New Study Identifies Mechanism of Breathing Muscle Shutdown in Sleep that is Critical for Effective Breathing

A novel brain mechanism mediating the inhibition of the critical breathing muscles during rapid  eye movement (REM) sleep has been identified for the first time in a new study titled “Identification of the Mechanism Mediating Genioglossus Muscle Inhibition in REM Sleep” published online ahead of print in the American Thoracic Society’s American Journal of  Respiratory and Critical Care Medicine., offering the possibility of a new treatment target for  sleep-related breathing problems.

“REM sleep is accompanied by profound  inhibition of muscle activity,” said researcher Richard Horner, PhD, professor of medicine and  physiology at the University of Toronto. This “paralysis” affects  breathing muscles and “is  a cause of snoring and other breathing problems in sleep, especially  obstructive sleep apnea.”

Sleep apnea is a common and serious problem that  increases the risk for heart attacks, high blood pressure, stroke, diabetes and  daytime sleepiness.

According to Dr. Horner, “the brain  mechanism mediating inhibition of the critical breathing muscles in REM sleep was  unknown, but a novel and powerful inhibitory mechanism is identified for the  first time in our study.”

In the study, performed by PhD student Kevin Grace, rats were studied across sleep-wake states. The  researchers targeted manipulation of the brain region that controls tongue  muscles during sleep.

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The tongue is an important breathing muscle because its activity keeps the airspace open behind the tongue  to allow for the effective passage of air into the lungs. Inhibition of tongue  muscle activity in sleep in some people leads to backward movement of the  tongue and blockage of the airspace. This blockage in sleep leads to episodes  of self-suffocation (sleep apnea) that are rescued by waking up from sleep.  Such episodes can occur hundreds of times a night.

Importantly, the muscle activating  effects of these interventions were largest during REM sleep and minimal or  absent in other sleep-wake states. The brain chemical mediating this powerful  inhibition of breathing muscle activity in REM sleep is acetylcholine, acting  via muscarinic receptors that are functionally linked to a particular class of  potassium channel.

“Since REM sleep recruits mechanisms that can abolish or suppress tongue  muscle activity during periods of REM sleep and cause obstructive sleep apnea,  identification of a mechanism mediating this inhibition is a significant  discovery,” said Dr. Horner.

“This newly identified process has fundamental  implications for understanding the common and serious problems of snoring and  other breathing problems such as obstructive sleep apnea, which are worse in  REM sleep,” said Dr. Horner. “Moreover, identifying the fundamental mechanism  responsible for the shutting down of a muscle in sleep that is critical for  effective breathing also identifies a rational drug target designed to prevent  this inactivity and so prevent obstructive sleep apnea and other sleep-related  breathing problems.”

Source: Provided by the American Thoracic Society

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