DO CLOCK GENES MAKE ADDICTION TICK?

A SURPRISE finding in fruit flies suggests that biological clocks may be
involved in cocaine addiction.

Last year, Jay Hirsh and his colleagues at the University of Virginia in
Charlottesville discovered that fruit flies respond to crack cocaine smoke
by grooming and walking in circles. Repeated exposure to the drug made the
flies respond more dramatically to the same doses, the same kind of
"sensitisation" found in humans. This kind of reaction is peculiar to drugs
like cocaine.

Now Hirsh's graduate student Rozi Andretic has found that flies with broken
clocks fail to become sensitised. The researchers report in the current
issue of Science (vol 285, p 1066) that flies missing any one of four
biological clock genes have a constant response to cocaine despite repeated
exposures. "This is not something that anyone would have predicted," says
Hirsh. "We still find it somewhat surprising."

Hirsh notes that people with certain psychiatric problems such as bipolar
disorder develop irregular sleep patterns and are more likely to abuse
drugs. He speculates that defects in clock genes could explain the
connection. "This opens the possibility that there could be some linkages
between these biological phenomena," he says.

Other circadian rhythm researchers were surprised by the finding but weren't
sure where it would lead. Michael Rosbash at Brandeis University in Waltham,
Massachusetts, for example, points out that this is the first time the clock
genes have been implicated in anything other than regulating clocks. "The
question is what does it mean," he says. "Only time will tell."