Twilight and Photoperiod Affect Behavioral Entrainment in the House Mouse (Mus musculus)

• Published in: Journal of biological rhythms Vol. 24; no. 5; pp. 403 - 412
• Main Authors: Comas, M, Hut, R.A
• Format: Journal Article
• Language: English
• Published: Los Angeles, CA SAGE Publications 01-10-2009; SAGE PUBLICATIONS, INC
• Subjects: Animal behavior; Animals; Behavior, Animal - physiology; Biological Clocks - physiology; Biology; Circadian rhythm; Circadian Rhythm - physiology; Darkness; Light; Mice; Mice, Inbred C57BL; Motor Activity - physiology; Mus musculus; Periodicity; Photoperiod; Rodents; Mus musculus; photoperiod; circadian clock; twilight; entrainment
• ISSN: 0748-7304; 1552-4531
• DOI: 10.1177/0748730409343873

The effect of twilight transitions on entrainment of C57BL/6JOlaHsd mice (Mus musculus) was studied using light-dark cycles of different photoperiods (6, 12, and 18 h) and twilight transitions of different durations (0, 1, and 2 h). Phase angle differences of the onset, center of gravity, and offset of activity, activity duration (α), as well as free-running period (τ) in continuous darkness were analyzed. The main finding was that for all conditions the onset of activity was close to dusk or lights-off except for the short photoperiod with 2 h of twilight where activity onset was on average 5.3 (SEM 1.07) h after lights-off. This finding contrasts with the results of Boulos and Macchi for Syrian hamsters where a 5.9-h earlier activity onset was observed when similar photoperiod and twilight conditions are compared with a rectangular LD cycle. The authors suggest the opposite effects of 2 h of twilight in the 2 species may be related to their different free-running periods under DD conditions following entrainment to short photoperiod with 2-h twilight conditions. Since the authors observed larger variation in phase angle of entrainment in longer twilight conditions, twilight does not necessarily form a stronger zeitgeber.