RESETTING THE BIOLOGICAL CLOCK - MEDIATION OF NOCTURNAL CREB PHOSPHORYLATION VIA LIGHT, GLUTAMATE, AND NITRIC-OXIDE

Synchronization between the environmental lighting cycle and the biolo gical clock in the suprachiasmatic nucleus (SCN) is correlated with ph osphorylation of the Ca2+/cAMP response element binding protein (CREB) at the transcriptional activating site Ser(133). Mechanisms mediating the formation of phospho-CREB (P-CREB) and their relation to clock re setting are unknown. To address these issues, we probed the signaling pathway between light and P-CREB. Nocturnal light rapidly and transien tly induced P-CREB-like immunoreactivity (P-CREB-lir) in the rat SCN. Glutamate (Glu) or nitric oxide (NO) donor administration in vitro als o induced P-CREB-lir in SCN neurons only during subjective night. Cloc k-controlled sensitivity to phase resetting by light, Glu, and NO is s imilarly restricted to subjective night. The effects of NMDA and nitri c oxide synthase (NOS) antagonists on Glu-mediated induction of P-CREB -lir paralleled their inhibition of phase shifting. Significantly, amo ng neurons in which P-CREB-lir was induced by light were NADPH-diaphor ase-positive neurons of the SCN's retinorecipient area. Glu treatment increased the intensity of a 43 kDa band recognized by anti-P-CREB ant ibodies in subjective night but not day, whereas anti-alpha CREB-lir o f this band remained constant between night and day. Inhibition of NOS during Glu stimulation diminished the anti-beta-CREB-lir of this 43 k Da band. Together, these data couple nocturnal light, Glu, NMDA recept or activation and NO signaling to CREB phosphorylation in the transduc tion of brief environmental light stimulation of the retina into molec ular changes in the SCN resulting in phase resetting of the biological clock.