| pubmed-article:11860521 | pubmed:abstractText | The circadian clockwork of the hypothalamic suprachiasmatic nuclei (SCN) is synchronized by light and by nonphotic cues. The core timing mechanism is cell-autonomous, based on an autoregulatory transcriptional/translational feedback loop of circadian genes and their products. This study investigated the effects of neuropeptide Y (NPY), a potent nonphotic resetting cue, and its interaction with light in regulating clock gene expression in the SCN in vivo. Injection of NPY adjacent to the SCN and transfer to darkness 7 h before scheduled lights out, shifted the circadian activity-rest cycle. Exposure to light for 1 h immediately after NPY infusion blocked this behavioural response. NPY-induced shifts were accompanied by suppression of both mPer1 and mPer2 mRNA in the SCN, assessed 3 h after infusion. mPer mRNAs were not altered 1 h after infusion. Levels of mClock mRNA or mCLOCK immunoreactivity in the SCN were not affected by NPY at either time point. In parallel to the behavioural response, the NPY-induced suppression of mPer genes in the SCN was attenuated when a light pulse was delivered immediately after the infusion. These results identify mPer1 and mPer2 as molecular targets for both photic and nonphotic (NPY-induced) resetting of the clockwork, and support a synthetic model of circadian entrainment based upon convergent up- and downregulation of mPer expression. | lld:pubmed |
