Calbindin expression in the hamster SCN is influenced by circadian genotype and by photic conditions

Circadian rhythmicity in mammals, is controlled by the suprachiasmatic nuclei (SCN) of the hypothalamus. We previously described a discrete subnucleus in the core of the hamster SCN containing calbindin-D28k-positive cells which are fos-positive in response to a light pulse. Ablation of this subnucleus results in loss of circadian locomotor rhythmicity even when other parts of the SCN are spared. Here we show that Tau mutant hamsters have significantly more calbindin-D28k in the SCN than do wild type hamsters, and that SCN calbindin-immunoreactivity in the SCN increases in the dark. This is correlated with changes in magnitude of light mediated phase shifts in locomotion. The data are consistent with a role for calbindin cells in light mediated entrainment and phase shifting.