CNS determinants of sleep-related worsening of airway functions: implications for nocturnal asthma

Association of Parasomnia Symptoms with Risk of Childhood Asthma and the Role of Preterm Birth

PURPOSE

To examine whether parasomnia symptoms are associated with increased odds of childhood asthma and wheeze, and the role of preterm birth.

PATIENTS AND METHODS

The Shanghai Children's Allergy Study was cross-sectionally conducted in 31 kindergartens and 17 primary schools in Shanghai, China. After excluding the missing data of gestational week and child's age, this study included a total of 16,487 individuals with a mean age of 7.74 years and 52.4% of males. The association between parasomnia symptoms and wheeze/asthma was assessed by univariate and multivariate analyses. The interaction effects of parasomnias and preterm birth were primarily evaluated by P for multiplicative interaction, and the relative excess risk due to interaction (RERI), attributable proportion due to interaction (AP), and synergy index (SI) were also measured.

RESULTS

Parasomnias, especially rapid eye movement (REM) parasomnia symptoms, were associated with an increased risk of childhood wheeze/asthma, and the interaction between parasomnia and preterm birth exhibited an excess risk of current wheeze (RERI, 1.43; 95% CI, 0.41-2.45) and ever asthma (RERI, 0.75; 95% CI, 0.01-1.50). In the stratification analyses, the combination of parasomnia symptoms and preterm birth had higher odds of wheeze/asthma. And the odds of current wheeze (OR, 4.55; 95% CI, 1.69-12.25; p=0.003) and ever asthma (OR, 6.17; 95% CI, 2.36-16.11; p<0.001) were much higher in cumulative parasomnia symptoms plus very preterm birth. And sensitive analyses were further conducted in populations without sleep disordered breathing (SDB), and an allergen test subgroup, yielding similar results.

CONCLUSION

Parasomnia symptoms are associated with increased odds of childhood wheeze/asthma, and the odds were even higher in premature population. The findings suggest that parasomnia symptoms, as a developmental sleep disorder, are supposed to be closely watched among children who have asthma or are at risk for asthma, and that preterm children deserve more attention.

Mini review: Neural mechanisms underlying airway hyperresponsiveness

Neural changes underly hyperresponsiveness in asthma and other airway diseases. Afferent sensory nerves, nerves within the brainstem, and efferent parasympathetic nerves all contribute to airway hyperresponsiveness. Inflammation plays a critical role in these nerve changes. Chronic inflammation and pre-natal exposures lead to increased airway innervation and structural changes. Acute inflammation leads to shifts in neurotransmitter expression of afferent nerves and dysfunction of M₂ muscarinic receptors on efferent nerve endings. Eosinophils and macrophages drive these changes through release of inflammatory mediators. Novel tools, including optogenetics, two photon microscopy, and optical clearing and whole mount microscopy, allow for improved studies of the structure and function of airway nerves and airway hyperresponsiveness.

Activation of α1-adrenoceptors facilitates excitatory inputs to medullary airway vagal preganglionic neurons

In mammals, the neural control of airway smooth muscle is dominated by a subset of airway vagal preganglionic neurons in the ventrolateral medulla. These neurons are physiologically modulated by adrenergic/noradrenergic projections, and weakened α₂-adrenergic inhibition of them is indicated to participate in the pathogenesis and exacerbation of asthma. This study tests whether these neurons are modulated by α₁-adrenoceptors, and if so, how. In anesthetized adult rats, microinjection of the α₁A-adrenoceptor agonist A61603 (1 pmol) unilaterally into the medullary region containing these neurons caused a significant increase in airway resistance, which was prevented by intraperitoneal atropine (0.5 mg/kg). In rhythmically firing medullary slices of newborn rats, A61603 (10 nM) caused depolarization in both the inspiratory-activated and inspiratory-inhibited airway vagal preganglionic neurons that were retrogradely labeled, and a significant increase in the spontaneous firing rate. Under voltage clamp, A61603 significantly enhanced the spontaneous excitatory inputs to both types of neurons and caused a tonic inward current in the inspiratory-activated neurons along with significantly increased peak amplitude of the inspiratory inward currents. The responses in vitro were prevented by α₁A-adrenoceptor antagonist RS100329 (1 μM), which alone significantly inhibited the spontaneous excitatory inputs to both types of the neurons. After pretreatment with tetrodotoxin (1 μM), A61603 (10 or 100 nM) had no effect on either type of neuron. We conclude that in rats, activation of α₁-adrenoceptors in the medullary region containing airway vagal preganglionic neurons increases airway vagal tone, and that this effect is primarily mediated by facilitation of the excitatory inputs to the preganglionic neurons.

Agonist of 5-HT1A/7 receptors but not that of 5-HT2 receptors disinhibits tracheobronchial-projecting airway vagal preganglionic neurons of rats

The vagus nerves supply the major cholinergic tone to airway smooth muscles physiologically and play critical roles in the genesis of airway hyperreactivity under some pathological conditions. Postganglionic airway cholinergic tone relies largely on the ongoing activity of medullary airway vagal preganglionic neurons (AVPNs), of which the tracheobronchial-projecting ones are primarily located in the external formation of the nucleus ambiguus (eNA). AVPNs are regulated by 5-HT, and 5-HT(1A/7) and 5-HT(2) receptors have been indicated to be involved. But the mechanisms at synaptic level are unknown. In the present study, tracheobronchial-projecting AVPNs (T-AVPNs) were retrogradely labeled from the trachea wall; fluorescently labeled T-AVPNs in the eNA were recorded with whole-cell voltage patch clamp; and the effects of 5-HT(1A/7) receptor agonist (±)-8-Hydroxy-2-(dipropylamino) tetralin hydrobromide (8-OH-DPAT) (1 μmol L(-1)) and 5-HT(2) receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) (10 μmol L(-1)) on the synaptic inputs were examined. 8-OH-DPAT significantly inhibited the GABAergic and glycinergic spontaneous inhibitory postsynaptic currents (sIPSCs) of T-AVPNs in both the frequency and amplitude but had no effect on the GABAergic and glycinergic miniature inhibitory postsynaptic currents (mIPSCs). The 8-OH-DPAT inhibition of the GABAergic and glycinergic sIPSCs was prevented by 5-HT(1A/7) receptor antagonist N-[2-[4-(2-Methoxyphenyl)-1-piperazinyl] ethyl]-N-2-pyridinylcyclohexanecarboxamide maleate salt (WAY-100635) (1 μmol L(-1)). 8-OH-DPAT had no effect on the glutamatergic spontaneous excitatory postsynaptic currents (sEPSCs) and caused no alterations in the baseline current and input resistance of T-AVPNs. DOI had no effect on any types of the synaptic inputs of T-AVPNs. These results suggest that 5-HT(1A/7) receptor agonist causes "disinhibition" of T-AVPNs, which might, in part, account for the reflex increase of airway resistance.

Central chemoreceptors: locations and functions

Central chemoreception traditionally refers to a change in ventilation attributable to changes in CO2/H(+) detected within the brain. Interest in central chemoreception has grown substantially since the previous Handbook of Physiology published in 1986. Initially, central chemoreception was localized to areas on the ventral medullary surface, a hypothesis complemented by the recent identification of neurons with specific phenotypes near one of these areas as putative chemoreceptor cells. However, there is substantial evidence that many sites participate in central chemoreception some located at a distance from the ventral medulla. Functionally, central chemoreception, via the sensing of brain interstitial fluid H(+), serves to detect and integrate information on (i) alveolar ventilation (arterial PCO2), (ii) brain blood flow and metabolism, and (iii) acid-base balance, and, in response, can affect breathing, airway resistance, blood pressure (sympathetic tone), and arousal. In addition, central chemoreception provides a tonic "drive" (source of excitation) at the normal, baseline PCO2 level that maintains a degree of functional connectivity among brainstem respiratory neurons necessary to produce eupneic breathing. Central chemoreception responds to small variations in PCO2 to regulate normal gas exchange and to large changes in PCO2 to minimize acid-base changes. Central chemoreceptor sites vary in function with sex and with development. From an evolutionary perspective, central chemoreception grew out of the demands posed by air versus water breathing, homeothermy, sleep, optimization of the work of breathing with the "ideal" arterial PCO2, and the maintenance of the appropriate pH at 37°C for optimal protein structure and function.

Central chemoreceptors: locations and functions

Central chemoreception traditionally refers to a change in ventilation attributable to changes in CO2/H(+) detected within the brain. Interest in central chemoreception has grown substantially since the previous Handbook of Physiology published in 1986. Initially, central chemoreception was localized to areas on the ventral medullary surface, a hypothesis complemented by the recent identification of neurons with specific phenotypes near one of these areas as putative chemoreceptor cells. However, there is substantial evidence that many sites participate in central chemoreception some located at a distance from the ventral medulla. Functionally, central chemoreception, via the sensing of brain interstitial fluid H(+), serves to detect and integrate information on (i) alveolar ventilation (arterial PCO2), (ii) brain blood flow and metabolism, and (iii) acid-base balance, and, in response, can affect breathing, airway resistance, blood pressure (sympathetic tone), and arousal. In addition, central chemoreception provides a tonic "drive" (source of excitation) at the normal, baseline PCO2 level that maintains a degree of functional connectivity among brainstem respiratory neurons necessary to produce eupneic breathing. Central chemoreception responds to small variations in PCO2 to regulate normal gas exchange and to large changes in PCO2 to minimize acid-base changes. Central chemoreceptor sites vary in function with sex and with development. From an evolutionary perspective, central chemoreception grew out of the demands posed by air versus water breathing, homeothermy, sleep, optimization of the work of breathing with the "ideal" arterial PCO2, and the maintenance of the appropriate pH at 37°C for optimal protein structure and function.

Julius H. Comroe, Jr., distinguished lecture: central chemoreception: then ... and now

The 2010 Julius H. Comroe, Jr., Lecture of the American Physiological Society focuses on evolving ideas in chemoreception for CO₂/pH in terms of what is "sensed," where it is sensed, and how the sensed information is used physiologically. Chemoreception is viewed as involving neurons (and glia) at many sites within the hindbrain, including, but not limited to, the retrotrapezoid nucleus, the medullary raphe, the locus ceruleus, the nucleus tractus solitarius, the lateral hypothalamus (orexin neurons), and the caudal ventrolateral medulla. Central chemoreception also has an important nonadditive interaction with afferent information arising at the carotid body. While ventilation has been viewed as the primary output variable, it appears that airway resistance, arousal, and blood pressure can also be significantly affected. Emphasis is placed on the importance of data derived from studies performed in the absence of anesthesia.

Role of central neurotransmission and chemoreception on airway control

This review summarizes work on central neurotransmission, chemoreception and CNS control of cholinergic outflow to the airways. First, we describe the neural transmission of bronchoconstrictive signals from airway afferents to the airway-related vagal preganglionic neurons (AVPNs) via the nucleus of the solitary tract (nTS) and, second, we characterize evidence for a modulatory effect of excitatory glutamatergic, and inhibitory GABAergic, noradrenergic and serotonergic pathways on AVPN output. Excitatory signals arising from bronchopulmonary afferents and/or the peripheral chemosensory system activate second order neurons within the nTS, via a glutamate-AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptor signaling pathway. These nTS neurons, using the same neurotransmitter-receptor unit, transmit information to the AVPNs, which in turn convey the central command through descending fibers and airway intramural ganglia to airway smooth muscle, submucosal secretory glands, and the vasculature. The strength and duration of this reflex-induced bronchoconstriction is modulated by GABAergic-inhibitory inputs. In addition, central noradrenergic and serotonergic inhibitory pathways appear to participate in the regulation of cholinergic drive to the tracheobronchial system. Down-regulation of these inhibitory influences results in a shift from inhibitory to excitatory drive, which may lead to increased excitability of AVPNs, heightened airway responsiveness, greater cholinergic outflow to the airways and consequently bronchoconstriction. In summary, centrally coordinated control of airway tone and respiratory drive serve to optimize gas exchange and work of breathing under normal homeostatic conditions. Greater understanding of this process should enhance our understanding of its disruption under pathophysiologic states.

Endogenous Excitatory Drive Modulating Respiratory Muscle Activity across Sleep–Wake States

RATIONALE

The concept of a tonic drive activating respiratory muscle in wakefulness but not sleep has been an important and enduring notion in respiratory medicine, not least because it is useful in modeling sleep effects on breathing and understanding the pathogenesis of sleep-related breathing disorders such as obstructive sleep apnea. However, a neurotransmitter substrate mediating respiratory muscle activation across sleep-wake states has not been identified.

OBJECTIVES

We determined if alpha1 receptor antagonism at the hypoglossal motor nucleus (HMN) decreases genioglossus (GG) activity consistent with a role for an endogenous noradrenergic drive contributing to GG activation across sleep-wake states. We also determined if alpha1 receptor stimulation could counteract reduced endogenous noradrenergic drive and increase sleeping GG activity.

METHODS

Thirty-five rats were implanted with electroencephalogram and neck electrodes to record sleep-wake states and GG and diaphragm electrodes for respiratory muscle recordings. Microdialysis probes were inserted into the HMN.

MEASUREMENTS AND MAIN RESULTS

Microdialysis perfusion of the alpha1 receptor antagonist terazosin into the HMN significantly decreased GG activity in wakefulness and nonrapid eye movement (non-REM) sleep but not REM sleep. The alpha1 receptor agonist phenylephrine increased GG activity in wakefulness and sleep, but periods of motor inactivity persisted in REM sleep; there was no potentiating effect of combined alpha1 and 5-HT2 receptor stimulation.

CONCLUSIONS

Identification of an endogenous noradrenergic drive contributing to GG activation in wakefulness and non-REM sleep, but not REM sleep, is important given the prevalence and clinical significance of sleep-induced hypoventilation and obstructive sleep apnea in humans and the potential for pharmacologic treatment.