・Behavioral rhythms in mice deficient in the Cryptochrome (Cry) clock gene, which genetically disturbs circadian rhythms, recover with postnatal constant light.

・Postnatal constant light partly restores the circadian rhythms of the suprachiasmatic nucleus (SCN) (see Note 1) in Cry-deficient mice

・Constant light from the postnatal period is important for restoring two different clock rhythms in the cycles that regulate the behavioral rhythms of Cry-deficient mice

Note 1: Suprachiasmatic nucleus (SCN)

An assembly of neurons located above the optic chiasm, where the optic nerves cross. This is the core of the biological clock in mammals.

The phenomenon whereby sleeping and waking are repeated on a daily basis is known as “circadian rhythm,” and these rhythms are generated by biological clocks. In mammals, the biological clock is centered in the brain, which sends information on time to the rest of the body.

When the Cryptochrome (Cry) gene, which is one of the clock genes that generate circadian rhythms, is missing, the circadian rhythms evident in biological clocks during the nursing period disappear after weaning, and the circadian rhythm of sleeping and waking is no longer seen.

In this study, the group focused on the mechanisms whereby the brain develops under the influence of environmental factors, and investigated how the light environment acts on genetically disturbed circadian rhythms.

The group discovered that if Cry-deficient mice were reared under constant light from immediately after birth to three weeks after weaning and were then transitioned to constant darkness, the behavioral rhythms that should have disappeared under a normal light cycle were restored.

Their results showed that although constant light did not suppress the disturbance of circadian rhythm after adulthood, postnatal light restored the rhythms of two clocks that control behavior, and is important in suppressing disturbance.

Ken-ichi Honma, Visiting professor, Graduate School of Medicine, Hokkaido University

TEL: +81-11-706-4737

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E-mail: kenhonma@med.hokudai.ac.jp