Sleep networks and the anatomic and physiologic connections with respiratory control.

A central neuronal network regulates airway functions from the nares to the bronchioles and is an integral component of a regulatory system for brain control of breathing and airway patency during wakefulness and sleep. This network, components of which include sleep generating sites and monoaminergic neurons in particular, is characterized by reciprocal interconnections, parallel organization, and state-dependent activity patterns, which can be influenced by both genes and environment. Sleep generating neurons are interconnected with the monoaminergic containing cells to the extent that sleep-related changes in upper and lower airway patency could be due to inhibitory influences of sleep-activated neurons on serotonergic and noradrenergic producing cells. Neurochemical studies and physiologic experiments show that serotonergic and noradrenergic producing cells can make parallel pathways, directly innervating the hypoglossal motor cells regulating upper airway dilating muscles, and vagal preganglionic neurons providing cholinergic outflow to the airways. Activation of serotonergic and noradrenergic cell groups preferentially increases activity of the genioglossus muscle, but diminishes cholinergic outflow to the airways. Hence, inhibition of monoaminergic neurons during sleep may lead to a decrease in upper airway dilating forces and an elevation of cholinergic outflow to the airways. Qualitatively different responses of hypoglossal and airway-related vagal preganglionic neurons (AVPNs) occur in response to endogenously released serotonin or norepinephrine and could be related to its simultaneous action on different serotonin or norepinephrine receptor subtypes. Dysfunction of monaminergic cell groups during sleep may predispose to upper airway occlusion as well as bronchoconstriction. Pharmacological corrections of alterations of these transmitter specific converging systems might be an avenue for treatment of sleep related airway disorders such as sleep apnea and worsening of asthma.