MICROSCOPY Vol.47▶No.2 2012
â– Feature Article: Morphology of Biological Clocks

The Mammalian Circadian Center Captures Environmental Time and Time Length

Yasufumi Shigeyoshi, Mamoru Nagano, Koh-hei Masumoto and Satoshi Koinuma

Abstract: The suprachiasmatic nucleus is the center of the mammalian circadian clock which is located in adjacent to the third ventricle and directly above the optic chiasm. The circadian rhythm has been modeled as a limit cycle which accounts for the behavior of the multiple circadian oscillators in the SCN. The light exposure shifts the circadian rhythm of the SCN via the induction of Per1/Per2. The anatomical fact that a light responsive region coexists with the light unresponsive region in the SCN leads to the jet lag syndrome after an abrupt shift of light-dark (LD) cycle; The slow shift of the light unresponsive region makes the desynchrony between the environmental LD cycle and the circadian rhythm in the central clock. Further, observations suggest that the SCN measures and stores the information of the day length by modulating the regional phase differences in the SCN.

Key words: Circadian rhythm, Internal clock, suprachiasmatic nucleus, jet lag, phase wave