FEEDING ENTRAINMENT OF FOOD-ANTICIPATORY ACTIVITY AND per1 EXPRESSION IN THE BRAIN AND LIVER OF ZEBRAFISH UNDER DIFFERENT LIGHTING AND FEEDING CONDITIONS

Abstract

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. (Author correspondence: [email protected])

Keywords:

• Central peripheral oscillators
• Clock gene expression
• Food-anticipatory activity
• Locomotor activity
• Zebrafish

ACKNOWLEDGMENTS

This research was supported by the Spanish Ministry of Science and Technology (MCYT) by projects AGL2007-66507-C02-02 and AQUAGENOMICS granted to F.J.S.V., by a fellowship and travel grant from the University of Murcia granted to J.F.L., by start-up funds from the Department of Biology, University of Washington, to H.O.D., and by the Mary Gates Research Scholarship to E.V.T. The authors also wish to thank C. Oliveira from the University of Murcia for her help during sampling; and Dr. David Parichy for providing us with fish for the quantitative PCR trials and to Joe R. Roberts and Billy Medina for their assistance with the quantitative PCR analyses.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.