Influence of photoperiod duration and light–dark transitions on entrainment of Per1 and Per2 gene and protein expression in subdivisions of the mouse suprachiasmatic nucleus

Oct 21, 2009The European journal of neuroscience

Day length and light changes affect daily rhythms of clock genes and proteins in different parts of the mouse brain's time-keeping center

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Abstract

Under the short photoperiod, twilight transitions significantly phase-advanced Per1 and Per2 profiles in all examined regions of the mouse suprachiasmatic nucleus (SCN).

The SCN responds differently to gradual twilight transitions compared to abrupt rectangular light-to-dark transitions.
Under short photoperiods, twilight conditions lead to stronger synchronization of Per1 and Per2 mRNA and protein levels across SCN regions.
In contrast, under long photoperiods, the differences in phase relationships between rostral and caudal SCN regions are reduced.
The phase advancement of Per1 and Per2 profiles is observed only under short photoperiods with twilight.

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The circadian clock located within the suprachiasmatic nuclei (SCN) of the hypothalamus responds to changes in the duration of day length, i.e. photoperiod. Recently, changes in phase relationships among the SCN cell subpopulations, especially between the rostral and caudal region, were implicated in the SCN photoperiodic modulation. To date, the effect of abrupt, rectangular, light-to-dark transitions have been studied while in nature organisms experience gradual dawn and twilight transitions. The aim of this study was to compare the effect of a long (18 h of light) and a short (6 h of light) photoperiod with twilight relative to that with rectangular light-to-dark transition on the daily profiles of Per1 and Per2 mRNA (in situ hybridization) and PER1 and PER2 protein (immunohistochemistry) levels within the rostral, middle and caudal regions of the mouse SCN. Under the short but not under the long photoperiod, Per1, Per2 and PER1, PER2 profiles were significantly phase-advanced under the twilight relative to rectangular light-to-dark transition in all SCN regions examined. Under the photoperiods with rectangular light-to-dark transition, Per1 and Per2 mRNA profiles in the caudal SCN were phase-advanced as compared with those in the rostral SCN. The phase differences between the SCN regions were reduced under the long, or completely abolished under the short, photoperiods with twilight. The data indicate that the twilight photoperiod provides stronger synchronization among the individual SCN cell subpopulations than the rectangular one, and the effect is more pronounced under the short than under the long photoperiod.

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Influence of photoperiod duration and light–dark transitions on entrainment of Per1 and Per2 gene and protein expression in subdivisions of the mouse suprachiasmatic nucleus

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