The Dependency of the Rat Estrous Cycle on the Daily Alternation of Light and Dark

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Using the rats kept under various experimental lighting conditions, the dependency of the estrous cycle on the light rhythm was investigated with special reference to the age. The lighting condition utilized was the normal lighting, the continuous lighting and continuous complete darkness. For the last condition, the special boxes were designed to feed the animals under complete light-proof condition. Two kind of estrous cycles were distinguished; one was dependent on the diurnal rhythm of light and dark (the “light dependent cycle”), and the other was independent of the rhythm (the “light independent cycle”). The former showed regular 4-day cycles, but in the latter each animal was repeating nearly 4-day cycles independently on chronological day and night. The “light dependent cycle” was seen in the animals which were provided the normal lighting from birth, and if these animals were transferred into the continuous lighting, the cycle was disturbed and the constant estrus resulted in about 15 days. This constant lighting stimuli, however, did not exert any detectable effects on the animals which had active corpora lutea. The “light independent cycle” was seen in the animals brought up without providing any light rhythms. But if the information of alternation of light and dark was provided for a certain period either after or even <I>before</I> the puberty, this cycle was replaced by the “light dependent cycle”. The “light independent cycle” persisted for about 200 days of age, while the “light dependent cycle” could persist further, upto 400 days of age. It is noteworthy that when the animals which had possessed the “light dependent cycle” were confined to the continuous complete darkness for a certain period, they came to aquire the “light independent cycle” and were hard to be induced constant estrus by exposing to the continuous lighting.
社団法人日本内分泌学会の論文

The Dependency of the Rat Estrous Cycle on the Daily Alternation of Light and Dark

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