Inhibition of monoamine oxidase B in the brains of smokers

The effect of stopping smoking on perceived stress levels

AIMS

Many smokers believe that smoking helps them to cope with stress, and that stopping smoking would deprive them of an effective stress management tool. Changes in stress levels following long-term smoking cessation are not well mapped. This longitudinal project was designed to provide more robust data on post-cessation changes in perceived stress levels by following a cohort of smokers admitted to hospital after myocardial infarction (MI) or for coronary artery bypass (CAB) surgery, as such patients typically achieve higher continuous abstinence rates than other comparable samples.

DESIGN

A total of 469 smokers hospitalized after MI or CAB surgery and wanting to stop smoking were seen in the hospital and completed 1-year follow-ups. Ratings of helpfulness of smoking in managing stress at baseline, smoking status (validated by salivary cotinine concentration) and ratings of perceived stress at baseline and at 1-year follow-up were collected.

FINDINGS

Of the patients, 41% (n = 194) maintained abstinence for 1 year. Future abstainers and future smokers did not differ in baseline stress levels or in their perception of coping properties of smoking. However, abstainers recorded a significantly larger decrease in perceived stress than continuing smokers, and the result held when possible confounding factors were controlled for (P < 0.001).

CONCLUSIONS

In highly dependent smokers who report that smoking helps them cope with stress, smoking cessation is associated with lowering of stress. Whatever immediate effects smoking may have on perceived stress, overall it may generate or aggravate negative emotional states. The results provide reassurance to smokers worried that stopping smoking may deprive them of a valuable coping resource.

Human dopamine receptor D2/D3 availability predicts amygdala reactivity to unpleasant stimuli

Dopamine (DA) modulates the response of the amygdala. However, the relation between dopaminergic neurotransmission in striatal and extrastriatal brain regions and amygdala reactivity to affective stimuli has not yet been established. To address this issue, we measured DA D2/D3 receptor (DRD2/3) availability in twenty-eight healthy men (nicotine-dependent smokers and never-smokers) using positron emission tomography with [18F]fallypride. In the same group of participants, amygdala response to unpleasant visual stimuli was determined using blood oxygen level-dependent (BOLD) functional magnetic resonance imaging. The effects of DRD2/3 availability in emotion-related brain regions and nicotine dependence on amygdala response to unpleasant stimuli were examined by multiple regression analysis. We observed enhanced prefrontal DRD2/3 availability in those individuals with higher amygdala response to unpleasant stimuli. As compared to never-smokers, smokers showed an attenuated amygdala BOLD response to unpleasant stimuli. Thus, individuals with high prefrontal DRD2/3 availability may be more responsive toward aversive and stressful information. Through this mechanism, dopaminergic neurotransmission might influence vulnerability for affective and anxiety disorders. Neuronal reactivity to unpleasant stimuli seems to be reduced by smoking. This observation could explain increased smoking rates in individuals with mental disorders.

The effects of nicotine, denicotinized tobacco, and nicotine-containing tobacco on cigarette craving, withdrawal, and self-administration in male and female smokers

The effects of the acute administration of nicotine [through nicotine inhalers (NI) and placebo inhalers (PI)], nicotine-containing tobacco (NT), and denicotinized tobacco (DT), on smokers' subjective responses and motivation to smoke were examined in 22 smokers (12 male, 10 female; 11 low dependent, 11 high dependent). During four randomized blinded sessions, participants self-administered NI, PI, NT, or DT, and assessed their effects using Visual Analogue Scales and the Brief Questionnaire of Smoking Urges. They could then self-administer their preferred brand of cigarettes using a progressive ratio task. NT and DT were each associated with increased satisfaction and relaxation as well as decreased craving relative to the inhalers and NT increased ratings of stimulation relative to each of the other products. Both NT and DT delayed the onset of preferred tobacco self-administration relative to NI and PI but only NT reduced the total amount self-administered. Sex differences were evident in the effects of DT on withdrawal-related cravings with women experiencing greater DT-induced craving relief than men. Findings suggest that DT is effective in acutely reducing many smoking abstinence symptoms, especially in women, but a combination of nicotine and non-nicotine tobacco ingredients may be necessary to suppress smoking behavior.

Age influences the effects of nicotine and monoamine oxidase inhibition on mood-related behaviors in rats

RATIONALE

Epidemiological studies have demonstrated a comorbidity of smoking with depression and anxiety, particularly during adolescence. However, few animal studies have considered possible synergistic interactions between nicotine and other tobacco smoke constituents, such as monoamine oxidase (MAO) inhibitors, in the regulation of mood.

OBJECTIVES

The aim of the study was to test the hypothesis that nicotine combined with the irreversible MAO inhibitor, tranylcypromine, will differentially affect depression- and anxiety-related behaviors in adolescent and adult rats.

METHODS

Nicotine (0, 0.05, 0.2 mg/kg, s.c.) and tranylcypromine (3 mg/kg, i.p.) were tested separately, or together, on male rats aged postnatal days 30 and 68, in three mood-related behavioral tests: forced swim test (FST), elevated plus maze (EPM), and open field.

RESULTS

Nicotine (0.2 mg/kg) in adults significantly decreased floating time in the FST and increased time spent in the open arm of the EPM, with no change in locomotor activity. Tranylcypromine pretreatment combined with nicotine (0.2 mg/kg) significantly increased locomotor activity and time spent in the center of the open field. Whereas nicotine alone had no significant effect on adolescents, it significantly increased locomotor activity and decreased floating time in the FST when combined with tranylcypromine pretreatment.

CONCLUSIONS

There is an age-dependent effect of nicotine, alone and in combination with MAO inhibition, on mood-related behaviors. Whereas nicotine alone induces mood improvement in adults, it has no effect on adolescents. Nicotine combined with tranylcypromine has unique, age-dependent effects. Thus, experimental studies of smoking should consider both age and other tobacco constituents, such as MAO inhibitors, as critical factors.

Smoking in schizophrenia: diagnostic specificity, symptom correlates, and illness severity

BACKGROUND

Cigarette smoking was consistently found to be more prevalent in individuals with schizophrenia than in other psychiatric groups and the general population. These findings have been interpreted as evidence of a specific association between schizophrenia and smoking. However, the supporting data come primarily from cross-sectional studies, which are susceptible to confounding. Our aim was to test specificity of this link longitudinally in an epidemiologic sample.

METHODS

A cohort of 542 inpatients with psychosis was followed for 10 years after first hospitalization, completing 5 face-to-face interviews. Assessments included ratings of specific symptoms (psychotic, negative, disorganized, and depressive), Global Assessment of Functioning, and a categorical measure of cigarette consumption. All participants were assigned longitudinal consensus diagnoses by study psychiatrists, and 229 were diagnosed with schizophrenia spectrum disorders (SZ).

RESULTS

At baseline, 52.4% of participants were current smokers and 69.3% were lifetime smokers. Smoking rates did not differ among the diagnostic groups (schizophrenia spectrum, major depressive, bipolar, or other psychotic disorder) at any assessment point. Smokers were more severely ill than nonsmokers but did not differ in specific symptoms either cross-sectionally or longitudinally. Among smokers, changes in cigarette consumption were linked only with changes in depression (beta = .16, P < .001).

CONCLUSIONS

Rates of smoking were elevated in subjects with schizophrenia but were just as high with other psychotic disorders. Smoking was not associated with psychotic symptoms, but cigarette consumption covaried with depression over time. Given the devastating health consequences of cigarette use, smoking cessation interventions are urgently needed in this population and should specifically address depression.

Negative affectivity in smokers applying to smoking cessation clinics: a case-control study

OBJECTIVE

The objective of this study was to assess whether subjects applying to smoking cessation clinics display a higher level of affective symptoms than smokers recruited from the general population.

METHODS

The study was conducted according to a cross-sectional, case-control design. Cases were smokers applying to public smoking cessation clinics for the first time and controls were smokers recruited from the general population. Socio-demographic data and clinical information were collected. Self- (Hospital Anxiety Depression Scale, Beck Depression Inventory, State-Trait Anxiety Inventory) and hetero-administered (Montgomery Asberg Depression Rating Scale, Hamilton Anxiety scale) rating scales were used to assess anxious and depressive symptoms. Nicotine dependence was measured via a self-administered questionnaire (Fagerström Tolerance Questionnaire).

RESULTS

Sixty-eight cases were recruited, individually matched, and compared to controls. Overall, cases had significantly higher scores than controls when the rating scales assessing anxious and depressive symptoms were evaluated.

CONCLUSIONS

Smokers applying to smoking cessation clinics for the first time have a higher level of negative affectivity than smokers from the general population. An evaluation of the level of negative affectivity could be introduced into clinical practice to have a complete assessment of the patient. We propose adding psychological or pharmacological support to complement the smoking cessation program.

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.

Smoking induces long-lasting effects through a monoamine-oxidase epigenetic regulation

BACKGROUND

Postulating that serotonin (5-HT), released from smoking-activated platelets could be involved in smoking-induced vascular modifications, we studied its catabolism in a series of 115 men distributed as current smokers (S), never smokers (NS) and former smokers (FS) who had stopped smoking for a mean of 13 years.

METHODOLOGY/PRINCIPAL FINDINGS

5-HT, monoamine oxidase (MAO-B) activities and amounts were measured in platelets, and 5-hydroxyindolacetic acid (5-HIAA)--the 5-HT/MAO catabolite--in plasma samples. Both platelet 5-HT and plasma 5-HIAA levels were correlated with the 10-year cardiovascular Framingham relative risk (P<0.01), but these correlations became non-significant after adjustment for smoking status, underlining that the determining risk factor among those taken into account in the Framingham risk calculation was smoking. Surprisingly, the platelet 5-HT content was similar in S and NS but lower in FS with a parallel higher plasma level of 5-HIAA in FS. This was unforeseen since MAO-B activity was inhibited during smoking (P<0.00001). It was, however, consistent with a higher enzyme protein concentration found in S and FS than in NS (P<0.001). It thus appears that MAO inhibition during smoking was compensated by a higher synthesis. To investigate the persistent increase in MAO-B protein concentration, a study of the methylation of its gene promoter was undertaken in a small supplementary cohort of similar subjects. We found that the methylation frequency of the MAOB gene promoter was markedly lower (P<0.0001) for S and FS vs. NS due to cigarette smoke-induced increase of nucleic acid demethylase activity.

CONCLUSIONS/SIGNIFICANCE

This is one of the first reports that smoking induces an epigenetic modification. A better understanding of the epigenome may help to further elucidate the physiopathology and the development of new therapeutic approaches to tobacco addiction. The results could have a larger impact than cardiovascular damage, considering that MAO-dependent 5-HT catabolism is also involved in addiction, predisposition to cancer, behaviour and mental health.

Negative emotionality: monoamine oxidase B gene variants modulate personality traits in healthy humans

Monoamine oxidase A and B (MAOA and MAOB) appear to be involved in the pathogenesis of Major Depression, and vulnerability of Major Depression is associated with personality traits relating to positive and negative affect. This study aimed to investigate associations between MAOA and MAOB polymorphisms and personality traits of positive and negative emotionality in healthy volunteers, to elucidate mechanisms underlying personality and the risk for depression. Healthy Caucasian volunteers (N = 150) completed the Multiphasic Personality Questionnaire (MPQ), which includes independent superfactors of Positive Emotionality and Negative Emotionality. Participants were genotyped for 8 MAOA and 12 MAOB single nucleotide polymorphisms (SNPs). Association analyses for both SNPs and haplotypes were performed using the permutation approach implemented in PLINK. Negative Emotionality was significantly associated with the two highly linked MAOB polymorphisms rs10521432 and rs6651806 (p < 0.002). Findings were extended in haplotype analyses. For MAOB the 4-SNP haplotype GACG formed from rs1799836, rs10521432, rs6651806 and rs590551 was significantly related to lower Negative Emotionality scores (p < 0.002). MAOA was not related to personality in this study. Our finding provides the first evidence that MAOB polymorphisms influence levels of negative emotionality in healthy human volunteers. If confirmed, these results could lead to a better understanding of personality traits and inter-individual susceptibility developing psychiatric disorders such as major depression.

Neurotransmission-related genetic polymorphisms, negative affectivity traits, and gender predict tobacco abstinence symptoms across 44 days with and without nicotine patch

Genetic and personality trait moderators of tobacco abstinence-symptom trajectories were assessed in a highly controlled study. Based on evidence suggesting their importance in stress reactivity and smoking, moderators studied were serotonin transporter gene (5-HTTLPR) and dopamine D2 receptor gene (DRD2) polymorphisms and personality traits related to negative affect (NA). Smokers were randomly assigned to quit smoking with nicotine or placebo patches. Financial incentives resulted in 80% verified abstinence across the 44-day study. Individuals with 1 or 2 short alleles of 5-HTTLPR (S carriers) experienced larger increases in NA symptoms than did those without a short allele. Nicotine replacement therapy (NRT) alleviated anxiety only in S carriers. NRT reduced NA to a greater extent in DRD2 A1 carriers than in A2A2 individuals during the 1st 2 weeks of treatment (when on the 21-mg patch); however, A1 carriers experienced a renewal of NA symptoms when switched to the 7-mg patch and when off the patch, while A2A2 individuals continued to benefit from NRT. The results suggest that the effects of genotype and treatment may vary across different durations of abstinence, treatment doses, and genotypes.

Smoking, nicotine and neuropsychiatric disorders

Tobacco smoking is an extremely addictive and harmful form of nicotine (NIC) consumption, but unfortunately also the most prevalent. Although disproportionately high frequencies of smoking and its health consequences among psychiatric patients are widely known, the neurobiological background of this epidemiological association is still obscure. The diverse neuroactive effects of NIC and some other major tobacco smoke constituents in the central nervous system may underlie this association. This present paper summarizes the pharmacology of NIC and its receptors (nAChR) based on a systematic review of the literature. The role of the brain's reward system(s) in NIC addiction and the results of functional and structural neuroimaging studies on smoking-related states and behaviors (i.e. dependence, craving, withdrawal) are also discussed. In addition, the epidemiological, neurobiological, and genetic aspects of smoking in several specific neuropsychiatric disorders are reviewed and the clinical relevance of smoking in these disease states addressed.

Evidence that folic acid deficiency is a major determinant of hyperhomocysteinemia in Parkinson's disease

In the present work we measured blood levels of total homocysteine ((t)Hcy), vitamin B(12) and folic acid in patients with Parkinson s disease (PD) and in age-matched controls and searched for possible associations between these levels with smoking, alcohol consumption, L-DOPA treatment and disease duration in PD patients. We initially observed that plasma (t)Hcy levels were increased by around 30 % in patients affected by PD compared to controls. Linear correlation, multiple regression and comparative analyses revealed that the major determinant of the increased plasma concentrations of (t)Hcy in PD patients was folic acid deficiency, whereas in controls (t)Hcy levels were mainly determined by plasma vitamin B(12) concentrations. We also observed that alcohol consumption, gender and L-DOPA treatment did not significantly alter plasma (t)Hcy, folic acid and vitamin B(12) levels in parkinsonians. Furthermore, disease duration was positively associated with (t)Hcy levels and smoking was linked with a deficit of folic acid in PD patients. Considering the potential synergistic deleterious effects of Hcy increase and folate deficiency on the central nervous system, we postulate that folic acid should be supplemented to patients affected by PD in order to normalize blood Hcy and folate levels, therefore potentially avoiding these risk factors for neurologic deterioration in this disorder.

Positron emission tomographic measure of brain dopamine dependence to nicotine as a model of drugs of abuse

RATIONALE

Nicotine/tobacco are prototypic substances used throughout the world. Nicotine abstinence produces some depressive-like effects which are treated by the dopamine (DA) and norepinephrine reuptake inhibitor bupropion. A quantitative measure of the regional brain utilization of these catecholamines (CA) during nicotine dependence and withdrawal is important.

OBJECTIVE

The aim of this study was to prove that regional brain DA utilization by nicotine can be quantified by positron emission tomography (PET) using L-[beta-(11)C]DOPA.

MATERIALS AND METHODS

Eight young Macaca mulatta monkeys were given 0.9% NaCl or nicotine in doses of 32 or 100 microg/kg i.m. bid for 9 days to produce minimal dependence. On the tenth day, PET measurements were repeated before and after i.v. nicotine administration. PET studies were done in habituated, trained, and fully conscious animals.

RESULTS

Compared to a 0.9% NaCl control, acute i.v. nicotine as a bolus plus infusion for 30 min in similar doses to maintain a steady-state level for 30 min did not affect the utilization rate constant (k (3)) in dorsal or ventral striatum as measured by L-[beta-(11)C]DOPA. When monkeys were given nicotine bid repeatedly after overnight nicotine abstinence, CA utilization was reduced. A subsequent nicotine dose normalized utilization to slightly above control levels. Changes in ventral striatum were similar to those in dorsal striatum. The reduced rate of utilization demonstrated with L-[beta-(11)C]DOPA after overnight nicotine abstinence and its reversal by nicotine the next day provides an important PET measure of brain nicotine dependence and withdrawal. This method can be applied to other substances of abuse that release DA.

Inhibition of monoamine oxidases desensitizes 5-HT1A autoreceptors and allows nicotine to induce a neurochemical and behavioral sensitization

Although nicotine is generally considered to be the main compound responsible for addictive properties of tobacco, experimental data indicate that nicotine does not exhibit all the characteristics of other substances of abuse. We recently showed that a pretreatment with mixed irreversible monoamine oxidases inhibitors (MAOIs), such as tranylcypromine, triggers a locomotor response to nicotine in mice and allows maintenance of behavioral sensitization to nicotine in rats. Moreover, we showed by microdialysis in mice that behavioral sensitization induced by compounds belonging to main groups of drugs of abuse, such as amphetamine, cocaine, morphine, or alcohol, was underlain by sensitization of noradrenergic and serotonergic neurons. Here, this neurochemical sensitization was tested after nicotine, tranylcypromine, or a mixture of both compounds. Data indicate that, whereas neither repeated nicotine nor repeated tranylcypromine alone has any effect by itself, a repeated treatment with a mixture of nicotine and tranylcypromine induces both behavioral sensitization and sensitization of noradrenergic and serotonergic neurons. The development of neurochemical and behavioral sensitizations is blocked by prazosin and SR46349B [(1Z,2E)-1-(2-fluoro-phenyl)-3-(4-hydroxyphenyl)-prop-2-en-one-O-(2-dimethylamino-ethyl)-oxime hemifumarate], two antagonists of alpha1b-adrenergic and 5-HT(2A) receptors, respectively, but not by SCH23390 [R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride], a D(1) receptor antagonist. Finally, we found that pretreatments with WAY 100635 [N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclo-hexane carboxamide trihydrochloride], a 5-HT(1A) receptor antagonist, can also induce a behavioral and neurochemical sensitization to repeated nicotine. Complementary experiments with 8-OHDPAT (8-hydroxy-dipropylamino-tetralin), a 5-HT(1A) receptor agonist, and analysis of 5-HT(1A) receptors expression in the dorsal raphe nucleus after a tranylcypromine injection indicate that MAOIs contained in tobacco desensitize 5-HT(1A) autoreceptors to trigger the strong addictive properties of tobacco.

Neuroimaging of Nicotine Dependence: Key Findings and Application to the Study of Smoking-Mental Illness Comorbidity

Modern neuroimaging techniques offer the opportunity to non-invasively study neuroanatomical and neurofunctional correlates of nicotine dependence and its treatment. In the present review, the most widely used neuroimaging techniques-magnetic resonance imaging (MRI), positron emission tomography (PET) and functional MRI (fMRI)-are briefly described and their strengths and limitations discussed. The use of these techniques has resulted in new insights into the neuropharmacology of tobacco addiction. Studies comparing smokers and nonsmokers have shown that smokers have less grey matter density in frontal brain regions and greater concentrations of nicotinic receptors. Research on the effects of smoking a cigarette confirms that smoking leads to the release of dopamine in brain reward areas and to nicotinic receptor binding. Studies of smoking abstinence have identified functional brain correlates of increased reactivity to smoking-related cues, and worsening of concentration. To date, neuroimaging studies of nicotine dependence among individuals with mental illness have focused almost exclusively on schizophrenia. A conceptual/methodological framework for studying dual diagnosis using neuroimaging measures is provided with the aim of spurring additional research in this area.

Ecstasy-induced oxidative stress to adolescent rat brain mitochondria in vivo: influence of monoamine oxidase type A

The administration of a neurotoxic dose of 3,4-methylenedioxymethamphetamine (MDMA; 'ecstasy') to the rat results in mitochondrial oxidative damage in the central nervous system, namely lipid and protein oxidation and mitochondrial DNA deletions with subsequent impairment of the correspondent protein expression. Although these toxic effects were shown to be prevented by monoamine oxidase B inhibition, the role of monoamine oxidase A (MAO-A) in MDMA-mediated mitochondrial damage remains to be evaluated. Thus, the aim of the present study was to clarify the potential interference of a specific inhibition of MAO-A by clorgyline, on the deleterious effects produced by a binge administration of a neurotoxic dose of MDMA (10 mg MDMA/kg of body weight, intraperitoneally, every 2 hours in a total of four administrations) to an adolescent rat model. The parameters evaluated were mitochondrial lipid peroxidation, protein carbonylation and expression of the respiratory chain protein subunits II of reduced nicotinamide adenine dinucleotide dehydrogenase (NDII) and I of cytochrome oxidase (COXI). Considering that hyperthermia has been shown to contribute to the neurotoxic effects of MDMA, another objective of the present study was to evaluate the body temperature changes mediated by MDMA with a MAO-A selective inhibition by clorgyline. The obtained results demonstrated that the administration of a neurotoxic binge dose of MDMA to an adolescent rat model previously treated with the specific MAO-A inhibitor, clorgyline, resulted in synergistic effects on serotonin- (5-HT) mediated behaviour and body temperature, provoking high mortality. Inhibition of MAO-A by clorgyline administration had no protective effect on MDMA-induced alterations on brain mitochondria (increased lipid peroxidation, protein carbonylation and decrease in the expression of the respiratory chain subunits NDII and COXI), although it aggravated MDMA-induced decrease in the expression of COXI. These results reinforce the notion that the concomitant use of MAO-A inhibitors and MDMA is counter indicated because of the resulting severe synergic toxicity.

In vivo brain imaging of human exposure to nicotine and tobacco

While most cigarette smokers endorse a desire to quit smoking, only 14-49% will achieve abstinence after 6 months or more of treatment. A greater understanding of the effects of smoking on brain function may result in improved pharmacological and behavioral interventions for this condition. Research groups have examined the effects of acute and chronic nicotine/cigarette exposure on brain activity using functional imaging; the purpose of this chapter 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 reduced 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 (accompanied by an overall upregulation of these receptors). These findings indicate that smoking enhances neurotransmission through cortico-basal ganglia-thalamic circuits by direct stimulation of nAChRs, indirect stimulation via DA release or MAO inhibition, or a combination of these and possibly other factors. Activation of this circuitry may be responsible for the effects of smoking seen in tobacco-dependent smokers, such as improvements in attentional performance, mood, anxiety, and irritability.

Smoking as a precipitating factor for migraine: a survey in medical students

Our aim was to analyse the relationship between migraine and smoking in medical students. Medical students who had already received teaching on migraine were asked to answer an ad hoc questionnaire. A total of 361 students filled in the questionnaire: 245 (68%) were women. International Headache Society criteria were fulfilled by 58 (prevalence of migraine 16%) students. A total of 74 (20%) were current smokers: 21 males (18% of men were smokers) and 53 females (22% smokers). Within those 58 students with migraine, 17 (29%) smoke: only 2 were males (14% of males with migraine smoked) while the remaining 15 were females (34% of women with migraine smoked). Within those 17 students who were smokers and migraineurs, 12 (71%) thought that smoking worsens migraine and 10 (59%) that smoking precipitates attacks. The minimum number of cigarettes which subjectively precipitates attacks was 5. Migraine prevalence in the 20s in Spain is 16%. Our data obtained in medical students suggest that smoking can be a precipitating factor for migraine attacks, as the prevalence of active smoking is one-third higher in migraineurs and as there seems to be a relationship between the number of cigarettes and the development of migraine attacks.

Pharmacotherapy for tobacco dependence

Pharmacotherapy can provide effective treatment of tobacco dependence and withdrawal, and thereby facilitate efforts to achieve and sustain tobacco abstinence. Currently approved medications for smoking cessation are nicotine replacement medications (NRT), including nicotine patch, gum, lozenge, sublingual tablet, inhaler and nasal spray, the antidepressant bupropion, and the nicotinic partial agonist varenicline. This review discusses the pharmacological basis for the use of these medications, and the properties that might contribute to their efficacy, safety, and abuse liability. The review also discusses how pharmacological principles can be used to improve existing medications, as well as assist in the development of new medications.

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.

[Role of tobacco use on the incidence of depression in the SUN cohort study]

BACKGROUND AND OBJECTIVE

Several investigations, most of them cross-sectional, have analyzed the association between smoking and depression, but there are not enough evidences to establish the direction of the association. Our objective was to prospectively assess the association between smoking habit and depression incidence in the SUN (Seguimiento Universidad de Navarra) cohort.

SUBJECTS AND METHOD

Dynamic cohort study (recruitment permanently open) based on 8,556 graduate participants where depression incidence was ascertained during 6 years of follow-up. Depression was defined as the presence of a self-reported physician diagnosis and/or use of antidepressant medication in at least one of the 2-year, 4-year or 6-year follow-up questionnaires. The association between smoking and depression incidence was estimated through the calculation of hazard ratios (HR) and their 95% confidence intervals (CI) using Cox regression models (proportional hazards).

RESULTS

The mean follow-up period was 47.4 months. One hundred and ninety participants initially free of depression reported a physician diagnosis of depression during follow-up. A significantly higher risk was found for smokers (HR = 1.39; 95% CI, 1.00-1.93) when they were compared to non smokers, whereas an inverse association was found for ex-smokers who had quit smoking more than 10 years ago (HR = 0.42; 95% CI, 0.19-0.94).

CONCLUSIONS

This study supports, with a prospective design, an increased risk of depression associated to smoking.

Disrupting nicotine reinforcement: from cigarette to brain

Cigarette smoking is a tenacious addiction that is maintained to a significant extent by the reinforcing effects of nicotine. An emerging theme in smoking cessation treatment is the development of methods for interfering with these reinforcing effects. By attenuating nicotine reinforcement, treatments may enhance a smoker's chances of successfully remaining abstinent. Several treatment approaches will be described, including the use of denicotinized cigarettes, nicotine vaccines, nicotinic receptor agonists and antagonists, and modulators of brain reinforcement processes. These techniques highlight the numerous sites along the path between the cigarette and the brain that can be targeted for intervention. In addition to unimodal therapies, treatment combinations will be discussed that might more effectively block cigarette reward and thereby further enhance smoking abstinence.

Novel pharmacological approaches for treating tobacco dependence and withdrawal: current status

Increasing the diversity and availability of medications for the treatment of tobacco dependence and/or withdrawal, to aid in the achievement of smoking cessation, is crucial to meet the diverse needs of tobacco users. Despite a general awareness that smoking is harmful and widespread interest in smoking cessation, nearly 50 million adults in the US and 1.3 billion worldwide continue to smoke. Nicotine replacement therapies are effective in the treatment of tobacco dependence and withdrawal, but do not meet the needs of all tobacco users. Improvement of tobacco dependence and/or withdrawal treatments is likely to rely on novel pharmacological approaches that include new chemical entities and new formulations of current drugs. In addition, new indications for treating tobacco dependence and withdrawal show promise for reducing tobacco use and associated disease. This article focuses on a range of novel pharmacological approaches for the treatment of tobacco dependence and/or withdrawal, including oral and pulmonary nicotine delivery and the following non-nicotinic medications: antidepressants, an alpha4beta2 nicotine partial agonist, an alpha2-noradrenergic agonist, cytochrome P450 (CYP) 2A6 inhibitors, opioid antagonists and GABAergic medications. In addition to existing medications, this article addresses novel medications in the clinical development stage and those that have been evaluated previously. Novel medications in the clinical development stage include at least three nicotine vaccines and the cannabinoid receptor acting drug rimonabant. Medications evaluated previously include lobeline, mecamylamine and an anticholinergic drug regimen comprising atropine, scopolamine and chlorpromazine. Having not been approved by major drug regulatory authorities for the treatment of tobacco dependence and/or withdrawal, these medications have been evaluated in an experimental capacity.

Subtypes of nicotinic acetylcholine receptors in nicotine reward, dependence, and withdrawal: evidence from genetically modified mice

Neuronal nicotinic acetylcholine receptors (nAChRs) can regulate the activity of many neurotransmitter pathways throughout the central nervous system and are considered to be important modulators of cognition and emotion. nAChRs are also the primary site of action in the brain for nicotine, the major addictive component of tobacco smoke. nAChRs consist of five membrane-spanning subunits (alpha and beta isoforms) that can associate in various combinations to form functional nAChR ion channels. Owing to a dearth of nAChR subtype-selective ligands, the precise subunit composition of the nAChRs that regulate the rewarding effects of nicotine and the development of nicotine dependence are unknown. The advent of mice with genetic nAChR subunit modifications, however, has provided a useful experimental approach to assess the contribution of individual subunits in vivo. Here, we review data generated from nAChR subunit knockout and genetically modified mice supporting a role for discrete nAChR subunits in nicotine reinforcement and dependence processes. Importantly, the rates of tobacco dependence are far higher in patients suffering from comorbid psychiatric illnesses compared with the general population, which may at least partly reflect disease-associated alterations in nAChR signaling. An understanding of the role of nAChRs in psychiatric disorders associated with high rates of tobacco addiction, therefore, may reveal novel insights into mechanisms of nicotine dependence. Thus, we also briefly review data generated from genetically modified mice to support a role for discrete nAChR subunits in anxiety disorders, depression, and schizophrenia.

Association of 5-HTT gene polymorphism, platelet MAO activity, and drive for thinness in a population-based sample of adolescent girls

OBJECTIVE

Several lines of evidence suggest that alterations in serotonergic activity contribute to the pathophysiology of abnormal eating behaviors. Since platelet monoamine oxidase (MAO) activity and the 5-HT transporter gene promoter polymorphism (5-HTTLPR) have been associated with eating disorders, the knowledge from a population-based sample may provide useful information which changes in 5-HT function observed in eating disorders represent trait vs. state effects.

METHOD

The sample was based on both cohorts of the Estonian Children Personality, Behavior and Health Study (ECPBHS). The current study was conducted during the second follow-up where altogether 82% from the original sample was recruited. EDI-2 subscales--Drive for Thinness and Bulimia--were used to determine eating attitudes and behaviors. Platelet MAO activity was measured and the participants were genotyped for the 5-HTTLPR.

RESULTS

Allelic variation of 5-HTTLPR or platelet MAO activity were not independently associated with drive for thinness or binge eating, but girls homozygous for the 5-HTTLPR long allele and with high platelet MAO activity, both considered indicators of a higher capacity 5-HT system, exhibited higher scores of drive for thinness.

CONCLUSION

The results suggest that drive for thinness is the highest in girls with the presence of two markers of higher serotonergic capacity.

SPECT and PET of the dopamine transporter in attention-deficit/hyperactivity disorder

Abnormalities of frontostriatal circuits, which are modulated by dopamine, have been found by brain imaging studies in patients with attention-deficit/hyperactivity disorder (ADHD). With special radiolabeled ligands selective imaging of the dopamine transporter (DAT), which has a key function in dopamine metabolism, can be performed by SPECT and PET. Most of the studies showed a higher DAT availability in untreated patients with ADHD compared with controls. The relationship between DAT availability and a polymorphism of DAT1 gene in patients with ADHD is not clear and the results are controversial. It has been shown that methylphenidate lowers DAT availability very effectively in normal people and in patients with ADHD. First results seem to indicate that nonresponders to methylphenidate among ADHD patients have a low primary DAT availability, whereas patients with a good response to the drug have high DAT. Nicotine seems to lower DAT availability such as stimulant medication; this may explain the high percentage of smokers among patients with ADHD. Zinc is a DAT inhibitor and seems to have a positive therapeutic effect on ADHD symptoms. This article reviews the function and structure of the DAT, the results of DAT imaging with SPECT and PET, the relations between DAT availability and the DAT1 gene polymorphism, the influence of stimulants on DAT and the significance of DAT for therapeutic response, nicotine, zinc and psychotic symptoms in patients with ADHD.

Cigarette smoke, nicotine and cotinine protect against 6-hydroxydopamine-induced toxicity in SH-SY5Y cells

Epidemiological studies consistently demonstrate a reduced incidence of Parkinson's disease in smokers. As an approach to evaluate whether nicotine in tobacco may be involved in this apparent protective effect, we compared the effect of mainstream 1R4F cigarette smoke solutions, which contain chemicals inhaled by active smokers, and nicotine against 6-hydroxydopamine (6-OHDA)-induced toxicity in an in vitro cell culture system. For this purpose we used terminally differentiated SH-SY5Y neuroblastoma cells that exhibit a catecholaminergic phenotype and express nicotinic receptors. Cells were pre-incubated for 24 h in mainstream-cigarette smoke solutions (0.06, 0.2, or 0.6 cigarette puffs/ml) made from University of Kentucky 1R4F research brand cigarettes, followed by the addition of 6-OHDA for another 24-48 h. The 0.2, but not 0.06, puffs/ml dose, significantly protected against 6-OHDA-induced toxicity in SH-SY5Y cells. This dose yielded final nicotine concentrations of approximately 5 x 10(-7) M, which is similar to plasma smoking levels. Although the 0.6 puffs/ml dose caused significant toxicity on its own, it also appeared to protect against 6-OHDA-induced damage. We next tested the effect of nicotine, as well as its metabolite cotinine. These agents protected against the toxic effects of 6-OHDA in SH-SY5Y cells at concentrations ranging from 10(-7) to 10(-5) M. These combined results support the idea that nicotine is one of the components in cigarette smoke that has a protective effect against neurotoxic insults. These data suggest that nicotine may be of potential therapeutic value for Parkinson's disease.

Smoking and tea consumption delay onset of Parkinson's disease

Cigarette smoking, coffee and tea drinking may protect against Parkinson's disease (PD). These factors were assessed, retrospectively, to measure their effect on the age of PD onset. The study population consisted of 278 consecutive PD patients. Smoking > or =10 pack-years delayed age of PD onset by 3.2 years (p<0.05). Consumption of tea more than 3 cups per day delayed age of motor symptoms onset by 7.7 years (p<0.01). Coffee consumption exceeding 3 cups per day advanced the age of PD onset by 4.8 years (p=0.03). Thus, tea consumption and smoking can delay the age of PD onset, while coffee drinking may have the opposite effect.

Platelet monoamine oxidase kinetics, alcoholism subtypes and cigarette smoking

In trying to dissociate the effect of alcohol and tobacco use on platelet monoamine oxidase-B (MAO-B) activity, we compared the enzyme kinetics in controls (n = 66) and alcohol-dependent patients (n = 81), subdivided according to the severity of both, alcohol and tobacco use. Platelet MAO-B kinetics was measured spectrophotofluorimetrically in chronic alcohol intoxication and after 3 weeks abstinence. In alcoholic patients, an increased Michaelis-Menten constant (16%, p < 0.01) was shown, notwithstanding smoking status. Maximal velocity did not differ between patients and controls when adjusted for smoking. In cigarette smokers, a highly significant dose-dependent reduction of platelet MAO velocity (40%, p < 0.001) was demonstrated, with a similar degree of reduction in patients and controls. Tobacco use itself had no influence on MAO affinity. No differences were shown between subtype 1 and 2 alcoholics, or between the day of admission and the 21st day of abstinence. In conclusion, it seems that both, alcohol and tobacco consumption, may contribute to the lowering of overall platelet MAO-B activity. The effect of alcohol is small, due to interference with substrate binding, and not alteration of catalytic activity. In contrast, the effect of cigarette smoking is pronounced and relates to the dose-dependent reduction of platelet MAO velocity, with no influence on its affinity.

Neurochemical pathways involved in the protective effects of nicotine and ethanol in preventing the development of Parkinson's disease: potential targets for the development of new therapeutic agents

In this short review, neurochemical targets are identified where nicotine, and possibly ethanol, may interact to prevent the occurrence of Parkinson's disease. These are (a) the nicotinic acetycholine receptors present in the nigrostriatal area or on the surface of microglia, (b) monoamine oxidases and (c) inducible nitric oxide synthase. If such induced changes can be verified in clinical studies, this may help in the design of new therapeutic drugs which may be of relevance to diminish the incidence and perhaps the progression of the debilitating condition of Parkinson's disease.

Nicotine and caffeine-mediated modulation in the expression of toxicant responsive genes and vesicular monoamine transporter-2 in 1-methyl 4-phenyl-1,2,3,6-tetrahydropyridine-induced Parkinson's disease phenotype in mouse

Epidemiological evidence revealed that cigarette smokers and coffee drinkers have lower risk of Parkinson's disease (PD). Nicotine inhibits monoamine oxidase activity, and induces expression of neurotrophic factors and nicotinic acetylcholinergic receptors. However, caffeine is capable of antagonizing adenosine A(2A) receptor. Toxicant responsive enzymes and vesicular monoamine transporter-2 (VMAT-2) play critical roles in chemically induced PD. Despite some known functions, the effects of nicotine and caffeine on the expression and activity of toxicant responsive genes and on VMAT-2 are still not known. The study was therefore undertaken to investigate the effect of nicotine and caffeine on the expression and activity of toxicant responsive genes, i.e., CYP1A1, CYP2E1, GST-ya, GST-yc, GSTA4-4 and VMAT-2 in the striatum of control and MPTP-induced PD phenotype in mouse. The animals were treated intraperitoneally daily with nicotine (1 mg/kg) or caffeine (20 mg/kg) for 8 weeks, followed by 1-methyl 4-phenyl-1,2,3,6-tetrahydropyridine (MPTP; 20 mg/kg)+nicotine or caffeine for 4 weeks. MPTP significantly attenuated CYP1A1 and VMAT-2, and augmented CYP2E1, GST-ya, GST-yc and GSTA4-4 expression/activity. Nicotine or caffeine-treated animals showed significant restoration against most of the MPTP-induced alterations. The results obtained thus suggest that nicotine and caffeine modulate MPTP-induced alterations in CYP1A1, CYP2E1, GST-ya, GST-yc, GSTA4-4 and VMAT-2 expression/activity.

The monoamine oxidase inhibitor phenelzine enhances the discriminative stimulus effect of nicotine in rats

In addition to delivering nicotine, tobacco smoke also inhibits monoamine oxidase (MAO). Although MAO inhibitors (MAOIs) can increase nicotine self-administration in rodents, the effects of MAOIs on the discriminative stimulus effect of nicotine are not known. This study examined the effects of three MAOIs (phenelzine, clorgyline and pargyline) with varying selectivity for MAOA and MAOB in the nicotine drug discrimination procedure in rats. Adult male Sprague-Dawley rats were trained to discriminate nicotine (0.3 mg/kg, subcutaneously) from saline in a standard, two-lever food-reinforced operant task. Once the discrimination was acquired, the ability of each MAOI to substitute for or alter the discriminative stimulus effect of nicotine was determined. In substitution tests, nicotine (0.03-0.3 mg/kg) produced full, dose-dependent substitution. Although the selective MAOA inhibitor clorgyline (3-56 mg/kg) and the selective MAOB inhibitor pargyline (3-56 mg/kg) did not elicit any nicotine-appropriate responding, partial substitution was obtained with the nonselective MAO inhibitor phenelzine (1-17 mg/kg). Phenelzine (10 mg/kg) also enhanced the discriminative stimulus effect of a low dose of nicotine (0.056 mg/kg) and prolonged the time course effect of the nicotine-training dose. These findings indicate that concomitant inhibition of MAOA and MAOB can enhance the discriminative stimulus effect of nicotine in rats.

Imaging the addicted human brain

Modern imaging techniques enable researchers to observe drug actions and consequences as they occur and persist in the brains of abusing and addicted individuals. This article presents the five most commonly used techniques, explains how each produces images, and describes how researchers interpret them. The authors give examples of key findings illustrating how each technique has extended and deepened our knowledge of the neurobiological bases of drug abuse and addiction, and they address potential clinical and therapeutic applications.

Monoamine oxidase inhibition dramatically prolongs the duration of nicotine withdrawal-induced place aversion

BACKGROUND

Long-lasting effects of withdrawal from nicotine are hypothesized to contribute to relapse and persistence of tobacco habits, and significant evidence supports a role of monoamine oxidase inhibitors (MAOI) contained in cigarette smoke as potent modulators of the rewarding effects of tobacco.

METHODS

With quantification of somatic signs of withdrawal and the place aversion conditioning paradigm, we assessed the effects of MAOI pretreatment on both somatic and aversive motivational components of mecamylamine-induced nicotine withdrawal in rats rendered dependent on nicotine by the subcutaneous implantation of osmotic minipumps (vehicle or nicotine tartrate 9 mg/kg/day).

RESULTS

In nicotine-infused rats, mecamylamine induced a place aversion that lasted 6 weeks. When nicotine-infused rats were also treated with a MAOI, mecamylamine-induced conditioned place aversion persisted for at least 8 months of abstinence. The MAOI treatment slightly decreased ratings of somatic signs induced by mecamylamine administration but had no effect on the threshold or the magnitude of mecamylamine-induced conditioned place aversion.

CONCLUSIONS

These results show that MAOI pretreatment induces a long-lasting conditioned placed aversion associated with nicotine withdrawal, possibly through a potentiation of learning and memory process, and provides some indications on protracted abstinence that might be useful for delineating the neurobiological substrate of relapse.

Nicotinic Receptors: Role in Addiction and Other Disorders of the Brain

Nicotine, the addictive component of cigarette smoke has profound effects on the brain. Activation of its receptors by nicotine has complex consequences for network activity throughout the brain, potentially contributing to the addictive property of the drug. Nicotinic receptors have been implicated in psychiatric illnesses like schizophrenia and are also neuroprotective, potentially beneficial for neurodegenerative diseases. These effects of nicotine serve to emphasize the multifarious roles the drug, acting through multiple nicotinic acetylcholine receptor subtypes. The findings also remind us of the complexity of signaling mechanisms and stress the risks of unintended consequences of drugs designed to combat nicotine addiction.