Internal Circadian Desynchrony Following 8 H Advance of the Light:dark Cycle in Per2::luc Mice

*Corresponding author e-mail; pmolyneu@smith.edu Introduction: Circadian rhythms regulate most physiological processes. Adjustments to circadian time, or phase-shifts, are necessary following international travel and on a more frequent basis for individuals who work non-traditional schedules such as rotating shifts. Since the disruption that results from frequent phaseshifts is deleterious to both animals and humans, we sought to better understand the kinetics of resynchronization of the mouse circadian system. Methods: We have previously examined responses of mice to 6 h advances of the light:dark (LD) cycle as well as following 12 h delay shifts to resynchronize following LD cycle reversal. Here we measured responses to an even more disruptive phase-shift, an 8 h phase advance. Mice bearing a luciferase reporter gene for mPer2 were subjected to an 8h advance of the light cycle, and molecular rhythms in suprachiasmatic nuclei (SCN), thymus, spleen, and esophagus explants were measured periodically for 1 week following the shift. We then subjected some mice to a second 8 h advance and measured rhythms from the same tissues in the subsequent week. Results: We observed significant internal desynchrony following these LD shifts. While the SCN normally maintains a circa 8 h phase separation from these peripheral tissues, this separation was drastically reduced following subsequent 8 h advances. Four days after the second 8 h advance, the peripheral tissues were widely dispersed in phase. Conclusion: This protocol provides an approach to disrupt internal phase coherence, allowing better understanding of health effects from internal circadian desynchrony. Publication History Article published online: 16 June 2026 © 2009. Brazilian Sleep Academy. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/) Thieme Revinter Publicações Ltda. Rua Rego Freitas, 175, loja 1, República, São Paulo, SP, CEP 01220-010, Brazil