Fig. 1.

The suprachiasmatic nucleus (SCN) receives exogenous environmental luminosity information through the retinohypothalamic tract as well as endogenous information from hormones (insulin, ghrelin, leptin), nutrients (amino acids, glucose, fatty acids) and metabolic sensors (NAD+/SIRT1/AMPK). The SCN provides several outputs from the hypothalamic nuclei, HPA axis, and pineal gland. It also regulates metabolism, energy expenditure, and hormones in peripheral tissues though hierarchical control of peripheral clock genes and clock-controlled genes.