WASHINGTON (dpa-AFX) - Researchers have recently discovered how the brain controls a key hormone released during sleep that helps build muscle and bone, burn fat, and support healthy growth, according to a study published in the journal Cell.
During the study, scientists at the University of California, Berkeley, identified the brain circuit located deep inside the hypothalamus, a region that regulates many essential body functions. These brain cells include growth hormone-releasing hormone (GHRH) neurons, along with two types of somatostatin neurons, which help control hormone release.
To understand how this system works, researchers studied mice by placing tiny electrodes in their brains. They used light to activate specific brain cells and recorded how the animals' brain activity changed during sleep and wakefulness. They observed repeated changes in growth hormone activity across multiple sleep cycles in the mice.
The team found that two hormones controlling growth hormone release behave differently depending on the stage of sleep. GHRH stimulates the release of growth hormone, while somatostatin slows it down. During REM sleep, the stage when most dreaming occurs, both GHRH and somatostatin increased, leading to a larger release of growth hormone. Meanwhile, during non-REM sleep, somatostatin levels dropped while GHRH rose only slightly, creating a different pattern of hormone release.
The researchers also discovered a new feedback system involving the locus coeruleus, a part of the brainstem involved in alertness, attention, thinking, and responding to new experiences. As growth hormone levels gradually rise during sleep, they activate this brain region and encourage wakefulness. Surprisingly, if activity in the locus coeruleus becomes too high, it begins to promote sleep instead. Interestingly, as growth hormone directly affects the locus coeruleus, which is important for staying alert during the day, the researchers believe this newly discovered brain circuit may also influence attention, memory, and other aspects of brain function.
These findings are expected to help researchers develop better treatments for sleep disorders linked to metabolic diseases such as diabetes, as well as brain disorders including Parkinson's and Alzheimer's disease.
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