Kalvimalar

Researchers at 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.

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 in waking but greatly increased during sleep, suggesting a key role for this peptide in making humans sleepy.

"The current findings explain the sleepiness of narcolepsy, as well as the depression that frequently accompanies this disorder. The findings also suggest that hypocretin deficiency may underlie depression from other causes," said senior author Jerome Siegel.

In 2000, Siegel's team published findings showing that people suffering from narcolepsy, a neurological disorder characterised by uncontrollable periods of deep sleep, had 95 per cent fewer hypocretin nerve cells in their brains than those without the illness.

Since depression is strongly associated with narcolepsy, Siegel's lab began to explore hypocretin and its possible link to depression.

In the current study, the researchers obtained their data on both hypocretin and MCH directly from the brains of eight patients who were being treated at Ronald Reagan UCLA Medical Center for intractable epilepsy.

The researchers found that hypocretin levels were not linked to arousal in general but were maximised during positive emotions, anger, social interactions and awakening.

In contrast, MCH levels were maximal during sleep onset and minimal during social interactions.

"These results suggest a previously unappreciated emotional specificity in the activation of arousal and sleep in humans," Siegel said.

"The findings suggest that abnormalities in the pattern of activation of these systems may contribute to a number of psychiatric disorders," Siegel added.

The study was published in the journal Nature Communications.