Reorganization of the suprachiasmatic nucleus by photic and non-photic environments

To better understand alterations in suprachiasmatic nucleus (SCN) physiology by photic and non-photic environments, we analyzed clock gene expression in the mouse SCN by in situ hybridization and real-time monitoring of mPer1::luc bioluminescence. An artificial light: dark: light: dark 7:5:7:5 condition induced antiphase oscillation of the clock gene in the dorsomedial-like (DM-like) and the ventrolateral-like (VL-like) subdivisions of the SCN, in parallel with maintaining synchronization between the two sides of the SCN. This antiphase oscillation seems to be responsible for the bimodal rhythms of mPer1 bioluminescence observed in the entire SCN and the components of splitting locomotor activity. A long photoperiod (LP) induced the phase advance of the rhythms of clock gene expression in the caudal SCN relative to those in the rostral SCN. In addition, in the middle SCN, the rhythms of the VL-like subdivision phase-led those in the DM-like subdivision. The mPer1::luc rhythms in the entire coronal slice obtained from the middle SCN exhibited two peaks with a wide peak width under LP conditions. Imaging analysis of the mPer1::luc rhythms revealed wide regional variations in the peak time in the rostral half of the SCN. These variations were not due to alterations in the waveform of a single SCN neuronal rhythm. In CS mice which easily entrain to daily restricted feeding (RF) cycles, the peak width for mPer1::luc bioluminescence rhythms in the SCN markedly increased during the RF schedule under LD conditions. These data in CS mice suggest non-photic cues alter SCN organization and provided a new method to reveal subdivisional changes of the SCN by feeding cues.