Thwarting science by protecting the received wisdom on tobacco addiction from the scientific method

Behavioral characterization of early nicotine withdrawal in the mouse: a potential model of acute dependence

BACKGROUND

Clinical and preclinical research have demonstrated that short-term exposure to nicotine during the initial experimentation stage can lead to early manifestation of withdrawal-like signs, indicating the state of "acute dependence". As drug withdrawal is a major factor driving the progression toward regular drug intake, characterizing and understanding the features of early nicotine withdrawal may be important for the prevention and treatment of drug addiction. In this study, we corroborate the previous studies by showing that withdrawal-like signs can be precipitated after short-term nicotine exposure in mice, providing a potential animal model of acute dependence on nicotine.

RESULTS

To model nicotine exposure from light tobacco use during the initial experimentation stage, mice were treated with 0.5 mg/kg (-)-nicotine ditartrate once daily for 3 days. On the following day, the behavioral tests were conducted after implementing spontaneous or mecamylamine-precipitated withdrawal. In the open field test, precipitated nicotine withdrawal reduced locomotor activity and time spent in the center zone. In the elevated plus maze test, the mecamylamine challenge increased the time spent in the closed arm and reduced the number of entries irrespective of nicotine experience. In the examination of the somatic aspect, precipitated nicotine withdrawal enhanced the number of somatic signs. Finally, nicotine withdrawal did not affect cognitive functioning or social behavior in the passive avoidance, spatial object recognition, or social interaction test.

CONCLUSIONS

Collectively, our data demonstrate that early nicotine withdrawal-like signs could be precipitated by the nicotinic antagonist mecamylamine in mice, and that early withdrawal from nicotine primarily causes physical symptoms.

Further pharmacological characterization of a preclinical model of the early development of nicotine withdrawal

BACKGROUND

Establishing preclinical models of the development of nicotine withdrawal following acute nicotine exposure could inform tobacco addiction-related research, treatment, and policy. To this end, this lab has previously reported that rats exhibit withdrawal-like elevations in intracranial self-stimulation (ICSS) thresholds (anhedonia-like behavior) following acute nicotine exposure. The goal of this study was to provide further pharmacological characterization of ICSS as a measure of spontaneous and antagonist-precipitated withdrawal from acute nicotine.

METHODS AND RESULTS

Rats exhibited a small increase in ICSS thresholds over time following a single nicotine injection (1.0 mg/kg, s.c.), suggesting a modest spontaneous withdrawal effect (Experiment 1). In Experiment 2, the antidepressant bupropion (5.0 mg/kg, i.p.), which is used to treat tobacco addiction and attenuates nicotine withdrawal in both humans and rodents, blocked elevations in ICSS thresholds induced by a single injection of nicotine (0.5 mg/kg, s.c.) followed ≈ 2 h later by the non-selective, non-competitive nicotinic acetylcholine receptor (nAChR) antagonist mecamylamine (3.0 mg/kg, s.c.). In Experiment 3a, s.c. administration of the competitive, relatively selective α4ß2 nAChR antagonist dihydro-beta-erythroidine (DHßE) (5.6 mg/kg, but not 3.0 mg/kg) following each of 5 daily injections of nicotine (0.5 mg/kg, s.c.) elevated ICSS thresholds. Mecamylamine (3.0 mg/kg, s.c.) also elevated ICSS thresholds when administered following all 5 daily nicotine injections (0.5 mg/kg, s.c., Experiment 3b).

CONCLUSIONS

These findings provide further characterization of elevations in ICSS thresholds as a measure of withdrawal from acute nicotine exposure. Further use of these models may be useful for understanding the early development of nicotine withdrawal.

Cigarette Smoking and Nicotine Dependence Trajectories Among Incident Adolescent Smokers

INTRODUCTION

Few interventions target adolescent cigarette smokers to prevent escalation in cigarette use or promote cessation, in part because little is known about co-developing smoking and nicotine dependence (ND). Our objectives were to: (1) estimate developmental trajectories of ND/cravings, withdrawal symptoms, the modified Fagerström Tolerance Questionnaire (mFTQ) and ICD-10 tobacco dependence in incident adolescent smokers; (2) describe concordance in number and shapes of trajectories across the four ND indicators; and (3) classify participants in each ND trajectory according to cigarette smoking trajectories.

METHODS

Data were drawn from an ongoing longitudinal investigation of 1294 grade 7 students recruited in 1999-2000 in 10 Montreal-area high schools. Group-based joint trajectory models were used to identify distinct subgroups defined by the four ND indicators, in 307 incident smokers.

RESULTS

The optimal trajectory model included five groups for ND/craving and four groups for each of withdrawal symptoms, the mFTQ and ICD-10 tobacco dependence. The four ND indicators showed similar developmental patterns and classification into smoking trajectory groups, although some discordance was observed. Smokers in the low-level decreaser group and stable low consumers who exhibited high ND were younger than those in the cigarette-low ND trajectory groups. Moderate or rapid escalators who exhibited no/low ND were less likely to have university-educated mothers and more likely to have parents who smoke.

CONCLUSIONS

Trajectories were similar across ND indicators, and generally reflected cigarette smoking trajectory shapes. Novice smokers may need education to become self-aware of developing ND symptoms, as well as to learn about alternative courses of action once ND symptoms manifest.

IMPLICATIONS

Trajectories of cigarette smoking and ND symptoms have rarely been investigated concurrently. This study provides evidence of high concordance across four distinct ND indicators in the proportion of participants with no/low-level dependence, and with high or increasing ND. Moreover, the development of cigarette smoking is concordant with ND symptom development. Interventions to prevent escalation and promote cessation should target adolescents before first puff to increase self-awareness of developing ND symptoms, as well as to learn about alternative courses of action once ND symptoms are experienced.

Acculturation-related predictors of very light smoking among Latinos in California and nationwide

The prevalence of light smoking has increased among Latinos. The purpose of this study was to identify demographic and acculturation-related factors associated with very light smoking, defined as smoking 1-5 cigarettes per day (CPD), among Latinos in California and nationwide. Latino smokers in the 2007-2008 National Health and Nutrition Examination Survey (NHANES) or the 2009 California Health Interview Survey (CHIS) were analyzed. Logistic regression assessed factors associated with very light smoking. Among NHANES smokers, those born in Mexico or who lived fewer years in the US were more likely to be very light smokers than 6+ CPD smokers. Among CHIS smokers, those born in Mexico, in another Spanish speaking country, or who spent smaller percentages of their life in the US were more likely to be very light smokers. Findings from this study can be used to design tobacco control media campaigns that include very light smokers.

Can tobacco dependence provide insights into other drug addictions?

Within the field of addiction research, individuals tend to operate within silos of knowledge focused on specific drug classes. The discovery that tobacco dependence develops in a progression of stages and that the latency to the onset of withdrawal symptoms after the last use of tobacco changes over time have provided insights into how tobacco dependence develops that might be applied to the study of other drugs.As physical dependence on tobacco develops, it progresses through previously unrecognized clinical stages of wanting, craving and needing. The latency to withdrawal is a measure of the asymptomatic phase of withdrawal, extending from the last use of tobacco to the emergence of withdrawal symptoms. Symptomatic withdrawal is characterized by a wanting phase, a craving phase, and a needing phase. The intensity of the desire to smoke that is triggered by withdrawal correlates with brain activity in addiction circuits. With repeated tobacco use, the latency to withdrawal shrinks from as long as several weeks to as short as several minutes. The shortening of the asymptomatic phase of withdrawal drives an escalation of smoking, first in terms of the number of smoking days/month until daily smoking commences, then in terms of cigarettes smoked/day.The discoveries of the stages of physical dependence and the latency to withdrawal raises the question, does physical dependence develop in stages with other drugs? Is the latency to withdrawal for other substances measured in weeks at the onset of dependence? Does it shorten over time? The research methods that uncovered how tobacco dependence emerges might be fruitfully applied to the investigation of other addictions.

A Two-Day Continuous Nicotine Infusion Is Sufficient to Demonstrate Nicotine Withdrawal in Rats as Measured Using Intracranial Self-Stimulation

Avoidance of the negative affective (emotional) symptoms of nicotine withdrawal (e.g., anhedonia, anxiety) contributes to tobacco addiction. Establishing the minimal nicotine exposure conditions required to demonstrate negative affective withdrawal signs in animals, as well as understanding moderators of these conditions, could inform tobacco addiction-related research, treatment, and policy. The goal of this study was to determine the minimal duration of continuous nicotine infusion required to demonstrate nicotine withdrawal in rats as measured by elevations in intracranial self-stimulation (ICSS) thresholds (anhedonia-like behavior). Administration of the nicotinic acetylcholine receptor antagonist mecamylamine (3.0 mg/kg, s.c.) on alternate test days throughout the course of a 2-week continuous nicotine infusion (3.2 mg/kg/day via osmotic minipump) elicited elevations in ICSS thresholds beginning on the second day of infusion. Magnitude of antagonist-precipitated withdrawal did not change with further nicotine exposure and mecamylamine injections, and was similar to that observed in a positive control group receiving mecamylamine following a 14-day nicotine infusion. Expression of a significant withdrawal effect was delayed in nicotine-infused rats receiving mecamylamine on all test days rather than on alternate test days. In a separate study, rats exhibited a transient increase in ICSS thresholds following cessation of a 2-day continuous nicotine infusion (3.2 mg/kg/day). Magnitude of this spontaneous withdrawal effect was similar to that observed in rats receiving a 9-day nicotine infusion. Our findings demonstrate that rats exhibit antagonist-precipitated and spontaneous nicotine withdrawal following a 2-day continuous nicotine infusion, at least under the experimental conditions studied here. Magnitude of these effects were similar to those observed in traditional models involving more prolonged nicotine exposure. Further development of these models, including evaluation of more clinically relevant nicotine dosing regimens and other measures of nicotine withdrawal (e.g., anxiety-like behavior, somatic signs), may be useful for understanding the development of the nicotine withdrawal syndrome.

A comparison of adolescent smoking initiation measures on predicting future smoking behavior

Objectives

Evidence suggests that age at smoking initiation has implications for tobacco use, nicotine dependence, and resulting long-term health and chronic disease outcomes. The objective of the current study was to examine two different measures of smoking onset and to compare their validity in predicting future adolescent smoking survey.

Methods

Data from grades 9–12 students who participated in the 2012/2013 Youth Smoking Survey, a nationally-generalizable Canadian survey, and who had ever tried a cigarette, even a few puffs (n = 8126) were used in a multivariable logistic regression analysis to examine the association between age at smoking onset and current smoking behavior.

Results

Both “age at first puff” and “age at first whole cigarette” were significantly associated with current smoking status. Specifically, a delay of one year in the age at first puff was associated with lower odds of being a current smoker by 24% (AOR = 0.76, 95% CI = 0.73–0.79). Similarly, high school students who smoked their first whole cigarette at old age were less likely to report being a current smoker (AOR = 0.66, 95% CI = 0.62–0.71).

Conclusion

Efforts to prevent smoking uptake among youth, especially younger youth, are especially important in tobacco control efforts.

Does one cigarette make an adolescent smoker, and is it influenced by age and age of smoking initiation? Evidence of association from the U.S. Youth Risk Behavior Surveillance System (2011)

OBJECTIVES

Evidence that age of smoking initiation represents a risk factor for regular smoking in adolescence is complicated by inconsistencies in the operational definition of smoking initiation and simultaneous inclusion of age as an explanatory variable. The aim of this study was to examine the relationship between age, age of smoking initiation and subsequent regular smoking.

METHODS

A secondary analysis was conducted of the U.S. Youth Risk Behavior Survey 2011. A sex stratified multivariable logistic regression analysis was used to model the likelihood of regular smoking with age and age of smoking initiation as explanatory variables and race/ethnicity as a covariate.

RESULTS

After controlling for race/ethnicity, age and age of smoking initiation were independently associated with regular smoking in males and females. Independent of age, a one year's decrease in the age of smoking initiation was associated with a 1.27 times increase in odds of regular smoking in females (95% CI: 1.192-1.348); and similar associations for males (OR: 1.28; 95% CI: 1.216-1.341).

CONCLUSION

While the majority of high school students do not become regular smokers after initiating smoking, earlier initiation of smoking is associated with subsequent regular smoking irrespective of sex or race/ethnicity. These findings have potentially important implications for intervention targeting.

Hooked on the nicotine addiction thesis: a response to DiFranza

DiFranza’s rebuttal to our critique of the “Hooked on Nicotine” research program misconstrues our arguments beyond recognition. The grossest misrepresentation of our critique by DiFranza is that we devise (by thwarting science) to rescue “the conventional wisdom” of the “threshold model of nicotine addiction.” In fact, the difference between our positions lies elsewhere: We believe that nicotine is not an addictive drug and that its contribution to the smoking habit is secondary; DiFranza believes that nicotine is so powerfully addictive that novice smokers can lose autonomy over their smoking behavior after one cigarette or even following a single puff. Our review aimed to critically examine the empirical basis of this extreme version of the nicotine “addiction” model. In this brief commentary we illustrate how the commitment to the nicotine “addiction” theory has biased the methodology and the interpretation of the data in “Hooked on Nicotine” research program.

Responses to environmental smoking in never-smoking children: can symptoms of nicotine addiction develop in response to environmental tobacco smoke exposure?

A recent line of studies has brought attention to the question whether repeated exposure to environmental tobacco smoke (ETS) is capable of producing psycho-physiological effects in non-smokers and whether symptoms of nicotine dependence can develop in the absence of active smoking. Children seem to be particularly vulnerable to the effects of ETS. We examined the occurrence of psycho-behavioural symptoms, designed to assess nicotine addiction and nicotine withdrawal, in a sample of 778 never-smoking children aged 9-12 years using cross-sectional survey data collected in 15 Dutch primary schools. In the present study, 6% of never-smoking children reported symptoms of craving, 8% reported cue-triggered wanting to smoke, and 20% reported subjective symptoms in response to ETS exposure. In never-smoking children, a higher number of smokers in the child's social environment was associated with more symptoms of cue-triggered wanting to smoke and more subjective symptoms in response to ETS. Never-smoking children and children who had initiated smoking were equally likely to report subjective symptoms in response to ETS exposure. In conclusion, environmental smoking is associated with self-reported psycho-behavioural symptoms in never-smoking children. Future research needs to investigate whether symptoms in children exposed to ETS are physiologically based or whether they reflect other characteristics which predispose youth for smoking initiation in the future.

Mecamylamine elicits withdrawal-like signs in rats following a single dose of nicotine

RATIONALE

The ability of nicotine to induce dependence (result in a withdrawal syndrome) is typically thought to require long-term, daily smoking. Emerging evidence suggests that symptoms of nicotine withdrawal may occur following only a few cigarettes. Whether acute exposure to nicotine can induce dependence in animals has not been well established.

OBJECTIVE

The objective of this paper is to examine whether the nicotinic acetylcholine receptor antagonist mecamylamine elicits withdrawal-like signs in rats following acute nicotine exposure.

METHODS AND RESULTS

Mecamylamine (3.0 mg/kg, s.c.) administered ≈2 h after a single dose of nicotine (0.5 mg/kg, s.c.) elicited increases in intracranial self-stimulation (ICSS) thresholds and somatic signs, two well-established effects of withdrawal from long-term (chronic) nicotine exposure. The magnitude of these effects remained constant across five daily test sessions. A lower dose of mecamylamine (1.5 mg/kg, s.c.) had little or no effect on ICSS thresholds or somatic signs following acute nicotine exposure, but precipitated robust increases in these measures during a chronic nicotine infusion. Finally, rats exhibited a small increase in ICSS thresholds over time following a single nicotine injection (0.5 mg/kg, s.c.), possibly reflecting a modest spontaneous withdrawal-like effect.

CONCLUSIONS

Mecamylamine elicited withdrawal-like signs in rats following a single dose of nicotine. The different effects of mecamylamine 1.5 mg/kg following acute versus chronic nicotine exposure supports the notion that these models simulate the early and more advanced stages of nicotine dependence, respectively. While further optimization and validation of these models is necessary, they may provide a novel approach for studying the earliest stages of nicotine dependence.

The relationship between age of smoking initiation and current smoking: an analysis of school surveys in three European countries

INTRODUCTION

It is held that younger smoking initiates are more likely to become regular smokers. The definitions of smoking initiation (a puff, part of a cigarette, a whole cigarette) are inconsistent and raise questions about the robustness of the view. We sought to re-examine the relationship using adolescent smoking data from 3 European countries.

METHODS

A stratified secondary, logistic regression analysis of Global Youth Tobacco Survey data was conducted using a design-based analysis. Subgroup analyses were conducted of 13- to 15-year olds from Latvia (high smoking prevalence), Slovenia (moderate prevalence), and Montenegro (low prevalence) who had initiated smoking. The outcome was current smoking--smoking everyday for the past 30 days, or smoking 10 or more days in the past 30 days. Smoking initiation was operationalized as a single puff of a cigarette, and age of smoking initiation was a derived continuous measure.

RESULTS

In Latvia, there was a significant association between age of smoking initiation and current smoking for males (p < .05) and females (p < .001) when smoking was operationalized as smoking every day. It was only significant in female adolescents (p < .001) for smoking 10 or more days. In Slovenia and Montenegro, there was no significant relationship between age of smoking initiation and current smoking for either males or females.

CONCLUSIONS

The evidence about the relationship between age of smoking initiation and current smoking is not clear. Explanations for the findings may relate to a lack of power, the specificity of the measure, or problems with the theory.

Neural systems governed by nicotinic acetylcholine receptors: emerging hypotheses

Cholinergic neurons and nicotinic acetylcholine receptors (nAChRs) in the brain participate in diverse functions: reward, learning and memory, mood, sensory processing, pain, and neuroprotection. Nicotinic systems also have well-known roles in drug abuse. Here, we review recent insights into nicotinic function, linking exogenous and endogenous manipulations of nAChRs to alterations in synapses, circuits, and behavior. We also discuss how these contemporary advances can motivate attempts to exploit nicotinic systems therapeutically in Parkinson's disease, cognitive decline, epilepsy, and schizophrenia.