Cardiorespiratory effects of nicotine exposure during development

Developmental nicotine exposure alters cardiovascular structure and function in neonatal and juvenile rats

Here we test the hypothesis that continuous nicotine exposure throughout pre- and postnatal development (developmental nicotine exposure, DNE) alters the cardiovascular structure and function in neonatal and juvenile rats. Echocardiography showed that DNE reduced left ventricular mass, left ventricular outflow tract (LVOT) diameter, and posterior wall thickness, but only in females. Both male and female DNE rats had a lower end-systolic volume, higher ejection fraction, and increased fractional shortening, with unchanged stroke volume and cardiac output. Left ventricular single cardiac myocytes from male and female DNE animals exhibited increased calcium-evoked maximal tension with no effect on EC50. Tail-cuff plethysmography in awake rats showed that DNE males had lower systolic blood pressure and higher heart rate than control males. No significant changes in preload, afterload, or the in vitro renal artery response to vasodilators were observed. The results suggest that DNE enhances myocyte tension-generating capacity, possibly compensating for an unknown developmental insult, which may differ in males and females. Although this adaptation maintains normal resting cardiac function, it may lead to reduced cardiac reserve, increased energy demand, and elevated oxidative stress, potentially compromising both short- and long-term cardiovascular health in developing neonates.NEW & NOTEWORTHY Developmental nicotine exposure (DNE) induced cardiovascular changes in neonatal/juvenile rats. Relative to controls, females had reduced left ventricular mass and dimensions, while both sexes had increased ejection fraction and fractional shortening. DNE increased calcium-evoked tension in cardiac myocytes, suggesting an adaptive mechanism as resting cardiac output was preserved. Despite normal resting function, these changes may reduce cardiac reserve, potentially compromising long-term cardiovascular health. These novel findings highlight how DNE disrupts cardiovascular development and function.

Association of maternal snuff use and smoking with Sudden Infant Death Syndrome: a national register study

BACKGROUND

The aim was to study whether non-combustible nicotine (Swedish snuff) use in pregnancy is associated with elevated risk of post neonatal mortality, Sudden Infant Death Syndrome (SIDS), and Sudden Unexpected Infant Death (SUID) and to study how cessation before the antenatal booking influenced these risks.

METHODS

This was a population-based register study of all infants with information on tobacco exposure in early pregnancy born in Sweden 1999-2019, n = 2,061,514. Self-reported tobacco use in early pregnancy was categorized as nonuse, snuff use, and moderate and heavy smoking. Multiple logistic regression models were used to estimate crude and adjusted odds ratios (aORs) with 95% confidence intervals (CIs).

RESULTS

Maternal snuff use was associated with increased risks of post neonatal mortality, SIDS, and SUID. The risks of snuff use and moderate smoking were of similar magnitude. Heavy smoking was associated with the highest risks. Cessation of smoking and snuff use before the antenatal booking was associated with lower risks of SIDS and SUID compared to that of continuous usage.

CONCLUSIONS

Maternal snuff use was associated with increased risks of post neonatal mortality, SIDS, and SUID. Nicotine is the common substance in cigarette smoke and snuff. These findings support the hypothesis that nicotine contributes to an elevated risk of SIDS.

IMPACT

Maternal snuff use and smoking in early pregnancy were associated with increased risks of post neonatal mortality, SIDS, and SUID. Cessation of smoking and snuff use before the first antenatal visit was associated with reduced risks of SIDS and SUID. The common substance in cigarette smoke and snuff is nicotine. Our findings suggest that nicotine contributes to an elevated risk of SIDS and SUID. The implication of our findings is that all forms of nicotine should be avoided in pregnancy.

Propensity score analysis of the association between maternal exposure to second-hand tobacco smoke and birth defects in Northwestern China

Previous studies have suggested that maternal active smoking can increase the risk of birth defects, but evidence on second-hand tobacco smoke (SHS) is limited. We aimed to assess the association between maternal exposure to SHS and birth defects in a Chinese population. The data were based on a large-scale cross-sectional survey conducted in Shaanxi Province, China. Considering the characteristics of survey design and the potential impact of confounding factors, we adopted propensity score matching (PSM) to match the SHS exposure group and the non-exposure group to attain a balance of the confounders between the two groups. Subsequently, conditional logistic regression was employed to estimate the effect of SHS exposure on birth defects. Furthermore, sensitivity analyses were conducted to verify the key findings. After nearest neighbor matching of PSM with a ratio of 2 and a caliper width of 0.03, there were 6,205 and 12,410 participants in the exposure and control group, respectively. Pregnant women exposed to SHS were estimated to be 58% more likely to have infants with overall birth defects (OR = 1.58, 95% CI: 1.30-1.91) and 75% more likely to have infants with circulatory system defects (OR = 1.75, 95% CI: 1.26-2.44). We also observed that the risk effect of overall birth defects had an increasing trend as the frequency of exposure increased. Additionally, sensitivity analyses suggested that our results had good robustness. These results indicate that maternal exposure to SHS likely increases the risk of overall birth defects, especially circulatory system defects, in Chinese offspring.

Chronic, Episodic Nicotine Alters Hypoglossal Motor Neuron Function at a Critical Developmental Time Point in Neonatal Rats

Developmental nicotine exposure (DNE), alters brainstem neurons that control breathing, including hypoglossal motor neurons (XIIMNs), which innervate the tongue. Here, we tested the hypothesis that chronic, episodic DNE (eDNE), which mimics nicotine replacement therapies such as e-cigarettes or nicotine gum, alters the function of nicotinic acetylcholine receptors (nAChRs), XIIMN intrinsic properties, and tongue muscle function in vivo similar to what we have observed with a chronic, sustained exposure model. We delivered nicotine to pregnant Sprague Dawley rats through drinking water and studied pups of either sex in two age groups: postnatal day (P)1-P5 and P10-P12, which encompasses a critical period in brain development. At P1-P5, eDNE was associated with delayed recovery of nAChRs from desensitization; however, there were no changes in the magnitude of desensitization, XIIMN intrinsic properties, or tongue muscle function in vivo. By P10-P12, eDNE XIIMNs had lower peak firing frequencies in response to depolarizing current injection, larger delayed rectifier potassium currents, and continued to exhibit delayed nAChR recovery. Moreover, this age group exhibited a blunted and delayed tongue muscle response to nasal occlusion in vivo, indicating that changes to XIIMN intrinsic properties is an important mechanism behind this effect, as it is not produced by altered nAChR function alone. Together, these results show that eDNE alters XIIMNs and tongue muscle function during a critical period in brain development and that the specific effects of chronic nicotine exposure may be pattern dependent.

Prenatal and Childhood Tobacco Smoke Exposure Are Associated With Sleep-Disordered Breathing Throughout Early Childhood

OBJECTIVE

To determine whether prenatal and childhood tobacco smoke exposure (TSE) are each independently associated with mild sleep-disordered breathing (SDB) symptoms throughout early childhood, and whether the association between childhood TSE and SDB differs according to the level of prenatal exposure.

METHODS

Longitudinal cohort study, using data from the Avon Longitudinal Study of Parents and Children, a population-based birth cohort from the United Kingdom. Primary exposures were repeated measures of mother-reported prenatal and childhood TSE through age 7 years. Outcomes were mother-reported measures of mild SDB symptoms, including snoring, mouth breathing, and witnessed apnea, repeated annually through age 7 years.

RESULTS

A total of 12,030 children were followed for a median duration of 7 years. About 24.2% were exposed to prenatal tobacco smoke, 46.2% were exposed at least once in childhood, and 20.6% were exposed during both periods. Both prenatal and childhood TSE were associated with SDB symptoms throughout early childhood (adjusted OR [aOR] for any prenatal TSE 1.23; 95% confidence interval [CI] 1.08, 1.40; aOR for any childhood TSE 1.17; 95% CI 1.06, 1.29). We observed a dose-response effect between TSE and SBD symptoms, and found evidence of effect modification for those exposed during both time periods (combined high level exposure both prenatally and during childhood: aOR snoring 2.43 [95% CI 1.50, 3.93], aOR apnea 2.65 [95% CI 1.46, 4.82]).

CONCLUSIONS

Prenatal and childhood TSE were both independently associated with mild SDB symptoms throughout early childhood in a dose-dependent manner, further supporting the critical importance of maintaining a tobacco-free environment throughout gestation and childhood.

Developmental Nicotine Exposure Alters Synaptic Input to Hypoglossal Motoneurons and Is Associated with Altered Function of Upper Airway Muscles

Nicotine exposure during the fetal and neonatal periods [developmental nicotine exposure (DNE)] is associated with ineffective upper airway protective reflexes in infants. This could be explained by desensitized chemoreceptors and/or mechanoreceptors, diminished neuromuscular transmission or altered synaptic transmission among central neurons, as each of these systems depend in part on cholinergic signaling through nicotinic AChRs (nAChRs). Here, we showed that DNE blunts the response of the genioglossus (GG) muscle to nasal airway occlusion in lightly anesthetized rat pups. The GG muscle helps keep the upper airway open and is innervated by hypoglossal motoneurons (XIIMNs). Experiments using the phrenic nerve-diaphragm preparation showed that DNE does not alter transmission across the neuromuscular junction. Accordingly, we used whole cell recordings from XIIMNs in brainstem slices to examine the influence of DNE on glutamatergic synaptic transmission under baseline conditions and in response to an acute nicotine challenge. DNE did not alter excitatory transmission under baseline conditions. Analysis of cumulative probability distributions revealed that acute nicotine challenge of P1–P2 preparations resulted in an increase in the frequency of nicotine-induced glutamatergic inputs to XIIMNs in both control and DNE. By contrast, P3–P5 DNE pups showed a decrease, rather than an increase in frequency. We suggest that this, together with previous studies showing that DNE is associated with a compensatory increase in inhibitory synaptic input to XIIMNs, leads to an excitatory-inhibitory imbalance. This imbalance may contribute to the blunting of airway protective reflexes observed in nicotine exposed animals and human infants.

Premature birth, homeostatic plasticity and respiratory consequences of inflammation

Infants who are born premature can have persistent apnea beyond term gestation, reemergence of apnea associated with inflammation during infancy, increased risk of sudden unexplained death, and sleep disorder breathing during infancy and childhood. The autonomic nervous system, particularly the central neural networks that control breathing and peripheral and central chemoreceptors and mechanoreceptors that modulate the activity of the central respiratory network, are rapidly developing during the last trimester (22-37 weeks gestation) of fetal life. With advances in neonatology, in well-resourced, developed countries, infants born as young as 23 weeks gestation can survive. Thus, a substantial part of maturation of central and peripheral systems that control breathing occurs ex-utero in infants born at the limit of viability. The balance of excitatory and inhibitory influences dictates the ultimate output from the central respiratory network. We propose in this review that simply being born early in the last trimester can trigger homeostatic plasticity within the respiratory network tipping the balance toward inhibition that persists in infancy. We discuss the intersection of premature birth, homeostatic plasticity and biological mechanisms leading to respiratory depression during inflammation in former premature infants.

Effects of prenatal exposure to chrysotile asbestos on hippocampal neurogenesis and long-term behavioral changes in adult male rat offspring

Prenatal development is a critical period of life that many environmental pollutants have been suggested to influence fetal growth. Nevertheless, there are still a few investigations into the prenatal exposure to chrysotile asbestos and its neurodevelopmental and behavioral outcome in offspring. In this study, twenty-eight pregnant Wistar rats were divided into four groups and received three-times repeated intraperitoneal injections of normal saline, chrysotile, ascorbic acid and the combination of chrysotile and ascorbic acid on gestational days 11, 14 and 17. The maternal serum levels of malondialdehyde (MDA) and prooxidant-antioxidant balance (PAB) and hippocampal MDA content in adult male offspring were measured. At postnatal day (PND) 60, elevated plus maze was performed to determine anxiety-like behavior, also depression-like behavior was examined using a forced swim test at PND 61- 62. Thereafter, the quantitative analysis of Ki-67, NeuN and GFAP positive cells in the hippocampal dentate gyrus were studied by immunostaining. Our data showed that prenatal exposure to chrysotile increased the maternal serum level of MDA and PAB as well as hippocampal MDA content in adult male offspring, also increased the depression- and anxiety-like behaviors of adult male offspring and decreased the hippocampal Ki-67⁺, NeuN⁺ and GFAP⁺ cells in dantate gyrus of adult male offspring. However, co-administration of ascorbic acid and chrysotile decreased hippocampal lipid peroxidation and increased the Ki-67⁺, NeuN⁺ and GFAP⁺ cells in adult male offspring. In summary, these results indicated that oxidative stress induced by prenatal exposure to chrysotile, lead to the long-lasting decrease of the hippocampal cell proliferation and neuronal differentiation as well as astrogliosis of adult male offspring that exhibit more depression- and anxiety-like behaviors in adulthood and co-treatment of ascorbic acid with chrysotile asbestos attenuated the changes.

Autonomic maturation from birth to 2 years: normative values

Background

While heart rate variability (HRV) constitutes a relevant non-invasive tool to assess the autonomic nervous system (ANS) function with recognized diagnostic or therapeutic implications, there is still a lack of established data on maturation of autonomic control of heart rate during the first months of life. The Autonomic Baby Evaluation (AuBE) cohort was built to establish, the normal autonomic maturation profile from birth up to 2 years, in a healthy population of full-term newborns.

Methods

Heart rate variability analysis was carried out in 271 full-term newborns (mean gestational age 39 wGA + 5 days) from reliable polysomnographic recordings at 0 (n = 270) and 6 (n = 221) months and from a 24-hour ambulatory electrocardiogram (ECG) at 12 (n = 210), 18 (n = 197), and 24 (n = 190) months. Indices of HRV analysis were calculated through the ANSLabTools software.

Results

Indices are dissociated according a temporal, geometrical, frequency, Poincaré, empirical mode decomposition, fractal, Chaos and DC/AC and entropy analysis. Each index is presented for five different periods of time, 0, 6, 12, 18 and 24 months and with smoothed values in the 3rd, 10th, 50th, 90th and 97th percentiles. Data are also presented for the full cohort and individualized by sex to account for gender variability.

Discussion & conclusion

The physiological autonomic maturation profile from birth to 2 years in a healthy population of term neonates results in a fine-tuning autonomic maturation underlying progressively a new equilibrium and privileging the parasympathetic activity over the sympathetic activity.

Pre- and early postnatal nicotine exposure exacerbates autoresuscitation failure in serotonin-deficient rat neonates

KEY POINTS

Sudden infant death syndrome (SIDS) is one of the leading causes of death during the first year of life and abnormalities linked to serotonin (5-HT) have been identified in many SIDS cases. Cigarette smoking and associated exogenous stressors, e.g. developmental nicotine exposure, may compound these serotonergic defects and any associated defects in cardiorespiratory function. Using neonatal rodent pups subjected to medullary 5-HT deficiency and perinatal nicotine exposure, we examined the impact of this interplay of factors on the neonates' ability to autoresuscitate at specific ages. In perinatal nicotine-exposed 5-HT deficient pups, impaired autoresuscitation along with significantly delayed post-anoxic recovery of normal breathing and heart rate was observed at postnatal day 10 (P10). We found that the interaction between 5-HT deficiency and perinatal nicotine exposure can significantly increase pups' vulnerability to environmental stressors and exacerbate defects in cardiorespiratory protective reflexes to repetitive anoxia during the development period.

ABSTRACT

Cigarette smoking during pregnancy increases the risk of sudden infant death syndrome (SIDS), and nicotine replacements, a key ingredient of cigarettes, have been recently prescribed to women who wish to quit smoking during their pregnancy. Serotonin (5-HT) abnormalities have been consistently identified in many SIDS cases. Here we investigated the effects of perinatal nicotine exposure in mild 5-HT deficiency rat neonates on autoresuscitation, a protective cardiorespiratory reflex. The mild 5-HT deficiency was induced by a maternal tryptophan-deficient diet, and nicotine was delivered from embryonic day (E) 4 to postnatal day (P) 10 at 6 mg kg^-1  day^-1 through an osmotic pump. In P10 rats, nicotine exposure exacerbates autoresuscitation failure (mortality) in mildly 5-HT-deficient rats to a greater extent than in controls (P = 0.029). The recovery of eupnoea and heart rate to baseline values following repetitive anoxic events (which elicit an apnoea accompanied by a bradycardia) is significantly delayed in 5-HT-deficient rats treated with nicotine, making them more susceptible to failure of autoresuscitation (eupnoea recovery: P = 0.0053; heart rate recovery: P = < 0.0001). Neither 5-HT deficiency nor nicotine exposure alone appears to affect the ability to autoresuscitate significantly when compared among the four treatments. The increased vulnerability to environmental stressors, e.g. severe hypoxia, asphyxia, or anoxia, in these nicotine-exposed 5-HT-deficient neonates during postnatal developmental period is evident.

Assessment of tobacco smoke effects on neonatal cardiorespiratory control using a semi-automated processing approach

A semi-automated processing approach was developed to assess the effects of early postnatal environmental tobacco smoke (ETS) on the cardiorespiratory control of newborn lambs. The system consists of several steps beginning with artifact rejection, followed by the selection of stationary segments, and ending with feature extraction. This approach was used in six lambs exposed to 20 cigarettes/day for the first 15 days of life, while another six control lambs were exposed to room air. On postnatal day 16, electrocardiograph and respiratory signals were obtained from a 6-h polysomnographic recording. The effects of postnatal ETS exposure on heart rate variability, respiratory rate variability, and cardiorespiratory interrelations were explored. The unique results suggest that early postnatal ETS exposure increases respiratory rate variability and decreases the coupling between cardiac and respiratory systems. Potentially harmful consequences in early life include unstable breathing and decreased adaptability of cardiorespiratory function, particularly during early life challenges, such as prematurity or viral infection. Graphical abstract ᅟ.

Developmental nicotine exposure alters potassium currents in hypoglossal motoneurons of neonatal rat

We previously showed that nicotine exposure in utero and after birth via breast milk [developmental nicotine exposure (DNE)] is associated with many changes in the structure and function of hypoglossal motoneurons (XIIMNs), including a reduction in the size of the dendritic arbor and an increase in cell excitability. Interestingly, the elevated excitability was associated with a reduction in the expression of glutamate receptors on the cell body. Together, these observations are consistent with a homeostatic compensation aimed at restoring cell excitability. Compensation for increased cell excitability could also occur by changing potassium conductance, which plays a critical role in regulating resting potential, spike threshold, and repetitive spiking behavior. Here we test the hypothesis that the previously observed increase in the excitability of XIIMNs from DNE animals is associated with an increase in whole cell potassium currents. Potassium currents were measured in XIIMNs in brain stem slices derived from DNE and control rat pups ranging in age from 0 to 4 days by whole cell patch-clamp electrophysiology. All currents were measured after blockade of action potential-dependent synaptic transmission with tetrodotoxin. Compared with control cells, XIIMNs from DNE animals showed significantly larger transient and sustained potassium currents, but this was observed only under conditions of increased cell and network excitability, which we evoked by raising extracellular potassium from 3 to 9 mM. These observations suggest that the larger potassium currents in nicotine-exposed neurons are an important homeostatic compensation that prevents "runaway" excitability under stressful conditions, when neurons are receiving elevated excitatory synaptic input.NEW & NOTEWORTHY Developmental nicotine exposure is associated with increased cell excitability, which is often accompanied by compensatory changes aimed at normalizing excitability. Here we show that whole cell potassium currents are also increased in hypoglossal motoneurons from nicotine-exposed neonatal rats under conditions of increased cell and network excitability. This is consistent with a compensatory response aimed at preventing instability under conditions in which excitatory synaptic input is high and is compatible with the concept of homeostatic plasticity.

Prenatal Opioid Exposure and Intermittent Hypoxemia in Preterm Infants: A Retrospective Assessment

INTRODUCTION

Intermittent hypoxemia (IH) is defined as episodic drops in oxygen saturation (SpO₂). Preterm infants are at increased risk for IH due to their immature respiratory control/apnea of prematurity. The clinical relevance of IH is a relatively new observation with rising evidence linking IH to neonatal morbidities and long-term impairment. Hence, assessing factors that influence IH in preterm infants is imperative. Given the epidemic of opioid misuse in the USA, there is an urgent need to understand the impact of prenatal opioid exposure on neonatal outcomes. Hence, we wanted to assess the relationship between isolated prenatal opioid exposure and IH in preterm infants.

METHODS

In order to accurately calculate IH, SpO₂ data were prospectively collected using high-resolution pulse oximeters during the first 8 weeks of life in preterm infants less than 30 weeks gestational age. Data related to prenatal opioid misuse were retrospectively collected from medical charts. Infants with tobacco or poly-drug exposure were excluded. The primary outcome measure is percent time spent with SpO₂ below 80% (%time-SpO₂ < 80). The secondary outcome measure is the number of severe IH events/week with SpO₂ less than 80% (IH-SpO₂ < 80).

RESULTS

A total of 82 infants with isolated opioid exposure (n = 14) or who were unexposed (n = 68) were included. There were no significant differences in baseline characteristics between opioid exposed and unexposed groups. There was a statistically significant increase of 0.23 (95% CI: 0.03, 0.43, p = 0.03) in mean of the square root of %time-SpO₂ < 80. The number of IH-SpO₂ < 80 events was higher in the opioid exposed group (mean difference = 2.95, 95% CI: -0.35, 6.25, p-value = 0.08), although statistical significance was not quite attained.

CONCLUSION

This study shows that preterm infants prenatally exposed to opioids have increased IH measures compared to unexposed infants. Interestingly, the increased IH in the opioid exposed group persists beyond the immediate postnatal period.

Lower hypoxic ventilatory response in smokers compared to non-smokers during abstinence from cigarettes

BACKGROUND

Carotid body O₂-chemosensitivity determines the hypoxic ventilatory response (HVR) as part of crucial regulatory reflex within oxygen homeostasis. Nicotine has been suggested to attenuate HVR in neonates of smoking mothers. However, whether smoking affects HVR in adulthood has remained unclear and probably blurred by acute ventilatory stimulation through cigarette smoke. We hypothesized that HVR is substantially reduced in smokers when studied after an overnight abstinence from cigarettes i.e. after nicotine elimination.

METHODS

We therefore determined the isocapnic HVR of 23 healthy male smokers (age 33.9 ± 2.0 years, BMI 24.2 ± 0.5 kg m^-2, mean ± SEM) with a smoking history of >8 years after 12 h of abstinence and compared it to that of 23 healthy male non-smokers matched for age and BMI.

RESULTS

Smokers and non-smokers were comparable with regard to factors known to affect isocapnic HVR such as plasma levels of glucose and thiols as well as intracellular levels of glutathione in blood mononuclear cells. As a new finding, abstinent smokers had a significantly lower isocapnic HVR (0.024 ± 0.002 vs. 0.037 ± 0.003 l min^-1 %^-1BMI^-1, P = 0.002) compared to non-smokers. However, upon re-exposure to cigarettes the smokers' HVR increased immediately to the non-smokers' level.

CONCLUSIONS

This is the first report of a substantial HVR reduction in abstinent adult smokers which appears to be masked by daily smoking routine and may therefore have been previously overlooked. A low HVR may be suggested as a novel link between smoking and aggravated hypoxemia during sleep especially in relevant clinical conditions such as COPD.

Nicotinic receptor activation contrasts pathophysiological bursting and neurodegeneration evoked by glutamate uptake block on rat hypoglossal motoneurons

KEY POINTS

Impaired uptake of glutamate builds up the extracellular level of this excitatory transmitter to trigger rhythmic neuronal bursting and delayed cell death in the brainstem motor nucleus hypoglossus. This process is the expression of the excitotoxicity that underlies motoneuron degeneration in diseases such as amyotrophic lateral sclerosis affecting bulbar motoneurons. In a model of motoneuron excitotoxicity produced by pharmacological block of glutamate uptake in vitro, rhythmic bursting is suppressed by activation of neuronal nicotinic receptors with their conventional agonist nicotine. Emergence of bursting is facilitated by nicotinic receptor antagonists. Following excitotoxicity, nicotinic receptor activity decreases mitochondrial energy dysfunction, endoplasmic reticulum stress and production of toxic radicals. Globally, these phenomena synergize to provide motoneuron protection. Nicotinic receptors may represent a novel target to contrast pathological overactivity of brainstem motoneurons and therefore to prevent their metabolic distress and death.

ABSTRACT

Excitotoxicity is thought to be one of the early processes in the onset of amyotrophic lateral sclerosis (ALS) because high levels of glutamate have been detected in the cerebrospinal fluid of such patients due to dysfunctional uptake of this transmitter that gradually damages brainstem and spinal motoneurons. To explore potential mechanisms to arrest ALS onset, we used an established in vitro model of rat brainstem slice preparation in which excitotoxicity is induced by the glutamate uptake blocker dl-threo-β-benzyloxyaspartate (TBOA). Because certain brain neurons may be neuroprotected via activation of nicotinic acetylcholine receptors (nAChRs) by nicotine, we investigated if nicotine could arrest excitotoxic damage to highly ALS-vulnerable hypoglossal motoneurons (HMs). On 50% of patch-clamped HMs, TBOA induced intense network bursts that were inhibited by 1-10 μm nicotine, whereas nAChR antagonists facilitated burst emergence in non-burster cells. Furthermore, nicotine inhibited excitatory transmission and enhanced synaptic inhibition. Strong neuroprotection by nicotine prevented the HM loss observed after 4 h of TBOA exposure. This neuroprotective action was due to suppression of downstream effectors of neurotoxicity such as increased intracellular levels of reactive oxygen species, impaired energy metabolism and upregulated genes involved in endoplasmic reticulum (ER) stress. In addition, HMs surviving TBOA toxicity often expressed UDP-glucose glycoprotein glucosyltransferase, a key element in repair of misfolded proteins: this phenomenon was absent after nicotine application, indicative of ER stress prevention. Our results suggest nAChRs to be potential targets for inhibiting excitotoxic damage of motoneurons at an early stage of the neurodegenerative process.

Evaluating the control: minipump implantation and breathing behavior in the neonatal rat

We evaluated genioglossus (GG) gross motoneuron morphology, electromyographic (EMG) activities, and respiratory patterning in rat pups allowed to develop without interference (unexposed) and pups born to dams subjected to osmotic minipump implantation in utero (saline-exposed). In experiment 1, 48 Sprague-Dawley rat pups (Charles-River Laboratories), ages postnatal day 7 (P7) through postnatal day 10 (P10), were drawn from two experimental groups, saline-exposed (n = 24) and unexposed (n = 24), and studied on P7, P8, P9, or P10. Pups in both groups were sedated (Inactin hydrate, 70 mg/kg), and fine-wire electrodes were inserted into the GG muscle of the tongue and intercostal muscles to record EMG activities during breathing in air and at three levels of normoxic hypercapnia [inspired CO2 fraction (FiCO2 ): 0.03, 0.06, and 0.09]. Using this approach, we assessed breathing frequency, heart rate, apnea type, respiratory event types, and respiratory stability. In experiment 2, 16 rat pups were drawn from the same experimental groups, saline-exposed (n = 9) and unexposed (n = 7), and used in motoneuron-labeling studies. In these pups a retrograde dye was injected into the GG muscle, and the brain stems were subsequently harvested and sliced. Labeled GG motoneurons were identified with microscopy, impaled, and filled with Lucifer yellow. Double-labeled motoneurons were reconstructed, and the number of primary projections and soma volumes were calculated. Whereas pups in each group exhibited the same number (P = 0.226) and duration (P = 0.093) of respiratory event types and comparable motoneuron morphologies, pups in the implant group exhibited more central apneas and respiratory instability relative to pups allowed to develop without interference.

Paternal exposure to cigarette smoke condensate leads to reproductive sequelae and developmental abnormalities in the offspring of mice

Paternal smoking is associated with infertility, birth defects and childhood cancers. Our earlier studies using cigarette smoke condensate (CSC) demonstrated several deleterious changes in male germ cells. Here, we hypothesize that chronic paternal exposure to CSC causes molecular and phenotypic changes in the sire and the offspring, respectively. In this mouse study, CSC caused DNA damage and cytotoxicity in testes via accumulation of benzo(a)pyrene (B[a]P) and cotinine. Decreased expression of growth arrest and DNA damage inducible alpha (Gadd45a), aryl hydrocarbon receptor (Ahr), and cyclin-dependent kinase inhibitor 1A (P21) was seen in CSC exposed testes. Apoptotic germ cell death was detected by induction of Fas, FasL, and activated caspase-3. The CSC-exposed males displayed reduction in sperm motility and fertilizing ability and sired pups with reduced body weight and crown-rump length, and smaller litter size with higher numbers of resorption. This model of CSC exposure demonstrates testicular toxicity and developmental defects in the offspring.

Influence of developmental nicotine exposure on glutamatergic neurotransmission in rhythmically active hypoglossal motoneurons

Developmental nicotine exposure (DNE) is associated with increased risk of cardiorespiratory, intellectual, and behavioral abnormalities in neonates, and is a risk factor for apnea of prematurity, altered arousal responses and Sudden Infant Death Syndrome. Alterations in nicotinic acetylcholine receptor signaling (nAChRs) after DNE lead to changes in excitatory neurotransmission in neural networks that control breathing, including a heightened excitatory response to AMPA microinjection into the hypoglossal motor nucleus. Here, we report on experiments designed to probe possible postsynaptic and presynaptic mechanisms that may underlie this plasticity. Pregnant dams were exposed to nicotine or saline via an osmotic mini-pump implanted on the 5th day of gestation. We used whole-cell patch clamp electrophysiology to record from hypoglossal motoneurons (XIIMNs) in thick medullary slices from neonatal rat pups (N=26 control and 24 DNE cells). To enable the translation of our findings to breathing-related consequences of DNE, we only studied XIIMNs that were receiving rhythmic excitatory drive from the respiratory central pattern generator. Tetrodotoxin was used to isolate XIIMNs from presynaptic input, and their postsynaptic responses to bath application of l-glutamic acid (glutamate) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) were studied under voltage clamp. DNE had no influence on inward current magnitude evoked by either glutamate or AMPA. However, in cells from DNE animals, bath application of AMPA was associated with a right shift in the amplitude distribution (P=0.0004), but no change in the inter-event interval distribution of miniature excitatory postsynaptic currents (mEPSCs). DNE had no influence on mEPSC amplitude or frequency evoked by glutamate application, or under (unstimulated) baseline conditions. Thus, in the presence of AMPA, DNE is associated with a small but significant increase in quantal size, but no change in the probability of glutamate release.

Plasticity in respiratory motor neurons in response to reduced synaptic inputs: A form of homeostatic plasticity in respiratory control?

For most individuals, the respiratory control system produces a remarkably stable and coordinated motor output-recognizable as a breath-from birth until death. Very little is understood regarding the processes by which the respiratory control system maintains network stability in the presence of changing physiological demands and network properties that occur throughout life. An emerging principle of neuroscience is that neural activity is sensed and adjusted locally to assure that neurons continue to operate in an optimal range, yet to date, it is unknown whether such homeostatic plasticity is a feature of the neurons controlling breathing. Here, we review the evidence that local mechanisms sense and respond to perturbations in respiratory neural activity, with a focus on plasticity in respiratory motor neurons. We discuss whether these forms of plasticity represent homeostatic plasticity in respiratory control. We present new analyses demonstrating that reductions in synaptic inputs to phrenic motor neurons elicit a compensatory enhancement of phrenic inspiratory motor output, a form of plasticity termed inactivity-induced phrenic motor facilitation (iPMF), that is proportional to the magnitude of activity deprivation. Although the physiological role of iPMF is not understood, we hypothesize that it has an important role in protecting the drive to breathe during conditions of prolonged or intermittent reductions in respiratory neural activity, such as following spinal cord injury or during central sleep apnea.

The human placental proteome is affected by maternal smoking

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The effects of maternal smoking on the term placental proteome was studied.

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Maternal smoking significantly affected 18% of protein spots.

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Maternal smoking affects systems controlling the development and function of placenta.

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The observed placental changes may contribute to the lowered birth weights.

Detrimental effects of maternal smoking on the term placental proteome and steroid-metabolizing activities, and maternal hormone levels, were studied by using seven non-smoker and seven smoker placentae. Smoking significantly affected 18% of protein spots. The functional networks affected were i) cell morphology, cellular assembly and organization, cellular compromise (15 hits) and ii) DNA replication, recombination, and repair, energy production, nucleic acid metabolism (6 hits). Smoking significantly up-regulated such proteins as, SERPINA1, EFHD1 and KRT8; and down-regulated SERPINB2, FGA and HBB. Although maternal plasma steroids were not significantly altered, the catalytic activity of CYP1A1 was increased whereas CYP19A1 activity was reduced by smoking. Furthermore, transcript expression of CYP1A1 and CYP4B1 were induced while HSD17B2, NFKB and TGFB1 were repressed by smoking. The observed smoking induced wide-spread changes on placental proteome and transcript levels may contribute to the lowered birth weights of the new-born child and placenta.

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.

Developmental nicotine exposure disrupts dendritic arborization patterns of hypoglossal motoneurons in the neonatal rat

Maternal smoking or use of other products containing nicotine during pregnancy can have significant adverse consequences for respiratory function in neonates. We have shown, in previous studies, that developmental nicotine exposure (DNE) in a model system compromises the normal function of respiratory circuits within the brainstem. The effects of DNE include alterations in the excitability and synaptic interactions of the hypoglossal motoneurons, which innervate muscles of the tongue. This study was undertaken to test the hypothesis that these functional consequences of DNE are accompanied by changes in the dendritic morphology of hypoglossal motoneurons. Hypoglossal motoneurons in brain stem slices were filled with neurobiotin during whole-cell patch clamp recordings and subjected to histological processing to reveal dendrites. Morphometric analysis, including the Sholl method, revealed significant effects of DNE on dendritic branching patterns. In particular, whereas within the first five postnatal days there was significant growth of the higher-order dendritic branches of motoneurons from control animals, the growth was compromised in motoneurons from neonates that were subjected to DNE. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 76: 1125-1137, 2016.

Influence of developmental nicotine exposure on the ventilatory and metabolic response to hyperthermia

To determine whether developmental nicotine exposure (DNE) alters the ventilatory and metabolic response to hyperthermia in neonatal rats (postnatal age 2-4 days), pregnant dams were exposed to nicotine (6 mg kg(-1) of nicotine tartrate daily) or saline with an osmotic mini-pump implanted subdermally on day 5 of gestation. Rat pups (a total of 72 controls and 72 DNE pups) were studied under thermoneutral conditions (chamber temperature 33°C) and during moderate thermal stress (37.5°C). In all pups, core temperature was similar to chamber temperature, with no treatment effects. The rates of pulmonary ventilation (V̇(I)), O2 consumption (V̇(O2)) and CO2 production (V̇(CO2)) did not change with hyperthermia in either control or DNE pups. However, V̇(I) was lower in DNE pups at both chamber temperatures, whereas the duration of spontaneous apnoeas was longer in DNE pups than in controls at 33°C. The V̇(I)/V̇(O2) ratio increased at 37.5°C in control pups, although it did not change in DNE pups. To simulate severe thermal stress, additional pups were studied at 33°C and 43°C. V̇(I) increased with heating in control pups but not in DNE pups. As heat stress continued, gasping was evoked in both groups, with no effect of DNE on the gasping pattern. Over a 20 min recovery period at 33°C, V̇(I) returned to baseline in control pups but remained depressed in DNE pups. In addition to altering baseline V̇(I) and apnoea duration, DNE is associated with subtle but significant alterations in the ventilatory response to hyperthermia in neonatal rats.

Electronic cigarettes. A position statement of the forum of international respiratory societies

BACKGROUND

Awareness and usage of electronic cigarettes has exponentially increased during the last few years, especially among young people and women in some countries. The rapid acceptance of electronic cigarettes may be attributed in part to the perception created by marketing and the popular press that they are safer than combustible cigarettes.

GOALS

To alert and advise policy makers about electronic cigarettes and their potential hazards.

METHODS

Using The Union's position paper on electronic cigarettes as the starting template, the document was written using an iterative process. Portions of the manuscript have been taken directly from the position papers of participating societies.

RESULTS

Because electronic cigarettes generate less tar and carcinogens than combustible cigarettes, use of electronic cigarettes may reduce disease caused by those components. However, the health risks of electronic cigarettes have not been adequately studied. Studies looking at whether electronic cigarettes can aid smoking cessation have had inconsistent results. Moreover, the availability of electronic cigarettes may have an overall adverse health impact by increasing initiation and reducing cessation of combustible nicotine delivery products.

CONCLUSIONS

The health and safety claims regarding electronic nicotine delivery devices should be subject to evidentiary review. The potential benefits of electronic cigarettes to an individual smoker should be weighed against potential harm to the population of increased social acceptability of smoking and use of nicotine, the latter of which has addictive power and untoward effects. As a precaution, electronic nicotine delivery devices should be restricted or banned until more information about their safety is available. If they are allowed, they should be closely regulated as medicines or tobacco products.

Methodology and recruitment for a randomised controlled trial to evaluate the safety of wahakura for infant bedsharing

BACKGROUND

Sudden Unexpected Death in Infancy (SUDI) has persistent high rates in deprived indigenous communities and much of this mortality is attributable to unsafe sleep environments. Whilst health promotion worldwide has concentrated on avoidance of bedsharing, the indigenous Māori community in New Zealand has reproduced a traditional flax bassinet (wahakura) designed to be used in ways that include bedsharing. To date there has been no assessment of the safety of this traditional sleeping device.

METHODS/DESIGN

This two arm randomised controlled trial is being conducted with 200 mother-baby dyads recruited from Māori communities in areas of high deprivation in the Hawkes Bay, New Zealand. They are randomised to wahakura or bassinet use and investigation includes questionnaires at baseline (pregnancy), when baby is 1, 3, and 6 months, and an overnight video sleep study at 1 month with monitoring of baby temperature and oxygen saturation, and measurement of baby urinary cotinine and maternal salivary oxytocin. Outcome measures are amount of time head covered, amount of time in thermal comfort zone, number of hypoxic events, amount of time in the assigned sleep device, amount of time breastfeeding, number of parental (non-feed related) touching infant events, amount of time in the prone sleep position, the number of behavioural arousals and the amount of time infant is awake overnight. Survey data will compare breastfeeding patterns at 1, 3, and 6 months as well as data on maternal mind-mindedness, maternal wellbeing, attachment to baby, and maternal sleep patterns.

DISCUSSION

Indigenous communities require creative SUDI interventions that fit within their prevailing world view. This trial, and its assessment of the safety of a wahakura relative to a standard bassinet, is an important contribution to the range of SUDI prevention research being undertaken worldwide.

TRIALS REGISTRATION

Australian New Zealand Clinical Trials Registry: ACTRN12610000993099 Registered 16th November 2010.

Maternal snuff use and smoking and the risk of oral cleft malformations--a population-based cohort study

Objective

To determine if maternal use of snuff (containing high levels of nicotine, low levels of nitrosamines and no combustion products) is associated with an increased risk of oral cleft malformations in the infant and whether cessation of snuff use or smoking before the antenatal booking influences the risk.

Method

A population-based cohort study was conducted on all live born infants, recorded in the Swedish Medical Birth Register from 1999 through 2009 (n = 1 086 213). Risks of oral clefts were evaluated by multivariate logistic regression analyses (using adjusted odds ratios, with 95% confidence intervals [CI]).

Results

Among 975 866 infants that had information on maternal tobacco use, 1761 cases of oral clefts were diagnosed. More than 50% of the mothers who used snuff or smoked three months prior pregnancy stopped using before the antenatal booking. Almost 8% of the mothers were smoking at the antenatal booking and 1,1% of the mothers used snuff. Compared with infants of non-tobacco users, the adjusted odds ratios (95% CI) of any oral cleft for infants of mothers who continued to use snuff or to smoke were 1.48 [1.00–2.21] and 1.19 [1.01–1.41], respectively. In contrast, in infants of mothers who stopped using snuff or stopped smoking before the antenatal booking, the corresponding risks were not increased (adjusted odds ratios [95% CI] were 0.71 [0.44–1.14] and 0.88 [0.73–1.05], respectively).

Conclusion

Maternal snuff use or smoking in early pregnancy is associated with an increased risk of oral clefts. Infants of mothers who stopped using snuff or stopped smoking before the antenatal booking had no increased risk of oral cleft malformations. Oral snuff or other sources of nicotine should not be recommended as an alternative for smoke-cessation during pregnancy.

Effects of maternal nicotine exposure on expression of laminin alpha 5 in lung tissue of newborn

Maternal smoking has been clearly demonstrated to be associated with increased health problems in infants and children. Nicotine is the chemical substance with high level of toxicity. It crosses through the placenta and accumulates in the developing organs of fetus. Previous investigation indicated that maternal nicotine exposures induce decreased fibronectin expression in lung parenchyma. In this study, the effect of maternal nicotine exposure on laminin expression of the newborn mice lungs has been evaluated. Female pregnant Balb/C mice were divided randomly in to four groups as fallow: Experimental group 1 (Exp D1); was received 3 mg kg(-1) nicotine intra peritoneal injection (IP) from gestational day 7 (GD7) to the last day of pregnancy, Experimental group 2 (Exp D14); was received 3 mg kg(-1) nicotine from GD7 to postnatal day 14, Groups 3 and 4; as sham control groups (Sha-Con) were received the same volume (3 mg kg(-1)) of normal saline parallel to experimental groups. At the end of exposure times, all of newborns were anesthetized; their lungs were removed and prepared for immunohistochemical method and real-time polymerase chain reaction. The finding indicated that laminin alpha 5 (Lama5) mRNA expressions in the lung of newborn in the nicotine treated Exp D1 decreased by 0.63 fold but increased in Exp D14 by 1.57 fold comparing to Sh-Con groups. Lama5 immunoreactivity was not similar in different parts of the lungs including alveoli and bronchiole, having a significant increase in the experimental groups in contrast to the Sh-Con groups. However, increase in immunoreactivity observed more in Exp D14. Immunoreactivity intensity in small vessels of all experimental groups was not significantly different. These data also indicate that maternal nicotine exposure may induce abnormal laminin expression which may cause defects in lung function during life time.

Smoking during pregnancy and risk of autism spectrum disorder in a Finnish National Birth Cohort

BACKGROUND

Results of previous population-based studies examining associations between smoking during pregnancy and autism spectrum disorders (ASD) are contradictory. Furthermore, there is a lack of population-based studies examining the relationship between smoking during pregnancy and the main diagnostic subtypes of ASD.

METHODS

We conducted a population-based nested case-control study based on the Finnish Prenatal Study of Autism (FIPS-A) among liveborn infants delivered in Finland between 1987 and 2005. Data on maternal smoking during pregnancy were available from the Finnish Medical Birth Register (FMBR) since October 1990. Data on ASD in the offspring were obtained from the Finnish Hospital Discharge Register (FHDR).

RESULTS

Among the three subtypes of ASD, maternal smoking during the whole pregnancy was associated with an increased risk of pervasive developmental disorder (PDD) (odds ratio 1.2, 95% confidence interval 1.0, 1.5). The increase in odds persisted after controlling for maternal age, mother's socio-economic and psychiatric status, and infant's weight for gestational age. However, smoking exposure limited to the first trimester was not associated with PDD or any of the other ASD subtypes.

CONCLUSIONS

Maternal smoking is related to a modest increase in risk of PDD, while no associations were observed for childhood autism and Asperger's syndrome.

Developmental nicotine exposure alters AMPA neurotransmission in the hypoglossal motor nucleus and pre-Botzinger complex of neonatal rats

Developmental nicotine exposure (DNE) impacts central respiratory control in neonates born to smoking mothers. We previously showed that DNE enhances the respiratory motor response to bath application of AMPA to the brainstem, although it was unclear which brainstem respiratory neurons mediated these effects (Pilarski and Fregosi, 2009). Here we examine how DNE influences AMPA-type glutamatergic neurotransmission in the pre-Bötzinger complex (pre-BötC) and the hypoglossal motor nucleus (XIIMN), which are neuronal populations located in the medulla that are necessary for normal breathing. Using rhythmic brainstem slices from neonatal rats, we microinjected AMPA into the pre-BötC or the XIIMN while recording from XII nerve rootlets (XIIn) as an index of respiratory motor output. DNE increased the duration of tonic activity and reduced rhythmic burst amplitude after AMPA microinjection into the XIIMN. Also, DNE led to an increase in respiratory burst frequency after AMPA injection into the pre-BötC. Whole-cell patch-clamp recordings of XII motoneurons showed that DNE increased motoneuron excitability but did not change inward currents. Immunohistochemical studies indicate that DNE reduced the expression of glutamate receptor subunits 2 and 3 (GluR2/3) in the XIIMN and the pre-BötC. Our data show that DNE alters AMPAergic synaptic transmission in both the XIIMN and pre-BötC, although the mechanism by which this occurs is unclear. We suggest that the DNE-induced reduction in GluR2/3 may represent an attempt to compensate for increased cell excitability, consistent with mechanisms underlying homeostatic plasticity.

Cardiorespiratory coupling in health and disease

Cardiac and respiratory activities are intricately linked both functionally as well as anatomically through highly overlapping brainstem networks controlling these autonomic physiologies that are essential for survival. Cardiorespiratory coupling (CRC) has many potential benefits creating synergies that promote healthy physiology. However, when such coupling deteriorates autonomic dysautonomia may ensue. Unfortunately there is still an incomplete mechanistic understanding of both normal and pathophysiological interactions that respectively give rise to CRC and cardiorespiratory dysautonomia. Moreover, there is also a need for better quantitative methods to assess CRC. This review addresses the current understanding of CRC by discussing: (1) the neurobiological basis of respiratory sinus arrhythmia (RSA); (2) various disease states involving cardiorespiratory dysautonomia; and (3) methodologies measuring heart rate variability and RSA.

Atomic force microscopy to characterize binding properties of α7-containing nicotinic acetylcholine receptors on neurokinin-1 receptor-expressing medullary respiratory neurons

In the present study, we used atomic force microscopy (AFM) to examine the ligand-binding properties of α7-containing nicotinic acetylcholine receptors (nAChRs) expressed on neurons from the ventral respiratory group. We also determined the effect of acute and prolonged exposure to nicotine on the binding probability of nAChRs. Neurons from neonatal (postnatal day 5-10) and juvenile rats (3-4 weeks old) were cultured. Internalization of Alexa Fluor 488-conjugated substance P was used to identify respiratory neurons that expressed the neurokinin-1 receptor (NK1-R), a recognized marker of ventral respiratory group neurons. To assess functional changes in nAChRs, AFM probes conjugated with anti-α7 subunit nAChR antibody were used to interact cyclically with the surface of the soma of NK1-R-positive neurons. Measurements were made of the frequency of antibody adhesion to the α7 receptor subunit and of the detachment forces between the membrane-attached receptor and the AFM probe tip. Addition of α-bungarotoxin (a specific antagonist of α7 subunit-containing nAChRs) to the cell bath produced a 69% reduction in binding to the α7 subunit (P < 0.05, n = 10), supporting specificity of binding. Acute exposure to nicotine (1 μM added to culture media) produced an 80% reduction in nAChR antibody binding to the α7 subunit (P < 0.05, n = 9). Prolonged incubation (72 h) of the cell culture in nicotine significantly reduced α7 binding in a concentration-dependent manner. Collectively, these findings demonstrate that AFM is a sensitive tool for assessment of functional changes in nAChRs expressed on the surface of living NK1-R-expressing medullary neurons. Moreover, these data demonstrate that nicotine exposure decreases the binding probability of α7 subunit-containing nAChRs.

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.

Optical coherence tomography captures rapid hemodynamic responses to acute hypoxia in the cardiovascular system of early embryos

BACKGROUND

The trajectory to heart defects may start in tubular and looping heart stages when detailed analysis of form and function is difficult by currently available methods. We used a novel method, Doppler optical coherence tomography (OCT), to follow changes in cardiovascular function in quail embryos during acute hypoxic stress. Chronic fetal hypoxia is a known risk factor for congenital heart diseases (CHDs). Decreased fetal heart rates during maternal obstructive sleep apnea suggest that studying fetal heart responses under acute hypoxia is warranted.

RESULTS

We captured responses to hypoxia at the critical looping heart stages. Doppler OCT revealed detailed vitelline arterial pulsed Doppler waveforms. Embryos tolerated 1 hr of hypoxia (5%, 10%, or 15% O(2) ), but exhibited changes including decreased systolic and increased diastolic duration in 5 min. After 5 min, slower heart rates, arrhythmic events and an increase in retrograde blood flow were observed. These changes suggested slower filling of the heart, which was confirmed by four-dimensional Doppler imaging of the heart itself.

CONCLUSIONS

Doppler OCT is well suited for rapid noninvasive screening for functional changes in avian embryos under near physiological conditions. Analysis of the accessible vitelline artery sensitively reflected changes in heart function and can be used for rapid screening. Acute hypoxia caused rapid hemodynamic changes in looping hearts and may be a concern for increased CHD risk.

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.

Isolated in vitro brainstem-spinal cord preparations remain important tools in respiratory neurobiology

Isolated in vitro brainstem-spinal cord preparations are used extensively in respiratory neurobiology because the respiratory network in the pons and medulla is intact, monosynaptic descending inputs to spinal motoneurons can be activated, brainstem and spinal cord tissue can be bathed with different solutions, and the responses of cervical, thoracic, and lumbar spinal motoneurons to experimental perturbations can be compared. The caveats and limitations of in vitro brainstem-spinal cord preparations are well-documented. However, isolated brainstem-spinal cords are still valuable experimental preparations that can be used to study neuronal connectivity within the brainstem, development of motor networks with lethal genetic mutations, deleterious effects of pathological drugs and conditions, respiratory spinal motor plasticity, and interactions with other motor behaviors. Our goal is to show how isolated brainstem-spinal cord preparations still have a lot to offer scientifically and experimentally to address questions within and outside the field of respiratory neurobiology.

Relationship of maternal snuff use and cigarette smoking with neonatal apnea

BACKGROUND

Maternal smoking is associated with disturbed cardiorespiratory control in the infant. Despite lacking knowledge of whether the harmful effects of smoking are caused by combustion products in tobacco smoke or by nicotine, it has been argued that nicotine-replacement therapy during pregnancy is safer than smoking.

OBJECTIVE

The goal of this study was to investigate if the disturbances in cardiorespiratory control associated with maternal smoking are also seen in infants prenatally exposed to snuff. We hypothesized that prenatal nicotine exposure (via moist snuff) causes disturbances in autonomic control and thereby increases the risk of apnea in the newborn.

METHODS

In a nationwide Swedish cohort study, we studied associations between maternal tobacco use during pregnancy and neonatal apnea. Of 609 551 live-born singleton infants, 7599 were born to snuff-using mothers, 41 391 and 16 928 were born to light (1-9 cigarettes per day) and heavy (≥ 10 cigarettes per day) smokers, respectively. Logistic regression was used to calculate odds ratios, using 95% confidence intervals.

RESULTS

Compared with infants of nontobacco users, infants with prenatal exposure to snuff were at an increased risk of apnea even after adjustment for differences in gestational age (odds ratio: 1.96 [95% confidence interval: [1.30-2.96]) Smoking was associated with increased risk of apnea before, but not after, adjusting for gestational age.

CONCLUSIONS

Snuff use during pregnancy is associated with a higher risk of neonatal apnea than smoking. Maternal use of snuff or nicotine-replacement therapy cannot be regarded as an alternative to smoking during pregnancy.

Developmental nicotine exposure alters neurotransmission and excitability in hypoglossal motoneurons

Hypoglossal motoneurons (XII MNs) control muscles of the mammalian tongue and are rhythmically active during breathing. Acetylcholine (ACh) modulates XII MN activity by promoting the release of glutamate from neurons that express nicotinic ACh receptors (nAChRs). Chronic nicotine exposure alters nAChRs on neurons throughout the brain, including brain stem respiratory neurons. Here we test the hypothesis that developmental nicotine exposure (DNE) reduces excitatory synaptic input to XII MNs. Voltage-clamp experiments in rhythmically active medullary slices showed that the frequency of excitatory postsynaptic currents (EPSCs) onto XII MNs from DNE animals is reduced by 61% (DNE = 1.7 ± 0.4 events/s; control = 4.4 ± 0.6 events/s; P < 0.002). We also examine the intrinsic excitability of XII MNs to test whether cells from DNE animals have altered membrane properties. Current-clamp experiments showed XII MNs from DNE animals had higher intrinsic excitability, as evaluated by measuring their response to injected current. DNE cells had high-input resistances (DNE = 131.9 ± 13.7 MΩ, control = 78.6 ± 9.7 MΩ, P < 0.008), began firing at lower current levels (DNE = 144 ± 22 pA, control = 351 ± 45 pA, P < 0.003), and exhibited higher frequency-current gain values (DNE = 0.087 ± 0.012 Hz/pA, control = 0.050 ± 0.004 Hz/pA, P < 0.02). Taken together, our data show previously unreported effects of DNE on XII MN function and may also help to explain the association between DNE and the incidence of central and obstructive apneas.

Effects of postnatal smoke exposure on laryngeal chemoreflexes in newborn lambs

Laryngeal chemoreflexes (LCR), which are elicited by the contact of liquids such as gastric refluxate with laryngeal mucosa, may trigger some cases of sudden infant death syndrome. Indeed, while LCR in mature mammals consist of protective responses, previous animal data have shown that LCR in immature newborns can include laryngospasm, apnea, bradycardia, and desaturation. The present study was aimed at testing the hypothesis that postnatal exposure to cigarette smoke is responsible for enhancing cardiorespiratory inhibition observed with LCR. Eight lambs were exposed to cigarette smoke (20 cigarettes/day) over 16 days and compared with seven control lambs. Urinary cotinine/creatinine ratio was measured at a level relevant to previously published levels in infants. On days 15 and 16, 0.5 ml of HCl (pH 2), milk, distilled water, or saline was injected onto the larynx via a chronic supraglottal catheter during sleep. Results showed that exposure to cigarette smoke enhanced respiratory inhibition (P < 0.05) and tended to enhance cardiac inhibition and decrease swallowing and arousal during LCR (P < 0.1). Overall, these results were observed independently of the state of alertness and the experimental solution tested. In conclusion, 16-day postnatal exposure to cigarette smoke increases cardiorespiratory inhibition and decreases protective mechanisms during LCR in nonsedated full-term lambs.

Effects of nicotine during pregnancy: human and experimental evidence

Prenatal exposure to tobacco smoke is a major risk factor for the newborn, increasing morbidity and even mortality in the neonatal period but also beyond. As nicotine addiction is the factor preventing many women from smoking cessation during pregnancy, nicotine replacement therapy (NRT) has been suggested as a better alternative for the fetus. However, the safety of NRT has not been well documented, and animal studies have in fact pointed to nicotine per se as being responsible for a multitude of these detrimental effects. Nicotine interacts with endogenous acetylcholine receptors in the brain and lung, and exposure during development interferes with normal neurotransmitter function, thus evoking neurodevelopmental abnormalities by disrupting the timing of neurotrophic actions. As exposure to pure nicotine is quite uncommon in pregnant women, very little human data exist aside from the vast literature on prenatal exposure to tobacco smoke.

The current review discusses recent findings in humans on effects on the newborn of prenatal exposure to pure nicotine and non-smoke tobacco. It also reviews the neuropharmacological properties of nicotine during gestation and findings in animal experiments that offer explanations on a cellular level for the pathogenesis of such prenatal drug exposure.

It is concluded that as findings indicate that functional nAChRs are present very early in neuronal development, and that activation at this stage leads to apoptosis and mitotic abnormalities, a total abstinence from all forms of nicotine should be advised to pregnant women for the entirety of gestation.

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

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

Influence of prenatal nicotine exposure on development of the ventilatory response to hypoxia and hypercapnia in neonatal rats

In a recent study (Huang YH et al. Respir Physiol Neurobiol 143: 1-8, 2004), we showed that prenatal nicotine exposure (PNE) increased the frequency of spontaneous apneic events on the first 2 days of life in unanesthetized neonatal rats. Here we test the hypothesis that PNE blunts chemoreceptor reflexes. Ventilatory responses to three levels each of hypoxia (inspired O(2) fraction: 16, 12, and 10%) and hypercapnia (3, 6, and 9% inspired CO(2) fraction, all in 50% O(2), balance N(2)), and one level each of combined hypoxia-hypercapnia (H/H; 12% inspired O(2) fraction/5% inspired CO(2) fraction) and hyperoxia (50% O(2), 50% N(2)) were recorded with head-out plethysmography in neonatal rats exposed to either nicotine (N = 12) or physiological saline (N = 12) in the prenatal period. Recordings were made on postnatal day 1 (P1), P3, P6, P9, P12, and P18, in each animal. The change in ventilation in response to hypoxia was blunted in PNE animals on P1 and P3, but there were no other treatment effects. Hyperoxia significantly depressed ventilation in both groups from P3-P18, but there were no significant treatment effects. The ventilatory response to 3, 6, and 9% inspired CO(2) was significantly blunted in PNE animals at all ages studied, due exclusively to a blunted tidal volume response. PNE also blunted the ventilatory response to H/H at all ages, due primarily to blunting of the tidal volume response. PNE had no significant effect on body mass or metabolic rate, except that PNE animals had a slightly higher mass on P18 and a lower metabolic rate on P1. As shown by others, PNE has small and inconsistent effects on hypoxic ventilatory responses, but here we show that responses to hypercapnia and H/H are consistently blunted by PNE due to a diminished tidal volume response. The combination of reduced hypoxic and hypercapnic sensitivity over the first 3 days of life may define an especially vulnerable developmental period.

Long-term consequences of fetal and neonatal nicotine exposure: a critical review

Cigarette smoking during pregnancy is associated with numerous obstetrical, fetal, and developmental complications, as well as an increased risk of adverse health consequences in the adult offspring. Nicotine replacement therapy (NRT) has been developed as a pharmacotherapy for smoking cessation and is considered to be a safer alternative for women to smoking during pregnancy. The safety of NRT use during pregnancy has been evaluated in a limited number of short-term human trials, but there is currently no information on the long-term effects of developmental nicotine exposure in humans. However, animal studies suggest that nicotine alone may be a key chemical responsible for many of the long-term effects associated with maternal cigarette smoking on the offspring, such as impaired fertility, type 2 diabetes, obesity, hypertension, neurobehavioral defects, and respiratory dysfunction. This review will examine the long-term effects of fetal and neonatal nicotine exposure on postnatal health.