The neurochemical changes underlying human emotions and social behavior are largely unknown. Now though, for the first time in humans, scientists at UCLA have measured the release of a specific peptide, a neurotransmitter called hypocretin, which greatly increased when subjects were happy, but decreased when they were sad. The finding suggests that boosting hypocretin could elevate both mood and alertness in humans, thus laying the foundation for possible future treatments of psychiatric disorders like depression by targeting measureable abnormalities in brain chemistry. In addition, the study measured for the first time the release of another peptide, this one called melanin concentrating hormone, or MCH. Researchers found that its release was minimal during waking periods, but greatly increased during sleep, suggesting a key role for this peptide in making humans sleepy. The study was published online on March 5, 2013 in Nature Communications. "The current findings explain the sleepiness of narcolepsy, as well as the depression that frequently accompanies this disorder," said senior author Dr. Jerome Siegel, a professor of psychiatry and director of the Center for Sleep Research at UCLA's Semel Institute for Neuroscience and Human Behavior. "The findings also suggest that hypocretin deficiency may underlie depression from other causes." In 2000, Dr. Siegel's team published findings showing that people suffering from narcolepsy, a neurological disorder characterized by uncontrollable periods of deep sleep, had 95 percent fewer hypocretin nerve cells in their brains than those without the illness. That study was the first to show a possible biological cause of the disorder. Because depression is strongly associated with narcolepsy, Dr.
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