A Phase Response Curve for Light-to-Dark Transitions in Mice

Abstract

The circadian clock coordinates the timing of many functions including hormone secretions, digestive function, brain activity, sleep, and a variety of behaviors. Evidence suggests that an improperly functioning biological clock can result in sleep disruption, clinical depression, and decreased lifespan. To function properly, the circadian clock must respond to stimuli from the environment. One way to reset the clock is via arousing stimuli. These stimuli include exercise, gentle handling, and treatment with various drugs. This type of clock resetting, termed nonphotic resetting, results in a phase advance of the circadian clock of about three hours when the stimuli are administered in the middle of the day, that is, at Zeitgeber Time 4 and 6 (ZT4 & ZT6). The amount of resetting is progressively less the earlier or later the stimulus is administered relative to ZT6. No one has studied nonphotic phase shifting in mice before. It is important we research this phenomenon as mice are the primary biomedical research organism.