Development of the motivational system during adolescence, and its sensitivity to disruption by nicotine

Nicotine dependence among young adults: Comparing exclusive ENDS users to exclusive cigarette smokers

PURPOSE

No studies of young adults have compared symptoms of nicotine dependence among exclusive past 30-day (P30D) ENDS users versus exclusive P30D cigarette smokers.

METHODS

Participants at Wave 14 (Fall 2021) of The Texas Adolescent and Tobacco Marketing Surveillance System (TATAMS) (n = 2,341; mean age = 20.95 years old) who reported P30D exclusive ENDS use (n = 212) and P30D exclusive cigarette smoking (n = 46). Symptoms of nicotine dependence were measured with the Hooked On Nicotine Checklist (the 10-item HONC scale). An independent samples t-test compared average HONC scores between groups, and a Pearson (or Fisher's Exact) Chi-Square (X2) test compared the prevalence of symptom(s) between groups.

RESULTS

The average HONC score was significantly higher for exclusive P30D ENDS users than exclusive P30D cigarette smokers (3.51 vs. 1.91, p ≤ 0.001). Compared to exclusive P30D cigarette smokers, a significantly higher proportion of exclusive P30D ENDS users reported having felt addicted (45.28% vs. 15.22%, p ≤ 0.001), having strong cravings (50.00% vs. 28.26%, p = 0.007), difficulty not using in prohibited places (i.e., school or work) (24.06% vs. 4.35%, p = 0.002), difficulty concentrating (21.23% vs. 6.52%, p = 0.021), and feeling nervous, restless, or anxious (28.77% vs. 10.87%, p = 0.012).

CONCLUSIONS

Symptoms of nicotine dependence were elevated among young adults who were exclusive P30D users of ENDS relative to exclusive P30D cigarette smokers.

Mechanisms of E-Cigarette Vape-Induced Epithelial Cell Damage

E-cigarette use has been reported to affect cell viability, induce DNA damage, and modulate an inflammatory response resulting in negative health consequences. Most studies focus on oral and lung disease associated with e-cigarette use. However, tissue damage can be found in the cardio-vascular system and even the bladder. While the levels of carcinogenic compounds found in e-cigarette aerosols are lower than those in conventional cigarette smoke, the toxicants generated by the heat of the vaping device may include probable human carcinogens. Furthermore, nicotine, although not a carcinogen, can be metabolized to nitrosamines. Nitrosamines are known carcinogens and have been shown to be present in the saliva of e-cig users, demonstrating the health risk of e-cigarette vaping. E-cig vape can induce DNA adducts, promoting oxidative stress and DNA damage and NF-kB-driven inflammation. Together, these processes increase the transcription of pro-inflammatory cytokines. This creates a microenvironment thought to play a key role in tumorigenesis, although it is too early to know the long-term effects of vaping. This review considers different aspects of e-cigarette-induced cellular changes, including the generation of reactive oxygen species, DNA damage, DNA repair, inflammation, and the possible tumorigenic effects.

Nicotinic Acetylcholine Receptor Dysfunction in Addiction and in Some Neurodegenerative and Neuropsychiatric Diseases

The cholinergic system plays an essential role in brain development, physiology, and pathophysiology. Herein, we review how specific alterations in this system, through genetic mutations or abnormal receptor function, can lead to aberrant neural circuitry that triggers disease. The review focuses on the nicotinic acetylcholine receptor (nAChR) and its role in addiction and in neurodegenerative and neuropsychiatric diseases and epilepsy. Cholinergic dysfunction is associated with inflammatory processes mainly through the involvement of α7 nAChRs expressed in brain and in peripheral immune cells. Evidence suggests that these neuroinflammatory processes trigger and aggravate pathological states. We discuss the preclinical evidence demonstrating the therapeutic potential of nAChR ligands in Alzheimer disease, Parkinson disease, schizophrenia spectrum disorders, and in autosomal dominant sleep-related hypermotor epilepsy. PubMed and Google Scholar bibliographic databases were searched with the keywords indicated below.

Nicotine on the developing brain

Developmental periods such as gestation and adolescence have enhanced plasticity leaving the brain vulnerable to harmful effects from nicotine use. Proper brain maturation and circuit organization is critical for normal physiological and behavioral outcomes. Although cigarette smoking has declined in popularity, noncombustible nicotine products are readily used. The misperceived safety of these alternatives lead to widespread use among vulnerable populations such as pregnant women and adolescents. Nicotine exposure during these sensitive developmental windows is detrimental to cardiorespiratory function, learning and memory, executive function, and reward related circuitry. In this review, we will discuss clinical and preclinical evidence of the adverse alterations in the brain and behavior following nicotine exposure. Time-dependent nicotine-induced changes in reward related brain regions and drug reward behaviors will be discussed and highlight unique sensitivities within a developmental period. We will also review long lasting effects of developmental exposure persisting into adulthood, along with permanent epigenetic changes in the genome which can be passed to future generations. Taken together, it is critical to evaluate the consequences of nicotine exposure during these vulnerable developmental windows due to its direct impact on cognition, potential trajectories for other substance use, and implicated mechanisms for the neurobiology of substance use disorders.

Adolescent nicotine administration impacts working memory and reversal learning but not cognitive flexibility

There has been increased interest in early exposure to nicotine through tobacco products and vaping specifically as it relates to addiction, yet fewer studies have focused on whether behavioral effects resulting from early nicotine exposure may persist into adulthood. Our experiments tested the hypothesis that exposure to nicotine during adolescence would impair selective aspects of behavioral cognition in rodents in adulthood. Male and female adolescent rats received either nicotine (0.4 mg/kg) or vehicle injections (intraperitoneal) once daily for 10 days (PND 29-38) followed by a washout period before behavioral testing. Animals were followed in a longitudinal design and evaluated on a battery of both behavioral and cognitive tasks during adulthood (PND 90+) that included locomotor activity, working memory (novel object recognition), cognitive flexibility (attentional set-shifting task, ASST), and anxiety-like behaviors. Data suggested that subchronic exposure to nicotine during adolescence produced significant changes in working memory, in two reversal problems in the ASST, and in anxiety-related behaviors. Taken together these data may suggest that limited early exposure to nicotine may produce selective longer term impairments in cognitive and behavioral processes related to working memory and reversal learning.

The mechanistic basis for the toxicity difference between juvenile rats and mice following exposure to the agricultural insecticide chlorpyrifos

At high exposure levels, organophosphorus insecticides (OPs) exert their toxicity in mammals through the inhibition of brain acetylcholinesterase (AChE) leading to the accumulation of acetylcholine in cholinergic synapses and hyperactivity of the nervous system. Currently, there is a concern that low-level exposure to OPs induces negative impacts in developing children and the chemical most linked to these issues is chlorpyrifos (CPF). Our laboratory has observed that a difference in the susceptibility to repeated exposure to CPF exists between juvenile mice and rats with respect to the inhibition of brain AChE. The basis for this difference is unknown but differences in the levels of the detoxification mechanisms could play a role. To investigate this, 10-day old rat and mice pups were exposed daily for 7 days to either corn oil or a range of dosages of CPF via oral gavage. Four hours following the last administration of CPF on day 16, brain, blood, and liver were collected. The inhibition of brain AChE activity was higher in juvenile rats as compared to juvenile mice. The levels of activity of the detoxification enzymes and the impact of CPF exposure on their activity were determined in the two species at this age. In blood and liver, the enzyme paraoxonase-1 (PON1) hydrolyzes the active metabolite of CPF (CPF-oxon), and the enzymes carboxylesterase (CES) and cholinesterase (ChE) act as alternative binding sites for CPF-oxon removing it from circulation and providing protection. Both species had similar levels of PON1 activity in the liver and serum. Mice had higher ChE activity in liver and serum than rats but, following CPF exposure, the percentage inhibition was similar between species at an equivalent dosage. Even though rats had slightly higher liver CES activity than mice, the level of inhibition following exposure was higher in rats. In serum, juvenile mice had an 8-fold higher CES activity than rats, and exposure to a CPF dosage that almost eliminated CES activity in rats only resulted in 22% inhibition in mice suggesting that the high serum CES activity in mice as compared to rats is a key component in this species difference. In addition, there was a species difference in the sensitivity of CES to inhibition by CPF-oxon with rats having a lower IC₅₀ in both liver and serum as compared to mice. This greater enzyme sensitivity suggests that saturation of CES would occur more rapidly in juvenile rats than in mice, resulting in more CPF reaching the brain to inhibit AChE in rats.

E-Cigarettes Reexamined: Product Toxicity

The introduction of e-cigarettes, or electronic nicotine delivery systems (ENDS), has been accompanied by controversy regarding their safety and effectiveness as a cessation aid and by an explosion in their use by youth. Their use does not involve the combustion of tobacco and the creation of harmful combustion products; they have been seen as a "harm reduction" tool that may be of assistance in promoting smoking cessation. Recognition that ENDS can deliver an array of chemicals and materials with known adverse consequences has spurred more careful examination of these products. Nicotine, nitrosamines, carbonyl compounds, heavy metals, free radicals, reactive oxygen species, particulate matter, and "emerging chemicals of concern" are among the constituents of the heated chemical aerosol that is inhaled when ENDS are used. They raise concerns for cardiovascular and respiratory health that merit the attention of clinicians and regulatory agencies. Frequently cited concerns include evidence of disordered respiratory function, altered hemodynamics, endothelial dysfunction, vascular reactivity, and enhanced thrombogenesis. The absence of evidence of the consequences of their long-term use is of additional concern. Their effectiveness as cessation aids and beneficial impact on health outcomes continue to be examined. It is important to ensure that their production and availability are thoughtfully regulated to optimise their safety and permit their use as harm reduction devices and potentially as smoking-cessation aids. It is equally vital to effectively prevent them from becoming ubiquitous consumer products with the potential to rapidly induce nicotine addiction among large numbers of youth. Clinicians should understand the nature of these products and the implications of their use.

Internalizing and externalizing problems on the age of e-cigarette initiation in youth: Findings from the Population Assessment of Tobacco and Health (PATH), 2013-2017

Previous research has established an association between internalizing and externalizing problems with e-cigarette use in youth. Secondary analysis of Population Assessment of Tobacco and Health youth waves 1-4(2013-2017). Age of initiation of ever e-cigarette use and age of first report of past 30-day e-cigarette use were prospectively estimated among never e-cigarette users(waves 1-3). Weighted interval-censoring multivariable Cox proportional hazard models were fit to assess differences in each e-cigarette outcome among youth with internalizing and externalizing problems, as well as the interaction between internalizing and externalizing problems, while adjusting for covariates. Weighted interval-censoring survival analyses estimated the age of initiation of ever and age of first report of past 30-day e-cigarette use stratified by internalizing and externalizing problems. Among youth never e-cigarette users, those with high internalizing problems and high externalizing problems had increased risk of initiating ever e-cigarette use at earlier ages compared to youth with none/low internalizing and externalizing problems, respectively. Youth with high internalizing problems and high externalizing problems had increased risk of first reporting past 30-day e-cigarette use at earlier ages compared to youth with none/low internalizing problems, respectively. By age 17, 36.3% of youth with high internalizing problems and 38.5% of youth with high externalizing problems initiated ever e-cigarette use. By age 17, 16.8% of youth with high internalizing and 18.7% of youth with high externalizing problems first reported past 30-day e-cigarette use. Youth with internalizing and externalizing problems should be screened for e-cigarette use and provided with proper resources to prevent onset of e-cigarette use.

Puff bars: a dangerous trend in adolescent disposable e-cigarette use

PURPOSE OF REVIEW

Puff Bars, a brand of disposable e-cigarettes, have skyrocketed in popularity recently, presenting significant health and safety risks to adolescents. Puff Bars and other disposable e-cigarette products are attractive to children and teenagers because of their vibrant colors and flavors, low cost, and ease of access. This review examines the rise in Puff Bar popularity, describes notable health and safety concerns, and provides advice for parents and pediatricians in identifying and preventing adolescent Puff Bar use.

RECENT FINDINGS

Puff Bars have increased in popularity as their product design evaded strict regulations imposed on alternate e-cigarette products, such as Juul. In addition, Puff Bars' sweet and fruit flavors and marketing on social media have made their use pervasive among youth. Puff Bar use can lead to increased risk of e-cigarette product use-associated lung injury (EVALI) and potential exposure to carcinogens. Furthermore, the developmental risks of nicotine use during adolescence include negative effects on cognitive function and detriments to short-term memory.

SUMMARY

Puff Bars present a significant danger to adolescents, and it is imperative that parents and pediatricians are aware of the health risks involved with vaping. Pediatricians should explore e-cigarette use during patient visits, and parents must communicate these dangers to their children and be able to identify these products to regulate their use.

Self-reported history of intensity of smoking is associated with risk factors for suicide among high school students

OBJECTIVE

To examine the relationship between current cigarette smoking patterns and three established risk factors for suicide using nationally representative data of high school students in the United States.

METHODS

We analyzed cross-sectional data from the national Youth Risk Behavior Surveillance Survey (YRBSS)-United States, 2017. Multivariable, logistic regressions examined the association between 3 cigarette smoking behaviors [i.e., past 30-day cigarette (n = 13,731), frequent (n = 1,093) and heavy (n = 880) smoking] and 3 risk factors for suicidal outcomes [feeling sad or hopeless, suicidal ideation, suicide plan] assessed over the previous year.

RESULTS

Among high school cigarette smokers, smoking 11 or more cigarettes per day (i.e., heavy smoking) was associated with 3.43 (95% CI: 1.69, 6.94) greater odds of reporting feeling sad or hopeless, 2.97 (95% CI: 1.60, 5.51) greater odds of reporting suicidal ideations, and 2.11 (95% CI: 1.34, 3.32) greater odds of reporting having ever planned a suicide attempt, controlling for covariates.

CONCLUSIONS

Our study shows that it is not simply cigarette smoking, but heavy cigarette smoking that is a risk factor for suicidal outcomes among adolescents.

PUBLIC HEALTH IMPLICATIONS

A comprehensive plan is needed to accommodate heavy adolescent smokers who are at increased suicidal risk.

Prevalence and Childhood Precursors of Opioid Use in the Early Decades of Life

IMPORTANCE

Opioid use disorder and opioid deaths have increased dramatically in young adults in the US, but the age-related course or precursors to opioid use among young people are not fully understood.

OBJECTIVE

To document age-related changes in opioid use and study the childhood antecedents of opioid use by age 30 years in 6 domains of childhood risk: sociodemographic characteristics; school or peer problems; parental mental illness, drug problems, or legal involvement; substance use; psychiatric illness; and physical health.

DESIGN, SETTING, AND PARTICIPANTS

This community-representative prospective longitudinal cohort study assessed 1252 non-Hispanic White individuals and American Indian individuals in rural counties in the central Appalachia region of North Carolina from January 1993 to December 2015. Data were analyzed from January 2019 to January 2020.

EXPOSURES

Between ages 9 and 16 years, participants and their parents were interviewed up to 7 times using the Child and Adolescent Psychiatric Assessment and reported risk factors in 6 risk domains.

MAIN OUTCOMES AND MEASURES

Participants were assessed again at ages 19, 21, 25, and 30 years for nonheroin opioid use (any and weekly) and heroin use using the structured Young Adult Psychiatric Assessment.

RESULTS

Of 1252 participants, 342 (27%) were American Indian. By age 30 years, 322 participants had used a nonheroin opioid (24.2%; 95% CI, 21.8-26.5), 155 had used a nonheroin opioid weekly (8.8%; 95% CI, 7.2-10.3), and 95 had used heroin (6.6%; 95% CI, 5.2-7.9). Childhood risk markers for later opioid use included male sex, tobacco use, depression, conduct disorder, cannabis use, having peers exhibiting social deviance, parents with legal involvement, and elevated systemic inflammation. In final models, childhood tobacco use, depression, and cannabis use were most robustly associated with opioid use in young adulthood (ages 19 to 30 years). Chronic depression and dysthymia were strongly associated with any nonheroin opioid use (OR. 5.43; 95% CI, 2.35-12.55 and OR, 7.13; 95% CI, 1.99-25.60, respectively) and with weekly nonheroin opioid use (OR, 8.89; 95% CI, 3.61-21.93 and OR, 11.51; 95% CI, 3.05-42.72, respectively). Among young adults with opioid use, those with heroin use had the highest rates of childhood psychiatric disorders and comorbidities.

CONCLUSIONS AND RELEVANCE

Childhood tobacco use and chronic depression may be associated with impaired reward system functioning, which may increase young adults' vulnerability to opioid-associated euphoria. Preventing and treating early substance use and childhood mental illness may help prevent later opioid use.

Does having one or more smoking friends mediate the transition from e-cigarette use to cigarette smoking: a longitudinal study of Canadian youth

PURPOSE

Studies have shown consistent associations between youth e-cigarette use and subsequent smoking uptake. However, it remains unclear why, as limited evidence exists regarding the mechanisms underlying these associations. Our study investigated whether having one or more smoking friends mediated the association between e-cigarette use and cigarette smoking onset among a longitudinal sample of Canadian youth who were never smokers at baseline.

METHODS

A longitudinal sample of youth that participated in three waves of the COMPASS study (2015-2016 to 2017-2018) was identified (N = 5,535). The product of coefficients method was used to assess whether having one or more smoking friends mediated the association between: (1) past 30-day e-cigarette use and cigarette smoking onset and (2) past 30-day e-cigarette use and subsequent dual use of e-cigarettes and cigarettes.

RESULTS

Having one or more smoking friends did not mediate the association between (1) past 30-day e-cigarette use and cigarette smoking onset (β = 0.38, 95% CI - 0.12, 0.89) or (2) past 30-day e-cigarette use and subsequent dual use (β = 0.46, 95% CI - 0.16, 1.07). Post hoc tests indicated that smoking friends significantly predicted past 30-day e-cigarette use and cigarette smoking at wave 3 (aOR 1.68 and 2.29, respectively).

CONCLUSION

Having smoking friends did not explain the association between e-cigarette use and smoking uptake despite being a common risk factor for both e-cigarette use and cigarette smoking. Prevention efforts should consider how best to incorporate effective programming to address these social influences.

Characterization of the intergenerational impact of in utero and postnatal oxycodone exposure

Prescription opioid abuse during and after pregnancy is a rising public health concern. While earlier studies have documented that offspring exposed to opioids in utero have impaired neurodevelopment, a significant knowledge gap remains in comparing the overall development between offspring exposed in utero and postnatally. Adding a layer of complexity is the role of heredity in the overall development of these exposed offspring. To fill in these important knowledge gaps, the current study uses a preclinical rat model mimicking oxycodone (oxy) exposure in utero (IUO) and postnatally (PNO) to investigate comparative and intergenerational effects in the two different treatment groups. While significant phenotypic attributes were observed with the two treatments and across the two generations, RNA sequencing revealed alterations in the expression of key synaptic genes in the two exposed groups in both generations. RNA sequencing and post validation of genes using RT-PCR highlighted the differential expression of several neuropeptides associated with the hypocretin system, a system recently implicated in addiction. Further, behavior studies revealed anxiety-like behaviors and social deficits that persisted even in the subsequent generations in the two treatment groups. To summarize, our study for the first time reveals a new line of investigation on the potential risks associated with oxy use during and after pregnancy, specifically the disruption of neurodevelopment and intergenerational impact on behavior.

Inhibition of fatty acid amide hydrolase by chlorpyrifos in juvenile rats results in altered exploratory and social behavior as adolescents

The organophosphorus insecticide chlorpyrifos (CPF) is suspected to cause developmental neurotoxicity in children leading to long term effects. Developmental exposure of rat pups to CPF at low levels disrupts degradation of the brain endocannabinoids through the inhibition of fatty acid amide hydrolase (FAAH) and decreases the reactivity of juvenile rats in an emergence test. In this study, we further investigated the effects of developmental CPF exposure on behavior but also included exposure to PF-04457845, a specific inhibitor of FAAH, for comparison of behavior altered by FAAH inhibition with behavior altered by CPF. Ten day old rat pups were exposed orally either to 0.5, 0.75, or 1.0 mg/kg CPF or 0.02 mg/kg PF-04457845 daily for 7 days. In an open field (day 23), the high CPF and PF-04457845 groups exhibited increased motor activity but no differences in the time spent in the field's center. In an elevated plus maze (day 29), all treatment groups had increased open arm activity but ethological behaviors associated with anxiety were not altered. Behaviors in the maze associated with increased general activity and exploratory drive were increased. Social interactions (day 36) were measured and all treatment groups exhibited increased levels of play behavior. The similarities in behavior between PF-04457845 and CPF suggest that enhanced endocannabinoid signaling during the exposure period plays a role in the persistent alteration of behavior observed following developmental CPF exposure.

Exploring the Bi-Directional Association between Tobacco and E-Cigarette Use among Youth in Canada

Research has demonstrated associations between e-cigarette use and tobacco use among youth. However, few studies have examined whether reciprocal relationships exist between e-cigarette and tobacco use. The objective of this study was to examine whether bi-directional associations exist between e-cigarette and tobacco use in a large longitudinal sample of Canadian youth. A longitudinal sample of secondary students (n = 6729) attending 87 schools in Ontario and Alberta, Canada, who completed the COMPASS student questionnaire across three waves (from 2014–2015 to 2016–2017) was identified. Using cross-lagged models, we explored bi-directional associations between current tobacco and e-cigarette use, adjusting for relevant covariates. Our findings showed that current e-cigarette use predicted subsequent tobacco use between Wave 1 (W₁) and Wave 2 (W₂) of the study (W_1–2: OR = 1.54, 95% CI = 1.37–1.74). Similarly, current tobacco use predicted e-cigarette use during earlier waves of the study (W_1–2: OR = 1.43, 95% CI = 1.30–1.58). However, these relationships dissipated in later waves, when tobacco use no longer predicted e-cigarette use (W_2–3: OR = 1.07, 95% CI = 0.99–1.16). This study extends prior work that focused mainly on the association between e-cigarette and subsequent tobacco use. Specifically, our findings portray a more complex relationship, where e-cigarette use may influence and be influenced by tobacco use.

Differences in Adolescent E-cigarette and Cigarette Prevalence in Two Policy Environments: South Korea and the United States

Introduction

In the context of different regulatory environments, different patterns of e-cigarette use have emerged among adolescents worldwide. The United States and South Korea are two examples, the latter of which has maintained much more extensive regulation of e-cigarettes.

Methods

This analysis compares the prevalence of e-cigarette and conventional cigarette use between 2011 and 2015 from the Korean Youth Risk Behavior Web-based Survey and the U.S. National Youth Tobacco Survey, both nationally representative samples of middle and high school students that use similar questions.

Results

E-cigarette prevalence (past 30 days) among South Korean adolescents decreased from 4.7% in 2011 (95% confidence interval [CI]: 4.4-5.0) to 4.0% (3.7-4.3) in 2015 but increased dramatically among US adolescents from 0.9% (0.7-1.2) to 11.2% (9.9-12.7). Cigarette prevalence (past 30 days) decreased in South Korea from 12.1% (11.6-12.7) to 7.8% (CI: 7.3-8.3) and in the United States from 11.1% (9.5-12.6) to 6.1% (5.1-7.3). Combined prevalence of cigarette and e-cigarette use (adjusting for dual users) decreased in South Korea from 13.2% (12.7-13.8) to 8.5% (8.0-9.1) but increased in the United States from 11.3% (9.7-12.9) to 14.0% (12.4-15.7).

Conclusions

In South Korea, where e-cigarettes are extensively regulated, adolescent e-cigarette use remained stable at a low level, whereas in the United States, where e-cigarette regulation has been limited, e-cigarette use increased. Combined e-cigarette plus cigarette use declined in South Korea whereas it increased in the United States. The restrictive policies in South Korea likely contributed to lower overall product use.

Implications

This paper compared the strength of regulation of South Korea and the United States with the prevalence of adolescents' e-cigarette and cigarette use and suggests that more restrictive policies likely to contribute to lower e-cigarette use and overall use of e-cigarette and cigarette.

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.

The influence of adolescent nicotine exposure on ethanol intake and brain gene expression

Nicotine and alcohol are often co-abused. Adolescence is a vulnerable period for the initiation of both nicotine and alcohol use, which can lead to subsequent neurodevelopmental and behavioral alterations. It is possible that during this vulnerable period, use of one drug leads to neurobiological alterations that affect subsequent consumption of the other drug. The aim of the present study was to determine the effect of nicotine exposure during adolescence on ethanol intake, and the effect of these substances on brain gene expression. Forty-three adolescent female C57BL/6J mice were assigned to four groups. In the first phase of the experiment, adolescent mice (PND 36-41 days) were exposed to three bottles filled with water or nicotine (200 μg/ml) for 22 h a day and a single bottle of water 2 h a day for six days. In the second phase (PND 42-45 days), the 4-day Drinking-in-the-Dark paradigm consisting of access to 20% v/v ethanol or water for 2h or 4h (the last day) was overlaid during the time when the mice did not have nicotine available. Ethanol consumption (g/kg) and blood ethanol concentrations (BEC, mg %) were measured on the final day and whole brains including the cerebellum, were dissected for RNA sequencing. Differentially expressed genes (DEG) were detected with CuffDiff and gene networks were built using WGCNA. Prior nicotine exposure increased ethanol consumption and resulting BEC. Significant DEG and biological pathways found in the group exposed to both nicotine and ethanol included genes important in stress-related neuropeptide signaling, hypothalamic-pituitary-adrenal (HPA) axis activity, glutamate release, GABA signaling, and dopamine release. These results replicate our earlier findings that nicotine exposure during adolescence increases ethanol consumption and extends this work by examining gene expression differences which could mediate these behavioral effects.

Morphine-alcohol treatment impairs cognitive functions and increases neuro-inflammatory responses in the medial prefrontal cortex of juvenile male rats

In the developed and developing world, opioid consumption in combination with alcohol has become one of the substances abused. In this experiment, we examined the effects of alcohol, morphine, and morphine+alcohol combination on cognitive functions and neuroinflammatory responses in the medial prefrontal cortex (mPFC) of juvenile male rats. Alcohol (1.0 ml of 15% v/v ethanol twice daily, subcutaneously, 7 hours apart), morphine (0.5 ml/kg of 0.4 mg/kg morphine chlorate twice daily, subcutaneously, 7 hours apart), morphine+alcohol co-treatment (0.5 ml/kg of 0.4 mg/kg morphine chlorate+1.0 ml of 15% v/v ethanol twice daily, subcutaneously, 7 hours apart) were administered for 21 days. Treatment with morphine+alcohol significantly impairs cognition functions in the Morris water maze, passive avoidance, and novel object recognition tests, furthermore, the treatment significantly increased the quantitative count of astrocytic cells and also conferred marked neuronal cell death in the mPFC, which were studied by glial fibrillary acidic protein immunochemistry for astrocytes and Cresyl violet for Nissl's substance distribution in neurons respectively. These results suggest that alcohol, morphine, and morphine+alcohol co-treatment may trigger cognitive deficits and neuroinflammatory responses in the brain.

Trajectories of E-Cigarette and Conventional Cigarette Use Among Youth

BACKGROUND

Electronic cigarette (e-cigarette) use is common among youth, and there are concerns that e-cigarette use leads to future conventional cigarette use. We examined longitudinal associations between past-month cigarette and e-cigarette use to characterize the stability and directionality of these tobacco use trajectories over time.

METHODS

High school students (N = 808, 53% female) completed surveys across 3 waves (2013, 2014, and 2015) in 3 public schools in Connecticut. Using autoregressive cross-lagged models, we examined bidirectional relationships between past-month cigarette and e-cigarette use over time. Models were adjusted for covariates related to tobacco use (ie, sex, race/ethnicity, socioeconomic status, and use of other tobacco products).

RESULTS

Past-month e-cigarette use predicted future cigarette use (wave 1-2: odds ratio [OR] = 7.08, 95% confidence interval [CI] = 2.34-21.42; wave 2-3: OR = 3.87, 95% CI = 1.86-8.06). However, past-month cigarette use did not predict future e-cigarette use (wave 1-2: OR = 2.02, 95% CI = 0.67-6.08; wave 2-3: OR = 1.90, 95% CI = 0.77-4.71). Additionally, frequency of cigarette and e-cigarette use increased over time. By wave 3, 26% of cigarette users and 20.5% of e-cigarette users reported using 21-30 days out of the past month.

CONCLUSIONS

E-cigarette use was associated with future cigarette use across 3 longitudinal waves, yet cigarette use was not associated with future e-cigarette use. Future research needs to examine mechanisms through which e-cigarette use leads to cigarette use. E-cigarette regulation and prevention programs may help prevent future use of cigarettes among youth.

Early age of e-cigarette use onset mediates the association between impulsivity and e-cigarette use frequency in youth

BACKGROUND

Identifying risk factors for youth e-cigarette use is critical, given high rates of e-cigarette use and unknown health effects of long-term use. The current study examined whether an early age of onset of e-cigarette use mediates the association between impulsivity and e-cigarette frequency.

METHODS

Cross-sectional survey data of e-cigarette users (n=927) were collected from 8 high schools in southeastern Connecticut. The sample was 44.7% female (mean age 16.2 [SD=1.2], mean age of e-cigarette onset 14.7 [SD=1.6]). Two domains of self-reported, trait impulsivity were assessed using the abbreviated Barratt Impulsiveness Scale: impaired self-regulation (e.g., problems with concentration or self-control) and behavioral impulsivity (e.g., doing things without thinking). Mediation was tested with Mplus, and the model included school as a cluster variable and controlled for covariates related to e-cigarette use (i.e., sex, age, race, peer use, and other tobacco products ever tried).

RESULTS

The hypothesized mediation was supported for both domains of impulsivity (impaired self-regulation a₁b=0.09, SE=0.02, 95%CI [0.03-0.14], p=.002; behavioral impulsivity a₂b=0.07, SE=0.03, 95%CI [.01-.14], p=0.03). Specifically, impaired self-regulation (B=-0.33, SE=0.06, p<0.001) and behavioral impulsivity (B=-0.26, SE=0.11, p=0.02) predicted trying e-cigarettes at an earlier age, and earlier initiation was associated with more days of e-cigarette use in the past month (B=-0.28, SE=0.08, p<0.001).

CONCLUSIONS

Adolescents who endorse aspects of impulsivity, such as acting without thinking, are at greater risk for more frequent e-cigarette use through an early age of e-cigarette initiation. Further research is needed to evaluate these relationships longitudinally and to develop targeted e-cigarette interventions for impulsive youth.

Classification of Twitter Users Who Tweet About E-Cigarettes

Background

Despite concerns about their health risks, e‑cigarettes have gained popularity in recent years. Concurrent with the recent increase in e‑cigarette use, social media sites such as Twitter have become a common platform for sharing information about e-cigarettes and to promote marketing of e‑cigarettes. Monitoring the trends in e‑cigarette–related social media activity requires timely assessment of the content of posts and the types of users generating the content. However, little is known about the diversity of the types of users responsible for generating e‑cigarette–related content on Twitter.

Objective

The aim of this study was to demonstrate a novel methodology for automatically classifying Twitter users who tweet about e‑cigarette–related topics into distinct categories.

Methods

We collected approximately 11.5 million e‑cigarette–related tweets posted between November 2014 and October 2016 and obtained a random sample of Twitter users who tweeted about e‑cigarettes. Trained human coders examined the handles’ profiles and manually categorized each as one of the following user types: individual (n=2168), vaper enthusiast (n=334), informed agency (n=622), marketer (n=752), and spammer (n=1021). Next, the Twitter metadata as well as a sample of tweets for each labeled user were gathered, and features that reflect users’ metadata and tweeting behavior were analyzed. Finally, multiple machine learning algorithms were tested to identify a model with the best performance in classifying user types.

Results

Using a classification model that included metadata and features associated with tweeting behavior, we were able to predict with relatively high accuracy five different types of Twitter users that tweet about e‑cigarettes (average F₁ score=83.3%). Accuracy varied by user type, with F₁ scores of individuals, informed agencies, marketers, spammers, and vaper enthusiasts being 91.1%, 84.4%, 81.2%, 79.5%, and 47.1%, respectively. Vaper enthusiasts were the most challenging user type to predict accurately and were commonly misclassified as marketers. The inclusion of additional tweet-derived features that capture tweeting behavior was found to significantly improve the model performance—an overall F₁ score gain of 10.6%—beyond metadata features alone.

Conclusions

This study provides a method for classifying five different types of users who tweet about e‑cigarettes. Our model achieved high levels of classification performance for most groups, and examining the tweeting behavior was critical in improving the model performance. Results can help identify groups engaged in conversations about e‑cigarettes online to help inform public health surveillance, education, and regulatory efforts.

Inhibition of Endocannabinoid-Metabolizing Enzymes in Peripheral Tissues Following Developmental Chlorpyrifos Exposure in Rats

Repeated developmental exposure to the organophosphate (OP) insecticide chlorpyrifos (CPF) inhibits brain fatty acid amide hydrolase (FAAH) activity at low levels, whereas at higher levels, it inhibits brain monoacylglycerol lipase (MAGL) activity. FAAH and MAGL hydrolyze the endocannabinoids anandamide (AEA) and 2-arachidonylglycerol (2-AG), respectively. Peripherally, AEA and 2-AG have physiological roles in the regulation of lipid metabolism and immune function, and altering the normal levels of these lipid mediators can negatively affect these processes. Exposure to CPF alters brain endocannabinoid hydrolysis activity, but it is unclear whether low-level exposure alters this activity in peripheral tissues important in metabolic and immune function. Therefore, rat pups were exposed orally from day 10 to 16 to 0.5, 0.75, or 1.0 mg/kg CPF or 0.02 mg/kg PF-04457845 (a specific FAAH inhibitor). At 12 hours postexposure, FAAH, MAGL, and cholinesterase (ChE) activities were determined. All treatments inhibited FAAH activity in brain, spleen, and liver. CPF inhibited ChE activity in spleen and liver (all dosages) and in brain (highest dosage only). CPF inhibited total 2-AG hydrolysis and MAGL-specific activity in brain and spleen (high dosage only). In liver, total 2-AG hydrolysis was inhibited by all treatments and could be attributed to inhibition of non-MAGL-mediated 2-AG hydrolysis, indicating involvement of other enzymes. MAGL-specific activity in liver was inhibited only by the high CPF dosage, whereas PF-04457845 slightly increased this activity. Overall, exposure to low levels of CPF and to PF-04457845 can alter endocannabinoid metabolism in peripheral tissues, thus potentially affecting physiological processes.

Chronic fluoxetine ameliorates adolescent chronic nicotine exposure-induced long-term adult deficits in trace conditioning

Development of the brain, including the prefrontal cortex and hippocampus, continues through adolescence. Chronic nicotine exposure during adolescence may contribute to long-term deficits in forebrain-dependent learning. It is unclear if these deficits emerge immediately after exposure and if they can be ameliorated. In this study, C57BL/6J mice were treated with chronic nicotine (6.3 or 12.6 mg/kg/day) over 12 days beginning at adolescence, postnatal day (PND) 38, or adulthood, PND 56-63 ± 3. We investigated the effects of short-term (24 h) abstinence on trace fear conditioning and found that adult treatment resulted in deficits (6.3 and 12.6 mg/kg/day), but adolescent chronic nicotine treatment had no effect. In contrast, adolescent treatment with chronic nicotine (12.6 mg/kg/day) elicited a long-term (30 days) learning deficit, but adult chronic nicotine treatment did not. Using the elevated plus maze (EPM) we found no long-term changes in anxiety-related behavior after chronic nicotine exposure at either time-point. We investigated if chronic fluoxetine (FLX) could ameliorate adolescent chronic nicotine-associated long-term deficits in trace conditioning. We found that chronic FLX (160 mg/L) in drinking water ameliorated the long-term deficit in trace fear conditioning associated with nicotine exposure during adolescence. Additionally, in the same animals, we examined changes in total BDNF protein in the dorsal hippocampus (DH), ventral hippocampus (VH), and prefrontal cortex (PFC). Chronic FLX increased DH BDNF. Our data indicate nicotine administration during adolescence leads to late onset, long-lasting deficits in hippocampus-dependent learning that chronic FLX treatment ameliorate.

Bans on electronic cigarette sales to minors and smoking among high school students

Many states have banned electronic cigarette sales to minors under the rationale that using e-cigarettes leads to smoking traditional combustion cigarettes. Such sales bans would be counterproductive, however, if e-cigarettes and traditional cigarettes are substitutes, as bans might push teenagers back to smoking the more dangerous combustion cigarettes. We provide evidence that these sales bans reduce the incidence of smoking conventional cigarettes among high school seniors. Moreover, we provide evidence suggesting that sales bans reduced e-cigarette usage as well. This evidence suggests that not only are e-cigarettes and smoking regular cigarettes positively related and not substitutes for young people, banning retail sales to minors is an effective policy tool in reducing tobacco use.

The Relation between Frequency of E-Cigarette Use and Frequency and Intensity of Cigarette Smoking among South Korean Adolescents

INTRODUCTION

The prevalence of adolescent electronic cigarette (e-cigarette) use has increased in most countries. This study aims to determine the relation between the frequency of e-cigarette use and the frequency and intensity of cigarette smoking. Additionally, the study evaluates the association between the reasons for e-cigarette use and the frequency of its use.

MATERIALS AND METHODS

Using the 2015 Korean Youth Risk Behavior Web-Based Survey, we included 6655 adolescents with an experience of e-cigarette use who were middle and high school students aged 13-18 years. We compared smoking experience, the frequency and intensity of cigarette smoking, and the relation between the reasons for e-cigarette uses and the frequency of e-cigarette use.

RESULTS

The prevalence of e-cigarette ever and current (past 30 days) users were 10.1% and 3.9%, respectively. Of the ever users, approximately 60% used e-cigarettes not within 1 month. On the other hand, 8.1% used e-cigarettes daily. The frequent and intensive cigarette smoking was associated with frequent e-cigarette uses. The percentage of frequent e-cigarette users (≥10 days/month) was 3.5% in adolescents who did not smoke within a month, but 28.7% among daily smokers. Additionally, it was 9.1% in smokers who smoked less than 1 cigarette/month, but 55.1% in smokers who smoked ≥20 cigarettes/day. The most common reason for e-cigarette use was curiosity (22.9%), followed by the belief that they are less harmful than conventional cigarettes (18.9%), the desire to quit smoking (13.1%), and the capacity for indoor use (10.7%). Curiosity was the most common reason among less frequent e-cigarette users; however, the desire to quit smoking and the capacity for indoor use were the most common reasons among more frequent users.

CONCLUSIONS

Results showed a positive relation between frequency or intensity of conventional cigarette smoking and the frequency of e-cigarette use among Korean adolescents, and frequency of e-cigarette use differed according to the reason for the use of e-cigarettes.

Does puberty mark a transition in sensitive periods for plasticity in the associative neocortex?

Postnatal brain development is studded with sensitive periods during which experience dependent plasticity is enhanced. This enables rapid learning from environmental inputs and reorganization of cortical circuits that matches behavior with environmental contingencies. Significant headway has been achieved in characterizing and understanding sensitive period biology in primary sensory cortices, but relatively little is known about sensitive period biology in associative neocortex. One possible mediator is the onset of puberty, which marks the transition to adolescence, when animals shift their behavior toward gaining independence and exploring their social world. Puberty onset correlates with reduced behavioral plasticity in some domains and enhanced plasticity in others, and therefore may drive the transition from juvenile to adolescent brain function. Pubertal onset is also occurring earlier in developed nations, particularly in unserved populations, and earlier puberty is associated with vulnerability for substance use, depression and anxiety. In the present article we review the evidence that supports a causal role for puberty in developmental changes in the function and neurobiology of the associative neocortex. We also propose a model for how pubertal hormones may regulate sensitive period plasticity in associative neocortex. We conclude that the evidence suggests puberty onset may play a causal role in some aspects of associative neocortical development, but that further research that manipulates puberty and measures gonadal hormones is required. We argue that further work of this kind is urgently needed to determine how earlier puberty may negatively impact human health and learning potential. This article is part of a Special Issue entitled SI: Adolescent plasticity.

Long-term effects of chronic nicotine on emotional and cognitive behaviors and hippocampus cell morphology in mice: comparisons of adult and adolescent nicotine exposure

Nicotine dependence is associated with increased risk for emotional, cognitive and neurological impairments later in life. This study investigated the long-term effects of nicotine exposure during adolescence and adulthood on measures of depression, anxiety, learning and hippocampal pyramidal cell morphology. Mice (C57BL/6J) received saline or nicotine for 12 days via pumps implanted on postnatal day 32 (adolescent) or 54 (adults). Thirty days after cessation of nicotine/saline, mice were tested for learning using contextual fear conditioning, depression-like behaviors using the forced swim test or anxiety-like behaviors with the elevated plus maze. Brains from nicotine- or saline-exposed mice were processed with Golgi stain for whole neuron reconstruction in the CA1 and CA3 regions of the hippocampus. Results demonstrate higher depression-like responses in both adolescent and adult mice when tested during acute nicotine withdrawal. Heightened depression-like behaviors persisted when tested after 30 days of nicotine abstinence in mice exposed as adolescents, but not adults. Adult, but not adolescent, exposure to nicotine resulted in increased open-arm time when tested after 30 days of abstinence. Nicotine exposure during adolescence caused deficits in contextual fear learning indicated by lower levels of freezing to the context as compared with controls when tested 30 days later. In addition, reduced dendritic length and complexity in the apical CA1 branches in adult mice exposed to nicotine during adolescence were found. These results demonstrate that nicotine exposure and withdrawal can have long-term effects on emotional and cognitive functioning, particularly when nicotine exposure occurs during the critical period of adolescence.

Reasons for Trying E-cigarettes and Risk of Continued Use

BACKGROUND

Longitudinal research is needed to identify predictors of continued electronic cigarette (e-cigarette) use among youth. We expected that certain reasons for first trying e-cigarettes would predict continued use over time (eg, good flavors, friends use), whereas other reasons would not predict continued use (eg, curiosity).

METHODS

Longitudinal surveys from middle and high school students from fall 2013 (wave 1) and spring 2014 (wave 2) were used to examine reasons for trying e-cigarettes as predictors of continued e-cigarette use over time. Ever e-cigarette users (n = 340) at wave 1 were categorized into those using or not using e-cigarettes at wave 2. Among those who continued using e-cigarettes, reasons for trying e-cigarettes were examined as predictors of use frequency, measured as the number of days using e-cigarettes in the past 30 days at wave 2. Covariates included age, sex, race, and smoking of traditional cigarettes.

RESULTS

Several reasons for first trying e-cigarettes predicted continued use, including low cost, the ability to use e-cigarettes anywhere, and to quit smoking regular cigarettes. Trying e-cigarettes because of low cost also predicted more days of e-cigarette use at wave 2. Being younger or a current smoker of traditional cigarettes also predicted continued use and more frequent use over time.

CONCLUSIONS

Regulatory strategies such as increasing cost or prohibiting e-cigarette use in certain places may be important for preventing continued use in youth. In addition, interventions targeting current cigarette smokers and younger students may also be needed.

Consequences of adolescent use of alcohol and other drugs: Studies using rodent models

Studies using animal models of adolescent exposure to alcohol, nicotine, cannabinoids, and the stimulants cocaine, 3,4-methylenedioxymethampethamine and methamphetamine have revealed a variety of persisting neural and behavioral consequences. Affected brain regions often include mesolimbic and prefrontal regions undergoing notable ontogenetic change during adolescence, although it is unclear whether this represents areas of specific vulnerability or particular scrutiny to date. Persisting alterations in forebrain systems critical for modulating reward, socioemotional processing and cognition have emerged, including apparent induction of a hyper-dopaminergic state with some drugs and/or attenuations in neurons expressing cholinergic markers. Disruptions in cognitive functions such as working memory, alterations in affect including increases in social anxiety, and mixed evidence for increases in later drug self-administration has also been reported. When consequences of adolescent and adult exposure were compared, adolescents were generally found to be more vulnerable to alcohol, nicotine, and cannabinoids, but generally not to stimulants. More work is needed to determine how adolescent drug exposure influences sculpting of the adolescent brain, and provide approaches to prevent/reverse these effects.

Preventing smoking in children and adolescents: Recommendations for practice and policy

Canada has witnessed a general decrease in smoking prevalence among all age groups in recent years. However, despite large numbers of campaigns and interventions, thousands of young Canadians continue to initiate cigarette smoking every year. The increasing popularity of alternative tobacco products and e-cigarettes is also creating new health challenges. Research has shown that the deleterious effects of nicotine and cigarette smoke are significant and long lasting. Health care professionals have key responsibilities in preventing tobacco use among youth and their families, and need to know more about effective smoking prevention and cessation strategies. Clinicians need to integrate tobacco counselling into health assessments of teenagers and be aware of the roles that families, communities and governments can play in promoting tobacco-free environments. Information, effective strategies and opportunities for health care professionals to intervene and advocate for Canadian adolescents are discussed.

Modifying effect of cigarette smoking on the association of organizational justice with serious psychological distress in Japanese employees: a cross-sectional study

PURPOSE

We examined the modifying effect of cigarette smoking (i.e., smokers vs. non-smokers) on the association of organizational justice (i.e., procedural justice and interactional justice) with serious psychological distress (SPD) in Japanese employees.

METHODS

Overall, 2838 participants from two factories of a manufacturing company in Japan completed a self-administered questionnaire comprising the scales on organizational justice (Organizational Justice Questionnaire), smoking status, psychological distress (K6 scale), demographic and occupational characteristics (i.e., gender, age, education, family size, history of depression, chronic physical conditions, occupation, and work form), and other health-related behaviors (i.e., drinking habit and physical activity). Multiple logistic regression analyses were conducted. In a series of analyses, interaction term of procedural justice or interactional justice with smoking status was included in the model.

RESULTS

After adjusting for demographic and occupational characteristics as well as other health-related behaviors, low procedural justice and low interactional justice were significantly associated with SPD (defined as K6 ≥ 13). Furthermore, marginally significant interaction effect of procedural justice with smoking status was observed. Specifically, the association of low procedural justice with SPD was greater among smokers [prevalence odds ratio 7.13 (95 % confidence interval 3.25-15.7) for low vs. high procedural justice subgroup] than among non-smokers [prevalence odds ratio 2.34 (95 % confidence interval 1.52-3.60) for low vs. high procedural justice subgroup]. On the other hand, interaction effect of interactional justice with smoking status was not significant.

CONCLUSIONS

Cigarette smoking seems to have a harmful effect on the association of the lack of procedural justice with SPD in Japanese employees.

Psychiatric comorbidity in adolescent electronic and conventional cigarette use

The popularity of electronic (e-) cigarettes has greatly increased recently, particularly in adolescents. However, the extent of psychiatric comorbidity with adolescent e-cigarette use and dual use of conventional (combustible) and e-cigarettes is unknown. This study characterized psychiatric comorbidity in adolescent conventional and e-cigarette use. Ninth grade students attending high schools in Los Angeles, CA (M age = 14) completed self-report measures of conventional/e-cigarette use, emotional disorders, substance use/problems, and transdiagnostic psychiatric phenotypes consistent with the NIMH-Research Domain Criteria Initiative. Outcomes were compared by lifetime use of: (1) neither conventional nor e-cigarettes (non-use; N = 2557, 77.3%); (2) e-cigarettes only (N = 412, 12.4%); (3) conventional cigarettes only (N = 152, 4.6%); and (4) conventional and e-cigarettes (dual use; N = 189, 5.6%). In comparison to adolescents who used conventional cigarettes only, e-cigarette only users reported lower levels of internalizing syndromes (depression, generalized anxiety, panic, social phobia, and obsessive-compulsive disorder) and transdiagnostic phenotypes (i.e., distress intolerance, anxiety sensitivity, rash action during negative affect). Depression, panic disorder, and anhedonia were higher in e-cigarette only vs. non-users. For several externalizing outcomes (mania, rash action during positive affect, alcohol drug use/abuse) and anhedonia, an ordered pattern was observed, whereby comorbidity was lowest in non-users, moderate in single product users (conventional or e-cigarette), and highest in dual users. These findings: (1) raise question of whether emotionally-healthier ('lower-risk') adolescents who are not interested in conventional cigarettes are being attracted to e-cigarettes; (2) indicate that research, intervention, and policy dedicated to adolescent tobacco-psychiatric comorbidity should distinguish conventional cigarette, e-cigarette, and dual use.

Adolescent methylphenidate treatment differentially alters adult impulsivity and hyperactivity in the Spontaneously Hypertensive Rat model of ADHD

Impulsivity and hyperactivity are two facets of attention deficit/hyperactivity disorder (ADHD). Impulsivity is expressed as reduced response inhibition capacity, an executive control mechanism that prevents premature execution of an intermittently reinforced behavior. During methylphenidate treatment, impulsivity and hyperactivity are decreased in adolescents with ADHD, but there is little information concerning levels of impulsivity and hyperactivity in adulthood after adolescent methylphenidate treatment is discontinued. The current study evaluated impulsivity, hyperactivity as well as cocaine sensitization during adulthood after adolescent methylphenidate treatment was discontinued in the Spontaneously Hypertensive Rat (SHR) model of ADHD. Treatments consisted of oral methylphenidate (1.5mg/kg) or water vehicle provided Monday-Friday from postnatal days 28-55. During adulthood, impulsivity was measured in SHR and control strains (Wistar Kyoto and Wistar rats) using differential reinforcement of low rate (DRL) schedules. Locomotor activity and cocaine sensitization were measured using the open-field assay. Adult SHR exhibited decreased efficiency of reinforcement under the DRL30 schedule and greater levels of locomotor activity and cocaine sensitization compared to control strains. Compared to vehicle, methylphenidate treatment during adolescence reduced hyperactivity in adult SHR, maintained the lower efficiency of reinforcement, and increased burst responding under DRL30. Cocaine sensitization was not altered following adolescent methylphenidate in adult SHR. In conclusion, adolescent treatment with methylphenidate followed by discontinuation in adulthood had a positive benefit by reducing hyperactivity in adult SHR rats; however, increased burst responding under DRL compared to SHR given vehicle, i.e., elevated impulsivity, constituted an adverse consequence associated with increased risk for cocaine abuse liability.

Decreased anxiety in juvenile rats following exposure to low levels of chlorpyrifos during development

Exposure to chlorpyrifos (CPF) during the late preweanling period in rats inhibits the endocannabinoid metabolizing enzymes fatty acid hydrolase (FAAH) and monoacylglycerol lipase (MAGL), resulting in accumulation of their respective substrates anandamide (AEA) and 2-arachidonylglycerol (2-AG). This occurs at 1.0mg/kg, but at a lower dosage (0.5mg/kg) only FAAH and AEA are affected with no measurable inhibition of either cholinesterase (ChE) or MAGL. The endocannabinoid system plays a vital role in nervous system development and may be an important developmental target for CPF. The endocannabinoid system plays an important role in the regulation of anxiety and, at higher dosages, developmental exposure to CPF alters anxiety-like behavior. However, it is not clear whether exposure to low dosages of CPF that do not inhibit ChE will cause any persistent effects on anxiety-like behavior. To determine if this occurs, 10-day old rat pups were exposed daily for 7 days to either corn oil or 0.5, 0.75, or 1.0mg/kg CPF by oral gavage. At 12h following the last CPF administration, 1.0mg/kg resulted in significant inhibition of FAAH, MAGL, and ChE, whereas 0.5 and 0.75mg/kg resulted in significant inhibition of only FAAH. AEA levels were significantly elevated in all three treatment groups as were palmitoylethanolamide and oleoylethanolamide, which are also substrates for FAAH. 2-AG levels were significantly elevated by 0.75 and 1.0mg/kg but not 0.5mg/kg. On day 25, the latency to emerge from a dark container into a highly illuminated novel open field was measured as an indicator of anxiety. All three CPF treatment groups spent significantly less time in the dark container prior to emerging as compared to the control group, suggesting a decreased level of anxiety. This demonstrates that repeated preweanling exposure to dosages of CPF that do not inhibit brain ChE can induce a decline in the level of anxiety that is detectable during the early postweanling period.

Nucleus accumbens injections of the mGluR2/3 agonist LY379268 increase cue-induced sucrose seeking following adult, but not adolescent sucrose self-administration

Adolescence is often portrayed as a period of enhanced sensitivity to reward, with long-lasting neurobiological changes upon reward exposure. However, we previously found that time-dependent increases in cue-induced sucrose seeking were more pronounced in rats trained to self-administer sucrose as adults than as adolescents. In addition, adult, but not adolescent sucrose self-administration led to a decreased α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/N-Methyl-D-aspartate (AMPA/NMDA) ratio in the nucleus accumbens core, suggesting that long-lasting changes in glutamatergic transmission may affect adult processing of natural rewards. Here we tested whether altering glutamatergic transmission in the nucleus accumbens core via local injection of an mGluR2/3 agonist and antagonist affects cue-induced sucrose seeking following abstinence and whether this is different in the two age groups. Rats began oral sucrose self-administration training (10 days) on postnatal day (P) 35 (adolescents) or P70 (adults). Following 21 days of abstinence, rats received microinjections of the mGluR2/3 agonist LY379268 (0.3 or 1.0 μg/side) or vehicle into the nucleus accumbens core, and 15 min later cue-induced sucrose seeking was assessed. An additional group of rats trained as adults received nucleus accumbens core microinjections of the mGluR2/3 antagonist (RS)-α-Methyl-4-phosphonophenylglycine (MPPG) (0.12 or 0.5 μg/side). Confirming our previous results, adult rats earned more sucrose reinforcers, while sucrose intake per body weight was similar across ages. On abstinence day 22, local injection of the mGluR2/3 agonist LY379268 increased cue-induced sucrose seeking only in adult rats, and had no effect in adolescents. Local injections of the mGluR2/3 antagonist MPPG had no effect on sucrose seeking in adult rats. These data suggest an important developmental difference in the neural substrates of natural reward, specifically a difference in glutamatergic transmission in the accumbens in cue-induced responding for sucrose between adolescent and adult rats.

Association of Electronic Cigarette Use With Initiation of Combustible Tobacco Product Smoking in Early Adolescence

IMPORTANCE

Exposure to nicotine in electronic cigarettes (e-cigarettes) is becoming increasingly common among adolescents who report never having smoked combustible tobacco.

OBJECTIVE

To evaluate whether e-cigarette use among 14-year-old adolescents who have never tried combustible tobacco is associated with risk of initiating use of 3 combustible tobacco products (ie, cigarettes, cigars, and hookah).

DESIGN, SETTING, AND PARTICIPANTS

Longitudinal repeated assessment of a school-based cohort at baseline (fall 2013, 9th grade, mean age = 14.1 years) and at a 6-month follow-up (spring 2014, 9th grade) and a 12-month follow-up (fall 2014, 10th grade). Ten public high schools in Los Angeles, California, were recruited through convenience sampling. Participants were students who reported never using combustible tobacco at baseline and completed follow-up assessments at 6 or 12 months (N = 2530). At each time point, students completed self-report surveys during in-classroom data collections.

EXPOSURE

Student self-report of whether he or she ever used e-cigarettes (yes or no) at baseline.

MAIN OUTCOMES AND MEASURES

Six- and 12-month follow-up reports on use of any of the following tobacco products within the prior 6 months: (1) any combustible tobacco product (yes or no); (2) combustible cigarettes (yes or no), (3) cigars (yes or no); (4) hookah (yes or no); and (5) number of combustible tobacco products (range: 0-3).

RESULTS

Past 6-month use of any combustible tobacco product was more frequent in baseline e-cigarette ever users (n = 222) than never users (n = 2308) at the 6-month follow-up (30.7% vs 8.1%, respectively; difference between groups in prevalence rates, 22.7% [95% CI, 16.4%-28.9%]) and at the 12-month follow-up (25.2% vs 9.3%, respectively; difference between groups, 15.9% [95% CI, 10.0%-21.8%]). Baseline e-cigarette use was associated with greater likelihood of use of any combustible tobacco product averaged across the 2 follow-up periods in the unadjusted analyses (odds ratio [OR], 4.27 [95% CI, 3.19-5.71]) and in the analyses adjusted for sociodemographic, environmental, and intrapersonal risk factors for smoking (OR, 2.73 [95% CI, 2.00-3.73]). Product-specific analyses showed that baseline e-cigarette use was positively associated with combustible cigarette (OR, 2.65 [95% CI, 1.73-4.05]), cigar (OR, 4.85 [95% CI, 3.38-6.96]), and hookah (OR, 3.25 [95% CI, 2.29-4.62]) use and with the number of different combustible products used (OR, 4.26 [95% CI, 3.16-5.74]) averaged across the 2 follow-up periods.

CONCLUSIONS AND RELEVANCE

Among high school students in Los Angeles, those who had ever used e-cigarettes at baseline compared with nonusers were more likely to report initiation of combustible tobacco use over the next year. Further research is needed to understand whether this association may be causal.

Impulsivity and cigarette craving among adolescent daily and occasional smokers

INTRODUCTION

Impulsivity is a multi-dimensional construct that is robustly related to cigarette smoking. While underlying factors that account for this relation are not well understood, craving has been proposed as a central mechanism linking impulsivity to smoking. In order to further refine our understanding of associations between impulsivity and cigarette craving, the current study examined the association between impulsivity and tonic and cue-elicited craving among a sample of adolescent smokers. We expected trait impulsivity would be positively associated with both tonic and cue-elicited craving, and that this relationship would be stronger among daily vs. occasional smokers.

METHODS

106 smokers (ages 16-20) completed the questionnaires and reported their cigarette craving prior to and immediately following presentation of each of three counterbalanced cue types: (a) in vivo smoking, (b) alcohol, and (c) neutral cue.

RESULTS

Impulsivity was positively associated with tonic craving for daily smokers (β=.38; p=.005), but not occasional smokers (β=.01; p=.95), with a significant impulsivity x smoker group interaction (β=1.31; p=.03). Impulsivity was unrelated to craving following smoking or alcohol cue, regardless of smoker group (all p's>.16).

CONCLUSIONS

Results suggest a moderated effect in which impulsivity is positively associated with tonic craving for daily smokers, but not occasional smokers. Tonic craving may serve as a mechanism linking impulsivity, smoking persistence, and nicotine dependence among daily smokers.

E-cigarettes: Are we renormalizing public smoking? Reversing five decades of tobacco control and revitalizing nicotine dependency in children and youth in Canada

An electronic cigarette (e-cigarette) is a battery attached to a chamber containing liquid that may (or may not) contain nicotine. The battery heats the liquid and converts it into a vapour, which is inhaled, mimicking tobacco smoking. The e-cigarette does not rely on tobacco as a source of nicotine but, rather, vaporizes a liquid for inhalation. E-liquids are often flavoured and may contain nicotine in various concentrations, although actual amounts are seldom accurately reflected in container labelling. The deleterious effects of nicotine on paediatric health are well established. The use of e-cigarettes in the paediatric age group is on the rise in Canada, as are associated nicotine poisonings. E-devices generate substantial amounts of fine particulate matter, toxins and heavy metals at levels that can exceed those observed for conventional cigarettes. Children and youth are particularly susceptible to these atomized products. Action must be taken before these devices become a more established public health hazard. Policies to denormalize tobacco smoking in society and historic reductions in tobacco consumption may be undermined by this new 'gateway' product to nicotine dependency.

Nicotinic, glutamatergic and dopaminergic synaptic transmission and plasticity in the mesocorticolimbic system: focus on nicotine effects

Cigarette smoking is currently the leading cause of preventable deaths and disability throughout the world, being responsible for about five million premature deaths/year. Unfortunately, fewer than 10% of tobacco users who try to stop smoking actually manage to do so. The main addictive agent delivered by cigarette smoke is nicotine, which induces psychostimulation and reward, and reduces stress and anxiety. The use of new technologies (including optogenetics) and the development of mouse models characterised by cell-specific deletions of receptor subtype genes or the expression of gain-of-function nAChR subunits has greatly increased our understanding of the molecular mechanisms and neural substrates of nicotine addiction first revealed by classic electrophysiological, neurochemical and behavioural approaches. It is now becoming clear that various aspects of nicotine dependence are mediated by close interactions of the glutamatergic, dopaminergic and γ-aminobutyric acidergic systems in the mesocorticolimbic system. This review is divided into two parts. The first provides an updated overview of the circuitry of the ventral tegmental area, ventral striatum and prefrontal cortex, the neurotransmitter receptor subtypes expressed in these areas, and their physiological role in the mesocorticolimbic system. The second will focus on the molecular, functional and behavioural mechanisms involved in the acute and chronic effects of nicotine on the mesocorticolimbic system.

Reduced nicotine product standards for combustible tobacco: building an empirical basis for effective regulation

INTRODUCTION

Both the Tobacco Control Act in the U.S. and Article 9 of the Framework Convention on Tobacco Control enable governments to directly address the addictiveness of combustible tobacco by reducing nicotine through product standards. Although nicotine may have some harmful effects, the detrimental health effects of smoked tobacco are primarily due to non-nicotine constituents. Hence, the health effects of nicotine reduction would likely be determined by changes in behavior that result in changes in smoke exposure.

METHODS

Herein, we review the current evidence on nicotine reduction and discuss some of the challenges in establishing the empirical basis for regulatory decisions.

RESULTS

To date, research suggests that very low nicotine content cigarettes produce a desirable set of outcomes, including reduced exposure to nicotine, reduced smoking, and reduced dependence, without significant safety concerns. However, much is still unknown, including the effects of gradual versus abrupt changes in nicotine content, effects in vulnerable populations, and impact on youth.

DISCUSSION

A coordinated effort must be made to provide the best possible scientific basis for regulatory decisions. The outcome of this effort may provide the foundation for a novel approach to tobacco control that dramatically reduces the devastating health consequences of smoked tobacco.

Sex differences in the effect of wheel running on subsequent nicotine-seeking in a rat adolescent-onset self-administration model

RATIONALE

Wheel running attenuates nicotine-seeking in male adolescent rats; however, it is not known if this effect extends to females.

OBJECTIVE

To determine if wheel running during abstinence would differentially attenuate subsequent nicotine-seeking in male and female rats that had extended access to nicotine self-administration during adolescence.

METHODS

Male (n = 49) and female (n = 43) adolescent rats self-administered saline or nicotine (5 μg/kg) under an extended access (23-h) paradigm. Following the last self-administration session, rats were moved to polycarbonate cages for an abstinence period where they either had access to a locked or unlocked running wheel for 2 h/day. Subsequently, nicotine-seeking was examined under a within-session extinction/cue-induced reinstatement paradigm. Due to low levels of nicotine-seeking in females in both wheel groups, additional groups were included that were housed without access to a running wheel during abstinence.

RESULTS

Females self-administered more nicotine as compared to males; however, within males and females, intake did not differ between groups prior to wheel assignment. Compared to saline controls, males and females that self-administered nicotine showed a significant increase in drug-seeking during extinction. Wheel running during abstinence attenuated nicotine-seeking during extinction in males. In females, access to either locked or unlocked wheels attenuated nicotine-seeking during extinction. While responding was reinstated by cues in both males and females, levels were modest and not significantly affected by exercise in this adolescent-onset model.

CONCLUSIONS

While wheel running reduced subsequent nicotine-seeking in males, access to a wheel, either locked or unlocked, was sufficient to suppress nicotine-seeking in females.

On the interaction between drugs of abuse and adolescent social behavior

RATIONALE

Social factors influence drug abuse. Conversely, drugs of abuse alter social behavior. This is especially pertinent during post-weaning development, when there are profound changes in the social repertoire, and the sensitivity to the positive and negative effects of drugs of abuse is altered.

OBJECTIVES

This study aimed to provide an overview of our current understanding of the interaction between drugs of abuse and juvenile/adolescent social behavior.

METHODS

We first provide evidence that a characteristic form of juvenile and adolescent social behavior, i.e., social play behavior, has reinforcing properties and is affected by drugs of abuse. Next, social risk factors for drug use and addiction are described, including antisocial personality traits and early social insults. Last, we discuss research that investigates social influences on drug use, as well as the consequences of perinatal drug exposure on later social interactions.

RESULTS

Social play behavior is highly rewarding in laboratory animals, and it is affected by low doses of opioids, cannabinoids, ethanol, nicotine, and psychostimulants. In humans, antisocial personality traits, most prominently in the form of conduct disorder, are a prominent risk factor for drug addiction. Preclinical studies have consistently shown altered sensitivity to drugs as a result of social isolation during post-weaning development. The social environment of an individual has a profound, but complex, influence on drug use, and perinatal drug exposure markedly alters later social interactions.

CONCLUSIONS

The studies reviewed here provide a framework to understand the interaction between drugs of abuse and adolescent social interaction, at the preclinical and the clinical level.

Time-dependent decreases in nucleus accumbens AMPA/NMDA ratio and incubation of sucrose craving in adolescent and adult rats

RATIONALE AND OBJECTIVE

There is evidence that cue-induced sucrose seeking progressively increases after cessation of oral sucrose self-administration (incubation of sucrose craving) in both adolescent and adult rats. The synaptic plasticity changes associated with this incubation at different age groups are unknown. We assessed whether incubation of sucrose craving in rats trained to self-administer sucrose as young adolescents, adolescents, or adults is associated with changes in 2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl)propanoic acid (AMPA)/N-methyl-D-aspartate (NMDA) ratio (a measure of postsynaptic changes in synaptic strength) in nucleus accumbens.

METHODS

Three age groups initiated oral sucrose self-administration training (10 days) on postnatal day (P) 35 (young adolescents), P42 (adolescents), or P70 (adults). They were then tested for cue-induced sucrose seeking (assessed in an extinction test) on abstinence days 1 and 21. Separate groups of rats were trained to self-administer sucrose or water (a control condition), and assessed for AMPA/NMDA ratio in nucleus accumbens on abstinence days 1-3 and 21.

RESULTS

Adult rats earned more sucrose rewards, but sucrose intake per body weight was higher in young adolescent rats. Time-dependent increases in cue-induced sucrose seeking (incubation of sucrose craving) were more pronounced in adult rats, less pronounced in adolescents, and not detected in young adolescents. On abstinence day 21, but not days 1-3, AMPA/NMDA ratio in nucleus accumbens were decreased in rats that self-administered sucrose as adults and adolescents, but not young adolescents.

CONCLUSIONS

Our data demonstrate age-dependent changes in magnitude of incubation of sucrose craving and nucleus accumbens synaptic plasticity after cessation of sucrose self-administration.

Low level chlorpyrifos exposure increases anandamide accumulation in juvenile rat brain in the absence of brain cholinesterase inhibition

The prevailing dogma is that chlorpyrifos (CPF) mediates its toxicity through inhibition of cholinesterase (ChE). However, in recent years, the toxicological effects of developmental CPF exposure have been attributed to an unknown non-cholinergic mechanism of action. We hypothesize that the endocannabinoid system may be an important target because of its vital role in nervous system development. We have previously reported that repeated exposure to CPF results in greater inhibition of fatty acid amide hydrolase (FAAH), the enzyme that metabolizes the endocannabinoid anandamide (AEA), than inhibition of either forebrain ChE or monoacylglycerol lipase (MAGL), the enzyme that metabolizes the endocannabinoid 2-arachidonylglycerol (2-AG). This exposure resulted in the accumulation of 2-AG and AEA in the forebrain of juvenile rats; however, even at the lowest dosage level used (1.0mg/kg), forebrain ChE inhibition was still present. Thus, it is not clear if FAAH activity would be inhibited at dosage levels that do not inhibit ChE. To determine this, 10 day old rat pups were exposed daily for 7 days to either corn oil or 0.5mg/kg CPF by oral gavage. At 4 and 12h post-exposure on the last day of administration, the activities of serum ChE and carboxylesterase (CES) and forebrain ChE, MAGL, and FAAH were determined as well as the forebrain AEA and 2-AG levels. Significant inhibition of serum ChE and CES was present at both 4 and 12h. There was no significant inhibition of the activities of forebrain ChE or MAGL and no significant change in the amount of 2-AG at either time point. On the other hand, while no statistically significant effects were observed at 4h, FAAH activity was significantly inhibited at 12h resulting in a significant accumulation of AEA. Although it is not clear if this level of accumulation impacts brain maturation, this study demonstrates that developmental CPF exposure at a level that does not inhibit brain ChE can alter components of endocannabinoid signaling.