A new study has found that chronic disruption of one of the most basic circadian (daily) rhythms -- the day/night cycle -- leads to weight gain, impulsivity, slower thinking, and other physiological and behavioral changes in mice, similar to those observed in people who experience shift work or jet lag.

The research, presented at Neuroscience 2009, the annual meeting of the Society for Neuroscience and the world's largest source of emerging news about brain science and health, is helping scientists better understand the neurobiological mechanisms behind circadian disruptions.

"Our findings have implications for humans," said lead author Ilia Karatsoreos, PhD, of Rockefeller University. "In our modern industrialized society, the disruption of our individual circadian rhythms has become commonplace, from shift work and jet lag to the constant presence of electric lighting. These disruptions are not only a nuisance, they can also lead to serious health and safety problems," he said.

Karatsoreos and his colleagues housed the animals in a day/night cycle of 20 hours (10 hours of light and 10 hours of dark), rather than the roughly 24-hour cycle to which the animals' internal brain and body clocks are normally set. After six to eight weeks, the mice exhibited numerous physiological changes not seen in a control group. These included greater weight gain, changes in body temperature rhythms, and alterations in metabolic hormones such as insulin and leptin (a key regulator of appetite). The mice with the disrupted rhythms also demonstrated behavioral changes -- specifically, increased impulsivity and decreased cognitive flexibility (the ability to adapt new strategies to new situations).

"We also found that the animals' brains displayed neural changes in the medial prefrontal cortex, an area important for regulating impulsivity and cognitive flexibility," Karatsoreos said. "Those changes may help explain some of the behavioral effects of circadian disruptions."

Research was supported by Canadian Institutes of Health Research, the National Institute of Mental Health, and Sepracor.