Food-anticipatory activity in Syrian hamsters: behavioral and molecular responses in the hypothalamus according to photoperiodic conditions.

Rosana F. Dantas-Ferreira,Etienne Challet,José Cipolla-Neto,Paul Pévet,Stéphanie Dumont,Sylviane Gourmelen,Valérie Simonneaux,Eric M Mintz

doi:10.1371/journal.pone.0126519

Abstract

When food availability is restricted, animals adjust their behavior according to the timing of food access. Most rodents, such as rats and mice, and a wide number of other animals express before timed food access a bout of activity, defined as food-anticipatory activity (FAA). One notable exception amongst rodents is the Syrian hamster, a photoperiodic species that is not prone to express FAA. The present study was designed to understand the reasons for the low FAA in that species. First, we used both wheel-running activity and general cage activity to assess locomotor behavior. Second, the possible effects of photoperiod was tested by challenging hamsters with restricted feeding under long (LP) or short (SP) photoperiods. Third, because daytime light may inhibit voluntary activity, hamsters were also exposed to successive steps of full and skeleton photoperiods (two 1-h light pulses simulating dawn and dusk). When hamsters were exposed to skeleton photoperiods, not full photoperiod, they expressed FAA in the wheel independently of daylength, indicating that FAA in the wheel is masked by daytime light under full photoperiods. During FAA under skeleton photoperiods, c-Fos expression was increased in the arcuate nuclei independently of the photoperiod, but differentially increased in the ventromedial and dorsomedial hypothalamic nuclei according to the photoperiod. FAA in general activity was hardly modulated by daytime light, but was reduced under SP. Together, these findings show that food-restricted Syrian hamsters are not prone to display FAA under common laboratory conditions, because of the presence of light during daytime that suppresses FAA expression in the wheel.

Highlights

Physiological and behavioral processes are endogenously timed by the circadian system on a daily basis
The master clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus is primarily synchronized by the daily variations of light intensity [1]
That motion detectors of the present study indicate that food-restricted hamsters under full photoperiods exhibit food-anticipatory activity (FAA), suggesting that during the period preceding food access, the animals are active in their cage, probably close to the feeder, waiting for the time of food availability

Summary

Introduction

Physiological and behavioral processes are endogenously timed by the circadian system on a daily basis. The master clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus is primarily synchronized by the daily variations of light intensity [1]. When restricted feeding schedules are imposed, animals manifest increased locomotor activity, called food-anticipatory activity (FAA), prior to food access. This behavioral response is best observed in nocturnal rodents when food is given during the light (resting) period, while their activity levels are normally low [3, 4]. FAA being expressed even in SCN-lesioned animals [5], a so-called feeding-entrainable clock or food clock, localized outside the SCN, has been proposed to be synchronized by meal time and to drive expression of FAA as a behavioral output. The metabolic hindbrain and the cerebellum are other possible components of the food clock network [9,10,11]

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Results

Discussion

Conclusion