Working for Food Shifts Nocturnal Mouse Activity into the Day

Abstract

Nocturnal rodents show diurnal food anticipatory activity when food access is restricted to a few hours in daytime. Timed food access also results in reduced food intake, but the role of food intake in circadian organization per se has not been described. By simulating natural food shortage in mice that work for food we show that reduced food intake alone shifts the activity phase from the night into the day and eventually causes nocturnal torpor (natural hypothermia). Release into continuous darkness with ad libitum food, elicits immediate reversal of activity to the previous nocturnal phase, indicating that the classical circadian pacemaker maintained its phase to the light-dark cycle. This flexibility in behavioral timing would allow mice to exploit the diurnal temporal niche while minimizing energy expenditure under poor feeding conditions in nature. This study reveals an intimate link between metabolism and mammalian circadian organization.

The clock genePeriod1regulates innate routine behaviour in mice

“…This is important in the context that hippocampal learning and memory processes differ between mice held in poor or enriched environments [39]. It is also known that mice show elevated activity during night-time when food and water is available ad libitum [6,40]. Therefore, innate routine behaviour must be tested during the dark period to avoid the influence of stress or arousal owing to waking the animals during their sleep phase [2,38,41].…”

“…One fundamental influence on innate routine behaviour of most animals is the temporal variation of environmental conditions like the light/dark cycle [3][4][5][6]. Current concepts on the usefulness of the circadian clock in terms of evolutionary fitness presume that it serves the anticipation of a rhythmically changing environment, important for proper feeding regulation and other physiological functions [6,7].…”

“…Current concepts on the usefulness of the circadian clock in terms of evolutionary fitness presume that it serves the anticipation of a rhythmically changing environment, important for proper feeding regulation and other physiological functions [6,7]. In a cold environment, temporal information may serve mice for anticipation of the next night in which temperature lowers, and building of a nest helps to save energy and protect adults as well as offspring.…”

“…In a cold environment, temporal information may serve mice for anticipation of the next night in which temperature lowers, and building of a nest helps to save energy and protect adults as well as offspring. Differences in daytime-dependent behaviour between laboratory and natural conditions have been described in mice, hamsters and fruitflies, suggesting a profound influence of light/dark cycle on the behavioural repertoire of model species [6,8,9]. One gene involved in the circadian clock system in flies and mice is Period1 (Per1) [10 -12].…”

Cold and hunger induce diurnality in a nocturnal mammal

“…Letting mice work for a food reward at gradually increasing workload levels (WFF protocol; ref. 18) at various T a s reduced energy intake without restricting food availability to a specific time of day (Fig. S1).…”