Figure 4. Central CLOCK synchronizes the peripheral CLOCKs and regulates peripheral organ activities via neural and humoral interactions. Light/dark information travels via the retinohypothalamic tract (RHT) from the retina (specifically from the retina ganglion cells which are intrinsically photosensitive) to the suprachiasmatic nucleus (SCN) where efferent neurons: (i) transfer timing information to other parts of the CNS, such as the paraventricular nucleus (PVN), medial preoptic area (MPO) and dorsomedial nucleus (DMH) of the hypothalamus and the pineal gland; and (ii) affect the autonomic nervous system (sympathetic and parasympathetic); in order to regulate the secretion of pituitary hormones and melatonin, which in turn control basic physiologic functions, including regulation of sleep, food intake and body temperature. DMV: dorsal motor nucleus of vagus. [Adapted from Nader, N, Chrousos, GP, Kino T. Trends Endocrinol Metab 2010;21:277].