Scheduled wheel access during daytime: A method for studying conflicting zeitgebers

Area of Science:

• Chronobiology
• Animal Behavior
• Circadian Rhythms

Background:

• Light is considered the main environmental cue (zeitgeber) for synchronizing circadian clocks.
• The relative importance of photic versus non-photic cues for circadian entrainment is not fully understood.

Purpose of the Study:

• To compare the strength of light (photic) as a zeitgeber against wheel availability (non-photic) in Syrian hamsters.
• To investigate how restricting non-photic cue access influences circadian re-entrainment.

Main Methods:

• A novel conflict test design was employed using Syrian hamsters.
• Re-entrainment to an inverted light-dark (LD) cycle was assessed under conditions of restricted wheel access.
• Experiments were conducted using different illuminance levels (0.1 lx vs. 6 lx).

Main Results:

• Restricting wheel access to the light phase of an inverted LD cycle significantly slowed re-entrainment in nocturnal hamsters.
• This disruption was more pronounced at a lower illuminance level (0.1 lx) compared to a higher one (6 lx).
• Hamsters failed to re-entrain to the inverted LD cycle for up to four weeks, running voluntarily during the light phase.

Conclusions:

• Non-photic cues, like wheel running, can significantly interfere with light-mediated circadian clock entrainment.
• The strength of the photic zeitgeber is context-dependent and can be overridden by non-photic cues under specific conditions.
• Findings have implications for understanding circadian disruption in humans experiencing shift work or jet lag.