MEAL TIMING AND THE SCN
Supervisors: Andries Kalsbeek, Susanne la Fleur & Eric Fliers
Circadian (~24 h) rhythms in mammals are generated by the suprachiasmatic nucleus (SCN), located in the anterior hypothalamus. The SCN transmits its rhythmicity to peripheral organs via hormonal, behavioural and autonomic signals. However, peripheral organs also possess a local, or peripheral, clock. Whereas light is an important timing cue (‘Zeitgeber’) for the SCN, feeding is an important Zeitgeber for peripheral clocks. Obviously, in the healthiest situation, central and peripheral rhythms act in synchrony. However, in our 24 h society the optimal settings of the biological clock are not always respected.
Although there is a close relationship between disruptions in the circadian clock and the development of metabolic abnormalities, the chicken-and-egg question remains.
Therefore, in this project we focus both on the role of the biological clock, and on the role of meal timing in energy homeostasis
1) In the first project we want to investigate, for different nutrients, the influence of timing (relative to the light/dark-cycle) on its consequences for body weight and fat tissue. Rats will be exposed to different feeding paradigms where we restrict the availability of fat and sugar to either the light or the dark period. We will study food intake, body weight gain and composition, and a number of metabolic parameters. Energy expenditure will be measured in metabolic cages. Eventually we hope to be able to determine which component, ingested at which moment of the day, has the most detrimental effects on energy homeostasis.
2) In the second project, we will focus on the role of the SCN in food preference, using three main components of our daily meal: fat, sugar and carbohydrates. We hypothesize that the central clock influences meal preference throughout a day. The results of this experiment will provide information about the influence of the central clock in preference of meal composition in relation to meal timing and indirectly, the contribution of the SCN in development of glucose intolerance.
Schematic of the circadian timing system. In the most optimal situation, central and peripheral clocks act in synchrony. However, conflicting external (feeding) signals can disrupt circadian clocks, possibly leading to metabolic abnormalities.