Decoding photoperiodic time through Per1 and ICER gene amplitude

The mammalian Per1 gene is expressed in the suprachiasmatic nucleus of the hypothalamus, where it is thought to play a critical role in the generation of circadian rhythms. Per1 mRNA also is expressed in other tissues. Its ex pression in the pars tuberalis (PT) of the pituitary is noteworthy because, like the suprachiasmatic nucleus, it is a known site of action of melatoni n, The duration of the nocturnal melatonin signal encodes photoperiodic tim e, and many species use this to coordinate physiological adaptations with t he yearly climatic cycle. This study reveals howl the duration of photoperi odic time, conveyed through melatonin, is decoded as amplitude of Per1 and ICER (inducible cAMP early repressor) gene expression in the PT. Syrian ham sters display a robust and transient peak of Per1 and ICER gene expression 3 h after lights-on (Zeitgeber time 3) in the PT, under both long (16 h lig ht/8 h dark) and short (8 h light/16 h dark) photoperiods. However, the amp litude of these peaks is greatly attenuated under a short photoperiod. The data show how amplitude of these genes may be important to the long-term me asurement of photoperiodic time intervals.