FEEDING ENTRAINMENT OF FOOD-ANTICIPATORY ACTIVITY ANDper1EXPRESSION IN THE BRAIN AND LIVER OF ZEBRAFISH UNDER DIFFERENT LIGHTING AND FEEDING CONDITIONS

Aug 28, 2010Chronobiology international

How feeding schedules affect activity and daily gene patterns in the brain and liver of zebrafish under different light and feeding setups

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Abstract

Zebrafish exhibit food-anticipatory activity when fed at scheduled times, indicating that feeding can synchronize their biological clocks.

Feeding at fixed times resulted in food-anticipatory activity across all tested groups.
Zebrafish under constant bright-light conditions displayed a free-running circadian rhythm with a period close to 24 hours after fasting.
The brain's expression of the clock gene per1 maintained a daily rhythm under a light-dark cycle, peaking at the end of the dark phase irrespective of the feeding schedule.
In constant bright-light conditions, the daily rhythm of per1 expression in the brain was lost regardless of the feeding schedule.
Scheduled feeding during the mid-dark phase advanced the liver's per1 expression phase by 7 hours compared to feeding during the mid-light phase.
Scheduled feeding also synchronized per1 expression rhythms in the liver under constant bright-light conditions.

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Food provided on a periodic basis can act as a potent synchronizer, being a stronger zeitgeber than light for peripheral oscillators in mammals. In fish, however, little is known about the influence of feeding time on the circadian pacemaker and the relationship between central and peripheral oscillators. The aim of this research was to investigate the influence of mealtime on the activity rhythms, and on central (brain) and peripheral (liver) oscillators in zebrafish. The authors tested different feeding times under a light-dark (LD) cycle and the endogenous origin of food-anticipatory activity (FAA) by feeding zebrafish at a fixed time under constant bright-light conditions (LL). The authors then measured locomotor activity and the expression of the clock gene per1 in animals under a LD cycle and fed at random times during the light phase, with restricted feeding at the mid-light phase (ML) or with restricted feeding during the mid-dark phase (MD). Finally, the authors measured locomotor activity and per1 expression in fish maintained under LL under either random feeding or scheduled feeding. Zebrafish displayed FAA in all the groups fed at a fixed time but not when feeding was randomly scheduled. Under LL, fish entrainment persisted, and when released under fasting conditions FAA free-ran with a circa-24-h period. The expression of per1 in the brain of fish under LD showed a daily rhythm with the acrophase (peak time) at the end of the dark phase regardless of feeding schedule. This brain rhythm disappeared in LL fish under both random feeding and scheduled feeding. Feeding at MD advanced the phase of per1 in the liver by 7 h compared with the ML-fed group phase (23:54 versus 07:23 h, respectively). In addition, under LL scheduled feeding entrained the rhythms of per1 expression in the liver. This study reveals for the first time that scheduled feeding entrains peripheral oscillators in a fish species, zebrafish, which is a powerful model widely used for molecular genetics and for the study of basic clock mechanisms of the vertebrate circadian system.

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FEEDING ENTRAINMENT OF FOOD-ANTICIPATORY ACTIVITY ANDper1EXPRESSION IN THE BRAIN AND LIVER OF ZEBRAFISH UNDER DIFFERENT LIGHTING AND FEEDING CONDITIONS

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