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The lower entrainable limit of rat circadian rhythm to sinusoidal light intensity cycles: A preliminary study
Author(s) -
Usui Setsuo,
Okazaki Terue,
Takahashi Yasuro
Publication year - 1999
Publication title -
psychiatry and clinical neurosciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.609
H-Index - 74
eISSN - 1440-1819
pISSN - 1323-1316
DOI - 10.1046/j.1440-1819.1999.00538.x
Subject(s) - entrainment (biomusicology) , circadian rhythm , light cycle , illuminance , rhythm , light intensity , darkness , luminous intensity , intensity (physics) , chronobiology , medicine , endocrinology , biology , zoology , optics , physics
The lower entrainable limit of the circadian behavioral rhythm was examined in rats exposed to sinusoidal light intensity cycles with maximum illuminance of 20 lux and the minimum of 0.01 lux. The period (T) of the light intensity cycle was initially kept at 23.5 h for 20 cycles, and then shortened to 23 h for 33 cycles. Thereafter the rats were released into constant darkness. Five out of 10 rats entrained their circadian rhythms to T = 23.5‐h cycle, and they also entrained to the T = 23‐h cycle. The phase angle of entrainment was almost unchanged when T was shortened from 23.5 h to 23 h. These results suggest that the T = 23‐h cycle was close to the lower limit of entrainment.