FEEDING ENTRAINMENT OF DAILY RHYTHMS OF LOCOMOTOR ACTIVITY AND CLOCK GENE EXPRESSION IN ZEBRAFISH BRAIN

Sep 5, 2009Chronobiology international

Feeding times influence daily movement patterns and internal clock gene activity in zebrafish brain

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Abstract

Zebrafish exhibited food anticipatory activity (FAA) when fed daily at a fixed time, regardless of light conditions.

Locomotor activity in zebrafish varied based on feeding time, with activity percentages ranging from 93.2% during mid-light feeding to 63.1% during mid-dark feeding.
The daily rhythm of clock genes per1 and cry1 in the zebrafish brain did not change with different feeding regimes under light/dark conditions.
Under constant light conditions, per1 and cry1 expression showed no significant daily rhythm independent of the feeding schedule.
Findings suggest that the mechanisms for synchronizing behavior with feeding may not directly influence the expression of these clock genes in the whole brain.

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Light and feeding cycles strongly synchronize daily rhythms in animals, which may, as a consequence, develop food anticipatory activity (FAA). However, the light/food entraining mechanisms of the central circadian oscillator remain unknown. In this study, we investigate the existence of FAA in seven groups of zebrafish subjected to a light/dark (LD) cycle or constant light (LL) and different feeding regimes (random, fasting, and feeding in the middle of the light phase or dark phase). The aim was to ascertain whether the daily rhythm of behavior and clock gene (per1 and cry1) expression in the zebrafish brain was entrained by the light and feeding regime. The results revealed that FAA developed in zebrafish fed daily at a fixed time, under LD and under LL. Zebrafish displayed locomotor activity mostly during the daytime, although the percentage of activity during the light phase varied depending on feeding time (ranging from 93.2% to 63.1% in the mid-light and mid-dark fed groups, respectively). However, the different feeding regimes failed to modify the daily rhythm of per1 and cry1 expression in the zebrafish brain under LD (approximate acrophases [peak times] at ZT22 and ZT4, respectively; lights-on = ZT0). Under LL, per1 and cry1 expression did not show significant daily rhythmicity, regardless of the feeding regime. These findings indicate that, although schedule-fed zebrafish developed FAA as regards locomotor activity, feeding had little effect on clock gene expression in whole brain homogenates, suggesting the feeding-entrainable oscillator may be located elsewhere or at specific brain sites.

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FEEDING ENTRAINMENT OF DAILY RHYTHMS OF LOCOMOTOR ACTIVITY AND CLOCK GENE EXPRESSION IN ZEBRAFISH BRAIN

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