From from PJH at editor's choice, Science Magazine.
Some neurotransmitters, such as dopamine, have been implicated in adjusting a person's mood. The circadian clock mechanisms, meanwhile, keep the organism's physiology tuned for appropriate responses to day or night. Hampp et al. have demonstrated how the molecular signaling pathways for circadian rhythms might intersect with the brain's establishment of general mood. They found that the promoter of the gene encoding monoamine oxidase A (Maoa), which stabilizes some aspects of mood and breaks down dopamine and serotonin, contains binding sites for several clock proteins and showed that circadian oscillation was driven by the Maoa promoter in neuroblastoma cells. Mice lacking Per2, a gene that stabilizes circadian rhythms, showed damped expression from the Maoa promoter. Observations of the Per2 mutant mice in response to an unavoidable problematic situation--taken as a proxy for despair in humans--showed correlations with disorders of mood.