Prenatal exposure to nicotine with associated in utero hypoxia decreased fetal brain muscarinic mRNA in the rat

Long-term effects of early postnatal nicotine exposure on cholinergic function in the mouse hippocampal CA1 region

In rodent models of smoking during pregnancy, early postnatal nicotine exposure results in impaired hippocampus-dependent memory, but the underlying mechanism remains elusive. Given that hippocampal cholinergic systems modulate memory and rapid development of hippocampal cholinergic systems occurs during nicotine exposure, here we investigated its impacts on cholinergic function. Both nicotinic and muscarinic activation produce transient or long-lasting depression of excitatory synaptic transmission in the hippocampal CA1 region. We found that postnatal nicotine exposure impairs both the induction and nicotinic modulation of NMDAR-dependent long-term depression (LTD). Activation of muscarinic receptors decreases excitatory synaptic transmission and CA1 network activity in both wild-type and α2 knockout mice. These muscarinic effects are still observed in nicotine-exposed mice. M1 muscarinic receptor activity is required for mGluR-dependent LTD. Early postnatal nicotine exposure has no effect on mGluR-dependent LTD induction, suggesting that it has no effect on the function of m1 muscarinic receptors involved in this form of LTD. Our results demonstrate that early postnatal nicotine exposure has more pronounced effects on nicotinic function than muscarinic function in the hippocampal CA1 region. Thus, impaired hippocampus-dependent memory may arise from the developmental disruption of nicotinic cholinergic systems in the hippocampal CA1 region.

Prenatal Exposure to Gutkha, a Globally Relevant Smokeless Tobacco Product, Induces Hepatic Changes in Adult Mice

Maternal exposures during pregnancy affect the onset and progression of adult diseases in the offspring. A prior mouse study indicated that maternal tobacco smoke exposure affects hepatic fibrosis in adult offspring. Gutkha, a broadly used smokeless tobacco (ST) product, is widely used by pregnant woman in many countries. The objective of this murine study was to evaluate whether oral maternal exposure to gutkha during pregnancy alters non-alcoholic fatty liver disease (NAFLD) in adult offspring: risk factors for the progression of NAFLD to cirrhosis in adults remain elusive. Buccal cavity 'painting' of pregnant mice with gutkha began on gestational days (GD) 2-4 and continued until parturition. Beginning at 12 weeks of age, a subset of offspring were transitioned to a high-fat diet (HFD). Results demonstrated that prenatal exposure to gutkha followed by an HFD in adulthood significantly increased the histologic evidence of fatty liver disease only in adult male offspring. Changes in hepatic fibrosis-related cytokines (interleukin (IL)-1b and IL-6) and in hepatic collagen mRNA expression were observed when comparing adult male offspring exposed to gutkha in utero to those not exposed. These findings indicate that maternal use of gutkha during pregnancy affects NAFLD in adult offspring in a sex-dependent manner.

Differential Effects of Nicotine Exposure on the Hippocampus Across Lifespan

BACKGROUND

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

METHODS

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

CONCLUSIONS

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

Developmental nicotine exposure alters cholinergic control of respiratory frequency in neonatal rats

Prenatal nicotine exposure with continued exposure through breast milk over the first week of life (developmental nicotine exposure, DNE) alters the development of brainstem circuits that control breathing. Here, we test the hypothesis that DNE alters the respiratory motor response to endogenous and exogenous acetylcholine (ACh) in neonatal rats. We used the brainstem-spinal cord preparation in the split-bath configuration, and applied drugs to the brainstem compartment while measuring the burst frequency and amplitude of the fourth cervical ventral nerve roots (C4VR), which contain the axons of phrenic motoneurons. We applied ACh alone; the nicotinic acetylcholine receptor (nAChR) antagonist curare, either alone or in the presence of ACh; and the muscarinic acetylcholine receptor (mAChR) antagonist atropine, either alone or in the presence of ACh. The main findings include: (1) atropine reduced frequency similarly in controls and DNE animals, while curare caused modest slowing in controls but no consistent change in DNE animals; (2) DNE greatly attenuated the increase in C4VR frequency mediated by exogenous ACh; (3) stimulation of nAChRs with ACh in the presence of atropine increased frequency markedly in controls, but not DNE animals; (4) stimulation of mAChRs with ACh in the presence of curare caused a modest increase in frequency, with no treatment group differences. DNE blunts the response of the respiratory central pattern generator to exogenous ACh, consistent with reduced availability of functionally competent nAChRs; DNE did not alter the muscarinic control of respiratory motor output. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 76: 1138-1149, 2016.

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.

Perinatal nicotine exposure increases vulnerability of hypoxic-ischemic brain injury in neonatal rats: role of angiotensin II receptors

BACKGROUND AND PURPOSE

Maternal cigarette smoking increases the risk of neonatal morbidity. We tested the hypothesis that perinatal nicotine exposure causes heightened brain vulnerability to hypoxic-ischemic (HI) injury in neonatal rats through aberrant expression patterns of angiotensin II type 1 (AT(1)R) and type 2 (AT(2)R) receptors in the developing brain.

METHODS

Nicotine was administered to pregnant rats through subcutaneous osmotic minipumps. HI brain injury was determined in 10-day-old pups. AT(1)R and AT(2)R expression patterns were assessed through Western blotting, quantitative polymerase chain reaction, immunofluorescence, and confocal imaging.

RESULTS

Perinatal nicotine exposure significantly increased HI brain infarct size in male, but not female, pups. In fetal brains, nicotine caused a decrease in mRNA and protein abundance of AT(2)R but not AT(1)R. The downregulation of AT(2)R persisted in brains of male pups, and nicotine treatment resulted in a significant increase in methylation of CpG locus 3 bases upstream of TATA-box at the AT(2)R gene promoter. In female brains, there was an increase in AT(2)R but a decrease in AT(1)R expression. Both AT(1)R and AT(2)R expressed in neurons but not in astrocytes in the cortex and hippocampus. Central application of AT(1)R antagonist losartan or AT(2)R antagonist PD123319 increased HI brain infarct size in both male and female pups. In male pups, AT(2)R agonist CGP42112 abrogated nicotine-induced increase in HI brain infarction. In females, PD123319 uncovered the nicotine's effect on HI brain infarction.

CONCLUSIONS

Perinatal nicotine exposure causes epigenetic repression of the AT(2)R gene in the developing brain resulting in heightened brain vulnerability to HI injury in neonatal male rats in a sex-dependent manner.

Nicotine-like effects of the neonicotinoid insecticides acetamiprid and imidacloprid on cerebellar neurons from neonatal rats

Background

Acetamiprid (ACE) and imidacloprid (IMI) belong to a new, widely used class of pesticide, the neonicotinoids. With similar chemical structures to nicotine, neonicotinoids also share agonist activity at nicotinic acetylcholine receptors (nAChRs). Although their toxicities against insects are well established, their precise effects on mammalian nAChRs remain to be elucidated. Because of the importance of nAChRs for mammalian brain function, especially brain development, detailed investigation of the neonicotinoids is needed to protect the health of human children. We aimed to determine the effects of neonicotinoids on the nAChRs of developing mammalian neurons and compare their effects with nicotine, a neurotoxin of brain development.

Methodology/Principal Findings

Primary cultures of cerebellar neurons from neonatal rats allow for examinations of the developmental neurotoxicity of chemicals because the various stages of neurodevelopment—including proliferation, migration, differentiation, and morphological and functional maturation—can be observed in vitro. Using these cultures, an excitatory Ca²⁺-influx assay was employed as an indicator of neural physiological activity. Significant excitatory Ca²⁺ influxes were evoked by ACE, IMI, and nicotine at concentrations greater than 1 µM in small neurons in cerebellar cultures that expressed the mRNA of the α3, α4, and α7 nAChR subunits. The firing patterns, proportion of excited neurons, and peak excitatory Ca²⁺ influxes induced by ACE and IMI showed differences from those induced by nicotine. However, ACE and IMI had greater effects on mammalian neurons than those previously reported in binding assay studies. Furthermore, the effects of the neonicotinoids were significantly inhibited by the nAChR antagonists mecamylamine, α-bungarotoxin, and dihydro-β-erythroidine.

Conclusions/Significance

This study is the first to show that ACE, IMI, and nicotine exert similar excitatory effects on mammalian nAChRs at concentrations greater than 1 µM. Therefore, the neonicotinoids may adversely affect human health, especially the developing brain.

Low doses of nicotine-induced fetal cardiovascular responses, hypoxia, and brain cellular activation in ovine fetuses

Prenatal exposure to nicotine is associated with a variety of adverse outcomes. The present study investigated the effect of low doses of nicotine during pregnancy on fetal blood gases, cardiovascular system, and cellular activation in the brain. Intravenous administration of nicotine 10 or 25 microg/kg into ewe did not affect maternal blood gases, blood pressure, and heart rate. Maternal administration of nicotine also had no effect on fetal blood electrolyte concentrations, osmolality levels, and lactic acid levels. However, it significantly reduced fetal blood pO2 levels and oxygen saturation, increased fetal arterial blood pressure and decreased heart rate in utero. In addition, exposure to low doses of nicotine increased the expression of Fos in the paraventricular nucleus (PVN) and subfornic organ (SFO) in the fetal brain. The data demonstrated that even low doses of nicotine could impact significantly on fetal cardiovascular and central nervous systems, as well as oxygen status, and suggested a toxic risk to fetuses of exposure to low levels nicotine or second-hand smoking during pregnancy.

Effect of nicotine exposure during pregnancy and lactation on maternal, fetal, and postnatal rat IGF-II profile

Smoking during pregnancy has been shown to result in an increased risk of low birth weight. However, the mechanisms underlying this association are poorly understood. The insulin-like growth factor (IGF) system plays a critical role in the regulation of feto-placental growth and development, and abnormal processing of proIGF-II may alter its biological function. Our goal was to investigate the effects of exposure to nicotine on maternal, fetal, and neonatal IGF-II processing. Nulliparous female Wistar rats were randomly assigned to receive saline (vehicle) or nicotine bitartrate (1 mg x kg(-1) x d(- 1)). After mating, dams were euthanized at embryonic days 15, 18, and 21, and fetal body weight was recorded. Serum (fetal and maternal) was collected for determination of the IGF-II profile by Western blot analysis. Nicotine exposure prevented the decrease in maternal IGF-II processing seen in controls with advancing gestation. However, there was no influence of nicotine on fetal levels of IGF-II. Postnatally (postnatal day [PND] 21), pups exposed to nicotine in utero had decreased levels of big IGF-II. Our results show, for the first time, that nicotine exposure prevents the decrease of IGF-II processing in the maternal compartment. This may represent a compensatory mechanism allowing the mother to counteract the negative influence of nicotine on fetal growth and development. Our postnatal findings of suppressed IGF-II may help explain some of the long-term health complications seen in individuals exposed to smoking in utero.

Respiratory dysfunctions induced by prenatal nicotine exposure

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

The effect of fetal and neonatal nicotine exposure on renal development of AT(1) and AT(2) receptors

AIMS

Maternal cigarette smoking accompanied with fetal and neonatal growth restriction causes abnormalities in organ development in the postnatal life. The present study determined the effect of maternal administration of nicotine on the development of the kidney in rats by examining the expression of renal angiotensin II receptors at mRNA and protein levels as well as kidney weight during postnatal development.

METHODS

Nicotine was administered to pregnant rats via subcutaneous osmotic minipumps throughout gestation and up to 10 days after delivery. Kidneys were removed and collected from both male and female offspring at ages of 14-day-old, 30-day-old, and 5-month-old. Maternal nicotine administration significantly reduced renal AT(2) receptor (AT(2)R) mRNA and protein abundance in both males and females at all three developmental ages examined.

RESULTS

Although AT(1) receptor (AT(1)R) mRNA and protein levels were not significantly changed between the control offspring and the offspring exposed to maternal nicotine during the early developmental period, the renal AT(1)R/AT(2)R ratio was significantly increased. This was associated with a significant decrease of kidney weight in both male and female offspring.

CONCLUSIONS

The results demonstrated that the development of renal angiotensin II receptor could be changed following exposure to perinatal nicotine, and such change in the kidney could be long-term in postnatal life.

Perinatal nicotine exposure alters AT 1 and AT 2 receptor expression pattern in the brain of fetal and offspring rats

The present study determined the effect of maternal nicotine exposure during the early developmental period on AT(1)R and AT(2)R mRNA and protein abundance in the rat brain. Pregnant rats of day-4 gestation were implanted with osmotic minipumps that delivered nicotine at a dose rate of 6 mg/kg/day for 28 days. Neither fetal nor offspring brain weight was significantly altered by the nicotine treatment. Nicotine significantly increased brain AT(1)R in fetuses at gestation 15 and 21 days and decreased central AT(2)R at gestation day 21. In the offspring, perinatal nicotine significantly increased brain AT(1)R protein in males but not females at 30 days, and increased it in both males and females at 5-month-old. AT(2)R protein levels were significantly decreased by nicotine in both male and female offspring regardless of ages. Whereas brain AT(1)R mRNA abundance did not change during postnatal development, AT(2)R mRNA levels in both sexes significantly decreased in 5-month-old, as compared with 30-day-old offspring. Nicotine significantly increased brain AT(1)R mRNA in the female offspring. In contrast, it decreased AT(2)R mRNA in the brain to the same extent in males and females. In control offspring, there was a developmental increase in the AT(1)R/AT(2)R mRNA ratio in the brain of adult animals, which was significantly up-regulated in nicotine-treated animals with females being more prominent than males. The results demonstrate that perinatal nicotine exposure alters AT(1)R and AT(2)R gene expression pattern in the developing brain and suggest maternal smoking-mediated pathophysiological consequences related to brain RAS development in postnatal life.