Hypothalamic control of liver and white adipose tissue metabolism

Living organisms have to adjust their physiological processes and behavior to the changes in the environment, and therefore they developed, amongst others, a well conserved circadian timing system. The central clock of the circadian timing system is located in the suprachiasmatic nucleus (SCN) of the hypothalamus. The SCN receives photic information about the environmental light/dark cycle via the retinohypothalamic tract (RHT). Another important component of the circadian clock system are the peripheral clocks that can be found in most tissues and organs. Since these peripheral clocks have no direct access to light/dark information, their daily rhythms have to be synchronized with the environmental day/night cycle via the SCN. It has been hypothesized that the SCN synchronizes the daily rhythms of the peripheral clocks via its neuronal, hormonal and/or behavioral output pathways. In the current thesis, we tested this hypothesis by investigating the essentiality of various pathways in synchronizing the daily peripheral rhythms. Apart from photic information, the SCN rhythms are also synchronized by non-photic information from the environment, such as food availability and predator risk. Neuropeptide Y (NPY) is one of the important neurotransmitters in the non-photic circuitry. In addition to being a non-photic entraining signal, NPY is also an important neurotransmitter in the brain circuitry controlling energy metabolism. In the current thesis, we investigated the role of central NPY in regulating energy metabolism and peripheral clock rhythms.