Biological basis for the co-morbidity between smoking and mood disorders

Pathophysiology of nAChRs: limbic circuits and related disorders

Human epidemiological studies have identified links between nicotine intake and stress disorders, including anxiety, depression and PTSD. Here we review the clinical evidence for activation and desensitization of nicotinic acetylcholine receptors (nAChRs) relevant to affective disorders. We go on to describe clinical and preclinical pharmacological studies suggesting that nAChR function may be involved in the etiology of anxiety and depressive disorders, may be relevant targets for medication development, and may contribute to the antidepressant efficacy of non-nicotinic therapeutics. We then review what is known about nAChR function in a subset of limbic system areas (amygdala, hippocampus and prefrontal cortex), and how this contributes to stress-relevant behaviors in preclinical models that may be relevant to human affective disorders. Taken together, the preclinical and clinical literature point to a clear role for ACh signaling through nAChRs in regulation of behavioral responses to stress. Disruption of nAChR homeostasis is likely to contribute to the psychopathology observed in anxiety and depressive disorders. Targeting specific nAChRs may therefore be a strategy for medication development to treat these disorders or to augment the efficacy of current therapeutics.

The relationships between use of alcohol, tobacco and coffee in adolescence and mood disorders in adulthood

INTRODUCTION

Alcohol, tobacco and coffee are commonly used substances and use in adolescence has previously been linked to mood disorders. However, few large prospective studies have investigated adolescent use in relation to mental health outcomes in adulthood. The main aim of this study was to examine the prospective associations between alcohol use, cigarette smoking and coffee consumption at age 16 and subsequent mood disorders up to 33 years of age.

METHODS

Data from The Northern Finland Birth Cohort 1986 Study were used and a total of 7660 participants (49.9% male) were included. Associations between alcohol use, cigarette smoking and coffee consumption at age 16 and later diagnoses of major depression and bipolar disorder were examined using multinomial logistic regression analyses.

RESULTS

Mean number of cigarettes/day (OR, 1.23 [95% CI 1.01-1.50]) and mean volume of alcohol consumption (OR, 1.22 [95% CI 1.01-1.47]), but not frequency of excessive drinking, in adolescence were associated with increased risk for subsequent bipolar disorder after adjustment for sex, parental psychiatric disorders, family structure, illicit substance use, and emotional and behavioral problems at age 16. An association between cigarette smoking and major depression attenuated to statistically non-significant when adjusted for emotional and behavioral problems. No associations were observed between adolescent coffee consumption and subsequent mood disorders.

CONCLUSIONS

This is the first study to report an association of adolescent cigarette smoking and subsequent bipolar disorder diagnosis providing grounds for further research and pointing to a place for preventive measures among adolescents.

Bidirectional associations between depressive symptoms and cigarette, e-cigarette, cannabis, and alcohol use: Cross-lagged panel analyses among young adults before and during COVID-19

BACKGROUND

The literature regarding bidirectional relationships of depressive symptoms to cigarette and alcohol use is mixed, and limited regarding e-cigarette and cannabis use. Moreover, COVID-19 has significantly impacted mental health and substance use, especially among young adults. Thus, this is a critical period for focused research on these relationships among young adults.

METHODS

We analyzed longitudinal data (assessments in Fall 2018, 2019, and 2020) from 3,006 young adults (Mage = 24.56 [SD = 4.72], 54.8% female, 31.6% sexual minority, 71.6% White, 5.3% Black, 12.2% Asian, 11.4% Hispanic) from 6 US metropolitan statistical areas. Cross-lagged panel models were conducted to examine bidirectional associations between depressive symptoms and past 30-day use of cigarettes, e-cigarettes, cannabis, and alcohol (respectively), controlling for sociodemographics.

RESULTS

During the study period, depressive symptoms decreased before the pandemic but increased during, cigarette and e-cigarette use decreased in both periods, alcohol use showed no change before but increases during the pandemic, and cannabis use increased in both periods. Additionally, each outcome demonstrated greater stability before versus during COVID-19. Finally, greater antecedent depressive symptoms correlated with more days of subsequent cigarette (β = 0.03, SE = 0.01, p =.011) and e-cigarette use (β = 0.03, SE = 0.01, p =.021), but fewer days of alcohol use (β = -0.02, SE = 0.01, p =.035). W2 cannabis use and alcohol use, respectively, were related to W3 depressive symptoms (cannabis: β = 0.09, SE = 0.02, p <.001; alcohol: β = 0.06, SE = 0.02, p =.002). No other cross-lagged associations were significant.

CONCLUSIONS

Intervention efforts targeting depression and substance use should explicitly address the potential for onset and escalation of substance use and depressive symptoms, respectively, especially during societal stressors.

The effect of aerobic exercises of different intensities on anxiety, cigarette addiction, sleep quality, and quality of life in former smokers

BACKGROUND

There is a worldwide struggle to quit smoking and prevent relapsing. Aerobic exercises are frequently utilized to aid in smoking cessation and prevent relapse.

AIMS

This study aimed to investigate the effects of aerobic exercises of different intensity on the level of anxiety, smoking addiction, and quality of sleep and life in former smokers.

METHODS

The study included 60 people aged 18 to 45 who had quit smoking within the previous month. Individuals were randomly assigned to control (CON), mild-intensity aerobic activity (MIA), and moderate-intensity aerobic activity (MoIA) groups. The MIA group did submaximal aerobic exercises at 40% of maximum heart rate (MHR), while the MoIA group did them at 60% of MHR for 8 weeks/3 days. Participants' anxiety levels were assessed using the Beck Anxiety Scale (BAS), smoking addiction was assessed using the Fagerström Test for Nicotine Dependence and Substance Craving Scale (SCS), sleep quality was assessed using the Pittsburgh Sleep Quality Index, and quality of life was assessed using the SF-36 Short Form Scale (SF-36).

RESULTS

The SCS score of the MoIA group declined more than the MIA and CON groups, and the MIA group had a lower sleep disturbance score than other groups when the influence of exercise training was assessed over time (p < 0.05). Aerobic exercise had no influence on SF-36 or BAS scores (p > 0.05).

CONCLUSIONS

The benefits of mild and moderate aerobic exercise on quality of life and anxiety are similar. However, mild-intensity aerobic exercises may be suitable for sleep difficulties while moderate-intensity aerobic exercises may be preferred for reducing smoking addiction.

The detrimental effects of smoking on the course and outcome in adults with bipolar disorder-A narrative review

BACKGROUND

Smoking is a substantial and avoidable risk for physical disability and premature death. Despite a declining tobacco use in the community of developed countries, smoking remains abundant in people with mental disorders. This narrative review highlights the epidemiology, consequences and treatment options of tobacco use disorder (TUD) and nicotine dependence (ND) in people with bipolar disorder (BD).

METHODS

The authors conducted a Medline literature search from 1970 to November 2022 using MeSH terms "bipolar disorder" x "smoking" or "nicotine" or "tobacco" that retrieved 770 results. Search results were complemented by additional literature retrieved from examining cross references and by hand search in text books. Finally, 92 references were considered as essential and selected for the educational purpose of this review.

SUMMARY OF FINDINGS

Lifetime and point prevalence of smoking in people with BD is in the range of 45-70% and thus about 2-3 times more frequent in BD than in community samples. Smoking, TUD and ND have a detrimental impact both on mental and physical health as well as mortality in people with BD. In the absence of large controlled studies in comorbid BD and TUD or ND, pharmacological treatment follows the individual guidance for each disorder. Community-based psychosocial interventions for TUD and ND appear to be suitable in people with BD, too, as well as Cognitive Behavioral (CBT) or Acceptance and Commitment (ACT) based psychotherapies.

CONCLUSIONS

Smoking is a modifiable risk factor causing increased risks both for mental and physical health in BD, and deserves more attention in treatment. More treatment research into pharmacological and psychosocial interventions in comorbid BD and TUD or ND are still needed to deliver evidence-based recommendations to physicians.

Neurotoxic Effects of Neonicotinoids on Mammals: What Is There beyond the Activation of Nicotinic Acetylcholine Receptors?-A Systematic Review

Neonicotinoids are a class of insecticides that exert their effect through a specific action on neuronal nicotinic acetylcholine receptors (nAChRs). The success of these insecticides is due to this mechanism of action, since they act as potent agonists of insect nAChRs, presenting low affinity for vertebrate nAChRs, which reduces potential toxic risk and increases safety for non-target species. However, although neonicotinoids are considered safe, their presence in the environment could increase the risk of exposure and toxicity. On the other hand, although neonicotinoids have low affinity for mammalian nAChRs, the large quantity, variety, and ubiquity of these receptors, combined with its diversity of functions, raises the question of what effects these insecticides can produce in non-target species. In the present systematic review, we investigate the available evidence on the biochemical and behavioral effects of neonicotinoids on the mammalian nervous system. In general, exposure to neonicotinoids at an early age alters the correct neuronal development, with decreases in neurogenesis and alterations in migration, and induces neuroinflammation. In adulthood, neonicotinoids induce neurobehavioral toxicity, these effects being associated with their modulating action on nAChRs, with consequent neurochemical alterations. These alterations include decreased expression of nAChRs, modifications in acetylcholinesterase activity, and significant changes in the function of the nigrostriatal dopaminergic system. All these effects can lead to the activation of a series of intracellular signaling pathways that generate oxidative stress, neuroinflammation and, finally, neuronal death. Neonicotinoid-induced changes in nAChR function could be responsible for most of the effects observed in the different studies.

Genetic overlap and causal associations between smoking behaviours and mental health

Cigarette smoking is a modifiable behaviour associated with mental health. We investigated the degree of genetic overlap between smoking behaviours and psychiatric traits and disorders, and whether genetic associations exist beyond genetic influences shared with confounding variables (cannabis and alcohol use, risk-taking and insomnia). Second, we investigated the presence of causal associations between smoking initiation and psychiatric traits and disorders. We found significant genetic correlations between smoking and psychiatric disorders and adult psychotic experiences. When genetic influences on known covariates were controlled for, genetic associations between most smoking behaviours and schizophrenia and depression endured (but not with bipolar disorder or most psychotic experiences). Mendelian randomization results supported a causal role of smoking initiation on psychiatric disorders and adolescent cognitive and negative psychotic experiences, although not consistently across all sensitivity analyses. In conclusion, smoking and psychiatric disorders share genetic influences that cannot be attributed to covariates such as risk-taking, insomnia or other substance use. As such, there may be some common genetic pathways underlying smoking and psychiatric disorders. In addition, smoking may play a causal role in vulnerability for mental illness.

Using Mendelian randomization analysis to better understand the relationship between mental health and substance use: a systematic review

BACKGROUND

Poor mental health has consistently been associated with substance use (smoking, alcohol drinking, cannabis use, and consumption of caffeinated drinks). To properly inform public health policy it is crucial to understand the mechanisms underlying these associations, and most importantly, whether or not they are causal.

METHODS

In this pre-registered systematic review, we assessed the evidence for causal relationships between mental health and substance use from Mendelian randomization (MR) studies, following PRISMA. We rated the quality of included studies using a scoring system that incorporates important indices of quality, such as the quality of phenotype measurement, instrument strength, and use of sensitivity methods.

RESULTS

Sixty-three studies were included for qualitative synthesis. The final quality rating was '-' for 16 studies, '- +' for 37 studies, and '+'for 10 studies. There was robust evidence that higher educational attainment decreases smoking and that there is a bi-directional, increasing relationship between smoking and (symptoms of) mental disorders. Another robust finding was that higher educational attainment increases alcohol use frequency, but decreases binge-drinking and alcohol use problems, and that mental disorders causally lead to more alcohol drinking without evidence for the reverse.

CONCLUSIONS

The current MR literature increases our understanding of the relationship between mental health and substance use. Bi-directional causal relationships are indicated, especially for smoking, providing further incentive to strengthen public health efforts to decrease substance use. Future MR studies should make use of large(r) samples in combination with detailed phenotypes, a wide range of sensitivity methods, and triangulate with other research methods.

Smoking and the risk for bipolar disorder: evidence from a bidirectional Mendelian randomisation study

BACKGROUND

There is increasing evidence that smoking is a risk factor for severe mental illness, including bipolar disorder. Conversely, patients with bipolar disorder might smoke more (often) as a result of the psychiatric disorder.

AIMS

We conducted a bidirectional Mendelian randomisation (MR) study to investigate the direction and evidence for a causal nature of the relationship between smoking and bipolar disorder.

METHOD

We used publicly available summary statistics from genome-wide association studies on bipolar disorder, smoking initiation, smoking heaviness, smoking cessation and lifetime smoking (i.e. a compound measure of heaviness, duration and cessation). We applied analytical methods with different, orthogonal assumptions to triangulate results, including inverse-variance weighted (IVW), MR-Egger, MR-Egger SIMEX, weighted-median, weighted-mode and Steiger-filtered analyses.

RESULTS

Across different methods of MR, consistent evidence was found for a positive effect of smoking on the odds of bipolar disorder (smoking initiation ORIVW = 1.46, 95% CI 1.28-1.66, P = 1.44 × 10-8, lifetime smoking ORIVW = 1.72, 95% CI 1.29-2.28, P = 1.8 × 10-4). The MR analyses of the effect of liability to bipolar disorder on smoking provided no clear evidence of a strong causal effect (smoking heaviness betaIVW = 0.028, 95% CI 0.003-0.053, P = 2.9 × 10-2).

CONCLUSIONS

These findings suggest that smoking initiation and lifetime smoking are likely to be a causal risk factor for developing bipolar disorder. We found some evidence that liability to bipolar disorder increased smoking heaviness. Given that smoking is a modifiable risk factor, these findings further support investment into smoking prevention and treatment in order to reduce mental health problems in future generations.

Nicotine treatment buffers negative behavioral consequences induced by exposure to physical and emotional stress in adolescent male mice

Early life stress influences adult psychopathology and is associated with an increase in the propensity for drug use/seeking throughout the lifespan. Animal models corroborate that stress exposure exacerbates maladaptive reactivity to stressful stimuli while also shifting the rewarding properties of many drugs of abuse, including nicotine (NIC), a stimulant commonly misused by adolescents. Interestingly, NIC treatment can also normalize some stress-induced behavioral deficits in adult rodents; however, little is known about NIC's therapeutic efficacy following stress experienced during adolescence. The goal of the following experiments was to elucidate NIC's ability to buffer the negative consequences of stress exposure, and to further assess behavioral responsivity while on the drug. Given that stress often occurs in both physical and non-physical forms, we employed the vicarious social defeat stress (VSDS) model which allows for investigation of both physical (PS) and emotional stress (ES) exposure. After 10 days, exposure to PS and ES decreased interaction with a social target in the social interaction test (SIT), confirming social avoidance. Groups were further divided and given NIC (0.0 or 160 mg/L) in their drinking water. After 1 month of NIC consumption, the mice were exposed to the SIT, elevated plus maze (EPM), and the forced swim test (FST), respectively. NIC-treated mice showed a reversal of stress-induced deficits in the EPM and FST. Surprisingly, the mice did not show improvement in the SIT regardless of treatment condition. Together, these data confirm NIC's ability to normalize some stress-induced behavioral deficits; however, NIC's effects on social behavior need further investigation.

Direct administration of ifenprodil and citalopram into the nucleus accumbens inhibits cue-induced nicotine seeking and associated glutamatergic plasticity

Nicotine use disorder has been associated with glutamatergic alterations within the basal ganglia that might contribute to relapse. Specifically, initiation of cue-induced nicotine seeking produces rapid, transient synaptic potentiation (t-SP) in nucleus accumbens core (NAcore) medium spiny neurons (MSNs), defined as increases in spine head diameter and AMPA to NMDA current ratios (A/N). Ifenprodil, which inhibits nicotine reinstatement when administered systemically, antagonizes GluN2B-containing NMDA receptors, has affinity for serotonin receptors, and blocks serotonin transporters (SERT). The mechanisms underlying its therapeutic efficacy, however, remain unknown. Using pharmacological and genetic approaches, the current study examined the role of NAcore GluN2B receptors as well as SERT in mediating cue-induced nicotine seeking and associated MSN structure and physiology. Prior to reinstatement, rats received intra-NAcore injections of either ifenprodil, citalopram or artificial cerebral spinal fluid (15 min prior), or GluN2B or control siRNAs (3 consecutive days prior). Rats were sacrificed after a 15-min cue-induced reinstatement session for dendritic spine analysis, western blotting or whole-cell electrophysiology. Intra-NAcore ifenprodil blocked nicotine-seeking behavior and promoted a higher frequency of shorter spines on MSN dendrites. However, a decrease in membrane-bound GluN2B receptor expression did not prevent cue-induced nicotine seeking or associated MSN cell physiology. Interestingly, intra-NAcore citalopram, an SSRI, prevented cue-induced nicotine seeking. Together, these results indicate that the therapeutic effects of ifenprodil on cue-induced nicotine seeking may, in part, be due to its actions at SERT rather than GluN2B, which may be specific to nicotine-seeking as opposed to other drugs of abuse.

A qualitative study exploring women's journeys to becoming smokers in the social context of urban India

In India, the prevalence of smoking among women is increasing, and the reasons behind this are unclear. We aimed to study the factors leading to initiation and maintenance of the smoking habit in women in Pune, India. Twenty-seven urban women smokers, ranging from 21 to 60 years of age (31.96 ± 10.70 years), were interviewed between September 2015 and February 2016. The in-depth interviews consisted of questions on pre-decided categories, including initiation, motivation to continue smoking, and risk perception. Thematic analysis revealed that peer pressure, curiosity, fascination, experimentation, and belonging to a group were factors that led to initiation, while lack of alternatives for stress relief, work environments, and lack of leisure time activities provided circumstances to continue smoking. Participants recognized a sense of liberation and independence from smoking cigarettes and perceived health risks as minor and distant. These findings can be used to develop or modify interventions to prevent and control smoking among urban Indian women.

Cigarette smoking and depression comorbidity: systematic review and proposed theoretical model

BACKGROUND AND AIMS

Despite decades of research on co-occurring smoking and depression, cessation rates remain consistently lower for depressed smokers than for smokers in the general population, highlighting the need for theory-driven models of smoking and depression. This paper provides a systematic review with a particular focus upon psychological states that disproportionately motivate smoking in depression, and frame an incentive learning theory account of smoking-depression co-occurrence.

METHODS

We searched PubMed, Scopus, PsychINFO and CINAHL to December 2014, which yielded 852 papers. Using pre-established eligibility criteria, we identified papers focused on clinical issues and motivational mechanisms underlying smoking in established, adult smokers (i.e. maintenance, quit attempts and cessation/relapse) with elevated symptoms of depression. Two reviewers determined independently whether papers met review criteria. We included 297 papers in qualitative synthesis.

RESULTS

Our review identified three primary mechanisms that underlie persistent smoking among depressed smokers: low positive affect, high negative affect and cognitive impairment. We propose a novel application of incentive learning theory which posits that depressed smokers experience greater increases in the expected value of smoking in the face of these three motivational states, which promotes goal-directed choice of smoking behavior over alternative actions.

CONCLUSIONS

The incentive learning theory accounts for current evidence on how depression primes smoking behavior and provides a unique framework for conceptualizing psychological mechanisms of smoking maintenance among depressed smokers. Treatment should focus upon correcting adverse internal states and beliefs about the high value of smoking in those states to improve cessation outcomes for depressed smokers.

Evaluation of the Nicotinic Acetylcholine Receptor-Associated Proteome at Baseline and Following Nicotine Exposure in Human and Mouse Cortex

Nicotinic acetylcholine receptors (nAChRs) support the initiation and maintenance of smoking, but the long-term changes occurring in the protein complex as a result of smoking and the nicotine in tobacco are not known. Human studies and animal models have also demonstrated that increasing cholinergic tone increases behaviors related to depression, suggesting that the nAChR-associated proteome could be altered in individuals with mood disorders. We therefore immunopurified nAChRs and associated proteins for quantitative proteomic assessment of changes in protein–protein interactions of high-affinity nAChRs containing the β2 subunit (β2*-nAChRs) from either cortex of mice treated with saline or nicotine, or postmortem human temporal cortex tissue from tobacco-exposed and nonexposed individuals, with a further comparison of diagnosed mood disorder to control subjects. We observed significant effects of nicotine exposure on the β2*-nAChR-associated proteome in human and mouse cortex, particularly in the abundance of the nAChR subunits themselves, as well as putative interacting proteins that make up core components of neuronal excitability (Na/K ATPase subunits), presynaptic neurotransmitter release (syntaxins, SNAP25, synaptotagmin), and a member of a known nAChR protein chaperone family (14-3-3ζ). These findings identify candidate-signaling proteins that could mediate changes in cholinergic signaling via nicotine or tobacco use. Further analysis of identified proteins will determine whether these interactions are essential for primary function of nAChRs at presynaptic terminals. The identification of differences in the nAChR-associated proteome and downstream signaling in subjects with various mood disorders may also identify novel etiological mechanisms and reveal new treatment targets.

Replication of the association between CHRNA4 rs1044396 and harm avoidance in a large population-based sample

Harm avoidance is a personality trait characterized by excessive worrying and fear of uncertainty, which has repeatedly been related to anxiety disorders. Converging lines of research in rodents and humans point towards an involvement of the nicotinic cholinergic system in the modulation of anxiety. Most notably, the rs1044396 polymorphism in the CHRNA4 gene, which codes for the α4 subunit of the nicotinic acetylcholine receptor, has been linked to negative emotionality traits including harm avoidance in a recent study. Against this background, we investigated the association between harm avoidance and the rs1044396 polymorphism using data from N=1673 healthy subjects, which were collected in the context of the German multi-centre study ׳Genetics of Nicotine Dependence and Neurobiological Phenotypes׳. Homozygous carriers of the C-allele showed significantly higher levels of harm avoidance than homozygous T-allele carriers, with heterozygous subjects exhibiting intermediate scores. The effect was neither modulated by age or gender nor by smoking status. By replicating previous findings in a large population-based sample for the first time, the present study adds to the growing evidence suggesting an involvement of nicotinic cholinergic mechanism in anxiety and negative emotionality, which may pose an effective target for medical treatment.

Variations of depression treatment among women with hypertension

The objective was to examine depression treatment among non-pregnant women, aged 22 and older, with hypertension, utilizing cross-sectional data from the 2006 and 2007 Medical Expenditure Panel Survey. Depression treatment patterns by demographic, socioeconomic, health care access, and health characteristics were analyzed utilizing chi-square tests and logistic and multinomial logistic regressions. Overall, 23.9% had no depression treatment, 56.8% had antidepressant use only, and 19.3% had psychotherapy with or without antidepressants. African Americans (adjusted odds ratio [AOR] = 0.47), Latinas (AOR = 0.46), and uninsured women (AOR = 0.39) were significantly less likely to report any treatment for depression compared with Whites and those with private insurance.

Mood and anxiety regulation by nicotinic acetylcholine receptors: A potential pathway to modulate aggression and related behavioral states

The co-morbidity between smoking and mood disorders is striking. Preclinical and clinical studies of nicotinic effects on mood, anxiety, aggression, and related behaviors, such as irritability and agitation, suggest that smokers may use the nicotine in tobacco products as an attempt to self-medicate symptoms of affective disorders. The role of nicotinic acetylcholine receptors (nAChRs) in circuits regulating mood and anxiety is beginning to be elucidated in animal models, but the mechanisms underlying the effects of nicotine on aggression-related behavioral states (ARBS) are still not understood. Clinical trials of nicotine or nicotinic medications for neurological and psychiatric disorders have often found effects of nicotinic medications on ARBS, but few trials have studied these outcomes systematically. Similarly, the increase in ARBS resulting from smoking cessation can be resolved by nicotinic agents, but the effects of nicotinic medications on these types of mental states and behaviors in non-smokers are less well understood. Here we review the literature on the role of nAChRs in regulating mood and anxiety, and subsequently on the closely related construct of ARBS. We suggest avenues for future study to identify how nAChRs and nicotinic agents may play a role in these clinically important areas. This article is part of the Special Issue entitled 'The Nicotinic Acetylcholine Receptor: From Molecular Biology to Cognition'.

Smoking and major depressive disorder in Chinese women

Objective

To investigate the risk factors that contribute to smoking in female patients with major depressive disorder (MDD) and the clinical features in depressed smokers.

Methods

We examined the smoking status and clinical features in 6120 Han Chinese women with MDD (DSM-IV) between 30 and 60 years of age across China. Logistic regression was used to determine the association between clinical features of MDD and smoking status and between risk factors for MDD and smoking status.

Results

Among the recurrent MDD patients there were 216(3.6%) current smokers, 117 (2.0%) former smokers and 333(5.6%) lifetime smokers. Lifetime smokers had a slightly more severe illness, characterized by more episodes, longer duration, more comorbid illness (panic and phobias), with more DSM-IV A criteria and reported more symptoms of fatigue and suicidal ideation or attempts than never smokers. Some known risk factors for MDD were also differentially represented among smokers compared to non-smokers. Smokers reported more stressful life events, were more likely to report childhood sexual abuse, had higher levels of neuroticism and an increased rate of familial MDD. Only neuroticism was significantly related to nicotine dependence.

Conclusions

Although depressed women smokers experience more severe illness, smoking rates remain low in MDD patients. Family history of MDD and environmental factors contribute to lifetime smoking in Chinese women, consistent with the hypothesis that the association of smoking and depression may be caused by common underlying factors.

The effects of prenatal stress on alpha4 beta2 and alpha7 hippocampal nicotinic acetylcholine receptor levels in adult offspring

Prenatal stress in humans is associated with psychiatric problems in offspring such as anxiety, depression, and schizophrenia. These same illnesses are also associated with neuronal nicotinic acetylcholine receptor (nAChR) dysfunction. Despite the known associations between prenatal stress exposure and offspring mental illness, and between mental illness and nAChR dysfunction, it is not known whether prenatal stress exposure impacts neuronal nAChRs. Thus, we tested the hypothesis that maternal stress alters the development of hippocampal alpha4 beta2 (α4β2∗) and alpha7 (α7∗) nicotinic receptor levels in adult offspring. Female Sprague-Dawley rats experienced unpredictable variable stressors two to three times daily during the last week of gestation. At weaning (21 days) the offspring of prenatally stressed (PS) and nonstressed (NS) dams were assigned to same-sex PS or NS groups. In young adulthood (56 days), the brains of offspring were collected and adjacent sections processed for quantitative autoradiography using [125I]-epibatidine (α4β2* nicotinic receptor-selective) and [125I]-α-bungarotoxin (α-BTX; α7* nicotinic receptor-selective) ligands. We found that PS significantly increased hippocampal α4β2* nAChRs of males and females in all subfields analyzed. In contrast, only females showed a trend toward PS-induced increases in α7* nAChRs in the dentate gyrus. Interestingly, NS females displayed a significant left-biased lateralization of α7* nAChRs in the laconosum moleculare of area CA1, whereas PS females did not, suggesting that PS interfered with normal lateralization patterns of α7* nAChRs during development. Taken together, our results suggest that PS impacts the development of hippocampal nAChRs, which may be an important link between PS exposure and risk for neuropsychiatric illness.

Smoking behaviour and mental health disorders--mutual influences and implications for therapy

Tobacco use is strongly associated with a variety of psychiatric disorders. Smokers are more likely than non-smokers to meet current criteria for mental health conditions, such as mood disorders, anxiety disorders and psychosis. Evidence also suggest that smokers with psychiatric disorders may have more difficulty quitting, offering at least a partial explanation for why smoking rates are higher in this population. The mechanisms linking mental health conditions and cigarette smoking are complex and likely differ across each of the various disorders. The most commonly held view is that patients with mental health conditions smoke in an effort to regulate the symptoms associated with their disorder. However some recent evidence suggests that quitting smoking may actually improve mental health symptoms. This is particularly true if the tobacco cessation intervention is integrated into the context of ongoing mental health treatment. In this paper we reviewed and summarized the most relevant knowledge about the relationship between tobacco use and dependence and psychiatric disorders. We also reviewed the most effective smoking cessation strategies available for patients with psychiatric comorbidity and the impact of smoking behavior on psychiatric medication.

Smoking and suicidality in subjects with major depressive disorder: results from the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC)

BACKGROUND

Detailed characteristics of depressive smokers and its association with suicidality were still less investigated. The aim of this study was to delineate characteristics of smokers with major depressive disorder (MDD) and examine the relationship between these characteristics and suicidality using an epidemiologic database, the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC).

METHODS

A total of 5695 subjects with MDD, defined by the DSM-IV criteria, were included in our analysis. Current smokers, former smokers, and lifetime nonsmokers were compared in terms of demographic, clinical characteristics, and functional level. Suicidality, evaluated by history of suicide ideation and attempts while in a low mood was evaluated and compared among the groups.

RESULTS

Current smokers with MDD showed a greater number of DSM-IV symptoms while in acute episodes, a higher rate of alcohol and drug-use disorders, and poorer functional levels than nonsmokers. Previous smokers displayed intermediate characteristics between current smokers and nonsmokers. The logistic regression analysis revealed that both current and former smoking status predicted the risk of having a history of attempted suicide (current smokers: odds ratio 1.62, 95% C.I. 1.42-1.86; former smokers: odds ratio 1.37, 95% C.I. 1.13-1.66) after adjusting for demographic data, a history of subthreshold hypomania, and a lifetime axis II/anxiety/alcohol use/substance-use disorder.

LIMITATIONS

Retrospective, cross-sectional evaluation; suicidality assessed only in the most severe depressive episode.

CONCLUSIONS

The present study corroborates that smokers with MDD showed distinct clinical characteristics, and cigarette smoking can predict attempted suicide in a community representative sample of people with MDD.

The moderating influence of nicotine and smoking on resting-state mood and EEG changes in remitted depressed patients during tryptophan depletion

Comorbidity between depression and tobacco use may reflect self-medication of serotonergically mediated mood dysregulation, which has been associated with aberrant cortical activation and hemispheric asymmetry in patients with major depressive disorders (MDD). This randomized, double-blind study in 28 remitted MDD patients examined the moderating effects of acute nicotine and smoker vs. nonsmoker status on mood and EEG changes accompanying transient reductions in serotonin induced by acute tryptophan depletion (ATD). In smokers, who exhibited greater posterior high alpha power and increased left frontal low alpha power (signs of deactivation) compared to nonsmokers, ATD increased self-ratings of depressed mood and elevated left frontal and right parietal high alpha power (i.e. further cortical deactivation). Smokers were not affected by nicotine administration. In nonsmokers, ATD did not influence depression ratings, but it reduced vigor ratings and increased frontal and posterior theta power; both of which were blocked by acute nicotine. These findings indicate a role for nicotinic receptors in disordered mood.

PPARα regulates cholinergic-driven activity of midbrain dopamine neurons via a novel mechanism involving α7 nicotinic acetylcholine receptors

Ventral tegmental area dopamine neurons control reward-driven learning, and their dysregulation can lead to psychiatric disorders. Tonic and phasic activity of these dopaminergic neurons depends on cholinergic tone and activation of nicotinic acetylcholine receptors (nAChRs), particularly those containing the β2 subunit (β2*-nAChRs). Nuclear peroxisome proliferator-activated receptors type-α (PPARα) tonically regulate β2*-nAChRs and thereby control dopamine neuron firing activity. However, it is unknown how and when PPARα endogenous ligands are synthesized by dopamine cells. Using ex vivo and in vivo electrophysiological techniques combined with biochemical and behavioral analysis, we show that activation of α7-nAChRs increases in the rat VTA both the tyrosine phosphorylation of the β2 subunit of nAChRs and the levels of two PPARα endogenous ligands in a Ca(2+)-dependent manner. Accordingly, in vivo production of endogenous PPARα ligands, triggered by α7-nAChR activation, blocks in rats nicotine-induced increased firing activity of dopamine neurons and displays antidepressant-like properties. These data demonstrate that endogenous PPARα ligands are effectors of α7-nAChRs and that their neuromodulatory properties depend on phosphorylation of β2*-nAChRs on VTA dopamine cells. This reveals an autoinhibitory mechanism aimed at reducing dopamine cell overexcitation engaged during hypercholinergic drive. Our results unveil important physiological functions of nAChR/PPARα signaling in dopamine neurons and how behavioral output can change after modifications of this signaling pathway. Overall, the present study suggests PPARα as new therapeutic targets for disorders associated with unbalanced dopamine-acetylcholine systems.

Association of menstrual phase with smoking behavior, mood and menstrual phase-associated symptoms among young Japanese women smokers

BACKGROUND

Previous studies of the relationship between the menstrual phases and smoking behavior have been problematic, so the association of menstrual phases with smoking behavior and correlations among smoking, psychological and physical conditions in each phase of the menstrual cycle are unclear.

METHODS

To accurately examine the association between menstrual phases and the amount of smoking (number of cigarettes smoked and breath CO concentration), craving of smoking on visual analogue scale (VAS), depression in the Center for Epidemiologic Studies Depression (CES-D) Scale, and menstrual phase-associated symptoms in the Menstrual Distress Questionnaire (MDQ), we improved various methodological issues, specifically, 1) Ovulation was confirmed by measuring the basal body temperature and identifying a urinary luteinizing hormone (LH) surge in two cycles; 2) The menstrual, follicular, and luteal phases were clearly defined for subjects with different menstrual cycles; 3) The breath CO concentration was measured every day. A notice was posted on public bulletin boards to recruit research subjects and twenty-nine young Japanese women smokers aged 19 to 25 years old were analyzed.

RESULTS

The number of cigarettes smoked was greater and the CO concentration was higher in the luteal phase than in the follicular phase. The levels of craving for smoking (VAS), depressiveness (CES-D), and menstrual phase-associated symptoms (MDQ) in the menstrual and luteal phases were higher than those in the follicular phase. The mean score for CES-D was 16 points (the cut-off value in screening for depression) or higher in the menstrual (16.9 ± 8.2) and luteal phases (17.2 ± 8.4).The number of cigarettes smoked and CO concentration were significantly correlated with the levels of craving for smoking, depressiveness, and menstrual phase-associated symptoms in all phases except for MDQ scores in follicular phase. The amount of smoking in the luteal phase was most strongly correlated with these symptoms.

CONCLUSIONS

In the menstrual and luteal phases, young Japanese women smokers increased their amount of smoking and suffered from greater craving for smoking, depressiveness and menstrual phase-associated symptoms. The amount of smoking was correlated with these symptoms, but their cause-effect relationship has not been determined yet.

Neural expression of nicotine's antidepressant properties during tryptophan depletion: an EEG study in healthy volunteers at risk for depression

Nicotine amelioration of serotonergically mediated mood dysregulation may contribute to the comorbidity between cigarette smoking and depression, a disorder which is associated with aberrant activation and hemispheric asymmetry in frontal and posterior cortical regions. This randomized, double-blind study in 20 healthy volunteers with a positive family history of depression examined the effects of transdermal nicotine on mood and EEG changes accompanying transient reductions in serotonin induced by acute tryptophan depletion (ATD). Increased self-ratings of depressed mood and elevation in left frontal high alpha power (decreased activation) were evidenced with ATD (vs. balanced mixture) in participants treated with the placebo but not the nicotine treated group. Nicotine alone increased vigor and posterior high alpha bilaterally, and during ATD it prevented the reduction in left frontal high alpha that was evident in the placebo patch group. These findings indicate that in depression prone individuals, nicotine acts to stabilize the mood lowering and associated frontal functional asymmetry elicited by an acute decrease in brain serotonin.

Racial/ethnic differences in the longitudinal progression of co-occurring negative affect and cigarette use: from adolescence to young adulthood

AIMS

This study examined the longitudinal progression of the co-occurrence of cigarette use and negative affect among the general population of U.S. adolescents and young adults and between racial/ethnic groups.

METHODS

Data for this study consisted of Waves 4, 6, and 8 of the NLSY97 longitudinal study containing a nationally representative sample of U.S. adolescents and young adults. A total of 7979 adolescents (Mean age at Wave 4=17.98, SD=1.44, 49% female) were included in the analyses. To investigate the co-morbidity between negative affect and cigarette use, a latent factor of negative affect and single indicator of cigarette consumption were examined at each wave. A three wave Bivariate Autoregressive Cross-Lagged Effect Model was estimated to test the conjoint trajectory of negative affect and smoking.

RESULTS

For all racial/ethnic groups prior negative affect status influenced future negative affect between waves and prior negative affect was positively related to increases in smoking in subsequent waves. The longitudinal trajectory of negative affect for the three racial/ethnic groups was the same, but racial/ethnic group differences were observed in the strength of the longitudinal relationship between previous and future cigarette use. Specifically, the following racial/ethnic differences were observed, even after controlling for the effect of SES; White young adults were found to exhibit the strongest association between cigarette use in the first two waves, followed by Hispanic individuals and lastly by African Americans. In the last two waves, African American young adults were found to have the strongest association between cigarette use at the latter two waves, followed by White individuals.

CONCLUSIONS

Both negative affect and cigarette consumption influence each other during the transition between late adolescence and young adulthood but the magnitude of the associations between cigarettes use across waves differed between racial/ethnic groups. Implications for prevention and treatment programs include considering both cigarette use and negative affect as two factors that jointly impact each other and that should be targeted simultaneously.

The nicotinic acetylcholine receptor as a target for antidepressant drug development

An important new area of antidepressant drug development involves targeting the nicotinic acetylcholine receptor (nAChR). This receptor, which is distributed widely in regions of the brain associated with depression, is also implicated in other important processes that are relevant to depression, such as stress and inflammation. The two classes of drugs that target nAChRs can be broadly divided into mecamylamine- and cytisine-based compounds. These drugs probably exert their effects via antagonism at α4β2 nAChRs, and strong preclinical data support the antidepressant efficacy of both classes when used in conjunction with other primary antidepressants (e.g., monoamine reuptake inhibitors). Although clinical data remain limited, preliminary results in this area constitute a compelling argument for further evaluation of the nAChR as a target for future antidepressant drug development.

Genetics of smoking and depression

Smoking and depression are significant public health problems with multiple etiological dimensions and outcomes. Although each condition is important by itself, they are important because they often potentiate each other. Consequently, it is also essential to understand the nature their relationship. This representative review focuses on the genetic etiology of the relationship in the context of reviewing first the epidemiology of depression and smoking, and then by exploring behavioral and molecular genetic studies, and other psychiatric and medical comorbidities. At this point, epidemiological evidence for a relationship between depression and smoking/nicotine dependence is compelling. Although behavioral genetic results differ somewhat by gender and in accordance with specific definitions of depression and smoking variables, recent studies show converging evidence for common genetic factors underlying the relationship, often in addition to non-shared environmental factors. The search for underlying genes and genetic mechanisms is at an early stage, but shows promising candidate genes and genetic approaches for future studies.

The combination of depressive symptoms and smoking shorten life expectancy among the aged

BACKGROUND

Depression is a potential risk factor for mortality among the aged and it is also associated with other chronic diseases and unhealthy lifestyles that may also affect mortality. The purpose of this study was to investigate the association between depressive symptoms and mortality, controlling for health, nutritional status, and life-style factors.

METHODS

A cohort of elderly people (N = 167) was followed-up for ten years. Information on socio-demographic characteristics, medical history, smoking, and alcohol consumption was collected. The primary outcome was all-cause mortality; the secondary outcome was cancer-specific mortality. The Geriatric Depression Scale (GDS-15) was used to assess depression. Using a multivariable Cox proportional hazards regression, we examined the association between depressive symptoms and mortality.

RESULTS

Elderly people with depression (scoring above the depression cut-off of 7) had a 53% increased risk of mortality (relative risk (RR) 1.53; 95%CI: 1.05-2.24) compared to non-depressed subjects. The combination of depressive symptoms with smoking was associated with a particularly higher risk of mortality (RR: 2.61; 95%CI: 1.28-5.31), after controlling for potential confounders.

CONCLUSIONS

Depressive symptoms are associated with a significantly increased risk of all-cause mortality. The combination of depressive symptoms and smoking shorten life expectancy among the aged.

Cigarette smoking and its relationship to mood disorder symptoms and co-occurring alcohol and cannabis use disorders following first hospitalization for bipolar disorder

OBJECTIVES

Cigarette smoking is highly prevalent among individuals with bipolar disorder (BD) and may adversely affect symptoms of the disorder, as well as the co-occurrence of other substance use disorders. However, anecdotal reports suggesting that smoking cessation caused a worsening of mood in smokers with BD have raised concerns about quitting. In the present study, we prospectively evaluated the course of BD, alcohol use disorders, and cannabis use disorders in relation to smoking and examined the relationship between smoking abstinence and changes in mood.

METHODS

Participants (N = 161) were adolescents (n=80) and adults (n = 81) with bipolar I disorder who were hospitalized for their initial mixed or manic episode. Participants were followed up to eight years post-hospitalization (median follow-up = 122 weeks) as part of a naturalistic, observational study of the longitudinal course of BD and substance use.

RESULTS

The course of BD symptoms in the 12 months following index hospitalization did not differ by smoking status in either the adolescent or the adult subsample. Among adolescents, smoking was associated with an increased risk of having a cannabis or alcohol use disorder, almost all of which were new-onset disorders, in the year following first hospitalization. Neither adolescents nor adults who were abstinent from smoking for at least two months experienced significant increases in depressive or manic symptoms.

CONCLUSIONS

Although cigarette smoking did not predict a worse course of BD, smoking was associated with an increased risk of developing alcohol and cannabis use disorders in adolescents with BD. Importantly, these data provide no evidence to suggest that abstinence from smoking is associated with worsening symptoms of depression or mania in the short term.

Analysis of detailed phenotype profiles reveals CHRNA5-CHRNA3-CHRNB4 gene cluster association with several nicotine dependence traits

INTRODUCTION

The role of the nicotinic acetylcholine receptor gene cluster on chromosome 15q24-25 in the etiology of nicotine dependence (ND) is still being defined. In this study, we included all 15 tagging single nucleotide polymorphisms (SNPs) within the CHRNA5-CHRNA3-CHRNB4 cluster and tested associations with 30 smoking-related phenotypes.

METHODS

The study sample was ascertained from the Finnish Twin Cohort study. Twin pairs born 1938-1957 and concordant for a history of cigarette smoking were recruited along with their family members (mainly siblings), as part of the Nicotine Addiction Genetics consortium. The study sample consisted of 1,428 individuals (59% males) from 735 families, with mean age 55.6 years.

RESULTS

We detected multiple novel associations for ND. DSM-IV ND symptoms associated significantly with the proxy SNP Locus 1 (rs2036527, p = .000009) and Locus 2 (rs578776, p = .0001) and tolerance factor of the Nicotine Dependence Syndrome Scale (NDSS) showed suggestive association to rs11636753 (p = .0059), rs11634351 (p = .0069), and rs1948 (p = .0071) in CHRNB4. Furthermore, we report significant association with DSM-IV ND diagnosis (rs2036527, p = .0003) for the first time in a Caucasian population. Several SNPs indicated suggestive association for traits related to ages at smoking initiation. Also, rs11636753 in CHRNB4 showed suggestive association with regular drinking (p = .0029) and the comorbidity of depression and ND (p = .0034).

CONCLUSIONS

We demonstrate novel associations of DSM-IV ND symptoms and the NDSS tolerance subscale. Our results confirm and extend association findings for other ND measures. We show pleiotropic effects of this gene cluster on multiple measures of ND and also regular drinking and the comorbidity of ND and depression.

α4β2 nicotinic acetylcholine receptor partial agonists with low intrinsic efficacy have antidepressant-like properties

Previous studies have suggested that treatment with antagonists or partial agonists of nicotinic acetylcholine receptors containing the β2-subunit (β2 nAChRs) results in antidepressant-like effects. In this study, we tested three novel compounds with different affinity and functional efficacy at α4β2 nAChRs, which were synthesized as part of nAChR discovery projects at Pfizer, in the tail-suspension, forced-swim, and novelty-suppressed feeding tests of antidepressant efficacy. All compounds tested reduced immobility in the forced-swim test and one of the compounds also reduced immobility in the tail-suspension test. All the compounds appeared to affect food intake on their own, with two compounds reducing feeding significantly in the home cage, precluding a clear interpretation of the results in the novelty-suppressed feeding test. None of the compounds altered locomotor activity at the doses and time points used here. Therefore, a subset of these compounds has pharmacological and behavioral properties that demonstrate the potential of nicotinic compounds as a treatment of mood disorders. Further development of nicotinic-based antidepressants should focus on increasing nAChR subtype selectivity to obtain consistent antidepressant properties with an acceptable side-effect profile.

Anxiety, depression and methods of stress coping in patients with nicotine dependence syndrome

BACKGROUND

Nicotinism is the most common addiction in Poland. Nicotine dependence is the cause of numerous behavioral diseases, including ischemic heart disease, neoplasms and chronic obstructive pulmonary disease. A question arises whether a tendency to anxiety and depressive reactions, as well as the strategies of coping with stressful situations, is involved in the clinical presentation of this addiction.

MATERIAL/METHODS

The study was conducted in a group of 88 nicotine addicts without serious systemic comorbidities and in 84 healthy subjects. All the participants were assessed with Beck Depression Inventory (BDI), Spielberger State-Trait Anxiety Inventory (STAI) and the Coping Inventory for Stressful Situations (CISS).

RESULTS

The mean intensity of anxiety as a trait and anxiety as a state, as well as its level, were found to differ between the groups (Sten 6.28±1.52 and 4.86±1.05, p=0,0000 for the trait, and 6.09±1.25 and 4.92±1.29, p=0.0000, for the state, respectively). Similarly, depression was demonstrated to be more intensive in nicotine addicts than in healthy subjects (12.76 points ±4.77 vs. 10.76±4.83, p=0.007). Among the 5 scales assessed by CISS, smokers demonstrated higher prevalence of emotion-oriented coping than controls (standard 9 6.27±1.70 in smokers vs. 5.67±1.57, p=0.019) and involvement in distracting activities (5.84±1.48 vs. 5.28±1.46, p=0.014).

CONCLUSIONS

The obtained results indicate that anxiety and depression, as well as differences in coping with stress situations, distinguish nicotine addicts from non-smokers.

Electrophysiological perspectives on the therapeutic use of nicotinic acetylcholine receptor partial agonists

Partial agonist therapies rely variously on two hypotheses: the partial agonists have their effects through chronic low-level receptor activation or the partial agonists work by decreasing the effects of endogenous or exogenous full agonists. The relative significance of these activities probably depends on whether acute or chronic effects are considered. We studied nicotinic acetylcholine receptors (nAChRs) expressed in Xenopus laevis oocytes to test a model for the acute interactions between acetylcholine (ACh) and weak partial agonists. Data were best-fit to a basic competition model that included an additional factor for noncompetitive inhibition. Partial agonist effects were compared with the nAChR antagonist bupropion in prolonged bath application experiments that were designed to mimic prolonged drug exposure typical of therapeutic drug delivery. A primary effect of prolonged application of nicotine was to decrease the response of all nAChR subtypes to acute applications of ACh. In addition, nicotine, cytisine, and varenicline produced detectable steady-state activation of α4β2* [(α4)(2)(β2)(3), (α4)(3)(β2)(2), and (α4)(2)(β2)(2)α5)] receptor subtypes that was not seen with other test compounds. Partial agonists produced no detectable steady-state activation of α7 nAChR, but seemed to show small potentiation of ACh-evoked responses; however, "run-up" of α7 ACh responses was also sometimes observed under control conditions. Potential off-target effects of the partial agonists therefore included the modulation of α7 responses by α4β2 partial agonists and decreases in α4β2* responses by α7-selective agonists. These data indicate the dual effects expected for α4β2* partial agonists and provide models and insights for utility of partial agonists in therapeutic development.

The co-occurrence of cigarette smoking and bipolar disorder: phenomenology and treatment considerations

OBJECTIVES

  Despite recent advances in understanding the causes and treatment of nicotine dependence among individuals with psychiatric disorders, smoking among individuals with bipolar disorder (BD) has received little attention. The goal of this review is to synthesize the literature on the epidemiology, consequences, and treatment of smoking and nicotine dependence among individuals with BD and to delineate a future research agenda.

METHODS

  We conducted a PubMed search of English-language articles using the search terms bipolar disorder, mania, tobacco, nicotine, and smoking, followed by a manual search of the literature cited in the identified articles. Articles were chosen by the authors on the basis of their relevance to the topic areas covered in this selective review.

RESULTS

  Adults with BD are two to three times more likely to have started smoking and, on the basis of epidemiological data, may be less likely to initiate and/or maintain smoking abstinence than individuals without psychiatric disorders. Smoking cessation is achievable for individuals with BD, but challenges such as chronic mood dysregulation, high prevalence of alcohol and drug use, more severe nicotine dependence, and limited social support can make quitting more difficult. Effective treatments for tobacco cessation are available, but no controlled trials in smokers with BD have been conducted.

CONCLUSIONS

  Cigarette smoking is a prevalent and devastating addiction among individuals with BD and should be addressed by mental health providers. Additional research on the mechanisms of, and optimal treatment for, smoking and nicotine dependence in this population is desperately needed.

Nicotinic acetylcholine receptors and depression: a review of the preclinical and clinical literature

Many patients with depression fail to derive sufficient benefit from available treatment options, with up to a third never reaching remission despite multiple trials of appropriate treatment. Novel antidepressant agents are needed, and drugs targeting nicotinic acetylcholine receptors (nAChRs) appear to hold promise in this regard. nAChRs are involved in a variety of neurobiological systems implicated in the pathophysiology of depression. In addition to their role in cholinergic neurotransmission, they modulate dopamine function and influence inflammation and hypothalamic-pituitary-adrenal axis activity. Preclinical studies have suggested antidepressant-like effects of drugs targeting nAChRs, with the most consistent results observed with alpha4beta2 nAChR modulators such as varenicline and nonspecific nAChR antagonists such as mecamylamine. These agents appear to offer the most potential antidepressant-like efficacy when used in conjunction with other established antidepressant treatments. nAChR modulators also influence neural processes that appear to mediate the behavioral effects of antidepressants, such as hippocampal cell proliferation. Clinical evidence, while limited, shows preliminary efficacy for mecamylamine and varenicline. Taken together, the preclinical and clinical evidence suggests that drugs targeting nAChRs may represent an important new approach to the treatment of depression.