University of Texas Southwestern Medical Center neuroscientists may have found cells that act like crucial gears in the brain’s clock. These cells control the circadian rhythm, the 24-hour cycle that keeps people in sync with light and the time of day. The cells could also control hormone production, metabolism, and blood pressure.
Researchers have long known that a brain area called the suprachiasmatic nucleus (SCN) located in a larger region known as the hypothalamus controls our ability to keep time and respond to light cues. But it was never clear until now exactly which cells are key for this function.
“We have found that a group of SCN neurons that express a neuropeptide called neuromedin S (NMS) is both necessary and sufficient for the control of circadian rhythms,” remarked Dr. Joseph Takahashi, Chairman of Neuroscience and Howard Hughes Medical Institute (HHMI) Investigator at UT Southwestern, also the Loyd B. Sands Distinguished Chair in Neuroscience.
NMS helps neurons to communicate. It is a type of molecule known as a neuropeptide, and is composed of 36-amino acids. NMS can be found in suprachiasmatic nucleus of the hypothalamus of humans and other mammals. It may regulate circadian rhythms and also acts as an appetite suppressant.
The scientists created genetic mouse models in which the function NMS-expressing neurons could be modified. They discovered that specifically manipulating NMS neurons changed circadian rhythms in animal models. The team was able to lengthen the circadian rhythms and behavior, such as sleeping, or to abolish the rhythms altogether. In their report, the investigators state: “We demonstrate that lengthening period within Nms neurons is sufficient to lengthen period of the SCN and behavioral circadian rhythms. Conversely, mice without a functional molecular clock within Nms neurons lack synchronous molecular oscillations and coherent behavioral daily rhythms.”
“Which of these neurons are responsible for producing circadian rhythms was a major unanswered question in neurobiology. This study marks a significant advancement in our understanding of the body clock” stated senior author Dr. Masashi Yanagisawa, Adjunct Professor of Molecular Genetics, former HHMI Investigator at UT Southwestern, and current Director of the World Premier International Institute for Integrative Sleep Medicine at the University of Tsukuba in Japan.
Author Dr. Takahashi has already greatly contributed to the understanding of circadian rhythms, by identifying Clock—which helps to control circadian rhythms. His laboratory has shown that blocking Clock and Bmal1 genes in mice can inhibit the release of insulin by the pancreas, causing diabetes. Moreover, Dr. Yanagisawa discovered orexin, which regulates sleep and appetite and may be involved in neurodegenerative diseases.