WASHINGTON (Agencies via Xinhua) _ Genes normally associated with an animal's internal clock may also affect its ability to become addicted to cocaine, researchers said on Thursday.
Similar genes may play a role in human addiction, the researchers reported in the journal Science, adding that the finding casts surprising new light on the role of biological clocks.

"This opens up the field of drug studies to thinking about how a totally unexpected set of genes function in response to drugs," Jay Hirsh, a molecular geneticist at the University of Virginia, who led the study, said in a statement.

The findings might explain why drugs such as cocaine keep people awake, Hirsh said.

"These important findings illustrate that the clock genes perform other important roles in regulating the physiology of fruit flies, and probably humans as well," added Dr Michael Sesma, a neurobiologist at the National Institute of General Medical Sciences, whose institute helped fund the study.

Hirsh and his colleagues were working with fruit flies _ tiny insects that, like all other animals, share many of their genes with humans.

They looked at five known genes that affect the biological clocks in the flies _ "period," "clock," "cycle," "doubletime" and "timeless." Flies that lacked "period," "clock," "cycle" and "doubletime" did not become sensitized to cocaine, the researchers said.

When animals or humans become sensitized to a drug, they require more and more of it to have the same effect.

"Only those that lacked 'timeless' had a normal response," Hirsh said.

Now his team will try to find out just what effects these genes have on cells.

But there should be clear analogies to human addiction, he said, because people possess versions of all five of these genes.

"We generally have three to four copies of every gene that a fly has a single copy of," Hirsh said."They have overlapping functions."

The research should shed light on a whole range of mental illnesses, Hirsh said.

Knowing more about biological clocks may also help scientists explain why people are more likely to have heart attacks in the morning and asthma attacks at night, why some animals hibernate and why some people can wake up at the same time every day without an alarm clock.