Abstract
Master circadian clock of mammals resides in the hypothalamic suprachiasmatic nucleus (SCN). Recently, brain areas outside the SCN and other peripheral organs are shown to have circadian clock(s). In order to examine the clock organization and its tissue specificity, we monitored clock gene expression rhythms in the SCN and other areas.
Circadian rhythms in single cells are stem from a transcription-translation feedback loop composed of clock genes, Clock, Bmal1, Per and Cry. Dec1 and Dec2 share many properties with Per and Cry. Clock mutation significantly reduced the expression of Dec1 and Dec2 in the SCN and other brain areas, but the suppression patterns were tissue specific. Light effects on Dec and Per expression were also tissue specific.
In the organotypic slice culture of the SCN in Clock mutant mice, single neuronal activities exhibited robust circadian rhythms with lengthened periods. The percentage of rhythmic neurons decreased in the dispersed cell culture, suggesting that relatively small group of clock neurons drive circadian neuronal and molecular rhythms in a large number of non-clock neurons, and increase of the intrinsic period and decrease of cell-to-cell communication may reduce the ability of clock neurons to drive rhythms.
Chronic methamphetamine treatment desynchronizes behavioral rhythm from clock gene rhythms in the SCN. Behavioral rhythms are in phase with clock gene rhythms in some brain areas but not in others, suggesting the hierarchical networks of the master and peripheral clocks can be modified by the treatment. [Jpn J Physiol 54 Suppl:S6 (2004)]
