Chapter 9 Regulation of entrainment pathways by the suprachiasmatic circadian clock: sensitivities to second messengers

Abstract

Publisher Summary The chapter explains that the clock properties predicted from in vivo studies are endogenous to the suprachiasmatic nucleus (SCN); they persist when the SCN is isolated in a brain slice and maintained under constant conditions in vitro. The SCN continues to generate a stable, near-24-hour rhythm of neuronal activity for up to three cycles in vitro, and this rhythm can be reset by a range of stimuli. At specific phases, or time domains, within the 24-hour cycle, the circadian clock in vitro is still receptive to only a subset of the various stimuli that can reset it. Therefore, the circadian clock regulates its own sensitivity to afferent signals. The chapter demonstrates that this gating is downstream from the second messengers in signaling pathways. It follows that the states of specific molecular gates regulated by the clock change over the 24-hour cycle and site(s) critical to gating signaling pathways that access the clock lie within the cells of the SCN.