The master pacemaker located in the suprachiasmatic nuclei (SCN) coordinates “wake” functions by inducing the circadian release of glucocorticoids (GCs). Unlike other neuroendocrine systems, it is still unclear whether GCs feedback on the adult SCN circuit in mice. While GCs directly influence the SCN during development (i.e., perinatal period), the low expression of GR in adult neurons led to the conclusion that the mature circuit is GC resistant. The project aims to understand how the sensitivity to GCs changes as the mouse SCN matures from the perinatal period to adulthood and the role of astrocytes as time-keepers. This project will allow us to understand how the SCN controls the physiological synchrony when the internal and external timing misalign, such as during jetlag.