Nocturnal and diurnal behavior assessed by the “work-for-food” protocol in small rodents

Plasticity in daily timing of activity has been observed in many species, even within an individual. The temporal phase of activity under a light–dark cycle can shift by changes in light, temperature, (perceived) predation risk, food timing, and abundance. A major determinant of the phase of locomotor activity relative to the (entrained) SCN is energy balance. In the majority of restricted feeding experiments, access to a limited amount of food is restricted to a specific time of day, thereby changing both timing of food intake and energy balance. To induce food scarcity in an ecologically appropriate way, we developed the “work-for-food” paradigm for small rodents. In this paradigm, food access is determined by wheel-running activity, and the levels of (simulated) food scarcity can therefore be titrated without imposing an externally imposed timing component. This “work-for-food” paradigm enables assessment of the effect of energy balance on the daily activity rhythms of an animal, including its decision to switch temporal niche. Adaptive behavioral strategies to cope with energetic challenges may vary depending on species, sex, age, and reproductive status. This chapter provides detailed guidelines on how to carry out the “work-for-food” paradigm as a laboratory tool to investigate (molecular) mechanisms and consequences underlying flexibility of circadian and ultradian activity patterns in small rodents. Defining the mechanisms through which metabolic feedback acts on the circadian system to shift the timing of activity relative to the light–dark cycle and entrained phase of the SCN can yield important implications for human sleep, shift-work, chronotherapy, metabolic health, and (athletic) performance.