Deletion of Clock Gene <i>Period1</i> (<i>Per1</i>) in Neurons but not in Astrocytes Shortens Clock Period and diminishes Light-Mediated Rapid Phase Advances in Mice

The circadian clock enables organisms to anticipate daily recurring events and syn-chronize their internal rhythms with environmental cues, such as light, aligning with the day/night cycle. Central to the molecular mechanisms of the circadian clock and light sensing are the Period (Per) 1 and 2 genes. While the roles of Per2 in astrocytes and neurons have been characterized, the specific contributions of Per1 remain less understood. Pre-vious research has shown that Per2 in neurons, but not astrocytes, influences phase shifts, whereas the regulation of circadian period involves Per2 in both cell types. In this study, we investigated the role of Per1 in neurons and astrocytes in modulating circadian period and phase shifts. Using an Aschoff Type I protocol (constant darkness) combined with 15-minute light pulses at circadian times (CT) 10, 14, and 22, we found that the absence of Per1 in neurons—but not in astrocytes—significantly affected both the circadian period and phase advance shifts in response to light at CT22.