Shortening or lengthening the 24-hour circadian light cycle can cause epigenetic changes in the mouse brain, and these changes can in turn affect circadian behavior such as physical activity, reports a study published online this week in Nature Neuroscience. Understanding these epigenetic regulations may be important in suppressing the negative consequences faced by people in certain occupations (such as night-shift workers) who are exposed to shortened day cycles for an extended period of time.
During the short days of autumn and winter, the neuroendocrine system alters its responsiveness to circadian cues such as shortened daylight and late dawn. These changes in exposure to daylight are also known to affect the fluctuation of molecular clock genes in the mammalian suprachiasmatic nuclei (SCN), a brain area responsible for controlling circadian behavior.
Steven Brown and colleagues find that mice exposed to short days (11 hours of light a day versus the normal 12 hours in a laboratory setting) for several weeks decrease the amount of voluntary exercise (wheel running) they do, and that this change in behavior is correlated with genome-wide changes in DNA methylation of SNC neurons. A pharmacological inhibitor that impairs DNA methylation also altered wheel-running behavior in mice exposed to normal 24-hour light cycle. The authors believe that these findings in mice suggest that epigenetic changes in mammalian brains may be critical to modulate behavior in response to change in exposure to daylight.