and nonsmokers

We conducted a meta-analysis of placebo-controlled laboratory studies of the subjective effects of nicotine. A total of 15 studies (11 with nasal spray, four with intravenous administration) with smokers and six studies (all with nasal spray) with never-smokers were included. Studies of other routes of administration (e.g., smoked tobacco) were not included because of insufficient numbers of available effect sizes. Meta-analysis results indicated that nicotine increased vigor for smokers but increased fatigue for never-smokers. Nicotine increased head rush for both smokers and never-smokers. In studies of smokers only, nicotine also increased ratings of drug high and drug liking. Contrary to expectations, nicotine decreased relaxation and increased tension/jitteriness for both smokers and never-smokers. Dose-response relationships were most clearly observed for head rush and drug high. Considerable variability was found across studies for a given nicotine dose and route of administration. Implications of the current findings about the role of subjective effects in nicotine reinforcement and self-administration are discussed along with commentary on methodological issues and recommendations for future studies.

The influence of caffeine on nicotine's discriminative stimulus, subjective, and reinforcing effects

Caffeine may acutely alter the discriminative stimulus and subjective effects of nicotine, perhaps explaining the association of coffee intake with smoking status. In this study, smokers were initially trained to discriminate 20 microg/kg nicotine by nasal spray from placebo (0). Then, generalization of nicotine discrimination was tested, using both 2- and 3-choice ("novel" option) procedures, across a range of doses (0-20 microg/kg) following pretreatment with 0, 2.5, and 5.0 mg/kg caffeine p.o. Nicotine reinforcement was assessed after the end of generalization testing using a choice procedure. Caffeine pretreatment did not alter nicotine discrimination and self-administration. Caffeine and nicotine influenced some subjective and cardiovascular responses, but there were no interaction effects except for diastolic blood pressure. These results do not support the notion that caffeine acutely alters nicotine's discriminative stimulus, subjective, or reinforcing effects.

The influence of alcohol pre-treatment on the discriminative stimulus, subjective, and relative reinforcing effects of nicotine

Alcohol intake may acutely alter the discriminative stimulus and subjective effects of nicotine, perhaps explaining why alcohol increases tobacco smoking. In this study, cigarette smokers were initially trained to discriminate 20 microg/kg nicotine by nasal spray from placebo. Three sessions then followed, in which the generalization of nicotine discrimination was tested across a range of doses (0--20 microg/kg) following pre-treatment with 0, 0.4, and 0.8 g/kg alcohol p.o. Intermittent 'topping' doses of alcohol maintained a steady breath alcohol level (BAL) throughout testing. Generalization testing involved both two- and three-choice ('novel' option) procedures. A visual discrimination task was also conducted to determine the specificity of effects of alcohol. Subjective and cardiovascular measures were obtained concurrent with discrimination responding. The relative reinforcing effects of nicotine were assessed after the end of generalization testing using a choice procedure. Alcohol pre-treatment had no significant effects on nicotine discrimination or self-administration behavior. Alcohol and nicotine each influenced selected subjective responses and heart rate, but virtually no interactions between the drugs were observed. Within the limitations of this study, these results do not support the notion that alcohol acutely alters nicotine's discriminative stimulus, subjective, or relative reinforcing effects at these low nicotine doses. Acute effects of alcohol on smoking behavior may be due to alterations in other effects of nicotine intake or in non-nicotine effects of tobacco smoking.

The discriminative stimulus, subjective, cardiovascular, and reinforcing effects of nicotine as a function of light physical activity

Smokers often experience the acute effects of cigarette smoking while they are engaged in the light physical activity of routine tasks. However, virtually all laboratory-based research on these effects is conducted under conditions of quiet rest and, thus, may not generalize to effects in the natural environment. We examined changes in the discriminative stimulus, subjective, cardiovascular, and reinforcing effects of nicotine in humans as a function of the level of concurrent physical activity. Men and women smokers (N = 17) were initially trained to discriminate 20 microg/kg nicotine by nasal spray from placebo (0 microg/kg) at rest. Three sessions then followed, in which the generalization of discrimination was tested across a range of doses (0-20 microg/kg) while at rest or engaged in very light or light physical activity (15% and 30% of heart rate reserve, respectively) via bicycle ergometer. Generalization testing involved both two- and three-choice ("novel" option) quantitative procedures. Self-reported mood via the Profile of Mood States and visual analog scales, and cardiovascular measures of heart rate and blood pressure were obtained concurrent with discrimination responding. Nicotine reinforcement was assessed after the end of generalization testing using a choice procedure under the same rest or activity conditions. Results showed that physical activity did not significantly alter nicotine discrimination or reinforcement, as no interactions between activity and nicotine were observed. When activity and nicotine influenced the same subjective and cardiovascular responses, they acted in a generally additive fashion. These findings suggest that research on the acute effects of nicotine conducted under typical resting laboratory conditions generally are not altered by light physical activity and so may generalize to the effects of nicotine under conditions common in the natural environment.

The blind spot in the nicotine replacement therapy literature: assessment of the double-blind in clinical trials

While clinical trials of medications often use a double-blind procedure, the integrity of the blind and its relationship to treatment outcome is seldom examined. In this review, 73 double-blind, placebo-controlled clinical trials of the nicotine replacement therapies (NRTs) in smoking cessation were identified. Seventeen articles were found that assessed blindness integrity, demonstrating major variations in the assessment, analysis, and reporting of blindness integrity. Although 12 studies found that subjects accurately judged treatment assignment at a rate significantly above chance, the available literature does not permit definitive conclusions about blindness integrity. Recommendations for the assessment, analysis, and reporting of blindness integrity are made.

Clinical neuropharmacology of drugs of abuse: a comparison of drug-discrimination and subject-report measures

Advances in molecular pharmacology and behavioral science have helped elucidate the structure and function of the central nervous system and its relationship to behavior and has sparked the development of pharmacological agents that have increasingly selective and potent effects with fewer adverse side effects. The sensitivity and predictive validity of the two most commonly used methodologies for assessing the neuropharmacological effects of centrally active drugs, subject report of drug effects and drug discrimination, were examined. The sensitivity of the measures was comparable across stimulant, sedative, and opioid drugs. Results with drug-discrimination methodologies were generally consistent with hypothesized neuropharmacological mechanisms across all drug classes, whereas subject reports conformed under more limited testing conditions. Firm conclusions regarding the relative utility of drug-discrimination and subject-report measures for clinical studies of neuropharmacological mechanisms are limited by the small number of studies in which the two methodologies have been tested using identical pharmacological pretreatment manipulations.

Subjective effects of an initial dose of nicotine nasal spray predict treatment outcome

RATIONALE

Nicotine nasal spray (NS) is recommended as one of five first-line smoking cessation products. A clinically convenient tool to identify smokers most likely to benefit from NS could assist healthcare practitioners in selecting the optimal treatment for individual patients.

OBJECTIVES

To evaluate whether the subjective effects of an initial pre-treatment dose of NS predict 6 month abstinence rates following NS treatment for tobacco dependence.

METHODS

One hundred and seventy-five smokers received an initial 1 mg pre-treatment dose of NS and completed a new measure of NS subjective effects (initial spray experience, ISE). This measure, together with demographic and smoking history variables, was examined as a predictor of 6-month point-prevalence (biochemically verified) abstinence rates.

RESULTS

Factor analysis revealed positive and negative effects subscales of the ISE. Smokers with higher ratings of positive effects from the pre-treatment NS dose were significantly more likely to be abstinent at 6-month follow-up. These effects were partially mediated by reduction in urge to smoke.

CONCLUSIONS

Pending additional validation in human laboratory and clinical studies, assessment of the acute positive subjective effects of initial NS delivery may be an efficient way to predict who will be successful with NS treatment for tobacco dependence.

Individual differences in smoking: gender and nicotine addiction

Understanding individual differences in smoking behavior and nicotine dependence can increase knowledge of smoking dynamics and aid in the development of treatment regimens. Nicotine dependence among smokers is variable, and in some cases, fails to develop even after years of smoking. This variation can influence treatment outcome and presents a challenge to treatment developers. Gender differences are evident sometimes in smoking prevalence, in smoking cessation, and smoking rate. Gender, however, may be a superficial indicator; reasons for smoking, individual reactions to nicotine, and cultural sanctions and role definitions may be more influential. Analyses of individual differences should focus on identifying the underlying processes that control smoking behavior.

Rats prefer cocaine over nicotine in a two-lever self-administration choice test

Smoking is considered the leading cause of preventable death in the United States, but studies in animals suggest that nicotine is only weakly reinforcing. The maintenance of a dangerous habit by a weakly reinforcing agent has been the topic of some dispute. Using a two-lever "choice" self-administration procedure developed in our laboratory, we evaluated drug preferences as an index of relative reward strength for nicotine versus cocaine in nicotine-trained rats. Rats were initially exposed to each drug separately in single-lever self-administration sessions and then allowed to choose between them in a two-lever choice test session offering both drugs. When offered choices between different nicotine doses [8, 25, and 75 microg/kg/injection (inj), free base], rats responded approximately equally for any dose, regardless of which doses were compared. Rats clearly preferred 267 or 800 microg/kg/inj cocaine hydrochloride to any of the nicotine doses. These results indicate that cocaine has greater reward strength than nicotine and supports previous findings that self-administering rats seek to maximize reward magnitude regardless of the self-administered drug or training history. It is possible that dependence elevates nicotine's reward magnitude or nicotine addiction may rely more importantly upon negative rather than pure positive reinforcement.

Cue dependency of nicotine self-administration and smoking

A paradox exists regarding the reinforcing properties of nicotine. The abuse liability associated with smoking equals or exceeds that of other addictive drugs, yet the euphoric, reinforcing and other psychological effects of nicotine, compared to these other drugs, are more subtle, are manifest under more restricted conditions, and do not readily predict the difficulty most smokers experience in achieving abstinence. One possible resolution to this apparent inconsistency is that environmental cues associated with drug delivery become conditioned reinforcers and take on powerful incentive properties that are critically important for sustaining smoking in humans and nicotine self-administration in animals. We tested this hypothesis by using a widely employed self-administration paradigm in which rats press a lever at high rates for 1 h/day to obtain intravenous infusions of nicotine that are paired with two types of visual stimuli: a chamber light that when turned on signals drug availability and a 1-s cue light that signals drug delivery. We show that these visual cues are at least as important as nicotine in sustaining a high rate of responding once self-administration has been established, in the degree to which withdrawing nicotine extinguishes the behavior, and in the reinstatement of lever pressing after extinction. Additional studies demonstrated that the importance of these cues was manifest under both fixed ratio and progressive ratio (PR) schedules of reinforcement. The possibility that nicotine-paired cues are as important as nicotine in smoking behavior should refocus our attention on the psychology and neurobiology of conditioned reinforcers in order to stimulate the development of more effective treatment programs for smoking cessation.

The discriminative stimulus and reinforcing effects of nicotine in humans following nicotine pretreatment

Smokers often report that the first cigarette of the day is the most rewarding, and subsequent smoking is less rewarding. Reduction in smoking enjoyment later in the day may be related to acute tolerance to the discriminative stimulus effects of nicotine. We examined changes in nicotine discrimination behaviour in humans as a function of acute nicotine pretreatment. Male and female dependent smokers (n = 15) were initially trained to discriminate 20 microg/kg nicotine by nasal spray from placebo (0 microg/kg) without nicotine pretreatment. They then were tested on generalization of discrimination across a range of spray doses from 0-20 microg/kg following pretreatment with placebo, moderate dose (14-21 mg) or high dose (28-42 mg) transdermal nicotine. Generalization testing involved both two- and three-response ('novel' option) quantitative procedures. Subjects also engaged in a self-administration phase at the end of each session, involving choices between nicotine (20 microg/kg) and placebo spray. Nicotine pretreatment significantly attenuated nicotine-appropriate responding at higher nicotine spray doses, suggesting acute tolerance, but only in women. Similar results were seen for subjective 'head rush', suggesting this effect may be related to discrimination behaviour in women. However, nicotine pretreatment also increased novel-appropriate responding, especially in men, following intermediate generalization doses, suggesting qualitatively different stimulus effects. Although differences were not significant, nicotine self-administration tended to be inversely associated with nicotine pretreatment dose in men but not in women. These results only modestly support the notion of acute tolerance to the discriminative stimulus effects of nicotine, and even then only in women and not in men.

Sex differences in nicotine effects and self-administration: review of human and animal evidence

Although both the human and animal literatures are notable for the general lack of attention paid to possible sex differences in drug self-administration behavior, evidence is accumulating to suggest that males and females may differ in factors that maintain tobacco smoking or nicotine self-administration. Self-administration of nicotine per se may be less robust in women, and women are less sensitive than men to some effects of nicotine that may be reinforcing. Compared to men, smoking behavior of women may be influenced more by non-nicotine stimuli associated with smoking, suggesting greater conditioned reinforcement of smoking in women. Moreover, nicotine replacement, the current standard treatment for smoking cessation, is sometimes less effective in women, further suggesting the need for greater consideration of non-nicotine factors that may maintain women's smoking. Very recent research on rats also indicates sex differences in nicotine self-administration. However, these differences are complex and suggest that nicotine-seeking behavior is composed of several components, including hedonic, incentive-motivational, and conditioning effects; males and females may differ in one or more of these components. Menstrual or estrous cycle phase effects on the maintenance of nicotine self-administration are not particularly apparent in humans or animals, although cycle phase may influence other stages of dependence (e.g., withdrawal symptoms during cessation). Future research should evaluate further the consistency of results across human and non-human species, identify the conditions and procedures under which sex differences are observed, and elucidate the specific components of reinforcement that may differ between males and females. Studies also should examine the possible generalizability of these sex differences to other drugs of abuse. Identification of specific factors responsible for these sex differences may lead to improved interventions for smoking cessation and other substance abuse in women.

Nicotine discrimination in men and women

Nicotine is the primary compound that maintains tobacco smoking behavior, and nicotine reinforcement may be related to its discriminative stimulus effects. Nicotine in novel form, isolated from tobacco smoke, is often reinforcing in men but not in women, and clinical trials with nicotine replacement via gum or patch have often shown less efficacy in women vs. men trying to quit smoking. We hypothesize that this sex difference in nicotine reinforcement or clinical efficacy may be related to reduced intensity of nicotine's discriminative stimulus effects in women. Using formal drug discrimination procedures, we have found in several studies that discrimination responding across nasal spray nicotine doses tends to be flatter for women than men (i.e., sex x dose interaction), suggesting reduced sensitivity to changes in dose. Results from the field of psychophysiology, involving detection of physiological changes, are generally consistent with our findings, and suggest that the environmental context accompanying physiological change is important in understanding this sex difference. The implications of this sex difference for smoking cessation treatment and future research directions are presented.