Reversible suppression of circadian-driven locomotor rhythms in mice using a gradual fragmentation of the day-night cycle.

Circadian rhythms are regulated by molecular clockwork and drive 24-h behaviors such as locomotor activity, which can be rendered non-functional through genetic knockouts of clock genes. Circadian rhythms are robust in constant darkness (DD) but are modulated to become exactly 24 h by the external day-night cycle. Whether ill-timed light and dark exposure can render circadian behaviors non-functional to the extent of genetic knockouts is less clear.

Fragmented day-night cycle induces reduced light avoidance, excessive weight gain during early development, and binge-like eating during adulthood in mice.

Fragmented day-night (FDN) cycles are environments in which multiple periods of light and dark alternate across a 24 h period. Exposure to FDN cycles disrupts circadian rhythms, resulting in period lengthening and alterations to mood in mice. A constant light environment, which also induces period lengthening, is linked to mood and metabolic disturbances and disruption to the development of the circadian clock.

Fragmented day-night cycle induces period lengthening, lowered anxiety, and anhedonia in male mice.

Light exposure at night disrupts circadian-regulated biological functions, including mood. However, the consequence of fragmenting the night period and distributing it across the 24-hr period is less understood. Here we show that fragmenting an 8 -h and 6 -h night into equally distributed 2 -h periods throughout the 24-hr day results in period lengthening of the circadian rhythm in mice.

Light Has Diverse Spatiotemporal Molecular Changes in the Mouse Suprachiasmatic Nucleus.

To be physiologically relevant, the period of the central circadian pacemaker, located in the suprachiasmatic nucleus (SCN), has to match the solar day in a process known as circadian photoentrainment. However, little is known about the spatiotemporal molecular changes that occur in the SCN in response to light. In this study, we sought to systematically characterize the circadian and light effects on activity-dependent markers of transcriptional (cFos), translational (pS6), and epigenetic (pH3) activities in the mouse SCN.

Jet Lag Recovery and Memory Functions Are Correlated with Direct Light Effects on Locomotion.

Jet lag is a circadian disruption that affects millions of people, resulting, among other things, in extreme sleepiness and memory loss. The hazardous implications of such effects are evident in situations in which focus and attention are required. Remarkably, there is a limited understanding of how jet lag recovery and associated memory loss vary year round under different photoperiods.