GoKawiilUnderstanding the sleeping airway
Horner’s journey in sleep research began in the early 90s as a PhD student at the University of London where he worked in one of the first sleep labs in the United Kingdom. He says U of T’s reputation as a leader in sleep research drew him to the city to pursue a postdoctoral fellowship with Eliot Phillipson, a clinician-scientist at U of T who established one of North America’s first human sleep labs in 1978 to study breathing disturbances.
After a second postdoc fellowship at the University of Pennsylvania, Horner returned to U of T as a faculty member in 1997. His first priority was to develop new tools and models that researchers could use to more effectively study sleep and breathing. Until that point, most models only mimicked sleep-like behaviour.
“No one had developed models to actually investigate natural sleep,” says Horner.
“That's what I wanted to set my lab up to do so that we could conduct very basic neuroscience studies looking at the circuits that control the muscles responsible for breathing.”
The Horner lab pioneered models to identify the key brain chemicals and receptors modulating breathing muscle activity in sleep.
In 2006, the researchers were the first to identify the neurotransmitter noradrenaline as playing a significant role in activating the tongue muscle during wakefulness and certain phases of sleep.
The tongue is important for speech and swallowing, but Horner says it is also the largest and most impactful upper airway muscle when it comes to maintaining airflow into our lungs.
Noradrenaline levels in the brain drop during rapid eye movement (REM) sleep — when most dreams occur and brain activity is high — leading to a loss of muscle tone in the tongue and, in some people, difficulties breathing.
In 2013, the researchers published another seminal discovery showing that a family of proteins called muscarinic receptors suppress tongue movement during REM sleep. When they blocked muscarinic receptors with a drug, they saw a strong activation of the tongue muscle.
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