By tracking which nerve cells in the mouse brain stimulate others, researchers in Japan and at UT Southwestern found that a type of neuron responsible for keeping animals awake receives inhibitory signals from neurons active only during sleep, as well as reinforcing, positive signals from nerve cells that are very active during wakefulness.
The findings, available online and appearing in the April 21 issue of the journal Neuron, shed light on the complex mechanisms involved in sleep regulation and may help to explain why once a person wakes up and moves around, he tends to stay awake.
"We all know subjectively and objectively that there is a very strong force regulating sleep, but there is very little knowledge about the actual biological mechanism controlling sleep," said Dr. Masashi Yanagisawa, professor of molecular genetics at UT Southwestern and senior author of the study. "Eventually my dream is to elucidate all the pathways regulating sleep."
Dr. Yanagisawa and his colleagues focused on neurons in the brain that produce the protein orexin, which helps keep animals awake. In humans, a lack of, or deficiency in, orexin causes narcolepsy, a rare disease in which people uncontrollably fall asleep, have excessive daytime sleepiness and experience sudden muscle weakness called cataplexy.
Because orexin-producing neurons play such a key role in regulating sleep, determining how they are connected to other neurons in the brain is an important step toward understanding how and why we sleep.
Mapping the neurons to which orexin neurons send signals has been relatively easy, Dr. Yanagisawa said, but determining which neurons send signals to orexin neurons has been a challenge. A brain-mapping technique developed recently by French scientists provided Dr. Yan
Source:University of Texas Southwestern Medical Center at Dallas