The dynamic effects of nicotine on the developing brain

Sex-specific alterations in GABA receptor-mediated responses in laterodorsal tegmentum are associated with prenatal exposure to nicotine

Smoking during pregnancy is associated with deleterious physiological and cognitive effects on the offspring, which are likely due to nicotine-induced alteration in the development of neurotransmitter systems. Prenatal nicotine exposure (PNE) in rodents is associated with changes in behaviors controlled in part by the pontine laterodorsal tegmentum (LDT), and LDT excitatory signaling is altered in a sex and age-dependent manner by PNE. As effects on GABAergic LDT signaling are unknown, we used calcium imaging to evaluate GABA_A receptor- (GABA_A R as well as GABA_A -_ρ R) and GABA_B receptor (GABA_B R)-mediated calcium responses in LDT brain slices from female and male PNE mice in two different age groups. Overall, in older PNE females, changes in calcium induced by stimulation of GABA_A R and GABA_B R, including GABA_A -_ρ R were shifted toward calcium rises. In both young and old males, PNE was associated with alterations in calcium mediated by all three receptors; however, the GABA_A R was the most affected. These results show for the first time that PNE is associated with alterations in GABAergic transmission in the LDT in a sex- and age-dependent manner, and these data are the first to show PNE-associated alterations in functionality of GABA receptors in any nucleus. PNE-associated alterations in LDT GABAergic transmission within the LDT would be expected to alter output to target regions and could play a role in LDT-implicated, negative behavioral outcomes following gestational exposure to smoking. Accordingly, our data provide further supportive evidence of the importance of eliminating the consumption of nicotine during pregnancy.

Exposure to elevated embryonic kynurenine in rats: Sex-dependent learning and memory impairments in adult offspring

Distinct abnormalities in kynurenine pathway (KP) metabolism have been reported in various psychiatric disorders, including schizophrenia (SZ). Kynurenic acid (KYNA), a neuroactive metabolite of the KP, is elevated in individuals diagnosed with SZ and has been linked to cognitive impairments seen in the disorder. To further understand the role of KYNA in SZ etiology, we developed a prenatal insult model where kynurenine (100 mg/day) is fed to pregnant Wistar rats from embryonic day (ED) 15 to ED 22. As sex differences in the prevalence and severity of SZ have been observed, we presently investigated the impact of prenatal kynurenine exposure on KP metabolism and spatial learning and memory in male and female offspring. Specifically, brain tissue and plasma from offspring (control: ECon; kynurenine-treated: EKyn) in prepuberty (postnatal day (PD) 21), adolescence (PD 32-35), and adulthood (PD 56-85) were collected. Separate cohorts of adult offspring were tested in the Barnes maze to assess hippocampus- and prefrontal cortex-mediated learning and memory. Plasma tryptophan, kynurenine, and KYNA were unchanged between ECon and EKyn offspring across all three ages. Hippocampal and frontal cortex KYNA were elevated in male EKyn offspring only in adulthood, compared to ECon, while brain KYNA levels were unchanged in adult females. Male EKyn offspring were significantly impaired during acquisition of the Barnes maze and during reversal learning in the task. In female EKyn offspring, learning and memory remained relatively intact. Taken together, our data demonstrate that exposure to elevated kynurenine during the last week of gestation results in intriguing sex differences and further support the EKyn model as an attractive tool to study the pathophysiology of schizophrenia.

Unique, long-term effects of nicotine on adolescent brain

Adolescence is a time of major plasticity of brain systems that regulate motivated behavior and cognition, and is also the age of peak onset of nicotine use. Although there has been a decline in teen use of cigarettes in recent years, there has been a huge increase in nicotine vaping. It is therefore critically important to understand the impact of nicotine on this critical phase of brain development. Animal studies have shown that nicotine has unique effects on adolescent brain. The goal of this review is therefore to systematically evaluate age- and sex-differences in the effects of nicotine on brain and behavior. Both acute and chronic effects of nicotine on brain biochemistry and behavior, particularly drug reward, aversion, cognition and emotion, are evaluated. Gaps in our current knowledge that need to be addressed are also highlighted. This review compares and integrates human and animals findings. Although there can be no experimental studies in humans to confirm similar behavioral effects of teen nicotine exposure, an emerging observational literature suggests similarities across species. Given the substantial evidence for long-term negative impact of adolescent nicotine exposure on brain and behavior, further longitudinal assessment of health outcomes in teen and young adult e-cigarette users is warranted.

Health Hazards and Complications Associated with Electronic Cigarettes: A Review

Electronic cigarettes (ECs) are devices that vaporize and release a sweetened liquid containing nicotine as a substitute for burning tobacco. EC manufacturers have suggested that "vaping" is a safer alternative to conventional smoking because of the potential reduction of exposure to toxic substances. In 2019, National Youth Tobacco Survey reported that 10.5% and 27.5% of middle and high school students used ECs in the previous 30 days (0.6% and 1.5% in 2011, 3.3% and 11.7% in 2017, and 4.9% and 20.8 in 2018), respectively. Increased EC use among younger individuals is mainly because of the widespread perception that ECs are relatively less harmful than conventional cigarettes as they do not involve smoking tobacco and contain little or no nicotine. This review suggests that ECs may not be completely harmless. There are increasing number of case reports on various complications arising from using ECs, which are especially popular among young individuals and could negatively affect their health. Reported complications include lipoid pneumonia, acute eosinophilic pneumonia, hypersensitivity pneumonia, organizing pneumonia, diffuse alveolar hemorrhage, multiple reactive pulmonary nodules, subacute bronchiolitis, mouth and tongue injuries, dental injuries, complex facial fractures, thermal injuries, nickel contact allergy, C1 and C2 fractures, and fatal intoxication after ingesting liquids. Complications that develop directly from the substances in the devices and those resulting from device explosion and burning are being reported with increasing frequency. There is an urgent need for legislation and restriction regarding the sale of these devices considering their increasing frequency of use by younger individuals.

Infant neurobehavioural consequences of prenatal cigarette exposure: A systematic review and meta-analysis

AIM

Prenatal exposure to cigarettes leads to alterations in brain development during pregnancy. This has an impact on postnatal psychological and behavioural processes, affecting an infant's neurobehavioural profile with little known about which aspects are affected. The evidence was synthesised to assess the effects of prenatal cigarette smoke exposure on neurobehavioural outcomes within the first year of life.

METHODS

Six databases were searched (Web of Science Core Collections, MEDLINE, PsycINFO, CINAHL, EBSCOhost eBook Collection and OpenGrey) in November 2018. Eligible studies (n = 17) had to include a measure of prenatal cigarette exposure and a neurobehavioural assessment ≤1 year of age.

RESULTS

In the first year of life, specific areas of neurobehavioural functioning are related to prenatal cigarette exposure with eight out of 10 areas of neurobehaviour having significant medium (negative affect, attention, excitability, irritability and orientation) or small (muscle tone, regulation and difficult temperament) pooled effect sizes. Only lethargy and stress did not show any significant pooled effects.

CONCLUSION

Prenatal cigarette exposure affects a significant range of behaviours during the first year of life.

Electronic nicotine delivery system use is related to higher odds of alcohol and marijuana use in adolescents: Meta-analytic evidence

Research suggests that electronic nicotine delivery system (ENDS) use is associated with other substance use in adolescents; however, the magnitude of this association and whether this differs between adolescents and adults is not yet well understood. This meta-analysis aimed to quantify the extent to which ENDS use is associated with alcohol and marijuana use among adolescents and to compare the odds across adolescent samples and a comparison group of adult samples. A comprehensive literature review was conducted examining the relationship between ENDS use and alcohol (adolescent k = 40 from 19 independent studies; adult k = 35 from 12 independent studies) and marijuana (adolescent k = 24 from 14 independent studies; adult k = 6 from 3 independent studies) use. Adolescents who use ENDS had greater odds of reporting co-occurring alcohol use (OR = 4.50, p < .001), particularly binge drinking (OR = 4.51), and marijuana use (OR = 6.04, p < .001) than adolescent who did not use ENDS. Adults who use ENDS were also more likely to use alcohol (OR = 1.57, p < .001) and marijuana (OR = 2.04, p < .001) than those who did not use ENDS. ENDS use was associated with significantly greater odds of alcohol use (log odds ratio; LOR = 0.96 (OR = 2.61), p < .001) and a trend of greater marijuana use (LOR = 0.93 (OR = 2.53), p = 0.08) in adolescents than in adults. Effects were large in adolescents and small in adults. Findings suggest that ENDS use should be assessed in adolescents in both research and clinical settings. Importantly, ENDS use is strongly associated with co-occurring alcohol or marijuana use in adolescents.

Factors Associated with Poly Drug Use in Adolescents

Poly drug use in adolescents represents a significant public health issue, heightening risk for abuse, dependency, and a variety of short- and long-term psychological, psychosocial, and health consequences. However, past studies have typically examined just one or two substances in isolation and there is a lack of research that has comprehensively examined possible predictors of poly drug use in adolescents. To inform the development of comprehensive prevention programs that can simultaneously target multiple substances, the present study sought to identify psychological, environmental, and demographic factors that are most strongly associated with alcohol, tobacco, and cannabis poly drug use. Adolescents aged 15 to 17 years (n = 1661; 50.9% male) completed a survey on their use of alcohol, tobacco, and cannabis over the last 30 days. Various psychological, environmental, and demographic factors were also assessed. Weighted multiple-level logistic regression was conducted to assess the factors associated with poly drug use. In total, 20.3% of respondents had used at least one substance, 6.7% reported using two substances, and 3.3% reported using all three substances. The most common combined pattern of use was alcohol and tobacco, followed by alcohol and cannabis. Several factors emerged as significant, with conduct problems, depression, and the school environment accounting for the most variance. Specific psychological and environmental factors appear to be particularly important domains to target in adolescent substance use prevention programs. Early identification of adolescent depression and conduct problems and the development of programs that address these symptoms in youth may be effective approaches to delaying or preventing poly drug use in this population.

Prenatal nicotine exposure in mice induces sex-dependent anxiety-like behavior, cognitive deficits, hyperactivity, and changes in the expression of glutamate receptor associated-genes in the prefrontal cortex

In rodents, prenatal nicotine exposure (PNE) has been associated with increased risk for development of cognitive and emotional disturbances, but the findings are somewhat conflicting. Lack of behavioral alterations following PNE could be due to the variety of methods available for nicotine delivery, exposure time and species used, with inbred strains being mostly employed. Such differences suggest the need to investigate the behavioral phenotype in each PNE model available if we are to find models with enhanced translational value. In this study, we assessed sex-dependent effects of PNE on ADHD-related behaviors and on the levels of mRNA coding for glutamate receptor subunits within the prefrontal cortex in the outbred NMRI mice exposed to nicotine via maternal drinking water during gestation. Cotinine levels were assessed in newborn pups. Behaviors related to anxiety, compulsivity, working memory, and locomotion were evaluated in both sexes of young adult offspring using the elevated zero maze, marble burying, spontaneous alternation behavior, and locomotor activity tests. Expression of mRNA coding for different glutamate receptors subunits within the prefrontal cortex (PFC) was measured using RT-qPCR. Cotinine levels in the serum of newborns confirmed fetal nicotine exposure. Both male and female offspring showed ADHD-like behaviors, such as deficit in the SAB test and hyperactivity. In addition, PNE male mice displayed anxiety- and compulsive-like behaviors, effects that were absent in female offspring. Finally, PNE reduced the mRNA expression of GluN1-, GluN2B-, and mGluR2-related genes within the PFC of male offspring, whereas it reduced the expression of mRNA coding for GluA2 subunit in female mice. PNE in NMRI mice induced sex-dependent behavioral changes, which parallels clinical findings following maternal cigarette smoke exposure. Alterations detected in PFC mRNA glutamate receptor proteins could contribute to the abnormal behavioral responses observed, but other signaling pathways or brain regions are likely involved in the behavioral susceptibility of PNE individuals.

Childhood/Adolescent Smoking and Adult Smoking and Cessation: The International Childhood Cardiovascular Cohort (i3C) Consortium

Background

Despite declining US adolescent smoking prevalence from 40% among 12th graders in 1995 to around 10% in 2018, adolescent smoking is still a significant problem. Using the International Childhood Cardiovascular Cohort (i3C) Consortium, which includes 7 international cohorts recruited in childhood and followed into adulthood, the present study was designed to confirm the important relation between adolescent smoking and daily adult smoking and present new data on adult smoking into the forties and comparison of smoking in the United States, Finland, and Australia.

Methods and Results

Childhood smoking experience during ages 6 to 19 in the 1970s and 1980s was classifiable in 6687 i3C participants who also provided smoking status in their twenties and forties through 2011–2018. Prevalence of daily smoking in their twenties was directly related to degree of smoking during adolescence and inversely related to the age at which that smoking experience occurred (P trend, <0.001). Similar patterns were observed for prediction of smoking during age forties. Among the 2465 smokers in their twenties, cessation by their forties was generally inverse to degree of smoking in ages 6 to 19 (P trend, <0.001). Prevalence of smoking during adolescence and adulthood was similar among US, Finnish, and Australian participants.

Conclusions

These long‐term follow‐up data show that smoking intensity increased throughout adolescence. Prevalence of adult smoking and cessation by the forties were both correlated with levels of childhood smoking intensity. These data lend support to preventive strategies designed to reduce, delay, or eliminate any youth access to cigarettes.

Neurotoxicity of e-cigarettes

It appears that electronic cigarettes (EC) are a less harmful alternative to conventional cigarette (CC) smoking, as they generate substantially lower levels of harmful carcinogens and other toxic compounds. Thus, switching from CC to EC may be beneficial for smokers. However, recent accounts of EC- or vaping-associated lung injury (EVALI) has raised concerns regarding their adverse health effects. Additionally, the increasing popularity of EC among vulnerable populations, such as adolescents and pregnant women, calls for further EC safety evaluation. In this state-of-the-art review, we provide an update on recent findings regarding the neurological effects induced by EC exposure. Moreover, we discuss possible neurotoxic effects of nicotine and numerous other chemicals which are inherent both to e-liquids and EC aerosols. We conclude that in recognizing pertinent issues associated with EC usage, both government and scientific researchers must address this public health issue with utmost urgency.

Neuroinflammatory and Behavioral Outcomes Measured in Adult Offspring of Mice Exposed Prenatally to E-Cigarette Aerosols

BACKGROUND

In an effort to decrease the rates of smoking conventional tobacco cigarettes, electronic cigarettes (e-cigarettes) have been proposed as an effective smoking cessation tool. However, little is known about their toxicological impacts. This is concerning given that e-cigarette use is perceived as less harmful than conventional tobacco cigarettes during pregnancy for both the mother and fetus.

OBJECTIVE

The goal of this study was to test the neurodevelopmental consequences of maternal e-cigarette use on adult offspring behavior and neuroimmune outcomes.

METHODS

Pregnant female CD-1 mice were randomly assigned to one of three treatment groups (n=8-10 per group) and exposed daily to either filtered air, propylene glycol and vegetable glycerol (50:50 PG/VG vehicle), or to PG/VG with 16mg/mL nicotine (+Nic). Whole-body exposures were carried out for 3 h/d, 7 d/week, from gestational day (GD)0.5 until GD17.5. Adult male and female offspring (8 weeks old) were assessed across a battery of behavioral assessments followed by region-specific quantification of brain cytokines using multiplex immunoassays.

RESULTS

Adult offspring of both sexes exposed to +Nic exhibited elevated locomotor activity in the elevated plus maze and altered stress-coping strategies in the forced swim task. Moreover, male and female offspring exposed to PG/VG with and without nicotine had a 5.2% lower object discrimination score in the novel object recognition task. In addition to differences in offspring behavior, maternal e-cigarette exposure with nicotine led to a reduction in interleukin (IL)-4 and interferon-gamma (IFNγ) in the diencephalon, as well as lower levels of hippocampal IFNγ (females only). E-cigarette exposure without nicotine resulted in a 2-fold increase of IL-6 in the cerebellum.

DISCUSSION

These findings support previous adverse findings of e-cigarette exposure on neurodevelopment in a mouse model and provide substantial evidence of persistent adverse behavioral and neuroimmunological consequences to adult offspring following maternal e-cigarette exposure during pregnancy. https://doi.org/10.1289/EHP6067.

Transitions across tobacco use profiles among adolescents: results from the Population Assessment of Tobacco and Health (PATH) study waves 1 and 2

BACKGROUND AND AIMS

To estimate progression to polytobacco use (PTU) over 1 year among a sample of US youth.

DESIGN

Prospective survey with two waves 1 year apart: wave 1 (2013-14) and wave 2 (2014-15). We conducted latent transition analysis (LTA) to identify latent class transitions and examine socio-demographic predictors of transition types.

SETTING

United States.

PARTICIPANTS

A total of 11, 996 people who were aged 12-17 years at wave 1.

MEASUREMENTS

Publicly available data were used from the Population Assessment of Tobacco and Health (PATH) study, a nationally representative sample of US civilian, non-institutionalized population aged 12 years and older. Tobacco use status was assessed and classified in terms of: never use, non-current (not in the past 30 days) and current (past 30-day) use of cigarettes, cigars, e-cigarettes, hookah and smokeless tobacco. Other nicotine products were excluded because rates of use were either too low to model (e.g. pipe) or the product was not assessed in the PATH youth sample (e.g. nicotine replacement products).

FINDINGS

We identified three distinct patterns: class 1, non-use (wave 1 prevalence = 86%; wave 2 prevalence = 78%); class 2, ever use of cigarettes and e-cigarettes (wave 1 prevalence = 11%; wave 2 prevalence = 14%); and class 3, current PTU (wave 1 prevalence = 4%; wave 2 prevalence = 7%). Probability of progression from non-use to ever use of cigarettes and e-cigarettes was 0.06 and ever use of cigarettes and e-cigarettes to current PTU was 0.32. Non-users were more likely to transition to ever use of cigarettes and e-cigarettes if they were older (versus younger), white (versus non-white) or if their parental education level was high school or less (versus more than high school); and ever users of cigarettes and e-cigarettes to current PTU if they were older, male or white.

CONCLUSIONS

US youth who had previously tried e-cigarettes and cigarettes at wave 1 (2013-14) had a 32% chance of transitioning to current use of two or more tobacco products within 1 year.

Nicotine enhances auditory processing in healthy and normal-hearing young adult nonsmokers

RATIONALE

Electrophysiological studies show that systemic nicotine narrows frequency receptive fields and increases gain in neural responses to characteristic frequency stimuli. We postulated that nicotine enhances related auditory processing in humans.

OBJECTIVES

The main hypothesis was that nicotine improves auditory performance. A secondary hypothesis was that the degree of nicotine-induced improvement depends on the individual's baseline performance.

METHODS

Young (18-27 years old), normal-hearing nonsmokers received nicotine (Nicorette gum, 6mg) or placebo gum in a single-blind, randomized, crossover design. Subjects performed four experiments involving tone-in-noise detection, temporal gap detection, spectral ripple discrimination, and selective auditory attention before and after treatment. The perceptual differences between posttreatment nicotine and placebo conditions were measured and analyzed as a function of the pre-treatment baseline performance.

RESULTS

Nicotine significantly improved performance in the more difficult tasks of tone-in-noise detection and selective attention (effect size = - 0.3) but had no effect on relatively easier tasks of temporal gap detection and spectral ripple discrimination. The two tasks showing significant nicotine effects further showed no baseline-dependent improvement.

CONCLUSIONS

Nicotine improves auditory performance in difficult listening situations. The present results support future investigation of nicotine effects in clinical populations with auditory processing deficits or reduced cholinergic activation.

Dual recombinase fate mapping reveals a transient cholinergic phenotype in multiple populations of developing glutamatergic neurons

Cholinergic transmission shapes the maturation of glutamatergic circuits, yet the developmental sources of acetylcholine have not been systematically explored. Here, we have used Cre-recombinase-mediated genetic labeling to identify and map both mature and developing CNS neurons that express choline acetyltransferase (ChAT). Correction of a significant problem with a widely used ChatCre transgenic line ensures that this map does not contain expression artifacts. ChatCre marks all known cholinergic systems in the adult brain, but also identifies several brain areas not usually regarded as cholinergic, including specific thalamic and hypothalamic neurons, the subiculum, the lateral parabrachial nucleus, the cuneate/gracilis nuclei, and the pontocerebellar system. This ChatCre fate map suggests transient developmental expression of a cholinergic phenotype in areas important for cognition, motor control, and respiration. We therefore examined expression of ChAT and the vesicular acetylcholine transporter in the embryonic and early postnatal brain to determine the developmental timing of this transient cholinergic phenotype, and found that it mirrored the establishment of relevant glutamatergic projection pathways. We then used an intersectional genetic strategy combining ChatCre with Vglut2Flp to show that these neurons adopt a glutamatergic fate in the adult brain. The transient cholinergic phenotype of these glutamatergic neurons suggests a homosynaptic source of acetylcholine for the maturation of developing glutamatergic synapses. These findings thus define critical windows during which specific glutamatergic circuits may be vulnerable to disruption by nicotine in utero, and suggest new mechanisms for pediatric disorders associated with maternal smoking, such as sudden infant death syndrome.

Maternal Nicotine Exposure During Gestation and Lactation Period Affects Behavior and Hippocampal Neurogenesis in Mouse Offspring

Cigarette smoking or nicotine exposure during pregnancy is associated with numerous obstetrical, fetal, and developmental complications, as well as an increased risk of adverse health consequences in the adult offspring. In this study, we examined the effects of maternal nicotine exposure during perinatal and lactation stages on behavioral performance and hippocampal neurogenesis in the adolescent stage of offspring mice. Female C57BL/mice received nicotine in drinking water (200 μg/ml nicotine) or vehicle (1% saccharin) starting from 2 weeks premating until the offspring were weaned on postnatal day 20. Experiments started on postnatal day 35. Female offspring with maternal nicotine exposure presented an increase in anxiety-like behavior in an open-field test. BrdU assay revealed that nicotine offspring presented an increase in cell proliferation in hippocampal dentate gyrus, but the number of BrdU⁺ cells was decreased in one week and further decreased in three weeks. The occurrence of disarray of DCX⁺ cells increased in both male and female nicotine offspring. The density of microglial marker protein Iba1 was significantly increased in the nicotine offspring. Furthermore, the expression of microglia marker Iba1, the CX3CL1, CX3CR1, and downstream molecules PKA and p-ErK were significantly increased in the nicotine group. In summary, maternal nicotine exposure affects both hippocampal neurogenesis and microglial activity in the adolescent offspring.

Comparison of Protective Effects of Electroacupuncture at ST 36 and LU 5 on Pulmonary and Hypothalamic Pituitary Adrenal Axis Changes in Perinatal Nicotine-Exposed Rats

BACKGROUND

Maternal smoking and/or exposure to environmental tobacco smoke continue to be significant factors in fetal and childhood morbidity and are a serious public health issue worldwide. Nicotine passes through the placenta easily with minimal biotransformation, entering fetal circulation, where it results in many harmful effects on the developing offspring, especially on the developing respiratory system.

OBJECTIVES

Recently, in a rat model, electroacupuncture (EA) at maternal acupoints ST 36 has been shown to block perinatal nicotine-induced pulmonary damage; however, the underlying mechanism and the specificity of ST 36 acupoints for this effect are unknown. Here, we tested the hypothesis that compared with EA at ST 36, EA at LU 5 acupoints, which are on lung-specific meridian, will be equally or more effective in preventing perinatal nicotine-induced pulmonary changes.

METHODS

Twenty-four pregnant rat dams were randomly divided into 4 groups: saline ("S"), nicotine ("N"), nicotine + ST 36 (N + ST 36), and nicotine + LU 5 (N + LU 5) groups. Nicotine (1 mg/kg, subcutaneously) and EA (at ST 36 or LU 5 acupoints, bilaterally) were administered from embryonic day 6 to postnatal day 21 once daily. The "S" group was injected saline. As needed, using ELISA, western analysis, q-RT-PCR, lung histopathology, maternal and offspring hypothalamic pituitary adrenal axes, offspring key lung developmental markers, and lung morphometry were determined.

RESULTS

With nicotine exposure, alveolar count decreased, but mean linear intercept and septal thickness increased. It also led to a decrease in pulmonary function and PPARγ and an increase of β-catenin and glucocorticoid receptor expression in lung tissue and corticosterone in the serum of offspring rats. Electroacupuncture at ST 36 normalized all of these changes, whereas EA at LU 5 had no obvious effect.

CONCLUSION

Electroacupuncture applied to ST 36 acupoints provided effective protection against perinatal nicotine-induced lung changes, whereas EA applied at LU 5 acupoints was ineffective, suggesting mechanistic specificity and HPA axis' involvement in mediating EA at ST 36 acupoints' effects in mitigating perinatal nicotine-induced pulmonary phenotype. This opens the possibility that other acupoints, besides ST 36, can have similar or even more robust beneficial effects on the developing lung against the harmful effect of perinatal nicotine exposure. The approach proposed by us is simple, cheap, quick, easy to administer, and is devoid of any significant side effects.

Microglial activation increases cocaine self-administration following adolescent nicotine exposure

With the rise of e-cigarette use, teen nicotine exposure is becoming more widespread. Findings from clinical and preclinical studies show that the adolescent brain is particularly sensitive to nicotine. Animal studies have demonstrated that adolescent nicotine exposure increases reinforcement for cocaine and other drugs. However, the mechanisms that underlie these behaviors are poorly understood. Here, we report reactive microglia are critical regulators of nicotine-induced increases in adolescent cocaine self-administration. Nicotine has dichotomous, age-dependent effects on microglial morphology and immune transcript profiles. A multistep signaling mechanism involving D2 receptors and CX3CL1 mediates nicotine-induced increases in cocaine self-administration and microglial activation. Moreover, nicotine depletes presynaptic markers in a manner that is microglia-, D2- and CX3CL1-dependent. Taken together, we demonstrate that adolescent microglia are uniquely susceptible to perturbations by nicotine, necessary for nicotine-induced increases in cocaine-seeking, and that D2 receptors and CX3CL1 play a mechanistic role in these phenomena.

Adolescents are particularly sensitive to nicotine. Here the authors show that in mice, microglial activation contributes to the enhanced sensitivity to cocaine caused by nicotine exposure in young mice.

Cannabis Use and Consequences

As an increasing number of states legalize cannabis use for recreational and/or medical purposes, it is increasingly important to understand the neural and cognitive consequences of recreational cannabis use in adolescent consumers. Adolescence is marked by ongoing neuromaturational processes, making this a particularly vulnerable period, particularly regarding exposure to drugs, including cannabis. This review highlights evidence from studies documenting the neural impact of cannabis use in adolescence and explores mediating factors related to cannabis use.

Risk factors for multiple tobacco product use among high school youth

PURPOSE

To examine how youth multiple tobacco product (MTP) users differ relative to non-users and to single-product users on risk factors at multiple levels of influence.

METHODS

We analyzed data on high school students from the North Carolina Youth Tobacco Survey, 2015 (n = 2922). Single- and MTP use were defined as use of one, or two or more tobacco products in the past month, respectively. Multinomial regressions estimated the association between risk factors and MTP use compared to single-product use and non-use of tobacco. Risk factors included intra-personal (e.g., harm perceptions), and interpersonal (e.g., household, peer tobacco use, secondhand smoke or vapor, and advertising) factors.

RESULTS

Of students, 12% and 13% were single product and MTP users, respectively. Many differences emerged between MTP users and non-tobacco users, with MTP users showing lower harm perceptions, higher perceived social benefits of smoking, significantly higher relative risk of having friends who use tobacco (RRR = 4.79, 95% CI 3.42, 6.70), of exposure to secondhand e-cigarette vapor (RRR = 1.35, 95% CI 1.23, 1.48), and of being receptive to tobacco marketing (RRR = 4.01, 95% CI 2.87, 5.61). Fewer differences emerged between MTP and single product users with MTP users having significantly higher relative risk of having friends who use tobacco (RRR = 2.31 95% CI 1.73, 3.07), of exposure to secondhand vapor (RRR = 1.10, 95% CI 1.02, 1.18), and of being receptive to tobacco marketing (RRR = 1.71, 95% CI 1.17, 2.50).

CONCLUSIONS

Efforts that target multiple tobacco product use should increase youth tobacco-related harm perceptions, and protect youth from social, peer, and industry influences.

Prenatal nicotine sex-dependently alters adolescent dopamine system development

Despite persistent public health initiatives, many women continue to smoke during pregnancy. Since maternal smoking has been linked to persisting sex-dependent neurobehavioral deficits in offspring, some consider nicotine to be a safer alternative to tobacco during pregnancy, and the use of electronic nicotine delivery systems is on the rise. We presently show, however, that sustained exposure to low doses of nicotine during fetal development, approximating plasma levels seen clinically with the nicotine patch, produces substantial changes in developing corticostriatal dopamine systems in adolescence. Briefly, pregnant dams were implanted on gestational day 4 with an osmotic minipump that delivered either saline (GS) or nicotine (3 mg/kg/day) (GN) for two weeks. At birth, pups were cross-fostered with treatment naïve dams and were handled daily. Biochemical analyses, signaling assays, and behavioral responses to cocaine were assessed on postnatal day 32, representative of adolescence in the rodent. GN treatment had both sex-dependent and sex-independent effects on prefrontal dopamine systems, altering Catechol-O-methyl transferase (COMT)-dependent dopamine turnover in males and norepinephrine transporter (NET) binding expression in both sexes. GN enhanced cocaine-induced locomotor activity in females, concomitant with GN-induced reductions in striatal dopamine transporter (DAT) binding. GN enhanced ventral striatal D2-like receptor expression and G-protein coupling, while altering the roles of D2 and D3 receptors in cocaine-induced behaviors. These data show that low-dose prenatal nicotine treatment sex-dependently alters corticostriatal dopamine system development, which may underlie clinical deficits seen in adolescents exposed to tobacco or nicotine in utero.

Developmental Nicotine Exposure Alters Synaptic Input to Hypoglossal Motoneurons and Is Associated with Altered Function of Upper Airway Muscles

Nicotine exposure during the fetal and neonatal periods [developmental nicotine exposure (DNE)] is associated with ineffective upper airway protective reflexes in infants. This could be explained by desensitized chemoreceptors and/or mechanoreceptors, diminished neuromuscular transmission or altered synaptic transmission among central neurons, as each of these systems depend in part on cholinergic signaling through nicotinic AChRs (nAChRs). Here, we showed that DNE blunts the response of the genioglossus (GG) muscle to nasal airway occlusion in lightly anesthetized rat pups. The GG muscle helps keep the upper airway open and is innervated by hypoglossal motoneurons (XIIMNs). Experiments using the phrenic nerve-diaphragm preparation showed that DNE does not alter transmission across the neuromuscular junction. Accordingly, we used whole cell recordings from XIIMNs in brainstem slices to examine the influence of DNE on glutamatergic synaptic transmission under baseline conditions and in response to an acute nicotine challenge. DNE did not alter excitatory transmission under baseline conditions. Analysis of cumulative probability distributions revealed that acute nicotine challenge of P1–P2 preparations resulted in an increase in the frequency of nicotine-induced glutamatergic inputs to XIIMNs in both control and DNE. By contrast, P3–P5 DNE pups showed a decrease, rather than an increase in frequency. We suggest that this, together with previous studies showing that DNE is associated with a compensatory increase in inhibitory synaptic input to XIIMNs, leads to an excitatory-inhibitory imbalance. This imbalance may contribute to the blunting of airway protective reflexes observed in nicotine exposed animals and human infants.

E-cigarette use as a potential cardiovascular disease risk behavior

Electronic cigarette (e-cigarette) use is rapidly increasing among youth and adults despite limited information regarding the long-term risks or benefits. The potential impact of e-cigarette use on public health is complex. E-cigarettes are sometimes considered as smoking cessation aids and, to the extent that they are successful in this regard, could have a net population benefit for adult smokers. However, limited knowledge exists about the long-term health effects of e-cigarette use, and research has suggested these novel tobacco products may lead to initiation and continued use among vulnerable populations, including youth. The current review aimed to summarize trends and available scientific information about e-cigarette use, focusing on the potential cardiovascular health risks and benefits, characteristics associated with e-cigarette use, and critical areas for future investigation to inform the research and clinical work of psychologists. Psychologists have a leadership role in mitigating health risks from smoking behavior, and there is a need for rigorous research assessing the impact of e-cigarette use on population health. In addition, psychologists are uniquely qualified to understand the underlying processes regarding decision-making and behaviors around e-cigarette use. Collectively, the research of psychologists in this area can have a substantial impact on patient education, policies, and the development of prevention and intervention programs to promote public health. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Adolescent neurodevelopment and substance use: Receptor expression and behavioral consequences

Adolescence is the transitional period between childhood and adulthood, during which extensive brain development occurs. Since this period also overlaps with the initiation of drug use, it is important to consider how substance use during this time might produce long-term neurobiological alterations, especially against the backdrop of developmental changes in neurotransmission. Alcohol, cannabis, nicotine, and opioids all produce marked changes in the expression and function of the neurotransmitter and receptor systems with which they interact. These acute and chronic alterations also contribute to behavioral consequences ranging from increased addiction risk to cognitive or neuropsychiatric behavioral dysfunctions. The current review provides an in-depth overview and update of the developmental changes in neurotransmission during adolescence, as well as the impact of drug exposure during this neurodevelopmental window. While most of these factors have been studied in animal models, which are the focus of this review, future longitudinal studies in humans that assess neural function and behavior will help to confirm pre-clinical findings. Furthermore, the neural changes induced by each drug should also be considered in the context of other contributing factors, such as sex. Further understanding of these consequences can help in the identification of novel approaches for preventing and reversing the neurobiological effects of adolescent substance use.

Associations of ADHD Symptoms With Smoking and Alternative Tobacco Product Use Initiation During Adolescence

Objective

Recently, use of alternative tobacco products, such as electronic cigarettes (e-cigarettes) and hookah (water-pipe tobacco), has increased among adolescents. It is unknown whether attention-deficit hyperactivity disorder (ADHD) symptoms are associated with initiation of alternative tobacco product use.

Methods

Ninth grade high school students who never used any tobacco product at baseline (N = 1,921) participated in a longitudinal survey from 2014 to 2015. Overall symptomatology and inattention (IN) and hyperactivity-impulsivity (HI) ADHD subtypes were assessed at baseline. Past 6-month e-cigarette, hookah, and combustible cigarette use (yes/no) were reported at three semi-annual follow-ups. Repeated measures logistic regression models assessed the association of baseline ADHD symptoms with likelihood of tobacco product initiation across follow-ups.

Results

For ADHD main effect estimates, unadjusted odds of reporting e-cigarette, hookah, and combustible cigarette use pooled across follow-up time points were 45%, 33%, and 37% greater, respectively, with each increase in one SD-unit of baseline ADHD symptoms in baseline never-users of tobacco products. ADHD was not associated with hookah or combustible cigarette use after adjusting for other risk factors. After adjustment, e-cigarette use initiation remained associated with overall ADHD (odds ratio, OR [95%confidence interval, 95% CI] = 1.22 [1.04, 1.42]) and HI (OR [95% CI] = 1.26 [1.09, 1.47]) symptoms, but not IN symptoms (OR [95% CI] = 1.13 [0.97, 1.32]). ADHD × Time interactions were not significant, suggesting ADHD increased odds of e-cigarette use initiation but did not alter the shape of use trajectory across follow-up among initiators.

Conclusions

Understanding the psychosocial mechanisms underlying the pathway from ADHD to e-cigarette use may advance tobacco product use etiologic theory and prevention practice in the current era in which e-cigarette use is popular among youth.

Does early maternal responsiveness buffer prenatal tobacco exposure effects on young children's behavioral disinhibition?

Children with prenatal tobacco exposure (PTE) exhibit early self-regulatory impairments, reflecting a life-course persistent propensity toward behavioral disinhibition. Previously, we demonstrated the protective role of parental responsiveness for reducing the risk of exposure-related disruptive behavior in adolescence. Here, we expanded this line of inquiry, examining whether responsiveness moderates the relation of PTE to a broader set of behavioral disinhibition features in early childhood and testing alternative diathesis-stress versus differential susceptibility explanatory models. PTE was assessed prospectively using interviews and bioassays in the Midwestern Infant Development Study (MIDS). Mother-child dyads (N = 276) were re-assessed at approximately 5 years of age in a preschool follow-up. We quantified maternal responsiveness and child behavioral disinhibition using a combination of directly observed activities in the lab and developmentally sensitive questionnaires. Results supported a diathesis-stress pattern. Children with PTE and less responsive mothers showed increased disruptive behavior and lower effortful control compared with children without PTE. In contrast, exposed children with more responsive mothers had self-regulatory profiles similar to their non-exposed peers. We did not observe sex differences. Findings provide greater specification of the protective role of maternal responsiveness for self-regulation in children with PTE and help clarify mechanisms that may underscore trajectories of exposure-related behavioral disinhibition.

Characterizing Polytobacco Use Trajectories and Their Associations With Substance Use and Mental Health Across Mid-Adolescence

Background

Polytobacco product use is suspected to be common, dynamic across time, and increase risk for adverse behavioral outcomes. We statistically modeled characteristic types of polytobacco use trajectories during mid-adolescence and tested their prospective association with substance use and mental health problems.

Methods

Adolescents (N = 3393) in Los Angeles, CA, were surveyed semiannually from 9th to 11th grade. Past 6-month combustible cigarette, e-cigarette, or hookah use (yes/no) over four assessments were analyzed using parallel growth mixture modeling to identify a parsimonious set of polytobacco use trajectories. A tobacco product use trajectory group was used to predict substance use and mental health at the fifth assessment.

Results

Three profiles were identified: (1) tobacco nonusers (N = 2291, 67.5%) with the lowest use prevalence (<3%) of all products across all timepoints; (2) polyproduct users (N = 920, 27.1%) with moderate use prevalence of each product (8–35%) that escalated for combustible cigarettes but decreased for e-cigarettes and hookah across time; and (3) chronic polyproduct users (N = 182, 5.4%) with high prevalence of each product use (38–86%) that escalated for combustible cigarettes and e-cigarettes. Nonusers, polyproduct users, and chronic polyproduct users reported successively higher alcohol, marijuana, and illicit drug use and ADHD at the final follow-up, respectively. Both tobacco using groups (vs. nonusers) reported greater odds of depression and anxiety at the final follow-up but did not differ from each other.

Conclusions

Adolescent polytobacco use may involve a common moderate risk trajectory and a less common high-risk chronic trajectory. Both trajectories predict substance use and mental health symptomology.

Implications

Variation in use and co-use of combustible cigarette, e-cigarette, and hookah use in mid-adolescence can be parsimoniously characterized by a small set common trajectory profiles in which polyproduct use are predominant patterns of tobacco product use, which predict adverse behavioral outcomes. Prevention and policy addressing polytobacco use (relative to single product use) may be optimal tobacco control strategies for youth, which may in turn prevent other forms of substance use and mental health problems.

Trends in Tobacco Product Use Patterns Among U.S. Youth, 1999-2014

Introduction

We examined trends in seven mutually exclusive tobacco product use patterns (T-PUPs) in nationally representative samples of U.S. youth over time and age.

Methods

We used time varying effect modeling on National Youth Tobacco Surveys, 1999-2014 (N = 38662, 9-17 years, M = 15.02). Regression coefficients were estimated as a non-parametric function of time. T-PUPs were cigarette only, non-cigarette combustible only, noncombustible only, non-cigarette combustible and noncombustible dual, cigarette and noncombustible dual, cigarette and non-cigarette combustible dual, and POLY (i.e. cigarettes, non-cigarette combustibles, and noncombustibles) use.

Results

Among youth tobacco users, cigarette only use was the predominant T-PUP from 1999 to 2010. After 2010 and 2013, non-cigarette combustible only (AOR 1.38, CI = 1.02-1.87) and noncombustible only (AOR 1.57, CI = 1.00-2.45) use became more prevalent than cigarette only use. In 2011, dual and POLY T-PUPs were on the rise although not significantly different from cigarette only use. Cigarette only use was the predominant T-PUP among 11- to 17-year-old tobacco users. Non-cigarette combustible only (AOR 0.14, CI = 0.10-0.19), noncombustible only (AOR 0.01, CI = 0.008-0.02), non-cigarette combustible and noncombustible (AOR 0.01, CI = 0.01-0.03), cigarette and noncombustible (AOR 0.02, CI = 0.01-0.04), cigarette and non-cigarette combustible (AOR 0.32, CI = 0.24-0.43), and POLY (AOR 0.02, CI = 0.01-0.04) use were less prevalent than cigarette only use at age 17.

Conclusions

Non-cigarette, dual, and POLY T-PUPs are rising among youth tobacco users. Screening for all tobacco use and delivering treatment during pediatrician visits should be standard clinical practice.

Implications

Tracking trends in tobacco product use patterns (T-PUPs) over time and age is necessary to achieve Healthy People 2020 goal of reducing tobacco use among youth. Trends over time show a rise of non-cigarette T-PUPs especially noncombustible products but cigarette only use remains the most prevalent among 11- to 17-year-old tobacco users. The recent extension of FDA's regulatory jurisdiction over all tobacco products (e.g. e-cigarettes, hookah) is a step toward comprehensive tobacco control especially among youth. Public health practitioners should extend prevention and cessation efforts among youth to T-PUPs beyond exclusive cigarette smoking.

Prenatal Nicotine Exposure Disrupts Infant Neural Markers of Orienting

Introduction

Prenatal nicotine exposure (PNE) from maternal cigarette smoking is linked to developmental deficits, including impaired auditory processing, language, generalized intelligence, attention, and sleep. Fetal brain undergoes massive growth, organization, and connectivity during gestation, making it particularly vulnerable to neurotoxic insult. Nicotine binds to nicotinic acetylcholine receptors, which are extensively involved in growth, connectivity, and function of developing neural circuitry and neurotransmitter systems. Thus, PNE may have long-term impact on neurobehavioral development. The purpose of this study was to compare the auditory K-complex, an event-related potential reflective of auditory gating, sleep preservation and memory consolidation during sleep, in infants with and without PNE and to relate these neural correlates to neurobehavioral development.

Methods

We compared brain responses to an auditory paired-click paradigm in 3- to 5-month-old infants during Stage 2 sleep, when the K-complex is best observed. We measured component amplitude and delta activity during the K-complex.

Results

Infants with PNE demonstrated significantly smaller amplitude of the N550 component and reduced delta-band power within elicited K-complexes compared to nonexposed infants and also were less likely to orient with a head turn to a novel auditory stimulus (bell ring) when awake.

Conclusions

PNE may impair auditory sensory gating, which may contribute to disrupted sleep and to reduced auditory discrimination and learning, attention re-orienting, and/or arousal during wakefulness reported in other studies.

Implications

Links between PNE and reduced K-complex amplitude and delta power may represent altered cholinergic and GABAergic synaptic programming and possibly reflect early neural bases for PNE-linked disruptions in sleep quality and auditory processing. These may pose significant disadvantage for language acquisition, attention, and social interaction necessary for academic and social success.

Warning Statements and Safety Practices Among Manufacturers and Distributors of Electronic Cigarette Liquids in the United States

Introduction

Prior to the US Food and Drug Administration's (FDA) regulation of electronic cigarettes and warning statements related to nicotine addiction, there was no critical examination of manufacturer/distributor voluntary practices that could potentially inform FDA actions aimed to protect consumers. This study examined the content of warning statements and safety characteristics of electronic cigarette liquid bottles using a national sample.

Methods

Research staff randomly selected four electronic cigarette liquid manufacturers/distributors from four US geographic regions. Staff documented the characteristics of product packaging and content of warning statements on 147 electronic cigarette liquids (0-30 mg/ml of nicotine) purchased online from 16 manufacturers/distributors in April of 2016.

Results

Data showed that 97.9% of the electronic cigarette liquid bottles included a warning statement, most of which focused on nicotine exposure rather than health. Only 22.4% of bottles used a warning statement that indicated the product "contained nicotine." Of bottles that advertised a nicotine-based concentration of 12 mg/ml, 26% had a warning statements stated that the product "contains nicotine." None of the statements that indicated that the product "contained nicotine" stated that nicotine was "addictive." All bottles had a safety cap and 12% were in plastic shrink-wrap. Fifty-six percent of the websites had a minimum age requirement barrier that prevented under-aged persons from entering.

Conclusions

Most manufacturers/distributors printed a warning statement on electronic cigarette liquid bottles, but avoided warning consumers about the presence and the addictiveness of nicotine. Studies are needed to examine manufacturer/distributor modifications to product packaging and how packaging affects consumer behaviors.

Implications

These data can inform future FDA requirements related to the packaging and advertising of e-cigarette liquids; regulation related to the content of warning statements, including exposure warning statements, which are not currently mandated; and requirements on websites or language on packaging to help manufacturers adhere to the minimum age of purchase regulation. The data can also be used to help FDA develop additional guidance on the framing of statements on packaging that helps consumers make informed decisions about purchasing the product or protecting young people from use or unintentional exposure to the product.

Experience during adolescence shapes brain development: From synapses and networks to normal and pathological behavior

Adolescence is a period of dramatic neural reorganization creating a period of vulnerability and the possibility for the development of psychopathology. The maturation of various neural circuits during adolescence depends, to a large degree, on one's experiences both physical and psychosocial. This occurs through a process of plasticity which is the structural and functional adaptation of the nervous system in response to environmental demands, physiological changes and experiences. During adolescence, this adaptation proceeds upon a backdrop of structural and functional alterations imparted by genetic and epigenetic factors and experiences both prior to birth and during the postnatal period. Plasticity entails an altering of connections between neurons through long-term potentiation (LTP) (which alters synaptic efficiency), synaptogenesis, axonal sprouting, dendritic remodeling, neurogenesis and recruitment (Skaper et al., 2017). Although most empirical evidence for plasticity derives from studies of the sensory systems, recent studies have suggested that during adolescence, social, emotional, and cognitive experiences alter the structure and function of the networks subserving these domains of behavior. Each of these neural networks exhibits heightened vulnerability to experience-dependent plasticity during the sensitive periods which occur in different circuits and different brain regions at specific periods of development. This report will summarize some examples of adaptation which occur during adolescence and some evidence that the adolescent brain responds differently to stimuli compared to adults and children. This symposium, "Experience during adolescence shapes brain development: from synapses and networks to normal and pathological behavior" occurred during the Developmental Neurotoxicology Society/Teratology Society Annual Meeting in Clearwater Florida, June 2018. The sections will describe the maturation of the brain during adolescence as studied using imaging technologies, illustrate how plasticity shapes the structure of the brain using examples of pathological conditions such as Tourette's' syndrome and attention deficit hyperactivity disorder, and a review of the key molecular systems involved in this plasticity and how some commonly abused substances alter brain development. The role of stimulants used in the treatment of attention deficit hyperactivity disorder (ADHD) in the plasticity of the reward circuit is then described. Lastly, clinical data promoting an understanding of peer-influences on risky behavior in adolescents provides evidence for the complexity of the roles that peers play in decision making, a phenomenon different from that in the adult. Imaging studies have revealed that activation of the social network by the presence of peers at times of decision making is unique in the adolescent. Since normal brain development relies on experiences which alter the functional and structural connections between cells within circuits and networks to ultimately alter behavior, readers can be made aware of the myriad of ways normal developmental processes can be hijacked. The vulnerability of developing adolescent brain places the adolescent at risk for the development of a life time of abnormal behaviors and mental disorders.

Initial e-cigarette flavoring and nicotine exposure and e-cigarette uptake among adolescents

OBJECTIVE

E-cigarettes are the most prevalent tobacco product used by adolescents. We sought to determine whether the presence of flavoring and/or the presence of nicotine at the first e-cigarette exposure predicted progression to current e-cigarette use (use in past 30 days) as well as escalation in use (number of days in the past 30 days) among adolescents.

METHODS

Adolescents from public high schools outside of Philadelphia, PA completed in-classroom surveys at baseline (9^th grade) and at 6-month intervals for the following 18 months (fall 2018, beginning of 11^th grade). Adolescents who reported ever having used e-cigarettes at baseline (N = 354) comprised the analytical sample.

RESULTS

We employed a two-part Latent Growth Curve Model including flavor, nicotine, and other covariates. Initial use of a flavored (vs unflavored) e-cigarette was associated with progression to current e-cigarette use (β = 0.54, z = 2.09, p = 0.04) and escalation in the number of days of e-cigarette use (β = 0.35, z = 2.58, p = 0.01) across the following 18 months. Initial use of an e-cigarette with nicotine (vs without nicotine) was associated with a greater number of days of e-cigarette use at baseline (β = 0.49, z = 2.16, p = 0.03).

CONCLUSIONS

The findings underscore the risk that flavoring and nicotine pose for progression beyond initial e-cigarette use. Regulations addressing flavoring and nicotine in e-cigarettes have the potential to reduce the number of adolescents who become current as well as frequent e-cigarette users.

Neonatal Nicotine Exposure Primes Midbrain Neurons to a Dopaminergic Phenotype and Increases Adult Drug Consumption

BACKGROUND

Nicotine intake induces addiction through neuroplasticity of the reward circuitry, altering the activity of dopaminergic neurons of the ventral tegmental area. Prior work demonstrated that altered circuit activity can change neurotransmitter expression in the developing and adult brain. Here we investigated the effects of neonatal nicotine exposure on the dopaminergic system and nicotine consumption in adulthood.

METHODS

Male and female mice were used for two-bottle-choice test, progressive ratio breakpoint test, immunohistochemistry, RNAscope, quantitative polymerase chain reaction, calcium imaging, and DREADD (designer receptor exclusively activated by designer drugs)-mediated chemogenic activation/inhibition experiments.

RESULTS

Neonatal nicotine exposure potentiates drug preference in adult mice, induces alterations in calcium spike activity of midbrain neurons, and increases the number of dopamine-expressing neurons in the ventral tegmental area. Specifically, glutamatergic neurons are first primed to express transcription factor Nurr1, then acquire the dopaminergic phenotype following nicotine re-exposure in adulthood. Enhanced neuronal activity combined with Nurr1 expression is both necessary and sufficient for the nicotine-mediated neurotransmitter plasticity to occur.

CONCLUSIONS

Our findings illuminate a new mechanism of neuroplasticity by which early nicotine exposure primes the reward system to display increased susceptibility to drug consumption in adulthood.

A narrative review evaluating the safety and efficacy of e-cigarettes as a newly marketed smoking cessation tool

Introduction:

E-cigarettes are an alternative to traditional tobacco-based cigarettes. While having considerable societal awareness, conflicting evidence exists to support their claims that they are an effective smoking cessation tool and are safe. Currently >7000 flavours exist with evidence that they exhibit detrimental cellular and tissue effects. A literature review was conducted utilising PubMed and Google Scholar Databases identifying papers between 2014 and 2019. The aims of this study were to accurately gauge the safety and efficacy of e-cigarettes as a smoking cessation tool.

Methods:

Search terms including ‘electronic cigarettes’ and ‘vaping’ were used to identify suitable references. A total of 314 articles were identified from which papers were excluded due to risk of bias, insufficient detail or were duplicate from which 58 papers were used in the final review.

Results:

Evidence shows that e-cigarettes can have detrimental effects on several cell lines and animal models with their flavourings and nicotine content implicated; this has, however, not translated into major health outcomes after 3.5 years follow-up but has been linked to chronic lung disease and cardiovascular disease. While advertised as an effective smoking cessation tool, no consensus can be made regarding their effectiveness although the first robust randomised controlled trial reports some success. This, however, is offset by the fact that the most common e-cigarette use is as a dual user and that there is evidence of threefold increased risk of future tobacco smoking.

Conclusion:

Future research is needed to evaluate the long-term health outcomes and efficacy of e-cigarettes as a smoking cessation tool with greater discussion between patients and clinicians regarding this smoking cessation tool.

The rise of e-cigarettes, pod mod devices, and JUUL among youth: Factors influencing use, health implications, and downstream effects

BACKGROUND

Electronic cigarettes (e-cigarettes) were first introduced in the U.S. market in 2006, with the more recent evolution of "pod-mod" e-cigarettes such as JUUL introduced in 2015. Although marketed as a smoking cessation tool, e-cigarettes are rarely used for this purpose in youth. This review aims to synthesize the literature regarding e-cigarette use among youth, and provides a resource for clinicians, educators, and families that helps answer commonly asked questions about e-cigarettes.

METHODS

PubMed, Scopus, and PsycINFO search was performed using search terms "Electronic Nicotine Delivery Systems," "e cigarettes," "e-cigarettes," "electronic cigarettes," "vaping," "JUUL," "e-cigs," and "vape pens." Search results were filtered to only include those related to adolescents and young adults.

RESULTS

E-cigarette use among youth is common, with rates of use increasing from 1.5% in 2011 to 20.8% in 2018. Pod mod devices such as JUUL have gained favor among youth for their sleek design, user-friendly function, desirable flavors, and ability to be used discreetly in places where smoking is forbidden. Adolescents are often uninformed about the constituents of e-cigarettes, and little is known about the long-term effects of e-cigarettes. Studies have suggested a "gateway" effect for combustible cigarettes and cannabis use.

CONCLUSIONS

E-cigarette use is becoming increasingly common among youth, leading to a myriad of questions and concerns from providers, educators, and family members. More research is needed to determine the ultimate public health impact of e-cigarette use. The authors provide a summary table of frequently asked questions in order to help clarify these common concerns.

Experimentation with tobacco during adolescence as a factor influencing treatment of smoking in adulthood. A retrospective cohort

BACKGROUND

There are still few studies on predictors of smoking cessation in Brazilian samples. Experimentation with tobacco during adolescence (ETA) may be one of the important predictors.

OBJECTIVE

This study aimed, within the context of a treatment-seeking group of subjects, to test the hypothesis that ETA negatively affects the outcome of smoking cessation during adulthood.

DESIGN AND SETTING

Retrospective (historic) cohort study conducted at a psychosocial care center in São Paulo, Brazil, between 2007 and 2010.

METHODS

Data on sociodemographics, smoking and medical profiles were obtained through self-report questionnaires that were completed at the baseline and at any follow-up appointment. Logistic regression models were constructed to describe factors associated with the outcome of smoking cessation, measured according to the self-reported four-week success rate among 367 outpatient smokers.

RESULTS

ETA was found to be associated with not quitting smoking through the treatment (odds ratio = 0.57; 95% confidence interval = 0.33-0.96; P < 0.05), even after adjustment for dependence level, sociodemographics, nicotine patch use and number of years of smoking.

CONCLUSIONS

Early exposure to nicotine may lead to higher risk of continuing smoking after treatment, in adulthood.

The association between exposure to secondhand smoke and psychological symptoms among Chinese children

Background

The effect of secondhand smoke (SHS) exposure on child psychological problems remained inconclusive in previous studies. The aim of this study is to explore the association between SHS exposure and psychological symptoms in children.

Methods

This population-based cross-sectional survey used cluster random probability sampling and recruited children aged 6–13 years in 26 primary schools in Shanghai, China, in 2014. Duration of SHS exposure in children were categorized as none, < 1 h/day, 1–2 h/day, ≥3 h/day. Psychological symptoms were assessed by the parental version of the Strengths and Difficulties Questionnaire (SDQ). We used logistic regression to estimate the adjusted associations of SHS exposure with total SDQ and its specific domains. Multiple imputation was used for handling missing data.

Results

A total of 17,571 children completed this survey, with a response rate of 99.7%. SDQ scores were available for 15,344 participants, of whom 20.9% were not exposed to SHS, 63.0% exposed for < 1 h/day, 10.4% for 1–2 h/day, and 5.7% for ≥3 h/day. Compared to children not exposed to SHS, SHS exposure was positively associated with total SDQ score: OR 1.42, 95% confidence interval (CI) 1.22 to 1.66 for SHS exposure < 1 h/day, OR 2.14, 95% CI 1.76 to 2.62 for 1–2 h/day and OR 2.53, 95% CI 2.01 to 3.18 for ≥3 h/day after adjusting for sex, age, mode of birth, family socio-economic status and place of birth. These associations did not vary by sex.

Conclusion

SHS exposure is an independent risk factor for psychological problems among children. Nonetheless, our study is unable to distinguish between fetal and child exposure to SHS.

Electronic supplementary material

The online version of this article (10.1186/s12889-019-7006-8) contains supplementary material, which is available to authorized users.

Mitochondrial Stress Response in Neural Stem Cells Exposed to Electronic Cigarettes

Stem cells provide a sensitive model to study exposure to toxicants, such as cigarette smoke. Electronic cigarettes (ECs) are popular nicotine delivery devices, often targeted to youth and pregnant mothers. However, little is known about how chemicals in ECs might affect neural stem cells, and in particular their mitochondria, organelles that maintain cell functionality and health. Here we show that the mechanism underlying EC-induced stem cell toxicity is stress-induced mitochondrial hyperfusion (SIMH), a transient survival response accompanied by increased mitochondrial oxidative stress. We identify SIMH as a survival response to nicotine, now widely available in EC refill fluids and in pure form for do-it-yourself EC products. These observed mitochondrial alterations combined with autophagy dysfunction to clear damaged mitochondria could lead to faulty stem cell populations, accelerate cellular aging, and lead to acquired mitochondriopathies. Any nicotine-containing product may likewise stress stem cells with long-term repercussions for users and passively exposed individuals. VIDEO ABSTRACT.

E-cigarettes: Tobacco policy and regulation

PURPOSE OF THE REVIEW

The purpose of this review is to describe current trends in e-cigarette use, provide an overview of the potential health risks and benefits, and discuss tobacco policy and regulatory considerations.

RECENT FINDINGS

E-cigarette use is popular among youth and adults, despite limited evidence about the long-term risks or benefits. Internationally there is wide variability in how e-cigarettes are classified, which has also led to large differences in regulations on these products. Regulatory policies that strike a balance between the potential benefit of these devices for adult smokers who are trying to quit smoking with reducing the appeal and addictive potential for youth are critically needed.

SUMMARY

Continued research on the health effects and consequences of e-cigarette use will be essential to inform e-cigarette product standards and tobacco regulatory policies as scientific research strives to keep pace with the ever-changing landscape of e-cigarette technology.

Early-life exposure to electronic cigarettes: cause for concern

Electronic nicotine delivery systems, or ENDS, are devices that heat and aerosolise a solution of propylene glycol, glycerine, nicotine, and flavourings. They have only achieved widespread use in the past 5 years or so, and therefore evidence around their potential to effect health is scarce. Importantly, they are often viewed as safer than tobacco cigarettes, meaning that at-risk populations, including pregnant women, might be more inclined to use them. No human studies, however, have assessed the potential for maternal ENDS use to effect the health of a developing baby. Experimental research suggests that nicotine alone is likely to adversely affect the fetus. Further, there is a misconception that ENDS do not produce second-hand aerosols. This misconception might put infants and young children at risk because their parents are more likely to use ENDS around them than they are to use tobacco cigarettes. Emerging evidence also proposes that nicotine and other substances produced by ENDS can deposit onto surfaces, and subsequently be exposed to infants and children; a process known as third-hand exposure. Finally, ENDS are often refillable, and instances of accidental poisonings of children who drink nicotine-containing refills have occurred. Thus, there are a multitude of ways that, with respect to early-life exposures and health, ENDS are a cause for concern.

Exposure to prenatal secondhand smoke and early neurodevelopment: Mothers and Children's Environmental Health (MOCEH) study

BACKGROUND

The association between exposure to secondhand smoke (SHS) during pregnancy and a child's neurodevelopment has not been established yet. We explored the association between prenatal exposure to SHS and neurodevelopment at 24 months of age considering genetic polymorphism and breastfeeding in 720 mothers and their offspring enrolled in the Korean multicenter birth cohort study (Mothers and Children Environmental Health, MOCEH).

METHODS

We quantified urine cotinine concentrations in mothers once from 12th to 20th gestational weeks and excluded those whose urine cotinine levels exceeded 42.7 ng/ml to represent SHS exposure in early pregnancy. Mental developmental index (MDI) and psychomotor developmental index (PDI) values were measured using the Korean version of the Bayley Scales of Infant Development II (K-BSID-II) at 24 months of age. A general linear model was used to assess the relationship between maternal urinary cotinine level and neurodevelopment.

RESULTS

MDI scores were inversely associated with cotinine [β = - 2.73; 95% confidence interval (CI): - 5.32 to - 0.15] in children whose mothers had early pregnancy urinary cotinine levels >1.90 ng/ml. No association was evident in children whose mothers had cotinine levels ≤1.90 ng/ml. This negative association was more pronounced in children whose mothers had both Glutathione S-transferases mu 1 (GSTM1) and theta 1 (GSTT1) null type [β = - 5.78; 95% CI: -10.69 to - 0.87], but not in children whose mothers had any present type of GSTM1/GSTT1 [β = - 1.64; 95% CI: -4.79 to 1.52]. The association was no longer significant when children received breast milk exclusively for up to 6 months [β = - 0.24; 95% CI: -4.69 to 4.20] compared to others [β = - 3.75; 95% CI: -7.51 to 0.00]. No significant association was found for PDI.

CONCLUSIONS

Maternal exposure to SHS during pregnancy may result in delayed MDI in early childhood. This effect might be modified by genetic polymorphism and breastfeeding behavior.

Cigarette smoking and gray matter brain volumes in middle age adults: the CARDIA Brain MRI sub-study

Cigarette smoking has been associated with dementia and dementia-related brain changes, notably gray matter (GM) volume atrophy. These associations are thought to reflect the co-morbidity of smoking and vascular, respiratory, and substance use/psychological conditions. However, the extent and localization of the smoking-GM relationship and the degree to which vascular, respiratory, and substance use/psychological factors influence this relationship remain unclear. In the Coronary Artery Risk Development in Young Adults CARDIA cohort (n = 698; 52% women; 40% black participants; age = 50.3 (SD = 3.5)), we examined the associations of smoking status with total GM volume and GM volume of brain regions linked to neurocognitive and addiction disorders. Linear regression models were used to adjust for vascular, respiratory, and substance use/psychological factors and to examine whether they modify the smoking-GM relationship. Compared to never-smokers, current smokers had smaller total GM volume (-8.86 cm³ (95%CI = -13.44, -4.29). Adjustment for substance use/psychological - but not vascular or respiratory - factors substantially attenuated this association (coefficients = -5.54 (95% CI = -10.32, -0.76); -8.33 (95% CI = -12.94, -3.72); -7.69 (95% CI = -6.95, -4.21), respectively). There was an interaction between smoking and alcohol use such that among alcohol non-users, smoking was not related to GM volumes and among alcohol users, those who currently smoked had -12 cm³ smaller total GM, specifically in the frontal and temporal lobes, amygdala, cingulate, and insula. Results suggest a large-magnitude association between smoking and smaller GM volume at middle age, accounting for vascular, respiratory, and substance use/psychological factors, and that the association was strongest in alcohol users. Regions suggested to be most vulnerable are those where cognition and addiction processes overlap.

The Messages Presented in Electronic Cigarette-Related Social Media Promotions and Discussion: Scoping Review

Background

There has been a rapid rise in the popularity of electronic cigarettes (e-cigarettes) over the last decade, with growth predicted to continue. The uptake of these devices has escalated despite inconclusive evidence of their efficacy as a smoking cessation device and unknown long-term health consequences. As smoking rates continue to drop or plateau in many well-developed countries, transnational tobacco companies have transitioned into the vaping industry and are now using social media to promote their products. Evidence indicates e-cigarettes are being marketed on social media as a harm reduction alternative, with retailers and manufacturers utilizing marketing techniques historically used by the tobacco industry.

Objective

This study aimed to identify and describe the messages presented in e-cigarette–related social media (Twitter, YouTube, Instagram, and Pinterest) promotions and discussions and identify future directions for research, surveillance, and regulation.

Methods

Data sources included MEDLINE, Scopus, ProQuest, Informit, the Journal of Medical Internet Research, and Google Scholar. Included studies were published in English between 2007 and 2017, analyzed content captured from e-cigarette–related social media promotions or discussions, and reported results for e-cigarettes separately from other forms of tobacco and nicotine delivery. Database search ceased in October 2017. Initial searches identified 536 studies. Two reviewers screened studies by title and abstract. One reviewer examined 71 full-text articles to determine eligibility and identified 25 studies for inclusion. This process was undertaken with the assistance of the Web-based screening and data extraction tool—Covidence. The review was registered with the Joanna Briggs Institute (JBI) Systematic Reviews database and followed the methodology for JBI Scoping Reviews.

Results

Several key messages are being used to promote e-cigarettes including as a safer alternative to cigarettes, efficacy as a smoking cessation aid, and for use where smoking is prohibited. Other major marketing efforts aimed at capturing a larger market involve promotion of innovative flavoring and highlighting the public performance of vaping. Discussion and promotion of these devices appear to be predominantly occurring among the general public and those with vested interests such as retailers and manufacturers. There is a noticeable silence from the public health and government sector in these discussions on social media.

Conclusions

The social media landscape is dominated by pro-vaping messages disseminated by the vaping industry and vaping proponents. The uncertainty surrounding e-cigarette regulation expressed within the public health field appears not to be reflected in ongoing social media dialogues and highlights the need for public health professionals to interact with the public to actively influence social media conversations and create a more balanced discussion. With the vaping industry changing so rapidly, real-time monitoring and surveillance of how these devices are discussed, promoted, and used on social media is necessary in conjunction with evidence published in academic journals.

E-Cigarettes and Similar Devices

Electronic cigarettes (e-cigarettes) are the most commonly used tobacco product among youth. The 2016 US Surgeon General's Report on e-cigarette use among youth and young adults concluded that e-cigarettes are unsafe for children and adolescents. Furthermore, strong and consistent evidence finds that children and adolescents who use e-cigarettes are significantly more likely to go on to use traditional cigarettes-a product that kills half its long-term users. E-cigarette manufacturers target children with enticing candy and fruit flavors and use marketing strategies that have been previously successful with traditional cigarettes to attract youth to these products. Numerous toxicants and carcinogens have been found in e-cigarette solutions. Nonusers are involuntarily exposed to the emissions of these devices with secondhand and thirdhand aerosol. To prevent children, adolescents, and young adults from transitioning from e-cigarettes to traditional cigarettes and minimize the potential public health harm from e-cigarette use, there is a critical need for e-cigarette regulation, legislative action, and counterpromotion to protect youth.