Gestational nicotine exposure modifies myelin gene expression in the brains of adolescent rats with sex differences

Genetic associations between orexin genes and phenotypes related to behavioral regulation in humans, including substance use

The hypothalamic neuropeptide system of orexin (hypocretin) neurons provides projections throughout the neuraxis and has been linked to sleep regulation, feeding and motivation for salient rewards including drugs of abuse. However, relatively little has been done to examine genes associated with orexin signaling and specific behavioral phenotypes in humans. Here, we tested for association of twenty-seven genes involved in orexin signaling with behavioral phenotypes in humans. We tested the full gene set, functional subsets, and individual genes involved in orexin signaling. Our primary phenotype of interest was Externalizing, a composite factor comprised of behaviors and disorders associated with reward-seeking, motivation, and behavioral regulation. We also tested for association with additional phenotypes that have been related to orexin regulation in model organism studies, including alcohol consumption, problematic alcohol use, daytime sleepiness, insomnia, cigarettes per day, smoking initiation, and body mass index. The composite set of 27 genes corresponding to orexin function was highly associated with Externalizing, as well as with alcohol consumption, insomnia, cigarettes per day, smoking initiation and BMI. In addition, all gene subsets (except the OXR2/HCRTR2 subset) were associated with Externalizing. BMI was significantly associated with all gene subsets. The "validated factors for PPOX/HCRT" and "PPOX/HCRT upregulation" gene subsets also were associated with alcohol consumption. Individually, 8 genes showed a strong association with Externalizing, 12 with BMI, 7 with smoking initiation, 3 with alcohol consumption, and 2 with problematic alcohol use, after correction for multiple testing. This study indicates that orexin genes are associated with multiple behaviors and disorders related to self-regulation in humans. This is consistent with prior work in animals that implicated orexin signaling in motivational activation induced by salient stimuli, and supports the hypothesis that orexin signaling is an important potential therapeutic target for numerous behavioral disorders.

Prenatal influences on postnatal neuroplasticity: Integrating DOHaD and sensitive/critical period frameworks to understand biological embedding in early development

Early environments can have significant and lasting effects on brain, body, and behavior across the lifecourse. Here, we address current research efforts to understand how experiences impact neurodevelopment with a new perspective integrating two well-known conceptual frameworks - the Developmental Origins of Health and Disease (DOHaD) and sensitive/critical period frameworks. Specifically, we consider how prenatal experiences characterized in the DOHaD model impact two key neurobiological mechanisms of sensitive/critical periods for adapting to and learning from the postnatal environment. We draw from both animal and human research to summarize the current state of knowledge on how particular prenatal substance exposures (psychoactive substances and heavy metals) and nutritional profiles (protein-energy malnutrition and iron deficiency) each differentially impact brain circuits' excitation/GABAergic inhibition balance and myelination. Finally, we highlight new research directions that emerge from this integrated framework, including testing how prenatal environments alter sensitive/critical period timing and learning and identifying potential promotional/buffering prenatal exposures to impact postnatal sensitive/critical periods. We hope this integrative framework considering prenatal influences on postnatal neuroplasticity will stimulate new research to understand how early environments have lasting consequences on our brains, behavior, and health.

Sex-dependent differences in the ability of nicotine to modulate discrimination learning and cognitive flexibility in mice

Nicotine, an addictive compound found in tobacco, functions as an agonist of nicotinic acetylcholine receptors (nAChRs) in the brain. Interestingly, nicotine has been reported to act as a cognitive enhancer in both human subjects and experimental animals. However, its effects in animal studies have not always been consistent, and sex differences have been identified in the effects of nicotine on several behaviors. Specifically, the role that sex plays in modulating the effects of nicotine on discrimination learning and cognitive flexibility in rodents is still unclear. Here, we evaluated sex-dependent differences in the effect of daily nicotine intraperitoneal (i.p.) administration at various doses (0.125, 0.25, and 0.5 mg/kg) on visual discrimination (VD) learning and reversal (VDR) learning in mice. In male mice, 0.5 mg/kg nicotine significantly improved performance in the VDR, but not the VD, task, while 0.5 mg/kg nicotine significantly worsened performance in the VD, but not VDR task in female mice. Furthermore, 0.25 mg/kg nicotine significantly worsened performance in the VD and VDR task only in female mice. Next, to investigate the cellular mechanisms that underlie the sex difference in the effects of nicotine on cognition, transcriptomic analyses were performed focusing on the medial prefrontal cortex tissue samples from male and female mice that had received continuous administration of nicotine for 3 or 18 days. As a result of pathway enrichment analysis and protein-protein interaction analysis using gene sets of differentially expressed genes, decreased expression of postsynaptic-related genes in males and increased expression of innate immunity-related genes in females were identified as possible molecular mechanisms related to sex differences in the effects of nicotine on cognition in discrimination learning and cognitive flexibility. Our result suggests that nicotine modulates cognitive function in a sex-dependent manner by alternating the expression of specific gene sets in the medial prefrontal cortex.

Prenatal Tobacco Exposure, Brain Subcortical Volumes, and Gray-White Matter Contrast

Importance

Maternal tobacco use during pregnancy (MTDP) remains a major public health challenge. However, the complete spectrum of effects of MTDP is not fully understood.

Objectives

To examine the longitudinal associations of MTDP and children's brain morphometric subcortical volume and gray-white matter contrast (GWC) development.

Design, Setting, and Participants

Cohort study of children aged 9 to 10 years at wave 1 (October 2016 to October 2018) and at a 2-year follow-up (wave 2; August 2018 to January 2021; aged 11-12 years) across 21 US sites in the Adolescent Brain Cognitive Development (ABCD) Study. Data were analyzed from October 2023 to October 2024.

Exposure

MTDP.

Main outcomes and measures

Morphometric brain measures of subcortical volume and GWC.

Results

Among the 11 448 children (51.5% male; 13.1% Black; 24.0% Hispanic; and 52.9% White) at wave 1, 1607 (16.6%; 95% CI, 13.0%-20.2%) were identified with MTDP exposure. At wave 1, children with MTDP exposure (vs no exposure) exhibited lower GWC in widespread brain regions primarily located in the frontal (eg, superior frontal; regression coefficient [B] = -0.0019; SE, 0.0006; P = .004), parietal (eg, supramarginal; B = -0.0021; SE, 0.0007; P = .002) and temporal lobes (eg, middle temporal; B = -0.0024; SE, 0.0007; P < .001). These differences in GWC continued to be significant at wave 2. In regard to subcortical volume, children with MTDP exposure demonstrated smaller volume of the lateral ventricle (B = -257.5; SE, 78.6; P = .001) and caudate (B = -37.7; SE, 14.0; P = .01) in the left hemisphere at wave 1, and lower volume of the caudate in both left (B = -48.7; SE, 15.9; P = .002) and right hemisphere (B = -45.5; SE, 16.1; P = .01) at wave 2.

Conclusions and Relevance

This cohort study found that MTDP exposure was associated with lower GWC across the whole cortex and smaller caudate nuclei volume compared with no exposure, signifying the importance of preventing MTDP and necessitating further research on this topic.

Smoking during pregnancy and risk of multiple sclerosis in offspring and mother: A Danish nationwide register-based cohort study

BACKGROUND

The association between intra-uterine exposure to maternal smoking and risk of multiple sclerosis (MS) has been little studied and with conflicting results.

OBJECTIVE

To examine the risk of MS in offspring exposed intra-uterine to maternal smoking. In addition, to re-examine prior observations of an elevated risk of MS among smokers, assuming that self-reported smoking during pregnancy reflects the woman's general smoking habits.

METHODS

The study cohort included all Danish women, pregnant in the period 1991-2018, (n = 789,299) and singletons from these pregnancies (n = 879,135). Nationwide information on maternal smoking during pregnancy and MS cases in the study cohort were obtained from the Medical Birth Register and the National Patient Register. Cox regression analysis was used to estimate hazard ratios (HRs) for the association between smoking and MS risk.

RESULTS

Women who smoked during pregnancy had a 42% increased risk of developing MS compared with non-smoking women (HR = 1.42 (1.32-1.52), n = 1,296). The risk of MS among singletons of women who smoked during pregnancy was 38% higher than that among singletons born to non-smoking women (HR = 1.38 (1.08-1.76), n = 110).

CONCLUSION

Our observations add further to the evidence implicating smoking in the development of MS and suggest that intra-uterine exposure to tobacco smoke may increase MS risk.

Nicotine neurotoxicity exacerbation following engineered Ag and Cu (50-60 nm) nanoparticles intoxication. Neuroprotection with nanowired delivery of antioxidant compound H-290/51 together with serotonin 5-HT3 receptor antagonist ondansetron

Nicotine abuse is frequent worldwide leading to about 8 millions people die every year due to tobacco related diseases. Military personnel often use nicotine smoking that is about 12.8% higher than civilian populations. Nicotine smoking triggers oxidative stress and are linked to several neurodegenerative diseases such as Alzheimer's disease. Nicotine neurotoxicity induces significant depression and oxidative stress in the brain leading to neurovascular damages and brain pathology. Thus, details of nicotine neurotoxicity and factors influencing them require additional investigations. In this review, effects of engineered nanoparticles from metals Ag and Cu (50-60 nm) on nicotine neurotoxicity are discussed with regard to nicotine smoking. Military personnel often work in the environment where chances of nanoparticles exposure are quite common. In our earlier studies, we have shown that nanoparticles alone induces breakdown of the blood-brain barrier (BBB) and exacerbates brain pathology in animal models. In present investigation, nicotine exposure in with Ag or Cu nanoparticles intoxicated group exacerbated BBB breakdown, induce oxidative stress and aggravate brain pathology. Treatment with nanowired H-290/51 a potent chain-breaking antioxidant together with nanowired ondansetron, a potent 5-HT3 receptor antagonist significantly reduced oxidative stress, BBB breakdown and brain pathology in nicotine exposure associated with Ag or Cu nanoparticles intoxication. The functional significance of this findings and possible mechanisms of nicotine neurotoxicity are discussed based on current literature.

Bio-psycho-social factors' associations with brain age: a large-scale UK Biobank diffusion study of 35,749 participants

Brain age refers to age predicted by brain features. Brain age has previously been associated with various health and disease outcomes and suggested as a potential biomarker of general health. Few previous studies have systematically assessed brain age variability derived from single and multi-shell diffusion magnetic resonance imaging data. Here, we present multivariate models of brain age derived from various diffusion approaches and how they relate to bio-psycho-social variables within the domains of sociodemographic, cognitive, life-satisfaction, as well as health and lifestyle factors in midlife to old age (N = 35,749, 44.6-82.8 years of age). Bio-psycho-social factors could uniquely explain a small proportion of the brain age variance, in a similar pattern across diffusion approaches: cognitive scores, life satisfaction, health and lifestyle factors adding to the variance explained, but not socio-demographics. Consistent brain age associations across models were found for waist-to-hip ratio, diabetes, hypertension, smoking, matrix puzzles solving, and job and health satisfaction and perception. Furthermore, we found large variability in sex and ethnicity group differences in brain age. Our results show that brain age cannot be sufficiently explained by bio-psycho-social variables alone. However, the observed associations suggest to adjust for sex, ethnicity, cognitive factors, as well as health and lifestyle factors, and to observe bio-psycho-social factor interactions' influence on brain age in future studies.

Sex-Specific Transcriptomic Signatures in Brain Regions Critical for Neuropathic Pain-Induced Depression

Neuropathic pain is a chronic debilitating condition with a high comorbidity with depression. Clinical reports and animal studies have suggested that both the medial prefrontal cortex (mPFC) and the anterior cingulate cortex (ACC) are critically implicated in regulating the affective symptoms of neuropathic pain. Neuropathic pain induces differential long-term structural, functional, and biochemical changes in both regions, which are thought to be regulated by multiple waves of gene transcription. However, the differences in the transcriptomic profiles changed by neuropathic pain between these regions are largely unknown. Furthermore, women are more susceptible to pain and depression than men. The molecular mechanisms underlying this sexual dimorphism remain to be explored. Here, we performed RNA sequencing and analyzed the transcriptomic profiles of the mPFC and ACC of female and male mice at 2 weeks after spared nerve injury (SNI), an early time point when the mice began to show mild depressive symptoms. Our results showed that the SNI-induced transcriptomic changes in female and male mice were largely distinct. Interestingly, the female mice exhibited more robust transcriptomic changes in the ACC than male, whereas the opposite pattern occurred in the mPFC. Cell type enrichment analyses revealed that the differentially expressed genes involved genes enriched in neurons, various types of glia and endothelial cells. We further performed gene set enrichment analysis (GSEA), which revealed significant de-enrichment of myelin sheath development in both female and male mPFC after SNI. In the female ACC, gene sets for synaptic organization were enriched, and gene sets for extracellular matrix were de-enriched after SNI, while such signatures were absent in male ACC. Collectively, these findings revealed region-specific and sexual dimorphism at the transcriptional levels induced by neuropathic pain, and provided novel therapeutic targets for chronic pain and its associated affective disorders.

White matter microstructure differences in individuals with dependence on cocaine, methamphetamine, and nicotine: Findings from the ENIGMA-Addiction working group

BACKGROUND

Nicotine and illicit stimulants are very addictive substances. Although associations between grey matter and dependence on stimulants have been frequently reported, white matter correlates have received less attention.

METHODS

Eleven international sites ascribed to the ENIGMA-Addiction consortium contributed data from individuals with dependence on cocaine (n = 147), methamphetamine (n = 132) and nicotine (n = 189), as well as non-dependent controls (n = 333). We compared the fractional anisotropy (FA), axial diffusivity (AD), radial diffusivity (RD) and mean diffusivity (MD) of 20 bilateral tracts. Also, we compared the performance of various machine learning algorithms in deriving brain-based classifications on stimulant dependence.

RESULTS

The cocaine and methamphetamine groups had lower regional FA and higher RD in several association, commissural, and projection white matter tracts. The methamphetamine dependent group additionally showed lower regional AD. The nicotine group had lower FA and higher RD limited to the anterior limb of the internal capsule. The best performing machine learning algorithm was the support vector machine (SVM). The SVM successfully classified individuals with dependence on cocaine (AUC = 0.70, p < 0.001) and methamphetamine (AUC = 0.71, p < 0.001) relative to non-dependent controls. Classifications related to nicotine dependence proved modest (AUC = 0.62, p = 0.014).

CONCLUSIONS

Stimulant dependence was related to FA disturbances within tracts consistent with a role in addiction. The multivariate pattern of white matter differences proved sufficient to identify individuals with stimulant dependence, particularly for cocaine and methamphetamine.

Sex-specific nicotine sensitization and imprinting of self-administration in rats inform GWAS findings on human addiction phenotypes

Repeated nicotine exposure leads to sensitization (SST) and enhances self-administration (SA) in rodents. However, the molecular basis of nicotine SST and SA and their biological relevance to the mounting genome-wide association study (GWAS) loci of human addictive behaviors are poorly understood. Considering a gateway drug role of nicotine, we modeled nicotine SST and SA in F1 progeny of inbred rats (F344/BN) and conducted integrative genomics analyses. We unexpectedly observed male-specific nicotine SST and a parental effect of SA only present in paternal F344 crosses. Transcriptional profiling in the ventral tegmental area (VTA) and nucleus accumbens (NAc) core and shell further revealed sex- and brain region-specific transcriptomic signatures of SST and SA. We found that genes associated with SST and SA were enriched for those related to synaptic processes, myelin sheath, and tobacco use disorder or chemdependency. Interestingly, SST-associated genes were often downregulated in male VTA but upregulated in female VTA, and strongly enriched for smoking GWAS risk variants, possibly explaining the male-specific SST. For SA, we found widespread region-specific allelic imbalance of expression (AIE), of which genes showing AIE bias toward paternal F344 alleles in NAc core were strongly enriched for SA-associated genes and for GWAS risk variants of smoking initiation, likely contributing to the parental effect of SA. Our study suggests a mechanistic link between transcriptional changes underlying the NIC SST and SA and human nicotine addiction, providing a resource for understanding the neurobiology basis of the GWAS findings on human smoking and other addictive phenotypes.

Human Oligodendrocytes and Myelin In Vitro to Evaluate Developmental Neurotoxicity

Neurodevelopment is uniquely sensitive to toxic insults and there are concerns that environmental chemicals are contributing to widespread subclinical developmental neurotoxicity (DNT). Increased DNT evaluation is needed due to the lack of such information for most chemicals in common use, but in vivo studies recommended in regulatory guidelines are not practical for the large-scale screening of potential DNT chemicals. It is widely acknowledged that developmental neurotoxicity is a consequence of disruptions to basic processes in neurodevelopment and that testing strategies using human cell-based in vitro systems that mimic these processes could aid in prioritizing chemicals with DNT potential. Myelination is a fundamental process in neurodevelopment that should be included in a DNT testing strategy, but there are very few in vitro models of myelination. Thus, there is a need to establish an in vitro myelination assay for DNT. Here, we summarize the routes of myelin toxicity and the known models to study this particular endpoint.

Multidimensional Intersection of Nicotine, Gene Expression, and Behavior

The cholinergic system plays a crucial role in nervous system function with important effects on developmental processes, cognition, attention, motivation, reward, learning, and memory. Nicotine, the reinforcing component of tobacco and e-cigarettes, directly acts on the cholinergic system by targeting nicotinic acetylcholine receptors (nAChRs) in the brain. Activation of nAChRs leads to a multitude of immediate and long-lasting effects in specific cellular populations, thereby affecting the addictive properties of the drug. In addition to the direct actions of nicotine in binding to and opening nAChRs, the subsequent activation of circuits and downstream signaling cascades leads to a wide range of changes in gene expression, which can subsequently alter further behavioral expression. In this review, we provide an overview of the actions of nicotine that lead to changes in gene expression and further highlight evidence supporting how these changes can often be bidirectional, thereby inducing subsequent changes in behaviors associated with further drug intake.

Effects of endocrine disrupting chemicals on myelin development and diseases

In the central and peripheral nervous systems, myelin is essential for efficient conduction of action potentials. During development, oligodendrocytes and Schwann cells differentiate and ensure axon myelination, and disruption of these processes can contribute to neurodevelopmental disorders. In adults, demyelination can lead to important disabilities, and recovery capacities by remyelination often decrease with disease progression. Among environmental chemical pollutants, endocrine disrupting chemicals (EDCs) are of major concern for human health and are notably suspected to participate in neurodevelopmental and neurodegenerative diseases. In this review, we have combined the current knowledge on EDCs impacts on myelin including several persistent organic pollutants, bisphenol A, triclosan, heavy metals, pesticides, and nicotine. Besides, we presented several other endocrine modulators, including pharmaceuticals and the phytoestrogen genistein, some of which are candidates for treating demyelinating conditions but could also be deleterious as contaminants. The direct impacts of EDCs on myelinating cells were considered as well as their indirect consequences on myelin, particularly on immune mechanisms associated with demyelinating conditions. More studies are needed to describe the effects of these compounds and to further understand the underlying mechanisms in relation to the potential for endocrine disruption.

Maternal smoking during pregnancy and offspring executive function: What do we know and what are the next steps?

Children exposed to maternal smoking during pregnancy (MSDP) exhibit difficulties in executive function (EF) from infancy through adolescence. Due to the developmental significance of EF as a predictor of adaptive functioning throughout the life span, the MSDP-EF relation has clear public health implications. In this paper, we provide a comprehensive review of the literature on the relationship between MSDP and offspring EF across development; consider brain-based assessments, animal models, and genetically informed studies in an effort to elucidate plausible pathways of effects; discuss implications for prevention and intervention; and make calls to action for future research.

Abnormal frontostriatal tracts in young male tobacco smokers

Dysfunctions in frontostriatal circuits have been associated with craving and cognitive control in smokers. However, the relevance of white matter (WM) diffusion properties of the ventral and dorsal frontostriatal tracts for behaviors associated with smoking remains relatively unknown, especially in young adulthood, a critical time period for the development and maintenance of addiction. Here, diffusion tensor imaging (DTI) and probabilistic tractography were used to investigate the WM tracts of the ventral and dorsal frontostriatal circuits in two independent studies (Study1: 36 male smokers (21.3 ± 1.3 years) vs. 35 male nonsmokers (21.2 ± 1.3 years); Study2: 29 male smokers (21.4 ± 1.1 years) vs. 25 male nonsmokers (21.0 ± 1.4 years)). Subjective craving was measured by the Questionnaire on Smoking Urges (QSU) and cognitive control ability was assessed with the Stroop task. In both studies, smokers committed more response errors than nonsmokers during the incongruent condition of the Stroop task. Relative to controls, smokers showed lower fractional anisotropy (FA) and higher radial diffusivity in left medial orbitofrontal cortex-to-nucleus accumbens fiber tracts (ventral frontostriatal path) and also lower FA in right dorsolateral prefrontal cortex-to-caudate fiber tracts (dorsal frontostriatal path). The FA values of the right dorsal fibers were negatively correlated with incongruent response Stroop errors in smokers, whereas the mean diffusivity values of the left ventral fibers were positively correlated with craving in smokers. Thus, WM diffusion properties of the dorsal and ventral frontostriatal tracts were associated with cognitive control and craving, respectively, in young male tobacco smokers. These data highlight the importance of studying WM in relation to neuropsychological changes underlying smoking.

Evidence of altered brain regulatory gene expression in tobacco-exposed fetuses

AIM

We sought to determine the association between prenatal smoking status and expression of fetal brain regulatory genes.

METHODS

At delivery, we collected information from parturient women on prenatal smoking habits and analyzed salivary cotinine levels. We obtained neonatal umbilical cord blood and extracted total RNA. We then employed the quantitative polymerase chain reaction (QPCR) analyses and the comparative CT method to calculate the relative gene expression of selected fetal brain regulatory genes responsible for (1) brain growth (brain-derived neutrotrophic factor, BDNF), (2) myelination (proteolipidic protein 1, PLP1 and myelin basic protein, MBP), and (3) neuronal migration and cell-cell interactions during fetal brain development or RLN. The χ2-test, analysis of variance (ANOVA), and the Grubb test were used to evaluate the relationship between prenatal smoking status and relative gene expression levels. Further analysis using bootstrapping was performed to assess the precision of our estimates.

RESULTS

Of the 39 maternal-infant dyads included in this study, 25.6% were non-smokers, 43.6% were passive smokers and 30.8% were active smokers. The results showed down-regulation of the selected fetal brain regulatory genes among active smokers.

CONCLUSIONS

These findings represent preliminary evidence in humans that intrauterine tobacco exposure impacts fetal brain programming. Future studies are warranted to examine whether our findings represent potential mechanisms through which adverse childhood/adult-onset cognitive and behavioral outcomes that have been previously linked to intrauterine exposure occur.

Transgenerational attenuation of opioid self-administration as a consequence of adolescent morphine exposure

The United States is in the midst of an opiate epidemic, with abuse of prescription and illegal opioids increasing steadily over the past decade. While it is clear that there is a genetic component to opioid addiction, there is a significant portion of heritability that cannot be explained by genetics alone. The current study was designed to test the hypothesis that maternal exposure to opioids prior to pregnancy alters abuse liability in subsequent generations. Female adolescent Sprague Dawley rats were administered morphine at increasing doses (5-25 mg/kg, s.c.) or saline for 10 days (P30-39). During adulthood, animals were bred with drug-naïve colony males. Male and female adult offspring (F1 animals) were tested for morphine self-administration acquisition, progressive ratio, extinction, and reinstatement at three doses of morphine (0.25, 0.75, 1.25 mg/kg/infusion). Grandoffspring (F2 animals, from the maternal line) were also examined. Additionally, gene expression changes within the nucleus accumbens were examined with RNA deep sequencing (PacBio) and qPCR. There were dose- and sex-dependent effects on all phases of the self-administration paradigm that indicate decreased morphine reinforcement and attenuated relapse-like behavior. Additionally, genes related to synaptic plasticity, as well as myelin basic protein (MBP), were dysregulated. Some, but not all, effects persisted into the subsequent (F2) generation. The results demonstrate that even limited opioid exposure during adolescence can have lasting effects across multiple generations, which has implications for mechanisms of the transmission of drug abuse liability in humans.

Cholinergic signaling in myelination

There is a long history of research on acetylcholine (ACh) function in myelinating glia, but a resurgence of interest recently as a result of the therapeutic potential of manipulating ACh signaling to promote remyelination, and the broader interest in neurotransmitter signaling in activity-dependent myelination. Myelinating glia express all the major types of muscarinic and nicotinic ACh receptors at different stages of development, and acetylcholinesterase and butyrylcholinesterase are highly expressed in white matter. This review traces the history of research on ACh signaling in Schwann cells, oligodendrocytes, and in the myelin sheath, and summarizes current knowledge on the intracellular signaling and functional consequences of ACh signaling in myelinating glia. Implications of ACh in diseases, such as Alzheimer's disease, multiple sclerosis, and white matter toxicity caused by pesticides are considered, together with an outline of major questions for future research. GLIA 2017;65:687-698.

Sex-Specific Alterations of White Matter Developmental Trajectories in Infants With Prenatal Exposure to Methamphetamine and Tobacco

IMPORTANCE

Methamphetamine is a common illicit drug used worldwide. Methamphetamine and/or tobacco use by pregnant women remains prevalent. However, little is known about the effect of comorbid methamphetamine and tobacco use on human fetal brain development.

OBJECTIVE

To investigate whether microstructural brain abnormalities reported in children with prenatal methamphetamine and/or tobacco exposure are present at birth before childhood environmental influences.

DESIGN, SETTING, AND PARTICIPANTS

A prospective, longitudinal study was conducted between September 17, 2008, and February 28, 2015, at an ambulatory academic medical center. A total of 752 infant-mother dyads were screened and 139 of 195 qualified neonates were evaluated (36 methamphetamine/tobacco exposed, 32 tobacco exposed, and 71 unexposed controls). They were recruited consecutively from the community.

EXPOSURES

Prenatal methamphetamine and/or tobacco exposure.

MAIN OUTCOMES AND MEASURES

Quantitative neurologic examination and diffusion tensor imaging performed 1 to 3 times through age 4 months; diffusivities and fractional anisotropy (FA) assessed in 7 white matter tracts and 4 subcortical brain regions using an automated atlas-based method.

RESULTS

Of the 139 infants evaluated, 72 were female (51.8%); the mean (SE) postmenstrual age at baseline was 41.5 (0.27) weeks. Methamphetamine/tobacco-exposed infants showed delayed developmental trajectories on active muscle tone (group × age, P < .001) and total neurologic scores (group × age, P = .01) that normalized by ages 3 to 4 months. Only methamphetamine/tobacco-exposed boys had lower FA (group × age, P = .02) and higher diffusivities in superior (SCR) and posterior corona radiatae (PCR) (group × age × sex, P = .002; group × age × sex, P = .01) at baseline that normalized by age 3 months. Only methamphetamine/tobacco- and tobacco-exposed girls showed persistently lower FA in anterior corona radiata (ACR) (group, P = .04; group × age × sex, P = .01). Tobacco-exposed infants showed persistently lower axial diffusion in the thalamus and internal capsule across groups (P = .02).

CONCLUSIONS AND RELEVANCE

Prenatal methamphetamine/tobacco exposure may lead to delays in motor development, with less coherent fibers and less myelination in SCR and PCR only in male infants, but these abnormalities may normalize by ages 3 to 4 months after cessation of stimulant exposure. In contrast, persistently less coherent ACR fibers were observed in methamphetamine/tobacco- and tobacco-exposed girls, possibly from increased dendritic branching or spine density due to epigenetic influences. Persistently lower diffusivity in the thalamus and internal capsule of all tobacco-exposed infants suggests aberrant axonal development. Collectively, prenatal methamphetamine and/or tobacco exposure may lead to delayed motor development and white matter maturation in sex- and regional-specific manners.

Sex Influences on the Brain: An Issue Whose Time Has Come

The issue of sex influences on the brain is rapidly moving center stage, driven by abundant results proving that subject sex can and regularly does alter, negate, and even reverse neuroscientific findings and conclusions down to the molecular level and thus can no longer be justifiably marginalized or ignored.

Frontal Cortex Transcriptome Analysis of Mice Exposed to Electronic Cigarettes During Early Life Stages

Electronic cigarettes (e-cigarettes), battery-powered devices containing nicotine, glycerin, propylene glycol, flavorings, and other substances, are increasing in popularity. They pose a potential threat to the developing brain, as nicotine is a known neurotoxicant. We hypothesized that exposure to e-cigarettes during early life stages induce changes in central nervous system (CNS) transcriptome associated with adverse neurobiological outcomes and long-term disease states. To test the hypothesis, pregnant C57BL/6 mice were exposed daily (via whole body inhalation) throughout gestation (3 h/day; 5 days/week) to aerosols produced from e-cigarettes either with nicotine (13-16 mg/mL) or without nicotine; following birth, pups and dams were exposed together to e-cigarette aerosols throughout lactation beginning at postnatal day (PND) 4-6 and using the same exposure conditions employed during gestational exposure. Following exposure, frontal cortex recovered from ~one-month-old male and female offspring were excised and analyzed for gene expression by RNA Sequencing (RNA-Seq). Comparisons between the treatment groups revealed that e-cigarette constituents other than nicotine might be partly responsible for the observed biological effects. Transcriptome alterations in both offspring sexes and treatment groups were all significantly associated with downstream adverse neurobiological outcomes. Results from this study demonstrate that e-cigarette exposure during early life alters CNS development potentially leading to chronic neuropathology.

Gender differences in white matter pathology and mitochondrial dysfunction in Alzheimer's disease with cerebrovascular disease

BACKGROUND

Dementia risk in women is higher than in men, but the molecular neuropathology of this gender difference remains poorly defined. In this study, we used unbiased, discovery-driven quantitative proteomics to assess the molecular basis of gender influences on risk of Alzheimer's disease with cerebrovascular disease (AD + CVD).

RESULTS

We detected modulation of several redox proteins in the temporal lobe of AD + CVD subjects, and we observed sex-specific alterations in the white matter (WM) and mitochondria proteomes of female patients. Functional proteomic analysis of AD + CVD brain tissues revealed increased citrullination of arginine and deamidation of glutamine residues of myelin basic protein (MBP) in female which impaired degradation of degenerated MBP and resulted in accumulation of non-functional MBP in WM. Female patients also displayed down-regulation of ATP sub-units and cytochromes, suggesting increased severity of mitochondria impairment in women.

CONCLUSIONS

Our study demonstrates that gender-linked modulation of white matter and mitochondria proteomes influences neuropathology of the temporal lobe in AD + CVD.

Prenatal Nicotine Exposure Impairs the Proliferation of Neuronal Progenitors, Leading to Fewer Glutamatergic Neurons in the Medial Prefrontal Cortex

Cigarette smoking during pregnancy is associated with various disabilities in the offspring such as attention deficit/hyperactivity disorder, learning disabilities, and persistent anxiety. We have reported that nicotine exposure in female mice during pregnancy, in particular from embryonic day 14 (E14) to postnatal day 0 (P0), induces long-lasting behavioral deficits in offspring. However, the mechanism by which prenatal nicotine exposure (PNE) affects neurodevelopment, resulting in behavioral deficits, has remained unclear. Here, we report that PNE disrupted the proliferation of neuronal progenitors, leading to a decrease in the progenitor pool in the ventricular and subventricular zones. In addition, using a cumulative 5-bromo-2'-deoxyuridine labeling assay, we evaluated the rate of cell cycle progression causing the impairment of neuronal progenitor proliferation, and uncovered anomalous cell cycle kinetics in mice with PNE. Accordingly, the density of glutamatergic neurons in the medial prefrontal cortex (medial PFC) was reduced, implying glutamatergic dysregulation. Mice with PNE exhibited behavioral impairments in attentional function and behavioral flexibility in adulthood, and the deficits were ameliorated by microinjection of D-cycloserine into the PFC. Collectively, our findings suggest that PNE affects the proliferation and maturation of progenitor cells to glutamatergic neuron during neurodevelopment in the medial PFC, which may be associated with cognitive deficits in the offspring.

Early weaning influences short-term synaptic plasticity in the medial prefrontal-anterior basolateral amygdala pathway

Early weaning in rodents reportedly influences behavioral and emotional traits and triggers precocious myelin formation in the anterior basolateral amygdala (aBLA; Ono et al., 2008), where prefrontal efferents terminate. We studied the correlation between behavior and the synaptic properties of the prefrontal-aBLA pathway. Open-field behaviors of adult male rats weaned at either 16 days or 30 days were measured on two consecutive days. On the first day, the rats received a slight footshock that was reportedly insufficient for fear conditioning. Electrophysiological recordings in the prefrontal-aBLA were then performed under urethane anesthesia. Without group differences in the stimulus intensity or the first evoked response, the overall paired-pulse facilitation was significantly lower in the early-weaned group from 25 to 100 ms. At the 25-ms interval, regression values between paired-pulse facilitation and locomotion on the second day were positive/insignificant and negative/significant in early- and control-weaned groups, respectively, and were statistically different between the groups.

Perinatal methylmercury exposure perturbs the expression of Plp1 and Cnp splice variants in cerebellum of rat pups

Early life exposure to environmental chemicals can interfere with myelin formation in the developing brain, leading to neurological disorders. The Proteolipid Protein 1 (Plp1), Myelin Basic Protein (Mbp) and 2',3'-Cyclic Nucleotide 3'Phosphodiesterase (Cnp) genes expressed in oligodendrocytes and involved in myelination processes can be useful biomarkers of potential developmental neurotoxicity. In an earlier study, we concluded that the reduction in the expression levels of Mbp splice variants in juvenile rat cerebellum following perinatal methylmercury (MeHg) exposure were compatible with an overall reduction of mature oligodendrocytes population. This observation prompted us to analyze the expression of Plp1 and Cnp in developing rat cerebellum to further confirm and investigate the toxic effects of MeHg on vulnerable oligodendrocytes. Splice variants of Plp1 in human and of Cnp in mouse are curated in NCBI RefSeq database, but not for rat. Lack of annotation of splice variants can pose significant challenge for the reliable quantification of gene expression levels in toxicological studies. Therefore, we applied a "comparative sequence analysis" approach, relying on annotated splice variants in human/mouse and on evolutionary conservation of intron-exon structures, to identify additional splice variants of Plp1 and Cnp in rat. Then, we confirmed their identity by nucleotide sequencing and characterized their temporal expression patterns during brain development by RT-PCR. The measurement of total transcripts and individual splice variants of Plp1 and Cnp in the cerebellum of MeHg-exposed rat pups revealed a relatively similar level of reduction in their expression levels. This study further confirms that perinatal exposure to MeHg can impact oligodendrocytes in pups. Based on these observations, we conclude that monitoring the expression of these oligodendrocyte-enriched genes can be useful to identify toxic chemicals affecting myelination.

Extended access nicotine self-administration with periodic deprivation increases immature neurons in the hippocampus

RATIONALE

Limited access nicotine self-administration decreases hippocampal neurogenesis, providing a mechanism for the deleterious effects of nicotine on hippocampal neuronal plasticity. However, recent studies have shown that limited access nicotine self-administration does not exhibit key features of nicotine dependence such as motivational withdrawal and increased motivation for nicotine after deprivation.

OBJECTIVES

The present study used extended access nicotine self-administration (0.03 mg/kg/infusion, 21 h/day, 4 days) with intermittent periods of deprivation (3 days) for 14 weeks, to test the hypothesis that this model enhances nicotine seeking and produces distinct responses in hippocampal neurogenesis when compared with limited access (1 h/day, 4 days) intake. Animals in the extended access group were either perfused prior to or following their final deprivation period, whereas animals in the limited access group were perfused after their last session.

RESULTS

Limited- and extended access nicotine self-administration with periodic deprivation did not affect proliferation and differentiation of oligodendrocyte progenitors in the medial prefrontal cortex (mPFC). Conversely, extended access nicotine self-administration with periodic deprivation enhanced proliferation and differentiation of hippocampal neural progenitors. Furthermore, in the hippocampus, the number of differentiating NeuroD-labeled cells strongly and positively correlated with enhanced nicotine seeking in rats that experienced extended access nicotine self-administration.

CONCLUSIONS

These findings demonstrate that extended versus limited access to nicotine self-administration differentially affects the generation of new oligodendroglia and new neurons during adulthood. The increases in the number of differentiating cells in extended access nicotine self-administering rats may consequently contribute to aberrant hippocampal neurogenesis and may contribute to maladaptive addiction-like behaviors dependent on the hippocampus.

Characterizing white matter changes in cigarette smokers via diffusion tensor imaging

BACKGROUND

Tobacco use remains the most preventable cause of death; however, its effects on the brain, and particularly white matter, remain elusive. Previous diffusion tensor imaging (DTI) studies have failed to yield consistent findings, with some reporting elevated measures of fractional anisotropy (FA) and others reporting lowered FA.

METHODS

In our study, we sought to elucidate the effects of tobacco on white matter by using enhanced imaging acquisition parameters and multiple analysis methods, including tract-based spatial statistics (TBSS) with crossing fiber measures and probabilistic tractography.

RESULTS

Our TBSS results revealed that chronic cigarette smokers have decreased FA in corpus callosum and bilateral anterior internal capsule, as well as specific reduced anisotropy in the two major fiber directions in a crossing fiber model. Further, our tractography results indicated that smokers have decreased FA in tracts projecting to the frontal cortex from (1) nucleus accumbens, (2) habenula, and (3) motor cortex. We also observed that smokers have greater disruptions in those regions when they had recently smoked compared to when they abstained from smoking for 24h. Our results also support previous evidence showing hemispheric asymmetry, with greater damage to the left side compared to the right.

CONCLUSIONS

These findings provide more conclusive evidence of white matter disruptions caused by nicotine use. By better understanding the neural disruptions correlating with cigarette smoking we can elucidate the addictive course and explore targeted treatment regimens for nicotine dependence.

Environmental tobacco smoke in the early postnatal period induces impairment in brain myelination

Environmental tobacco smoke (ETS) is associated with high morbidity and mortality, mainly in children. However, few studies focus on the brain development effects of ETS exposure. Myelination mainly occurs in the early years of life in humans and the first three postnatal weeks in rodents and is sensitive to xenobiotics exposure. This study investigated the effects of early postnatal ETS exposure on myelination. BALB/c mice were exposed to ETS generated from 3R4F reference research cigarettes from the third to the fourteenth days of life. The myelination of nerve fibers in the optic nerve by morphometric analysis and the levels of Olig1 and myelin basic protein (MBP) were evaluated in the cerebellum, diencephalon, telencephalon, and brainstem in infancy, adolescence, and adulthood. Infant mice exposed to ETS showed a decrease in the percentage of myelinated fibers in the optic nerve, compared with controls. ETS induced a decrease in Olig1 protein levels in the cerebellum and brainstem and an increase in MBP levels in the cerebellum at infant. It was also found a decrease in MBP levels in the telencephalon and brainstem at adolescence and in the cerebellum and diencephalon at adulthood. The present study demonstrates that exposure to ETS, in a critical phase of development, affects the percentage of myelinated fibers and myelin-specific proteins in infant mice. Although we did not observe differences in the morphological analysis in adolescence and adulthood, there was a decrease in MBP levels in distinctive brain regions suggesting a delayed effect in adolescence and adulthood.

Cigarette exposure, dependence, and craving are related to insula thickness in young adult smokers

The age period spanning late adolescence to emergent adulthood is associated with the highest prevalence of cigarette smoking in the United States, and is also a time of continued brain development. Nonetheless, although prior research has shown group differences in brain structure associated with smoking status in adults, few studies have examined how smoking and associated behavioral states relate to brain structure in this age group. Neuroimaging and lesion studies have suggested that the insula, a cortical region that integrates heterogeneous signals about internal states and contributes to executive functions, plays an important role in cigarette smoking behavior. Using high-resolution structural magnetic resonance imaging, we therefore measured cortical thickness of the insula in 18 smokers and 24 nonsmokers between the ages of 16 and 21 years. There were no group differences in insula thickness, but cigarette exposure (pack-years) was negatively associated with thickness in right insula. Cigarette dependence and the urge to smoke were negatively related to cortical thickness in the right ventral anterior insula. Although the results do not demonstrate causation, they do suggest that there are effects of cigarette exposure on brain structure in young smokers, with a relatively short smoking history. It is possible that changes in the brain due to prolonged exposure or to the progression of dependence lead to more extensive structural changes, manifested in the reported group differences between adult smokers and nonsmokers. Structural integrity of the insula may have implications for predicting long-term cigarette smoking and problems with other substance abuse in this population.

Capacity building and collaborative research on cross-national studies in the Asian region

To build capacity and collaborative research for future cross-national studies in the Asian and Pacific Islander (API) region, priority research topics were identified and discussed at the April 2013 Conference to Promote Global Health in Taipei. These topics included (1) Neuroscience on HIV/HCV and amphetamine-type stimulants (ATS), led by Drs. Linda Chang, Gene-Jack Wang, and Betty Tai; (2) ATS and mental health disorders, led by Drs. Richard Rawson and Wilson Compton; and (3) HIV/HCV transmission and social networks, led by Drs. Steven Shoptaw and Jacques Normand. Potential genetic studies spanning these topical areas as well as the importance of smoking cessation were further discussed, led by Dr. Ming Li. Additional priority research topics were also identified: (4) Drug use prevention, and (5) Family involvement to improve treatment adherence and recovery. Workgroups on these topics will be formed to prioritize research questions within the respective topical area and to determine the next steps. The ultimate goal of these workgroups is to stimulate collaboration that will eventually lead to research studies addressing critical issues related to the rising substance abuse and HIV infection rates in many Asian countries and, at the same time, to advance the scientific knowledge of substance abuse and HIV infection.

Central myelin gene expression during postnatal development in rats exposed to nicotine gestationally

Abnormal myelin gene expression in the central nervous system (CNS) is associated with many mental illnesses, including psychiatric disorders and drug addiction. We have previously shown that prenatal exposure to nicotine, the major psychoactive component in cigarette smoke, alters myelin gene expression in the CNS of adolescent rats. To examine whether this effect is specific for adolescents, we examined myelin gene expression in the CNS of juveniles and adults. Pregnant Sprague-Dawley rats were treated with nicotine (3 mg/kg/day; GN) or saline (GS) via osmotic mini pumps from gestational days 4-18. Both male and female offspring were sacrificed at postnatal day P20-21 (juveniles), P35-36 (adolescents), or P59-60 (adults). Three limbic brain regions, the prefrontal cortex (PFC), caudate putamen (CPu), and nucleus accumbens (NAc), were dissected. The expression of genes encoding major myelin components was evaluated using quantitative RT-PCR. We found that GN altered myelin gene expression in juveniles with brain region and sex differences. The pattern of alteration was different from that observed in adolescents. Although these genes were expressed normally in male adults, we observed decreased expression in GN-treated female adults, especially in the CPu. Thus, GN altered myelin gene expression throughout postnatal development and adulthood. The effect on adolescents was quite different from that at other ages, which correlated with the unique symptoms of many psychiatric disorders during adolescence.