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MONDAY, July 7, 2003 (HealthDayNews) -- Two new studies have found apparent links between different sleep disorders and brain chemistry.
Although these links do not yet mean there is a cause-and-effect relationship, they may be revealing of some of the basic processes underlying sleep disorders.
The studies appear in the July 8 issue of Neurology.
Both studies looked at the same 13 people who have a relatively rare disorder known as multiple system atrophy (MSA), a fatal, degenerative neurological disease that is almost always accompanied by sleep disorders. All the MSA patients in the study also had obstructive sleep apnea and REM (rapid eye movement) behavior disorder.
REM sleep behavior disorder is when people thrash about in their sleep, moan, speak, act out their dreams, get out of bed and even pummel their bed partners, explains study author Dr. Sid Gilman, chairman of the department of neurology at the University of Michigan School of Medicine. This activity occurs during the rapid eye movement -- or REM -- phase of sleep.
Obstructive sleep apnea may affect as much as 3 percent of Americans, many of them undiagnosed. In people with the condition, breathing temporarily stops or diminishes dozens or hundreds of times during sleep. And they snore and have excessive daytime sleepiness. The disorder is also associated with high blood pressure, heart disease and a higher incidence of stroke.
These two studies explored the links between these sleeping disorders and the neurotransmitters dopamine and acetylcholine.
The 13 study participants slept in the clinical research center for two nights, hooked up to machinery that measured neurotransmitter levels, brain waves, eye movements, respiration, limb movements and more. They were also videotaped. The study participants also were compared to 27 healthy controls.
In the first study, the researchers wanted to see if dopamine was related to REM sleep behavior disorder.
"We already knew that in Parkinson's disease there's a very high prevalence of REM sleep behavior disorder," Gilman says. "We were suspicious that since Parkinson's is associated with a deficiency in the brain of this neurotransmitter, that we would find an abnormality that is related to the severity of REM sleep behavior disorder. We thought we'd see a correlation, which is exactly what we saw."
The results were exciting and yet not altogether surprising. "We found a very tight correlation [between the severity of REM sleep behavior disorder and the level of decrease in dopamine], so this suggests that there's a causal effect," Gilman says. "We can't prove that. It's a correlation only, but it certainly suggests that the amount of dopamine loss in the brain is related to this disorder."
This finding has led Gilman to wonder if REM sleep behavior disorder could be a very early symptom of Parkinson's.
The second study looked to see if there was a relationship between the severity of obstructive sleep apnea and the degree of decrease of a different neurotransmitter -- acetylcholine.
"Here again, we found a good correlation," Gilman says. "It's not allowing us to conclude but it's certainly suggesting that there might be a causative relationship between obstructive sleep apnea and this neurotransmitter."
Again, this finding raises a number of questions, not the least of which is whether obstructive sleep apnea in healthy people is due to the same type of chemical disturbance. If so, Gilman says, "there might be a whole other way of treating this." Right now, obstructive sleep apnea is typically treated by having the person wear a "continuous positive airway pressure" mask at night to keep the airways open.
"It's an interesting area because it leads to the question of basic science underlying sleep," Gilman says. "It's a somewhat unexpected finding. It could be central to so many things."
More information
For more on obstructive sleep apnea, visit the American Sleep Apnea Association. For more on REM sleep behavior disorder, visit the National Sleep Foundation.
