Additive and synergistic effects of fetal nicotine and dexamethasone exposure on cholinergic synaptic function in adolescence and adulthood: Implications for the adverse consequences of maternal smoking and pharmacotherapy of preterm delivery

Dexamethasone effect on heart rate variability in preterm infants on mechanical ventilation

BACKGROUND

Dexamethasone is administered to some preterm infants with chronic lung disease to facilitate weaning from mechanical ventilation. Heart rate characteristics (HRC), including heart rate variability (HRV), may be impacted by glucocorticoids and may predict extubation readiness. A commercially available monitor developed for sepsis detection continuously calculates HRV and an HRC index, which are inversely related.

OBJECTIVES

Determine the impact of dexamethasone on HRV and the HRC index, in relation to extubation success.

METHODS

We identified 109 preterm infants who received dexamethasone while on mechanical ventilation and had HRC index monitoring data available. Average hourly HRV and HRC index were compared the day before and the day after initiation of dexamethasone in three groups: infants who remained on mechanical ventilation, those who were successfully extubated, and those who were extubated and required reintubation in < 3 days.

RESULTS

There was a significant increase in HRV and decrease in the HRC index the day after dexamethasone was started (HRV 16.2±0.5 vs 27.6±1.1 ms; HRC index 1.51±0.11 vs. 0.79±0.06 mean SE, p < 0.001). The 63 infants who were extubated within a day of starting dexamethasone had significantly higher HRV compared to those who remained on mechanical ventilation. There was no difference in HRV or its change with dexamethasone in the 45 infants who remained successfully extubated compared to the 18 infants who required reintubation within 3 days.

CONCLUSION

Dexamethasone improves HRV and lowers the HRC index in preterm infants with chronic lung disease on mechanical ventilation.

Prenatal nicotine alters the developmental neurotoxicity of postnatal chlorpyrifos directed toward cholinergic systems: better, worse, or just "different?"

This study examines whether prenatal nicotine exposure sensitizes the developing brain to subsequent developmental neurotoxicity evoked by chlorpyrifos, a commonly-used insecticide. We gave nicotine to pregnant rats throughout gestation at a dose (3mg/kg/day) producing plasma levels typical of smokers; offspring were then given chlorpyrifos on postnatal days 1-4, at a dose (1mg/kg) that produces minimally-detectable inhibition of brain cholinesterase activity. We evaluated indices for acetylcholine (ACh) synaptic function throughout adolescence, young adulthood and later adulthood, in brain regions possessing the majority of ACh projections and cell bodies; we measured nicotinic ACh receptor binding, hemicholinium-3 binding to the presynaptic choline transporter and choline acetyltransferase activity, all known targets for the adverse developmental effects of nicotine and chlorpyrifos given individually. By itself nicotine elicited overall upregulation of the ACh markers, albeit with selective differences by sex, region and age. Likewise, chlorpyrifos alone had highly sex-selective effects. Importantly, all the effects showed temporal progression between adolescence and adulthood, pointing to ongoing synaptic changes rather than just persistence after an initial injury. Prenatal nicotine administration altered the responses to chlorpyrifos in a consistent pattern for all three markers, lowering values relative to those of the individual treatments or to those expected from simple additive effects of nicotine and chlorpyrifos. The combination produced global interference with emergence of the ACh phenotype, an effect not seen with nicotine or chlorpyrifos alone. Given that human exposures to nicotine and chlorpyrifos are widespread, our results point to the creation of a subpopulation with heightened vulnerability.

Maternal smoking during pregnancy and infant stress response: test of a prenatal programming hypothesis

BACKGROUND

Maternal smoking during pregnancy (MSDP) is associated with early and long-term neurobehavioral deficits; however mechanisms remain unknown. We tested the hypothesis that MSDP programs the hypothalamic pituitary adrenocortical (HPA) axis of the offspring leading to adverse outcomes. In an intensive, prospective study, we investigated associations between MSDP and infant cortisol stress response and explored whether alterations in cortisol response were mediated by epigenetic modulation of the placental glucocorticoid receptor gene (NR3C1).

METHODS

Participants were 100 healthy mother-infant pairs (53% MSDP-exposed; 42% female) from a low income, racially/ethnically diverse sample (55% minorities). MSDP was assessed by timeline followback interview verified by saliva and meconium cotinine. Infant cortisol responses to a neurobehavioral exam were assessed seven times over the first postnatal month. Methylation of placental NR3C1 promoter exon 1F was assessed using bisulfite pyrosequencing in a subsample (n=45).

RESULTS

MSDP-exposed infants showed significantly and persistently attenuated basal and reactive cortisol levels over the first postnatal month vs. unexposed infants. Exploratory analyses revealed that MSDP was associated with altered methylation of the placental NR3C1 promoter; degree of methylation of the placental NR3C1 was associated with infant basal and reactive cortisol over the first postnatal month and mediated effects of MSDP on infant basal cortisol.

CONCLUSIONS

Results provide initial support for our hypothesis that MSDP programs offspring HPA (dys)regulation. Epigenetic regulation of placental GR may serve as a novel underlying mechanism. Results may have implications for delineating pathways to adverse outcomes from MSDP.

Smoking cessation

Cigarette smoking is a major preventable cause of morbidity and mortality. It is the major risk factor for chronic obstructive pulmonary disease in the developed world. Smoking is a chronic relapsing disease. Optimal treatment includes nonpharmacologic support, together with pharmacotherapy. All clinicians should be comfortable with the use of nicotine replacement therapy, bupropion, and varenicline. Second-line therapies can be used by those familiar with their use. Effective use of these medications requires their integration into an effective management plan, which is likely to be a long-term undertaking, involving several cycles of remission and relapse.

Prenatal glucocorticoids and maternal smoking during pregnancy independently program adult nicotine dependence in daughters: a 40-year prospective study

BACKGROUND

Maternal smoking during pregnancy (MSDP) is an independent risk factor for offspring nicotine dependence (ND), but mechanisms remain unknown. We investigated prenatal glucocorticoid (cortisol) and androgen (testosterone) associations with offspring ND over 40 years and the possibility that prenatal glucocorticoids and androgens would mediate links between MSDP and offspring ND.

METHODS

Participants were 1086 mother-adult offspring pairs (59% female) from the New England Family Study, a 40-year longitudinal follow-up of the Collaborative Perinatal Project. MSDP was assessed prospectively at each prenatal visit. Maternal cortisol, testosterone, and cotinine (nicotine metabolite) were assayed from third trimester maternal sera. Offspring lifetime ND was assessed via structured interview.

RESULTS

Significant bivariate associations emerged for: 1) MSDP/cotinine and lifetime ND; and 2) maternal cortisol and lifetime ND, for daughters only. In multivariate models, maternal cortisol and MSDP/cotinine remained significantly and independently associated with increased odds of lifetime ND of daughters. However, cortisol did not mediate the MSDP-lifetime ND relation. No associations emerged between maternal testosterone and offspring ND.

CONCLUSIONS

Results provide the first evidence in support of prenatal glucocorticoid programming of adult ND over 40 years in daughters only. Our study highlights two independent prenatal pathways leading to increased risk for ND in daughters: elevated prenatal glucocorticoids and MSDP/nicotine exposure. Daughter-specific effects of glucocorticoid and MSDP programming over 40 years highlight the breadth and persistence of sexually dimorphic programming effects in humans. Results do not support androgen programming of offspring ND.

Mimicking maternal smoking and pharmacotherapy of preterm labor: fetal nicotine exposure enhances the effect of late gestational dexamethasone treatment on noradrenergic circuits

Smoking during pregnancy increases the risk of preterm delivery, which in turn necessitates the common use of glucocorticoids to prevent respiratory distress syndrome. Accordingly, there is a substantial population exposed conjointly to fetal nicotine and glucocorticoids (typically dexamethasone). We administered nicotine to pregnant rats throughout gestation, using a regimen (3 mg/kg/day by osmotic minipump) that maintains plasma nicotine levels within the range seen in smokers; on gestational days 17, 18 and 19, we gave 0.2 mg/kg of dexamethasone. We assessed norepinephrine levels in three brain regions (frontal/parietal cortex, brainstem, cerebellum) throughout adolescence, young adulthood and later adulthood, and contrasted the persistent effects with comparable measures in peripheral tissues (heart, liver). In adolescence, males showed initial deficits in the frontal/parietal cortex with either dexamethasone alone or the combined treatment, with resolution to normal by young adulthood; the group exposed to both nicotine+dexamethasone showed subsequent elevations that emerged in full adulthood and persisted through five months of age, an effect not seen with either agent separately. In females, the combined exposure produced an initial deficit that resolved by young adulthood, without any late-emerging changes. We did not see comparable effects in the other brain regions or peripheral tissues. This indicates that nicotine exposure sensitizes the developing brain to the adverse effects of dexamethasone treatment, producing sex-selective changes in innervation and/or activity of specific noradrenergic circuits. The fact that the combined treatment produced greater effects points to potentially worsened neurobehavioral outcomes after pharmacotherapy of preterm labor in the offspring of smokers.

Nicotine: alcohol reward interactions

It is well established that the continued intake of drugs of abuse is reinforcing-that is repeated consumption increases preference. This has been shown in some studies to extend to other drugs of abuse; use of one increases preference for another. In particular, the present review deals with the interaction of nicotine and alcohol as it has been shown that smoking is a risk factor for alcoholism and alcohol use is a risk factor to become a smoker. The review discusses changes in the brain caused by chronic nicotine and chronic alcohol intake to approach the possible mechanisms by which one drug increases the preference for another. Chronic nicotine administration was shown to affect nicotine receptors in the brain, affecting not only receptor levels and distribution, but also receptor subunit composition, thus affecting affinity to nicotine. Other receptor systems are also affected among others catecholamine, glutamate, GABA levels and opiate and cannabinoid receptors. In addition to receptor systems and transmitters, there are endocrine, metabolic and neuropeptide changes as well induced by nicotine. Similarly chronic alcohol intake results in changes in the brain, in multiple receptors, transmitters and peptides as discussed in this overview and also illustrated in the tables. The changes are sex and age-dependent-some changes in males are different from those in females and in general adolescents are more sensitive to drug effects than adults. Although nicotine and alcohol interact-not all the changes induced by the combined intake of both are additive-some are opposing. These opposing effects include those on locomotion, acetylcholine metabolism, nicotine binding, opiate peptides, glutamate transporters and endocannabinoid content among others. The two compounds lower the negative withdrawal symptoms of each other which may contribute to the increase in preference, but the mechanism by which preference increases-most likely consists of multiple components that are not clear at the present time. As the details of induced changes of nicotine and alcohol differ, it is likely that the mechanisms of increasing nicotine preference may not be identical to that of increasing alcohol preference. Stimulation of preference of yet other drugs may again be different -representing one aspect of drug specificity of reward mechanisms.

Mimicking maternal smoking and pharmacotherapy of preterm labor: interactions of fetal nicotine and dexamethasone on serotonin and dopamine synaptic function in adolescence and adulthood

Fetal coexposure to nicotine and dexamethasone is common: maternal smoking increases the incidence of preterm delivery and glucocorticoids are the consensus treatment for prematurity. We gave pregnant rats 3mg/kg/day of nicotine throughout gestation, a regimen that reproduces smokers' plasma levels, and then on gestational days 17, 18 and 19, we administered 0.2mg/kg of dexamethasone. We evaluated developmental indices for serotonin (5HT) and dopamine synaptic function throughout adolescence, young adulthood and later adulthood, assessing the brain regions possessing major 5HT and dopamine projections and cell bodies. Males displayed persistent upregulation of 5HT(1A) and 5HT(2) receptors and the 5HT transporter, with a distinct hierarchy of effects: nicotine<dexamethasone<combined treatment. Females showed downregulation of the 5HT(1A) receptor with the same rank order; both sexes displayed presynaptic hyperactivity of 5HT and dopamine pathways as evidenced by increased neurotransmitter turnover. Superimposed on these overall effects, there were significant differences in temporal and regional relationships among the different treatments, often involving effects that emerged later in life, after a period of apparent normality. This indicates that nicotine and dexamethasone do not simply produce an initial neuronal injury that persists throughout the lifespan but rather, they alter the developmental trajectory of synaptic function. The fact that the combined treatment produced greater effects for many parameters points to potentially worse neurobehavioral outcomes after pharmacotherapy of preterm labor in the offspring of smokers.