Recurring circadian disruption alters circadian clock sensitivity to resetting

Area of Science:

• Chronobiology
• Neuroscience
• Circadian Rhythms

Background:

• Circadian rhythms regulate physiological processes, synchronized by the light:dark (LD) cycle.
• Modern lifestyles often involve chronic exposure to disruptive light conditions, impacting circadian synchrony.
• The suprachiasmatic nucleus (SCN) is the master circadian pacemaker, coordinating peripheral tissue rhythms.

Purpose of the Study:

• To model chronic circadian disruption using mice exposed to an non-entrainable LD10:10 cycle.
• To investigate the impact of prior light exposure on circadian rhythms in the SCN and peripheral tissues.
• To assess the influence of dissection timing on ex vivo circadian bioluminescence rhythms.

Main Methods:

• Male mice were housed under LD10:10 (chronic disruption) or LD12:12 (control) for over a month.
• Locomotor activity and body temperature rhythms were measured in vivo.
• PER2::LUC bioluminescence rhythms were measured ex vivo in SCN and peripheral tissues (white adipose tissue, thymus).

Main Results:

• Dissection time significantly impacted circadian phase of PER2::LUC rhythms, with tissue-specific variations.
• White adipose tissue showed strong resetting by dissection, while thymus phase was independent of dissection timing.
• Mice under chronic LD10:10 showed strong SCN resetting by dissection, unlike control LD12:12 mice.

Conclusions:

• Chronic circadian disruption desynchronizes SCN neurons, increasing network sensitivity to perturbations.
• Tissues with weakened circadian networks (e.g., SCN under disruption) or poor coupling (some peripheral tissues) exhibit increased resetting.
• Inconsistent light exposure disrupts circadian rhythms and alters SCN pacemaker sensitivity to experimental manipulation.