The neural pathways between two areas of the brain that control the tongue -- and their interactions with each other -- may hold the key as to why men suffer sleep apnea much more than women.
A University of Wisconsin research team has theorized that either the caudal raphe or the hypoglossal nucleus -- or both together -- play roles in sleep apnea. The researchers have turned their attention to these two areas of the brain because of the roles they play in controlling the tongue. Diminished tongue control is a major cause of obstructive sleep apnea, a serious condition which strikes men much more frequently than pre-menopausal women, said lead researcher Jessica R. Barker.
Sleep apnea affects millions of Americans, produces loud snoring and may interfere with the sleep of other family members. It leaves sufferers drowsy during the day and places them at greater risk of getting into an automobile accident and of developing serious illnesses such as hypertension and heart disease.
Previous research from Behan's lab has found evidence that estrogen plays a role in respiratory control and may provide protection against hypoxia. Other research shows that post-menopausal women on hormone replacement therapy suffer less from sleep apnea than post-menopausal women not on hormones, further strengthening the theory that estrogen plays a protective role.
The unique theory could explain why men and post-menopausal women not on hormone therapy are much more likely to suffer from the condition than pre-menopausal women, Barker said.
Estrogen is associated with serotonin, a neurotransmitter that helps control the tongue. In obstructive sleep apnea, the tongue relaxes too much during sleep and blocks the upper airway, causing the individual to temporarily stop breathing. The cycle repeats throughout the sleep period, creates periods of insufficient oxygen and disrupts sleep.
The purpose of the Barker study is to determine if the difference in estrogen levels between men and women plays a role in serotonin expression in the caudal raphe and hypoglossal nucleus -- leading to a difference in tongue control.
The researchers hypothesized that females would have greater numbers of serotonin-activated neurons running between the hypoglossal nucleus and the tongue. They first looked at the caudal raphe because that is where serotonin - which plays a role in preventing the tongue from relaxing and blocking the airway -- is manufactured.