Measuring Food Anticipation in Mice

Abstract

The interplay between the circadian system and metabolism may give animals an evolutionary advantage by allowing them to anticipate food availability at specific times of the day. Physiological adaptation to feeding time allows investigation of animal parameters and comparison of food anticipation between groups of animals with genetic alterations and/or post pharmacological intervention. Such an approach is vital for understanding gene function and mechanisms underlying the temporal patterns of both food anticipation and feeding. Exploring these mechanisms will allow better understanding of metabolic disorders and might reveal potential new targets for pharmacological intervention. Changes that can be easily monitored and that represent food anticipation on the level of the whole organism are a temporarily restricted increase of activity and internal body temperature.

Keywords: Period2 (Per2); chronobiology; circadian rhythms; feeding; food anticipation; food-entrainable oscillator (FEO); metabolic disease; mouse activity; peripheral oscillators; wheel running.

Figure 1

Schematic representation of the molecular clock. The transactivational complex BMAL1-CLOCK activates genes with E-BOX regulatory sites. PER-CRY complexes reduce this transactivational activity of BMAL1-CLOCK and provide a negative feedback. However, PER2 can also interact with nuclear receptors, for example, PPARα (peroxisome proliferator-activated receptor α) and positively regulate Bmal1 through activation of nuclear receptor response elements (NRE). On the level of transcriptional regulation of Bmal1, there is also competition between RORα and REV-ERBα, providing either transcriptional activation or repression, respectively, by binding to ROR response elements (RORE) and thereby stabilizing the molecular clock [1,10,21,22].

Figure 2

Representative results of restricted feeding experiments shown as double-plotted actograms, in which column height over time shows the activity of an animal. Two days are represented in each row, with the day on the right being repeated in the following row. Times of day when lights were off are shaded in grey and food-anticipatory activity during ZT 2–4 is highlighted, with additional emphasis on the last week of restricted feeding, visible within a rectangle. The green and red bars under the actograms represent time of analysis and food availability, like in Figure 3. AL—ad libitum; RF—restricted feeding. (A) A control animal shows food-anticipatory activity before food availability at ZT 4. (B) A genetically modified animal shows strongly reduced food-anticipatory activity, suggesting an involvement of the missing gene in anticipation of food.

Figure 3

Schematic representation of the experimental setup for restricted feeding. Mice are subjected to 12 h light, 12 h dark cycles. First, the mice are adapted to the setup, then subjected to temporal (ZT 4–12) and caloric food restriction (80% of daily intake for the first week and 70% for the following two weeks). The wheels in cages are coupled to a magnet that, for each revolution, closes the circuit in a connector located just next to the axis. This creates binary data that can be digitalized and processed.