Suprachiasmatic nucleus (SCN) is the central circadian clock in mammals. Thousands of neurons in the SCN exhibit autonomous circadian rhythms. According to the current model, a transcriptional and translational negative feedback loop composed of several clock genes is involved in the rhythm generation. Circadian rhythms in the SCN entrain to environmental light dark cycles, which reflect on various behaviors including sleep-wake cycle. Recently we found that clock genes, Cryptochrome (Cry) 1 and Cry2, are not essential for generation or synchronization of cellular circadian rhythms in the neonatal SCN but indispensable for coherent circadian rhythm expression in the adult SCN. However, it is still unclear what factor(s) is involved in CRY-dependent and -independent cellular networks in the SCN and how oscillator networks are formed by the factor(s) during the postnatal period.
In order to elucidate the mechanisms of cellular networks in the SCN during postnatal development, we examined the roles of two major neuropeptides, arginine vasopressin and vasoactive intestinal polypeptide, in the SCN networks using mice carrying a bioluminescence reporter for PER2::LUC. We also investigate the role of signal transduction of these neuropeptides in coherent circadian rhythm expression. Both peptides seem to be critical differentially in postnatal stages. We will discuss the roles of neuropeptide signaling in the SCN in relationship with CRY.