Prenatal exposure of rats to nicotine causes persistent alterations of nicotinic cholinergic receptors

Combined and sequential exposure to prenatal second hand smoke and postnatal maternal distress is associated with cingulo-opercular global efficiency and attention problems in school-age children

BACKGROUND

Prenatal exposure to secondhand (environmental) tobacco smoke (SHS) is associated with adverse neurodevelopmental outcomes, including altered functional activation of cognitive control brain circuitry and increased attention problems in children. Exposure to SHS is more common among Black youth who are also disproportionately exposed to socioeconomic disadvantage and concomitant maternal distress. We examine the combined effects of exposure to prenatal SHS and postnatal maternal distress on the global efficiency (GE) of the brain's cingulo-opercular (CO) and fronto-parietal control (FP) networks in childhood, as well as associated attention problems.

METHODS

Thirty-two children of non-smoking mothers followed in a prospective longitudinal birth cohort at the Columbia Center for Children's Environmental Health (CCCEH) completed magnetic resonance imaging (MRI) at ages 7-9 years old. GE scores were extracted from general connectivity data collected while children completed the Simon Spatial Incompatibility functional magnetic resonance imaging (fMRI) task. Prenatal SHS was measured using maternal urinary cotinine from the third trimester; postnatal maternal distress was assessed at child age 5 using the Psychiatric Epidemiology Research Interview (PERI-D). The Child Behavior Checklist (CBCL) measured Attention and Attention Deficit Hyperactivity Disorder (ADHD) problems at ages 7-9. Linear regressions examined the interaction between prenatal SHS and postnatal maternal distress on the GE of the CO or FP networks, as well as associations between exposure-related network alterations and attention problems. All models controlled for age, sex, maternal education at prenatal visit, race/ethnicity, global brain correlation, and mean head motion.

RESULTS

The prenatal SHS by postnatal maternal distress interaction term associated with the GE of the CO network (β = 0.673, Bu = 0.042, t(22) = 2.427, p = .024, D = 1.42, 95% CI [0.006, 0.079], but not the FP network (β = 0.138, Bu = 0.006, t(22) = 0.434, p = .668, 95% CI [-0.022, 0.033]). Higher GE of the CO network was associated with more attention problems (β = 0.472, Bu = 43.076, t(23) = 2.780, p = .011, D = 1.74, n = 31, 95% CI [11.024, 75.128], n = 31) and ADHD risk (β = 0.436, Bu = 21.961, t(29) = 2.567, p = .018, D = 1.81, 95% CI [4.219, 39.703], n = 30).

CONCLUSIONS

These preliminary findings suggest that sequential prenatal SHS exposure and postnatal maternal distress could alter the efficiency of the CO network and increase risk for downstream attention problems and ADHD. These findings are consistent with prior studies showing that prenatal SHS exposure is associated with altered function of brain regions that support cognitive control and with ADHD problems. Our model also identifies postnatal maternal distress as a significant moderator of this association. These data highlight the combined neurotoxic effects of exposure to prenatal SHS and postnatal maternal distress. Critically, such exposures are disproportionately distributed among youth from minoritized groups, pointing to potential pathways to known mental health disparities.

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.

Prenatal tobacco smoke exposure and risk of brain abnormalities on magnetic resonance imaging at term in infants born very preterm

BACKGROUND

Prenatal tobacco smoke exposure and preterm birth are associated with abnormal brain and neurodevelopmental outcomes in infants. Studies that can disentangle indirect mediating effects from direct effects of prenatal tobacco smoke exposure on sensitive early brain magnetic resonance imaging biomarkers in very preterm infants are needed.

OBJECTIVE

This study aimed to determine whether prenatal tobacco smoke exposure in preterm infants posed any direct effects on magnetic resonance imaging-determined global brain abnormality score and secondary measures of brain abnormalities after removing any indirect mediating effects of preterm birth on neurostructural outcomes.

STUDY DESIGN

We examined brain magnetic resonance imaging findings collected at 39 to 44 weeks postmenstrual age from a prospective cohort of 395 infants born very preterm (gestational age of ≤32 weeks). The primary outcome was global brain abnormality score, and the secondary outcomes were global efficiency of structural connectome, diffuse white matter abnormality volume, total brain tissue volume, total gray and white matter volumes, and cerebellar volume. Maternal reports of smoking during pregnancy were obtained. We performed multivariable linear regression analyses to examine the association between prenatal tobacco smoke exposure and our magnetic resonance imaging outcomes, controlling for prospectively collected confounders. Moreover, we performed a mediation analysis to estimate the direct effects of prenatal tobacco smoke exposure on brain abnormalities and any indirect effects through preterm birth.

RESULTS

Overall, 12.6% of infants had prenatal tobacco smoke exposure. Infants with prenatal tobacco smoke exposure had a higher median global brain abnormality score than nonexposed infants (7 [interquartile range, 0-41] vs 5 [interquartile range, 0-34]; P≤.001); the findings remained significant (P<.001) after controlling for antenatal confounders. Global efficiency (P<.001), diffuse white matter volume (P=.037), and total brain tissue volume (P=.047) were significantly different between TSE groups in multivariable analyses. On mediation analysis, preterm birth mediated between 0% and 29% of the indirect effect of prenatal tobacco smoke exposure on several measures of brain abnormality outcomes. Thus, prenatal tobacco smoke exposure had a direct adverse effect between 71% and 100% on brain injury or abnormal development.

CONCLUSION

Our study has identified multiple adverse effects of prenatal tobacco smoke exposure on sensitive and objective measures of neonatal brain injury and abnormal development; most cases seemed to be a direct effect of prenatal tobacco smoke exposure on fetal brain development. The results underscored the significant adverse neurostructural effects of prenatal tobacco smoke exposure to tobacco smoke pollutants.

Investigating the Modulation of the VTA Neurons in Nicotine-Exposed Pups during Early Maturation Using Optogenetics

Advancing the understanding of the relationship between perinatal nicotine addiction and the reward mechanism of the brain is crucial for uncovering and implementing new treatments for addiction control and prevention. The mesolimbic pathway of the brain, also known as the reward pathway, consists of two main areas that regulate dopamine (DA) and addiction-related behaviors. The ventral tegmental area (VTA) releases DA when stimulated, causing the propagation of neuronal firing along the pathway. This ends in the release of DA into the extracellular space of the nucleus accumbens (NAc), which is directly modulated by the uptake of DA. Much research has been conducted on the effects of nicotine addiction, but little research has been conducted concerning nicotine addiction and the mesolimbic pathway regarding maturation due to the small brain size. In this study, we apply our novel microstimulation experimental system to rat pups that have been perinatally exposed to nicotine. By using our self-fabricated photo-stimulation (PS) device, we can stimulate the VTA and collect dialysate, which is then used to estimate DA released into the NAc. The proposed platform has demonstrated the potential to monitor neural pathways as the pups mature.

Investigating the Influence of GABA Neurons on Dopamine Neurons in the Ventral Tegmental Area Using Optogenetic Techniques

Dopamine (DA) is the key regulator of reward behavior. The DA neurons in the ventral tegmental area (VTA) and their projection areas, which include the prefrontal cortex (PFC), nucleus accumbens (NAc), and amygdala, play a primary role in the process of reward-driven behavior induced by the drugs of addiction, including nicotine and alcohol. In our previous study, we developed a novel platform consisting of micro-LED array devices to stimulate a large area of the brain of rats and monkeys with photo-stimulation and a microdialysis probe to estimate the DA release in the PFC. Our results suggested that the platform was able to detect the increased level of dopamine in the PFC in response to the photo-stimulation of both the PFC and VTA. In this study, we used this platform to photo-stimulate the VTA neurons in both ChrimsonR-expressing (non-specific) wild and dopamine transporter (DAT)-Cre (dopamine specific) mice, and measured the dopamine release in the nucleus accumbens shell (NAcShell). We measured the DA release in the NAcShell in response to optogenetic stimulation of the VTA neurons and investigated the effect of GABAergic neurons on dopaminergic neurons by histochemical studies. Comparing the photo-stimulation frequency of 2 Hz with that of 20 Hz, the change in DA concentration at the NAcShell was greater at 20 Hz in both cases. When ChrimsonR was expressed specifically for DA, the release of DA at the NAcShell increased in response to photo-stimulation of the VTA. In contrast, when ChrimsonR was expressed non-specifically, the amount of DA released was almost unchanged upon photo-stimulation. However, for nonspecifically expressed ChrimsonR, intraperitoneal injection of bicuculline, a competitive antagonist at the GABA-binding site of the GABA_A receptor, also significantly increased the release of DA at the NAcShell in response to photo-stimulation of the VTA. The results of immunochemical staining confirm that GABAergic neurons in the VTA suppress DA activation, and also indicate that alterations in GABAergic neurons may have serious downstream effects on DA activity, NAcShell release, and neural adaptation of the VTA. This study also confirms that optogenetics technology is crucial to study the relationship between the mesolimbic dopaminergic and GABAergic neurons in a neural-specific manner.

DNA methylome perturbations: an epigenetic basis for the emergingly heritable neurodevelopmental abnormalities associated with maternal smoking and maternal nicotine exposure†

Maternal smoking during pregnancy is associated with an ensemble of neurodevelopmental consequences in children and therefore constitutes a pressing public health concern. Adding to this burden, contemporary epidemiological and especially animal model research suggests that grandmaternal smoking is similarly associated with neurodevelopmental abnormalities in grandchildren, indicative of intergenerational transmission of the neurodevelopmental impacts of maternal smoking. Probing the mechanistic bases of neurodevelopmental anomalies in the children of maternal smokers and the intergenerational transmission thereof, emerging research intimates that epigenetic changes, namely DNA methylome perturbations, are key factors. Altogether, these findings warrant future research to fully elucidate the etiology of neurodevelopmental impairments in the children and grandchildren of maternal smokers and underscore the clear potential thereof to benefit public health by informing the development and implementation of preventative measures, prophylactics, and treatments. To this end, the present review aims to encapsulate the burgeoning evidence linking maternal smoking to intergenerational epigenetic inheritance of neurodevelopmental abnormalities, to identify the strengths and weaknesses thereof, and to highlight areas of emphasis for future human and animal model research therein.

Assessment of the Relationship Between Smoking and Depression in Pregnant Women

Smoking during pregnancy has negative effects on both maternal and fetal health. One of these negative maternal effects is the potential for depression. A high rate of cigarette smoking in pregnancy is an important public health issue since it affects not only the pregnant woman but also the newborn and its healthy development. The aim of this study is to investigate the relationship between smoking, influencing factors, and depression prevalence in pregnant Syrian refugees and pregnant citizens of the Republic of Turkey (TR). Pregnant citizens in the TR and pregnant Syrian refugees who were registered at health centers between 15.04.2017 and 15.10.2017 in the border city of Ceylanpınar in the Province of Şanlıurfa in Syria were visited in their living areas in the district center and at a tent village, respectively. A total of 414 pregnant women agreed to participate in the study and were included in the survey. To collect data for the cross-sectional study, a sociodemographic and pregnancy characteristics questionnaire was used, in addition to the Fageström Test for Nicotine Dependence (FTND) and the Beck Depression Inventory (BDI). The rate of smoking in all pregnant women was determined to be 49.3% (n = 204) before pregnancy and 37.9% (n = 157) during pregnancy. A statistically significant difference was found between age groups and educational status in relation to smoking status (p = 0.005, p = 0.001). There was also a statistically significant difference between the smoking status of pregnant women and that of their partners and family members (p = 0.001, p = 0.002). The percentage of pregnant women who were passive smokers was 80.2% (n = 332), and a statistically significant difference was found between passive smoking and smoking status (Fisher; 0.000). The presence of risk for depression was detected in 49.8% (n = 206) of all pregnant women surveyed; the rate of depression risk was 50.5% (n = 104) in pregnant TR citizens and 49.5% (n = 102) in pregnant refugees, with no significant difference between the two groups. There was a statistically significant difference between smoking status in pregnancy and the presence of depression risk (p = 0.001). 32.5% of pregnant women were highly nicotine dependent. A moderate positive correlation was determined between the FTND and BDI scores of pregnant women (r = 0.346; p = 0.001). It was found that one-third of all pregnant women smoked and that one of every two showed a risk for depression. A statistically significant correlation was found between smoking status and risk for depression. No statistically significant difference was determined between the two groups, despite high levels of smoking, nicotine dependence, and depression in both. These data suggest the need to develop new preventive strategies in regard to smoking among pregnant women.

Maternal Nicotine Exposure Alters Hippocampal Microglia Polarization and Promotes Anti-inflammatory Signaling in Juvenile Offspring in Mice

Accumulating evidence reveal that maternal smoking or perinatal nicotine replacement therapy impairs hippocampal neurogenesis, neural development, and cognitive behaviors in the offspring. Microglia is a source of non-neural regulation of neuronal development and postnatal neurogenesis. In this study, we explored the impact of nicotine on the microglia during the development of hippocampus. Developmental nicotine exposure in a mouse model was conducted by supplementing nicotine in the drinking water to mother mice during gestation and lactation period. We found that juvenile offspring with maternal nicotine exposure presented physical and neurobehavioral development delay and an increase in anxiety-like behavior in the open field test on postnatal day (PND) 20. To further detect possible developmental neurotoxic effects of nicotine in offspring and underlying mechanism, whole genome microarray analysis of the expression profile of the hippocampus was performed on postnatal day 20. Significant alterations in the expression of genes related to inflammatory, neurotransmitter, and synapsis were observed in the hippocampus after maternal nicotine exposure, as compared to the vehicle control. Concurrently, an increase in microglial markers and the presence of M2 polarity state in the hippocampus of the nicotine offspring were observed by histological analysis and confocal z-stacking scanning. The M2 microglial polarization state was further confirmed with in vitro primary microglia culture by cytokine array, and double-positive expression of BDNF/Iba1 in microglia by immunohistochemical staining in the juvenile offspring hippocampus was visualized. We also found that nicotine offspring showed an increase of neurite length in the molecular layer and CA1 by Tuj1 staining, as well as an increase in the expression of synapse associated protein, PSD95, but the expression of NeuroD1 in CA1 and CA3 reduced. In summary, maternal nicotine exposure dysregulates immune-related genes expression by skewing the polarity of M2 microglia in the hippocampus, which may cause abnormal cognitive and behavioral performance in the offspring.

Investigating the effects of chronic perinatal alcohol and combined nicotine and alcohol exposure on dopaminergic and non-dopaminergic neurons in the VTA

The ventral tegmental area (VTA) is the origin of dopaminergic neurons and the dopamine (DA) reward pathway. This pathway has been widely studied in addiction and drug reinforcement studies and is believed to be the central processing component of the reward circuit. In this study, we used a well-established rat model to expose mother dams to alcohol, nicotine-alcohol, and saline perinatally. DA and non-DA neurons collected from the VTA of the rat pups were used to study expression profiles of miRNAs and mRNAs. miRNA pathway interactions, putative miRNA-mRNA target pairs, and downstream modulated biological pathways were analyzed. In the DA neurons, 4607 genes were differentially upregulated and 4682 were differentially downregulated following nicotine-alcohol exposure. However, in the non-DA neurons, only 543 genes were differentially upregulated and 506 were differentially downregulated. Cell proliferation, differentiation, and survival pathways were enriched after the treatments. Specifically, in the PI3K/AKT signaling pathway, there were 41 miRNAs and 136 mRNAs differentially expressed in the DA neurons while only 16 miRNAs and 20 mRNAs were differentially expressed in the non-DA neurons after the nicotine-alcohol exposure. These results depicted that chronic nicotine and alcohol exposures during pregnancy differentially affect both miRNA and gene expression profiles more in DA than the non-DA neurons in the VTA. Understanding how the expression signatures representing specific neuronal subpopulations become enriched in the VTA after addictive substance administration helps us to identify how neuronal functions may be altered in the brain.

Investigating the influence of perinatal nicotine and alcohol exposure on the genetic profiles of dopaminergic neurons in the VTA using miRNA-mRNA analysis

Nicotine and alcohol are two of the most commonly used and abused recreational drugs, are often used simultaneously, and have been linked to significant health hazards. Furthermore, patients diagnosed with dependence on one drug are highly likely to be dependent on the other. Several studies have shown the effects of each drug independently on gene expression within many brain regions, including the ventral tegmental area (VTA). Dopaminergic (DA) neurons of the dopamine reward pathway originate from the VTA, which is believed to be central to the mechanism of addiction and drug reinforcement. Using a well-established rat model for both nicotine and alcohol perinatal exposure, we investigated miRNA and mRNA expression of dopaminergic (DA) neurons of the VTA in rat pups following perinatal alcohol and joint nicotine-alcohol exposure. Microarray analysis was then used to profile the differential expression of both miRNAs and mRNAs from DA neurons of each treatment group to further explore the altered genes and related biological pathways modulated. Predicted and validated miRNA-gene target pairs were analyzed to further understand the roles of miRNAs within these networks following each treatment, along with their post transcription regulation points affecting gene expression throughout development. This study suggested that glutamatergic synapse and axon guidance pathways were specifically enriched and many miRNAs and genes were significantly altered following alcohol or nicotine-alcohol perinatal exposure when compared to saline control. These results provide more detailed insight into the cell proliferation, neuronal migration, neuronal axon guidance during the infancy in rats in response to perinatal alcohol/ or nicotine-alcohol exposure.

Investigating the influence of perinatal nicotine exposure on genetic profiles of neurons in the sub-regions of the VTA

Chronic nicotine exposure during pregnancy has been shown to induce physiological and anatomical alterations in offspring. Previously, we investigated the complexity of dopamine (DA) neuron firing in the sub-regions of the ventral tegmental area (VTA) following perinatal nicotine exposure. Using approximate entropy, we found that within the middle sub-region, the parainterfascicular nucleus (PIF), there was higher complexity indicating more random neural firing and a less homogeneous neuron population. Therefore, we sought to investigate the neuron populations within the sub-regions of the VTA following perinatal nicotine exposure. We used real time PCR in order to find the relative quantity of glutamate to γ-aminobutyric acid (GABA), DA, and glutamate neurons within three sub-regions: the parabrachial pigmented nucleus (PBP), parainterfascicular nucleus (PIF), and paranigral nucleus (PN). Our results showed that the PIF region of the VTA contained a more diverse population of neurons resulting in a more complex system. In addition, we found that DA neurons are more activated in PN sub-region of the VTA, which mediates the rewarding effects of drugs including nicotine. Lastly, using immunohistochemistry, we observed an overall decrease in DA neurons following perinatal nicotine exposure.

Prenatal Nicotine Exposure in Rodents: Why Are There So Many Variations in Behavioral Outcomes?

Introduction

The World Health Organization (WHO) reported that smoking cessation rates among women have stagnated in the past decade and estimates that hundreds of millions of women will be smokers in the next decade. Social, environmental, and biological conditions render women more susceptible to nicotine addiction, imposing additional challenges to quit smoking during gestation, which is likely why more than 8% of pregnancies in Europe are associated with smoking. In epidemiological investigations, individuals born from gestational exposure to smoking exhibit a higher risk of development of attention-deficit/hyperactive disorder (ADHD) and liability to drug dependence. Among other teratogenic compounds present in tobacco smoke, nicotine actions during neuronal development could contribute to the observed outcomes as nicotine misleads signaling among progenitor cells during brain development. Several experimental approaches have been developed to address the consequences of prenatal nicotine exposure (PNE) to the brain and behavior but, after four decades of studies, inconsistent data have been reported and the lack of consensus in the field has compromised the hypothesis that gestational nicotine exposure participates in cognitive and emotional behavioral deficits.

Aims

In this review, we discuss the most commonly used PNE models with focus on their advantages and disadvantages, their relative validity, and how the different technical approaches could play a role in the disparate outcomes.

Results

We propose methodological considerations, which could improve the translational significance of the PNE models.

Conclusions

Such alterations might be helpful in reconciling experimental findings, as well as leading to development of treatment targets for maladaptive behaviors in those prenatally exposed.

Implications

In this article, we have reviewed the advantages and disadvantages of different variables of the commonly used experimental models of PNE. We discuss how variations in the nicotine administration methods, the timing of nicotine exposure, nicotine doses, and species employed could contribute to the disparate findings in outcomes for PNE offspring, both in behavior and neuronal changes. In addition, recent findings suggest consideration of epigenetic effects extending across generations. Finally, we have suggested improvements in the available PNE models that could contribute to the enhancement of their validity, which could assist in the reconciliation of experimental findings.

Prenatal Tobacco Exposure Modulated the Association of Genetic variants with Diagnosed ADHD and its symptom domain in children: A Community Based Case-Control Study

The purpose of our study was to test the hypothesis that prenatal tobacco smoking exposure (PSE) could modulate the association of genetic variants with ADHD. A community based case-control study was conducted among Chinese children and 168 ADHD patients and 233 controls were recruited by using combination diagnosis of DSM-IV, SNAP-IV and semi-structured clinical interview. Logistic regression analysis was performed to estimate the effect of prenatal tobacco smoking exposure and genotype frequencies on ADHD susceptibility individually by adjustment for potential confounders. Multiplicative and additive interaction analysis were performed to evaluate the interactions between risk genes and PSE with regard to ADHD. Prenatal tobacco smoke exposure was a significant risk factor of ADHD even after adjusted for other potential confounders. ADRA2A rs553668, DRD2 rs1124491 and SLC6A4 rs6354 were identified to be associated with ADHD. A significant multiplicative and additive gene-environment interactions were observed between the PSE and the ADRA2A rs553668 in relation to ADHD and ADHD-ODD. The risk of the genetic variants in ADHD was increased significantly if the child had prenatal tobacco exposure. The genetic risk for ADHD could be influenced by the presence of environmental risks. The environmental and the genetic risks are not distinct to each other. More gene-environment interaction studies were needed to reveal the etiology of ADHD.

Comparison between dopaminergic and non-dopaminergic neurons in the VTA following chronic nicotine exposure during pregnancy

Exposure to nicotine during pregnancy through maternal smoking or nicotine replacement therapy is associated with adverse birth outcomes as well as several cognitive and neurobehavioral deficits. Several studies have shown that nicotine produces long-lasting effects on gene expression within many brain regions, including the ventral tegmental area (VTA), which is the origin of dopaminergic neurons and the dopamine reward pathway. Using a well-established rat model for perinatal nicotine exposure, we sought to investigate altered biological pathways using mRNA and miRNA expression profiles of dopaminergic (DA) and non-dopaminergic (non-DA) neurons in this highly-valuable area. Putative miRNA-gene target interactions were assessed as well as miRNA-pathway interactions. Our results indicate that extracellular matrix (ECM) receptor interactions were significantly altered in DA and non-DA neurons due to chronic nicotine exposure during pregnancy. They also show that the PI3K/AKT signaling pathway was enriched in DA neurons with multiple significant miRNA-gene targets, but the same changes were not seen in non-DA neurons. We speculate that nicotine exposure during pregnancy could differentially affect the gene expression of DA and non-DA neurons in the VTA.

Parental Risk Factors among Children with Reactive Attachment Disorder Referred to Specialized Services: A Nationwide Population-Based Study

This nationwide population-based register study examined the family and parental risk factors associated with offspring reactive attachment disorder (RAD). We identified 614 children diagnosed with RAD from the Finnish Care Register for Health Care and each case was matched with four controls. Univariate and multivariate models examined the associations between risk factors and RAD. In the multivariate model, offspring RAD was associated with only mother, only father and both parents having psychiatric diagnoses. Increased odds were observed for maternal smoking during pregnancy, single motherhood and paternal age ≥ 45 years. This study provides information on several parental adversities and offspring RAD that have important implications for public health, when planning early prevention and interventions in infant mental health.

Investigating the genetic profile of dopaminergic neurons in the VTA in response to perinatal nicotine exposure using mRNA-miRNA analyses

Maternal smoking during pregnancy is associated with an increased risk of developmental, behavioral, and cognitive deficits. Nicotine, the primary addictive component in tobacco, has been shown to modulate changes in gene expression when exposure occurs during neurodevelopment. The ventral tegmental area (VTA) is believed to be central to the mechanism of addiction because of its involvement in the reward pathway. The purpose of this study was to build a genetic profile for dopamine (DA) neurons in the VTA and investigate the disruptions to the molecular pathways after perinatal nicotine exposure. Initially, we isolated the VTA from rat pups treated perinatally with either nicotine or saline (control) and collected DA neurons using fluorescent-activated cell sorting. Using microarray analysis, we profiled the differential expression of mRNAs and microRNAs from DA neurons in the VTA in order to explore potential points of regulation and enriched pathways following perinatal nicotine exposure. Furthermore, mechanisms of miRNA-mediated post-transcriptional regulation were investigated using predicted and validated miRNA-gene targets in order to demonstrate the role of miRNAs in the mesocorticolimbic DA pathway. This study provides insight into the genetic profile as well as biological pathways of DA neurons in the VTA of rats following perinatal nicotine exposure.

The interaction of the Chrna5 D398N variant with developmental nicotine exposure

A single nucleotide polymorphism (SNP) in CHRNA5 (rs16969968, change from an aspartic acid [D] to asparagine [N] at position 398 of the human α5 nicotinic acetylcholine receptor subunit) has been associated with increased risk for nicotine dependence. Consequently, carriers of the risk variant may be at elevated risk for in utero nicotine exposure. To assess whether this gene-environment interaction might impact nicotine intake in developmental nicotine-exposed offspring, we utilized a mouse expressing this human SNP. D and N dams drank nicotine (100 μg/mL) in 0.2% saccharin water or 0.2% saccharin water alone (vehicle) as their sole source of fluid from 30 days prior to breeding until weaning of offspring. The nicotine (D Nic, N Nic) or vehicle (D Veh, N Veh) exposed offspring underwent a 2-bottle choice test between postnatal ages of 30 to 46 days. N Nic offspring consumed the most nicotine at the highest concentration (400 μg/mL) compared with all other groups. In contrast, D Nic offspring drank the least amount of nicotine at all concentrations tested. Nicotine-stimulated dopamine (DA) release measured from striatal synaptosomes was increased in D Nic offspring, while decreased in N Nic offspring relative to their genotype-matched controls. These data suggest that the α5 variant influences the effect of developmental nicotine exposure on nicotine intake of exposed offspring. This gene-environment interaction on striatal DA release may provide motivation for increased nicotine seeking in N Nic offspring and reduced consumption in D Nic offspring.

Influence of exposure to nicotine during pregnancy on the learning and memory for adult offspring

We aimed to investigate the indirect influence of exposure to nicotine during pregnancy on the learning and memory of adult offspring mice. Thirty pregnant C57 mice were randomly divided into either the control group (CON) or the nicotine group (NIC), with 15 mice each. The CON group was given access to drug-free water, and the NIC group was given 60 g/ml nicotine in drinking water. Sixteen adult mice were randomly selected from the 8 litters for Morris water maze test. The level of products of related factors in the hippocampus of mice in the NIC and the CON groups were compared using the ¹H-MRS method. The escape latency time that the adult offspring mice in the NIC group took in the place navigation test was significantly longer than that of the CON group. In addition, the NIC group took longer time to arrive at the plate than the CON group (P<0.05). mRNA and protein levels of NR1 in the hippocampus of the NIC group was significantly higher than that in the CON group (P<0.05).α7nACh mRNA in the hippocampus of the NIC group was not significantly different from that of the CON group (P>0.05), while the expression levels of α7nACh protein in the hippocampus of the NIC group was significantly lower than that in the CON group (P<0.05). Detection of protein level of muscarinic receptors in the hippocampus of adult offspring mice in the NIC group showed that when compared to the CON group, the expression levels of M1, M3, M5 of the NIC group was not significantly different from that of the CON group (P>0.05). Therefore, exposure to nicotine during pregnancy can cause damage to the learning ability of adult offspring mice but do not significantly influence their working memory.

Prenatal nicotine exposure decreases the release of dopamine in the medial frontal cortex and induces atomoxetine-responsive neurobehavioral deficits in mice

Increased risk of attention-deficit/hyperactivity disorder (AD/HD) is partly associated with the early developmental exposure to nicotine in tobacco smoke. Emerging reports link tobacco smoke exposure or prenatal nicotine exposure (PNE) with AD/HD-like behaviors in rodent models. We have previously reported that PNE induces cognitive behavioral deficits in offspring and decreases the contents of dopamine (DA) and its turnover in the prefrontal cortex (PFC) of offspring It is well known that the dysfunction of DAergic system in the brain is one of the core factors in the pathophysiology of AD/HD. Therefore, we examined whether the effects of PNE on the DAergic system underlie the AD/HD-related behavioral changes in mouse offspring. PNE reduced the release of DA in the medial PFC (mPFC) in mouse offspring. PNE reduced the number of tyrosine hydroxylase (TH)-positive varicosities in the mPFC and in the core as well as the shell of nucleus accumbens, but not in the striatum. PNE also induced behavioral deficits in cliff avoidance, object-based attention, and sensorimotor gating in offspring. These behavioral deficits were attenuated by acute treatment with atomoxetine (3 mg/kg, s.c.) or partially attenuated by acute treatment with MPH (1 mg/kg, s.c.). Taken together, our findings support the notion that PNE induces neurobehavioral abnormalities in mouse offspring by disrupting the DAergic system and improve our understanding about the incidence of AD/HD in children whose mothers were exposed to nicotine during their pregnancy.

Increased risk of developing schizophrenia in animals exposed to cigarette smoke during the gestational period

Cigarette smoking during the prenatal period has been investigated as a causative factor of obstetric abnormalities, which lead to cognitive and behavioural changes associated with schizophrenia. The aim of this study was to investigate behaviour and AChE activity in brain structures in adult rats exposed to cigarette smoke during the prenatal period. Pregnant rats were divided into non-PCSE (non-prenatal cigarette smoke exposure) and PCSE (prenatal cigarette smoke exposure) groups. On post-natal day 60, the rats received saline or ketamine for 7days and were subjected to behavioural tasks. In the locomotor activity task, the non-PCSE+ketamine and PCSE+ketamine groups exhibited increased locomotor activity compared with the saline group. In the social interaction task, the non-PCSE+ketamine and PCSE+ketamine groups exhibited an increased latency compared with the control groups. However, the PCSE+ketamine group exhibited a decreased latency compared with the non-PCSE+ketamine group, which indicates that the cigarette exposure appeared to decrease, the social deficits generated by ketamine. In the inhibitory avoidance task, the non-PCSE+ketamine, PCSE, and PCSE+ketamine groups exhibited impairments in working memory, short-term memory, and long-term memory. In the pre-pulse inhibition (PPI) test, cigarette smoke associated with ketamine resulted in impaired PPI in 3 pre-pulse (PP) intensity groups compared with the control groups. In the biochemical analysis, the AChE activity in brain structures increased in the ketamine groups; however, the PCSE+ketamine group exhibited an exacerbated effect in all brain structures. The present study indicates that exposure to cigarette smoke during the prenatal period may affect behaviour and cerebral cholinergic structures during adulthood.

Consumption of Substances of Abuse during Pregnancy Increases Consumption in Offspring: Possible Underlying Mechanisms

Correlative human observational studies on substances of abuse have been highly dependent on the use of rodent models to determine the neuronal and molecular mechanisms that control behavioral outcomes. This is particularly true for gestational exposure to non-illicit substances of abuse, such as excessive dietary fat, ethanol, and nicotine, which are commonly consumed in our society. Exposure to these substances during the prenatal period has been shown in offspring to increase their intake of these substances, induce other behavioral changes, and affect neurochemical systems in several brain areas that are known to control behavior. More importantly, emerging studies are linking the function of the immune system to these neurochemicals and ingestion of these abused substances. This review article will summarize the prenatal rodent models used to study developmental changes in offspring caused by prenatal exposure to dietary fat, ethanol, or nicotine. We will discuss the various techniques used for the administration of these substances into rodents and summarize the published outcomes induced by prenatal exposure to these substances. Finally, this review will cover some of the recent evidence for the role of immune factors in causing these behavioral and neuronal changes.

Nicotinic acetylcholine receptors: upregulation, age-related effects and associations with drug use

Nicotinic acetylcholine receptors are ligand-gated ion channels that exogenously bind nicotine. Nicotine produces rewarding effects by interacting with these receptors in the brain's reward system. Unlike other receptors, chronic stimulation by an agonist induces an upregulation of receptor number that is not due to increased gene expression in adults; while upregulation also occurs during development and adolescence there have been some opposing findings regarding a change in corresponding gene expression. These receptors have also been well studied with regard to human genetic associations and, based on evidence suggesting shared genetic liabilities between substance use disorders, numerous studies have pointed to a role for this system in comorbid drug use. This review will focus on upregulation of these receptors in adulthood, adolescence and development, as well as the findings from human genetic association studies which point to different roles for these receptors in risk for initiation and continuation of drug use.

Nicotine during pregnancy: changes induced in neurotransmission, which could heighten proclivity to addict and induce maladaptive control of attention

Prenatal exposure to nicotine, occurring either via maternal smoking or via use of transdermal nicotine patches to facilitate cigarette abstinence by pregnant women, is associated with ∼ 13% of pregnancies worldwide. Nicotine exposure during gestation has been correlated with several negative physiological and psychosocial outcomes, including heightened risk for aberrant behaviors involving alterations in processing of attention as well as an enhanced liability for development of drug dependency. Nicotine is a terotogen, altering neuronal development of various neurotransmitter systems, and it is likely these alterations participate in postnatal deficits in attention control and facilitate development of drug addiction. This review discusses the alterations in neuronal development within the brain's major neurotransmitter systems, with special emphasis placed on alterations within the laterodorsal tegmental nucleus, in light of the role this cholinergic nucleus plays in attention and addiction. Changes induced within this nucleus by gestational exposure to nicotine, in combination with changes induced in other brain regions, are likely to contribute to the transgenerational burden imposed by nicotine. Although neuroplastic changes induced by nicotine are not likely to act in isolation, and are expected to interact with epigenetic changes induced by preconception exposure to drugs of abuse, unraveling these changes within the developing brain will facilitate eventual development of targeted treatments for the unique vulnerability for arousal disorders and development of addiction within the population of individuals who have been prenatally exposed to nicotine.

Electrophysiological changes in laterodorsal tegmental neurons associated with prenatal nicotine exposure: implications for heightened susceptibility to addict to drugs of abuse

Prenatal nicotine exposure (PNE) is a risk factor for developing an addiction to nicotine at a later stage in life. Understanding the neurobiological changes in reward related circuitry induced by exposure to nicotine prenatally is vital if we are to combat the heightened addiction liability in these vulnerable individuals. The laterodorsal tegmental nucleus (LDT), which is comprised of cholinergic, GABAergic and glutamatergic neurons, is importantly involved in reward mediation via demonstrated excitatory projections to dopamine-containing ventral tegmental neurons. PNE could lead to alterations in LDT neurons that would be expected to alter responses to later-life nicotine exposure. To examine this issue, we monitored nicotine-induced responses of LDT neurons in brain slices of PNE and drug naive mice using calcium imaging and whole-cell patch clamping. Nicotine was found to induce rises in calcium in a smaller proportion of LDT cells in PNE mice aged 7-15 days and smaller rises in calcium in PNE animals from postnatal ages 11-21 days when compared with age-matched control animals. While inward currents induced by nicotine were not found to be different, nicotine did induce larger amplitude excitatory postsynaptic currents in PNE animals in the oldest age group when compared with amplitudes induced in similar-aged control animals. Immunohistochemically identified cholinergic LDT cells from PNE animals exhibited slower spike rise and decay slopes, which likely contributed to the wider action potential observed. Further, PNE was associated with a more negative action potential afterhyperpolarization in cholinergic cells. Interestingly, the changes found in these parameters in animals exposed prenatally to nicotine were age related, in that they were not apparent in animals from the oldest age group examined. Taken together, our data suggest that PNE induces changes in cholinergic LDT cells that would be expected to alter cellular excitability. As the changes are age related, these PNE-associated alterations could contribute differentially across ontogeny to nicotine-mediated reward and may contribute to the particular susceptibility of in utero nicotine exposed individuals to addict to nicotine upon nicotine exposure in the juvenile period.

The effects of co-administration of opium and morphine with nicotine during pregnancy on spatial learning and memory of adult male offspring rats

OBJECTIVES

Smoking opium/cigarette is a global health concern. The aim of this study was to examine learning and memory of rat male offsprings whose mothers had been exposed to either opium or morphine with nicotine during pregnancy.

MATERIALS AND METHODS

Wistar rats were used for the experiments. In the female rats, opium, morphine and nicotine dependencies were induced by daily injections of drug solution for 10 days before mating. Spatial memory was tested by Morris water maze test in male pups at the postnatal day 60. The duration that took until the rats found the platform in the maze and also their swimming speed were recorded.

RESULTS

An increase in the platform finding duration was observed for the pups of dependent mothers in comparison with the control in the training trial (P<0.05). Prenatal exposure to opium/morphine and nicotine significantly decreased the time spent in the trigger zone to find the hidden platform (P<0.05) but had no significant effect on the swimming speed in the probe test. However, no significant difference was observed in the learning and memory behavior of offspring whose mothers received morphine, opium, nicotine or the co-administration of either morphine or opium with nicotine.

CONCLUSION

The present study showed that the opium, morphine and nicotine abuse and co-administration of opium/morphine with nicotine during pregnancy may cause deficits in spatial learning of male rat offspring. Based on our data, no synergistic effects of co-drug administration were observed on learning and memory in male rat offspring.

Physical, behavioral, and cognitive effects of prenatal tobacco and postnatal secondhand smoke exposure

The purpose of this review is to examine the rapidly expanding literature regarding the effects of prenatal tobacco and postnatal secondhand smoke (SHS) exposure on child health and development. Mechanisms of SHS exposure are reviewed, including critical periods during which exposure to tobacco products appears to be particularly harmful to the developing fetus and child. The biological, biochemical, and neurologic effects of the small fraction of identified components of SHS are described. Research describing these adverse effects of both in utero and childhood exposure is reviewed, including findings from both animal models and humans. The following adverse physical outcomes are discussed: sudden infant death syndrome, low birth weight, decreased head circumference, respiratory infections, otitis media, asthma, childhood cancer, hearing loss, dental caries, and the metabolic syndrome. In addition, the association between the following adverse cognitive and behavioral outcomes and such exposures is described: conduct disorder, attention-deficit/hyperactivity disorder, poor academic achievement, and cognitive impairment. The evidence supporting the adverse effects of SHS exposure is extensive yet rapidly expanding due to improving technology and increased awareness of this profound public health problem. The growing use of alternative tobacco products, such as hookahs (a.k.a. waterpipes), and the scant literature on possible effects from prenatal and secondhand smoke exposure from these products are also discussed. A review of the current knowledge of this important subject has implications for future research as well as public policy and clinical practice.

Prenatal tobacco exposure and response inhibition in school-aged children: an event-related potential study

Prenatal cigarette smoke exposure (PCSE) has been linked to problems in behavioral inhibition and attention deficit hyperactivity disorder in children in several epidemiological studies. We used event-related potentials (ERPs) to examine the effects of PCSE on neural correlates of inhibitory control of behavior. In a prospective longitudinal study on child development in the Canadian Arctic, we assessed 186 Inuit children (mean age=11.3years) on a visual Go/No-go response inhibition paradigm. PCSE was assessed through maternal recall. Potential confounders were documented from a maternal interview, and exposure to neurotoxic environmental contaminants was assessed from umbilical cord and child blood samples. PCSE was not related to behavioral performance on this simple response inhibition task. Nevertheless, this exposure was associated with smaller amplitudes of the N2 and P3 components elicited by No-go stimuli, suggesting an impairment in the neural processes underlying response inhibition. Amplitude of the No-go P3 component was also inversely associated with behavioral measures of externalizing problems and hyperactivity/impulsivity in the classroom. This study is the first to report neurophysiological evidence of impaired response inhibition in school-aged children exposed to tobacco smoke in utero. Effects were found on ERP components associated with conflict processing and inhibition of a prepotent response, indicating neurophysiological deficits that may play a critical role in the attention and behavior problems observed in children with PCSE.

Neonatal nicotine exposure increases excitatory synaptic transmission and attenuates nicotine-stimulated GABA release in the adult rat hippocampus

Developmental exposure to nicotine has been linked to long-lasting changes in synaptic transmission which may contribute to behavioral abnormalities seen in offspring of women who smoke during pregnancy. Here, we examined the long-lasting effects of developmental nicotine exposure on glutamatergic and GABAergic neurotransmission, and on acute nicotine-induced glutamate and GABA release in the adult hippocampus, a structure important in cognitive and emotional behaviors. We utilized a chronic neonatal nicotine treatment model to administer nicotine (6 mg/kg/day) to rat pups from postnatal day (P) 1-7, a period that falls developmentally into the third human trimester. Using whole-cell voltage clamp recordings from CA1 pyramidal neurons in hippocampal slices, we measured excitatory and inhibitory postsynaptic currents in neonatally control- and nicotine-treated young adult males. Neonatal nicotine exposure significantly increased AMPA receptor-mediated spontaneous and evoked excitatory signaling, with no change in glutamate release probability in adults. Conversely, there was no increase in spontaneous GABAergic neurotransmission in nicotine-males. Chronic neonatal nicotine treatment had no effect on acute nicotine-stimulated glutamate release in adults, but acute nicotine-stimulated GABA release was significantly attenuated. Thus, neonatal nicotine exposure results in a persistent net increase in excitation and a concurrent loss of nicotinic acetylcholine receptor (nAChR)-mediated regulation of presynaptic GABA but not glutamate release, which would exacerbate excitation following endogenous or exogenous nAChR activation. Our data underscore an important role for nAChRs in hippocampal excitatory synapse development, and suggest selective long-term changes at specific presynaptic nAChRs which together could explain some of the behavioral abnormalities associated with maternal smoking.

Evaluation of cognitive behaviors in young offspring of C57BL/6J mice after gestational nicotine exposure during different time-windows

Gestational nicotine exposure is associated with cognitive abnormalities in young offspring. However, practical strategies for prevention or treatment of impaired cognitive behaviors of offspring are not available due to the lack of systematic investigation of underlying mechanism. Therefore, this study aimed at examining the effects of gestational and/or perinatal nicotine exposure (GPNE) on cognitive behaviors in offspring of C57BL/6J mice to provide systematic behavioral data. Pregnant mice were exposed to nicotine via sweetened drinking water during six time-windows, including gestational day 0 to day 13 (G0-G13), G14-postnatal day 0 (P0), G0-P0, G14-P7, G0-P7, and P0-P7. During P42-P56 days, both male and female offspring were given a battery of behavioral tests. Depending on the time of exposure, GPNE impaired working memory, object-based attention, and prepulse inhibition in male and female offspring to different extents. Nicotine exposure during G14-P0 also decreased norepinephrine turnover in the prefrontal cortex on P28 and P56. Overall results indicate that nicotine exposure during any time-windows of development impairs cognitive behaviors in offspring, and suggest that certain time-windows, e.g., G14-P0, should be selected for further studies on the underlying neurochemical or molecular mechanisms.

Gene-environment interactions affect long-term depression (LTD) through changes in dopamine receptor affinity in Snap25 deficient mice

Genes and environmental conditions interact in the development of cognitive capacities and each plays an important role in neuropsychiatric disorders such as attention deficit/hyperactivity disorder (ADHD) and schizophrenia. Multiple studies have indicated that the gene for the SNARE protein SNAP-25 is a candidate susceptibility gene for ADHD, as well as schizophrenia, while maternal smoking is a candidate environmental risk factor for ADHD. We utilized mice heterozygous for a Snap25 null allele and deficient in SNAP-25 expression to model genetic effects in combination with prenatal exposure to nicotine to explore genetic and environmental interactions in synaptic plasticity and behavior. We show that SNAP-25 deficient mice exposed to prenatal nicotine exhibit hyperactivity and deficits in social interaction. Using a high frequency stimulus electrophysiological paradigm for long-term depression (LTD) induction, we examined the roles of dopaminergic D2 receptors (D2Rs) and cannabinoid CB1 receptors (CB1Rs), both critical for LTD induction in the striatum. We found that prenatal exposure to nicotine in Snap25 heterozygote null mice produced a deficit in the D2R-dependent induction of LTD, although CB1R regulation of plasticity was not impaired. We also show that prenatal nicotine exposure altered the affinity and/or receptor coupling of D2Rs, but not the number of these receptors in heterozygote null Snap25 mutants. These results refine the observations made in the coloboma mouse mutant, a proposed mouse model of ADHD, and illustrate how gene×environmental influences can interact to perturb neural functions that regulate behavior.

Exploring alternate processes contributing to the association between maternal smoking and the smoking behavior among young adult offspring

INTRODUCTION

Maternal smoking during pregnancy (MSP) is a known risk factor for regular smoking in young adulthood and may pose a risk independently of mother's lifetime smoking. The processes through which MSP exerts this influence are unknown but may occur through greater smoking quantity and frequency following initiation early in adolescence or increased sensitivity to nicotine dependence (ND) at low levels of smoking.

METHODS

This study used path analysis to investigate adolescent smoking quantity, smoking frequency, and ND as potential simultaneous mediating pathways through which MSP and mother's lifetime smoking (whether she has ever smoked) increase the risk of smoking in young adulthood among experimenters (at baseline, <100 cigarettes/lifetime) and current smokers (>100 cigarettes/lifetime).

RESULTS

For experimenters, MSP was directly associated with more frequent young adult smoking and was not mediated by adolescent smoking behavior or ND. Independently of MSP, the effect of mother's lifetime smoking was fully mediated through frequent smoking and was heightened ND during adolescence. Controlling for MSP eliminated a previously observed direct association between mother's lifetime smoking and future smoking among experimenters. For current smokers, only prior smoking behavior was associated with future smoking frequency.

CONCLUSIONS

These results seem to rule out sensitivity to ND and increased smoking behavior as contributing pathways of MSP. Further, the impact of MSP on young adult smoking extends beyond that of having an ever-smoking mother. Future work should test other possible mediators; for example, MSP-related epigenetic changes or gene variants influencing the brain's nicotine response.

Chronic exposure to cigarette smoke during gestation results in altered cholinesterase enzyme activity and behavioral deficits in adult rat offspring: potential relevance to schizophrenia

Prenatal cigarette smoke exposure (PCSE) has been associated with physiological and developmental changes that may be related to an increased risk for childhood and adult neuropsychiatric diseases. The present study investigated locomotor activity and cholinesterase enzyme activity in rats, following PCSE and/or ketamine treatment in adulthood. Pregnant female Wistar rats were exposed to 12 commercially filtered cigarettes per day for a period of 28 days. We evaluated motor activity and cholinesterase activity in the brain and serum of adult male offspring that were administered acute subanesthetic doses of ketamine (5, 15 and 25 mg/kg), which serves as an animal model of schizophrenia. To determine locomotor activity, we used the open field test. Cholinesterase activity was assessed by hydrolysis monitored spectrophotometrically. Our results show that both PCSE and ketamine treatment in the adult offspring induced increase of locomotor activity. Additionally, it was observed increase of acetylcholinesterase and butyrylcholinesterase activity in the brain and serum, respectively. We demonstrated that animals exposed to cigarettes in the prenatal period had increased the risk for psychotic symptoms in adulthood. This also occurs in a dose-dependent manner. These changes provoke molecular events that are not completely understood and may result in abnormal behavioral responses found in neuropsychiatric disorders, such as schizophrenia.

How cigarette smoking may increase the risk of anxiety symptoms and anxiety disorders: a critical review of biological pathways

Multiple studies have demonstrated an association between cigarette smoking and increased anxiety symptoms or disorders, with early life exposures potentially predisposing to enhanced anxiety responses in later life. Explanatory models support a potential role for neurotransmitter systems, inflammation, oxidative and nitrosative stress, mitochondrial dysfunction, neurotrophins and neurogenesis, and epigenetic effects, in anxiety pathogenesis. All of these pathways are affected by exposure to cigarette smoke components, including nicotine and free radicals. This review critically examines and summarizes the literature exploring the role of these systems in increased anxiety and how exposure to cigarette smoke may contribute to this pathology at a biological level. Further, this review explores the effects of cigarette smoke on normal neurodevelopment and anxiety control, suggesting how exposure in early life (prenatal, infancy, and adolescence) may predispose to higher anxiety in later life. A large heterogenous literature was reviewed that detailed the association between cigarette smoking and anxiety symptoms and disorders with structural brain changes, inflammation, and cell-mediated immune markers, markers of oxidative and nitrosative stress, mitochondrial function, neurotransmitter systems, neurotrophins and neurogenesis. Some preliminary data were found for potential epigenetic effects. The literature provides some support for a potential interaction between cigarette smoking, anxiety symptoms and disorders, and the above pathways; however, limitations exist particularly in delineating causative effects. The literature also provides insight into potential effects of cigarette smoke, in particular nicotine, on neurodevelopment. The potential treatment implications of these findings are discussed in regards to future therapeutic targets for anxiety. The aforementioned pathways may help mediate increased anxiety seen in people who smoke. Further research into the specific actions of nicotine and other cigarette components on these pathways, and how these pathways interact, may provide insights that lead to new treatment for anxiety and a greater understanding of anxiety pathogenesis.

Risk factors for adolescent smoking: parental smoking and the mediating role of nicotine dependence

BACKGROUND

Parental smoking and early-emerging nicotine dependence symptoms are well-documented risk factors for adolescent smoking. However, very little is known about the mediating pathways through which these risk factors may act, or whether parental smoking may cause or signal early-emerging nicotine dependence symptoms.

METHODS

Data were drawn from the longitudinal Social and Emotional Contexts of Adolescent Smoking Patterns Study. Adolescents who had smoked under 100 cigarettes in their lifetime (n=594; low-exposure group) and adolescents who had smoked over 100 cigarettes, but fewer than 5 cigarettes per day (n=152) were included in the analyses. Path analysis was performed on longitudinal data to investigate the association between parental smoking and smoking frequency at the 48 months follow-up, both directly and through mediating variables of smoking frequency, smoking quantity, and nicotine dependence.

RESULTS

Father's smoking was associated with higher adolescent nicotine dependence scores at the baseline assessment wave. Structural equation modeling revealed that mother's smoking at baseline was associated with adolescent's smoking frequency at the 48-month follow-up, and its effect was partially mediated by both smoking frequency and nicotine dependence among low-exposure adolescent smokers.

CONCLUSIONS

Parental smoking is a risk factor for future smoking in low-exposure adolescent smokers, above and beyond the risks posed by smoking behavior and nicotine dependence. Moreover, parental smoking is associated with early-onset nicotine dependence in low-exposure adolescent smokers. As an easily measureable risk factor, parent smoking status can be used to identify and intervene with novice adolescent smokers who are at high risk for chronic smoking behavior.

Is maternal smoking during pregnancy a causal environmental risk factor for adolescent antisocial behavior? Testing etiological theories and assumptions

BACKGROUND

Although many studies indicate that maternal smoking during pregnancy (SDP) is correlated with later offspring antisocial behavior (ASB), recent quasi-experimental studies suggest that background familial factors confound the association. The present study sought to test alternative etiological hypotheses using multiple indices of adolescent ASB, comparing differentially exposed siblings, and testing assumptions in the sibling-comparison design.

METHOD

The study examined the association between maternal SDP and adolescent-reported ASB, criminal convictions and membership in a group of individuals with early-starting and chronic ASB among 6066 offspring of women from the National Longitudinal Survey of Youth, a representative sample of women in the USA. The analyses controlled for statistical covariates and examined associations while comparing differentially exposed siblings.

RESULTS

At the population level, each additional pack of cigarettes per day predicted greater mean adolescent-reported ASB symptoms [ratio of means 1.15, 95% confidence interval (CI) 1.08-1.22], odds of being in the top 10% of ASB [odds ratio (OR) 1.34, 95% CI 1.10-1.65], hazard of a criminal conviction [hazard ratio (HR) 1.51, 95% CI 1.34-1.68] and odds of chronic ASB (OR 1.57, 95% CI 1.25-1.99). SDP robustly predicted most assessments of ASB while controlling for measured covariates. When siblings exposed to differing levels of SDP were compared, however, all of the associations were attenuated and were not statistically significant: adolescent-reported mean ASB (ratio of means 0.86, 95% CI 0.74-1.01), high ASB (OR 0.67, 95% CI 0.41-1.12), criminal conviction (HR 0.98, 95% CI 0.66-1.44) and chronic ASB (OR 0.80, 95% CI 0.46-1.38).

CONCLUSIONS

The results strongly suggest that familial factors account for the correlation between SDP and offspring adolescent ASB, rather than a putative causal environmental influence of SDP.

Effects of chronic nicotine on heteromeric neuronal nicotinic receptors in rat primary cultured neurons

Nicotine increases the number of neuronal nicotinic acetylcholine receptors (nAChRs) in brain. This study investigated the effects of chronic nicotine treatment on nAChRs expressed in primary cultured neurons. In particular, we studied the chronic effects of nicotine exposure on the total density, surface expression and turnover rate of heteromeric nAChRs. The receptor density was measured by [¹²⁵I]epibatidine ([¹²⁵I]EB) binding. Untreated and nicotine-treated neurons were compared from several regions of embryonic (E19) rat brain. Twelve days of treatment with 10 μM nicotine produced a twofold up-regulation of nAChRs. Biotinylation and whole-cell binding studies indicated that up-regulation resulted from an increase in the number of cell surface receptors as well as intracellular receptors. nAChR subunit composition in cortical and hippocampal neurons was assessed by immunoprecipitation with subunit-selective antibodies. These neurons contain predominantly α4, β2 and α5 subunits, but α2, α3, α6 and β4 subunits were also detected. Chronic nicotine exposure yielded a twofold increase in the β2-containing receptors and a smaller up-regulation in the α4-containing nAChRs. To explore the mechanisms of up-regulation we investigated the effects of nicotine on the receptor turnover rate. We found that the turnover rate of surface receptors was > 2 weeks and chronic nicotine exposure had no effect on this rate.

Fetal growth retardation and risk of febrile seizures

OBJECTIVE

The goal was to examine the associations between fetal growth characteristics in different trimesters of pregnancy and the occurrence of febrile seizures in early childhood.

METHODS

This study was embedded in a population-based, prospective, cohort study from early fetal life onward. Fetal growth characteristics (femur length, abdominal circumference, estimated fetal weight, head circumference, biparietal diameter, and transverse cerebellar diameter [TCD]) were measured with ultrasonography in the second and third trimesters of pregnancy. Information on the occurrence of febrile seizures was collected with questionnaires at the ages of 12 and 24 months. Analyses were based on data for 3372 subjects.

RESULTS

In the second trimester, children in the lowest tertile of TCDs were at increased risk of developing febrile seizures, compared with children in the highest tertile (odds ratio 2.87 [95% confidence interval: 1.31-6.28]). In the third trimester, children in the lowest tertile of all general growth characteristics (femur length, abdominal circumference, and estimated fetal weight) were at increased risk of developing febrile seizures. This association was strongest for children in the lowest tertile of estimated fetal weight (odds ratio: 2.57 [95% confidence interval: 1.34-4.96]). Children in the lowest tertile of biparietal diameter in the third trimester also were at increased risk of febrile seizures. Similar but not statistically significant tendencies were observed for head circumference and TCD.

CONCLUSIONS

Fetal growth retardation is associated with increased risk of febrile seizures in the first 2 years of life. Adverse environmental and genetic factors during pregnancy may be important in the development of febrile seizures.

Gestational exposure to nicotine in drinking water: teratogenic effects and methodological issues

Individual differences in nicotine effects lead to questions about appropriate experimental procedures for prenatal nicotine exposure in rodent models. The objective of this study was to develop a method for gestational studies in rats based on oral nicotine exposure, and to evaluate the neurodevelopmental effects. Female Lister hooded rats were exposed to nicotine solutions both before and during pregnancy. These female rats were divided into groups consuming solutions of different concentrations such that animals that initially consumed the solutions most readily were exposed to progressively higher concentrations. Offspring of these female rats were evaluated in a test battery measuring maturational and developmental milestones. Female rats ingested nicotine solutions at levels that provided blood nicotine concentrations of 10-60 ng/ml, at daily dose levels of 2.9-6.2 mg/kg. Solutions with concentrations below 0.06 mg/ml were well tolerated with some moderate adverse effects at the highest dose. Concentrations above 0.08 mg/ml led to a large drop in fluid consumption and in body weight. Strong teratogenic effects of prenatal nicotine exposure were observed at concentrations above 0.04 mg/ml, including developmental and maturational delays shown by measures of pinnae detachment, fur appearance, incisor eruption, eye opening and righting reflex. Negative geotaxis, grip strength and weight gain were impaired and postnatal mortality was increased. This study design provides a model for the impact of prenatal exposure to nicotine at blood levels comparable with those in medium and heavy smokers. There were marked developmental and behavioural deficits induced in the offspring of nicotine-exposed female rats.

Persistent gene expression changes in ventral tegmental area of adolescent but not adult rats in response to chronic nicotine

Because adolescent brains are undergoing extensive developmental changes, they may be uniquely sensitive to effects of addictive drugs like nicotine. We exposed adolescent and adult rats to nicotine infusion for two weeks, and then used whole genome microarray analysis to determine effects on gene expression in the ventral tegmental area. We examined brains immediately after two weeks of nicotine or saline, and also four weeks after termination of nicotine exposure. After identifying genes with a significant agextreatment interaction, we employed template matching to find specific patterns of expression across age and treatment. Of those genes that were transiently regulated (up- or down-regulated immediately following the end of nicotine treatment, but back to saline baseline 30 days later), two-thirds were specific to adult animals, while only 30% were specific to adolescents and 4% were shared across the two ages. In contrast, significant genes that were persistently regulated (altered following nicotine treatment and still altered 30 days later) were more likely (59%) to be adolescent, with only 32% in adults and 8% shared. The greatest number of significant genes was late-regulated (no change immediately after nicotine, but regulated 30 days later). Again, most were in adolescents (54%), compared to adults (10%) or shared (36%). Pathway analysis revealed that adolescent-specific genes were over-represented in several biological functions and canonical pathways, including nervous system development and function and long-term potentiation. Furthermore, adolescent-specific genes formed extensive interaction networks, unlike those specific for adults or shared. This age-specific expression pattern may relate to the heightened vulnerability of adolescents to the effects of addictive drugs. In particular, the propensity of adolescents to show persistent alterations in gene expression corresponds to the persistence of drug dependence among smokers who began their habit as adolescents. These findings support a model whereby adolescent brains are uniquely vulnerable to long-term changes in gene expression in the brain's reward pathway caused by early exposure to nicotine.

Early exposure to nicotine during critical periods of brain development: Mechanisms and consequences

Tobacco use during pregnancy continues to be a major problem with more than 16% of pregnant women in the United States continuing to smoke during pregnancy. Tobacco smoke is known to contain more than 4,000 different chemicals, and while many of these compounds have the potential to interfere with proper neurodevelopment, there is direct evidence that nicotine, the major psychoactive substance present in tobacco, acts as a neuroteratogen. Nicotine activates, and subsequently desensitizes, neuronal nicotinic acetylcholine receptor subtypes (AChRs), which are expressed in the developing central nervous system (CNS) prior to the in-growth of cholinergic neurons. Nicotinic AChRs are present by the first trimester of development in both humans and rodents, and activation of these receptors by acetylcholine is thought to play a critical role in CNS development. The purpose of the current review is to provide an overview of the role that nicotinic AChRs play in the developing CNS and to describe the effects of nicotine exposure during early development on neuronal cell biology, nicotinic AChR expression and neurotransmitter system (e.g., dopamine, norepinephrine, serotonin) function. In particular, differences that occur as a result of the timing and duration of nicotine exposure will be discussed. Emphasis will be placed on preclinical studies examining particular periods of time which correspond to periods of prenatal development in humans (i.e., first, second and third trimesters). Finally, the effects of early nicotine exposure on neurobehavioral development as it pertains to specific disorders, i.e., attention deficit hyperactivity disorder (ADHD), depression and addiction, will be discussed.