In mice, the circadian gene Clock is involved in regulating the brain's dopaminergic reward pathway, researchers report in this week's PNAS. They found that animals with no functional CLOCK protein were more susceptible to the behavioral effects of cocaine and had elevated dopamine transmission in the reward pathway for drugs, food, and sex.

A link between circadian rhythms and behavioral response to cocaine has been suggested by previous work, lead author Colleen McClung, of the University of Texas Southwestern Medical Center, told The Scientist. "But there wasn't a whole lot showing that the individual genes involved in circadian rhythms are also involved in reward pathways," McClung said.

She and her colleagues examined the effect of cocaine in mice that did not make the CLOCK protein, which is a transcription factor with a central role in the body's suprachiasmatic nucleus circadian clock.

The investigators found that Clock mutants...

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