Researchers Look To The Brain To Explain Gender Differences In Sleep Apnea

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Researchers Look To The Brain To Explain Gender Differences In Sleep

Apnea

http://www.medicalnewstoday.com/medicalnews.php?newsid=40979

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

R. Barker.

*Paper presentation: " Sexual dimorphism in serotonergic input to the

hypoglossal nucleus, " by R. Barker and Behan of the

University of Wisconsin-Madison School of Veterinary Medicine, was

presented Monday April 3, Control of Breathing: Central Connectivity

and Neurotransmission, 479.8 /board # C566 in the Convention Center

Exhibit Hall.

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.

Estrogen, serotonin play roles

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.

Targets: serotonin, hypoglossal nucleus, caudal raphe,

The researchers used six young male rats and six females. They

injected the rats' tongues under anesthesia with a tracer, Bartha

pseudorabies virus (PRV). They examined the pathway of the virus into

the brain and were able to " see " the path of the PRV and the

serotonin-activated neurons projecting from the caudal raphe to the

tongue.

They looked at the number and distribution of neurons activated by

serotonin in the caudal raphe, expecting there would be differences

between males and females. Instead, they found male and female rats

have the same number of serotonin producing neurons in this area of

the brain.

The study suggests the caudal raphe does not play a role -- at least

by itself -- in obstructive sleep apnea. Researchers will next look

at the neurons producing serotonin that run from the hypoglossal

nucleus to the tongue, explained Barker.

Also in the future: a look at the interactions among the caudal

raphe, the hypoglossal nucleus and the tongue. The key may be in how

these structures interact, she said.

If this line of research eventually pans out, it may be possible to

adjust hormone levels to relieve the sleep apnea and avoid the

resultant health problems, Barker said.

Funding: National Institutes of Health and National Center for

Research Resources