Inhibition of monoamine oxidase B in the brains of smokers

Specific binding of [3H]Ro 19-6327 (lazabemide) to monoamine oxidase B is increased in frontal cortex of suicide victims after controlling for age at death

Previous studies have reported negative findings for the association among brain monoamine oxidase B (MAO-B) and suicidal behaviour. However those studies did not adequately control their main results for the influence of confounding variables such as age at death. We have evaluated the association of MAO-B density (assessed by [3H]Ro 19-6327 - lazabemide - binding) with type of death (suicide victims vs non-suicide controls) after controlling for age at death. Frontal cortex samples from 43 subjects (21 suicides, 22 controls) were assayed for MAO-B density at a single concentration of lazabemide (8 nM). A linear regression modelling approach comparing nested models resulted with both type of death (p<0.05) and age of death (p<0.01) as main explanatory variables for the variability of MAO-B density. Suicide victims had >30% more binding sites for lazabemide than controls. Contrary to previous reports, MAO-B density seems to increase in suicide victims.

Smoking cessation therapy with varenicline

Smoking cessation is the only available intervention proven to halt progression of chronic obstructive pulmonary disease (COPD). The authors discuss the current existing treatment modalities and the role of a newly approved agent, varenicline, in promotion of smoking cessation. Varenicline is a novel agent that is a centrally acting partial nicotinic acetylcholine receptor agonist. It has both agonistic and antagonistic properties that together are believed to account for reduction of craving and withdrawal as well as blocking the rewarding effects of smoking. Its targeted mechanism of action, better efficacy and tolerability makes varenicline a useful therapeutic option for smoking cessation. In this article, we discuss presently available options for smoking cessation and review the literature on efficacy of varenicline.

Drugs of abuse and the aging brain

Substance abuse among older adults has received little attention in the past, presumably because this population has traditionally accounted for only a small percentage of the drug abuse problem in the United States. The aging of the baby boomer generation (born 1946-1964), however, will soon swell the ranks of older adults and dramatically alter the demography of American society. Several observations suggest that this expansion will likely be accompanied by a precipitous increase in the abuse of drugs, including prescription medications and illicit substances, among older adults. While it is now evident that the brain changes continuously across life, how drugs of abuse interact with these age-related changes remains unclear. The dynamic nature of brain function, however, suggests that substance abuse during older age may augment the risks and require unique considerations for diagnosis and treatment. In addition to describing current and projected prevalence estimates of substance abuse among older adults, the present review discusses how aging affects brain systems involved in drug abuse, and explores the potential impact of drug abuse on the aging brain. Future directions for substance abuse research among older adults will also be considered.

Decreased dopamine transporter availability in male smokers -- a dual isotope SPECT study

INTRODUCTION

Although the mesolimbic dopaminergic system has been shown to play a role in reinforcing tobacco smoking, results of imaging studies that examine the relationship between tobacco smoking and the central dopamine system remain discrepant. To delineate the role of tobacco addiction in central pre- and post-synaptic dopaminergic activities, we analyzed the central D2-family receptors, the dopamine transporters (DAT), and degrees of dependence in male smokers.

METHODS

Eleven male smokers and 11 healthy non-smokers were recruited. The striatal dopamine D2/D3 receptor availability was approximated using SPECT and [123 I] IBZM while the DAT availability was approximated using SPECT and [99m Tc] TRODAT-1. All of the smokers completed the Fagerström Test for Nicotine Dependence (FTND) and other related questionnaires.

RESULTS

A decrease in DAT availability in the striatum of male smokers is noted (p<05). However, the striatal D2/D3 receptor availability in male smokers does not differ from that of non-smokers.

CONCLUSIONS

These findings suggest that cigarette smoking may alter central dopamine functions in males, particularly at the pre-synaptic sites.

Monoamine oxidase inhibition for tobacco pharmacotherapy

Tobacco addiction is the most significant preventable cause of morbidity and mortality in the Western world, with >430,000 deaths annually from tobacco-related diseases being reported in the United States. Although effective treatments are available for cessation of smoking (e.g., nicotine replacement therapies, sustained-release bupropion and varenicline), they do not work for all smokers. Therefore the development of more effective medications for treating tobacco dependence, based on novel mechanisms, is a high priority. This article reviews the links between smoking and monoamine oxidase (MAO) inhibition, which could lead to the development of novel pharmacotherapies to treat tobacco dependence.

Selegiline is a mechanism-based inactivator of CYP2A6 inhibiting nicotine metabolism in humans and mice

Selegiline (l-deprenyl) is in clinical treatment trials as a potential smoking cessation drug. We investigated the affect of selegiline and its metabolites on nicotine metabolism. In mice, selegiline was a potent inhibitor of nicotine metabolism in hepatic microsomes and cDNA-expressed CYP2A5; the selegiline metabolites desmethylselegiline, l-methamphetamine, and l-amphetamine, also inhibited nicotine metabolism. Pretreatment with selegiline and desmethylselegiline increased inhibition (IC(50)) in microsomes by 3.3- and 6.1-fold, respectively. In mice in vivo, selegiline increased AUC (90.7 +/- 5.8 versus 57.4 +/- 5.3 ng/h/ml, p < 0.05), decreased clearance (4.6 +/- 0.4 versus 7.3 +/- 0.3 ml/min, p < 0.05), and increased elimination half-life (12.5 +/- 6.3 versus 6.6 +/- 1.4 min, p < 0.05) of nicotine. In vitro, selegiline was a potent inhibitor of human nicotine metabolism in hepatic microsomes and cDNA-expressed CYP2A6; desmethylselegiline and l-amphetamine also inhibited nicotine metabolism. Selegiline preincubation increased inhibition in microsomes (3.7-fold) and CYP2A6 (14.8-fold); the K(i) for CYP2A6 was 4.2 muM. Selegiline dose- and time-dependently inhibited nicotine metabolism by CYP2A6 (K(i) = 15.6 +/- 2.7 muM; k(inact) = 0.34 +/- 0.04 min(-1)), and the inhibition was irreversible in the presence of NADPH, indicating that it is a mechanism-based inhibitor of CYP2A6. Thus, inhibition of mouse nicotine metabolism by selegiline was competitive in vitro and significantly increased plasma nicotine in vivo. In humans, where selegiline is both a competitive and mechanism-based inhibitor, it is likely to have even greater effects on in vivo nicotine metabolism. Our findings suggest that an additional potential mechanism of selegiline in smoking cessation is through inhibition of nicotine metabolism.

Treatment of tobacco dependence: integrating recent progress into practice

Tobacco use is one of the leading preventable causes of death in developed countries. Adoption of approaches that have demonstrated efficacy to improve the treatment of tobacco dependence are critical to reduce the health consequences of tobacco use. We summarize the latest epidemiologic data on tobacco use, the mechanisms that underlie tobacco dependence, and advances in pharmacotherapy and nonpharmacologic interventions available for the treatment of tobacco dependence. Specifically, we discuss the use of nicotine replacement therapy, bupropion and varenicline in primary care settings.

Smoking cessation: significance and implications for children

A number of people in the USA who are still current smokers remain a staggering figure. Although this number continues to decrease, there is still a considerable amount of second-hand smoke. More importantly and for the purpose of this review, the detrimental effects of passive smoke in children is significant. We will not review the specific health effects of passive smoke, but for pediatricians, in particular, it is important to place in perspective programs that are available to influence the parents of children to stop smoking. Indeed, approximately 25% of all children aged 3-11 live in a household with at least one smoker. Despite the increasing number of communities in the states that have instituted restrictions or complete bans on smoking in the workplace and in many public areas, the principal site of smoking remains the home.

Epidemiologic studies of environmental exposures in Parkinson's disease

Parkinson's disease (PD) is the most common cause of the parkinsonian syndromes and the most frequent neurodegenerative disease after Alzheimer's disease. Because of the ageing of Western populations, an increasing number of persons will be affected with PD in the future and neither curative treatments nor preventive measures have been identified. PD is considered as a multifactorial disease, resulting from the effect of environmental factors and genetic susceptibility. Increasing age and male sex appear to be associated with an increased risk of PD. In addition, recent epidemiological studies have identified environmental exposures that influence the risk of PD. This review provides an overview of the epidemiologic evidence for environmental etiologies in PD; we will focus on two environmental exposures that have been quite consistently associated with PD -- cigarette smoking and pesticide exposure -- and will summarize briefly the findings for other exposures. Understanding the mechanisms underlying these epidemiological associations is an essential step for the understanding of the etiology of this neurodegenerative condition and, ideally, to develop neuroprotective drugs.

Medications Development for the Treatment of Nicotine Dependence in Individuals with Schizophrenia

The development of medications for the treatment of nicotine dependence in patients with schizophrenia is a public health priority due to its high prevalence rates, devastating medical consequences, and difficulty to treat. It has been hypothesized that the high prevalence of nicotine dependence among patients with schizophrenia may be due to a shared neurobiological vulnerability. This shared vulnerability has been evidenced in reports showing that nicotine improves neuropsychological deficits associated with schizophrenia such as in the P50 evoked auditory potentials, spatial working memory, and attention. The common pathophysiologic pathways of smoking and schizophrenia may serve as the basis for the pharmacological evaluation of medications for the treatment of these concurrent disorders. Currently, little research of medications for the treatment of this comorbidity has been conducted. Studies have evaluated the efficacy of smoking cessation medications in patients with schizophrenia. These include the nicotine replacement therapy (patch, nasal spray) and sustained release bupropion. Others have evaluated the anti-smoking effect of medications (e.g., clozapine, haloperidol) used for the treatment of schizophrenia. In both cases, the results have not been conclusive. Newer smoking cessation approaches such as varenicline, selegiline, rimonabant, and nicotine vaccine, among others, have yet to be tested in this population. The purpose of this article is to review the results of the studies conducted to date and propose some potential pharmacotherapies based on the current knowledge of the pathophysiology of both disorders.

Identification and occurrence of beta-carboline alkaloids in raisins and inhibition of monoamine oxidase (MAO)

Monoamine oxidase (MAO) is a mitochondrial enzyme involved in the oxidative catabolism of neurotransmitters and xenobiotic amines, including vasopressor and neurotoxic amines, and a current target for antidepressant and neuroprotective drugs. Raisin extracts and homogenates exhibited reversible in vitro inhibition of MAO isozymes, particularly MAO-A, suggesting the presence of MAO-inhibiting substances. Chromatographic and spectrometric studies showed the occurrence of aromatic beta-carboline alkaloids in raisins, and norharman and harman were identified as the key contributors to MAO inhibition. On average, harman ranged from 6 to 644 ng/g and norharman from 2 to 120 ng/g. Several technological variables appeared to determine the presence of these compounds in raisins. Dark-brown raisins (i.e., sun-dried) contained much higher levels than golden raisins. Tetrahydro-beta-carboline-3-carboxylic acid compounds that are direct precursors of aromatic beta-carbolines were also identified in raisins and appeared in a higher amount, reaching up to 50 microg/g. beta-Carbolines were isolated from raisins and acted as good competitive inhibitors of MAO-A (harman) and MAO-B (norharman) isozymes. These results suggest that beta-carboline alkaloids and perhaps raisins containing a high level of beta-carbolines might exhibit potential activity as MAO inhibitors. The results also show that some raisins can be a source of dietary exposure to bioactive beta-carbolines.

Translational research in medication development for nicotine dependence

A major obstacle to the development of medications for nicotine dependence is the lack of animal and human laboratory models with sufficient predictive clinical validity to support the translation of knowledge from laboratory studies to clinical research. This Review describes the animal and human laboratory paradigms commonly used to investigate the pathophysiology of nicotine dependence, and proposes how their predictive validity might be determined and improved, thereby enhancing the development of new medications.

Effect of catechol O-methyltransferase val(158)met polymorphism on the p50 gating endophenotype in schizophrenia

BACKGROUND

Studies have implicated prefrontal dopamine in cortical information filtering. Deficit in stimulus filtering, an endophenotype of schizophrenia, can be demonstrated using the auditory P50 paired-click gating paradigm. The role of prefrontal dopamine on P50 gating was investigated, using catechol-O-methyltransferase (COMT) valine (val)(158)methionine (met) polymorphism as a predictor of prefrontal dopamine activity.

METHODS

Twenty-five comparison and 42 schizophrenia subjects underwent P50 gating measurement and COMT genotyping.

RESULTS

In the combined sample, COMT polymorphism accounted for a unique 10% of gating variance (p = .02), after variance due to diagnosis, smoking status, and antipsychotic use was removed. Valine homozygous individuals exhibited the greatest gating deficit.

CONCLUSIONS

Valine homozygous individuals are more likely to have gating deficits, supporting COMT as a genetic determinant of the P50 endophenotype, as well as a role for prefrontal dopamine in auditory filtering.

Involvement of alpha1-adrenergic receptors in tranylcypromine enhancement of nicotine self-administration in rat

RATIONALE

The mechanisms mediating tobacco addiction remain elusive. Nicotine, the psychoactive component in tobacco, is generally believed to be the main cause of reward and addiction. However, tobacco smoke contains thousands of constituents, some of which may interact with nicotine to enhance reward. It has previously been shown that monoamine oxidase (MAO) inhibition, known to result from smoking, can enhance nicotine self-administration. The aim of the present study was to evaluate the role of noradrenergic systems in mediating this enhancement of nicotine reward.

OBJECTIVE

The objective of this study was to test the hypothesis that MAO inhibitor pretreatment enhances nicotine self-administration by activation of noradrenergic pathways that regulate dopamine release in the nucleus accumbens (NAc).

METHODS

The effect of prazosin (0.0625-0.5 mg/kg, i.p.), a specific alpha1-adrenergic receptor antagonist, was examined on male rats pretreated with tranylcypromine (3 mg/kg), an irreversible inhibitor of MAO A and B. Acquisition of nicotine (10 mug kg(-1) inj(-1), i.v.) self-administration behavior was examined over a 5-day period. Nicotine (60 mug kg(-1) inj(-1), i.v.)-induced increase in NAc extracellular dopamine levels was examined by in vivo microdialysis in non-self-administering animals.

RESULTS

We have shown that (1) tranylcypromine enhances nicotine self-administration, (2) prazosin pretreatment blocks both the acquisition and the expression of nicotine self-administration, and (3) prazosin pretreatment diminishes nicotine-induced dopamine release in the NAc.

CONCLUSION

These data indicate that the stimulation of alpha1-adrenergic receptors is critical for tranylcypromine enhancement of nicotine reward and suggest a critical interplay between the noradrenergic and dopaminergic systems in tobacco addiction.

Evidence that brain MAO A activity does not correspond to MAO A genotype in healthy male subjects

BACKGROUND

A functional polymorphism in the promoter region of the monoamine oxidase A (MAO A) gene has two common alleles that are referred to as the high and low MAO A genotypes. We report the first in vivo human study to determine whether there is an association between MAO A genotype and brain MAO A activity in healthy male subjects.

METHODS

Brain MAO A activity was measured with positron emission tomography and [(11)C]clorgyline in 38 healthy adult male nonsmokers genotyped for MAO A polymorphism.

RESULTS

There was no significant difference in brain MAO A activity between the high (n = 26) and low (n = 12) MAO A genotypes.

CONCLUSIONS

The lack of an association between the high and low MAO A genotype and brain MAO A activity suggests that this polymorphism by itself does not contribute to differences in brain MAO A activity in healthy adult male subjects.

The influence of genetics on nicotine dependence and the role of pharmacogenetics in treating the smoking habit

Despite the considerable efforts made in the fight against smoking in the last decades, there are still substantial numbers of people who, in full knowledge of the health hazards, begin smoking or continue smoking. Recent studies have focused on the genetic bases of the nicotine addiction. Various genetic polymorphisms have been associated with smoking. However, environmental factors have also been shown to play a role. In this review, we present some of the principal data collected in genetic studies of smoking behavior. The results obtained through this line of research will eventually aid clinicians in individualizing the type, dosage and duration of treatment for patients with nicotine dependence in accordance with the genotype of each smoker, thereby maximizing the efficacy of the proposed treatment regimen.

Bupropion inhibits the cellular effects of nicotine in the ventral tegmental area

Each year, tobacco use causes over 4 million deaths worldwide and billions of dollars are spent on treatment for tobacco-related illness. Bupropion, an atypical antidepressant, improves the rates of successful smoking cessation, however, the mechanisms by which bupropion reduces cigarette smoking and depression are unknown. Here we show that clinical concentrations of bupropion inhibit nicotine's stimulatory effects on brain reward areas. Many drugs of abuse, including nicotine, stimulate dopamine (DA) release in the mesoaccumbens reward system. Nicotinic acetylcholine receptors in the ventral tegmental area (VTA) mediate nicotine's stimulation of DA release, as well as its rewarding effects. Nicotinic receptors are expressed by excitatory and inhibitory neurons that control DA neuron excitability, and by the DA neurons themselves. Bupropion is a broad-spectrum non-competitive nicotinic receptor antagonist. Here we report that pre-treatment of brain slices with a clinically relevant concentration of bupropion dramatically reduces the effects of nicotine on DA neuron excitability. Nicotinic receptors on VTA DA neurons and their synaptic inputs are inhibited by 75 - 95% after bupropion treatment. We also find that bupropion alone reduces GABAergic transmission to DA neurons, thereby diminishing tonic inhibition of these neurons. This increases DA neuron excitability during bupropion treatment in the absence of nicotine, and may contribute to bupropion's antidepressant actions.

Tobacco smoking within psychiatric inpatient settings: biopsychosocial perspective

Tobacco smoking remains a neglected issue within general psychiatry despite high rates of associated morbidity and mortality. While there has been a coordinated community campaign to reduce tobacco smoking within the general population, mental health facilities have been reluctant to adopt such regulatory controls, and rarely target smoking prevention or treatment. This paper summarizes and discusses evidence relating to the clinical impact of tobacco smoking within inpatient psychiatric settings. A selective review of psychiatric and psychological research on smoking within inpatient settings was conducted, with a particular focus on the influence of smoking on the physical and mental health, pharmacotherapy, and social interactions of patients during their inpatient stay. Patients frequently alter their smoking habits during inpatient treatment, which can affect both their presentation and pharmacotherapeutic management. Smoking also appears to play a central role in social interactions on the ward, with staff frequently using cigarettes to reinforce certain behaviours. Despite current guidelines, mental health professionals rarely address nicotine use among their patients. Nevertheless, programmes that assist patients to quit during an inpatient stay have been shown to be both efficacious and cost-effective. Strategies that address staff concerns and assist in the implementation of effective smoking bans on psychiatric units are also available. Cessation should be a key component of inpatient treatment planning because this setting provides a safe and timely opportunity to help patients quit. A flowchart of interventions that could be incorporated within standard inpatient settings is proposed.

Attentional control and brain metabolite levels in methamphetamine abusers

BACKGROUND

Methamphetamine abuse is associated with neurotoxicity to frontostriatal brain regions with concomitant deleterious effects on cognitive processes.

METHODS

By using a computerized measure of selective attention and single-voxel proton magnetic resonance spectroscopy, we examined the relationship between attentional control and brain metabolite levels in the anterior cingulate cortex (ACC) and primary visual cortex (PVC) in 36 currently abstinent methamphetamine abusers and 16 non-substance-using controls.

RESULTS

The methamphetamine abusers exhibited reduced attentional control (i.e., increased Stroop interference) compared with the controls (p = .04). Bonferroni-adjusted comparisons revealed that ACC levels of N-acetyl aspartate (NAA)-creatine and phosphocreatine (Cr) were lower and that levels of choline (Cho)-NAA were higher in the methamphetamine abusers compared with the controls, at the adjusted p value of .0125. Levels of NAA-Cr, but not of Cho-NAA, within the ACC correlated with measures of attentional control in the methamphetamine abusers (r = -.41; p = .01) but not in controls (r = .22; p = .42). No significant correlations were observed in the PVC (methamphetamine abusers, r = .19; p = .28, controls, r = .38; p = .15).

CONCLUSIONS

Changes in neurochemicals within frontostriatal brain regions including ACC may contribute to deficits in attentional control among chronic methamphetamine abusers.

Nicotine neuroprotection against nigrostriatal damage: importance of the animal model

Parkinson's disease is a neurodegenerative movement disorder that is characterized by a loss of nigrostriatal dopamine-containing neurons. Unexpectedly, there is a reduced incidence of Parkinson's disease in tobacco users. This finding is important because the identification of the component(s) responsible for this effect could lead to therapeutic strategies to slow down or halt the progression of Parkinson's disease. Results from cell culture models consistently show that nicotine protects against neurotoxicity. However, data from animal models of nigrostriatal damage are conflicting, thus raising questions about a neuroprotective role of nicotine. Accumulating evidence indicates that discrepancies are observed primarily in mouse models of the disease. By contrast, reproducible protection occurs in rat models and in a nonhuman primate parkinsonian model that closely resembles the human disease. These findings highlight the need to use the appropriate animal model and treatment conditions when testing putative neuroprotective agents.

Long-term upregulation of protein kinase A and adenylate cyclase levels in human smokers

Repeated injections of cocaine and morphine in laboratory rats cause a variety of molecular neuroadaptations in the cAMP signaling pathway in nucleus accumbens and ventral tegmental area. Here we report similar neuroadaptations in postmortem tissue from the brains of human smokers and former smokers. Activity levels of two major components of cAMP signaling, cAMP-dependent protein kinase A (PKA) and adenylate cyclase, were abnormally elevated in nucleus accumbens of smokers and in ventral midbrain dopaminergic region of both smokers and former smokers. Protein levels of the catalytic subunit of PKA were correspondingly higher in the ventral midbrain dopaminergic region of both smokers and former smokers. Protein levels of other candidate neuroadaptations, including glutamate receptor subunits, tyrosine hydroxylase, and other protein kinases, were within normal range. These findings extend our understanding of addiction-related neuroadaptations of cAMP signaling to tobacco smoking in human subjects and suggest that smoking-induced brain neuroadaptations can persist for significant periods in former smokers.

Mapping the amphetamine-evoked changes in [11C]raclopride binding in living rat using small animal PET: Modulation by MAO-inhibition

The performance of small animal PET for neuroreceptor studies in a psychopharmacological challenge paradigm is not yet well-described. Therefore, we used microPET and [(11)C]raclopride to map the availability of dopamine D(2/3) receptors in brain of anesthetized rats, first in a baseline condition, and again after challenge with saline or d-amphetamine. Parametric maps of the specific binding (binding potential, pB) were calculated using a reference tissue input from cerebellum, and spatially normalized to a digitized stereotaxic coordinate system for rat brain. In volumes of interest (VOIs), the mean baseline pB (n=6) was 2.05 in dorsal striatum (caudate-putamen), and 1.34 in ventral striatum (nucleus accumbens), and did not significantly differ upon retest 2 h later. The availability of [(11)C]raclopride binding sites at baseline was 8% higher in the right striatum. Challenge with amphetamine sulfate (1 mg/kg, i.v., n=4) decreased pB by 19% in both ventral and dorsal striatum. We have earlier predicted that blockade of monoamine oxidase (MAO) should potentiate the amphetamine-evoked dopamine release, thus enhancing the displacement of [(11)C]raclopride binding in vivo. However, pretreatment of rats with pargyline hydrochloride (4 mg/kg, n=4; 20 mg/kg, n=4) 1 day prior to PET did not potentiate the amphetamine-evoked reduction in dopamine receptor availability within the extended striatum. We conclude that small animal PET can be used to investigate stimulant-induced dopamine release, but that the spatial resolution is insufficient to detect differences between relative changes in dorsal vs. ventral divisions of the rat striatum. Furthermore, the present results do not reveal potentiation of the amphetamine-evoked release of dopamine in rats with MAO inhibition.

High reinforcing efficacy of nicotine in non-human primates

Although tobacco appears highly addictive in humans, there has been persistent controversy about the ability of its psychoactive ingredient nicotine to induce self-administration behavior in laboratory animals, bringing into question nicotine's role in reinforcing tobacco smoking. Because of ethical difficulties in inducing nicotine dependence in naïve human subjects, we explored reinforcing effects of nicotine in experimentally-naive non-human primates given access to nicotine for periods of time up to two years. Five squirrel monkeys with no experimental history were allowed to intravenously self-administer nicotine by pressing one of two levers. The number of presses on the active lever needed to obtain each injection was fixed (fixed-ratio schedule) or increased progressively with successive injections during the session (progressive-ratio schedule), allowing evaluation of both reinforcing and motivational effects of nicotine under conditions of increasing response cost. Over time, a progressive shift toward high rates of responding on the active lever, but not the inactive lever, developed. The monkeys' behavior was clearly directed toward nicotine self-administration, rather than presentation of environmental stimuli associated with nicotine injection. Both schedules of reinforcement revealed a high motivation to self-administer nicotine, with monkeys continuing to press the lever when up to 600 lever-presses were needed for each injection of nicotine. Thus, nicotine, by itself, in the absence of behavioral or drug-exposure history, is a robust and highly effective reinforcer of drug-taking behavior in a non-human primate model predictive of human behavior. This supports the use of nicotinic ligands for the treatment of smokers, and this novel preclinical model offers opportunities to test future medications for the treatment of nicotine dependence.

Tranylcypromine enhancement of nicotine self-administration

Tobacco use has one of the highest rates of addiction of any abused drug. Paradoxically, in animal models, nicotine appears to be a weak reinforcer. We report here that the inhibition of monoamine oxidase (MAO), a major effect of tobacco smoke, increases the reinforcing effect of nicotine. Rats (aged postnatal day 27 and 90) were tested for self-administration, without prior response training, in five daily 3-h sessions. Whereas control rats did not self-administer nicotine, low doses of nicotine (2.5 to 21 microg/kg/injection) were avidly self-administered following a pretreatment with tranylcypromine (3 mg/kg), an irreversible and non-selective MAO inhibitor. Tranylcypromine-enhanced nicotine (10 microg/kg/injection, i.v.) self-administration was reduced by systemic injection of a D1-dopaminergic receptor antagonist, SCH23390 (0.02 mg/kg). Moreover, an increase in extracellular dopamine in the nucleus accumbens was detected, using microdialysis, following nicotine (60 microg/kg) injection in tranylcypromine pre-treated rats. Depending on the time of tranylcypromine pretreatment (20 or 1 h), MAO activity was decreased by 72% and 99% and nicotine intake at day 5 was increased by 619 and 997%, respectively. Taken together, these results indicate that in a stringent self-administration acquisition test, MAO inhibition increases the rewarding effect of low doses of nicotine, possibly via a dopamine-dependent mechanism.

Inhibitory Effects of Neurotransmitters and Steroids on Human CYP2A6

Human CYP2A6 catalyzes the metabolism of nicotine, cotinine, and coumarin as well as some pharmaceutical drugs. CYP2A6 is highly expressed in liver and, also, in brain and steroid-related tissues. In this study, we investigated the inhibitory effects of neurotransmitters and steroid hormones on CYP2A6 activity. We found that coumarin 7-hydroxylation and cotinine 3'-hydroxylation by recombinant CYP2A6 expressed in baculovirus-infected insect cells were competitively inhibited by tryptamine (both K(i) = 0.2 microM), serotonin (K(i) = 252 microM and 167 microM), dopamine (K(i) = 49 microM and 22 microM), and histamine (K(i) = 428 microM and 359 microM). Cotinine formation from nicotine was inhibited by tryptamine (K(i) = 0.7 microM, competitive), serotonin (K(i) = 272 microM, noncompetitive), dopamine, noradrenaline, and adrenaline (K(i) = 11 microM, 54 microM, and 81 microM, uncompetitive). Estrogens (K(i) = 0.6-3.8 microM), androgens (K(i) = 60-149 microM), and corticosterone (K(i) = 36 microM) also inhibited cotinine formation, but coumarin 7-hydroxylation and cotinine 3'-hydroxylation did not. Nicotine-Delta(5'(1'))-iminium ion formation from nicotine was not affected by these steroid hormones, indicating that the inhibition of cotinine formation was due to the inhibitory effects on aldehyde oxidase. The nicotine-Delta(5'(1'))-iminium ion formation was competitively inhibited by tryptamine (K(i) = 0.3 microM), serotonin (K(i) = 316 microM), dopamine (K(i) = 66 microM), and histamine (K(i) = 209 microM). Thus, we found that some neurotransmitters inhibit CYP2A6 activity, being related with inter- and intraindividual differences in CYP2A6-dependent metabolism. The inhibitory effects of steroid hormones on aldehyde oxidase may also contribute to interindividual differences in nicotine metabolism.

Epidemiology of Parkinson's disease

This chapter discusses the epidemiology of Parkinson's disease (PD). Classically, PD refers to progressive parkinsonism caused by loss of pigmented aminergic brainstem neurons without an identifiable cause, while parkinsonism refers simply to the syndrome of bradykinesia, resting tremor, rigidity and postural reflex impairment. Over nearly two centuries, Parkinson's clinical description has provided the framework for clinical investigations, including epidemiologic ones. Descriptions of PD were limited to selected clinical settings until the middle of the 20th century. Since then, epidemiologic approaches have been used not only to investigate the population distribution of PD, but also as a way to glean clues as to the cause of this “idiopathic” disorder. Because PD is relatively infrequent, a large base population must be surveyed to identify sufficient numbers of cases for a study. In some instances, PD cases can be identified through health service rosters within defined geographic areas or in enumerated populations. In others, cases of PD are sought independently of the health care system, such as through door-to-door surveys. While the latter approach is theoretically least likely to exclude cases, the time and cost involved are also greatest using this approach.

Monoamine oxidase and tobacco dependence

Tobacco smoking is a leading cause of preventable death around the world, and there are major public health and research efforts in many countries aimed at reducing its usage. However, the molecular mechanisms underlying tobacco dependence are still not completely understood. Nicotine's action on nicotinic acetylcholine receptors, and the downstream release of dopamine, is believed to be the major pathway underlying tobacco dependence. However there is mounting evidence indicating that non-nicotinic components of tobacco smoke also play a role by inhibiting monoamine oxidase (MAO) and subsequently altering neurotransmitter levels. This article provides a review of the current knowledge of the association between MAO and tobacco dependence and suggests that further research into this topic is likely to lead to more effective pharmacotherapies for smoking cessation.

Differential nicotinic regulation of the nigrostriatal and mesolimbic dopaminergic pathways: implications for drug development

Neuronal nicotinic acetylcholine receptors (nAChRs) modulate dopaminergic function. Discovery of their multiplicity has lead to the search for subtype-selective nAChR agonists that might be therapeutically beneficial in diseases linked to brain dopaminergic pathways. The regulation and responses of the nigrostriatal and mesolimbic dopaminergic pathways are often similar, but some differences do exist. The cerebral distribution and characteristics of various nAChR subtypes differ between nigrostriatal and mesolimbic dopaminergic pathways. Comparison of nicotine and epibatidine, two nAChR agonists whose relative affinities for various nAChR subtypes differ, revealed differences in the nAChR-mediated regulation of dopaminergic activation between these dopamine systems. Nicotine preferentially stimulates the mesolimbic pathway, whereas epibatidine's stimulatory effect falls on the nigrostriatal pathway. Thus, it may be possible to stimulate the nigrostriatal pathway with selective nAChR agonists that do not significantly affect the mesolimbic pathway, and thus lack addictive properties. Furthermore, dopamine uptake inhibition revealed a novel inhibitory effect of epibatidine on accumbal dopamine release, which could form a basis for novel antipsychotics that could alleviate the elevated accumbal dopaminergic tone found in schizophrenia during the active psychotic state. Different regulation of nigrostriatal and mesolimbic dopaminergic pathways by nAChRs could be an important basis for developing novel drugs for treatment of Parkinson's disease and schizophrenia.

Monoamine oxidase A rather than monoamine oxidase B inhibition increases nicotine reinforcement in rats

Although nicotine is considered to be responsible for the addictive properties of tobacco, growing evidence underlines the importance of non-nicotine components in smoking reinforcement. It has been shown that tobacco smoke contains monoamine oxidase (MAO) A and B inhibitors and decreases MAO-A and MAO-B activity in smokers. Here, we investigated the effects of clorgyline hydrochloride (irreversible MAO-A inhibitor; 2 mg/kg/day), selegiline (irreversible MAO-B inhibitor; 4 mg/kg) and the beta-carboline norharmane hydrochloride (reversible MAO-B inhibitor; 5 mg/kg/day) treatments on nicotine self-administration (30 microg/kg/infusion, free base) in rats. Independent of the responsiveness to novelty and locomotor activity stimulation, only clorgyline hydrochloride treatment increased the intake of nicotine in a fixed-ratio schedule (FR5) of reinforcement. When a progressive-ratio schedule was implemented, both clorgyline hydrochloride and norharmane hydrochloride treatments potentiated the reinforcing effects of nicotine, whereas selegiline had no effect. Taken together, these results indicate that MAO-A inhibition interacts with nicotine to enhance its rewarding effects in rats and suggest that other compounds present in tobacco, such as beta-carboline, may also play an important role in sustaining smoking behavior in humans.

Transdermal nicotine attenuates depression symptoms in nonsmokers: a double-blind, placebo-controlled trial

RATIONALE

Despite established links between nicotine dependence and depression, little research has examined the effects of nicotine on depression symptoms.

OBJECTIVE

This study evaluated the acute and chronic effects of transdermal nicotine in nonsmokers with baseline depression symptoms during a 4-week, double-blind, placebo-controlled trial.

METHODS

Nonsmokers with scores >or=10 on the Center for Epidemiological Studies Depression scale (CES-D) were recruited from the community. Mood and cognitive performance were measured at baseline (day 0) and at 1, 8, 21, and 28 days. Participants were randomly assigned to wear a placebo or nicotine patch for 4 weeks (3.5 mg/day during weeks 1 and 4; 7 mg/day during weeks 2 and 3). The final sample consisted of 11 nonsmokers with a mean baseline CES-D score of 27.36 (SD=10.53).

RESULTS

Salivary nicotine levels indicated the majority of participants were compliant with treatment. Acute nicotine did not alter mood. After adjusting for baseline values, chronic nicotine resulted in a significant decline in CES-D scores at day 8 (3.5 mg/day), but returned to placebo levels by the last visit. This return to baseline levels was coincident with a decrease in nicotine administration from 7 to 3.5 mg/day. A similar trend for improved response inhibition as measured by the Conners Continuous Performance Task was also observed. Reported side effects were infrequent and minimal.

CONCLUSION

These findings suggest a role for nicotinic receptor systems in the pathophysiology of depression and that nicotinic compounds should be evaluated for treating depression symptoms.

Contribution of monoamine oxidase (MAO) inhibition to tobacco and alcohol addiction

Whole-body PET-scan studies in brains of tobacco smokers have shown a decrease in monoamine oxidase (MAO) activity, which reverts to control level when they quit smoking. The observed decrease in MAO activity in smokers is presumably due to their exposure to tobacco constituents that possess MAO-inhibiting properties. The inhibition of MAO activity seems, however, not to be a unique feature of tobacco smoking as subjects with Type II alcoholism have been reported to show a similar decrease in MAO activity that reverses when they cease to use alcohol. The present review summarizes the data on MAO-inhibiting tobacco constituents and explains that the decrease in MAO activity observed in alcoholics is probably due to concomitant tobacco use. It is concluded that the inhibition of MAO by constituents contained in tobacco and tobacco smoke, enhances the addiction induced by tobacco smoking.

Current and emerging pharmacotherapies for treating tobacco dependence

Tobacco dependence remains the leading cause of death and disease in the US and a major cause of mortality around the world, yet 1 out of 5 American adults smoke and 1.3 billion adults smoke worldwide. Nicotine replacement therapies (NRTs), bupropion and varenicline, are approved by the US FDA as first-line treatments for nicotine dependence. Clonidine and nortriptyline are recommended as second-line treatments by the Agency for Healthcare Research and Quality. Although recent data suggest that varenicline is superior to bupropion for treating nicotine dependence, a majority of smokers fail to maintain long-term abstinence from smoking using FDA-approved pharmacotherapies. Thus, continued investigation of novel medications for nicotine dependence remains a critical priority. Guided by research on multiple neurobiological mechanisms of nicotine dependence, several novel medications that mimic and/or attenuate nicotine's rewarding effects, or reduce nicotine withdrawal, are under investigation. Although existing data are limited or conflicting, there is some evidence for the efficacy of selegiline, fluoxetine, naltrexone and mecamylamine in certain subgroups of smokers. New research directions, such as fast-acting NRTs, the tailored use of NRTs for subtypes of smokers, and pharmacogenetics, hold promise for new treatment approaches and, ultimately, for reducing rates of tobacco use in the US and worldwide.

Chronic oral nicotine treatment protects against striatal degeneration in MPTP-treated primates

The present studies were done to investigate the effect of long-term nicotine treatment against nigrostriatal damage in non-human primates. Monkeys were administered nicotine in drinking water for 6 months to provide chronic but intermittent delivery as with smoking. Plasma nicotine levels ranged from 10 to 15 ng/mL, which were within the range in cigarette smokers. Animals were then lesioned with low doses of the dopaminergic neurotoxin MPTP for several months while nicotine was continued. The results showed that levels of striatal tyrosine hydroxylase, dopamine transporter, vesicular monoamine transporter, dopamine and nicotinic receptors were greater in nicotine-treated MPTP-lesioned primates than in lesioned animals not receiving nicotine. Nicotine had no effect in unlesioned animals. Monoamine oxidase activity was similar in unlesioned and lesioned animals treated with or without nicotine, suggesting that nicotine did not exert its effects through changes in MPTP or dopamine metabolism. MPTP-induced cell loss in the substantia nigra was unaffected by nicotine treatment, indicating that nicotine acts at the striatal level to restore/maintain dopaminergic function. These data further support the possibility that nicotine contributes to the lower incidence of Parkinson's disease in smokers.

Monoamine oxidase inhibitors allow locomotor and rewarding responses to nicotine

Although nicotine is generally considered to be the main compound responsible for the addictive properties of tobacco, experimental data indicate that nicotine does not exhibit all the characteristics of other abused substances, such as psychostimulants and opiates. For example, nicotine is only a weak locomotor enhancer in rats and generally fails to induce a locomotor response in mice. This observation contradicts the general consensus that all drugs of abuse release dopamine in the nucleus accumbens, a subcortical structure, and thus increase locomotor activity in rodents. Because tobacco smoke contains monoamine oxidase inhibitors (MAOIs) and decreases MAO activity in smokers, we have combined MAOIs with nicotine to determine whether it is possible to obtain a locomotor response to nicotine in C57Bl6 mice. Among 15 individual or combined MAOIs, including harmane, norharmane, moclobemide, selegiline, pargyline, clorgyline, tranylcypromine and phenelzine, only irreversible inhibitors of both MAO-A and -B (tranylcypromine, phenelzine, and clorgyline+selegiline) allowed a locomotor response to nicotine. The locomotor stimulant interaction of tranylcypromine and nicotine was absent in beta2-nicotinic acetylcholine receptor subunit knockout mice. Finally, it was found that, whereas naïve rats did not readily self-administer nicotine (10 microg/kg/injection), a robust self-administration of nicotine occurred when animals were pretreated with tranylcypromine (3 mg/kg). Our data suggest that MAOIs contained in tobacco and tobacco smoke act in synergy with nicotine to enhance its rewarding effects.

Functional brain imaging of tobacco use and dependence

While most cigarette smokers endorse a desire to quit smoking, only about 14% to 49% will achieve abstinence after 6 months or more of treatment. A greater understanding of the effects of smoking on brain function may (in conjunction with other lines of research) result in improved pharmacological (and behavioral) interventions. Many research groups have examined the effects of acute and chronic nicotine/cigarette exposure on brain activity using functional imaging; the purpose of this paper is to synthesize findings from such studies and present a coherent model of brain function in smokers. Responses to acute administration of nicotine/smoking include: a reduction in global brain activity; activation of the prefrontal cortex, thalamus, and visual system; activation of the thalamus and visual cortex during visual cognitive tasks; and increased dopamine (DA) concentration in the ventral striatum/nucleus accumbens. Responses to chronic nicotine/cigarette exposure include decreased monoamine oxidase (MAO) A and B activity in the basal ganglia and a reduction in alpha4beta2 nicotinic acetylcholine receptor (nAChR) availability in the thalamus and putamen. Taken together, these findings indicate that smoking enhances neurotransmission through cortico-basal ganglia-thalamic circuits either by direct stimulation of nAChRs, indirect stimulation via DA release or MAO inhibition, or a combination of these factors. Activation of this circuitry may be responsible for the effects of smoking seen in tobacco dependent subjects, such as improvements in attentional performance, mood, anxiety, and irritability.

The role of amine oxidases in xenobiotic metabolism

The amine oxidases of mammalian tissues are a heterogeneous family of enzymes that metabolise various monoamines, diamines and polyamines produced endogenously, or being absorbed as dietary or xenobiotic substances. The heterogeneous class of amine oxidases can be divided on an arbitrary basis of the chemical nature of their cofactors into two types. Monoamine oxidase (MAO) and an intracellular form of polyamine oxidase (PAO) contain flavin adenine dinucleotide (FAD) as their cofactor, whereas a second group of amine oxidases without FAD contain a cofactor possessing one or more carbonyl groups, making them sensitive to inhibition by carbonyl reagents such as semicarbazide; this group includes semicarbazide-sensitive amine oxidase (SSAO) and the connective tissue enzyme, lysyl oxidase. This article focuses on the general aspects of MAO's contribution to the metabolism of foreign toxic substances including toxins and illegal drugs. Another main objective of this review is to discuss the properties of PAO and SSAO and their involvement in the metabolism of xenobiotics.

Associations between platelet monoamine oxidase-B activity and acquired colour vision loss in a fish-eating population

Platelet monoamine oxidase-B (MAO-B) has been considered a surrogate biochemical marker of neurotoxicity, as it may reflect changes in the monoaminergic system in the brain. Colour vision discrimination, in part a dopamine dependent process, has been used to identify early neurological effects of some environmental and industrial neurotoxicants. The objective of this cross-sectional study was to explore the relationship between platelet MAO-B activity and acquired colour discrimination capacity in fish-consumers from the St. Lawrence River region of Canada. Assessment of acquired dyschromatopsia was determined using the Lanthony D-15 desaturated panel test. Participants classified with dyschromatopsia (n=81) had significantly lower MAO-B activity when compared to those with normal colour vision (n=32) (26.5+/-9.6 versus 31.0+/-9.9 nmol/min/20 microg, P=0.030)). Similarly, Bowman's Colour Confusion Index (CCI) was inversely correlated with MAO-B activity when the vision test was performed with the worst eye only (r=-0.245, P=0.009), the best eye only (r=-0.188, P=0.048) and with both eyes together (r=-0.309, P=0.001). Associations remained significant after adjustment for age and gender when both eyes (P=0.003) and the worst eye (P=0.045) were tested. Adjustment for heavy smoking weakened the association between MAO-B and CCI in the worst eye (P=0.140), but did not alter this association for both eyes (P=0.006). Adjustment for blood-mercury concentrations did not change the association. This study suggests a relationship between reduced MAO-B activity and acquired colour vision loss and both are associated with tobacco smoking. Therefore, results show that platelet MAO-B may be used as a surrogate biochemical marker of acquired colour vision loss.

Return to smoking following a smoke-free psychiatric hospitalization

This study examined the smoking behaviors and motivations of 100 patients hospitalized in a smoke-free psychiatry unit. The sample averaged nineteen cigarettes per day and had a history of repeated failed quit attempts, yet 65% expressed interest in quitting. During hospitalization, nicotine replacement was provided to 70% of smokers to manage nicotine withdrawal. Provider counseling for smoking cessation, however, was rare, and all patients returned to smoking within five weeks of hospital discharge. The inpatient setting provides a potential site for initiating tobacco dependence treatment; however to maintain abstinence following hospital discharge, greater support is needed.

Isolation and characterization of a monoamine oxidase B selective inhibitor from tobacco smoke

It is well established that tobacco smokers have reduced levels of monoamine oxidase activities both in the brain and peripheral organs. Furthermore, extensive evidence suggests that smokers are less prone to develop Parkinson's disease. These facts, plus the observation that inhibition of monoamine oxidase B protects against the parkinsonian inducing effects of the nigrostriatal neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, have prompted studies to identify monoamine oxidase inhibitors in the tobacco plant and tobacco cigarette smoke. Our previous efforts on cured tobacco leaf extracts have led to the characterization of 2,3,6-trimethyl-1,4-naphthoquinone, a non-selective monoamine oxidase inhibitor, and farnesylacetone, a selective monoamine oxidase B inhibitor. We now have extended these studies to tobacco smoke constituents. Fractionation of the smoke extracts has confirmed and extended the qualitative results of an earlier report [J. Korean Soc. Tob. Sci.1997, 19, 136] demonstrating the inhibitory activity of the terpene trans,trans-farnesol on rat brain MAO-B. In the present study, K(i) values for the inhibition of human, baboon, monkey, dog, rat, and mouse liver MAO-B have been determined. Noteworthy is the absence of inhibitory effects on human placental MAO-A and beef liver MAO-B. A limited structure-activity relationship study of analogs of trans,trans-farnesol is reported. Although the health hazards associated with the use of tobacco products preclude any therapeutic opportunities linked to smoking, these results suggest the possibility of identifying novel structures of compounds that could lead to the development of neuroprotective agents.

Relationship between platelet monoamine oxidase-B (MAO-B) activity and mercury exposure in fish consumers from the Lake St. Pierre region of Que., Canada

Mercury (Hg) is a widespread neurotoxic compound that bio-accumulates in fish and marine mammals. Monoamine oxidase (MAO; EC 1.4.3.4) regulates biogenic amine concentration in the brain and peripheral tissue and has been shown to be a molecular target of Hg compounds in animal models. Blood platelet monoamine oxidase-B (MAO-B) activity may reflect MAO function in the central nervous tissue. Therefore, the objective of this study was to evaluate the relationship between platelet MAO-B and Hg exposure in fish-eating adults (n=127) living along the St. Lawrence River (Lake St. Pierre, Que., Canada). Hg concentrations were determined in blood and hair samples. A significant negative association was observed between platelet MAO-B activity and blood-Hg (r=-0.193, p=0.029) but not with hair-Hg levels (r=-0.125, p=0.169). Multiple linear regression analysis demonstrated that blood-Hg (beta=-4.6, p=0.011) and heavy smoking (beta=-8.5, p=0.001) were associated with reduced platelet MAO activity in the total population. In addition, this reduction in MAO-B activity appeared to be associated with blood-Hg concentrations above 3.4 microg/L (75th percentile). Possible gender related differences were also observed and are discussed. Our results suggest that MAO-B activity in blood platelets may be a useful tool to assess biochemical effects of Hg exposure in human populations. These changes in platelet MAO-B may reflect enzymatic changes in nervous tissue and should be further investigated as a surrogate marker of neurotoxicity.

P50 sensory gating: Impact of high vs. low schizotypal personality and smoking status

Sensory gating deficits are seen in individuals with schizophrenia and schizotypal disorders, yet smoking influence, regional or lateral difference effects are rarely assessed. We examined sensory gating in smokers and non-smokers within university-level high and low schizotypal personality (HiS and LoS) groups using [Raine, A., 1991. The Schizotypal Personality Questionnaire (SPQ): A measure of schizotypal personality based on DSM-III-R criteria. Schizophr. Bull. 17, 555-564] Schizotypal Personality Questionnaire. Among 39 (18 men; 19 smokers) right-handed undergraduates, a paired-tone paradigm (40 pairs; 10 s ISI; 70 dB, 1000 Hz) was presented in two conditions (smokers while abstaining and after smoking). Sensory gating [S2(P50-N40)/S1(P50-N40)] was assessed at frontal, fronto-central, central, centro-parietal, and parietal midline and lateralized sites. Sensory gating was better at (1) midline than left/right hemispheric sites, and (2) fronto-central and central midline sites. At fronto-central/central lateral sites, (1) among non-smokers, better sensory gating occurred in LoS than HiS, (2) among smokers, better sensory gating occurred in HiS than LoS, and (3) among LoSs, smokers showed less sensory gating than non-smokers. No acute smoking effects emerged. Unlike schizophrenia studies, smoking did not impact sensory gating. Differences among smokers and non-smokers in LoS and HiS groups reinforce need to evaluate both smoking and schizotypal characteristics, as well as midline and lateral sites in anterior to posterior regions, in sensory gating studies.

Translational neuroimaging: positron emission tomography studies of monoamine oxidase

Positron emission tomography (PET) using radiotracers with high molecular specificity is an important scientific tool in studies of monoamine oxidase (MAO), an important enzyme in the regulation of the neurotransmitters dopamine, norepinephrine, and serotonin as well as the dietary amine, tyramine. MAO occurs in two different subtypes, MAO A and MAO B, which have different substrate and inhibitor specificity and which are different gene products. The highly variable subtype distribution with different species makes human studies of special value. MAO A and B can be imaged in the human brain and certain peripheral organs using PET and carbon-11 (half-life 20.4 minutes) labeled mechanism-based irreversible inhibitors, clorgyline and L -deprenyl, respectively. In this article we introduce MAO and describe the development of these radiotracers and their translation from preclinical studies to the investigation of variables affecting MAO in the human brain and peripheral organs.

Monoamine oxidase inhibition dramatically increases the motivation to self-administer nicotine in rats

Nicotine is the major neuroactive compound of tobacco, which has, by itself, weak reinforcing properties. It is known that levels of the enzymes monoamine oxidase A (MAO-A) and MAO-B are reduced in the platelets and brains of smokers and that substances, other than nicotine, present in tobacco smoke have MAO-inhibitory activities. Here, we report that inhibition of MAO dramatically and specifically increases the motivation to self-administer nicotine in rats. These effects were more prominent in rats selected for high responsiveness to novelty than in rats with low responsiveness to novelty. The results suggest that the inhibition of MAO activity by compounds present in tobacco smoke may combine with nicotine to produce the intense reinforcing properties of cigarette smoking that lead to addiction.

Nicotine and nonnicotine factors in cigarette addiction

RATIONALE

A great deal of research supports the role of nicotine in cigarette addiction. However, the effectiveness of nicotine replacement therapy (NRT) as a smoking cessation treatment has fallen short of initial hopes. A key reason may be that NRT does not address nonnicotine components of smoking reinforcement. These include constituents that provide reinforcing sensory stimulation, components that minimize excessive irritation from inhaled nicotine and other pharmacologically active compounds in cigarette smoke.

OBJECTIVE

Studies using various paradigms to dissociate nicotine from other components of smoking are summarized.

RESULTS

Nonnicotine components provide many rewarding effects, often surpassing the direct effects of nicotine. Substitutes for the sensory effects of smoking may be effective in relieving craving for cigarettes and in facilitating smoking cessation. Moreover, techniques for devaluing smoking-related cues may decrease craving and enhance subsequent abstinence. Promising approaches for devaluing smoke cues include extinction-based treatments employing denicotinized cigarettes and the use of nicotinic agonist and/or antagonist treatment during the weeks leading up to a quit attempt. Recent studies suggest that incorporating these approaches into a treatment program may significantly increase smoking abstinence rates. Preliminary findings also suggest that replacement of the effects of monoamine oxidase inhibitors contained in cigarette smoke may enhance quit rates.

CONCLUSIONS

While current NRT methods have been the mainstay of smoking cessation treatment and will likely continue to serve a useful role, the next stage of progress will likely entail the development of tools designed with recognition of the importance of nonnicotine components of cigarette smoking.

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.

Cigarette smoking and incidence of first depressive episode: an 11-year, population-based follow-up study

Smoking has been found to be associated with depression. Biologic hypotheses support causation in both directions. This study examined the association between cigarette smoking and a subsequent first depression. In 1990, 2,014 adults in Norway were interviewed about their lifestyle and mental health. A 2001 reinterview by trained interviewers defined the study cohort of 1,190 participants. The cases were those who experienced a first depression whose onset was estimated to occur during the follow-up period, based on retrospective assessment by the Composite International Diagnostic Interview (International Classification of Diseases, Tenth Revision). Cox regression was used to estimate the hazard rate of depression during follow-up. Alternative explanations for a direct causal influence from smoking on subsequent depression were assessed, and a sensitivity analysis was performed. The risk of depression was four times as high for heavy smokers compared with never smokers. A dose-response relation with an increasing hazard for past smokers and for an increasing number of cigarettes smoked per day for current smokers was found. Similarly, increasing smoking time was associated with increasing risk. Failure of other plausible alternatives to explain the observed association between smoking and depression might reflect a direct causal influence of smoking on depression.