Current smoking and reduced gray matter volume-a voxel-based morphometry study

The anterior hypothalamus in cluster headache

Objective To evaluate the presence, localization, and specificity of structural hypothalamic and whole brain changes in cluster headache and chronic paroxysmal hemicrania (CPH). Methods We compared T1-weighted magnetic resonance images of subjects with cluster headache (episodic n = 24; chronic n = 23; probable n = 14), CPH ( n = 9), migraine (with aura n = 14; without aura n = 19), and no headache ( n = 48). We applied whole brain voxel-based morphometry (VBM) using two complementary methods to analyze structural changes in the hypothalamus: region-of-interest analyses in whole brain VBM, and manual segmentation of the hypothalamus to calculate volumes. We used both conservative VBM thresholds, correcting for multiple comparisons, and less conservative thresholds for exploratory purposes. Results Using region-of-interest VBM analyses mirrored to the headache side, we found enlargement ( p < 0.05, small volume correction) in the anterior hypothalamic gray matter in subjects with chronic cluster headache compared to controls, and in all participants with episodic or chronic cluster headache taken together compared to migraineurs. After manual segmentation, hypothalamic volume (mean±SD) was larger ( p < 0.05) both in subjects with episodic (1.89 ± 0.18 ml) and chronic (1.87 ± 0.21 ml) cluster headache compared to controls (1.72 ± 0.15 ml) and migraineurs (1.68 ± 0.19 ml). Similar but non-significant trends were observed for participants with probable cluster headache (1.82 ± 0.19 ml; p = 0.07) and CPH (1.79 ± 0.20 ml; p = 0.15). Increased hypothalamic volume was primarily explained by bilateral enlargement of the anterior hypothalamus. Exploratory whole brain VBM analyses showed widespread changes in pain-modulating areas in all subjects with headache. Interpretation The anterior hypothalamus is enlarged in episodic and chronic cluster headache and possibly also in probable cluster headache or CPH, but not in migraine.

Chronic cigarette smoking is linked with structural alterations in brain regions showing acute nicotinic drug-induced functional modulations

Background

Whereas acute nicotine administration alters brain function which may, in turn, contribute to enhanced attention and performance, chronic cigarette smoking is linked with regional brain atrophy and poorer cognition. However, results from structural magnetic resonance imaging (MRI) studies comparing smokers versus nonsmokers have been inconsistent and measures of gray matter possess limited ability to inform functional relations or behavioral implications. The purpose of this study was to address these interpretational challenges through meta-analytic techniques in the service of clarifying the impact of chronic smoking on gray matter integrity and more fully contextualizing such structural alterations.

Methods

We first conducted a coordinate-based meta-analysis of structural MRI studies to identify consistent structural alterations associated with chronic smoking. Subsequently, we conducted two additional meta-analytic assessments to enhance insight into potential functional and behavioral relations. Specifically, we performed a multimodal meta-analytic assessment to test the structural–functional hypothesis that smoking-related structural alterations overlapped those same regions showing acute nicotinic drug-induced functional modulations. Finally, we employed database driven tools to identify pairs of structurally impacted regions that were also functionally related via meta-analytic connectivity modeling, and then delineated behavioral phenomena associated with such functional interactions via behavioral decoding.

Results

Across studies, smoking was associated with convergent structural decreases in the left insula, right cerebellum, parahippocampus, multiple prefrontal cortex (PFC) regions, and the thalamus. Indicating a structural–functional relation, we observed that smoking-related gray matter decreases overlapped with the acute functional effects of nicotinic agonist administration in the left insula, ventromedial PFC, and mediodorsal thalamus. Suggesting structural-behavioral implications, we observed that the left insula’s task-based, functional interactions with multiple other structurally impacted regions were linked with pain perception, the right cerebellum’s interactions with other regions were associated with overt body movements, interactions between the parahippocampus and thalamus were linked with memory processes, and interactions between medial PFC regions were associated with face processing.

Conclusions

Collectively, these findings emphasize brain regions (e.g., ventromedial PFC, insula, thalamus) critically linked with cigarette smoking, suggest neuroimaging paradigms warranting additional consideration among smokers (e.g., pain processing), and highlight regions in need of further elucidation in addiction (e.g., cerebellum).

Electronic supplementary material

The online version of this article (doi:10.1186/s12993-016-0100-5) contains supplementary material, which is available to authorized users.

Severity of dependence modulates smokers' functional connectivity in the reward circuit: a preliminary study

RATIONALE

Nicotine dependence is characterized as a neural circuit dysfunction, particularly with regard to the reward circuit. Although dependence severity moderates cue reactivity in the brain regions involved in reward processing, the direction of its influence remains controversial.

OBJECTIVES

Investigating the functional organization of the reward circuit may provide complementary information. Here, we used resting-state functional connectivity (rsFC) to evaluate the integrity of the reward circuit in smokers with different severities of nicotine dependence.

METHODS

Totals of 65 smokers and 37 non-smokers underwent resting-state functional magnetic resonance imaging (fMRI). The smokers were divided into low-dependent (FTND < 5, n = 26) and high-dependent smoker groups (FTND ≥ 5, n = 39) based on their nicotine-dependence severity (as measured by the Fagerström test for nicotine dependence [FTND]). The region of interest (ROI)-wise rsFC within the reward circuit was compared between smokers and non-smokers as well as between low-dependent and high-dependent smokers and then correlated with smokers' FTND scores.

RESULTS

Widespread rsFC attenuation was observed in the reward circuit of smokers compared with non-smokers. Compared with low-dependent smokers, high-dependent smokers showed greater rsFC between the right amygdala and the left nucleus accumbens (NAcc) as well as between the bilateral hippocampus. Furthermore, a positive correlation between the inter-hippocampus rsFC and the severity of nicotine dependence (FTND) was detected among all smokers (r = 0.416, p = 0.001).

CONCLUSIONS

Our results indicate a dysfunction of the reward circuit in nicotine-dependent individuals. Moreover, our study improves the understanding of the neuroplastic changes that occur during the development of nicotine dependence.

Tobacco use is associated with reduced amplitude and intensity dependence of the cortical auditory evoked N1-P2 component

RATIONALE

Tobacco use is linked to cerebral atrophy and reduced cognitive performance in later life. However, smoking-related long-term effects on brain function remain largely uncertain. Previous studies suggest that nicotine affects serotonergic signaling, and the intensity dependence (alias loudness dependence) of the auditory evoked N1-P2 potential has been proposed as a marker of serotonergic neurotransmission.

OBJECTIVE

In the present study, we assesed the effects of chronic smoking on amplitude and intensity dependence of the auditory evoked N1-P2 potential.

METHODS

Subjects underwent a 15-min intensity dependence of auditory evoked potentials (IAEP) paradigm. From N = 1739 eligible subjects (40-79 years), we systematically matched current smokers, ex-smokers, and never-smokers by sex, age, alcohol and caffeine consumption, and socioeconomic status. Between-group differences and potential dose-dependencies were evaluated.

RESULTS

Analyses revealed higher N1-P2 amplitudes and intensity dependencies in never-smokers relative to ex- and current smokers, with ex-smokers exhibiting intermediate intensity dependencies. Moreover, we observed pack years and number of cigarettes consumed per day to be inversely correlated with amplitudes in current smokers.

CONCLUSIONS

According to the IAEP serotonin hypothesis, our results suggest serotonin activity to be highest in current smokers, intermediate in ex-smokers, and lowest in never-smokers. To our knowledge, the present study is the first providing evidence for a dose-dependent reduction in N1-P2 amplitudes. Further, we extend prior research by showing reduced amplitudes and intensity dependencies in ex-smokers even 25 years, on average, after cessation. While we can rule out several smoking-related confounders to bias observed associations, causal inferences remain to be established by future longitudinal studies.

The effects of chronic smoking on the pathology of alcohol-related brain damage

Both pathological and neuroimaging studies demonstrate that chronic alcohol abuse causes brain atrophy with widespread white matter loss limited gray matter loss. Recent neuroimaging studies suggest that tobacco smoking also causes brain atrophy in both alcoholics and neurologically normal individuals; however, this has not been confirmed pathologically. In this study, the effects of smoking and the potential additive effects of concomitant alcohol and tobacco consumption were investigated in autopsied human brains. A total of 44 cases and controls were divided into four groups: 16 non-smoking controls, nine smoking controls, eight non-smoking alcoholics, and 11 smoking alcoholics. The volumes of 26 gray and white matter regions were measured using an established point-counting technique. The results showed trends for widespread white matter loss in alcoholics (p < 0.007) but no effect on gray matter regions. In contrast, smoking alone had no effect on brain atrophy and the combination of smoking and alcohol showed no additional effect. Neuronal density was analyzed as a more sensitive assay of gray matter integrity. Similar to the volumetric analysis, there was a reduction in neurons (29%) in the prefrontal cortex of alcoholics, albeit this was only a trend when adjusted for potential confounders (p < 0.06). There were no smoking or combinatorial effects on neuronal density in any of the three regions examined. These results do not support the hypothesis that smoking exacerbates alcohol-related brain damage. The trends here support previous studies that alcohol-related brain damage is characterized by focal neuronal loss and generalized white matter atrophy. These disparate effects suggest that two different pathogenic mechanisms may be operating in the alcoholic brain. Future studies using ultrastructural or molecular techniques will be required to determine if smoking has more subtle effects on the brain and how chronic alcohol consumption leads to widespread white matter loss.

Brain Anatomy in Latino Farmworkers Exposed to Pesticides and Nicotine

OBJECTIVE

Migrant tobacco farmworkers experience regular occupational exposure to pesticides and nicotine. The present study was designed to determine whether there are differences in brain anatomy between Latino farmworkers and non-farmworkers.

METHODS

Magnetic resonance brain images were compared between farmworkers and non-farmworkers. In addition, blood cholinesterase activity and urinary cotinine levels were also used to identify associations with pesticide and nicotine exposure.

RESULTS

Farmworkers had greater gray matter signal in putamen and cerebellum, and lower gray matter signal in frontal and temporal lobes. Urinary cotinine was associated with the observed differences in brain anatomy, but blood cholinesterase activity was not.

CONCLUSIONS

Nicotine exposure was associated with neuroanatomical differences between Latino farmworkers and non-farmworkers. Future studies are needed to differentiate iron deposition from brain atrophy and to further assess the potential role of nicotine and pesticide exposure.

Voxelwise meta-analysis of gray matter anomalies in chronic cigarette smokers

BACKGROUND

Evidence from previous voxel-based morphometry (VBM) studies revealed that widespread brain regions are involved in chronic smoking. However, the spatial localization reported for gray matter (GM) abnormalities is heterogeneous. The aim of the present study was quantitatively to integrate studies on GM abnormalities observed in chronic smokers.

METHODS

A systematic search of the PubMed, Web of Knowledge and Science Direct databases from January 1, 2000 to July 31, 2015 was performed to identify eligible whole-brain VBM studies. Comprehensive meta-analyses to investigate regional GM abnormalities in chronic smokers were conducted with the Seed-based d Mapping software package.

RESULTS

Eleven studies comprising 686 chronic cigarette smokers and 1024 nonsmokers were included in the meta-analyses. Consistently across studies, the chronic smokers showed a robust GM decrease in the bilateral prefrontal cortex and a GM increase in the right lingual cortex. Moreover, meta-regression demonstrated that smoking years and cigarettes per day were partly correlated with GM anomalies in chronic cigarette smokers.

CONCLUSIONS

The convergent findings of this quantitative meta-analysis reveal a characteristic neuroanatomical pattern in chronic smokers. Future longitudinal studies should investigate whether this brain morphometric pattern can serve as a useful target and a prognostic marker for smoking intervention.

Comparative Analysis of Lipid Extracts and Imaging Mass Spectrometry for Evaluating Cerebral White Matter Biochemical Pathology in an Experimental Second-Hand Cigarette Smoke Exposure Model

Background

White matter injury and degeneration are common features of developmental and aging-associated diseases, yet their pathobiological bases are poorly understood. However, recent advances in Matrix-Assisted Laser Desorption Ionization (MALDI) instruments and chemistry have provided critical tools for myelin-lipid analytical research.

Design

This study characterizes Cigarette Smoke (CS) exposure effects on frontal lobe lipid ion profiles in adult male A/J mice that had been exposed to air for 8 weeks (A8), CS for 4 (CS4) or 8 weeks (CS8), or CS8 followed by 2 weeks recovery (CS8+R). MALDI data acquired by analysis of lipid extracts plated onto a ground steel target (high through-put) were compared with Imaging Mass Spectrometry (IMS).

Results

MALDI-time-of-flight (TOF) detected 120 lipid ions with m/z’s of 600 to 1300 (phospholipids and sulfatides) in samples plated onto the steel target or analyzed by IMS, but just 25 ions (18%) were detected by both methods. IMS more effectively detected ions in the highest m/z range, whereas the extracts had abundant middle-range m/z ions. The experimental groups were better discriminated by PCA and R-generated heat map hierarchical clustering of IMS data than lipid extract data. On the other hand, both methods clearly delineated the CS4, CS8 and CS8+R experimental groups from control.

Conclusions

MALDI analysis of brain lipid extracts plated onto a ground steel target for high through-put studies, or imaged directly in tissue can be used to assess biochemical pathology of white matter neurodegeneration and responses to treatment.

Tobacco nitrosamines as culprits in disease: mechanisms reviewed

The link between tobacco abuse and cancer is well-established. However, emerging data indicate that toxins in tobacco smoke cause cellular injury due to enhanced toxic/metabolic effects of metabolites, disruption of intracellular signaling mechanisms, and formation of DNA, protein, and lipid adducts that impair function and promote oxidative stress and inflammation. These effects of smoking, which are largely non-carcinogenic, can be produced by tobacco-specific nitrosamines and their metabolites. These factors could account for the increased rates of neurodegeneration and insulin resistance diseases among smokers. Herein, we review nicotine and tobacco-specific nitrosamine metabolism, mechanisms of adduct formation, DNA damage, mutagenesis, and potential mechanisms of disease.

Altered Spontaneous Brain Activity in Betel Quid Dependence: A Resting-state Functional Magnetic Resonance Imaging Study

It has been suggested by the first voxel-based morphometry investigation that betel quid dependence (BQD) individuals are presented with brain structural changes in previous reports, and there may be a neurobiological basis for BQD individuals related to an increased risk of executive dysfunction and disinhibition, subjected to the reward system, cognitive system, and emotion system. However, the effects of BQD on neural activity remain largely unknown. Individuals with impaired cognitive control of behavior often reveal altered spontaneous cerebral activity in resting-state functional magnetic resonance imaging and those changes are usually earlier than structural alteration.Here, we examined BQD individuals (n = 33) and age-, sex-, and education-matched healthy control participants (n = 32) in an resting-state functional magnetic resonance imaging study to observe brain function alterations associated with the severity of BQD. Amplitude of low-frequency fluctuation (ALFF) and regional homogeneity (ReHo) values were both evaluated to stand for spontaneous cerebral activity. Gray matter volumes of these participants were also calculated for covariate.In comparison with healthy controls, BQD individuals demonstrated dramatically decreased ALFF and ReHo values in the prefrontal gurus along with left fusiform, and increased ALFF and ReHo values in the primary motor cortex area, temporal lobe as well as some regions of occipital lobe. The betel quid dependence scores (BQDS) were negatively related to decreased activity in the right anterior cingulate.The abnormal spontaneous cerebral activity revealed by ALFF and ReHo calculation excluding the structural differences in patients with BQD may help us probe into the neurological pathophysiology underlying BQD-related executive dysfunction and disinhibition. Diminished spontaneous brain activity in the right anterior cingulate cortex may, therefore, represent a biomarker of BQD individuals.

Effect of the interaction between childhood abuse and rs1360780 of the FKBP5 gene on gray matter volume in a general population sample

OBJECTIVE

The FKBP5 gene codes for a co-chaperone that regulates glucocorticoid receptor sensitivity and thereby impacts the reactivity of the hypothalamic-pituitary-adrenal (HPA)-axis. Evidence suggested that subjects exposed to childhood abuse and carrying the TT genotype of the FKBP5 gene single nucleotide polymorphism (SNP) rs1360780 have an increased susceptibility to stress-related disorders.

METHOD

The hypothesis that abused TT genotype carriers show changes in gray matter (GM) volumes in affect-processing brain areas was investigated. About 1,826 Caucasian subjects (age ≤ 65 years) from the general population [Study of Health in Pomerania (SHIP)] in Germany were investigated. The interaction between rs1360780 and child abuse (Childhood Trauma Questionnaire) and its effect on GM were analyzed.

RESULTS

Voxel-based whole-brain interaction analysis revealed three large clusters (FWE-corrected) of reduced GM volumes comprising the bilateral insula, the superior and middle temporal gyrus, the bilateral hippocampus, the right amygdala, and the bilateral anterior cingulate cortex in abused TT carriers. These results were not confounded by major depressive disorders. In region of interest analyses, highly significant volume reductions in the right hippocampus/parahippocampus, the bilateral anterior and middle cingulate cortex, the insula, and the amygdala were confirmed in abused TT carriers compared with abused CT/CC carriers.

CONCLUSION

The results supported the hypothesis that the FKBP5 rs1360780 TT genotype predisposes subjects who have experienced childhood abuse to widespread structural brain changes in the subcortical and cortical emotion-processing brain areas. Those brain changes might contribute to an increased vulnerability of stress-related disorders in TT genotype carriers.

Cigarette Smoke-Induced Alterations in Frontal White Matter Lipid Profiles Demonstrated by MALDI-Imaging Mass Spectrometry: Relevance to Alzheimer's Disease

BACKGROUND

Meta-analysis has shown that smokers have significantly increased risks for Alzheimer's disease (AD), and neuroimaging studies showed that smoking alters white matter (WM) structural integrity.

OBJECTIVE

Herein, we characterize the effects of cigarette smoke (CS) exposures and withdrawal on WM myelin lipid composition using matrix assisted laser desorption and ionization-imaging mass spectrometry (MALDI-IMS).

METHODS

Young adult male A/J mice were exposed to air (8 weeks; A8), CS (4 or 8 weeks; CS4, CS8), or CS8 followed by 2 weeks recovery (CS8 + R). Frontal lobe WM was examined for indices of lipid and protein oxidation and lipid profile alterations by MALDI-IMS. Lipid ions were identified by MS/MS with the LIPID MAPS prediction tools database. Inter-group comparisons were made using principal component analysis and R-generated heatmap.

RESULTS

CS increased lipid and protein adducts such that higher levels were present in CS8 compared with CS4 samples. CS8 + R reversed CS8 effects and normalized the levels of oxidative stress. MALDI-IMS demonstrated striking CS-associated alterations in WM lipid profiles characterized by either reductions or increases in phospholipids (phosphatidylinositol, phosphatidylserine, phosphatidylcholine, or phosphatidylethanolamine) and sphingolipids (sulfatides), and partial reversal of CS's inhibitory effects with recovery. The heatmap hierarchical dendrogram and PCA distinguished CS exposure, duration, and withdrawal effects on WM lipid profiles.

CONCLUSION

CS-mediated WM degeneration is associated with lipid peroxidation, protein oxidative injury, and alterations in myelin lipid composition, including shifts in phospholipids and sphingolipids needed for membrane integrity, plasticity, and intracellular signaling. Future goals are to delineate WM abnormalities in AD using MALDI-IMS, and couple the findings with MRI-mass spectroscopy to improve in vivo diagnostics and early detection of brain biochemical responses to treatment.

Sex Effects on Smoking Cue Perception in Non-Smokers, Smokers, and Ex-Smokers: A Pilot Study

INTRODUCTION

Recent neuroimaging research suggests sex-related brain differences in smoking addiction. In the present pilot study, we assessed gender-related differences in brain activation in response to cigarette-related video cues, investigating non-smokers, smokers, and ex-smokers.

METHODS

First, we compared 29 females (28.6 ± 5.3) vs. 23 males (31.5 ± 6.4), regardless of current smoking status to assess global gender-related effects. Second, we performed a post hoc analysis of non-smokers (9 females and 8 males), smokers (10 females and 8 males), and ex-smokers (10 females and 7 males). Participants performed a block-design functional magnetic resonance imaging paradigm contrasting smoking with control cue video exposures. Data analyses included task-related general linear model, voxel-based morphometry of gray matter (GM), and tract-based spatial statistics of white matter (WM).

RESULTS

First, the global effect regardless of current smoking status revealed higher activation in the bilateral superior frontal gyrus and anterior cingulate cortex (ACC) for females compared to males. Second, the analysis according to current smoking status demonstrated higher activation in female vs. male smokers vs. non-smokers in the superior frontal gyrus, anterior and posterior cingulate cortex, and precuneus, and higher activation in female vs. male ex-smokers vs. non-smokers in the right precentral gyrus, in the right insula and ACC. No structural differences were found in GM or WM.

CONCLUSION

The current study identifies gender-related brain functional differences in smokers and ex-smokers compared to non-smokers. The current work can be considered as a starting point for future investigations into gender differences in brain responses to cigarette-related cues.

Tobacco Smoke-Induced Brain White Matter Myelin Dysfunction: Potential Co-Factor Role of Smoking in Neurodegeneration

BACKGROUND

Meta-analysis studies showed that smokers have increased risk for developing Alzheimer's disease (AD) compared with non-smokers, and neuroimaging studies revealed that smoking damages white matter structural integrity.

OBJECTIVE

The present study characterizes the effects of side-stream (second hand) cigarette smoke (CS) exposures on the expression of genes that regulate oligodendrocyte myelin-synthesis, maturation, and maintenance and neuroglial functions.

METHODS

Adult male A/J mice were exposed to air (8 weeks; A8), CS (4 or 8 weeks; CS4, CS8), or CS8 followed by 2 weeks recovery (CS8 + R). The frontal lobes were used for histology and qRT-PCR analysis.

RESULTS

Luxol fast blue, Hematoxylin and Eosin stained histological sections revealed CS-associated reductions in myelin staining intensity and narrowing of the corpus callosum. CS exposures broadly decreased mRNA levels of immature and mature oligodendrocyte myelin-associated, neuroglial, and oligodendrocyte-related transcription factors. These effects were more prominent in the CS8 compared with CS4 group, suggesting that molecular abnormalities linked to white matter atrophy and myelin loss worsen with duration of CS exposure. Recovery normalized or upregulated less than 25% of the suppressed genes; in most cases, inhibition of gene expression was either sustained or exacerbated.

CONCLUSION

CS exposures broadly inhibit expression of genes needed for myelin synthesis and maintenance. These adverse effects often were not reversed by short-term CS withdrawal. The results support the hypothesis that smoking contributes to white matter degeneration, and therefore could be a key risk factor for a number of neurodegenerative diseases, including AD.

Cigarette smoking leads to persistent and dose-dependent alterations of brain activity and connectivity in anterior insula and anterior cingulate

Although many smokers try to quit smoking, only about 20-25 percent will achieve abstinence despite 6 months or more of gold-standard treatment. This low success rate suggests long-term changes in the brain related to smoking, which remain poorly understood. We compared ex-smokers to both active smokers and non-smokers using functional magnetic resonance imaging (fMRI) to explore persistent modifications in brain activity and network organization. This prospective and consecutive study includes 18 non-smokers (29.5 ± 6.7 years of age, 11 women), 14 smokers (≥10 cigarettes a day >2 years of smoking, 29.3 ± 6.0 years of age, 10 women) and 14 ex-smokers (>1 year of quitting 30.5 ± 5.7 years of age, 10 women). Participants underwent a block-design fMRI study contrasting smoking cue with control (neutral cue) videos. Data analyses included task-related general linear model, seed-based functional connectivity, voxel-based morphometry (VBM) of gray matter and tract-based spatial statistics (TBSS) of white matter. Smoking cue videos versus control videos activated the right anterior insula in ex-smokers compared with smokers, an effect correlating with cumulative nicotine intake (pack-years). Moreover, ex-smokers had a persistent decrease in functional connectivity between right anterior insula and anterior cingulate cortex (ACC) compared with control participants, but similar to active smokers. Potentially confounding alterations in gray or white matter were excluded in VBM and TBSS analyses. In summary, ex-smokers with long-term nicotine abstinence have persistent and dose-dependent brain network changes notably in the right anterior insula and its connection to the ACC.

Multivariate classification of smokers and nonsmokers using SVM-RFE on structural MRI images

Voxel-based morphometry (VBM) studies have revealed gray matter alterations in smokers, but this type of analysis has poor predictive value for individual cases, which limits its applicability in clinical diagnoses and treatment. A predictive model would essentially embody a complex biomarker that could be used to evaluate treatment efficacy. In this study, we applied VBM along with a multivariate classification method consisting of a support vector machine with recursive feature elimination to discriminate smokers from nonsmokers using their structural MRI data. Mean gray matter volumes in 1,024 cerebral cortical regions of interest created using a subparcellated version of the Automated Anatomical Labeling template were calculated from 60 smokers and 60 nonsmokers, and served as input features to the classification procedure. The classifier achieved the highest accuracy of 69.6% when taking the 139 highest ranked features via 10-fold cross-validation. Critically, these features were later validated on an independent testing set that consisted of 28 smokers and 28 nonsmokers, yielding a 64.04% accuracy level (binomial P = 0.01). Following classification, exploratory post hoc regression analyses were performed, which revealed that gray matter volumes in the putamen, hippocampus, prefrontal cortex, cingulate cortex, caudate, thalamus, pre-/postcentral gyrus, precuneus, and the parahippocampal gyrus, were inversely related to smoking behavioral characteristics. These results not only indicate that smoking related gray matter alterations can provide predictive power for group membership, but also suggest that machine learning techniques can reveal underlying smoking-related neurobiology.

Differential Contributions of Alcohol and Nicotine-Derived Nitrosamine Ketone (NNK) to White Matter Pathology in the Adolescent Rat Brain

AIM

Epidemiologic studies have demonstrated high rates of smoking among alcoholics, and neuroimaging studies have detected white matter atrophy and degeneration in both smokers and individuals with alcohol-related brain disease (ARBD). These findings suggest that tobacco smoke exposure may be a co-factor in ARBD. The present study examines the differential and additive effects of tobacco-specific nitrosamine (NNK) and ethanol exposures on the structural and functional integrity of white matter in an experimental model.

METHODS

Adolescent Long Evans rats were fed liquid diets containing 0 or 26% ethanol for 8 weeks. In weeks 3-8, rats were treated with nicotine-derived nitrosamine ketone (NNK) (2 mg/kg, 3×/week) or saline by i.p. injection. In weeks 7-8, the ethanol group was binge-administered ethanol (2 g/kg; 3×/week).

RESULTS

Ethanol, NNK and ethanol + NNK caused striking degenerative abnormalities in white matter myelin and axons, with accompanying reductions in myelin-associated glycoprotein expression. Quantitative RT-PCR targeted array and heatmap analyses demonstrated that ethanol modestly increased, whereas ethanol + NNK sharply increased expression of immature and mature oligodendroglial genes, and that NNK increased immature but inhibited mature oligodendroglial genes. In addition, NNK modulated expression of neuroglial genes in favor of growth cone collapse and synaptic disconnection. Ethanol- and NNK-associated increases in FOXO1, FOXO4 and NKX2-2 transcription factor gene expression could reflect compensatory responses to brain insulin resistance in this model.

CONCLUSION

Alcohol and tobacco exposures promote ARBD by impairing myelin synthesis, maturation and integrity via distinct but overlapping mechanisms. Public health measures to reduce ARBD should target both alcohol and tobacco abuses.

Reduced frontal cortical thickness and increased caudate volume within fronto-striatal circuits in young adult smokers

BACKGROUND

Smoking during early adulthood results in neurophysiological and brain structural changes that may promote nicotine dependence later in life. Previous studies have revealed the important roles of fronto-striatal circuits in the pathology of nicotine dependence; however, few studies have focused on both cortical thickness and subcortical striatal volume differences between young adult smokers and nonsmokers.

METHODS

Twenty-seven young male adult smokers and 22 age-, education- and gender-matched nonsmokers were recruited in the present study. The cortical thickness and striatal volume differences of young adult smokers and age-matched nonsmokers were investigated in the present study and then correlated with pack-years and Fagerström Test for Nicotine Dependence (FTND).

RESULTS

The following results were obtained: (1) young adult smokers showed significant cortical thinning in the frontal cortex (left caudal anterior cingulate cortex (ACC), right lateral orbitofrontal cortex (OFC)), left insula, left middle temporal gyrus, right inferior parietal lobule, and right parahippocampus; (2) in regards to subcortical striatal volume, the volume of the right caudate was larger in young adult smokers than nonsmokers; and (3) the cortical thickness of the right dorsolateral prefrontal cortex (DLPFC) and OFC were associated with nicotine dependence severity (FTND) and cumulative amount of nicotine intake (pack-years) in smokers, respectively.

CONCLUSIONS

This study revealed reduced frontal cortical thickness and increased caudate volume in the fronto-striatal circuits in young adult smokers compared to nonsmokers. These deficits suggest an imbalance between cognitive control (reduced protection factors) and reward drive behaviours (increased risk factors) associated with nicotine addiction and relapse.

Brain volume in male patients with recent onset schizophrenia with and without cannabis use disorders

BACKGROUND

Schizophrenia is highly comorbid with cannabis use disorders (CUDs), and this comorbidity is associated with an unfavourable course. Early onset or frequent cannabis use may influence brain structure. A key question is whether comorbid CUDs modulate brain morphology alterations associated with schizophrenia.

METHODS

We used surface-based analysis to measure the brain volume, cortical thickness and cortical surface area of a priori-defined brain regions (hippocampus, amygdala, thalamus, caudate, putamen, orbitofrontal cortex, anterior cingulate cortex, insula, parahippocampus and fusiform gyrus) in male patients with schizophrenia or related disorders with and without comorbid CUDs and matched healthy controls. Associations between age at onset and frequency of cannabis use with regional grey matter volume were explored.

RESULTS

We included 113 patients with (CUD, n = 80) and without (NCUD, n = 33) CUDs and 84 controls in our study. As expected, patients with schizophrenia (with or without a CUD) had smaller volumes of most brain regions (amygdala, putamen, insula, parahippocampus and fusiform gyrus) than healthy controls, and differences in cortical volume were mainly driven by cortical thinning. Compared with the NCUD group, the CUD group had a larger volume of the putamen, possibly driven by polysubstance use. No associations between age at onset and frequency of use with regional grey matter volumes were found.

LIMITATIONS

We were unable to correct for possible confounding effects of smoking or antipsychotic medication.

CONCLUSION

Patients with psychotic disorders and comorbid CUDs have larger putamen volumes than those without CUDs. Future studies should elaborate whether a large putamen represents a risk factor for the development of CUDs or whether (poly)substance use causes changes in putamen volume.

Sex-related and tissue-specific effects of tobacco smoking on brain atrophy: assessment in a large longitudinal cohort of healthy elderly

We investigated the cross-sectional and longitudinal effects of tobacco smoking on brain atrophy in a large cohort of healthy elderly participants (65–80 years). MRI was used for measuring whole brain (WB), gray matter (GM), white matter (WM), and hippocampus (HIP) volumes at study entry time (baseline, N = 1451), and the annualized rates of variation of these volumes using a 4-year follow-up MRI in a subpart of the cohort (N = 1111). Effects of smoking status (never, former, or current smoker) at study entry and of lifetime tobacco consumption on these brain phenotypes were studied using sex-stratified AN(C)OVAs, including other health parameters as covariates. At baseline, male current smokers had lower GM, while female current smokers had lower WM. In addition, female former smokers exhibited reduced baseline HIP, the reduction being correlated with lifetime tobacco consumption. Longitudinal analyses demonstrated that current smokers, whether men or women, had larger annualized rates of HIP atrophy, as compared to either non or former smokers, independent of their lifetime consumption of tobacco. There was no effect of smoking on the annualized rate of WM loss. In all cases, measured sizes of these tobacco-smoking effects were of the same order of magnitude than those of age, and larger than effect sizes of any other covariate. These results demonstrate that tobacco smoking is a major factor of brain aging, with sex- and tissue specific effects, notably on the HIP annualized rate of atrophy after the age of 65.