Los Angeles, March 8 : What makes us happy? Family? Money? Love? How about a peptide? For the first time, scientists have found a link between happiness and levels of a chemical within the body, which could offer hope for patients with psychiatric disorders, says a study.

The neuro-chemical changes underlying human emotions and social behaviour have hitherto remained largely unknown. Now, though, for the first time in humans, scientists at UCLA (University of California, Los Angeles) have measured the release of a specific peptide, a neurotransmitter called hypocretin, that 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 treatment of psychiatric disorders like depression by targeting measurable abnormalities in brain chemistry, reports Science Daily.

In addition, the study measured for the first time the release of another peptide, called melanin concentrating hormone, or MCH.

Researchers found that its release was minimal on waking, but greatly increased during sleep, suggesting a key role for this peptide in making humans sleepy.

The study is published in the March 5 online edition of the journal Nature Communications.

"The current findings explain the sleepiness of narcolepsy, as well as the depression that frequently accompanies this disorder," said senior author Jerome Siegel, a professor of psychiatry and director of the Centre for Sleep Research at UCLA's Semel Institute for Neuroscience and Human Behaviour.

"The findings also suggest that hypocretin deficiency may underlie depression from other causes," Siegel said. (IANS)