Gestational Nicotine Exposure Research Articles

Sex Differences in the Behavioural Outcomes of Prenatal Nicotine and Tobacco Exposure.

Smoking remains the leading cause of preventable death worldwide. A combination of biological and environmental risk factors make women especially vulnerable to nicotine addiction, making it harder for them to quit smoking. Smoking during pregnancy, therefore, is still a major health concern, with epidemiological data suggesting a role for gestational nicotine exposure in the development of several behavioural disorders. Given there are significant sex-specific behavioural outcomes related to smoking in adolescence and adulthood, it is probable that the behavioural outcomes following gestational nicotine or tobacco exposure are similarly sex-dependent. This is an especially relevant topic as the current landscape of nicotine use shifts toward vaping, a mode of high doses of nicotine delivery that is largely believed to be a safer alternative to cigarettes among the public as well as among pregnant women. Here we review existing clinical and preclinical findings regarding the sex-dependent behavioural outcomes of prenatal nicotine exposure. We also highlight the challenges within this literature, particularly those areas in which further research is necessary to improve consistency within, and between, clinical and preclinical findings.

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

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

Distribution of α7 Nicotinic Acetylcholine Receptor Subunit mRNA in the Developing Mouse.

Homomeric α7 nicotinic acetylcholine receptors (nAChRs) are abundantly expressed in the central and peripheral nervous system (CNS and PNS, respectively), and spinal cord. In addition, expression and functional responses have been reported in non-neuronal tissue. In the nervous system, α7 nAChR subunit expression appears early during embryonic development and is often transiently upregulated, but little is known about their prenatal expression outside of the nervous system. For understanding potential short-term and long-term effects of gestational nicotine exposure, it is important to know the temporal and spatial expression of α7 nAChRs throughout the body. To that end, we studied the expression of α7 nAChR subunit mRNA using highly sensitive isotopic in situ hybridization in embryonic and neonatal whole-body mouse sections starting at gestational day 13. The results revealed expression of α7 mRNA as early as embryonic day 13 in the PNS, including dorsal root ganglia, parasympathetic and sympathetic ganglia, with the strongest expression in the superior cervical ganglion, and low to moderate levels were detected in brain and spinal cord, respectively, which rapidly increased in intensity with embryonic age. In addition, robust α7 mRNA expression was detected in the adrenal medulla, and low to moderate expression in selected peripheral tissues during embryonic development, potentially related to cells derived from the neural crest. Little or no mRNA expression was detected in thymus or spleen, sites of immune cell maturation. The results suggest that prenatal nicotine exposure could potentially affect the nervous system with limited effects in non-neural tissues.

Prenatal Exposure to Gestational Nicotine before Neurulation is Detrimental to Neurodevelopment of Wistar Rats' Offspring.

Background and aimThis study aimed to determine the effect of gestational nicotine exposure before neurodevelopment on the morphology and histology of the prefrontal cortex (PFC) in rats.MethodologyAdult female Wistar rats were time-mated and grouped into three categories: (a) control–given 0.1 mL of normal saline, (b) low-dose nicotine–given 6.88 mg/ kg/d/0.05 mL, and (c) high-dose nicotine–given 13.76 mg/kg/d/0.1 mL in two divided doses. Treatment was given intraperitoneally from gestational days 2 to 6. On postnatal day 15 (P15), the pups were separated from their mothers, anaesthetised and sacrificed, followed by intracardial perfusion with 4% paraformaldehyde. PFC was excised from the brain and processed for tissue histology, histochemistry, and morphology of brain cells.ResultsGestational nicotine exposure during the first week of gestation in rats significantly reduced birth weights in nicotine-treated groups compared with control; it, however, accelerated body weights, altered neuronal morphology, and elevated astrocytic count significantly, while oligodendroglial count was slightly increased in the PFC of juvenile rats examined at P15.ConclusionThese alterations revealed that gestational nicotine exposure before the commencement of the cellular processes involved in brain development negatively affects neurodevelopment, and this could result in neurological dysfunctions in later life.

Impact of gestational nicotine exposure on intrauterine and fetal infection in a rodent model†

We investigated the interaction between prenatal nicotine exposure and intrauterine infection using established rat models. Beginning at gestation day (GD) 6, dams were continuously infused with either saline or 6 mg/kg/day nicotine (Nic). At GD 14, dams received either sterile broth or 105 colony-forming units Mycoplasma pulmonis (MP), resulting in four treatment groups: control (4 dams, 33 fetal units); MP only (5 dams, 55 fetal units); Nic only (5 dams, 61 fetal units), and Nic + MP (7 dams, 82 fetal units). At GD 18, nicotine exposure significantly increased (P ≤ 0.02) the percentage of amniotic fluids and fetuses infected by MP but did not impact colonization rates of maternal sites. Nicotine exposure significantly reduced the numbers of MP in the placenta required for high microbial loads (≥104 color-changing units) in the amniotic fluid (P < 0.01). Fetal inflammatory response lesions were most extensive in the Nic only and Nic + MP groups (P < 0.0001). Control and MP only placentas were interleukin (IL)10-dominant, consistent with an M2/Th2 environment. Placentas exposed to nicotine shifted to a neutral environment, with equivalent levels of interferon gamma (IFNG) and IL10. Both IL6 and tumor necrosis factor (TNF) levels in amniotic fluid were highly elevated when both nicotine and infection were present. Our study suggests that prenatal exposure to nicotine increases the risk for intrauterine infection, lowers the infectious dose required to breach the placental barrier and infect the amniotic fluid and fetus, and alters the pathology and inflammatory profile associated with maternal and fetal sites.

Epigenomic and metabolic responses of hypothalamic POMC neurons to gestational nicotine exposure in adult offspring.

BackgroundEpidemiological and animal studies have reported that prenatal nicotine exposure (PNE) leads to obesity and type-2 diabetes in offspring. Central leptin-melanocortin signaling via hypothalamic arcuate proopiomelanocortin (POMC) neurons is crucial for the regulation of energy and glucose balance. Furthermore, hypothalamic POMC neurons were recently found to mediate the anorectic effects of nicotine through activation of acetylcholine receptors. Here, we hypothesized that PNE impairs leptin-melanocortinergic regulation of energy balance in first-generation offspring by altering expression of long non-coding RNAs (lncRNAs) putatively regulating development and/or function of hypothalamic POMC neurons.MethodsC57BL/6J females were exposed ad libitum to nicotine through drinking water and crossed with C57BL/6J males. Nicotine exposure was sustained during pregnancy and discontinued at parturition. Offspring development was monitored from birth into adulthood. From the age of 8 weeks, central leptin-melanocortin signaling, diabetes, and obesity susceptibility were assessed in male offspring fed a low-fat or high-fat diet for 16 weeks. Nicotine-exposed and non-exposed C57BL/6J females were also crossed with C57BL/6J males expressing the enhanced green fluorescent protein specifically in POMC neurons. Transgenic male offspring were subjected to laser microdissections and RNA sequencing (RNA-seq) analysis of POMC neurons for determination of nicotine-induced gene expression changes and regulatory lncRNA/protein-coding gene interactions.ResultsContrary to expectation based on previous studies, PNE did not impair but rather enhanced leptin-melanocortinergic regulation of energy and glucose balance via POMC neurons in offspring. RNA-seq of laser microdissected POMC neurons revealed only one consistent change, upregulation of Gm15851, a lncRNA of yet unidentified function, in nicotine-exposed offspring. RNA-seq further suggested 82 cis-regulatory lncRNA/protein-coding gene interactions, 19 of which involved coding genes regulating neural development and/or function, and revealed expression of several previously unidentified metabolic, neuroendocrine, and neurodevelopment pathways in POMC neurons.ConclusionsPNE does not result in obesity and type 2 diabetes but instead enhances leptin-melanocortinergic feeding and body weight regulation via POMC neurons in adult offspring. PNE leads to selective upregulation of Gm15851, a lncRNA, in adult offspring POMC neurons. POMC neurons express several lncRNAs and pathways possibly regulating POMC neuronal development and/or function.Electronic supplementary materialThe online version of this article (doi:10.1186/s13073-016-0348-2) contains supplementary material, which is available to authorized users.

Gene expression profiling of midbrain dopamine neurons upon gestational nicotine exposure.

Maternal smoking during pregnancy is associated with low birth weight, increased risk of stillbirth, conduct disorder, attention-deficit/hyperactivity disorder and neurocognitive deficits. Ventral tegmental area dopamine (DA) neurons in the mesocorticolimbic pathway were suggested to play a critical role in these pathological mechanisms induced by nicotine. Nicotine-mediated changes in genetic expression during pregnancy are of great interest for current researchers. We used patch clamp methods to identify and harvest DA and non-DA neurons separately and assayed them using oligonucleotide arrays to elucidate the alterations in gene expressions in these cells upon gestational nicotine exposure. Microarray analysis identified a set of 135 genes as significantly differentially expressed between DA and non-DA neurons. Some of the genes were found to be related to neurological disease pathways, such as Alzheimer's disease, Parkinson's disease and Huntington's disease. Significantly up-/down-regulated genes found in DA neurons were mostly related to G-protein-coupled protein receptor signaling and developmental processes. These alterations in gene expressions may explain, partially at least, the possible pathological mechanisms for the diseases induced by maternal smoking.

Gestational Nicotine Exposure Alters Oligodendrocyte Morphology and Axonal Myelination in the Lateral Prefrontal Cortex of Young Wistar Rats

Prenatal exposure of the foetus to chemical insults has implications on the overall growth and development of the baby before and after birth. This study examined the effects of prenatal exposure to nicotine on the morphology of oligodendrocytes which are responsible for the development of myelin in the central nervous system, and are critical in neurodevelopment. Twenty adult female Wistar rats were used for the study. Their oestrous cycle was determined by vaginal smearing, and subsequently exposed to male rats for mating. The female Wistar rats were thereafter grouped into two and each group was further subdivided into a saline-treated control and a nicotine-treated subgroup. Each treatment lasted 5 consecutive days between days 9-13 (Group A) and days 16-20 (Group B) of pregnancy. The pups were allowed to grow and, at postnatal day 15, were euthanized and perfusion-fixed transcardially. The lateral prefrontal cortex was processed for histochemical, immunohistochemical and electron microscopic studies. Findings indicated marked decrease in oligodendrocyte count, reduced expression of myelin basic protein (MBP), and impaired myelin formation. These changes can affect the normal growth and development of the brain with severe implications on cognitive and motor functions after birth.

Nicotine Exposure During Pregnancy Results in Persistent Midline Epithelial Seam With Improper Palatal Fusion.

Nonsyndromic cleft palate is a common birth defect (1:700) with a complex etiology involving both genetic and environmental risk factors. Nicotine, a major teratogen present in tobacco products, was shown to cause alterations and delays in the developing fetus. To demonstrate the postpartum effects of nicotine on palatal development, we delivered three different doses of nicotine (1.5, 3.0, and 4.5mg/kg/d) and sterile saline (control) into pregnant BALB/c mice throughout their entire pregnancy using subcutaneous micro-osmotic pump. Dams were allowed to deliver (~day 21 of pregnancy) and neonatal assessments (weight, length, nicotine levels) were conducted, and palatal tissues were harvested for morphological and molecular analyses, as well as transcriptional profiling using microarrays. Consistent administration of nicotine caused developmental retardation, still birth, low birth weight, and significant palatal size and shape abnormality and persistent midline epithelial seam in the pups. Through microarray analysis, we detected that 6232 genes were up-regulated and 6310 genes were down-regulated in nicotine-treated groups compared to the control. Moreover, 46% of the cleft palate-causing genes were found to be affected by nicotine exposure. Alterations of a subset of differentially expressed genes were illustrated with hierarchal clustering and a series of formal pathway analyses were performed using the bioinformatics tools. We concluded that nicotine exposure during pregnancy interferes with normal growth and development of the fetus, as well results in persistent midline epithelial seam with type B and C patterns of palatal fusion. Although there are several studies analyzing the genetic and environmental causes of palatal deformities, this study primarily shows the morphological and large-scale genomic outcomes of gestational nicotine exposure in neonatal mice palate.The previous version was incorrect. New authors Ali Nawshad, Hasan Otu, Janki Sharma, and Elizabeth Sheldon have been included in this version; the funding and acknowledgement sections have been updated accordingly; the article title, some text, and one supplementary data file have been edited; and the corresponding author has been changed. The original corresponding author regrets these earlier errors.

IV prenatal nicotine exposure increases the reinforcing efficacy of methamphetamine in adult rat offspring

BackgroundMaternal smoking during pregnancy is correlated with increased substance use in offspring. Research using rodent models shows that gestational nicotine exposure produces enduring alterations in the neurodevelopment of motivational systems, and that rats prenatally treated with nicotine have altered motivation for drug reinforcement on fixed-ratio (FR) schedules of reinforcement. ObjectiveThe present study investigated methamphetamine (METH) self-administration in adult offspring prenatally exposed to intravenous (IV) nicotine or saline using a progressive-ratio (PR) schedule of reinforcement. MethodsPregnant rats were administered IV prenatal saline (PS) or nicotine (PN; 0.05mg/kg/infusion), 3×/day during gestational days 8–21. At postnatal day 70, offspring acquired a lever-press response for sucrose (26%, w/v; FR1-3). Rats were trained with METH (0.05mg/kg/infusion), and following stable FR responding, animals were tested using a progressive-ratio (PR) schedule for three different doses of METH (0.005, 0.025, and 0.05mg/kg/infusion). ResultsMETH infusion, active lever presses, and the ratio breakpoint are reported. PN-exposed animals exhibited more METH-maintained responding than PS controls, according to a dose×prenatal treatment interaction (e.g., infusions). PN rats self-administered more METH infusions between the range of 0.025 and 0.05, but not for the 0.005mg/kg/infusion dose. ConclusionsIV PN-exposure produced enhanced motivation to self-administer METH. These findings indicate that pregnant women who smoke tobacco may impart neurobiological changes in offspring's motivational systems that render them increasingly vulnerable to drug abuse during adulthood.

Long-term effects of gestational nicotine exposure and food-restriction on gene expression in the striatum of adolescent rats.

Gestational exposure to environmental toxins such as nicotine may result in detectable gene expression changes in later life. To investigate the direct toxic effects of prenatal nicotine exposure on later brain development, we have used transcriptomic analysis of striatal samples to identify gene expression differences between adolescent Lister Hooded rats exposed to nicotine in utero and controls. Using an additional group of animals matched for the reduced food intake experienced in the nicotine group, we were also able to assess the impact of imposed food-restriction on gene expression profiles. We found little evidence for a role of gestational nicotine exposure on altered gene expression in the striatum of adolescent offspring at a significance level of p<0.01 and |log2 fold change >0.5|, although we cannot exclude the possibility of nicotine-induced changes in other brain regions, or at other time points. We did, however, find marked gene expression differences in response to imposed food-restriction. Food-restriction resulted in significant group differences for a number of immediate early genes (IEGs) including Fos, Fosb, Fosl2, Arc, Junb, Nr4a1 and Nr4a3. These genes are associated with stress response pathways and therefore may reflect long-term effects of nutritional deprivation on the development of the stress system.

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

Gestational nicotine exposure is associated with cognitive abnormalities in young offspring. However, practical strategies for prevention or treatment of impaired cognitive behaviors of offspring are not available due to the lack of systematic investigation of underlying mechanism. Therefore, this study aimed at examining the effects of gestational and/or perinatal nicotine exposure (GPNE) on cognitive behaviors in offspring of C57BL/6J mice to provide systematic behavioral data. Pregnant mice were exposed to nicotine via sweetened drinking water during six time-windows, including gestational day0 to day13 (G0-G13), G14-postnatal day0 (P0), G0-P0, G14-P7, G0-P7, and P0-P7. During P42-P56days, both male and female offspring were given a battery of behavioral tests. Depending on the time of exposure, GPNE impaired working memory, object-based attention, and prepulse inhibition in male and female offspring to different extents. Nicotine exposure during G14-P0 also decreased norepinephrine turnover in the prefrontal cortex on P28 and P56. Overall results indicate that nicotine exposure during any time-windows of development impairs cognitive behaviors in offspring, and suggest that certain time-windows, e.g., G14-P0, should be selected for further studies on the underlying neurochemical or molecular mechanisms.

Gestational nicotine exposure modifies myelin gene expression in the brains of adolescent rats with sex differences

Myelination defects in the central nervous system (CNS) are associated with various psychiatric disorders, including drug addiction. As these disorders are often observed in individuals prenatally exposed to cigarette smoking, we tested the hypothesis that such exposure impairs central myelination in adolescence, an important period of brain development and the peak age of onset of psychiatric disorders. Pregnant Sprague Dawley rats were treated with nicotine (3 mg kg−1 per day; gestational nicotine (GN)) or gestational saline via osmotic mini pumps from gestational days 4–18. Both male and female offsprings were killed on postnatal day 35 or 36, and three limbic brain regions, the prefrontal cortex (PFC), caudate putamen and nucleus accumbens, were removed for measurement of gene expression and determination of morphological changes using quantitative real-time PCR (qRT-PCR) array, western blotting and immunohistochemical staining. GN altered myelin gene expression at both the mRNA and protein levels, with striking sex differences. Aberrant expression of myelin-related transcription and trophic factors was seen in GN animals, which correlated highly with the alterations in the myelin gene expression. These correlations suggest that these factors contribute to GN-induced alterations in myelin gene expression and also indicate abnormal function of oligodendrocytes (OLGs), the myelin-producing cells in the CNS. It is unlikely that these changes are attributable solely to an alteration in the number of OLGs, as the cell number was changed only in the PFC of GN males. Together, our findings suggest that abnormal brain myelination underlies various psychiatric disorders and drug abuse associated with prenatal exposure to cigarette smoke.

Intravenous gestational nicotine exposure results in increased motivation for sucrose reward in adult rat offspring

BackgroundPrenatal tobacco smoke exposure is associated with alterations in motivated behavior in offspring, such as increased consumption of highly palatable foods and abused drugs. Animal models show that gestational nicotine (GN) exposure mediates changes in responding for sucrose and drug reward. MethodsA novel, intermittent low-dose intravenous (IV) exposure model was used to administer nicotine (0.05mg/kg/injection) or saline 3×/day to rats on gestational days 8–21. Two experiments investigated the effect of IV GN on (1) the habituation of spontaneous locomotor activity and on (2) sucrose reinforced responding in offspring. For the operant experiments, animals acquired fixed-ratio (FR-3) responding for sucrose, 26% (w/v), and were tested on varying concentrations (0, 3, 10, 30, and 56%; Latin-square) according to a FR-3, and then a progressive-ratio (PR) schedule. Male and female adult offspring were used. ResultsIV GN did not alter birth or growth weight, or the number of pups born. No between-group differences in habituation to spontaneous locomotor activity were observed. FR testing produced an inverted U-shaped response curve, and rats showed peak responding for 10% sucrose reinforcement. Neither gestation nor sex affected responding, suggesting equivalent sensitivity to varying sucrose concentrations. PR testing revealed that GN rats showed greater motivation for sucrose reinforcement relative to controls. ConclusionsA low-dose, IV GN exposure model resulted in increased motivation to respond for sucrose reinforcement in adult offspring. This suggests that using a low number of cigarettes throughout pregnancy will result in increased motivation for highly palatable foods in adult, and perhaps, adolescent offspring.

Gestational IV nicotine produces elevated brain‐derived neurotrophic factor in the mesocorticolimbic dopamine system of adolescent rat offspring

Maternal smoking during pregnancy is associated with enduring psychopathology, such as increased likelihood of substance use, in offspring. Various animal models demonstrate that continuous nicotine exposure produces teratogenic effects in offspring, as well. In this experiment, a novel intravenous (IV) exposure model was used to determine if gestational nicotine (GN) treatment produced alterations in methamphetamine-induced sensitization and the expression of brain-derived neurotrophic factor (BDNF) in the mesocorticolimbic dopamine (DA) system of adolescent offspring. Dams were injected with IV saline or nicotine (0.05 mg/kg/injection) three times per day on gestational days 8-21. Habituation was measured on postnatal day (PND) 25-27 and baseline activity on PND 28. On PND 29-35, offspring were injected with saline or methamphetamine (0.3 mg/kg) and locomotor activity was measured after the first and seventh injections. On PND 36, brains were removed, flash frozen, and BDNF protein levels in the nucleus accumbens (NAcc), dorsal striatum (Str), frontal cortex (FC), and hippocampus (Hipp) were analyzed. GN did not affect habituation or the induction of methamphetamine-induced sensitization. Interestingly, GN, but not adolescent methamphetamine treatment, elevated levels of BDNF in the NAcc and Str; however, the GN-induced increase in BDNF in the FC was attenuated by adolescent methamphetamine treatment. Both GN and adolescent methamphetamine treatment increased BDNF in the Hipp. These findings indicate that GN exposure will result in increased levels of BDNF protein throughout the mesocorticolimbic DA system during adolescent development and suggests that methamphetamine abuse will modulate the expression of BDNF in motivational circuitries of adolescent offspring exposed to GN.

Gestational nicotine exposure regulates expression of AMPA and NMDA receptors and their signaling apparatus in developing and adult rat hippocampus

Untimely activation of nicotinic acetylcholine receptors (nAChRs) by nicotine results in short- and long-term consequences on learning and behavior. In this study, the aim was to determine how prenatal nicotine exposure affects components of glutamatergic signaling in the hippocampus during postnatal development. We investigated regulation of both nAChRs and glutamate receptors for AMPA and N-methyl-D-aspartate (NMDA), from postnatal day 1 (P1) to P63 after a temporally restricted exposure to saline or nicotine for 14 days in utero. We analyzed postsynaptic density components associated with AMPA receptor (AMPAR) and NMDA receptor (NMDAR) signaling: calmodulin (CaM), CaM Kinase II alpha (CaMKIIα), and postsynaptic density-95 (PSD95), as well as presynaptically localized synaptosomal-associated protein 25 (SNAP25). At P1, there was significantly heightened expression of AMPAR subunit GluR1 but not GluR2, and of NMDAR subunits NR1, NR2a, and NR2d but not NR2b. NR2c was not detectable. CaM, CaMKIIα, and PSD95 were also significantly upregulated at P1, together with presynaptic SNAP25. This enhanced expression of glutamate receptors and signaling proteins was concomitant with elevated levels of [³H]epibatidine (³H]EB) binding in prenatal nicotine-exposed hippocampus, indicating that α4β2 nAChR may influence glutamatergic function in the hippocampus at P1. By P14, neither [³H]EB binding nor the expression levels of subunits GluR1, GluR2, NR1, NR2a, NR2b, NR2c, or NR2d seemed changed with prenatal nicotine. However, CaMKIIα was significantly upregulated with nicotine treatment while CaM showed downregulation at P14. The effects of nicotine persisted in P63 young adult brains which exhibited significantly downregulated GluR2, NR1, and NR2c expression levels in hippocampal homogenates and a considerably muted overall distribution of [³H]AMPA binding in areas CA1, CA2 and CA3, and the dentate gyrus. Our results suggest that prenatal nicotine exposure can regulate the glutamatergic signaling system throughout postnatal development by enhancing or inhibiting availability of AMPAR and NMDAR or their signaling components. The persistent depression, in adults, of the requisite NR1 subunit for NMDAR assembly, and of GluR2, important for assembly, trafficking, and biophysical properties of AMPAR, indicates that nicotine may alter ionotropic glutamate receptor stoichiometry and functional properties in adults after prenatally restricted nicotine exposure.

Prenatal exposure to nicotine impairs performance of the 5-choice serial reaction time task in adult rats.

Cigarette smoking is associated with a wide variety of adverse reproductive outcomes, including increased infant mortality and decreased birth weight. Prenatal exposure to tobacco smoke, of which nicotine is a major teratogenic component, has also been linked to the acceleration of the risk for different psychiatric disorders, including conduct disorder and attention deficit hyperactivity disorder (ADHD). Whether this increased risk is influenced by the direct effects of gestational nicotine exposure on the developing fetus remains uncertain. In this study we provide experimental evidence for the effects of prenatal nicotine exposure on measures of attention and impulsivity in adult male rats. Offspring of females exposed during pregnancy to 0.06 mg/ml nicotine solution as the only source of water (daily consumption: 69.6±1.4 ml/kg; nicotine blood level: 96.0±31.9 ng/ml) had lower birth weight and delayed sensorimotor development measured by negative geotaxis, righting reflex, and grip strength. In the 5-choice serial reaction time test, adult rats showed increased numbers of anticipatory responses and omissions errors, more variable response times, and lower accuracy with evidence of delayed learning of the task demands when the 1 s stimulus duration was introduced. In contrast, prenatal nicotine exposure had no effect on exploratory locomotion or delay-discounting test. Prenatal nicotine exposure increased expression of the D5 dopamine receptor gene in the striatum, but did not change expression of other dopamine-related genes (DRD4, DAT1, NR4A2, and TH) in either the striatum or the prefrontal cortex. These data suggest a direct effect of prenatal nicotine exposure on important aspects of attention, inhibitory control, or learning later in life.

Gestational nicotine treatment modulates cell death/survival-related pathways in the brains of adolescent female rats

Gestational exposure to nicotine affects brain development, leading to numerous behavioural and physiological deficits in the offspring during adolescence. To analyse the molecular mechanisms underlying these effects, a pathway-focused oligonucleotide microarray was used to determine gene expression profiles in five brain regions (i.e. amygdala, prefrontal cortex, nucleus accumbens, periventricular nucleus of the hypothalamus, and caudate putamen CPu) of adolescent rats that received nicotine or saline during gestation. Following appropriate statistical and Gene Set Enrichment Analyses, 24 cell death/survival-related pathways were found to be significantly modulated by gestational nicotine. On the basis of their biological functions, these pathways can be classified into three categories: growth factor, death receptor, and kinase cascade. We employed a quantitative real-time PCR array to verify the findings by measuring the expression of 29 genes involved in cell death/survival-related pathways. Together, our findings indicate that gestational nicotine exposure has significant effects on gene expression in cell death/survival-related pathways in the brains of adolescent offspring. Such effects appear to be brain region-specific and are realized through regulation of the expression of growth factors and receptors, caspases, kinases, and transcription factors. On the basis of these findings, we offer a hypothetical model to explain how gestational nicotine exposure may affect cell death and survival in the brains of adolescent offspring by regulating the balance between growth-factor and death-receptor pathways.

Prenatal IV nicotine exposure produces a sex difference in sensorimotor gating of the auditory startle reflex in adult rats

Maternal smoking during pregnancy is associated with auditory processing deficits in children; these effects have been confirmed with animal models of continuous high-dose prenatal nicotine exposure. The present experiments utilized a novel, low-dose, intermittent, intravenous (IV) gestational nicotine exposure model to investigate potential deficits on the preattentive process of sensorimotor gating, as indexed by prepulse inhibition (PPI), in preweanling and adult rat offspring. Pregnant dams received bolus IV injections of nicotine (0.05mg/kg/injection) 3×/day on gestational days 8–21. Auditory and tactile stimulus modalities were probed with tone and air puff prepulse stimuli, respectively. These prepulse stimuli preceded a 100dB(A) startle tone by six different interstimulus intervals (ISIs; 0, 8, 40, 80, 120, 4000ms) to define a curve of response inhibition. The magnitude of PPI increased with age, from 59 to 81% inhibition. Preweanlings (PNDs 14 and 18) and adults (PND 75) gestationally exposed to nicotine exhibited altered startle responding relative to controls, but the nature of the deficit became more localized at later ages. The entire curve of response inhibition in preweanlings exposed to prenatal nicotine (PND 14) was shifted up relative to controls, and notably, did not interact with prepulse stimulus modality, suggesting a generalized increased sensorimotor responsiveness as a function of prenatal nicotine. At PND 18, a shift in the response curve across all ISIs was again noted, but varied as a function of prepulse stimulus modality; the increased sensorimotor responsiveness was specific to the auditory, but not tactile, sensory modality. In adulthood, male and female animals prenatally exposed to nicotine were differentially sensitive to modulation by the ISIs, relative to control male and female animals. Specifically, despite robust PPI, adult females exposed to gestational nicotine were relatively insensitive to changes in ISI from 8 to 120ms; in contrast, the robust PPI of nicotine-exposed males demonstrated a clear focal point of inhibition at 40ms. These findings indicate that a low, daily dosing of IV prenatal nicotine produces long-lasting alterations in auditory PPI. An important implication of this research is that “chipping” with smoked-tobacco products during pregnancy may produce enduring changes in sensorimotor processing.

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.