Nicotine exposure during adolescence alters the rules for prefrontal cortical synaptic plasticity during adulthood

Neurite Orientation Dispersion and Density Imaging (NODDI) of Brain Microstructure in Adolescent Cannabis and Nicotine Use

INTRODUCTION

Despite evidence suggesting deleterious effects of cannabis and nicotine tobacco product (NTP) use on white matter integrity, there have been limited studies examining white matter integrity among users of both cannabis and nicotine. Further, updated white matter methodology provides opportunities to investigate use patterns on neurite orientation dispersion and density (NODDI) indices and subtle tissue changes related to the intra- and extra-neurite compartment. We aimed to investigate how cannabis and NTP use among adolescents and young adults interacts to impact the white matter integrity microstructure.

MATERIALS AND METHODS

A total of 221 participants between the ages of 16 and 22 completed the Customary Drinking and Drug Use Record (CDDR) to measure substance use, and underwent a magnetic resonance imaging (MRI) session. Participants were divided into NTP-control and NTP groupings and cannabis-control and cannabis groupings (≥26 NTP/cannabis uses in past 6 months). Tract-Based Spatial Statistics (TBSS) and two-way between-subjects ANOVA investigated the effects of NTP use group, cannabis use group, and their interaction on fractional anisotropy (FA) and NODDI indices while controlling for age and biological sex.

RESULTS

NTP use was associated with decreased FA values and increased orientation dispersion in the left anterior capsule. There were no significant effects of cannabis use or the interaction of NTP and cannabis use on white matter outcomes.

DISCUSSION

NTP use was associated with altered white matter integrity in an adolescent and young adult sample. Findings suggest that NTP-associated alterations may be linked to altered fiber tract geometry and dispersed neurite structures versus myelination, as well as differential effects of NTP and cannabis use on white matter structure. Future work is needed to investigate how altered white matter is related to downstream behavioral effects from NTP use.

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.

Nicotine Differentially Modulates Emotional-Locomotor Interactions for Adult or Adolescent Rats

Previous research has shown that exposure to nicotine and other drugs of abuse stimulate dopaminergic neurons in the mesolimbic circuit. Sustained activation of this circuit by prolonged exposure to drugs promotes locomotor sensitization. However, there are inconsistent reports about nicotine-induced locomotor sensitization when assessed among different developmental stages. We evaluated exploratory behavior on specific areas of the open field as an indicator of behavioral disinhibition and general locomotor activity as an indicator of nicotine-induced locomotor sensitization, to further explore the mechanisms underlying behavioral adaptations to nicotine exposure in animals from different developmental stages. We found that while adolescent and adult rats are equally responsive to nicotine-induced locomotor sensitization, nicotine disrupts inhibition of risk-related behavior only in adolescent rats. Together, our results suggest that chronic daily exposure to nicotine promotes potentiation of its stimulant effects on locomotor activity. In adolescents, this effect is accompanied by a decreased capacity to inhibit risk-related behaviors under the acute effect of the drug.   How to cite this article: Novoa, C., Solano, J. L., Ballesteros-Acosta, H., Lamprea, R. M., & Ortega, L. A. (2021). Nicotine Differentially Modulates Emotional-Locomotor Interactions for Adult or Adolescent Rats. Revista Colombiana de Psicología, 31(1), 13-22. https://doi.org/10.15446/rcp.v31n1.89822

The Periaqueductal Gray and Its Extended Participation in Drug Addiction Phenomena

The periaqueductal gray (PAG) is a complex mesencephalic structure involved in the integration and execution of active and passive self-protective behaviors against imminent threats, such as immobility or flight from a predator. PAG activity is also associated with the integration of responses against physical discomfort (e.g., anxiety, fear, pain, and disgust) which occurs prior an imminent attack, but also during withdrawal from drugs such as morphine and cocaine. The PAG sends and receives projections to and from other well-documented nuclei linked to the phenomenon of drug addiction including: (i) the ventral tegmental area; (ii) extended amygdala; (iii) medial prefrontal cortex; (iv) pontine nucleus; (v) bed nucleus of the stria terminalis; and (vi) hypothalamus. Preclinical models have suggested that the PAG contributes to the modulation of anxiety, fear, and nociception (all of which may produce physical discomfort) linked with chronic exposure to drugs of abuse. Withdrawal produced by the major pharmacological classes of drugs of abuse is mediated through actions that include participation of the PAG. In support of this, there is evidence of functional, pharmacological, molecular. And/or genetic alterations in the PAG during the impulsive/compulsive intake or withdrawal from a drug. Due to its small size, it is difficult to assess the anatomical participation of the PAG when using classical neuroimaging techniques, so its physiopathology in drug addiction has been underestimated and poorly documented. In this theoretical review, we discuss the involvement of the PAG in drug addiction mainly via its role as an integrator of responses to the physical discomfort associated with drug withdrawal.

Multifactorial Etiology of Adolescent Nicotine Addiction: A Review of the Neurobiology of Nicotine Addiction and Its Implications for Smoking Cessation Pharmacotherapy

Nicotine is the primary pharmacologic component of tobacco, and its highly addictive nature is responsible for its widespread use and significant withdrawal effects that result in challenges to smoking cessation therapeutics. Nicotine addiction often begins in adolescence and this is at least partially attributed to the fact that adolescent brain is most susceptible to the neuro-inflammatory effects of nicotine. There is increasing evidence for the involvement of microglial cells, which are the brain's primary homeostatic sensor, in drug dependence and its associated behavioral manifestations particularly in the adolescent brain. A hallmark of neuro-inflammation is microglial activation and activation of microglia by nicotine during adolescent development, which may result in long-term addiction to nicotine. This non-systematic review examines multifactorial etiology of adolescent nicotine addiction, neurobiology of nicotine addiction and the potential mechanisms that underlie the effects of nicotine on inflammatory signaling in the microglia, understanding how nicotine affects the adolescent brain. We speculate, that modulating homeostatic balance in microglia, could have promising therapeutic potential in withdrawal, tolerance, and abstinence-related neural adaptations in nicotine addiction, in the adolescent brain. Further, we discuss nicotine addiction in the context of the sensitization-homeostasis model which provides a theoretical framework for addressing the potential role of microglial homeostasis in neural adaptations underlying nicotine abuse.

Recommendations for Assessment of Environmental Exposures in Longitudinal Life Course Studies Such as the National Children's Study

An important step toward understanding the relationship between the environment and child health and development is the comprehensive cataloging of external environmental factors that may modify health and development over the life course. Our understanding of the environmental influences on health is growing increasingly complex. Significant key questions exist as to what genes, environment, and life stage mean to defining normal variations and altered developmental trajectories throughout the life course and also across generations. With the rapid advances in genetic technology came large-scale genomic studies to search for the genetic etiology of complex diseases. While genome-wide association studies (GWAS) have revealed genetic factors and networks that advance our understanding to some extent, it is increasingly recognized that disease causation is largely non-genetic and reflects interactions between an individual's genetic susceptibility and his or her environment. Thus, the full promise of the human genome project to prevent or treat disease and promote good health arguably depends on a commitment to understanding the interactions between our environment and our genetic makeup and requires a design with prospective environmental data collection that considers critical windows of susceptibility that likely correspond to the expression of specific genes and gene pathways. Unlike the genome, which is static, relevant exposures as well as our response to exposures, change over time. This has fostered the complementary concept of the exposome ideally defined as the measure of all exposures of an individual over a lifetime and how those exposures relate to health. The exposome framework considers multiple external exposures (e.g., chemical, social) and behaviors that may modify exposures (e.g., diet), as well as consequences of environmental exposures indexed via biomarkers of physiological response or measures of behavioral response throughout the lifespan. The exposome concept can be applied in prospective developmental studies such as the National Children's Study (NCS) with the practical understanding that even a partial characterization will bring major advances to health. Lessons learned from the NCS provide an important opportunity to inform future studies that can leverage these evolving paradigms in elucidating the role of environment on health across the life course.

The Impact of Electronic Nicotine Delivery System (ENDS) Flavors on Nicotinic Acetylcholine Receptors and Nicotine Addiction-Related Behaviors

Over the past two decades, combustible cigarette smoking has slowly declined by nearly 11% in America; however, the use of electronic cigarettes has increased tremendously, including among adolescents. While nicotine is the main addictive component of tobacco products and a primary concern in electronic cigarettes, this is not the only constituent of concern. There is a growing market of flavored products and a growing use of zero-nicotine e-liquids among electronic cigarette users. Accordingly, there are few studies that examine the impact of flavors on health and behavior. Menthol has been studied most extensively due to its lone exception in combustible cigarettes. Thus, there is a broad understanding of the neurobiological effects that menthol plus nicotine has on the brain including enhancing nicotine reward, altering nicotinic acetylcholine receptor number and function, and altering midbrain neuron excitability. Although flavors other than menthol were banned from combustible cigarettes, over 15,000 flavorants are available for use in electronic cigarettes. This review seeks to summarize the current knowledge on nicotine addiction and the various brain regions and nicotinic acetylcholine receptor subtypes involved, as well as describe the most recent findings regarding menthol and green apple flavorants, and their roles in nicotine addiction and vaping-related behaviors.

Secondhand Smoke Exposure and Depressive Symptoms in Children: A Longitudinal Study

INTRODUCTION

We investigated whether secondhand smoke (SHS) exposure is associated with depressive symptoms in a population-based sample of children.

METHODS

Never-smoking students from 29 French-language elementary schools in Greater Montréal, Canada, were followed from 5th to 11th grade (2005-2011) in five waves: 1 (5th grade), 2 (spring 6th grade), 3 (7th grade), 4 (9th grade), and 5 (11th grade). Associations between depressive symptoms and SHS exposure at home and in cars were examined in cross-sectional and longitudinal gamma generalized regression models adjusted for sex, maternal education, and neighborhood socioeconomic status.

RESULTS

The sample comprised 1553 baseline never-smokers (mean [SD] age = 10.7 [0.5] years; 44% male; 89% French-speaking). SHS exposure at home and in cars was associated with higher depressive symptom scores in cross-sectional analyses pooled across grades and adjusted for demographics (B [95% confidence interval (CI)] = 0.041 [0.017 to 0.068] for home exposure; 0.057 [0.030 to 0.084] for car exposure). In longitudinal analyses from fifth to sixth grade, B (95% CI), adjusted for demographics and baseline depressive symptoms, was 0.042 (0.003 to 0.080) for home exposure and 0.061 (0.019 to 0.103) for car exposure. From sixth to seventh grade, B (95% CI) was 0.057 (0.003 to 0.110) for home exposure and 0.074 (0.015 to 0.133) for car exposure. SHS exposure at any age did not predict depressive symptoms 2 years later.

CONCLUSIONS

SHS exposure is associated with depressive symptoms in young persons, both concurrently and 1 year later. This finding adds to the evidence base supporting that children should be protected from SHS exposure.

IMPLICATIONS

SHS exposure has deleterious effects on physical health and results of this study raise concerns that such exposure might also affect the mental health of young persons. Clearly, protecting children from SHS in all locations is a critical public health priority. Although research is needed to determine if the association between SHS exposure and depressive symptoms is causal, continued implementation of smoking bans and educational efforts to discourage smoking in vehicles when children are present are warranted.

Reasons for Transition From Electronic Cigarette Use to Cigarette Smoking Among Young Adult College Students

PURPOSE

Longitudinal studies indicate that e-cigarette use among youth and young adults is associated with cigarette smoking initiation. The purpose of this study was to identify reasons why nonsmoking young adults transition from e-cigarette use to cigarette smoking.

METHODS

The study used concept mapping (CM), a mixed-method participatory approach. Fifty-five college students who endorsed initiation of e-cigarettes before cigarettes (lifetime e-cigarette uses ≥ 100 and ≥ 100 cigarettes in lifetime) completed at least one part of the study. In an online program, participants brainstormed (n = 54) statements describing reasons for transition from e-cigarette use to cigarette smoking, sorted statements (n = 46) into conceptually similar categories, and rated (n = 47) how true each statement was for them.

RESULTS

Participants generated 60 unique statements, and multidimensional scaling analysis generated eight thematic clusters characterizing reasons for transition which included the following: "Sharing with Others," "Psychological Coping," "Cigarette Appeal," "Reinforcing Effects of Cigarettes," "Accessibility," "Social Influence," "Vaping Stigma," and "Vaping Deficiencies." Participants rated "Sharing with Others" and "Psychological Coping" highest (most true) and "Vaping Deficiencies" lowest (least true). For college students, the ability to share cigarettes with peers and access cigarettes from peers and smoking for stress/anxiety management were among the top reasons for transition.

CONCLUSIONS

Results suggest that tailored prevention efforts aimed at reducing cigarette smoking uptake among college students who use tobacco as a means for psychological coping or social facilitation may be warranted. Furthermore, regulatory decisions aimed at limiting cigarette appeal, reinforcing effects, and accessibility may be relevant to reducing transition.

Use of a physiologically-based pharmacokinetic model to explore the potential disparity in nicotine disposition between adult and adolescent nonhuman primates

The widespread use and high abuse liability of tobacco products has received considerable public health attention, in particular for youth, who are vulnerable to nicotine addiction. In this study, adult and adolescent squirrel monkeys were used to evaluate age-related metabolism and pharmacokinetics of nicotine after intravenous administration. A physiologically-based pharmacokinetic (PBPK) model was created to characterize the pharmacokinetic behaviors of nicotine and its metabolites, cotinine, trans-3'-hydroxycotinine (3'-OH cotinine), and trans-3'-hydroxycotinine glucuronide (3'-OH cotinine glucuronide) for both adult and adolescent squirrel monkeys. The PBPK nicotine model was first calibrated for adult squirrel monkeys utilizing in vitro nicotine metabolic data, plasma concentration-time profiles and cumulative urinary excretion data for nicotine and metabolites. Further model refinement was conducted when the calibrated adult model was scaled to the adolescents, because adolescents appeared to clear nicotine and cotinine more rapidly relative to adults. More specifically, the resultant model parameters representing systemic clearance of nicotine and cotinine for adolescent monkeys were approximately two- to three-fold of the adult values on a per body weight basis. The nonhuman primate PBPK model in general captured experimental observations that were used for both model calibration and evaluation, with acceptable performance metrics for precision and bias. The model also identified differences in nicotine pharmacokinetics between adolescent and adult nonhuman primates which might also be present in humans.

Association Between Electronic Cigarette Use and Marijuana Use Among Adolescents and Young Adults: A Systematic Review and Meta-analysis

IMPORTANCE

Use of electronic cigarettes (often called e-cigarettes) has increased considerably among young people in the past 5 years. Use of e-cigarettes has been associated with higher rates of marijuana use, which is associated with several adverse health outcomes in youth.

OBJECTIVE

To characterize and quantify the association between e-cigarette and marijuana use among youth using a meta-analysis.

DATA SOURCES

PubMed, Embase, and Web of Science & ProQuest Dissertations and Theses were searched from inception to October 2018. A gray-literature search was also conducted on conference abstracts, government reports, and other sources.

STUDY SELECTION

Included studies compared rates of marijuana use among youth aged 10 to 24 years who had used e-cigarettes vs those who had not used e-cigarettes. Two reviewers independently assessed studies for inclusion; disagreements were discussed with a third reviewer and resolved by consensus.

DATA EXTRACTION AND SYNTHESIS

Data were extracted by 2 independent reviewers following Meta-analyses of Observational Studies in Epidemiology (MOOSE) reporting guidelines and pooled using a random-effects analysis. The Newcastle-Ottawa Scale was used to assess data quality and validity of individual studies.

MAIN OUTCOMES AND MEASURES

Adjusted odds ratios (AORs) of self-reported past or current marijuana use by youth with vs without past or current e-cigarette use.

RESULTS

Twenty-one of 835 initially identified studies (2.5%) met selection criteria. The meta-analysis included 3 longitudinal and 18 cross-sectional studies that included 128 227 participants. Odds of marijuana use were higher in youth who had an e-cigarette use history vs those who did not (AOR, 3.47 [95% CI, 2.63-4.59]; I2, 94%). Odds of marijuana use were significantly increased in youth who used e-cigarettes in both longitudinal studies (3 studies; AOR, 2.43 [95% CI, 1.51-3.90]; I2, 74%) and cross-sectional studies (18 studies; AOR, 3.70 [95% CI, 2.76-4.96]; I2, 94%). Odds of using marijuana in youth with e-cigarette use were higher in adolescents aged 12 to 17 years (AOR, 4.29 [95% CI, 3.14-5.87]; I2, 94%) than young adults aged 18 to 24 years (AOR, 2.30 [95% CI, 1.40-3.79]; I2, 91%).

CONCLUSIONS AND RELEVANCE

This meta-analysis found a significant increase in the odds of past or current and subsequent marijuana use in adolescents and young adults who used e-cigarettes. These findings highlight the importance of addressing the rapid increases in e-cigarette use among youths as a means to help limit marijuana use in this population.

The relationship between nicotine and psychosis

Cigarette smoking is strongly associated with psychotic disorders such as schizophrenia. For several decades it was assumed that the relationship could be explained by reverse causation; that smoking was secondary to the illness itself, either through self-medication or a process of institutionalization, or was entirely explained by confounding by cannabis use or social factors. However, studies have exposed that such hypotheses cannot fully explain the association, and more recently a bidirectional relationship has been proposed wherein cigarette smoking may be causally related to risk of psychosis, possibly via a shared genetic liability to smoking and psychosis. We review the evidence for these candidate explanations, using findings from the latest epidemiological, neuroimaging, genetic and preclinical work.

Electronic Cigarettes and Youth in the United States: A Call to Action (at the Local, National and Global Levels)

E-cigarettes have emerged and soared in popularity in the past ten years, making them the most common tobacco product used among youth in the United States (US). In this review, we discuss what the Surgeon General has called a public health “epidemic”—the precipitous increase in youth use of e-cigarettes and the health consequences of this behavior. Further, we review tobacco control policy efforts (e.g., Tobacco 21, banning flavors, advertising restrictions, and clean indoor air laws)—efforts proven to be critical in reducing cigarette smoking and smoking-related disease and death among US children and adults—including their potential and challenges regarding managing and mitigating the emergence of e-cigarettes. Finally, we close with a discussion of the efforts of transnational tobacco companies to rebrand themselves using e-cigarettes and other new products.

Adolescent and adult nicotine exposure differentially impacts oral nicotine and oral saccharin self-administration in mice

Smokers that begin during adolescence are more likely to develop nicotine dependence than those who begin as adults. However, the factors that contribute to this remain largely unknown. Here we utilized a novel operant oral nicotine self-administration procedure in mice to assess the consequences of adolescent nicotine exposure on nicotine and saccharin (non-drug) reinforcement in adults. Animals were given non-contingent exposure to either saline or nicotine using the osmotic minipumps during both adolescence and adulthood for 2 weeks. Reinforcing efficacy for oral nicotine and saccharin was assessed using the progressive ratio schedule 2-weeks following the washout period in adults. Non-contingent nicotine exposure in adolescence drastically increased operant responding for oral nicotine but reduced responding for oral saccharin in the group re-exposed to nicotine in adulthood. Interestingly, adolescent nicotine-exposed mice that received saline exposure as adults exhibited higher preference for oral saccharin. However, breakpoints for oral nicotine in these mice remained comparable to control animals. Surprisingly, both adolescent and adult nicotine exposure increased inactive lever responding during self-administration presumably reflecting impulsive responding. Our data suggest that adolescent nicotine exposure produces an increase in reinforcement sensitivity in adulthood as reflected by increased saccharin self-administration but this sensitivity becomes biased towards nicotine self-administration when re-exposed to nicotine in adulthood. Moreover, nicotine/saccharin reinforcement could be impacted by changes in cognitive control, such as increased impulsivity. These distinct behavioral mechanisms may act in concert to facilitate maladaptive nicotine taking in smokers that initiate nicotine use during adolescence.

Chronic nicotine exposure in preadolescence enhances later spontaneous recovery of fear memory

Preadolescent mice have been shown to be differentially susceptible to the effects of both acute and chronic nicotine exposure on contextual fear learning relative to adults. For this study, we tested the effects of chronic nicotine exposure in preadolescence on adulthood extinction and spontaneous recovery of fear memory in a model in which contextual fear acquisition occurred prior to nicotine exposure. Preadolescent (postnatal day 23) and adult (postnatal day 53) male C57BL/6J mice underwent contextual fear conditioning and were then exposed to chronic nicotine at 12.6 mg/kg/day for 12 days via osmotic minipump. Eighteen days following the removal of nicotine, both groups of mice underwent fear extinction, followed by a spontaneous recovery session a week later. History of chronic nicotine did not affect later extinction of fear memory in adult-trained mice, whereas adolescent-trained mice exhibited a global impairment in retention of fear memory that precluded detection of effects of early nicotine on later fear extinction. However, it was found that adult spontaneous recovery of fear memory was impaired in mice exposed to nicotine as adults and enhanced in mice exposed to nicotine as preadolescents. These results may indicate greater vulnerability to recurrence of traumatic memory as well as compromised inhibitory control in young smokers. (PsycINFO Database Record

Prenatal nicotine exposure alters postsynaptic AMPA receptors and glutamate neurotransmission within the laterodorsal tegmentum (LDT) of juvenile mice

Despite dissemination of information regarding the harm on fetal development of smoking while pregnant, the number of pregnancies associated with nicotine exposure appears to have stagnated. Presence of nicotine during neural formulation is associated with a higher susceptibility of drug dependence, suggesting an altered development of neurons in circuits involved in saliency and motivation. The laterodorsal tegmental nucleus (LDT) plays a role in coding stimuli valence via afferents to mesolimbic nuclei. Accordingly, alterations in development of neural mechanisms in the LDT could be involved in vulnerability to drug dependency. Therefore, we examined the effect of prenatal nicotine exposure (PNE) on glutamatergic functioning of LDT neurons in mouse brain slices using whole-cell, patch clamp concurrent with fluorescence-based calcium imaging. PNE was associated with larger amplitudes of AMPA-induced currents, and greater AMPA-mediated rises in intracellular calcium. AMPA/NMDA ratios and the AMPA-current rectification index were lower and higher, respectively, consistent with changes in the functionality of AMPA receptors in the PNE, which was substantiated by a greater inhibition of evoked and spontaneous glutamatergic synaptic events by a selective inhibitor of GluA2-lacking AMPA receptors. Paired pulse ratios showed a decreased probability of glutamate release from presynaptic inputs, and fluorescent imaging indicated a decreased action potential-dependent calcium increase associated with PNE. When taken together, our data suggest that PNE alters LDT glutamatergic functioning, which could alter output to mesolimbic targets. Such an alteration could play a role in altered coding of relevancy of drug stimuli that could enhance risk for development of drug dependency.

Differential Effects of Nicotine Exposure on the Hippocampus Across Lifespan

BACKGROUND

Nicotine exposure affects the hippocampus through activation of hippocampal nicotinic acetylcholine receptors (nAChRs), which are present throughout excitatory and inhibitory hippocampal circuitry. The role of cholinergic functioning in the hippocampus varies across developmental stages so that nicotine exposure differentially affects this region depending upon timing of exposure, producing developmentally distinct changes in structure, function, and behavior.

METHODS

We synthesize findings across literature in this area to comprehensively review current understanding of the unique effects of nicotine exposure on the hippocampus throughout the lifespan with a focus on hippocampal morphology, cholinergic functioning, and hippocampusdependent learning and memory.

CONCLUSIONS

Chronic and acute nicotine exposure differentially affect hippocampus structure, functioning, and related learning and memory in the perinatal period, adolescence, and aging. Age-related differences in sensitivity to nicotine exposure should be considered in the research of nicotine addiction and the development of nicotine addiction treatments.

Smoking status and cognitive performance among vocational school students in Beijing, China

INTRODUCTION

In countries where smoking is associated with lower socioeconomic status, smokers tend to perform worse on cognitive tasks than non-smokers. China is now undergoing a similar process with a recent study showing that there is a reduced cognitive performance in middle aged but not in elderly smokers. We examined the links between smoking status and cognitive functioning among vocational school students in Beijing, China.

METHODS

A total of 213 students aged 16-20 (98 smokers and 115 non-smokers) were recruited from three vocational schools in Beijing. Participants completed three subtests of Wechsler Adult Intelligence Scale (WAIS) (information, arithmetic, digit span) and Dysexecutive Questionnaire (DEX). Smokers also completed a cigarette smoking questionnaire and Fagerstrom Test of Nicotine Dependence (FTND).

RESULTS

Smokers performed worse than non-smokers in tests of arithmetic and digit span forward (t = 4.25, 2.05, both P < .05). Scores on digit span backward did not differentiate smokers and non-smokers, but among smokers, the performance on this subtest was related to the age of starting smoking (r = 0.26, p < .001). Cognitive performance in smokers was not related to tobacco dependence or intensity of smoking. Compared to non-smokers, smokers had a higher total DEX score and higher scores on three of its five subscales (Inhibition, Knowing-doing dissociation and Social regulation, all p < .05). Another subscale, In-resistance, did not differentiate smokers and non-smokers, but differentiated smokers with lower and higher levels of nicotine dependence (t = -2.12, p < .05).

CONCLUSION

Smokers performed worse on some cognitive tasks than non-smokers and scored higher on a questionnaire assessing executive dysfunction.

ELSA 2016 Cohort: Alcohol, Tobacco, and Marijuana Use and Their Association with Age of Drug Use Onset, Risk Perception, and Social Norms in Argentinean College Freshmen

The transition from high school to college is a high-risk stage for the initiation and escalation of substance use. Substance use and its associated risk factors have been thoroughly described in developed countries, such as the United States, but largely neglected in Argentina, a South American country with patterns of a collectivist culture. The present cross-sectional study describes the occurrence of alcohol, tobacco, and marijuana use and the association between these behaviors and the age of onset of substance use and cognitive (i.e., risk perception) and social (i.e., prescriptive) variables in a large sample of Argentinean college freshmen (n = 4083, 40.1% men; mean age = 19.39 ± 2.18 years). The response rate across courses was ≥90% and was similarly distributed across sex. Participants completed a survey that measured substance use (alcohol [with a focus on heavy drinking and binge drinking behaviors], tobacco, and marijuana), age of onset of the use of each substance, perceived risk associated with various substance use behaviors, prescriptive norms associated with substance use, and descriptive norms for alcohol use (AU). The results indicated that AU is nearly normative (90.4 and 80.3% with last year and last month use, respectively) in this population, and heavy drinking is highly prevalent (68.6 and 54.9% with heavy episodic and binge drinking, respectively), especially among those with an early drinking onset (97.8 and 93.6% with last year and last month use and 87.8 and 76.3% with heavy episodic and binge drinking, respectively). The last-year occurrence of tobacco and marijuana use was 36 and 28%, respectively. Early substance use was associated with the greater use of that specific substance. The students overestimated their same-sex friend's AU, and women overestimated the level of AU of their best male friend. At the multivariate level, all of the predictors, with the exception of the parents' prescriptive norms, significantly explained the frequency of marijuana and tobacco use and frequency of hazardous drinking. Overall, despite important cultural and contextual differences between Argentina and the United States, our findings suggest that certain vulnerability factors have a similar influence across these cultural contexts.

Pre-adolescent and adolescent mice are less sensitive to the effects of acute nicotine on extinction and spontaneous recovery

Adolescence is a period of high risk for the initiation of nicotine product usage and exposure to traumatic events. In parallel, nicotine exposure has been found to age-dependently modulate acquisition of contextual fear memories; however, it is unknown if adolescent nicotine exposure alters extinction of fear related memories. Age-related differences in sensitivity to the effects of nicotine on fear extinction could increase or decrease susceptibility to anxiety disorders. In this study, we examined the effects of acute nicotine administration on extinction and spontaneous recovery of contextual fear memories in pre-adolescent (PND 23), late adolescent (PND 38), and adult (PND 53) C57B6/J mice. Mice were first trained in a background contextual fear conditioning paradigm and given an intraperitoneal injection of one of four doses of nicotine (0.045, 0.09, 0.18, or 0.36mg/kg, freebase) prior to subsequent extinction or spontaneous recovery sessions. Results indicated that all acute nicotine doses impaired extinction of contextual fear in adult mice. Late adolescent mice exhibited impaired extinction of contextual fear only following higher doses of acute nicotine, and extinction of contextual fear was unaffected by acute nicotine exposure in pre-adolescent mice. Finally, acute nicotine exposure enhanced spontaneous recovery of fear memory, but only in adult mice. Overall, our results suggest that younger mice were less sensitive to nicotine's impairing effects on extinction of contextual fear and to nicotine's enhancing effects on spontaneous recovery of contextual fear memory.

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.

Adolescent Awareness and Use of Electronic Cigarettes: A Review of Emerging Trends and Findings

Adult electronic cigarette (e-cigarette) use is increasing globally, and early studies have suggested that similar trends may be observed among the adolescent population, albeit at lower levels. The current literature review presents data collected since 2014 from 21 cross-sectional studies and one cohort study that were all published in English. In particular, it focuses on awareness, ever use, past 30-day use, and regular use of e-cigarettes. The article suggests that adolescents are nearing complete awareness of e-cigarettes. Furthermore, in relation to ever use and past 30-day use, higher prevalence rates continue to be reported across time, especially in the United States. Nonetheless, reported regular use of e-cigarettes remains much lower than past 30-day use, although conclusions are limited due to inconsistencies with measurement and consequent lack of cross-cultural applicability. The majority of studies do not report whether adolescents use non-nicotine e-cigarettes. There is a current absence of longitudinal studies that explore any association between e-cigarettes and tobacco use and little qualitative data that may illuminate how and why adolescents use e-cigarettes. Through addressing these methodological limitations, future research will be able to inform health care and policy more effectively.

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.

White matter development and tobacco smoking in young adults: A systematic review with recommendations for future research

BACKGROUND

Adolescence and young adulthood are critical vulnerability periods for initiation of tobacco smoking. White matter development is ongoing during this time and may be influenced by exposure to nicotine. Synthesis of findings from diffusion tensor imaging (DTI) studies of adolescent and young adult smokers may be helpful in understanding the relationship between neurodevelopment and initiation and progression of tobacco-use behaviors and in guiding further research.

METHODS

A systematic literature review was conducted to identify DTI studies comparing adolescent and young adult (mean age <30 years) smokers versus nonsmokers. A total of 5 studies meeting inclusion criteria were identified. Primary study findings are reviewed and discussed within the context of neurodevelopment and in relation to findings from adult studies. Directions for further research are also discussed.

RESULTS

All identified studies reported increases in fractional anisotropy (FA) among adolescent/young adult smokers in comparison to non-smokers. Increased FA was most frequently reported in regions of the corpus callosum (genu, body and spenium), internal capsule and superior longitudinal fasciculus.

CONCLUSIONS

Findings of increased FA among adolescent/young adult smokers are contrary to those from most adult studies and thus raise the possibility of differential effects of nicotine on white matter across the lifespan. Further research including multiple time points is needed to test this hypothesis. Other areas warranting further research include DTI studies of e-cigarette use and studies incorporating measures of pubertal stage.

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.

Targeting glutamate homeostasis for potential treatment of nicotine dependence

Several studies demonstrated that impairment in glutamatergic neurotransmission is linked to drug dependence and drug-seeking behavior. Increased extracellular glutamate concentration in mesocorticolimbic regions has been observed in animals developing nicotine dependence. Changes in glutamate release might be associated with stimulatory effect of nicotinic acetylcholine receptors (nAChRs) via nicotine exposure. We and others have shown increased extracellular glutamate concentration, which was associated with down regulation of the major glutamate transporter, glutamate transporter 1 (GLT-1), in brain reward regions of animals exposed to drug abuse, including nicotine and ethanol. Importantly, studies from our laboratory and others showed that upregulation of GLT-1 expression in the mesocorticolimbic brain regions may have potential therapeutic effects in drug dependence. In this review article, we discussed the effect of antagonizing presynaptic nAChRs in glutamate release, the upregulatory effect in GLT-1 expression and the role of glutamate receptors antagonists in the treatment of nicotine dependence.

Regulation of α4β2α5 nicotinic acetylcholinergic receptors in rat cerebral cortex in early and late adolescence: Sex differences in response to chronic nicotine

Chronic nicotine administration in animals, and smoking in humans, causes up-regulation of α4β2* neuronal nicotinic receptors (nAChRs), which has been hypothesized to contribute to the addictive actions of nicotine. We used a rat model to test whether such up-regulatory effects differ in adolescents versus adults, and in males versus females. Following chronic treatment with nicotine or saline via subcutaneous osmotic minipumps, we measured α4β2 and α4β2α5 nAChRs in cerebral cortex using [3H]epibatidine to label assembled nAChRs, and selective antibodies to measure the individual subunits via immunoprecipitation. For the first time, we provide a detailed characterization of the response of both α4β2 and α4β2α5 nAChRs in female adolescent rat cerebral cortex. We found differences in nicotine-induced up-regulation between males and females in early adolescence that are absent in both late adolescence and adulthood. Males showed significant up-regulation at PN28 which was absent in age-matched females. These results demonstrate sex differences in the susceptibility of α4β2* nAChRs to the effects of chronic nicotine exposure in the cerebral cortex based on age.

Adolescent nicotine induces persisting changes in development of neural connectivity

Adolescent nicotine induces persisting changes in development of neural connectivity. A large number of brain changes occur during adolescence as the CNS matures. These changes suggest that the adolescent brain may still be susceptible to developmental alterations by substances which impact its growth. Here we review recent studies on adolescent nicotine which show that the adolescent brain is differentially sensitive to nicotine-induced alterations in dendritic elaboration, in several brain areas associated with processing reinforcement and emotion, specifically including nucleus accumbens, medial prefrontal cortex, basolateral amygdala, bed nucleus of the stria terminalis, and dentate gyrus. Both sensitivity to nicotine, and specific areas responding to nicotine, differ between adolescent and adult rats, and dendritic changes in response to adolescent nicotine persist into adulthood. Areas sensitive to, and not sensitive to, structural remodeling induced by adolescent nicotine suggest that the remodeling generally corresponds to the extended amygdala. Evidence suggests that dendritic remodeling is accompanied by persisting changes in synaptic connectivity. Modeling, electrophysiological, neurochemical, and behavioral data are consistent with the implication of our anatomical studies showing that adolescent nicotine induces persisting changes in neural connectivity. Emerging data thus suggest that early adolescence is a period when nicotine consumption, presumably mediated by nicotine-elicited changes in patterns of synaptic activity, can sculpt late brain development, with consequent effects on synaptic interconnection patterns and behavior regulation. Adolescent nicotine may induce a more addiction-prone phenotype, and the structures altered by nicotine also subserve some emotional and cognitive functions, which may also be altered. We suggest that dendritic elaboration and associated changes are mediated by activity-dependent synaptogenesis, acting in part through D1DR receptors, in a network activated by nicotine. The adolescent nicotine effects reviewed here suggest that modification of late CNS development constitutes a hazard of adolescent nicotine use.

Cholinergic systems are essential for late-stage maturation and refinement of motor cortical circuits

Previous studies reported that early postnatal cholinergic lesions severely perturb early cortical development, impairing neuronal cortical migration and the formation of cortical dendrites and synapses. These severe effects of early postnatal cholinergic lesions preclude our ability to understand the contribution of cholinergic systems to the later-stage maturation of topographic cortical representations. To study cholinergic mechanisms contributing to the later maturation of motor cortical circuits, we first characterized the temporal course of cortical motor map development and maturation in rats. In this study, we focused our attention on the maturation of cortical motor representations after postnatal day 25 (PND 25), a time after neuronal migration has been accomplished and cortical volume has reached adult size. We found significant maturation of cortical motor representations after this time, including both an expansion of forelimb representations in motor cortex and a shift from proximal to distal forelimb representations to an extent unexplainable by simple volume enlargement of the neocortex. Specific cholinergic lesions placed at PND 24 impaired enlargement of distal forelimb representations in particular and markedly reduced the ability to learn skilled motor tasks as adults. These results identify a novel and essential role for cholinergic systems in the late refinement and maturation of cortical circuits. Dysfunctions in this system may constitute a mechanism of late-onset neurodevelopmental disorders such as Rett syndrome and schizophrenia.

Adolescent brain maturation and smoking: what we know and where we're headed

Smoking is a leading cause of mortality and morbidity worldwide. Smoking initiation often occurs during adolescence. This paper reviews and synthesizes adolescent development and nicotine dependence literatures to provide an account of adolescent smoking from onset to compulsive use. We extend neurobiological models of adolescent risk-taking, that focus on the interplay between incentive processing and cognitive control brain systems, through incorporating psychosocial and contextual factors specific to smoking, to suggest that adolescents are more vulnerable than adults to cigarette use generally, but that individual differences exist placing some adolescents at increased risk for smoking. Upon smoking, adolescents are more likely to continue smoking due to the increased positive effects induced by nicotine during this period. Continued use during adolescence, may be best understood as reflecting drug-related changes to neural systems underlying incentive processing and cognitive control, resulting in decision-making that is biased towards continued smoking. Persistent changes following nicotine exposure that may underlie continued dependence are described. We highlight ways that interventions may benefit from a consideration of cognitive-neuroscience findings.

Nicotinic acetylcholine receptors controlling attention: behavior, circuits and sensitivity to disruption by nicotine

Attention is a central cognitive function that enables long-term engagement in a task and suppression of irrelevant information to obtain future goals. The prefrontal cortex (PFC) is the main link in integrating emotional and motivational state of an animal to regulate top-down attentional processes. Acetylcholine modulates PFC neuronal networks by activating nicotinic acetylcholine receptors (nAChRs) to support attention. However, how neuronal activity changes in the PFC during attention and which nAChR subtypes mediate this is only rudimentarily understood, but progress is being made. Recently, exciting new insights were obtained in the dynamics of cholinergic signaling in the PFC and modes of acetylcholine transmission via nAChRs in the cortex. In addition, mechanisms are uncovered on how the PFC circuitry is regulated by nAChRs. Novel studies show that endogenous activation of nAChRs in the PFC plays a central role in controlling attention. Here, we review current insights into how different subtypes of nAChRs expressed by distinct types of neurons in the PFC circuitry shape attention. In addition we discuss the impact of nicotine on the cholinergic system and prefrontal cortical circuits. Low concentrations of nicotine, as experienced by smokers, interfere with cholinergic signaling. In the long-term exposure to nicotine during adolescence leads to maladaptive adaptations of the PFC circuitry, which ultimately leads to a decrement in attention performance, again emphasizing the importance of nAChRs in attention.

Layer-specific interference with cholinergic signaling in the prefrontal cortex by smoking concentrations of nicotine

Adolescence is a period in which the developing prefrontal cortex (PFC) is sensitive to maladaptive changes when exposed to nicotine. Nicotine affects PFC function and repeated exposure to nicotine during adolescence impairs attention performance and impulse control during adulthood. Nicotine concentrations experienced by smokers are known to desensitize nicotinic acetylcholine receptors (nAChRs), but the impact thereof on PFC circuits is poorly understood. Here, we investigated how smoking concentrations of nicotine (100-300 nm) interfere with cholinergic signaling in the mouse PFC. nAChR desensitization depends on subunit composition. Since nAChR subunits are differentially expressed across layers of the PFC neuronal network, we hypothesized that cholinergic signaling through nAChRs across layers would suffer differentially from exposure to nicotine. Throughout the PFC, nicotine strongly desensitized responses to ACh in neurons expressing β2* nAChRs, whereas ACh responses mediated by α7 nAChRs were not hampered. The amount of desensitization of β2* nAChR currents depended on neuron type and cortical layer. β2*-mediated responses of interneurons in LII-III and LVI completely desensitized, while cholinergic responses in LV interneurons and LVI pyramidal cells showed less desensitization. This discrepancy depended on α5 subunit expression. Two-photon imaging of neuronal population activity showed that prolonged exposure to nicotine limited cholinergic signaling through β2* nAChRs to deep PFC layers where α5 subunits were expressed. Together, our results demonstrate a layer-dependent decrease in cholinergic activation of the PFC through nAChRs by nicotine. These mechanisms may be one of the first steps leading up to the pathophysiological changes associated with nicotine exposure during adolescence.

Effects of Neonatal C-Fiber Depletion on Interaction between Neocortical Short-Term and Long-Term Plasticity

INTRODUCTION

The primary somatosensory cortex has an important role in nociceptive sensory-discriminative processing. Altered peripheral inputs produced by deafferentation or by long-term changes in levels of afferent stimulation can result in plasticity of cortex. Capsaicin-induced depletion of C-fiber afferents results in plasticity of the somatosensory system. Plasticity includes short-term and long-term changes in synaptic strength. We studied the interaction between paired-pulse facilitation, as one form of short-term plasticity, with long-term potentiation (LTP) in the neocortex of normal and C-fiber depleted freely moving rat.

METHODS

Neonatally capsaicin-treated rats and their controls were allowed to mature until they reached a weight between 250 and 300g. Then animals were anesthetized with ketamine and xylazine. For recording and stimulation, twisted teflon-coated stainless steel wires were implanted into somatosensory cortex or corpus callusom. In experiments for LTP induction, after two weeks of recovery period, 30 high frequency pulse trains were delivered once per day for 12 days. Paired-pulse ratio (PPR) was monitored before and after the induction of LTP in capsaicin-treated and control rats.

RESULTS

Paired-pulse stimulation affected all field potential components at intervals < 200 ms. The largest changes occurred at intervals between 20-30 ms. C-fiber depletion postponed the development of LTP, whereas it had no effect on PPR.

DISCUSSION

This finding provides further evidence that the expression of this form of LTP is postsynaptic. Furthermore, these results suggest that the effect of C-fiber depletion on cortical LTP is also postsynaptic and, therefore, is not caused by a decrease in neurotransmitter release.