Fetal nicotine exposure ablates the ability of postnatal nicotine challenge to release norepinephrine from rat brain regions

Ongoing effects of preterm birth on the dopaminergic and noradrenergic pathways in the frontal cortex and hippocampus of guinea pigs

Children born preterm have an increased likelihood of developing neurobehavioral disorders such as attention-deficit hyperactivity disorder (ADHD) and anxiety. These disorders have a sex bias, with males having a higher incidence of ADHD, whereas anxiety disorder tends to be more prevalent in females. Both disorders are underpinned by imbalances to key neurotransmitter systems, with dopamine and noradrenaline in particular having major roles in attention regulation and stress modulation. Preterm birth disturbances to neurodevelopment may affect this neurotransmission in a sexually dimorphic manner. Time-mated guinea pig dams were allocated to deliver by preterm induction of labor (gestational age 62 [GA62]) or spontaneously at term (GA69). The resultant offspring were randomized to endpoints as neonates (24 h after term-equivalence age) or juveniles (corrected postnatal day 40, childhood equivalence). Relative mRNA expressions of key dopamine and noradrenaline pathway genes were examined in the frontal cortex and hippocampus and quantified with real-time PCR. Myelin basic protein and neuronal nuclei immunostaining were performed to characterize the impact of preterm birth. Within the frontal cortex, there were persisting reductions in the expression of dopaminergic pathway components that occurred in preterm males only. Conversely, preterm-born females had increased expression of key noradrenergic receptors and a reduction of the noradrenergic transporter within the hippocampus. This study demonstrated that preterm birth results in major changes in dopaminergic and noradrenergic receptor, transporter, and synthesis enzyme gene expression in a sex- and region-based manner that may contribute to the sex differences in susceptibility to neurobehavioral disorders. These findings highlight the need for the development of sex-based treatments for improving these conditions.

Cellular and Molecular Changes in Hippocampal Glutamate Signaling and Alterations in Learning, Attention, and Impulsivity Following Prenatal Nicotine Exposure

Over 70 million European pregnant women are smokers during their child-bearing years. Consumption of tobacco-containing products during pregnancy is associated with several negative behavioral outcomes for the offspring, including a higher susceptibility for the development of attention-deficit/hyperactive disorder (ADHD). In efforts to minimize fetal exposure to tobacco smoke, many women around the world switch to nicotine replacement therapies (NRTs) during the gestational period; however, prenatal nicotine exposure (PNE) in any form has been associated with alterations in cognitive processes, including learning, memory, and attention. These processes are controlled by glutamatergic signaling of hippocampal pyramidal neurons within the CA1 region, suggesting actions of nicotine on glutamatergic transmission in this region if present prenatally. Accordingly, we aimed to investigate hippocampal glutamatergic function following PNE treatment in NMRI mice employing molecular, cellular electrophysiology, and pharmacological approaches, as well as to evaluate cognition in the rodent continuous performance task (rCPT), a recently developed mouse task allowing assessment of learning, attention, and impulsivity. PNE induced increases in the expression levels of mRNA coding for different glutamate receptors and subunits within the hippocampus. Functional alterations in AMPA and NMDA receptors on CA1 pyramidal neurons of PNE mice were suggestive of higher GluA2-lacking and lower GluN2A-containing receptors, respectively. Finally, PNE was associated with reduced learning, attention, and enhanced impulsivity in the rCPT. Alterations in glutamatergic functioning in CA1 neurons parallel changes seen in the spontaneously hypertensive rat ADHD model and likely contribute to the lower cognitive performance in the rCPT.

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.

Gestational exposure to nicotine and/or benzo[a]pyrene causes long-lasting neurobehavioral consequences

Tobacco smoke is a complex mixture that includes thousands of compounds. Previously, we have found that gestational exposure to the complex mixture of tobacco smoke extract caused long-term neurobehavioral impairments. In this study, we examined the interaction of two of the most biologically active, nicotine and benzo[a]pyrene (BaP). Developmental effects were determined in Sprague-Dawley rats prenatally exposed to low doses of BaP and nicotine (0.03 mg/kg/day of BaP and 2 mg/kg/day of nicotine) via maternal osmotic minipumps throughout gestation. Behavioral function was assessed in the offspring via a battery of tests through adolescence into adulthood. There were sex-selective effects in four of the behavioral tests. In the elevated plus maze, there was a significant interaction of BaP and sex, where BaP-treated males showed a trend for increased activity. In the novelty suppressed feeding test, there were significant sex selective effects in males such that the normal sex difference in the behavior in this test was eliminated. Male offspring with prenatal exposure to either nicotine or BaP showed significant reductions in fear response. In the Figure-8 locomotor activity test, BAP-exposed male offspring were significantly hyperactive. This also eliminated the sex difference typically seen in this test. This effect persisted into adulthood. In the attention task, males exposed to nicotine during gestation showed a significant percent hit impairment. BaP reversed this effect. No significant effects were seen with percent correct rejection. These data show that both nicotine and BaP cause persisting sex-selective behavioral effects that persist into adulthood.

Environmental Tobacco Smoke Exposure at Home and Attributable Problem Behaviors in Korean Children and Adolescents for 2012-2014 in a Nationally Representative Survey

BACKGROUND

This study aimed to examine the environmental tobacco smoke (ETS) exposure at home and associated problem behaviors in Korean children and adolescents.

METHODS

Approximately 2,167 children aged 3-18 years were included in the study after excluding 163 active smokers from the Korean Environmental Health Survey in Children and Adolescents (2012-2014). ETS data were obtained using a questionnaire; problem behaviors were measured using the Child Behavior Checklist administered to parents. The relationship between ETS exposure and problem behavior was evaluated using a survey regression model adjusted for region, age, sex, income, and father's education. The population-attributable fraction (PAF%) was calculated based on problem behaviors related to ETS exposure at home.

RESULTS

The rates of ETS exposure at home were 20%, 28%, and 39% in children aged 3-5, 6-11, and 12-18 years, respectively; ETS exposure at home was associated with behavioral problems: the exposed group having higher total behavioral problem score (95% confidence interval [CI]) than the non-exposed by 2.46 (0.60-4.32) and 2.74 (0.74-4.74) in children aged 6-11 and 12-18 years, respectively, with no significant association in those aged 3-5 years. The PAF% (95% CI) of total problem behaviors for ETS exposure at home were 2.68 (-10.11-17.78), 10.66 (3.25-17.55), and 11.62 (3.03-18.96) in children aged 3-5, 6-11, and 12-18 years, respectively. Children with externalizing problems had higher PAF% than those with internalizing problems.

CONCLUSION

In Korea, ETS exposure at home is associated with problem behaviors in children and adolescents with about more than 10% population attributable fraction.

Calcium rises induced by AMPA and nicotine receptors in the ventral tegmental area show differences in mouse brain slices prenatally exposed to nicotine

Nicotine exposure during gestation is associated with a higher risk of adverse behavioral outcomes including a heightened liability for dependency to drugs of abuse, which can exhibit drug-specificity influenced by gender. This enhanced liability suggests that nicotine use during pregnancy alters neural development in circuits involved in motivation and reward-based learning. The ventral tegmental area (VTA) is critical in motivated behaviors and we hypothesized that gestational exposure to nicotine alters the development of excitatory circuits in this nucleus. Accordingly, in VTA brain slices from male and female mice exposed to nicotine during the prenatal period (PNE) and controls, we compared cellular rises in calcium induced by AMPA receptor and nicotinic acetylcholine receptor (nAChR) stimulation by use of the ratiometric calcium binding dye, Fura-2AM. We found that AMPA induced smaller amplitude calcium rises in the PNE VTA, which was an effect only detected in males. Further, while the amplitude did not vary between treatment and control in females, a greater number of cells responded with rises in calcium in the PNE. Conversely, the proportions of cells responding with calcium rises induced by nAChR stimulation did not change in either gender according to treatment. However, larger rises in calcium in PNE females were detected. When taken together our data show that excitatory signaling in the VTA is altered in a gender-specific manner by PNE and suggest that alterations in signaling could play a role in drug-specific differences in maladaptive, motivated behaviors exhibited by males and females born to mothers exposed to nicotine during pregnancy. © 2018 Wiley Periodicals, Inc. Develop Neurobiol 2018.

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.

Developmental toxicity of nicotine: A transdisciplinary synthesis and implications for emerging tobacco products

While the health risks associated with adult cigarette smoking have been well described, effects of nicotine exposure during periods of developmental vulnerability are often overlooked. Using MEDLINE and PubMed literature searches, books, reports and expert opinion, a transdisciplinary group of scientists reviewed human and animal research on the health effects of exposure to nicotine during pregnancy and adolescence. A synthesis of this research supports that nicotine contributes critically to adverse effects of gestational tobacco exposure, including reduced pulmonary function, auditory processing defects, impaired infant cardiorespiratory function, and may contribute to cognitive and behavioral deficits in later life. Nicotine exposure during adolescence is associated with deficits in working memory, attention, and auditory processing, as well as increased impulsivity and anxiety. Finally, recent animal studies suggest that nicotine has a priming effect that increases addiction liability for other drugs. The evidence that nicotine adversely affects fetal and adolescent development is sufficient to warrant public health measures to protect pregnant women, children, and adolescents from nicotine exposure.

Prenatal Nicotine Exposure Impairs Executive Control Signals in Medial Prefrontal Cortex

Prenatal nicotine exposure (PNE) is linked to numerous psychiatric disorders including attention deficit hyperactivity disorder (ADHD). Current literature suggests that core deficits observed in ADHD reflect abnormal inhibitory control governed by the prefrontal cortex. Yet, it is unclear how neural activity in the medial prefrontal cortex (mPFC) is modulated during tasks that assess response inhibition or if these neural correlates, along with behavior, are affected by PNE. To address this issue, we recorded from single mPFC neurons in control and PNE rats as they performed a stop-signal task. We found that PNE rats were faster for all trial-types, made more premature responses, and were less likely to inhibit behavior on 'STOP' trials during which rats had to inhibit an already initiated response. Activity in mPFC was modulated by response direction and was positively correlated with accuracy and movement time in control but not PNE rats. Although the number of single neurons correlated with response direction was significantly reduced by PNE, neural activity observed on general STOP trials was largely unaffected. However, dramatic behavioral deficits on STOP trials immediately following non-conflicting (GO) trials in the PNE group appear to be mediated by the loss of conflict monitoring signals in mPFC. We conclude that prenatal nicotine exposure makes rats impulsive and disrupts firing of mPFC neurons that carry signals related to response direction and conflict monitoring.

Prenatal drug exposures sensitize noradrenergic circuits to subsequent disruption by chlorpyrifos

We examined whether nicotine or dexamethasone, common prenatal drug exposures, sensitize the developing brain to chlorpyrifos. We gave nicotine to pregnant rats throughout gestation at a dose (3mg/kg/day) producing plasma levels typical of smokers; offspring were then given chlorpyrifos on postnatal days 1-4, at a dose (1mg/kg) that produces minimally-detectable inhibition of brain cholinesterase activity. In a parallel study, we administered dexamethasone to pregnant rats on gestational days 17-19 at a standard therapeutic dose (0.2mg/kg) used in the management of preterm labor, followed by postnatal chlorpyrifos. We evaluated cerebellar noradrenergic projections, a known target for each agent, and contrasted the effects with those in the cerebral cortex. Either drug augmented the effect of chlorpyrifos, evidenced by deficits in cerebellar β-adrenergic receptors; the receptor effects were not due to increased systemic toxicity or cholinesterase inhibition, nor to altered chlorpyrifos pharmacokinetics. Further, the deficits were not secondary adaptations to presynaptic hyperinnervation/hyperactivity, as there were significant deficits in presynaptic norepinephrine levels that would serve to augment the functional consequence of receptor deficits. The pretreatments also altered development of cerebrocortical noradrenergic circuits, but with a different overall pattern, reflecting the dissimilar developmental stages of the regions at the time of exposure. However, in each case the net effects represented a change in the developmental trajectory of noradrenergic circuits, rather than simply a continuation of an initial injury. Our results point to the ability of prenatal drug exposure to create a subpopulation with heightened vulnerability to environmental neurotoxicants.

In utero nicotine exposure epigenetically alters fetal chromatin structure and differentially regulates transcription of the glucocorticoid receptor in a rat model

BACKGROUND

Fetal exposure to nicotine is not limited to maternal tobacco smoke, as electronic cigarettes have an increased prevalence of use among reproductive aged women. Animal models have shown that nicotine exposure in utero is associated with increased risk of asthma and cognitive deficits, as well as increased expression of the hippocampal glucocorticoid receptor. We hypothesized that in utero nicotine exposure is associated with epigenetic changes in the offspring lung and brain which may contribute to a memory of this exposure

METHODS

Sprague-Dawley rat dams received either saline or 2 mg/kg of nicotine by intraperitoneal injection once daily from embryonic day 6 (e6) to e22. Pups were killed on day 1 of life, and brain and lung tissues were harvested (N = 3/ group).

RESULTS

We found that nicotine exposed offspring have altered histone modifications in the brain. Dimethylation of lysine 9 of histone H3 is decreased (0.43-fold; p = 0.03) while acetylation is increased (1.79-fold; p = 0.031). Histone deacetylase activity is significantly decreased with nicotine exposure in brain and lung (0.11-fold; p < 0.001; 0.12-fold; p < 0.001, respectively). Expression of splice variant 1.7 of the glucocorticoid receptor is reduced in the nicotine exposed offspring lung (0.25-fold; p = 0.038).

CONCLUSION

We conclude that nicotine exposure is associated with epigenetic alterations in the offspring and may lead to susceptibility to adult disease,. Our finding that in utero exposure to nicotine is associated with inhibition of histone deacetylase activity in the brain of offspring is of importance as a similar inhibition has been suggested as a mechanism for the potentiation of addiction.

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.

Is there evidence for potential harm of electronic cigarette use in pregnancy?

BACKGROUND

Use of electronic cigarettes (e-cigarettes) and other nicotine containing products is increasing among women of reproductive age. The short- and long-term effects of these products on both mother and fetus are unknown.

METHODS

Because e-cigarettes are nicotine delivery systems, we sought to conduct a comprehensive review of the effects of nicotine on the fetus.

RESULTS

In utero nicotine exposure in animal models is associated with adverse effects for the offspring lung, cardiovascular system and brain. In the lung, this included reduced surface area, weight, and volume, as well as emphysema-like lesions. In adulthood, exposed offspring demonstrate elevated blood pressure and increased perivascular adipose tissue. In the brain, exposure alters offspring serotonergic, dopaminergic, and norepinephrine networks, which in turn are associated with behavioral and cognitive impairments. We also review current data on the lack of efficacy of nicotine replacement therapy in pregnant women, and highlight different nicotine containing products such as snuff, snus, and hookah.

CONCLUSION

We conclude that no amount of nicotine is known to be safe during pregnancy, and studies specifically addressing this risk are crucial and an imminent public health issue.

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.

Maternal smoking during pregnancy and offspring conduct problems: evidence from 3 independent genetically sensitive research designs

IMPORTANCE

Several studies report an association between maternal smoking during pregnancy and offspring conduct disorder. However, past research evidences difficulty in disaggregating prenatal environmental influences from genetic and postnatal environmental influences.

OBJECTIVE

To examine the relationship between maternal smoking during pregnancy and offspring conduct problems among children reared by genetically related mothers and genetically unrelated mothers.

DESIGN, SETTING, AND PARTICIPANTS

The following 3 studies using distinct but complementary research designs were used: The Christchurch Health and Development Study (a longitudinal cohort study that includes biological and adopted children), the Early Growth and Development Study (a longitudinal adoption-at-birth study), and the Cardiff IVF (In Vitro Fertilization) Study (an adoption-at-conception study among genetically related families and genetically unrelated families). Maternal smoking during pregnancy was measured as the mean number of cigarettes per day (0, 1-9, or 10) smoked during pregnancy. Possible covariates were controlled for in the analyses, including child sex, birth weight, race/ethnicity, placement age, and breastfeeding, as well as maternal education and maternal age at birth and family breakdown, parenting practices, and family socioeconomic status.

MAIN OUTCOMES AND MEASURE

Offspring conduct problems (age range, 4-10 years) reported by parents or teachers using the behavior rating scales by Rutter and Conners, the Child Behavior Checklist and the Children's Behavior Questionnaire Short Form, and the Strengths and Difficulties Questionnaire.

RESULTS

A significant association between maternal smoking during pregnancy and offspring conduct problems was observed among children reared by genetically related mothers and genetically unrelated mothers. Results from a meta-analysis affirmed this pattern of findings across pooled study samples.

CONCLUSIONS AND RELEVANCE

Findings across 3 studies using a complement of genetically sensitive research designs suggest that smoking during pregnancy is a prenatal risk factor for offspring conduct problems when controlling for specific perinatal and postnatal confounding factors.

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.

Molecular mechanisms of maternal cannabis and cigarette use on human neurodevelopment

Prenatal development is highly sensitive to maternal drug use due to the vulnerability for disruption of the fetal brain with its ongoing neurodevelopment, resulting in lifelong consequences that can enhance risk for psychiatric disorders. Cannabis and cigarettes are the most commonly used illicit and licit substances, respectively, among pregnant women. Although the behavioral consequences of prenatal cannabis and cigarette exposure have been well-documented in epidemiological and clinical studies, only recently have investigations into the molecular mechanisms associated with the developmental impact of early drug exposure been addressed. This article reviews the literature relevant to long-term gene expression disturbances in the human fetal brain in relation to maternal cannabis and cigarette use. To provide translational insights, we discuss animal models in which protracted molecular consequences of prenatal cannabis and cigarette exposure can be better explored and which enable future evaluation of epigenetic pathways, such as DNA methylation and histone modification, that could potentially maintain abnormal gene regulation and related behavioral disturbances. Altogether, this information may help to address the current gaps of knowledge regarding the impact of early drug exposure that set in motion lifelong molecular disturbances that underlie vulnerability to psychiatric disorders.

Modulation of cell adhesion systems by prenatal nicotine exposure in limbic brain regions of adolescent female rats

Maternal smoking during pregnancy (MS) has long-lasting neurobehavioural effects on the offspring. Many MS-associated psychiatric disorders begin or change symptomatology during adolescence, a period of continuous development of the central nervous system. However, the underlying molecular mechanisms are largely unknown. Given that cell adhesion molecules (CAMs) modulate various neurotransmitter systems and are associated with many psychiatric disorders, we hypothesize that CAMs are altered by prenatal treatment of nicotine, the major psychoactive component in tobacco, in adolescent brains. Pregnant Sprague-Dawley rats were treated with nicotine (3 mg/kg.d) or saline via osmotic mini-pumps from gestational days 4 to 18. Female offspring at postnatal day 35 were sacrificed, and several limbic brain regions (the caudate putamen, nucleus accumbens, prefrontal cortex, and amygdala) were dissected for evaluation of gene expression using microarray and quantitative RT-PCR techniques. Various CAMs including neurexin, immunoglobulin, cadherin, and adhesion-GPCR superfamilies, and their intracellular signalling pathways were modified by gestational nicotine treatment (GN). Among the CAM-related pathways, GN has stronger effects on cytoskeleton reorganization pathways than on gene transcription pathways. These effects were highly region dependent, with the caudate putamen showing the greatest vulnerability. Given the important roles of CAMs in neuronal development and synaptic plasticity, our findings suggest that alteration of CAMs contributes to the neurobehavioural deficits associated with MS. Further, our study underscores that low doses of nicotine produce substantial and long-lasting changes in the brain, implying that nicotine replacement therapy during pregnancy may carry many of the same risks to the offspring as MS.

Prenatal tobacco exposure: developmental outcomes in the neonatal period

Smoking during pregnancy is a persistent public health problem that has been linked to later adverse outcomes. The neonatal period--the first month of life--carries substantial developmental change in regulatory skills and is the period when tobacco metabolites are cleared physiologically. Studies to date mostly have used cross-sectional designs that limit characterizing potential impacts of prenatal tobacco exposure on the development of key self-regulatory processes and cannot disentangle short-term withdrawal effects from residual exposure-related impacts. In this study, pregnant participants (N = 304) were recruited prospectively during pregnancy, and smoking was measured at multiple time points, with both self-report and biochemical measures. Neonatal attention, irritable reactivity, and stress dysregulation were examined longitudinally at three time points during the first month of life, and physical growth indices were measured at birth. Tobacco-exposed infants showed significantly poorer attention skills after birth, and the magnitude of the difference between exposed and nonexposed groups attenuated across the neonatal period. In contrast, exposure-related differences in irritable reactivity largely were not evident across the 1st month of life, differing marginally at 4 weeks of age only. Third-trimester smoking was associated with pervasive, deleterious, dose–response impacts on physical growth measured at birth, whereas nearly all smoking indicators throughout pregnancy predicted level and growth rates of early attention. The observed neonatal pattern is consistent with the neurobiology of tobacco on the developing nervous system and fits with developmental vulnerabilities observed later in life.

The long-term effects of prenatal nicotine exposure on neurologic development

A large body of documented evidence has found that smoking during pregnancy is harmful to both the mother and the fetus. Prenatal exposure to nicotine in various forms alters neurologic development in experimental animals and may increase the risk for neurologic conditions in humans. There is a positive association between maternal smoking and sudden infant death syndrome (SIDS); however, the connection between nicotine addiction, depression, attention disorders, and learning and behavior problems in humans is not straightforward. Nicotine's action on the production and function of neurotransmitters makes it a prime suspect in the pathology of these diseases. Nicotine accentuates neurotransmitter function in adults but desensitizes these functions in prenatally exposed infants and children. This desensitization causes an abnormal response throughout the lifespan. Furthermore, nicotine use by adolescents and adults can alleviate some of the symptoms caused by these neurotransmitter problems while they increase the risk for nicotine addiction. Although nicotine replacement drugs are used by pregnant women, there is no clear indication that they improve outcomes during pregnancy, and they may add to the damage that occurs to the developing neurologic system in the fetus. Understanding the effects of nicotine exposure is important in providing safe care for pregnant women, children, and families and for developing appropriate smoking cessation programs during pregnancy.

The effects of strain and prenatal nicotine exposure on ethanol consumption by adolescent male and female rats

Two studies of variables affecting voluntary ethanol consumption by adolescent male and female rats are reported. Sprague-Dawley (SD) and spontaneously hypertensive rats (SHRs) were compared in Experiment 1. Starting on postnatal day 30 all had 24-h access to 2%, then 4%, and then 6% ethanol, followed by 1-h access to the 6% until intake stabilized. During the 1-h access SHR females consumed more ethanol than all other groups. In Experiment 2, the same procedure was used to compare SD groups prenatally exposed to nicotine, with controls. Nicotine-exposed females consumed more ethanol during 1-h access than both nicotine-exposed and control males; but after using water intake as a covariate, the differences were not significant. These data show that deprivation conditions need to be considered when generalizing the results of voluntary consumption studies, and that estrogens may be a modulator of addictive behavior.

Respiratory dysfunctions induced by prenatal nicotine exposure

1. Maternal tobacco smoking is the principal risk factor associated with sudden infant death syndrome (SIDS), a leading cause of death of infants under 1 year of age. Victims of SIDS show a higher incidence of respiratory control abnormalities, including central apnoeas, delayed arousal responses and diminished ventilatory chemoreflexes. 2. Nicotine is likely the link between maternal tobacco smoking and SIDS. Prenatal nicotine exposure can alter the breathing pattern and can reduce hypoxia- and hypercarbia-induced ventilatory chemoreflexes. In vitro approaches have revealed that prenatal nicotine exposure impairs central chemosensitivity, switching the cholinergic contribution from a muscarinic to a nicotinic receptor-based drive. In addition, serotonergic, noradrenergic, GABAergic, glycinergic and glutamatergic, among others, are affected by prenatal nicotine. 3. Here we propose that prenatal nicotine affects the respiratory network through two main processes: (i) reorganization of neurotransmitter systems; and (ii) remodelling of neural circuits. These changes make breathing more vulnerable to fail in early postnatal life, which could be related to the pathogenesis of SIDS.

Sexual function in adult male rats after prenatal modulation of the cholinergic system

Prenatal administration of the n-cholinolytic ganglerone to pregnant female rats at different periods of gestation was found to lead to long-term changes in sexual behavior in pubescent offspring: there was a reduced dynamic of acquiring sexual experience and a very low level of sexual activity, with significant impairment to the motivational and ejaculatory components of sexual behavior. The number of males with reduced sexual activity in the experimental groups was significantly greater than that in control offspring. The results obtained here provide evidence that impairments of sexual function in adult offspring induced by prenatal administration of the n-cholinolytic ganglerone at 9-11 and 12-14 days of gestation and, to a lesser extent, the m-cholinolytic metamyzil at 9-11 days of gestation, were due to impairment to the central mechanisms regulating sexual function due to stable changes in neurotransmitter activity in the hippocampus and hypothalamus, along with a significant reduction in the blood testosterone level.

If nicotine is a developmental neurotoxicant in animal studies, dare we recommend nicotine replacement therapy in pregnant women and adolescents?

Tobacco use in pregnancy is a leading cause of perinatal morbidity and contributes in major ways to attention deficit hyperactivity disorder, conduct disorders and learning disabilities that emerge in childhood and adolescence. Over the past two decades, animal models of prenatal nicotine exposure have demonstrated that nicotine is a neurobehavioral teratogen that disrupts brain development by preempting the natural, neurotrophic roles of acetylcholine. Through its actions on nicotinic cholinergic receptors, nicotine elicits abnormalities of neural cell proliferation and differentiation, promotes apoptosis and produces deficits in the number of neural cells and in synaptic function. The effects eventually compromise multiple neurotransmitter systems because of the widespread regulatory role of cholinergic neurotransmission. Importantly, the long-term alterations include effects on reward systems that reinforce the subsequent susceptibility to nicotine addiction in later life. These considerations strongly question the appropriateness of nicotine replacement therapy (NRT) for smoking cessation in pregnant women, especially as the pharmacokinetics of the transdermal patch may actually enhance fetal nicotine exposure. Further, because brain maturation continues into adolescence, the period when smoking typically commences, adolescence is also a vulnerable period in which nicotine can change the trajectory of neurodevelopment. There are also serious questions as to whether NRT is actually effective as an aid to smoking cessation in pregnant women and adolescents. This review considers the ramifications of the basic science findings of nicotine's effects on brain development for NRT in these populations.

Hot and cool forms of inhibitory control and externalizing behavior in children of mothers who smoked during pregnancy: an exploratory study

This study examined whether children exposed to prenatal smoking show deficits in “hot” and/or “cool” executive functioning (EF). Hot EF is involved in regulation of affect and motivation, whereas cool EF is involved in handling abstract, decontextualized problems. Forty 7 to 9-year-old children (15 exposed to prenatal smoking, 25 non-exposed) performed two computerized tasks. The Sustained Attention Dots (SA-Dots) Task (as a measure of “cool” inhibitory control) requires 400 non-dominant hand and 200 dominant hand responses. Inhibitory control of the prepotent response is required for dominant hand responses. The Delay Frustration Task (DeFT) (as a measure of “hot” inhibitory control) consists of 55 simple maths exercises. On a number of trials delays are introduced before the next question appears on the screen. The extent of response-button pressing during delays indicates frustration-induced inhibitory control. Prenatally exposed children showed poorer inhibitory control in the DeFT than non-exposed children. A dose–response relationship was also observed. In addition, prenatally exposed children had significantly higher (dose-dependent) conduct problem- and hyperactivity-inattention scores. There were no significant group differences in inhibitory control scores from the SA-Dots. These results indicate that children exposed to prenatal smoking are at higher risk of hot but not cool executive function deficits.

Separate or sequential exposure to nicotine prenatally and in adulthood: Persistent effects on acetylcholine systems in rat brain regions

Nicotine is a developmental neurotoxicant but the proposed "sensitization-homeostasis" model postulates that even in adulthood nicotine permanently reprograms synaptic function. We administered nicotine to rats throughout gestation or in adulthood (postnatal days PN90-107), simulating plasma levels in smokers, with evaluations on PN105, PN110, PN120, PN130 and PN180. We assessed nicotinic acetylcholine receptor (nAChR) binding, choline acetyltransferase activity, a marker for acetylcholine (ACh) terminals, and hemicholinium-3 (HC3) binding to the choline transporter, an index of ACh presynaptic activity. Prenatal nicotine exposure elicited persistent deficits in HC3 binding in male cerebral cortex and female striatum, but little change in other parameters. Nicotine given in adulthood produced profound nAChR upregulation lasting 2 weeks after discontinuing treatment. Decrements in cerebrocortical and striatal HC3 binding emerged during withdrawal and persisted through PN180, indicative of reduced ACh synaptic activity. Prenatal nicotine did not evoke any major alterations in the response to nicotine given in adulthood. The effects seen here are substantially different from those found previously for nicotine given to adolescent rats, which showed more prolonged nAChR upregulation and profound, widespread and persistent deficits in markers of ACh synaptic function; for adolescents, prenatal nicotine exposure desensitized nAChR responses, exacerbated withdrawal-induced ACh functional deficits, and worsened the long-term outcome. Our results indicate that the effects of nicotine during prenatal or adolescent stages are indeed distinct from the effects in adults, but that even adults show persistent changes after nicotine exposure, commensurate with the sensitization-homeostasis model. These effects may contribute to lifelong vulnerability to readdiction.

Environmental risk factors for attention-deficit hyperactivity disorder

Attention-deficit hyperactivity disorder (ADHD) is the most common cognitive and behavioural disorder diagnosed among school children. It is characterized by deficient attention and problem solving, along with hyperactivity and difficulty withholding incorrect responses. This highly prevalent disorder is estimated to affect 5-10% of children and in many cases, persists into adulthood, leading to 4% prevalence among adults. Converging evidence from epidemiologic, neuropsychology, neuroimaging, genetic and treatment studies shows that ADHD is a valid medical disorder. The majority of studies performed to assess genetic risk factors in ADHD have supported a strong familial nature of this disorder. Family studies have identified a 2- to 8-fold increase in the risk for ADHD in parents and siblings of children with ADHD. Various twin and adoption studies have also highlighted the highly genetic nature of ADHD. In fact the mean heritability of ADHD was shown to be 0.77, which is comparable to other neuropsychiatric disorders such as schizophrenia or bipolar disorder. However, several biological and environmental factors have also been proposed as risk factors for ADHD, including food additives/diet, lead contamination, cigarette and alcohol exposure, maternal smoking during pregnancy, and low birth weight. Many recent studies have specifically examined the relationships between ADHD and these extraneous factors. This review describes some of these possible risk factors.

CONCLUSION

Although a substantial fraction of the aetiology of ADHD is due to genes, the studies reviewed in this article show that many environmental risk factors and potential gene-environment interactions also increase the risk for the disorder.

Permanent, sex-selective effects of prenatal or adolescent nicotine exposure, separately or sequentially, in rat brain regions: indices of cholinergic and serotonergic synaptic function, cell signaling, and neural cell number and size at 6 months of age

Nicotine is a neuroteratogen that disrupts neurodevelopment and synaptic function, with vulnerability extending into adolescence. We assessed the permanence of effects in rats on indices of neural cell number and size, and on acetylcholine and serotonin (5HT) systems, conducting assessments at 6 months of age, after prenatal nicotine exposure, adolescent exposure, or sequential exposure in both periods. For prenatal nicotine, indices of cell number and size showed few abnormalities by 6 months, but there were persistent deficits in cerebrocortical choline acetyltransferase activity and hemicholinium-3 binding to the presynaptic choline transporter, a pattern consistent with cholinergic hypoactivity; these effects were more prominent in males than females. The expression of 5HT receptors also showed permanent effects in males, with suppression of the 5HT(1A) subtype and upregulation of 5HT(2) receptors. In addition, cell signaling through adenylyl cyclase showed heterologous uncoupling of neurotransmitter responses. Nicotine exposure in adolescence produced lasting effects that were similar to those of prenatal nicotine. However, when animals were exposed to prenatal nicotine and received nicotine subsequently in adolescence, the adverse effects then extended to females, whereas the net effect in males was similar to that of prenatal nicotine by itself. Our results indicate that prenatal or adolescent nicotine exposure evoke permanent changes in synaptic function that transcend the recovery of less-sensitive indices of structural damage; further, prenatal exposure sensitizes females to the subsequent adverse effects of adolescent nicotine, thus creating a population that may be especially vulnerable to the lasting behavioral consequences of nicotine intake in adolescence.

Perinatal nicotine exposure eliminates peak in nicotinic acetylcholine receptor response in adolescent rats

Maternal smoking is a risk factor associated with nicotine abuse, so the effect of perinatal nicotine exposure was studied on the responsiveness to nicotine across adolescence in the rat. Pregnant Sprague-Dawley rats were implanted with s.c. Alzet osmotic minipumps delivering nicotine (L-nicotine hydrogen tartrate, 2 mg/kg/day free base) or vehicle (0.9% saline) on gestational day 7. There was no effect of nicotine on dam weight gain, food consumption, or water consumption or on the number of live pups or weights at the time of birth. Pups were cross-fostered to obtain the following prenatal/postnatal exposure groups: control/control, nicotine/nicotine, nicotine/control, and control/nicotine. On postnatal days 28, 35, 49, and 63, nicotine-stimulated (86)Rb(+) efflux was measured in synaptosomes prepared from the frontal cortex, hippocampus, striatum (STR), and thalamus (THL), using a previously developed method. Significant effects of treatment and concentration were detected in all four brain regions, and significant effects of age were observed in the STR and THL. Significant interactions of age and treatment were observed in each of the four brain regions. Nicotine-stimulated (86)Rb(+) efflux peaked during adolescence in control rats. However, perinatal exposure to nicotine eliminated this peak during adolescence. These results are consistent with recent behavioral and receptor binding results from other laboratories and are the first direct evidence at the cellular level that the nicotinic acetylcholine receptor response varies during adolescence and is affected by perinatal nicotine exposure.

Prenatal nicotine exposure alters the responses to subsequent nicotine administration and withdrawal in adolescence: Serotonin receptors and cell signaling

Offspring of women who smoke during pregnancy are themselves more likely to take up smoking in adolescence, effects that are associated with a high rate of depression and increased sensitivity to withdrawal symptoms. To evaluate the biological basis for this relationship, we assessed effects on serotonin (5-hydroxytryptamine, 5HT) receptors and 5HT-mediated cellular responses in rats exposed to nicotine throughout prenatal development and then given nicotine in adolescence (postnatal days PN30-47.5), using regimens that reproduce plasma nicotine levels found in smokers. Evaluations were then made during the period of adolescent nicotine treatment and for up to one month after the end of treatment. Prenatal nicotine exposure, which elicits damage to 5HT projections in the cerebral cortex and striatum, produced sex-selective changes in the expression of 5HT(1A) and 5HT2 receptors, along with induction of adenylyl cyclase (AC), leading to sensitization of heterologous inputs operating through this signaling pathway. Superimposed on these effects, the AC response to 5HT was shifted toward inhibition. By itself, adolescent nicotine administration, which damages the same pathways, produced similar effects on receptors and the 5HT-mediated response, but a smaller overall induction of AC. Animals exposed to prenatal nicotine showed a reduced response to nicotine administered in adolescence, results in keeping with earlier findings of persistent desensitization. Our results indicate that prenatal nicotine exposure alters parameters of 5HT synaptic communication lasting into adolescence and changes the response to nicotine administration and withdrawal in adolescence, actions which may contribute to a subpopulation especially vulnerable to nicotine dependence.

Visuospatial memory deficits emerging during nicotine withdrawal in adolescents with prenatal exposure to active maternal smoking

Active maternal smoking during pregnancy elevates the risk of cognitive deficits and tobacco smoking among offspring. Preclinical work has shown that combined prenatal and adolescent exposure to nicotine produces more pronounced hippocampal changes and greater deficits in cholinergic activity upon nicotine withdrawal than does prenatal or adolescent exposure to nicotine alone. Few prior studies have examined the potential modifying effects of gestational exposure to active maternal smoking on cognitive or brain functional response to tobacco smoking or nicotine withdrawal in adolescents. We examined visuospatial and verbal memory in 35 adolescent tobacco smokers with prenatal exposure to active maternal smoking and 26 adolescent tobacco smokers with no prenatal exposure to maternal smoking who were similar in age, educational attainment, general intelligence, and baseline plasma cotinine. Subjects were studied during ad libitum smoking and after 24 h of abstinence from smoking. A subset of subjects from each group also underwent functional magnetic resonance imaging while performing a visuospatial encoding and recognition task. Adolescent tobacco smokers with prenatal exposure experienced greater nicotine withdrawal-related deficits in immediate and delayed visuospatial memory relative to adolescent smokers with no prenatal exposure. Among adolescent smokers with prenatal exposure, nicotine withdrawal was associated with increased activation of left parahippocampal gyrus during early recognition testing of visuospatial stimuli and increased activation of bilateral hippocampus during delayed recognition testing of visuospatial stimuli. These findings extend prior preclinical work and suggest that, in human adolescent tobacco smokers, prenatal exposure to active maternal smoking is associated with alterations in medial temporal lobe function and concomitant deficits in visuospatial memory.

alpha7 Nicotinic acetylcholine receptors and temporal memory: synergistic effects of combining prenatal choline and nicotine on reinforcement-induced resetting of an interval clock

We previously showed that prenatal choline supplementation could increase the precision of timing and temporal memory and facilitate simultaneous temporal processing in mature and aged rats. In the present study, we investigated the ability of adult rats to selectively control the reinforcement-induced resetting of an internal clock as a function of prenatal drug treatments designed to affect the alpha7 nicotinic acetylcholine receptor (alpha7 nAChR). Male Sprague-Dawley rats were exposed to prenatal choline (CHO), nicotine (NIC), methyllycaconitine (MLA), choline + nicotine (CHO + NIC), choline + nicotine + methyllycaconitine (CHO + NIC + MLA), or a control treatment (CON). Beginning at 4-mo-of-age, rats were trained on a peak-interval timing procedure in which food was available at 10-, 30-, and 90-sec criterion durations. At steady-state performance there were no differences in timing accuracy, precision, or resetting among the CON, MLA, and CHO + NIC + MLA treatments. It was observed that the CHO and NIC treatments produced a small, but significant increase in timing precision, but no change in accuracy or resetting. In contrast, the CHO + NIC prenatal treatment produced a dramatic increase in timing precision and selective control of the resetting mechanism with no change in overall timing accuracy. The synergistic effect of combining prenatal CHO and NIC treatments suggests an organizational change in alpha7 nAChR function that is dependent upon a combination of selective and nonselective nAChR stimulation during early development.

Alpha7 nicotinic acetylcholine receptors targeted by cholinergic developmental neurotoxicants: nicotine and chlorpyrifos

Alpha7 nicotinic acetylcholine receptors (nAChRs) play a role in axonogenesis, synaptogenesis and synaptic plasticity, and are therefore potential targets for developmental neurotoxicants. We administered nicotine to neonatal rats during discrete periods spanning the onset and peak of axonogenesis/synaptogenesis, focusing on three brain regions with disparate distributions of cell bodies and neural projections: brainstem, forebrain and cerebellum. Nicotine treatment on postnatal days (PN) 1-4 had little or no effect on alpha7 nAChRs but treatment during the second (PN11-14) or third (PN21-24) weeks elicited significant decrements in receptor expression in brainstem and cerebellum, regions containing cell bodies that project to the forebrain. Exposure to chlorpyrifos, a neurotoxicant pesticide that acts partially through cholinergic mechanisms, also elicited deficits in alpha7 nAChRs during the second postnatal week but not the first week. For both nicotine and chlorpyrifos, the effects on alpha7 nAChRs were distinct from those on the alpha4beta2 subtype. Continuous prenatal nicotine exposure, which elicits subsequent, postnatal deficits in axonogenesis and synaptogenesis, also produced delayed-onset changes in alpha7 nAChRs, characterized by reductions in the forebrain and upregulation in the brainstem and cerebellum, a pattern consistent with impaired axonogenesis/synaptogenesis and reactive sprouting. Males were more sensitive to the persistent effects of prenatal nicotine exposure on alpha7 nAChRs, a pattern that mimics neurobehavioral deficits resulting from this treatment. The present findings reinforce the mechanistic involvement of alpha7 nAChRs in the actions of developmental neurotoxicants, and its biomarker potential for neuroteratogens that target neuritic outgrowth.

Dampened ventilatory response to added dead space in newborns of smoking mothers

BACKGROUND

Term newborns can compensate fully for an imposed dead space (tube breathing) by increasing their minute ventilation.

OBJECTIVE

To test the hypothesis that infants of smoking mothers would have an impaired response to tube breathing.

DESIGN

Prospective study.

SETTING

Perinatal service.

PATIENTS

Fourteen infants of smoking and 24 infants of non-smoking mothers (median postnatal age 37 (11-85) hours and 26 (10-120) hours respectively) were studied.

INTERVENTIONS

Breath by breath minute volume was measured at baseline and when a dead space of 4.4 ml/kg was incorporated into the breathing circuit.

MAIN OUTCOME MEASURES

The maximum minute ventilation during tube breathing was determined and the time constant of the response calculated.

RESULTS

The time constant of the infants of smoking mothers was longer than that of the infants of non-smoking mothers (median (range) 37.3 (22.2-70.2) v 26.2 (13.8-51.0) seconds, p = 0.016). Regression analysis showed that maternal smoking status was related to the time constant independently of birth weight, gestational or postnatal age, or sex (p = 0.018).

CONCLUSIONS

Intrauterine exposure to smoking is associated with a dampened response to tube breathing.

Cholinergic systems in brain development and disruption by neurotoxicants: nicotine, environmental tobacco smoke, organophosphates

Acetylcholine and other neurotransmitters play unique trophic roles in brain development. Accordingly, drugs and environmental toxicants that promote or interfere with neurotransmitter function evoke neurodevelopmental abnormalities by disrupting the timing or intensity of neurotrophic actions. The current review discusses three exposure scenarios involving acetylcholine systems: nicotine from maternal smoking during pregnancy, exposure to environmental tobacco smoke (ETS), and exposure to the organophosphate insecticide, chlorpyrifos (CPF). All three have long-term, adverse effects on specific processes involved in brain cell replication and differentiation, synaptic development and function, and ultimately behavioral performance. Many of these effects can be traced to the sequence of cellular events surrounding the trophic role of acetylcholine acting on its specific cellular receptors and associated signaling cascades. However, for chlorpyrifos, additional noncholinergic mechanisms appear to be critical in establishing the period of developmental vulnerability, the sites and type of neural damage, and the eventual outcome. New findings indicate that developmental neurotoxicity extends to late phases of brain maturation including adolescence. Novel in vitro and in vivo exposure models are being developed to uncover heretofore unsuspected mechanisms and targets for developmental neurotoxicants.

Prenatal nicotine exposure alters the response to nicotine administration in adolescence: effects on cholinergic systems during exposure and withdrawal

Maternal smoking during pregnancy increases the likelihood that the offspring will become smokers in adolescence. In the current study, we evaluated effects of prenatal and adolescent nicotine exposure in rats to assess whether there is a biological basis for this relationship. Pregnant rats were given nicotine or vehicle throughout pregnancy and the offspring then again received nicotine or vehicle during adolescence (postnatal days PN30-47.5), using a regimen (6 mg/kg/day by subcutaneous infusion) that produces plasma nicotine levels similar to those in smokers. Evaluations were made in the cerebral cortex and midbrain during adolescent nicotine administration (PN45) and for up to 1 month after the end of treatment. We assessed the magnitude and persistence of nicotinic acetylcholine receptor (nAChR) upregulation; in addition, we evaluated cholinergic synaptic activity by comparing the effects on choline acetyltransferase (ChAT), a constitutive marker for cholinergic nerve terminals, with those on hemicholinium-3 (HC-3) binding to the presynaptic choline transporter, which is regulated by nerve impulse activity. Prenatal nicotine exposure had only minor effects on nAChRs but produced persistent cholinergic hypoactivity (reduced HC-3 binding relative to ChAT) throughout adolescence and into adulthood (PN75). Adolescent nicotine exposure evoked robust nAChR upregulation and also suppressed cholinergic activity. Prenatal nicotine exposure reduced the upregulation of nAChRs evoked by adolescent nicotine but worsened the cholinergic hypoactivity during withdrawal. Our results indicate that prenatal nicotine exposure alters the subsequent response to nicotine in adolescence, effects that may contribute to the association between maternal smoking during pregnancy and subsequent adolescent smoking in the offspring.

Heroin neuroteratogenicity: delayed-onset deficits in catecholaminergic synaptic activity

Prenatal heroin exposure evokes neurochemical and behavioral deficits that, in part, reflect disruption of septohippocampal cholinergic function. In earlier studies, we found that cholinergic synaptic defects involve primary changes in cell signaling proteins that are shared by other transmitter systems. In the current study, we determined whether heroin also targets noradrenergic and dopaminergic inputs that operate through the same signaling cascades. Mice exposed to prenatal heroin showed significant deficits in norepinephrine and dopamine levels and much more pronounced effects on neurotransmitter turnover, an index of synaptic activity. Adverse effects were not present in the immediate postnatal period but rather emerged just before weaning and worsened subsequently. By young adulthood, the most highly-affected regions (hippocampus, cerebral cortex) displayed almost complete inactivation of noradrenergic and dopaminergic tonic activity. These effects arise after prior deficits in cell signaling are discernible, suggesting that the presynaptic effects are secondary to actions on signal transduction cascades shared by numerous neurotransmitter inputs and targeted by other neuroteratogens. These results may explain why apparently unrelated developmental neurotoxicants may ultimately produce a common set of neurochemical and behavioral anomalies.

Functional alterations in CNS catecholamine systems in adolescence and adulthood after neonatal chlorpyrifos exposure

Chlorpyrifos (CPF), one of the most widely used pesticides, is a neurobehavioral teratogen in animals. We administered CPF to neonatal rats on postnatal days (PN) 1-4 (1 mg/kg) or PN11-14 (5 mg/kg), regimens devoid of overt systemic toxicity. We then examined the impact on catecholaminergic systems in adolescence (PN30) and adulthood (PN60), assessing basal neurotransmitter content and transmitter utilization rates (turnover) in brain regions comprising the major noradrenergic and dopaminergic projections. Although CPF had only sporadic effects on basal norepinephrine and dopamine content, it profoundly suppressed norepinephrine turnover across multiple regions, indicative of net reductions in presynaptic activity. Dopamine turnover showed less consistent effects, with subnormal turnover in some regions and activation in others. We also evaluated whether CPF exposure altered the ability of catecholamine systems to respond to acute cholinergic stimulation, elicited by administration of a single challenge dose of nicotine. In the normal brain, nicotine increases the utilization of norepinephrine and dopamine. With only a few exceptions, animals receiving neonatal CPF exposure showed lasting desensitization of the nicotine response; not only was the activation by nicotine blunted in the CPF group, but in some regions the nicotine response was reversed, eliciting a reduction in transmitter turnover. These results indicate that neonatal CPF exposure produces widespread deficiencies in catecholaminergic synaptic function that persist into adulthood, and that are best revealed by dynamic measures of synaptic activity and responsiveness, as opposed to static markers like basal transmitter levels. The effects seen here are likely to contribute to alterations in behavioral performance that persist or emerge long after the termination of CPF exposure.

Prenatal nicotine exposure evokes alterations of cell structure in hippocampus and somatosensory cortex

Offspring of women who smoke during pregnancy show behavioral abnormalities, including increased incidence of attentional deficit, learning disabilities, and cognitive dysfunction. Animal models indicate that nicotine elicits changes in neural cell replication and differentiation, leading to deficits in synaptic neurochemistry and behavioral performance, many of which first emerge at adolescence. We evaluated cellular morphology and regional architecture in the juvenile and adolescent hippocampus and the somatosensory cortex in rats exposed to nicotine prenatally. Pregnant rats were given nicotine throughout gestation via minipump infusion of 2 mg/kg/day, a regimen that elicits nicotine plasma levels comparable with those found in smokers. On postnatal days 21 and 30, brains were perfusion-fixed, coronal slices were taken between the anterior commissure and median eminence, and the morphology of the dorsal hippocampus and somatosensory cortex was characterized. In the hippocampal CA3 region and dentate gyrus, we found a substantial decrease in cell size, with corresponding decrements in cell layer thickness, and increments in cell packing density. Smaller, transient changes were seen in CA1. In layer 5 of the somatosensory cortex, although there was no significant decrement in the average cell size, there was a reduction in the proportion of medium-sized pyramidal neurons, and an increase in the proportion of smaller, nonpyramidal cells. All regions showed elevated numbers of glia. Taken together with previous work on neurochemical and functional defects, these data demonstrate that prenatal nicotine exposure compromises neuronal maturation, leading to long-lasting alterations in the structure of key brain regions involved in cognition, learning, and memory.

Prenatal nicotine exposure alters pulmonary function in newborn rhesus monkeys

Epidemiological studies have shown that offspring of women who smoke during pregnancy have abnormal lung function and associated higher incidences of lower respiratory disorders. The recent identification of nicotinic acetylcholine receptors (nAChR) in fetal lung suggests that the direct interaction between nicotine and nAChR in fetal lung may underlie the postnatal pulmonary abnormalities seen in such infants. This hypothesis was tested in monkeys to determine if maternal nicotine exposure would produce changes in lung mechanics in newborn monkeys similar to those observed in human infants whose mothers smoked during pregnancy. Timed pregnant rhesus monkeys were infused with either nicotine (1.5 mg/kg/d, n = 7) or saline (n = 7) using subcutaneous osmotic pumps from Day 26 to 160 of gestation. On Day 160 of pregnancy (term = 165 d), fetuses were delivered by C-section, and the following day were subjected to pulmonary function testing. After testing, animals were sacrificed, and lungs weighed and fixed. Lung weight and fixed lung volume decreased (16% and 14%, respectively) significantly following in utero nicotine exposure. Peak tidal expiratory flow, FEV(0.2), mean mid-expiratory flow, forced expiratory volume at peak expiratory flow (FEV(PEF)), and FEV(PEF)/FVC% were significantly lower in newborns exposed to nicotine during gestation. Absolute and specific pulmonary resistance increased significantly whereas absolute and specific dynamic compliance remained unchanged in prenatally nicotine-treated pups. These changes in pulmonary function are strikingly similar to the changes observed in offspring of human smokers. This suggests that the interaction of nicotine with nAChR in developing lung is responsible for the altered pulmonary mechanics observed in human infants whose mothers smoked during pregnancy.

Risks and benefits of nicotine to aid smoking cessation in pregnancy

Cigarette smoking during pregnancy is the single largest modifiable risk for pregnancy-related morbidity and mortality in the US. Addiction to nicotine prevents many pregnant women who wish to quit smoking from doing so. The safety and efficacy of nicotine replacement therapy (NRT) for smoking cessation during pregnancy have not been well studied. Nicotine is classified by the US Food and Drug Administration as a Pregnancy Category D drug. Animal studies indicate that nicotine adversely affects the developing fetal CNS, and nicotine effects on the brain may be involved in the pathophysiology of sudden infant death syndrome (SIDS). It has been assumed that the cardiovascular effects of nicotine resulting in reduced blood flow to the placenta (uteroplacental insufficiency) is the predominant mechanism of the reproductive toxicity of cigarette smoking during pregnancy. Short term high doses of nicotine in pregnant animals do adversely affect the maternal and fetal cardiovascular systems. However, studies of the acute effects of NRT in pregnant humans indicate that nicotine alone has minimal effects upon the maternal and fetal cardiovascular systems. Cigarette smoking delivers thousands of chemicals, some of which are well documented reproductive toxins (e.g. carbon monoxide and lead). A myriad of cellular and molecular biological abnormalities have been documented in placentas, fetuses, and newborns of pregnant women who smoke. The cumulative abnormalities produced by the various toxins in cigarette smoke are probably responsible for the numerous adverse reproductive outcomes associated with smoking. It is doubtful that the reproductive toxicity of cigarette smoking is primarily related to nicotine. We recommend the following. Efficacy trials of NRT as adjunctive therapy for smoking cessation during pregnancy should be conducted. The initial dose of nicotine in NRT should be similar to the dose of nicotine that the pregnant woman received from smoking. Intermittent-use formulations of NRT (gum, spray, inhaler) are preferred because the total dose of nicotine delivered to the fetus will be less than with continuous-use formulations (transdermal patch). A national registry for NRT use during pregnancy should be created to prospectively collect obstetrical outcome data from NRT efficacy trials and from individual use. The goal of this registry would be to determine the safety of NRT use during pregnancy, especially with respect to uncommon outcomes such as placental abruption. Finally, our review of the data indicate that minimal amounts of nicotine are excreted into breast milk and that NRT can be safely used by breast-feeding mothers.

Prenatal tobacco effects on neuropsychological outcomes among preadolescents

This study evaluated the relationships between maternal smoking during pregnancy and 10-year-old children's performance on measures of learning, memory, and problem-solving. In this prospective cohort study, mothers were recruited from an urban prenatal clinic in 1982 and 1983 and observed from their fourth prenatal month until the time of the study. At the 10-year visit, 593 children and mothers were evaluated. The prevalence of tobacco use was high in this cohort: 54.3%, 53.3%, and 60% of the women smoked in the first trimester, third trimester, and 10-year assessment, respectively. After controlling statistically for other prenatal substance use, current tobacco, other substance use variables, and multiple sociodemographic covariates, prenatal tobacco exposure was significantly associated with deficits in learning and memory. Specifically, prenatal tobacco exposure was associated with deficits in verbal learning and design memory, as well as slowed responding on a test of eye-hand coordination. In addition, these children demonstrated a reduced ability for flexible problem solving and more impulsivity, as indicated by an increase in perseverative responses on a card-sorting test. Prenatally exposed children did not show attention deficits or increased activity on a continuous performance test.

Behavioral and neural consequences of prenatal exposure to nicotine

OBJECTIVE

To review evidence for the neurodevelopmental effects of in utero exposure to nicotine. Concerns about long-term cognitive and behavioral effects of prenatal exposure to nicotine arise from reports of increased rates of disruptive behavioral disorders in children whose mothers smoked during pregnancy. The relatively high rate of tobacco smoking among pregnant women (25% of all pregnancies in the U.S.) underlines the seriousness of these concerns.

METHOD

This review examines the largest and most recent epidemiological and clinical studies that investigated the association of prenatal nicotine exposure with health, behavioral, and cognitive problems. Because of the numerous potential confounding variables in human research, findings from animal studies, in which environmental factors are strictly controlled, are also discussed. Finally, neural and molecular mechanisms that are likely to underlie neurodevelopmental disruptions produced by prenatal nicotine exposure are outlined.

RESULTS

A dose-response relationship between maternal smoking rates and low birth weight (potentially associated with lower cognitive ability) and spontaneous abortion is consistently found, whereas long-term developmental and behavioral effects in the offspring are still controversial, perhaps because of the difficulty of separating them from other genetic and environmental factors. Despite the wide variability of experimental paradigms used in animal studies, common physical and behavioral effects of prenatal exposure to nicotine have been observed, including low birth weight, enhanced locomotor activity, and cognitive impairment. Finally, disturbances in neuronal pathfinding, abnormalities in cell proliferation and differentiation, and disruptions in the development of the cholinergic and catecholaminergic systems all have been reported in molecular animal studies of in utero exposure to nicotine.

CONCLUSIONS

Prenatal exposure to nicotine may lead to dysregulation in neurodevelopment and can indicate higher risk for psychiatric problems, including substance abuse. Knowledge of prenatal exposure to nicotine should prompt child psychiatrists to closely monitor at-risk patients.

Adolescent nicotine exposure produces immediate and long-term changes in CNS noradrenergic and dopaminergic function

Animal studies have only recently begun to address whether nicotine evokes unique or persistent effects on brain structure or function during adolescence, the period in which smokers typically begin their habit. In the current study, we examined the impact of adolescent nicotine treatment on catecholaminergic synaptic function in rats infused with nicotine on postnatal days 30-47.5, using a paradigm that reproduces the plasma levels of nicotine found in smokers. We assessed norepinephrine and dopamine content, turnover (an index of neural activity), and the response to an acute challenge dose of nicotine. In the midbrain, the region most closely associated with addiction, both norepinephrine and dopamine turnover were activated during the infusion period, an effect not seen in any other region for norepinephrine, and only in the striatum for dopamine. In the immediate post-infusion period (PN50-60), there was a decrement in midbrain catecholamine turnover restricted to males, whereas there was a later-emerging (PN80) activation of these pathways. Again, this pattern was not observed in any other region: the cerebral cortex showed post-treatment increases in turnover without gender selectivity, the striatum showed late-emerging deficits in dopamine turnover and the hippocampus displayed a profound deficit in noradrenergic activity that was limited to females. We also assessed the catecholaminergic response to an acute challenge with nicotine (0.3 mg/kg s.c.). The midbrain once more displayed unique properties; there was initial suppression of responses followed by post-treatment rebound elevations that were more prominent in males and eventual deficits that, in the case of dopamine, were selective for males. With the exception of the cerebellum, other regions showed the initial loss of response during the infusion period but no persistent changes in responsiveness. The current results indicate that adolescent nicotine produces immediate and long-term changes in CNS catecholaminergic systems, with regional targeting and gender selectivity corresponding to the changes seen previously in nicotinic receptor upregulation or indices of cell damage. These effects may underlie long-term behavioral changes associated with adolescent nicotine exposure.

Contribution of maternal smoking during pregnancy and lead exposure to early child behavior problems

Maternal smoking during pregnancy elevates risk for later child behavior problems. Because prior studies considered only Western settings, where smoking co-occurs with social disadvantage, we examined this association in Yugoslavia, a different cultural setting. Mothers enrolled in pregnancy as the low-exposure group in a prospective study of lead exposure were interviewed about health, including smoking history. A total of 199 children were assessed on the Child Behavior Checklist (CBCL) at ages 4, 4 1/2, and 5 years. Average cumulative blood lead (BPb) was determined from serial samples taken biannually since delivery. Longitudinal analyses were derived from 191 children with available data on behavior and covariates. Smoking was unrelated to social adversity. Controlling for age, gender, birthweight, ethnicity, maternal education, and Home Observation for Measurement of the Environment (HOME) Acceptance, smoking was associated with worse scores on almost all subscales; BPb concentration was related to small increases in the Delinquency subscale. Daughters of smokers received significantly higher scores on Somatic Complaints compared to daughters of nonsmokers, consistent with other work relating biological factors and internalizing problems in young girls. Because the present smoking/child behavior associations persist after control for individual and social factors also related to behavior problems, possible biological mediators are considered.