Probing the circadian pacemaker of a mouse using two light pulses

Area of Science:

• Chronobiology
• Animal Behavior
• Circadian Rhythms

Background:

• The locomotor activity rhythm in nocturnal rodents is governed by a circadian pacemaker.
• Understanding how this pacemaker responds to external stimuli like light is crucial for chronobiology.

Purpose of the Study:

• To investigate the phase response curve (PRC) of the circadian pacemaker in Mus booduga using two light pulses (LPs).
• To compare the PRC generated by two LPs with a single LP PRC.
• To determine if transient cycles accurately reflect the state of the pacemaker oscillator.

Main Methods:

• Two sets of experiments were conducted on Mus booduga.
• In the first set, a resetting LP1 perturbed the circadian pacemaker, followed by a probing LP2 to generate an LP2 PRC, which was compared to a single LP PRC.
• In the second set, LP1 was administered, and LP2 was applied at different times during the subsequent transient cycle to assess its effect on steady-state phase shifts.

Main Results:

• The LP2 PRC showed a resemblance to the single LP PRC but was phase-shifted.
• The LP1 PRC exhibited smaller delay zones compared to the single LP PRC, suggesting rapid pacemaker phase shifts.
• Steady-state phase shifts were correlated differently with day 1 phase shifts depending on LP2 timing, indicating transient cycles do not mirror pacemaker state.

Conclusions:

• The circadian pacemaker in Mus booduga exhibits rapid phase shifts following light perturbations.
• The phase response curve generated by two light pulses provides insights into pacemaker dynamics.
• Transient cycles following perturbations do not reliably represent the underlying state of the circadian pacemaker oscillator.