Molecular Basis of Circadian Cytosolic Calcium Rhythms

The present study also analyzed process of photic inputs to SCN neurons regarding the mobilization of cytosolic Ca^(2+) and expression of clock genes. We found light-pulse-induced mPer1/2 gene expression in the SCN and behavioral-phase-shifts were significantly reduced in cholecystokinin (CCK)-A receptor knockout mice. We demonstrated that CCK-A receptors were located predominately on glycinergic amacrine cells, but not retino-recipient SCN neurons. Moreover, Ca^(2+) imaging analysis demonstrated that the CCK-A agonist, CCK-8s, mobilized intracellular Ca^(2+) in amacrine cells but not retino-recipent SCN neurons. These data indicate a novel function of CCK-A receptors as part of the cellular mechanism underlying circadian photo-entrainment via amacrine-cell-mediated signal transduction pathways.