Prenatal nicotine exposure affects the development of the central serotonergic system as well as the dopaminergic system in rat offspring: involvement of route of drug administrations

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.

Early Health Risk Factors for Violence: Conceptualization, Review of the Evidence, and Implications

Violence and aggression are public health problems that can benefit from ongoing research into risk reduction and prevention. Current developmental theories of violence and aggression emphasize biological and psychosocial factors, particularly during adolescence. However, there has been less focus on understanding the interactive, multiplicative effects of these processes. Furthermore, little attention has been given to the pre-, peri-, and postnatal periods, where prevention and intervention may yield effective results. Early health risk factors that influence negative behavioral outcomes include prenatal and postnatal nutrition, tobacco use during pregnancy, maternal depression, birth complications, traumatic brain injury, lead exposure, and child abuse. There is an ample literature to suggest that these early health risk factors may increase the likelihood of childhood externalizing behaviors, aggression, juvenile delinquency, adult criminal behavior, and/or violence. This paper proposes an early health risk factors framework for violence prediction, built on existing developmental theories of criminal behavior and supported by empirical findings. This framework addresses gaps in the adolescent psychopathology literature and presents a novel conceptualization of behavioral disturbance that emphasizes the pre-, peri-, and post-natal periods, when a child's development is critical and the opportunity for behavioral and environmental modification is high. Implications for such a framework on violence prevention programs are discussed.

Childhood obesity and parental smoking as risk factors for childhood ADHD in Liverpool children

ADHD prevalence has risen in parallel with rising prevalence of pregnancy smoking and childhood obesity. The objective was to determine the epidemiological association of pregnancy smoking and childhood obesity with ADHD. A cross-sectional community study was conducted in 2006 using a parental questionnaire. A total of 1,074 schoolchildren aged 5-11 years were enrolled from 15 primary schools in a lower socio-economic area of Merseyside. ADHD was defined by the question "does your child have Attention Deficit Hyperactivity Disorder, (ADHD), which has been diagnosed by a doctor?" The prevalence estimates for childhood obesity, maternal smoking during pregnancy and childhood ADHD were 14.9% (116/777), 28.0% (269/955), and 3.4% (32/945), respectively. ADHD prevalence increased fivefold in children with obesity (RR, 4.80, 95% CI 2.2-10.4, P < 0.001) and more than twofold in children of mothers who smoked during pregnancy (RR, 2.44, 95% CI 1.2-4.9, P = 0.02). Regression analysis adjusting for obesity, overweight, maternal smoking during pregnancy, heavy maternal smoking, household member smoking during pregnancy, doctor-diagnosed asthma, preterm birth, and low birthweight showed significant independent associations of ADHD prevalence with obesity (AOR, 4.66, 95% CI 1.57-13.89, P = 0.006) and pregnancy smoking (AOR, 3.19, 95% CI 1.08-9.49, P = 0.04). There was a positive dose-response association of ADHD with the number of maternal cigarettes smoked during pregnancy. Measures to reduce both smoking among pregnant women and childhood obesity might reduce prevalence of childhood ADHD.

CYP1A1 modifies the effect of maternal exposure to environmental tobacco smoke on child behavior

INTRODUCTION

Maternal environmental tobacco smoke (ETS) has been identified as a key risk factor for problem behavior in children, but the role of genetic susceptibility is not clear. The purpose of this study was to examine the metabolic genetic modification effect of exposure to ETS in nonsmoking mothers on child behavior at 2 years of age.

METHODS

A prospective cohort study was conducted among 191 mothers who gave births between 2004 and 2005 and their infants in Taiwan. The mothers completed a questionnaire before delivery in which they provided information on exposure to ETS during pregnancy. Four metabolic genes, CYP1A1 MspI, CYP1A1 Ile462Val, GSTT1, and GSTM1 were isolated from both maternal and infant DNA samples. Children's behavior problems at 2 years of age were reported by their mothers using the Child Behavior Checklist/1.5-5. Multiple linear models were used to estimate the effects of ETS and genotype on child behavior.

RESULTS

Maternal ETS exposure was associated with the anxious score. The ETS-exposed group with both the CYP1A1 MspI and the CYP1A1 Ile462Val variants had higher scores, as reflected in total CBCL score as well as scores on the internalizing scale and its emotional subdomain, the anxious scale, and the externalizing scale and its aggressive subdomain.

CONCLUSIONS

Child behavioral problems may be associated with prenatal ETS exposure, and this effect may be modified by infant CYP1A1 MspI and CYP1A1 Ile462Val genes.

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.

Medullary serotonin defects and respiratory dysfunction in sudden infant death syndrome

Sudden infant death syndrome (SIDS) is defined as the sudden and unexpected death of an infant less than 12 months of age that occurs during sleep and remains unexplained after a complete autopsy, death scene investigation, and review of the clinical history. It is the leading cause of postneonatal mortality in the developed world. The cause of SIDS is unknown, but is postulated to involve impairment of brainstem-mediated homeostatic control. Extensive evidence from animal studies indicates that serotonin (5-HT) neurons in the medulla oblongata play a role in the regulation of multiple aspects of respiratory and autonomic function. A subset of SIDS infants have several abnormalities in medullary markers of 5-HT function and genetic polymorphisms impacting the 5-HT system, informing the hypothesis that SIDS results from a defect in 5-HT brainstem-mediated control of respiratory (and autonomic) regulation. Here we review the evidence from postmortem human studies and animal studies to support this hypothesis and discuss how the pathogenesis of SIDS is likely to originate in utero during fetal development.

Early-life origins of schizotypal traits in adulthood

BACKGROUND

Although schizotypal traits, such as anhedonia and aberrant perceptions, may increase the risk for schizophrenia-spectrum disorders, little is known about early-life characteristics that predict more pronounced schizotypal traits.

AIMS

To examine whether birth size or several other early-life factors that have been previously linked with schizophrenia predict schizotypal traits in adulthood.

METHOD

Participants of the Northern Finland 1966 Birth Cohort Study (n = 4976) completed a questionnaire on positive and negative schizotypal traits at the age of 31 years.

RESULTS

Lower placental weight, lower birth weight and smaller head circumference at 12 months predicted elevated positive schizotypal traits in women after adjusting for several confounders (P<0.02). Moreover, higher gestational age, lower childhood family socioeconomic status, undesirability of pregnancy, winter/autumn birth, higher birth order and maternal smoking during pregnancy predicted some augmented schizotypal traits in women, some in men and some in both genders.

CONCLUSIONS

The results point to similarities in the aetiology of schitzotypal traits and schizophrenia-spectrum disorders.

Sudden infant death syndrome and sudden intrauterine unexplained death: correlation between hypoplasia of raphé nuclei and serotonin transporter gene promoter polymorphism

This study, besides to delineate the cytoarchitecture and the localization in the brainstem of the human raphé nuclei, aims to evaluate the correlation between neuropathological raphé defects and serotonin transporter gene (5-HTT) promoter region polymorphisms in a cohort of 28 SIDS victims, 12 sudden intrauterine unexplained deaths (SIUD), and 17 controls. Hypoplasia of one or more nuclei of both the rostral and caudal raphé groups was found in 57% of SIDS, in 67% of SIUD, and only in 12% of controls. Furthermore, a significant correlation among 5-HTT Long (L) allele, hypoplasia of the raphé nuclei, and maternal smoking in pregnancy was observed in sudden fetal and infant deaths. The presence of the L allele represents a predisposing factor for sudden fetal and infant death in association with morphologic developmental defects of the raphé nuclei and prenatal smoke exposure. A further consideration of the authors is that SIUD should not be regarded as a separate entity from SIDS, given the potentially shared neuropathological and genetic bases.

Neuroimaging of children following prenatal drug exposure

Recent advances in MR-based brain imaging methods have provided unprecedented capabilities to visualize the brain. Application of these methods has allowed identification of brain structures and patterns of functional activation altered in offspring of mothers who used licit (e.g., alcohol and tobacco) and illicit (e.g., cocaine, methamphetamine, and marijuana) drugs during pregnancy. Here we review that literature, which though somewhat limited by the complexities of separating the specific effects of each drug from other confounding variables, points to sets of interconnected brain structures as being altered following prenatal exposure to drugs of abuse. In particular, dopamine-rich cortical (e.g., frontal cortex) and subcortical (e.g., basal ganglia) fetal brain structures show evidence of vulnerability to intrauterine drug exposure suggesting that during brain development drugs of abuse share a specific profile of developmental neurotoxicity. Such brain malformations may shed light on mechanisms underlying prenatal drug-induced brain injury, may serve as bio-markers of significant intrauterine drug exposure, and may additionally be predictors of subsequent neuro-developmental compromise. Wider clinical use of these research-based non-invasive methods will allow for improved diagnosis and allocation of therapeutic resources for affected infants, children, and young adults.

GSTM1 polymorphisms modify the effect of maternal smoking during pregnancy on cognitive functioning in preschoolers

BACKGROUND

Maternal smoking during pregnancy is associated with cognitive deficits in children. Parental factors are proposed as an explanatory. We studied the influence of GSTM1 and GSTT1 polymorphisms on the cognition effects induced by active maternal smoking during pregnancy.

METHODS

Children (n = 384) from a prospective population-based birth cohort were assessed at 4 years. The McCarthy Scales of Children's Abilities (MCSA) was administrated. Maternal smoking was measured by questionnaire. Genotyping was conducted for null alleles from GSTM1 and GSTT1. Multivariable linear regression models were used to examine the association between active maternal smoking during pregnancy and MCSA outcomes by GSTM1 and GSTT1 genotypes.

RESULTS

Maternal smoking during pregnancy (reporting, yes) was inversely associated with global cognitive score among children having null allele for GSTM1 (beta = -4.73, 95% CI -9.45 to -0.02); but not among children with present allele (beta = -1.04, 95% CI -7.88 to 5.81) (P for interaction 0.089). The interaction remained after adjusting by post-natal maternal smoking (P = 0.081). The effect was stronger for perceptual-performance (beta = -3.68, 95% CI -8.39 to 1.03; P for interaction 0.087), quantitative (beta = -7.00, 95% CI -17.39 to 3.39; P for interaction 0.048), verbal (beta = -3.63, 95% CI -8.43 to 1.17; P for interaction 0.264) and executive function (beta = -4.87, 95% CI -9.55 to -0.20; P for interaction 0.127). No interaction was found for GSTT1.

CONCLUSIONS

GSTM1 deficiency increases the adverse effects of active maternal smoking during pregnancy on cognition in preschoolers, suggesting a biological interaction between child metabolic genes and tobacco smoke components in detoxification process during foetal neurodevelopment.

Gene-environment interactions across development: Exploring DRD2 genotype and prenatal smoking effects on self-regulation

Genetic factors dynamically interact with both pre- and postnatal environmental influences to shape development. Considerable attention has been devoted to gene-environment interactions (G x E) on important outcomes (A. Caspi & T. E. Moffitt, 2006). It is also important to consider the possibility that these G x E effects may vary across development, particularly for constructs like self-regulation that emerge slowly, depend on brain regions that change qualitatively in different developmental periods, and thus may be manifested differently. To illustrate one approach to exploring such developmental patterns, the relation between variation in the TaqIA polymorphism, related to D2 dopamine receptor expression and availability, and prenatal exposure to tobacco was examined in two exploratory studies. First, in 4-week-old neonates, genotype-exposure interactions were observed for attention and irritable reactivity, but not for stress dysregulation. Second, in preschool children, genotype was related to Preschool Trail Making Test (K. A. Espy and M. F. Cwik, 2004) task performance on conditions requiring executive control; children with both the A1+ genotype and a history of prenatal tobacco exposure displayed disproportionately poor performance. Despite study limitations, these results illustrate the importance of examining the interplay between genetic and prenatal environmental factors across development.

Prenatal nicotine exposure changes natural and drug-induced reinforcement in adolescent male rats

Clinical studies have demonstrated an increased incidence of substance misuse and obesity in adolescents whose mothers smoked during pregnancy. Although dopamine systems that mediate natural and drug-induced reinforcement have been shown in animal studies to be altered by gestational nicotine treatment, it is not clear whether there are concomitant changes in reinforcement sensitivity. To test whether prenatal nicotine exposure influences sensitivity to natural and drug rewards, timed pregnant rats were implanted with osmotic minipumps delivering saline or nicotine (3 mg/kg/day) from gestational day 4 to 18. Male offspring were tested as adolescents, on postnatal day 32, for operant responding maintained by sucrose pellets or i.v. cocaine (200 or 500 mug/kg per injection). Cocaine-induced stereotypy and c-fos mRNA expression in cortex and striatum were also examined. Complex changes in reward circuitry were observed in the offspring of nicotine-exposed dams. Nicotine-exposed adolescents did not self-administer the low dose of cocaine, but, at the higher dose, exhibited significantly greater cocaine intake and c-fos mRNA expression in nucleus accumbens than did controls. In contrast, control animals showed significantly greater drug-induced stereotypy at both cocaine doses. Operant responding maintained by sucrose was also influenced by gestational nicotine exposure. At a fixed ratio (FR) 1 schedule, although the number of pellets eaten by the two experimental groups was equivalent, more pellets were left uneaten by nicotine-exposed offspring. At FR2 and FR5 schedules, the responding maintained by sucrose pellets was lower in nicotine-exposed offspring. These findings suggest that nicotine exposure during gestation may induce changes in both natural and drug reward pathways.

Nicotine-induced plasticity during development: modulation of the cholinergic system and long-term consequences for circuits involved in attention and sensory processing

Despite a great deal of progress, more than 10% of pregnant women in the USA smoke. Epidemiological studies have demonstrated correlations between developmental tobacco smoke exposure and sensory processing deficits, as well as a number of neuropsychiatric conditions, including attention deficit hyperactivity disorder. Significantly, data from animal models of developmental nicotine exposure have suggested that the nicotine in tobacco contributes significantly to the effects of developmental smoke exposure. Consequently, we hypothesize that nicotinic acetylcholine receptors (nAChRs) are important for setting and refining the strength of corticothalamic-thalamocortical loops during critical periods of development and that disruption of this process by developmental nicotine exposure can result in long-lasting dysregulation of sensory processing. The ability of nAChR activation to modulate synaptic plasticity is likely to underlie the effects of both endogenous cholinergic signaling and pharmacologically administered nicotine to alter cellular, physiological and behavioral processes during critical periods of development.

Prenatal smoking and internalizing and externalizing problems in children studied from childhood to late adolescence

OBJECTIVE

To study whether prenatal smoking only relates to externalizing problems or whether it is associated with both internalizing and externalizing problems from childhood into late adolescence.

METHOD

Child Behavior Checklist-derived, parent-reported internalizing and externalizing problems of 396 children were longitudinally assessed at ages 5, 10 to 11, and 18 years. The influence of self-reported prenatal smoking on the course of internalizing and externalizing problems over these ages was assessed, controlling for the co-occurrence of internalizing and externalizing problems and co-occurring pre- and perinatal risk factors, demographic characteristics, maternal mental health, and child social and attention problems.

RESULTS

Children whose mothers had smoked during pregnancy had increased levels of both internalizing and externalizing problems over the period of ages 5 to 18 years when compared with children whose mothers did not smoke during pregnancy. These associations remained significant after controlling internalizing for externalizing and vice versa and possible confounding variables.

CONCLUSIONS

Maternal smoking during pregnancy is a predictor of internalizing as well as externalizing psychopathology in offspring. The association between prenatal smoking and internalizing and externalizing problems persists throughout childhood and late adolescence.

Nicotine and brain development

Preclinical studies, using primarily rodent models, have shown acetylcholine to have a critical role in brain maturation via activation of nicotinic acetylcholine receptors (nAChRs), a structurally diverse family of ligand-gated ion channels. nAChRs are widely expressed in fetal central nervous system, with transient upregulation in numerous brain regions during critical developmental periods. Activation of nAChRs can have varied developmental influences that are dependent on the pharmacologic properties and localization of the receptor. These include regulation of transmitter release, gene expression, neurite outgrowth, cell survival, and synapse formation and maturation. Aberrant exposure of fetal and neonatal brain to nicotine, through maternal smoking or nicotine replacement therapy (NRT), has been shown to have detrimental effects on cholinergic modulation of brain development. These include alterations in sexual differentiation of the brain, and in cell survival and synaptogenesis. Long-term alterations in the functional status and pharmacologic properties of nAChRs may also occur, which result in modifications of specific neural circuitry such as the brainstem cardiorespiratory network and sensory thalamocortical gating. Such alterations in brain structure and function may contribute to clinically characterized deficits that result from maternal smoking, such as sudden infant death syndrome and auditory-cognitive dysfunction. Although not the only constituent of tobacco smoke, there is now abundant evidence that nicotine is a neural teratogen. Thus, alternatives to NRT should be sought as tobacco cessation treatments in pregnant women.

Prenatal nicotine alters maturation of breathing and neural circuits regulating respiratory control

While perinatal nicotine effects on ventilation have been widely investigated, the prenatal impact of nicotine treatment during gestation on both breathing and neural circuits involved in respiratory control remains unknown. We examined the effects of nicotine, from embryonic day 5 (E5) to E20, on baseline ventilation, the two hypoxic ventilatory response components and in vivo tyrosine hydroxylase (TH) activity in carotid bodies and brainstem areas, assessed at postnatal day 7 (P7), P11 and P21. In pups prenatally exposed to nicotine, baseline ventilation and hypoxic ventilatory response were increased at P7 (+48%) and P11 (+46%), with increased tidal volume (p<0.05). Hypoxia blunted frequency response at P7 and revealed unstable ventilation at P11. In carotid bodies, TH activity increased by 20% at P7 and decreased by 48% at P11 (p<0.05). In most brainstem areas it was reduced by 20-33% until P11. Changes were resolved by P21. Prenatal nicotine led to postnatal ventilatory sequelae, partly resulting from impaired maturation of peripheral chemoreceptors and brainstem integrative sites.

The relationship of maternal smoking to psychological problems in the offspring

There is strong evidence for an association between maternal smoking in pregnancy and psychological problems in offspring. The problems most frequently associated are attention problems, hyperactivity, and conduct problems, although there is some evidence for an association with substance use problems as well. The nature of this association is unclear, but it is likely the result of a number of different mechanisms. Animal studies provide evidence for a causal relationship, in which exposure to nicotine has detrimental effects on foetal development. Other studies suggest that factors that correlate with maternal prenatal smoking may be the real risk factors for behavioural problems, although evidence that the associations remain after controlling for such risks goes some way to dispel this as the only explanation. Finally, maternal prenatal smoking may index underlying psychological problems in the mother that are inherited by the offspring. In all likelihood, a combination of these mechanisms may contribute to observed relationships between prenatal smoking and offspring psychological problems. Now that the association is well established, future research needs to focus more strongly on disentangling underlying mechanisms. Although animal studies demonstrate a casual relationship, it appears from other research that this may not be the whole story in human samples. Furthermore, the relationship may only exist under certain conditions (i.e. against a certain genetic background), and this possibility warrants further examination, particularly in relation to other genetic risks, and outcomes other than ADHD. Application of the children-of-twins design may also cast further light on the processes involved.

Combined exposure to nicotine and ethanol throughout full gestation results in enhanced acquisition of nicotine self-administration in young adult rat offspring

RATIONALE

Epidemiological evidence shows positive correlation between either maternal cigarette smoking or alcohol consumption on subsequent drug-taking behavior in offspring. However, the consequences of full gestational exposure to both drugs have not been studied experimentally despite concurrent use frequently reported among women of childbearing age. Such comorbid gestational drug exposure may increase susceptibility to acquiring cigarette smoking (i.e., nicotine self-administration), a major gateway drug.

OBJECTIVES

We developed a noninvasive rat model for exposure to both nicotine (2-6 mg kg(-1) day(-1)) and EtOH (4 g/kg gavage) that continued throughout pregnancy and postnatal (P) days 2-12, the rodent equivalent of the human third trimester, a critical brain developmental period. Offspring with this full gestational exposure to both drugs (Nic+EtOH) were compared to controls: nicotine alone, EtOH alone, pair-fed (comparable nutrition and handling), and ad libitum chow-fed. At P60-90, offspring had unlimited chronic access to acquire i.v. nicotine self-administration.

RESULTS

There were no differences in gender ratio, stillbirths, birth weights, righting reflex, eye opening age, or weight gain. However, Nic+EtOH offspring of both genders acquired nicotine self-administration (15 or 30 microg kg(-1) injection(-1)) more rapidly, at a higher percentage, and at a higher level than offspring in the other cohorts.

CONCLUSION

Full gestational Nic+EtOH exposure produced no overt alterations in standard postnatal measures but resulted in an enhanced acquisition of nicotine self-administration in young adult offspring.

Selective breeding for infant rat separation-induced ultrasonic vocalizations: developmental precursors of passive and active coping styles

Human depression and anxiety disorders show inherited biases across generations, as do antisocial disorders characterized by aggression. Each condition is preceded in children by behavioral inhibition or aggressive behavior, respectively, and both are characterized by separation anxiety disorders. In affected families, adults and children exhibit different forms of altered autonomic nervous system regulation and hypothalamic-pituitary-adrenal activity in response to stress. Because it is difficult to determine mechanisms accounting for these associations, animal studies are useful for studying the fundamental relationships between biological and behavioral traits. Pharmacologic and behavioral studies suggest that infant rat ultrasonic vocalizations (USV) are a measure of an early anxiety-like state related to separation anxiety. However, it was not known whether or not early ultrasound emissions in infant rats are markers for genetic risk for anxiety states later in life. To address these questions, we selectively bred two lines of rats based on high and low rates of USV to isolation at postnatal (P) 10 days of age. To our knowledge, ours is the only laboratory that has ever selectively bred on the basis of an infantile trait related to anxiety. The High and Low USV lines show two distinct sets of patterns of behavior, physiology and neurochemistry from infancy through adulthood. As adults High line rats demonstrate "anxious"/"depressed" phenotypes in behavior and autonomic nervous system (ANS) regulation to standard laboratory tests. In Lows, on the other hand, behavior and autonomic regulation are consistent with an "aggressive" phenotype. The High and Low USV lines are the first genetic animal models implicating long-term associations of contrasting "coping styles" with early attachment responses. They thus present a potentially powerful model for examining gene-environment interactions in the development of life-long affective regulation.

Maternal cigarette smoking during pregnancy and child aggressive behavior

This study's objective was to examine the association between maternal smoking during pregnancy and childhood aggressive behavior in African-American and Puerto Rican children, as well as the relationship between maternal unconventional behavior, low maternal affection, and offspring aggression. Participants consisted of African-American and Puerto Rican children (N = 203; mean age = 8.6, SD = 0.87) and their mothers living in an inner city community. An interview consisting of a structured questionnaire was administered to the mothers and their children. Scales with adequate psychometric properties were adapted from previous validated measures. They included maternal smoking during pregnancy, maternal education, unconventionality, and warmth. Controlling for demographic factors, maternal unconventional behavior, and low maternal warmth, maternal smoking during pregnancy was associated with having offspring who were aggressive. Maternal unconventionality and warmth were independently related to childhood aggression. Although causal limitations are noted, it may be that a decrease in smoking during pregnancy is associated with a reduction in aggression in the offspring.

Developmental regulation of nicotinic acetylcholine receptors within midbrain dopamine neurons

We have combined anatomical and functional methodologies to provide a comprehensive analysis of the properties of nicotinic acetylcholine receptors (nAChRs) on developing dopamine (DA) neurons of Sprague-Dawley rats. Double-labeling in situ hybridization was used to examine the expression of nAChR subunit mRNAs within developing midbrain DA neurons. As brain maturation progressed there was a change in the pattern of subunit mRNA expression within DA neurons, such that alpha3 and alpha4 subunits declined and alpha6 mRNA increased. Although there were strong similarities in subunit mRNA expression in substantia nigra (SNc) and ventral tegmental area (VTA), there was higher expression of alpha4 mRNA in SNc than VTA at gestational day (G) 15, and of alpha5, alpha6 and beta3 mRNAs during postnatal development. Using a superfusion neurotransmitter release paradigm to functionally characterize nicotine-stimulated release of [(3)H]DA from striatal slices, the properties of the nAChRs on DA terminals were also found to change with age. Functional nAChRs were detected on striatal terminals at G18. There was a decrease in maximal release in the first postnatal week, followed by an increase in nicotine efficacy and potency during the second and third postnatal weeks. In the transition from adolescence (postnatal days (P) 30 and 40) to adulthood, there was a complex pattern of functional maturation of nAChRs in ventral, but not dorsal, striatum. In males, but not females, there were significant changes in both nicotine potency and efficacy during this developmental period. These findings suggest that nAChRs may play critical functional roles throughout DA neuronal maturation.

Alterations of serotonin synaptic proteins in brain regions of neonatal Rhesus monkeys exposed to perinatal environmental tobacco smoke

Serotonin (5HT) systems play important roles in brain development, and early perturbations of 5HT receptor expression produce permanent changes in 5HT synaptic function and associated behaviors. We exposed pregnant Rhesus monkeys to environmental tobacco smoke (ETS) during gestation and for up to 3 months postnatally and examined the expression of 5HT(1A) and 5HT(2) receptors, and of the presynaptic 5HT transporter in brain regions containing 5HT projections (frontal, temporal and occipital cortex) and cell bodies (midbrain). Perinatal ETS exposure elicited upregulation of 5HT(1A) receptor expression without parallel changes in the other two proteins, a pattern consistent with specific 5HT receptor dysregulation, rather than universal disruption of 5HT synaptic development. The effects seen here for ETS in a primate model are virtually identical in direction, magnitude and regional selectivity to those obtained previously for prenatal nicotine administration in rats. Specifically, early 5HT(1A) overexpression alters the program for future synaptic and behavioral 5HT responses, thus providing a mechanistic link for the shared effects of ETS and nicotine on a specific pathway responsible for behavioral anomalies associated with perinatal tobacco exposure. These results reinforce the need to reduce ETS exposure of pregnant women and young children.

Exposure to smoke during development: fetal programming of adult disease

It is well established that smoking has potent effects on a number of parameters including food intake, body weight, metabolism, and blood pressure. For example, it is well documented that 1) there is an inverse relationship between smoking and body weight, and 2) smoking cessation is associated with weight gain. However, there is increasing evidence that smoking can exert deleterious effects on energy balance through maternal exposure during fetal development. Specifically, there appears to be an increased incidence of metabolic disease (including obesity), and cardiovascular disease in children and adults that were exposed to smoke during fetal development. The present review will examine the relationship between maternal smoke and adult disease in offspring. The epidemiological studies highlighting this relationship will be reviewed as well as the experimental animal models that point to potential mechanisms underlying this relationship. A better understanding of how smoking effects changes in energy balance may lead to treatments to ameliorate the long-lasting effects of perinatal exposure to smoke as well as increasing the health benefits associated with smoking cessation.

In vitro regulation of serotonin transporter activity by protein kinase A and nicotinic acetylcholine receptors in the prefrontal cortex of rats

We investigated the effect of in vitro exposure to nicotinic acetylcholine receptors (nAChRs), agonists, antagonists, and protein kinase A (PKA) modulators on the activity of the serotonin transporter (SERT) in prefrontocortical (PFC) synaptosomes. The plasma membrane SERT is an active transport mechanism specific for serotonin. Receptors and second messengers capable of altering transporter activity would be expected to have profound effects on serotonergic neurotransmission and on functions involving serotonergic input, such as cognition, anxiety, and mood. Our data suggest that activation of nAChRs, quite likely via PKA, increase the activity of the SERT in the PFC and, thereby, can alter 5-HT levels in a region important in the behavioral effects of nicotine and 5-HT. Nicotine at 4 microM increased [(3)H]5-HT uptake by 75%. Because the nAChR antagonists mecamylamine and dihydro-beta-erythrodine (DHbetaE) both decreased [(3)H]5-HT uptake into synaptosomes, it appeared that the SERT might be tonically activated by acetylcholine present within our synaptosomal preparations. Blocking PKA significantly decreased [(3)H]5-HT, while stimulation of PKA activity significantly increased the uptake. A 66% decrease compared with control was produced by 100 microM Rp-cAMP, and a 41% increase in 5-HT uptake over control was observed with 30 microM Sp-cAMPs. Furthermore, the enhancement in uptake produced by 4 microM nicotine was inhibited in a time-dependent fashion by preincubation with 10 microM Rp-cAMP. A better understanding of the influence of the cholinergic system and the receptors involved in the trafficking of SERT would help clarify the important relationship between the cholinergic and serotonergic systems and the role these systems play in behavior.

The effects of selective breeding for infant ultrasonic vocalizations on play behavior in juvenile rats

For over 25 generations, two lines of rats (High and Low USV lines) have been selectively bred for extreme rates of infantile (45 kHz) ultrasonic vocalizations (USV) in response to maternal separation at postnatal day (P)10. High and low line juveniles (P30-P40) were socially isolated and allowed to play in same-sex sibling pairs for 10 min per day over three days. Measures of play were nape contacts and pinning. Other social and nonsocial behaviors were also scored during the three sessions; two of these, 55 kHz USV and walk-overs, were statistically associated with play. Compared to the Random control line, both High and Low line juveniles showed deficits in play behavior. In the High line, play initiatory behavior (nape contacts) was reduced, but pinning, USV and walk-overs were relatively unchanged. In contrast, nape contacts, pinning, USV and walk-overs were all reduced in Low line juveniles compared to Random line controls. The results suggest that selection for extremes of infant USV rates has produced temperamental differences that are expressed in juvenile play in the High and Low USV lines.

Mode of action: disruption of brain cell replication, second messenger, and neurotransmitter systems during development leading to cognitive dysfunction--developmental neurotoxicity of nicotine

Developmental exposure to nicotine in rats results in neurobehavioral effects such as reduced locomotor and cognitive function. Key events in the animal mode of action (MOA) include binding to the nicotinic cholinergic receptor during prenatal and/or early postnatal development. This leads to premature onset of cell differentiation at the expense of cell replication, which leads to brain cell death or structural alterations in regional brain areas. Other events include an initial increase followed by a decrease in adenyl cyclase activity, as well as effects on the noradrenergic, dopaminergic, and serotonergic neurotransmitter systems. Because the nicotine receptor is also present in the developing human brain and the underlying biology for DNA synthesis and cell signaling is comparable, this MOA is likely to be relevant for humans. Although the effects of nicotine exposure in developing humans is not well documented, nicotine exposure as a result of cigarette smoking during pregnancy is associated with several physiological and behavioral outcomes that are reminiscent of the effects of nicotine alone in animal models. As data become available with the advent of the use of the nicotine patch in pregnant humans, the question as to the relative importance of smoking per se versus nicotine alone may be determined.

Prenatal stress reduces interneuronal connectivity in the rat cerebellar granular layer

The development and functioning of the central nervous system have been shown to be affected by maternal stress. To investigate the effects of prenatal stress on the cerebellar interneuronal connectivity, rat embryos are exposed to stress on their embryonic day (E) 7 and 14, by keeping the dam in close-fitting wire mesh cylinders, for 6 h. After completion of the cerebellar development at postnatal day (P) 30, stereological procedures were used at the light and electron microscopic level to analyze growth parameters of the granule cells and synapse-to-neuron ratios. Neither the volume fraction (V(V)) of the granular layer to whole cortex, nor the numerical density of granule cells (N(Vg)) per unit volume of granular layer was affected by exposure to stress. However, the mean granule cell nuclear diameter was significantly decreased in stressed animals. Within the neuropil region, the number and mean diameter of synaptic disc profiles were used to estimate the numerical density of synapses (N(Vs)). Synapse-to-neuron ratio was obtained by dividing N(Vs) with N(Vg), and found significantly lower in the stressed group than the control group. In addition, synaptophysin immunoreactivity showed a significant decrease (41%) in the granular layer of the cerebellum. Collectively, these results demonstrate that intrauterine stress alters the morphology of granule cells and causes a profound and fairly long-lasting deficit in their interneuronal connectivity.

Biosocial bases of aggressive and violent behavior—implications for nursing studies

Although aggression and violence have been increasingly viewed as a major public health problem with a biological and health basis, it has been under-researched in the nursing and health context. This paper reviews early biological risk factors for violence. These factors include pregnancy/birth complications, fetal exposure to nicotine, alcohol, and drugs, low cholesterol, malnutrition, lead and manganese exposure, head injuries and brain dysfunction, low arousal, low serotonin, low cortisol, and high testosterone. A biopsychosocial violence mode is proposed. Finally, the paper argues that nursing is ideally placed to develop a new body of knowledge based on a biosocial perspective that can lead to more effective prevention programs for violence.

Prenatal cocaine and/or nicotine exposure produces depression and anxiety in aging rats

The adult use of cocaine and nicotine has been linked to depression and/or anxiety. Changes in emotional behavior were assessed using behavioral paradigms developed as animal analogs of psychiatric disorders in 12-14 month old Sprague-Dawley rats exposed daily on gestational days 8-20 to cocaine and nicotine, either alone or in combination. Results from the elevated plus maze (EPM), used to assess anxiety-related behaviors, indicated that offspring prenatally exposed to either high-dose cocaine (40 mg/kg/day) or high-dose nicotine (5.0 mg/kg/day) were less timid/more impulsive. Animals from these two groups spent the most time on the open arms, and had the highest percentage of entries into the open arms of the EPM. Combined in utero exposure to cocaine and nicotine nullified these effects. Cocaine challenge (20 mg/kg) did not interact with prenatal treatment, but increased activity on all arms of the EPM in all groups. Sucrose preference was used as a measure of anhedonia, a cardinal symptom of depressive illness. Reduced sucrose preference was seen only in the group of offspring prenatally exposed to high-dose cocaine (40 mg/kg) plus low-dose nicotine (2.5 mg/kg/day). Exposure to a water-deprivation stress normalized sucrose preference in this group, without altering preference or intake in the other prenatal treatment groups. Transient hyperactivity was seen in the offspring of dams treated with high-dose nicotine, an effect that was again reversed in combined drug groups. Traditional gender differences in activity levels and sucrose intake, that is, females greater than males, were still evident in this population of aging rats. These data indicate that prenatal exposure to cocaine and/or nicotine has long-term effects on emotional behavior. Combined drug exposure contributed to the development of depressive symptoms, but not anxiety-like behavior, in a dose-dependent manner. In contrast, exposure to high doses of either drug alone reduced cautionary behavior. Data from this line of research could provide insight into the pathogenesis of emotional disorders, especially during the aging process.

Nicotinic receptors mediate changes in spinal motoneuron development and axonal pathfinding in embryonic zebrafish exposed to nicotine

We show that transient exposure of embryonic zebrafish to nicotine delays the development of secondary spinal motoneurons. Furthermore, there is a long-lasting alteration in axonal pathfinding in secondary motoneurons that is not ameliorated by drug withdrawal. These effects of nicotine were reversed by mammalian nicotinic receptor antagonists. Coupled with these changes is a long-term alteration in swimming behavior. Our results show that transient embryonic exposure to nicotine leads to long-lasting effects on the vertebrate nervous system. These results also demonstrate that the zebrafish is a useful model to examine the effects of nicotine specifically, and drugs of abuse in general, on the development of the CNS in vertebrates.

Fetal exposure to nicotine does not alter the core temperature response of 7- to 8-week-old rats to intracerebroventricular administration of PGE(1)

Prenatal exposure to nicotine attenuates stress-induced hyperthermia in adult male and female rats upon exposure to a novel environment. Given that prostaglandins play an important role in mediating stress-induced hyperthermia, our current experiments were carried out to determine if prenatal exposure to nicotine alters the thermogenic response of adult rats to an E-series prostaglandin. Forty-eight chronically instrumented adults rats (24 males and 24 females) received an intracerebroventricular injection of prostaglandin E(1) (PGE(1); 0.2 microg in 10 microl of artificial cerebrospinal fluid [aCSF]) or vehicle (10 microl aCSF) at 7-8 weeks of postnatal life (i.e. adulthood as defined by the ability to reproduce) following prenatal exposure to nicotine (6 mg of nicotine tartrate per kilogram of maternal body weight per day) or vehicle via a maternally implanted osmotic mini-pump from Day 6 or 7 of gestation to term. In female rats, intracerebroventricular injection of PGE(1) following prenatal exposure to vehicle produced a monophasic fever with a magnitude of approximately 1.5 degrees C and a duration of approximately 66 min. In male rats, however, intracerebroventricular injection of PGE(1) following prenatal exposure to vehicle produced a monophasic fever with a magnitude of only approximately 0.9 degrees C and a duration of approximately 42 min. Prenatal exposure to nicotine did not significantly alter the febrile responses of male or female rats to intracerebroventricular injection of PGE(1) as compared to that observed following prenatal exposure to vehicle. Thus, prenatal exposure to nicotine does not significantly alter the thermogenic response of adult rats to central administration of the pyrogen PGE(1). It is unlikely, therefore, that an altered thermoregulatory effector response to E-series prostaglandins is responsible for mediating the attenuated stress-induced hyperthermia in adult male and female rats upon exposure to a novel environment following prenatal exposure to nicotine.

Nicotinic--serotonergic interactions in brain and behaviour

This review focuses on nicotinic--serotonergic interactions in the central nervous system (CNS). Nicotine increases 5-hydroxytryptamine (5-HT) release in the cortex, striatum, hippocampus, dorsal raphé nucleus (DRN), hypothalamus, and spinal cord. As yet, there is little firm evidence for nicotinic receptors on serotonergic terminals and thus nicotine's effects on 5-HT may not necessarily be directly mediated, but there is strong evidence that the 5-HT tone plays a permissive role in nicotine's effects. The effects in the cortex, hippocampus, and DRN involve stimulation of 5-HT(1A) receptors, and in the striatum, 5-HT(3) receptors. The 5-HT(1A) receptors in the DRN play a role in mediating the anxiolytic effects of nicotine and the 5-HT(1A) receptors in the dorsal hippocampus and lateral septum mediate its anxiogenic effects. The increased startle and anxiety during nicotine withdrawal is mediated by 5-HT(1A) and 5-HT(3) receptors. The locomotor stimulant effect of acute nicotine is mediated by 5-HT(1A) receptors and 5-HT(2) receptors may play a role in the expression of a sensitised response after chronic nicotine treatment. Unfortunately, the role of 5-HT(1A) receptors in mediating nicotine seeking has not yet been investigated and would seem an important area for future research. There is also evidence for nicotinic--serotonergic interactions in the acquisition of the water maze, passive avoidance, and impulsivity in the five-choice serial reaction task.

Serotonin and brain development: role in human developmental diseases

Serotonin is known to play a role in brain development prior to the time it assumes its role as a neurotransmitter in the mature brain. Serotonin regulates both the development of serotonergic neurons (termed autoregulation of development) and the development of target tissues. In both cases, the astroglial-derived protein, S-100beta plays a role. Disruption of serotonergic development can leave permanent alterations in brain function and behavior. This may be the case in such human developmental illnesses as autism and Down Syndrome.

Prenatal exposure to nicotine attenuates stress-induced hyperthermia in 7- to 8-week-old rats upon exposure to a novel environment

Given that approximately 25% of women in the United States continue to smoke cigarettes during pregnancy, it is important to know if exposure to nicotine during development alters the physiological response of the adult to the "stressors" of everyday life. Our current experiments were carried out to determine if prenatal exposure to nicotine alters "stress-induced hyperthermia" in adult rats upon exposure to a novel environment such as a simulated open field. Forty-eight rats (23 males and 25 females) were exposed to a simulated open field or left in their home cage at 7 to 8 weeks of postnatal life (i.e., adulthood as defined by the ability to reproduce) following prenatal exposure to vehicle or nicotine (6 mg of nicotine tartrate per kilogram of maternal body weight per day) via a maternally implanted osmotic minipump from Day 6 or 7 of gestation. The simulated open field consisted of a 30(W)x60(L)x24(H)-in. white acrylic finish box illuminated by two hanging fluorescent lights and core temperature was measured by telemetry. Exposure to a simulated open field following prenatal exposure to vehicle elicited an increase in core temperature in male and female rats with a magnitude of approximately 1.2 degrees C and a duration of greater than 170 min. Prenatal exposure to nicotine significantly attenuated the thermogenic response of both genders; this was not only evident in the latency, magnitude and duration of the core temperature response but also in the core temperature index determined from the 3-h period following exposure to a simulated open field. Thus, our data provide evidence that prenatal exposure to nicotine attenuates stress-induced hyperthermia in male and female 7- to 8-week-old rats upon exposure to a "stressor" of everyday life (i.e., a novel environment).

Fetal and adolescent nicotine administration: effects on CNS serotonergic systems

Nicotine is a neuroteratogen that targets synaptic function during critical developmental stages and recent studies indicate that CNS vulnerability extends into adolescence, the time that smoking typically commences. We administered nicotine to pregnant or adolescent rats via continuous minipump infusions, using dose rates that replicate the plasma nicotine levels found in smokers. Fetal nicotine exposure (gestational days 4-21) decreased the cerebrocortical binding of paroxetine (PXT), a marker for the serotonin (5HT) transporter, likely indicative of a decrease in nerve terminals in that region; the effect lasted into adulthood. There was a corresponding increase in PXT binding in the midbrain/brainstem, the region containing the 5HT cell bodies that project to the cerebral cortex, a pattern typical of reactive sprouting in response to nerve terminal damage. After adolescent nicotine treatment (postnatal days 30-47), PXT binding was reduced in the hippocampus and striatum instead of the cerebral cortex, again accompanied by increased binding in the midbrain and brainstem; the patterns of effects within each region were gender-selective, although both males and females displayed abnormalities. Superimposed on this overall effect, there were transient increases in PXT binding, likely due to acute stimulant effects of nicotine. We also assessed 5HT presynaptic activity (5HIAA/5HT ratio). Withdrawal from adolescent nicotine treatment led to suppression of activity in the cerebral cortex and activation in the midbrain. These results indicate that both fetal and adolescent nicotine exposure elicit apparent damage to 5HT projections with reactive increases in regions containing 5HT cell bodies. Long-term changes in 5HT innervation and/or synaptic activity may play a role in the subsequent development of depression in the offspring of women who smoke during pregnancy or in adolescent smokers.

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 exposure to nicotine impairs protective responses of rat pups to hypoxia in an age-dependent manner

Experiments were carried out on rat pups to investigate the interaction between prenatal exposure to nicotine and postnatal age on protective responses that promote survival during exposure to hypoxia. From days 6 or 7 of gestation, pregnant rats received either nicotine (approximately 6 mg of nicotine tartrate/kg of body weight per day) or vehicle continuously via a 28-day osmotic minipump. On postnatal days 1--2, 5--6 and 10--11, the pups were exposed either to a single period of hypoxia produced by breathing an anoxic gas mixture (97% N(2) and 3% CO(2)) and their time to last gasp determined, or they were exposed repeatedly to hypoxia and their ability to autoresuscitate from primary apnea determined. Prenatal exposure to nicotine decreased the time to last gasp, but only in the 1--2-day-old animals. The total number of gasps was, however, increased in this age group due to the effect of nicotine on the gasping pattern. Furthermore, prenatal exposure to nicotine decreased the number of successful autoresuscitations and influenced the cardiorespiratory events preceding death in the 1--2- and 5--6-day-old pups but not in the 10--11-day-old pups. Thus, our experiments show that prenatal exposure to nicotine impairs protective responses of rat pups that may sustain life during exposure to hypoxia in an age-dependent manner.

Threshold levels of maternal nicotine impairing protective responses of newborn rats to intermittent hypoxia

Experiments were carried out to determine the threshold level of maternal nicotine that impairs protective responses of rat pups to hypoxia. From days 6 or 7 of gestation, pregnant rats received either vehicle or nicotine (1.50, 3.00, or 6.00 mg of nicotine tartrate. kg body wt(-1).day(-1)) or vehicle continuously via a subcutaneous osmotic minipump. On postnatal days 5 or 6, pups were exposed to a single period of hypoxia produced by breathing an anoxic gas mixture (97% N(2) or 3% CO(2)) and their time to last gasp was determined, or they were exposed to intermittent hypoxia and their ability to autoresuscitate from hypoxic-induced primary apnea was determined. Perinatal exposure to nicotine did not alter the time to last gasp or the total number of gasps when the pups were exposed to a single period of hypoxia. The number of successful autoresuscitations on repeated exposure to hypoxia was, however, decreased in pups whose dams had received either 3.00 or 6.00 mg of nicotine tartrate/kg body wt; these dosage regimens produced maternal serum nicotine concentrations of 19 +/- 6 and 35 +/- 8 ng/ml, respectively. Thus our experiments define the threshold level of maternal nicotine that significantly impairs protective responses of 5- to 6-day-old rat pups to intermittent hypoxia such as may occur in human infants during episodes of prolonged sleep apnea or positional asphyxia.

Nicotine exposure during pregnancy is a factor which influences serotonin transporter density in the rat brain

We examined the effects of nicotine exposure during pregnancy on serotonin transporter (SERT) expression in the brain. Nicotine (6 mg/kg/day) was administered to pregnant rats via subcutaneous injections or infusion pumps. Irrespective of the route of administration, nicotine increased SERT density in the forebrain on postnatal day 22, but not in the other brain regions. Our results suggest that nicotine use by pregnant women might be an environmental factor influencing SERT expression in their children.

Nicotine exposure during the neonatal brain growth spurt produces hyperactivity in preweanling rats

Despite warning labels and increases in evidence of the adverse effects of tobacco use, women continue to use tobacco products during pregnancy. Cigarette smoking has been linked to increased prenatal mortality, increased incidence of SIDS, reductions in birth weight, and disruptions in CNS and behavioral development. Animal model systems have critically established the causal relationship between nicotine and adverse developmental outcome. The present study examines the behavioral effects of nicotine exposure in the rat during the third trimester equivalent of the human brain growth spurt, a period of rapid development of the cholinergic systems and a period during which the CNS is particularly vulnerable to a number of insults. Sprague-Dawley rat pups were exposed to nicotine (6.0 mg/kg/day) from postnatal days (PD) 4-9 via an artificial rearing procedure. This procedure ensures that observed effects are not due to nutritional deficits. Two control groups were employed, an artificially reared control group and a normally reared control group. Activity level was measured on PD 18-19. Nicotine-exposed subjects were significantly overactive compared to both control groups, which did not differ significantly from one another. This behavioral alteration was observed in the absence of nicotine-induced body weight deficits. These results suggest that women who use tobacco products during late gestation may place their fetuses at risk for hyperactivity later in life, particularly during early adolescence.

Effects of neonatal melatonin administration on the extra-hypothalamic regions in rat brains: effects on the serotonergic system

The effects of 100microg melatonin injection at postnatal day 5 (PD 5) on the development of the central serotonergic systems in male and female rats were investigated. The contents of serotonin (5-HT) and 5-hydroxy-3-indolacetic acid (5-HIAA) were measured in several extrahypothalamic regions at 3, 10 and 42 weeks of age. The neonatal melatonin administration increased both 5-HT and 5-HIAA levels in the striatum throughout the examined period. In the hippocampus, an increase in 5-HIAA contents by neonatal melatonin administration was found at 3 weeks but not 10 or 42 weeks of age. There were no significant differences in the effects of melatonin between male and female rats. These results indicated that exogenous melatonin administration during the early neonatal period influenced the development of the serotonergic systems in extrahypothalamic regions including the hippocampus and the striatum.

Testing methods for developmental neurotoxicity of environmental chemicals

Human brain development is slow and delicate, involving many unique, though interrelated, cellular events. The fetus and child are often more susceptible to chemical toxins that alter the structure and/or function of the brain, although susceptibility varies for individual neurotoxicants. Early exposure to neurotoxins has been implicated in neurological diseases and mental retardation. Pesticide exposures pose a particular concern since many are designed to be neurotoxic to pests and can also affect humans. Acknowledging the potential for vulnerability of the developing brain, EPA recently began to "call in" data on developmental neurotoxicity (DNT) from manufacturers of pesticides already registered and considered to be neurotoxic-around 140 pesticides. Chemicals are to be tested following the DNT testing guideline (OPPTS 870.6300). This paper assesses whether tests performed according to this guideline can effectively identify developmental neurotoxicants. We found the testing guideline deficient in several respects, including: It is not always triggered appropriately within the current tiered system for testing; It does not expose developing animals during all critical periods of vulnerability; It does not assess effects that may become evident later in life; It does not include methodology for consideration of pharmacokinetic variables; Methodology for assessment of neurobehavioral, neuropathological, and morphometry is highly variable; Testing of neurochemical changes is limited and not always required. We propose modifications to the EPA testing guideline that would improve its adequacy for assessing and predicting risks to infants and children. This paper emphasizes that deficiencies in the testing methodology for developmental neurotoxicants represent a significant gap and increase the uncertainty in the establishment of safe levels of exposure to developing individuals.

Prenatal administration of nicotine results in dopaminergic alterations in the neocortex

This study examined the effect of two high doses (3 or 6 mg/kg/day) of nicotine administrations via injections to pregnant rats on the dopaminergic, serotonergic, and noradrenergic systems in six brain regions in young adult male rats. The 3 mg/kg/day and 6 mg/kg/ day nicotine exposure resulted in significant decreases in dihydroxyphenylacetic acid (DOPAC) content in the neocortex and in both the neocortex and in the midbrain plus pons medulla, respectively, without any effects on the other brain regions such as the hypothalamus or striatum. No significant effects of prenatal nicotine were found on norepinephrine, serotonin, or 5-hydroxy-3-indolacetic acid levels. These data demonstrated that prenatal nicotine induced disturbances in the dopaminergic system in the young adult period. Furthermore, the region-specific reductions in the DOPAC content suggests that the exposure to a high dose of nicotine in utero might cause a predisposition to diseases related to a dopaminergic dysfunction in the frontal cortex.

Neuron loss in the mouse hippocampus following prenatal injection of tritiated thymidine or saline

To investigate possible effects of injections of tritiated thymidine ([3H]dThd) into pregnant mice or the injection procedure itself on the proliferation of neuronal precursor cells in the fetuses, pregnant mice received intraperitoneal injections of either [3H]dThd or saline on embryonic days 12, 14, and 19, while their offspring remained untreated. A second group of dams was not injected but their male offspring received a subcutaneous injection of again either [3H]dThd or saline on postnatal day 10. Then total numbers of hippocampal pyramidal cells (areas CA1 to CA3) and granular cells (dentate gyrus) were determined stereologically for 20-day-old as well as for 80-day-old male pups. No significant differences were found for the mean total number of pyramidal cells between the investigated groups of pups. However, the mean total number of granular cells was significantly reduced in those groups in which the dams had received an intraperitoneal injection, irrespective of whether [3H]dThd or saline was injected. This revives the repeated warning in the literature to consider the effect of the injection procedure on the developing brain when interpreting possible effects of agents administered during pregnancy.