title: Interruption of the rat circadian clock by short light-dark cycles.
abstract: Ninety male Sprague-Dawley rats were exposed to 1:1-h light-dark (LD1:1) cycles for 50-90 days, and then they were released into constant darkness (DD). During LD1:1 cycles, behavioral rhythms were gradually disintegrated, and circadian rhythms of locomotor activity, drinking, and urine 6-sulfatoxymelatonin excretion were eventually abolished. After release into DD, 44 (49%) rats showed arrhythmic behavior for >10 days. Seven (8%) animals that remained arrhythmic for >50 days in DD were exposed to brief light pulses or 12:12-h light-dark cycles, and then they restored their circadian rhythms. These results indicate that the circadian clock was stopped, at least functionally, by LD1:1 cycles and was restarted by subsequent light stimulation.
authors.affiliation: Department of Psychology, Tokyo Metropolitan Institute for Neuroscience, Fuchu, Tokyo 183-8526, Japan. usui@tmin.ac.jp
authors.forename: Setsuo
authors.initials: S
authors.lastname: Usui
authors.forename: Terue
authors.initials: T
authors.lastname: Okazaki
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Honda
mesh_terms: D000204:Activity Cycles / Q000502:physiology; D000222:Adaptation, Physiological; D000818:Animals; D001683:Biological Clocks / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D003624:Darkness; D004326:Drinking / Q000502:physiology; D008027:Light; D008297:Male; D008550:Melatonin / Q000031:analogs & derivatives* / Q000652:urine; D009043:Motor Activity / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
chemical_list: C054513:6-sulfatoxymelatonin; D008550:Melatonin