Nicotine delays arousal during hypoxemia in lambs

Nicotine replacement therapy and e-cigarettes in pregnancy and infant respiratory outcomes

BACKGROUND

Nicotine replacement therapy (NRT) and e-cigarettes are recommended to pregnant women who wish to stop smoking. Albeit eliminating other harmful components of cigarettes, those alternatives still expose the developing fetus to nicotine. The lungs may be particularly vulnerable to damage by nicotine as there is widespread nicotinic-acetylcholine receptor expression in the lungs. There is, however, a paucity of information about the effect of NRT and e-cigarette use in pregnancy on infant respiratory outcomes.

AIMS

To explore the effect of NRT and e-cigarettes on the developing lung.

STUDY DESIGN

A literature search was undertaken to examine the use and safety of nicotine-replacement strategies in pregnancy, with a focus on infant respiratory outcomes. This included experimental studies investigating the effect of isolated "gestational" nicotine on the developing lung.

OUTCOME MEASURES

Respiratory outcomes in animal studies and infants.

RESULTS

Animal studies investigating the effect of gestational nicotine exposure on fetal lung development demonstrated abnormal lung growth; including abnormal airway branching and alveolar development. Consequently, offspring display altered pulmonary mechanics, including both increased respiratory rate and airway resistance. These findings mirror respiratory pathology observed in infants born to smoking mothers. Human trials of NRT and e-cigarette use in pregnancy have not identified adverse perinatal outcomes regarding reduced birthweight or prematurity, but have not considered infant and childhood respiratory outcomes.

CONCLUSIONS

Nicotine can impair fetal lung development, leading to concerns regarding the safety of NRT and e-cigarettes in pregnancy. Studies have yet to explore the impact of these nicotine-containing products on infant respiratory outcomes.

Nicotinic Receptors in the Brainstem Ascending Arousal System in SIDS With Analysis of Pre-natal Exposures to Maternal Smoking and Alcohol in High-Risk Populations of the Safe Passage Study

Pre-natal exposures to nicotine and alcohol are known risk factors for sudden infant death syndrome (SIDS), the leading cause of post-neonatal infant mortality. Here, we present data on nicotinic receptor binding, as determined by 125I-epibatidine receptor autoradiography, in the brainstems of infants dying of SIDS and of other known causes of death collected from the Safe Passage Study, a prospective, multicenter study with clinical sites in Cape Town, South Africa and 5 United States sites, including 2 American Indian Reservations. We examined 15 pons and medulla regions related to cardiovascular control and arousal in infants dying of SIDS (n = 12) and infants dying from known causes (n = 20, 10 pre-discharge from time of birth, 10 post-discharge). Overall, there was a developmental decrease in 125I-epibatidine binding with increasing postconceptional age in 5 medullary sites [raphe obscurus, gigantocellularis, paragigantocellularis, centralis, and dorsal accessory olive (p = 0.0002-0.03)], three of which are nuclei containing serotonin cells. Comparing SIDS with post-discharge known cause of death (post-KCOD) controls, we found significant decreased binding in SIDS in the nucleus pontis oralis (p = 0.02), a critical component of the cholinergic ascending arousal system of the rostral pons (post-KCOD, 12.1 ± 0.9 fmol/mg and SIDS, 9.1 ± 0.78 fmol/mg). In addition, we found an effect of maternal smoking in SIDS (n = 11) combined with post-KCOD controls (n = 8) on the raphe obscurus (p = 0.01), gigantocellularis (p = 0.02), and the paragigantocellularis (p = 0.002), three medullary sites found in this study to have decreased binding with age and found in previous studies to have abnormal indices of serotonin neurotransmission in SIDS infants. At these sites, 125I-epibatidine binding increased with increasing cigarettes per week. We found no effect of maternal drinking on 125I-epibatidine binding at any site measured. Taken together, these data support changes in nicotinic receptor binding related to development, cause of death, and exposure to maternal cigarette smoking. These data present new evidence in a prospective study supporting the roles of developmental factors, as well as adverse exposure on nicotinic receptors, in serotonergic nuclei of the rostral medulla-a finding that highlights the interwoven and complex relationship between acetylcholine (via nicotinic receptors) and serotonergic neurotransmission in the medulla.

Perinatal Nicotine Reduces Chemosensitivity of Medullary 5-HT Neurons after Maturation in Culture

Perinatal exposure to nicotine produces ventilatory and chemoreflex deficits in neonatal mammals. Medullary 5-HT neurons are putative central chemoreceptors that innervate respiratory nuclei and promote ventilation, receive cholinergic input and express nicotinic acetylcholine receptors (nAChRs). Perforated patch clamp recordings were made from cultured 5-HT neurons dissociated from the medullary raphé of 0-3 day old mice expressing enhanced yellow fluorescent protein driven by the enhancer region for PET1 (ePet-EYFP). The effect of exposure to low (6 mg kg^-1day^-1) or high (60 mg kg^-1day^-1) doses of nicotine in utero (prenatal), in culture (postnatal), or both and the effect of acute nicotine exposure (10 μM), were examined on baseline firing rate (FR at 5% CO₂, pH = 7.4) and the change in FR with acidosis (9% CO₂, pH 7.2) in young (12-21 days in vitro, DIV) and older (≥22 DIV) acidosis stimulated 5-HT neurons. Nicotine exposed neurons exhibited ∼67% of the response to acidosis recorded in neurons given vehicle (p = 0.005), with older neurons exposed to high dose prenatal and postnatal nicotine, exhibiting only 28% of that recorded in the vehicle neurons (p < 0.01). In neurons exposed to low or high dose prenatal and postnatal nicotine, acute nicotine exposure led to a smaller increase in FR (∼+51% vs +168%, p = 0.026) and response to acidosis (+6% vs +67%, p = 0.014) compared to vehicle. These data show that exposure to nicotine during development reduces chemosensitivity of 5-HT neurons as they mature, an effect that may be related to the abnormal chemoreflexes reported in rodents exposed to nicotine in utero, and may cause a greater risk for sudden infant death syndrome (SIDS).

Ambient Air Pollution and Sudden Infant Death Syndrome in Korea: A Time-Stratified Case-Crossover Study

Sudden infant death syndrome (SIDS) is an occasional cause of unexpected mortality in infancy. While various etiological factors have been hypothesized, air pollution has been consistently presented as an environmental factor. In this study, we aimed to estimate the risk of SIDS in relation to exposure to air pollution and the effects of its modifying factors. A mortality dataset with supplementary infant mortality survey data from Statistics Korea was used and combined the concentration of ambient air pollution data from AirKorea based on the date of death and residential addresses of the SIDS cases. Odds ratios (ORs) were estimated according to birthweight, gestational age, maternal age, and infant age using a time-stratified case-crossover study design. The risk of exposure to particulate matter of less than 10 μm in diameter (PM₁₀), nitrogen dioxide (NO₂), carbon monoxide (CO), and sulfur dioxide was estimated. The number of deaths due to SIDS was 454 (253 males and 201 females). The OR per 27.8 µg/m³ increment of PM₁₀ was 1.14 (95% confidence interval [CI]: 1.03–1.25) and that per 215.8 ppb of CO was 1.20 (95% CI: 1.03–1.40) in all infants. In females, an increase in NO₂ and CO levels was associated with a higher risk of SIDS in low-birthweight and preterm infants. The OR per 15.7 ppb increment in NO₂ was highest among preterm infants, with a value of 5.12 (95% CI: 1.27–20.63), and low-birthweight individuals, with a value of 4.11 (95% CI: 1.74–9.72), at a moving average of 0 to 3 days. In males, however, no significant association was found. In the present study, exposure to air pollution was associated with an increased risk of SIDS. This association was more evident in susceptible infants with a low-birthweight or in cases of preterm birth.

Cigarette smoke exposure effects on the brainstem expression of nicotinic acetylcholine receptors (nAChRs), and on cardiac, respiratory and sleep physiologies

Cigarette smoking during pregnancy is the largest modifiable risk factor for adverse outcomes in the infant. Investigations have focused on the psychoactive component of cigarettes, nicotine. One proposed mechanism leading to adverse effects is the interaction between nicotine and its nicotinic acetylcholine receptors (nAChRs). Much data has been generated over the past three decades on the effects of cigarette smoke exposure (CSE) on the expression of the nAChRs in the brainstem and physiological parameters related to cardiac, respiration and sleep, in the offspring of smoking mothers and animal models of nicotine exposure. This review summarises this data and discusses the main findings, highlighting that findings in animal models closely correlate with those from human studies, and that the major brainstem sites where the expression level for the nAChRs are consistently affected include those that play vital roles in cardiorespiration (hypoglossal nucleus, dorsal motor nucleus of the vagus, nucleus of the solitary tract), chemosensation (nucleus of the solitary tract, arcuate nucleus) and arousal (rostral mesopontine sites such as the locus coeruleus and nucleus pontis oralis). These findings provide evidence for the adverse effects of CSE during and after pregnancy to the infant and the need to continue with the health campaign advising against CSE.

Prenatal nicotine exposure increases hyperventilation in α4-knock-out mice during mild asphyxia

Prenatal nicotine exposure alters breathing and ventilatory responses to stress through stimulation of nicotine acetylcholine receptors (nAChRs). We tested the hypothesis that α4-containing nAChRs are involved in mediating the effects of prenatal nicotine exposure on ventilatory and metabolic responses to intermittent mild asphyxia (MA). Using open-flow plethysmography, we measured ventilation (V̇(E)) and rate of O2 consumption ( V̇(O2)) of wild-type (WT) and α4-knock-out (KO) mice, at postnatal (P) days 1-2 and 7-8, with and without prenatal nicotine exposure (6 mg kg(-1) day(-1) beginning on embryonic day 14). Mice were exposed to seven 2 min cycles of mild asphyxia (10% O2 and 5% CO2), each interspersed with 2 min of air. Compared to WT, α4 KO mice had increased air V̇(E) and V̇(O2) at P7-8, but not P1-2. Irrespective of age, genotype had no effect on the hyperventilatory response (increase in V̇(E)/V̇(O2)) to MA. At P1-2, nicotine suppressed air V̇(E) and V̇(O2) in both genotypes but did not affect the hyperventilatory response to MA. At P7-8 nicotine suppressed air V̇(E) and V̇(O2) of only α4 KO's but also significantly enhanced V̇(E) during MA (nearly double that of WT; p<0.001). This study has revealed complex effects of α4 nAChR deficiency and prenatal nicotine exposure on ventilatory and metabolic interactions and responses to stress.

Effects of postnatal environmental tobacco smoke on non-nutritive swallowing-breathing coordination in newborn lambs

While prenatal environmental tobacco smoke (ETS) exposure is a well-known risk factor for sudden infant death syndrome, the effect of postnatal ETS exposure is less clear. The objective of this study was to investigate the effect of postnatal ETS exposure on non-nutritive swallowing (NNS) and NNS-breathing coordination, which are crucial to prevent aspiration related-cardiorespiratory events. Eighteen newborn lambs (6 per group) were randomly exposed to either 10 cigarettes/day, 20 cigarettes/day or room air for 15 days. Lambs were instrumented for recording states of alertness, swallowing, electrocardiogram and breathing; recordings were performed in non-sedated lambs at the end of ETS exposure. Urinary cotinine/creatinine ratio confirmed relevant real-life exposure. Postnatal ETS exposure had no effect on NNS frequency but tended to decrease inspiratory NNS (p=0.07) during quiet sleep. No effect on respiratory or heart rate (p>0.6), apnea index (p=0.2) or sleep states (p=0.3) was observed. In conclusion, postnatal ETS exposure in lambs had only mild effects on NNS-breathing coordination.

Perinatal nicotine/smoking exposure and carotid chemoreceptors during development

Tobacco smoking is still a common habit during pregnancy and is the most important preventable cause of many adverse perinatal outcomes. Prenatal smoking exposure can produce direct actions of nicotine in the fetus with the disruption of body and brain development, and actions on the maternal-fetal unit by causing repeated episodes of hypoxia and exposure to many toxic smoke products (such as carbon monoxide). Specifically, nicotine through binding to nicotinic acetylcholine receptors have ubiquitous effects and can affect carotid chemoreception development through structural, functional and neuroregulatory alterations of the neural circuits involved in the chemoafferent pathway, as well as by interfering with the postnatal resetting of the carotid bodies. Reduced carotid body chemosensitivity and tonic activity have thus been reported by the majority of the human and animal studies. This review focuses on the effects of perinatal exposure to tobacco smoke and nicotine on carotid chemoreceptor function during the developmental period. A description of the effects of smoking and nicotine on the control of breathing related to carotid body activity, and of the possible physiopathological mechanisms at the origin of these disturbances is presented.

Increased nicotinic receptor desensitization in hypoglossal motor neurons following chronic developmental nicotine exposure

Neuronal nicotinic acetylcholine receptors (nAChRs) are expressed on hypoglossal motor neurons (XII MNs) that innervate muscles of the tongue. Activation of XII MN nAChRs evokes depolarizing currents, which are important for regulating the size and stiffness of the upper airway. Although data show that chronic developmental nicotine exposure (DNE) blunts cholinergic neurotransmission in the XII motor nucleus, it is unclear how nAChRs are involved. Therefore, XII MN nAChR desensitization and recovery were examined in tissues from DNE or control pups using a medullary slice preparation and tight-seal whole cell patch-clamp recordings. nAChR-mediated inward currents were evoked by brief pressure pulses of nicotine or the α4β2 nAChR agonist RJR-2403. We found that, regardless of treatment, activatable nAChRs underwent desensitization, but, following DNE, nAChRs exhibited increased desensitization and delayed recovery. Similar results were produced using RJR-2403, showing that DNE influences primarily the α4β2 nAChR subtype. These results show that while some nAChRs preserve their responsiveness to acute nicotine following DNE, they more readily desensitize and recover more slowly from the desensitized state. These data provide new evidence that chronic DNE modulates XII MN nAChR function, and suggests an explanation for the association between DNE and the incidence of central and obstructive apneas.

The effect of prenatal nicotine exposure on PDGFR-mediated anti-apoptotic mechanism in the caudal brainstem of developing rat

Maternal cigarette smoking is a major risk factor for sudden infant death syndrome (SIDS); however, the mechanism underlying this association is currently unknown. Prenatal nicotine exposure is accompanied by a decrease in the magnitude of hypoxic ventilatory depression, the component of hypoxic ventilatory response that activates the PDGF-beta receptor (PDGFR) and its downstream anti-apoptotic cascade in the caudal brainstem (CB) of developing rats. In this study, we evaluated the effect of prenatal nicotine exposure on PDGFR activation and the subsequent activation of downstream anti-apoptotic processes through the Akt/BAD pathway. The 5-day timed-pregnant Sprague-Dawley rats underwent surgical implantation of an osmotic pump containing either normal saline (control) or a solution of nicotine tartrate. The CB was harvested from 5-day-old rat pups (n=8-10 for each time point) in each group after exposure to normoxia or hypoxic challenges with 10% O(2) for 5, 15, 30, 60 or 120 min. Immunoprecipitation and immunoblots of CB lysates revealed phosphorylation of PDGFR, Akt and BAD-136 during hypoxia in control pups. Prenatal nicotine exposure was associated with attenuation of these responses at all time points. Analysis of an early apoptotic marker in the CB revealed that activation of cleaved caspase-3 occurred only at 120 min of hypoxic exposure in the control. Prenatal nicotine exposure accelerated this response, causing early activation at 30 and 60 min. We conclude that prenatal nicotine exposure attenuates the phosphorylation of PDGFR, Akt and Bad-136 during hypoxia in the CB of developing rats. This modulation of anti-apoptotic cascades accelerates activation of the early apoptotic marker. We speculate that prenatal nicotine exposure affects apoptosis in the CB of developing animals and may increase the vulnerability of neural cells in the respiratory control area, a process that may underlie the association between maternal smoking and SIDS.

Developmental maturation of chemosensitivity to hypoxia of peripheral arterial chemoreceptors--invited article

Peripheral arterial chemoreceptors, particularly the carotid body chemoreceptors, are the primary sites for the detection of hypoxia and reflexly increase ventilatory drive and behavioral arousal during hypoxic or asphyxial events. Newborn infants are at risk for hypoxic and asphyxial events during sleep, yet, the strength of the chemoreceptor responses is low or absent at birth and then progressively increases with early postnatal development. This review summarizes the available data showing that even though the "oxygen sensor" in the glomus cells has not been unequivocally identified, it is clear that development affects many of the other properties of the chemoreceptor unit (glomus cell, afferent nerve fibers and neurotransmitter profile at the synapse) that are necessary and essential for the propagation of the "sensing" response, and exposure to hypoxia, hyperoxia and nicotine can modify normal development of each of the components leading to altered peripheral chemoreceptor responses.

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.

Antenatal environmental stress and maturation of the breathing control, experimental data

The nervous respiratory system undergoes postnatal maturation and yet still must be functional at birth. Any antenatal suboptimal environment could upset either its building prenatally and/or its maturation after birth. Here, we would like to briefly summarize some of the major stresses leading to clinical postnatal respiratory dysfunction that can occur during pregnancy, we then relate them to experimental models that have been developed in order to better understand the underlying mechanisms implicated in the respiratory dysfunctions observed in neonatal care units. Four sections are aimed to review our current knowledge based on experimental data. The first will deal with the metabolic factors such as oxygen and glucose, the second with consumption of psychotropic substances (nicotine, cocaine, alcohol, morphine, cannabis and caffeine), the third with psychoactive molecules commonly consumed by pregnant women within a therapeutic context and/or delivered to premature neonates in critical care units (benzodiazepine, caffeine). In the fourth section, we take into account care protocols involving extended maternal-infant separation due to isolation in incubators. The effects of this stress potentially adds to those previously described.

Prenatal nicotine exposure and development of nicotinic and fast amino acid-mediated neurotransmission in the control of breathing

There is mounting evidence that neonatal animals exposed to nicotine in the prenatal period exhibit a variety of anatomic and functional abnormalities that adversely affect their respiratory and cardiovascular control systems, but how nicotine causes these developmental alterations is unknown. The principle that guides our work is that PNE impairs the ability of nicotinic acetylcholine receptors (nAChRs) to modulate the pre-synaptic release of both inhibitory (particularly GABA) and excitatory (glutamate) neurotransmitters, leading to marked alterations in the density and/or function of receptors on the (post-synaptic) membrane of respiratory neurons. Such changes could lead to impaired ventilatory responses to sensory afferent stimulation, and altered breathing patterns, including central apneic events. In this brief review we summarize the work that lead to the development of this hypothesis, and introduce some new data that support and extend it.

Prenatal nicotine exposure alters glycinergic and GABAergic control of respiratory frequency in the neonatal rat brainstem-spinal cord preparation

Bath application of GABA-A receptor agonists in neonatal rat brainstem-spinal cord preparations (BSSC) reduces respiratory frequency, an effect that is enhanced by prenatal nicotine exposure. Here we test the hypothesis that these effects can be reproduced by microinjection of GABAergic and glycinergic agonists into the pre-Botzinger complex region (PBC). We recorded the activity of phrenic motor axons from the fourth cervical ventral root in 1-3 days old BSSC that were exposed to either nicotine (6 mg/(kg day)) or saline prenatally. Microinjection of glycine or muscimol into the PBC caused abrupt, reversible apnea in all experiments. Apnea duration with glycine averaged 50.3+/-5 s in saline-exposed (N=12), and 95.7+/-9.9 s in nicotine-exposed (N=12) neonates (P<0.001). Apnea duration with muscimol averaged 51+/-5.1 s in saline-exposed (N=10), and 86+/-10.6 s in nicotine-exposed (N=12) neonates (P<0.05). These data show that prenatal nicotine exposure alters development of central ventilatory control, and that neurons in the PBC region are involved.

From oxygen sensing to heart failure: role of thioredoxin

Oxidative stress has been widely recognized to be involved in the pathogenesis of cardiopulmonary disorders. In ischemic heart diseases, it is involved not only in the development of atherosclerosis but also in ongoing ischemic injury, especially in the reperfusion process. Cardiomyopathy is another cardiac disorder in which oxidative stress is involved. In diabetic cardiomyopathy, homocysteine, a well-known source of oxidative stress, is believed to play major roles in its development. Thioredoxin (TRX) is a redox-acting protein ubiquitously present in the human body. It also is inducible by a wide variety of oxidative stresses. TRX is a multifunctional protein and has anti-inflammatory and antiapoptotic effects, as well as antioxidative effects. It is therefore feasible to think that TRX is a potential therapy for cardiac disease. Moreover, serum TRX is a well-recognized biomarker of various diseases involving oxidative stress, and this is also the case for cardiac disorders. Here we discuss how TRX is useful as a biomarker of and therapeutic agent for cardiopulmonary disorders, especially focusing on ischemic heart disease, myocarditis and oxygen sensing, and acute respiratory distress syndrome.

Differences in infant and parent behaviors during routine bed sharing compared with cot sleeping in the home setting

OBJECTIVES

To observe the behavior of infants sleeping in the natural physical environment of home, comparing the 2 different sleep practices of bed sharing and cot sleeping quantifying to factors that have been identified as potential risks or benefits.

METHODS

Forty routine bed-sharing infants, aged 5-27 weeks were matched for age and season of study with 40 routine cot-sleeping infants. Overnight video and physiologic data of bed-share infants and cot-sleep infants were recorded in the infants' own homes. Sleep time, sleep position, movements, feeding, blanket height, parental checks, and time out of the bed or cot were logged.

RESULTS

The total sleep time was similar in both groups (bed-sharing median: 8.6 hours; cot-sleeping median: 8.2 hours). Bed-sharing infants spent most time in the side position (median: 5.7 hours, 66% of sleep time) and most commonly woke at the end of sleep in this position, whereas cot-sleeping infants most commonly slept supine (median: 7.5 hours, 100%) and woke at the end of sleep in the supine position. Prone sleep was uncommon in both groups. Head covering above the eyes occurred in 22 bed-sharing infants and 1 cot-sleeping infant. Five of these bed-sharing infants were head covered at final waking time, but the cot-sleeping infant was not. Bed-sharing parents looked at or touched their infant more often (median: 11 vs 4 times per night) but did not always fully wake to do so. Movement episodes were shorter in the bed-sharing group as was total movement time (37 vs 50 minutes respectively), whereas feeding was 3.7 times more frequent in the bed-sharing group than the cot-sleeping group.

CONCLUSIONS

Bed-share infants without known risk factors for sudden infant death syndrome (SIDS) experience increased maternal touching and looking, increased breastfeeding, and faster and more frequent maternal responses. This high level of interaction is unlikely to occur if maternal arousal is impaired, for example, by alcohol or overtiredness. Increased head covering and side sleep position occur during bed-sharing, but whether these factors increase the risk of SIDS, as they do in cot sleeping, requires further investigation.

Stop SIDS--sleeping solitary supine, sucking soother, stopping smoking substitutes

The recognition of prone sleeping and maternal smoking as modifiable risk factors for sudden infant death syndrome (SIDS), has drastically decreased SIDS incidence. However, during the last years other factors have become necessary to consider to further reduce the risk of SIDS. Side sleeping implies a greater risk than supine sleeping but is still common. Bed sharing may increase the risk of SIDS, while use of a pacifier seems to be protective. Replacement of maternal smoking with nicotine substitutes is not harmless.

CONCLUSION

To further reduce the risk of SIDS, exclusive supine sleeping should be encouraged and side sleeping discouraged. When the breast-feeding is established, a pacifier can very well be used at bedtime. Bed sharing can increase the risk of SIDS if the infant is below 2-3 months of age, especially if the mother is a smoker. Any nicotine use should be avoided during pregnancy and breast-feeding.

Cardiorespiratory effects of nicotine exposure during development

Exposure to tobacco smoke is a major risk factor for the sudden infant death syndrome. Nicotine is thought to be the ingredient in tobacco smoke that is responsible for a multitude of cardiorespiratory effects during development, and pre- rather than postnatal exposure is considered to be most detrimental. Nicotine interacts with endogenous acetylcholine receptors in the brain and lung, and developmental exposure produces structural changes as well as alterations in neuroregulation. Abnormalities have been described in sympathicovagal balance, arousal threshold and latency, breathing pattern at rest and apnea frequency, ventilatory response to hyperoxia or hypoxia, heart rate regulation and ability to autoresuscitate during severe hypoxia. This review discusses studies performed on infants of smoking mothers and nicotine-exposed animals yielding varying and sometimes inconsistent results that may be due to differences in experimental design, species and the dose of exposure. Taken together however, developmental nicotine exposure appears to induce vulnerability during hypoxia and a potential inability to survive severe asphyxia.

Proteomic analysis of nicotine-associated protein expression in the striatum of repeated nicotine-treated rats

Through the proteomic analysis using 2-dimensional electrophoresis, the nicotine addiction-associated proteins were extensively screened in the striatum of rat brains. The nicotine addiction was developed by repeated nicotine injection (0.4mg/kg s.c.), twice daily for 7 days, followed by one challenge injection after a 3 day withdrawal period, and then confirmed by observing a 2.3-fold increase in locomoter activity. The 3 up- and 4 down-regulated proteins were selected and identified to be zinc-finger binding protein-89 (ZBP-89), 2'3'-cyclic nucleotide 3'-phosphodiesterase 1, deoxyribonuclease 1-like 3 (DNase1l3), tandem pore domain halothane inhibited K(+) channel (THIK-2), brain-specific hyaluronan-binding protein (BRAL-1), death effector domain-containing DNA binding protein (DEDD), and brain-derived neurotrophic factor (BDNF) by mass spectrophotometric fingerprinting. Among them, the expression patterns of ZEB-89, DNase1l3, THIK-2, DEDD, and BDNF mRNAs were found to be coincident with those of cognate proteins, by using RT-PCR analysis. These proteins could be suggested as drug targets to develop a new therapy for nicotine-associated diseases, as well as the clues to understand the mechanism of nicotine.

Uncoupling of rhythmic hypoglossal from phrenic activity in the rat

During eupnoea, rhythmic motor activities of the hypoglossal, vagal and phrenic nerves are linked temporally. The inspiratory discharges of the hypoglossal and vagus motor neurones commence before the onset of the phrenic burst. The vagus nerve also discharges in expiration. Upon exposure to hypocapnia or hypothermia, the hypoglossal discharge became uncoupled from that of the phrenic nerve. This uncoupling was evidenced by variable times of onset of hypoglossal discharge before or after the onset of phrenic discharge, extra bursts of hypoglossal activity in neural expiration, or complete absence of any hypoglossal discharge during a respiratory cycle. No such changes were found for vagal discharge, which remained linked to the phrenic bursts. Intracellular recordings in the hypoglossal nucleus revealed that all changes in hypoglossal discharge were due to neuronal depolarization. These results add support to the conclusion that the brainstem control of respiratory-modulated hypoglossal activity differs from control of phrenic and vagal activity. These findings have implications for any studies in which activity of the hypoglossal nerve is used as the sole index of neural inspiration. Indeed, our results establish that hypoglossal discharge alone is an equivocal index of the pattern of overall ventilatory activity and that this is accentuated by hypercapnia and hypothermia.

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

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

Influences of maternal cigarette smoking on infant arousability

Since the reduction in the incidence of the prone sleeping position, maternal cigarette smoking has become the strongest modifiable risk factor for Sudden Infant Death Syndrome (SIDS). This risk is dose dependent. Various mechanisms have been postulated to explain the increased risk of SIDS associated with maternal smoking, among these, impairment of arousal from sleep. This paper reviews the effects of maternal smoking on infant arousability from sleep, cardiorespiratory controls and sleep architecture. Infants exposed to maternal smoking have been shown to have both decreased spontaneous and evoked arousability from sleep. Such impairment of arousal has been demonstrated to be associated with changes in control of autonomic cardiac function. Sleep architecture appears not to be altered by smoking. During arousal, heart rate, blood pressure and breathing movements increase, while gross body movements occur to avoid the stimulus. Any impairment in arousability from sleep could occur when infants are exposed to maternal cigarette smoking, and could possibly contribute to the final pathway to SIDS.

The effect of parental smoking on lung function and development during infancy

While the adverse effects of parental smoking on respiratory health during childhood are well recognized, its potential impact on early lung development is less clear. This review summarizes current evidence on the effect of parental smoking on lung function during infancy. It is difficult to separate the effects of pre- and postnatal exposure, since the majority of mothers who smoke in pregnancy (currently around 30% worldwide) continue to do so thereafter. Nevertheless, measurements undertaken prior to any postnatal exposure have consistently demonstrated significant changes in tidal flow patterns in infants whose mothers smoked in pregnancy. While there is, as yet, no convincing evidence from studies in human infants that smoking during pregnancy is associated with increased airway responsiveness at birth, many studies have demonstrated a reduction in forced expiratory flows (on average by 20%) in infants exposed to parental smoking. While maternal smoking during pregnancy remains the most significant source of such exposure and is likely to be responsible for diminished airway function in early life, continuing postnatal tobacco smoke exposure will increase the risk of respiratory infections, the combination of both being responsible for the two- to fourfold increased risk of wheezing illnesses observed during the first year of life in infants whose parents smoke. These findings emphasize the need to keep infants in a smoke-free environment both before and after birth, not least because of growing awareness that airway function in later life is largely determined by that during foetal development and early infancy.

Postnatal nicotine exposure does not further compromise hypoxia defense mechanisms in prenatally nicotine-exposed lambs

AIMS

To determine whether combined pre- and postnatal nicotine exposure compared with prenatal exposure alone results in more compromised postnatal hypoxia defense mechanisms and further alteration of the postnatal breathing pattern (reduced tidal volume and increased respiratory rate).

METHODS

Seven lambs exposed to nicotine prenatally (pN) (approximate maternal dose: 0.5 mg/kg/d) and seven lambs exposed to nicotine pre- and postnatally (ppN) (postnatal dose: 1.6-2 mg/kg/d) were studied without sedation at an average age of 5 d and 21 d during resting (room air) conditions, during exposure to 10% O2 and during a brief exposure to 100% O2.

RESULTS

Resting minute ventilation, occlusion pressure, effective impedance, heart rate and mean arterial blood pressure were similar in the two groups during wakefulness and quiet sleep. Resting tidal volume was significantly higher in ppN than in pN lambs during wakefulness (9.4 +/- 0.7 vs 7.7 +/- 1.4 ml/kg, p < 0.05) and quiet sleep (9.8 +/- 0.6 vs 7.6 +/- 1.5 ml/kg, p < 0.01) at 5 d and also at 21 d during wakefulness (7.7 +/- 1.0 vs 6.2 +/- 1.1 ml/kg, p < 0.05). The ventilatory, heart rate and blood pressure responses to hypoxia were comparable in the two groups during both activity states. Time to arousal from quiet sleep in response to hypoxia was equivalent in the two groups. The ventilatory response to hyperoxia was not significantly different in the two groups during either activity state.

CONCLUSION

Continued postnatal nicotine exposure after prenatal exposure did not further compromise hypoxia defense mechanisms after birth.

Intermittent hypoxia induces transient arousal delay in newborn mice

Previous studies suggested that defective arousal might be a major mechanism in sleep-disordered breathing such as sudden infant death syndrome and obstructive sleep apnea. In this study, we examined the effects of intermittent hypoxia (IH) on the arousal response to hypoxia in 4-day-old mice. We hypothesized that IH would increase arousal latency, as previously reported in other species, and we measured the concomitant changes in ventilation to shed light on the relationship between breathing and arousal. Arousal was scored according to behavioral criteria. Breathing variables were measured noninvasively by use of whole-body flow plethysmography. In the hypoxic group ( n = 14), the pups were exposed to 5% O2 in N2 for 3 min and returned to air for 6 min. This test was repeated eight times. The normoxic mice ( n = 14) were constantly exposed to normoxia. The hypoxic mice showed a 60% increase in arousal latency ( P < 0.0001). Normoxic controls showed virtually no arousals. IH depressed normoxic ventilation below baseline prehypoxic levels, while preserving the ventilatory response to hypoxia. The breathing pattern and arousal responses recovered fully after 2 h of normoxia. We conclude that IH rapidly and reversibly depressed breathing and delayed arousal in newborn mice. Both effects may be due to hypoxia-induced release of inhibitory neurotransmitters acting concomitantly on both functions.

The effect of maternal smoking on respiratory and arousal patterns in preterm infants during sleep

Prenatal exposure to cigarette smoke is associated with an increased risk of sudden infant death syndrome. The effect of maternal smoking on apnea and arousal patterns in preterm infants is currently unknown. Multichannel polysomnographic studies were performed in preterm infants. Thirty infants were enrolled into the study: 16 exposed prenatally to cigarette smoke (S) and 14 control infants (C). There was no difference in the gestational and postconceptional ages at the time of study. Maternal smoking was associated with a significant increase in the apneic index in these infants (28.6 +/- 6.4/hour [S] vs. 13.2 +/- 3.9 [C]; p<0.05), and the difference was noted for obstructive events and only during active sleep. The arousal index was significantly decreased in the maternal smoking group (34.5 +/- 2.3/hour [S] vs. 46.3 +/- 5.6/hour [C]; p<0.05), with a specific decrease in percentage of arousal after respiratory events (10.7 +/- 2.1% [S] vs. 29.4 +/- 5.4% [C]; p<0.05). In conclusion, preterm infants exposed prenatally to cigarette smoke have increased respiratory events during active sleep, predominantly due to obstructive apnea, and possibly a higher arousal threshold during apneic events. These alterations in respiratory and arousal patterns in preterm infants born to smoking mothers may lead to significant vulnerability in this population.

Adverse health effects of prenatal and postnatal tobacco smoke exposure on children

Parents who choose to smoke are possibly not aware of, or deny, the negative effects of passive smoking on their offspring. This review summarises a wide range of effects of passive smoking on mortality and morbidity in children. It offers paediatricians, obstetricians, specialists in preventive child health care, general practitioners, and midwives an approach to promote smoking cessation in smoking parents before, during, and after pregnancy.

Impaired cardiorespiratory recovery after laryngeal stimulation in nicotine-exposed young lambs

The hypothesis that postnatal nicotine exposure weakens cardiorespiratory recovery from reflex apnea and bradycardia was tested in eight lambs continuously infused with nicotine from the day of birth at a dose of 1 to 2 mg.kg(-1).d(-1). Eight age-matched lambs infused with saline served as controls. Apnea and bradycardia were elicited by laryngeal stimulation with 1 mL of water (laryngeal chemoreflex) both during air breathing [0.21 fraction of inspired oxygen (FiO(2))] and mild hypoxia (0.10 FiO(2)) at a mean postnatal age of 5 +/- 1, 14 +/- 1, and 28 +/- 1 d. Ventilation, heart rate, and blood pressure were similar in the two groups at rest. In response to laryngeal chemoreflex stimulation, nicotine-treated lambs had a more pronounced decrease in ventilation (p < 0.05), longer reflex apnea (p < 0.001 in 0.21 FiO(2); p < 0.01 in 0.10 FiO(2)), and greater reflex bradycardia (p < 0.01). During reflex apnea, sighs were less efficient in restoring heart rate to prestimulation level, and a greater decrease in heart rate was observed before sighs in nicotine-treated lambs. These effects were most apparent at 5 d of age, when nicotine-treated lambs also had lower ventilation during hypoxia (p < 0.05). The response to hyperoxia was comparable in the two groups at all ages. The ability to terminate laryngeal chemoreflex-induced apnea is attenuated in young lambs continuously exposed to nicotine. This attenuation is present both in normoxia and in hypoxia and is accompanied by reduced effects from sighing on cardiac autoresuscitation.

Prenatal nicotine exposure blunts the cardiorespiratory response to hypoxia in lambs

Because smoking during pregnancy is a major risk factor for late fetal death and the sudden infant death syndrome, we investigated cardiorespiratory defense mechanisms to hypoxia in 7 prenatally nicotine-exposed (N) lambs (approximate maternal dose: 0.5 mg/kg/day) and 11 control (C) lambs all at an average age of 5 days. The ventilatory response to 10% oxygen (hyperpnea) was significantly attenuated during quiet sleep in N lambs compared with C lambs and in N lambs aroused from sleep later compared with C lambs (161 +/- 90 versus 75 +/- 66 seconds, p < 0.05). The ventilatory response to hypoxia was similar in the two groups during wakefulness (W), whereas the heart rate response (tachycardia) was significantly lower in N lambs compared with C lambs during both activity states. The ventilatory response to hyperoxia was significantly lower in N lambs compared with C lambs during both activity states. Transition from W to quiet sleep was associated with a significant decrease in ventilation in C lambs but not in N lambs. In conclusion, prenatal nicotine exposure, at a dose comparable with moderate smoking, blunts major elements of the cardiorespiratory defense to hypoxia, i.e., the heart rate and ventilatory and arousal responses, and abolishes the normal decrease in ventilation during sleep compared with W.

Prenatal smoking and alterations in newborn heart rate during transition

OBJECTIVE

To evaluate the effects of prenatal cigarette smoke exposure on newborn heart rate following the physiologic challenge of birth.

DESIGN

Nonexperimental, comparative.

PARTICIPANTS

A convenience sample of 130 full-term, healthy newborns who were born at a suburban medical center.

MAIN OUTCOME MEASURES

Cotinine is the major metabolite of nicotine and was measured in venous cord blood. The heart rate was monitored at 1 minute intervals during the first 4 hours of life. Infants were categorized into three groups based on the cotinine level: < 0.05 ng/ml (n = 68), 0.05-6.0 ng/ml (n = 39), and > 6.0 ng/ml (n = 23). These levels corresponded, respectively, to no exposure, passive, and active exposure of the mother to nicotine.

RESULTS

A one-way ANOVA was significant for maximum heart rate, F(2, 127) = 9.26, p = .001; range of heart rate, F(2, 127) = 5.4, p = .006; and variance of heart rate, F(2, 127) = 5.24, p = .007. Post hoc multiple comparisons found that newborns with cotinine levels > 6.0 ng/ml differed significantly from infants with cotinine levels < 0.05 ng/ml and 0.05-6.0 ng/ml in maximum heart rate, range of heart rate, and variance of heart rate.

CONCLUSIONS

These findings suggest that newborns with cotinine levels > 6.0 ng/ml have a limited ability to maximize and vary their heart rate. Cardiac output in the newborn is primarily dependent on heart rate. If unable to maximize cardiac output during times of stress, the newborn is potentially at an increased risk for morbidity and possible mortality.

beta 2 nicotinic acetylcholine receptor subunit modulates protective responses to stress: A receptor basis for sleep-disordered breathing after nicotine exposure

Nicotine exposure diminishes the protective breathing and arousal responses to stress (hypoxia). By exacerbating sleep-disordered breathing, this disturbance could underpin the well established association between smoking and the increased risk of sudden infant death syndrome. We show here that the protective responses to stress during sleep are partially regulated by particular nicotinic acetylcholine receptors (nAChRs). We compared responses of sleeping wild-type and mutant mice lacking the beta2 subunit of the nAChR to episodic hypoxia. Arousal from sleep was diminished, and breathing drives accentuated in mutant mice indicating that these protective responses are partially regulated by beta2-containing nAChRs. Brief exposure to nicotine significantly reduced breathing drives in sleeping wild-type mice, but had no effect in mutants. We propose that nicotine impairs breathing (and possibly arousal) responses to stress by disrupting functions normally regulated by beta2-containing, high-affinity nAChRs.

Altered breathing pattern after prenatal nicotine exposure in the young lamb

Maternal smoking during pregnancy is a risk factor for sudden fetal and infant death as well as obstructive airway disease in childhood. Fetal nicotine exposure affects organ development. The aim of the present study was to investigate effects of fetal nicotine exposure on lung function in young lambs. Nine unanesthetized, awake, prenatally nicotine-exposed lambs (N) (approximate maternal dose: 0.5 mg/kg) and 12 nonexposed control lambs (C) were studied repeatedly for 5 weeks after birth using a pneumotachograph and a computerized method for breath-by-breath determinations. N and C lambs had similar minute ventilation but a markedly different breathing pattern. At both 5 and 21 days, average age, N lambs had significantly lower tidal volumes and higher respiratory rates than C lambs. Inspiratory drive (P(0.1)) and effective impedance were significantly higher in N lambs compared with C lambs only at 5 days. Prenatal nicotine exposure appears to have long-term effects on the postnatal breathing pattern, suggesting altered lung function, e.g., increased airway resistance, decreased lung compliance, or both. The increased inspiratory drive is most likely secondary to increased impedance of the respiratory system. These changes are most marked close to birth but persist during the initial postnatal period.

Depression of hypoxic arousal response in adolescent mice following antenatal vasoactive intestinal polypeptide blockade

Late-gestation blockade of vasoactive intestinal polypeptide (VIP) activity in pregnant mice produces discrete morphological abnormalities in the somatosensory cortex of offspring. We investigated the functional implications of this lesion on the behavioural arousal response to moderate hypoxia. Pregnant mice received twice-daily injections of 200 microl saline (control), or saline + 50 microg VIP antagonist (anti-VIP) on embryonic days 17 and 18. Offspring were studied unrestrained at 6-7 weeks after birth, in a bias-flow whole-body plethysmograph during behavioural quiet sleep. Arousal was defined by movement (MVT) lasting > or =1 s. Hypoxic ventilatory (HVR) and arousal responses were measured during a 5 min exposure to 10 % O(2)-3 % CO(2) (hypoxia); peripheral chemoreflex drive was estimated by transient hyperoxia administered at rest and end-hypoxia (Dejours-type test). MVTs increased in all mice during hypoxia, but in anti-VIP mice: (a) MVT onset was delayed (174 +/- 90 vs. 108 +/- 59 s from the start of hypoxia, anti-VIP vs. control; P = 0.008); and (b) MVTs were less frequent, and total MVT time in hypoxia was less (8 +/- 7 vs. 15 +/- 9 %; P = 0.03). The HVR, and peripheral drive at rest and end-hypoxia were comparable in control and anti-VIP mice. In conclusion, a significant arousal deficit was evident in anti-VIP mice. This was not associated with obviously deranged peripheral or brainstem-mediated responses to hypoxia during sleep. This may signal a general deficit in the way hypoxic distress is monitored and processed, and arousal initiated and sustained in these mice.

Perinatal exposure to environmental tobacco smoke upregulates nicotinic cholinergic receptors in monkey brain

In humans, perinatal exposure to environmental tobacco smoke (ETS) is associated with neurobehavioral deficits. In the current study, we exposed Rhesus monkeys to ETS in late gestation and in the early neonatal period, and examined changes in neurotransmitter receptors in the brainstem and caudal portion of the cerebral cortex. Nicotinic acetylcholine receptors were markedly upregulated and the effect was selective in that there were no changes in m(2)-muscarinic acetylcholine receptors or in beta-adrenergic receptors. Nicotinic receptor upregulation is indicative of chronic cell stimulation by nicotine, and is a hallmark of nicotine-induced neuroteratogenesis. These results indicate that perinatal ETS exposes the fetus and neonate to quantities of nicotine that are sufficient to alter brain development.

Perinatal exposure to environmental tobacco smoke induces adenylyl cyclase and alters receptor-mediated cell signaling in brain and heart of neonatal rats

Perinatal exposure to environmental tobacco smoke (ETS) has adverse effects on neurobehavioral development. In the current study, rats were exposed to ETS during gestation, during the early neonatal period, or both. Brains and hearts were examined for alterations in adenylyl cyclase (AC) activity and for changes in beta-adrenergic and m2-muscarinic cholinergic receptors and their linkage to AC. ETS exposure elicited induction of total AC activity as monitored with the direct enzymatic stimulant, forskolin. In the brain, the specific coupling of beta-adrenergic receptors to AC was inhibited in the ETS groups, despite a normal complement of beta-receptor binding sites. In the heart, ETS evoked a decrease in m2-receptor expression. In both tissues, the effects of postnatal ETS, mimicking passive smoking, were equivalent to (AC) or greater than (m2-receptors) those seen with prenatal ETS mimicking active smoking; the effects of combined prenatal and postnatal exposure were equivalent to those seen with postnatal exposure alone. These data indicate that ETS exposure evokes changes in cell signaling that recapitulate those caused by developmental nicotine treatment. Since alterations in AC signaling are known to affect cardiorespiratory function, the present results provide a mechanistic link reinforcing the participation of ETS exposure, including postnatal ETS, in disturbances culminating in events like Sudden Infant Death Syndrome.