Working for Food Shifts Nocturnal Mouse Activity into the Day

Roelof A Hut,Violetta Pilorz,Serge Daan,Ate S Boerema,Arjen M Strijkstra,Shin Yamazaki

doi:10.1371/journal.pone.0017527

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.

Highlights

Mice and rats are nocturnal, but their activity shifts to the day when food access is restricted to a few hours in daytime
food anticipatory activity (FAA) is thought to be the behavioral output of a separate circadian oscillator called the food entrainable oscillator (FEO) which is entrained by periodic food availability and capable of driving peripheral [2,3] and behavioral rhythms [4]
Since the activity pattern gradually shifts towards diurnality when energy intake is reduced (Fig. 1A–B; 2A–B), it is plausible that this activity pattern is controlled by a slave oscillator that changes its phase position with respect to the suprachiasmatic nucleus (SCN)

Summary

Introduction

Mice and rats are nocturnal, but their activity shifts to the day when food access is restricted to a few hours in daytime In such restricted schedules the food received is limited both in time and in quantity (typically 60–70% of normal daily food intake). FAA is thought to be the behavioral output of a separate circadian oscillator called the food entrainable oscillator (FEO) which is entrained by periodic food availability and capable of driving peripheral [2,3] and behavioral rhythms [4]. Under these conditions the FEO drives the activity rhythm independently of the suprachiasmatic nucleus (SCN), which controls nocturnal activity under standard ad libitum conditions [5,6]. The anatomical substrate of the FEO remains elusive in spite of intense investigation and debate [4,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23]

Methods

Results

Conclusion