Feeling sleepy during the day?

Scientists have identified a sleep-promoting molecule in fruit fly and claim this can help in understanding the genetic basis of sleep and, eventually, address sleep disorders, reports Seema Singh.

Mankind may finally get to the bottom of mysteries regarding sleep, thanks to the fruit fly. Scientists have identified a sleep-promoting molecule in the insect and claim this can help in understanding the genetic basis of sleep and, eventually, address sleep disorders.

In Friday's issue of the journal Science, researchers from Howard Hughes Medical Institute and Division of Sleep Medicine, University of Pennsylvania, report they have found a gene, named 'sleepless', responsible for silencing of specific neurons in the brain critical for sleep. "Identification of similar molecules in mammals may lead to therapies for sleeplessness," said Amita Sehgal, a neurobiologist from University of Pennsylvania.

Not much is understood about sleep, said B. Gitanjali, who specialises in sleep medicine at the Jawaharlal Institute of Postgraduate Medical Education and Research, or JIPMER, in Puducherry, and set up the first sleep lab in south India in 1994. "For the first time there is evidence suggesting that reduced membrane excitability (or neuronal silencing) may be a central feature of sleep," Gitanjali said.

The sleepless gene encodes a specific protein, the levels of which correlate with the amount of sleep — its deficiency causes severe reduction in sleep. "The discovery of genes like 'sleepless' could have major implications towards research on pharmaco-therapeutic agents for sleep disorders like insomnia, which is prevalent worldwide," says Suresh Kumar, consultant in neurology and sleep medicine at Vijaya Health Centre and Fortis Malar Hospital in Chennai.

Sleep deprived humans feel miserable and fare poorly in mental tasks just as sleep-deprived rats deteriorate in health and fail in their laboratory fitness tests.

Still, it's difficult to imagine a slumbering fly can shed light on how sleep maintains the brain and metabolism. But animals like worms, fruit flies and zebrafish are turning out to be the new genetic models in sleep laboratories across the world because their genomes and nervous systems are easy to study.

The first published description of fruit fly sleep came in 2000. Besides, fruit flies, with four pairs of chromosomes (human beings have 23) including one pair that determines sex just as it does in humans, have always been the preferred test-animals for genetic studies.

All animals seem to require sleep, as distinct from rest, and quite often this is linked to their day-night activity or circadian rhythm, said K VijayRaghavan, director of the National Centre of Biological Sciences in Bangalore, who studies neurobiology of movement in fruit flies. "If sleep can be studied in the fruit fly it will be greatly valuable for understanding sleep in humans as many neuronal circuits and mechanisms are conserved between fly and human as also the genes involved," he added.

Sleep is regulated by circadian and homeostatic. The circadian clock regulates the timing of sleep, whereas the homeostatic mechanism controls the need for sleep. It is the latter, which is thought to influence sleep under normal conditions as well as recovery sleep after deprivation. The research unravels the molecular mechanisms underlying homeostatic regulation.

Clinicians like Dr Kumar and Dr Gitanjali said they are increasingly finding insomnia as a "major problem" per se as well as in relation to medical disorders such as heart disease, stroke, diabetes and depression and claim it accounts for up to 50 per cent of sleep related complaints that require medical intervention.