The ontogeny of sleep-wake cycles in zebrafish: a comparison to humans.

Amanda Sorribes

doi:10.3389/fncir.2013.00178

Amanda Sorribes

Open Access

https://doi.org/10.3389/fncir.2013.00178

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Abstract

Zebrafish (Danio rerio) are used extensively in sleep research; both to further understanding of sleep in general and also as a model of human sleep. To date, sleep studies have been performed in larval and adult zebrafish but no efforts have been made to document the ontogeny of zebrafish sleep–wake cycles. Because sleep differs across phylogeny and ontogeny it is important to validate the use of zebrafish in elucidating the neural substrates of sleep. Here we describe the development of sleep and wake across the zebrafish lifespan and how it compares to humans. We find power-law distributions to best fit wake bout data but demonstrate that exponential distributions, previously used to describe sleep bout distributions, fail to adequately account for the data in either species. Regardless, the data reveal remarkable similarities in the ontogeny of sleep cycles in zebrafish and humans. Moreover, as seen in other organisms, zebrafish sleep levels are highest early in ontogeny and sleep and wake bouts gradually consolidate to form the adult sleep pattern. Finally, sleep percentage, bout duration, bout number, and sleep fragmentation are shown to allow for meaningful comparisons between zebrafish and human sleep.

Highlights

We characterize the ontogeny of sleep–wake cycles in zebrafish and by defining sleep architecture in terms of state transitions, we demonstrate that sleep–wake cycles in zebrafish develop in a trajectory that can be meaningfully compared to humans (Kleitman and Engelman, 1951; Roffwarg et al, 1966; Jenni et al, 2006)
By showing that sleep architecture in humans and zebrafish can be directly contrasted using multiple measures, zebrafish are further validated as a highly useful sleep model (Rihel et al, 2010b).The similarities demonstrated between zebrafish and humans is consistent with the notion of evolutionarily conserved neural substrates controlling the sleep states
We show that sleep percentage overnight decreases with age whereas sleep bout length, sleep bout www.frontiersin.org

Summary

Introduction

In all species studied so far, sleep levels are highest and sleep bouts are shortest early in ontogeny (Kleitman and Engelman, 1951; Roffwarg et al, 1966; Jouvet-Mounier et al, 1970; Blumberg et al, 2005; Jenni et al, 2006). Human infants spend about two-thirds of the day (i.e., 24-h) asleep whereas adults sleep for only one-third of the day (Roffwarg et al, 1966) This reduction in sleep levels across ontogeny has been reported in many other species (Jouvet-Mounier et al, 1970; Hoppenbrouwers and Sterman, 1975; McGinty et al, 1977). Another seemingly universal feature of sleep development is the gradual consolidation of sleep and wake bouts (Blumberg et al, 2005; Arnardóttir et al, 2010; Karlsson et al, 2011). Even though sleep has been studied in larvae and adults, no such description of sleep–wake ontogeny exists for zebrafish (Danio rerio), a recent, promising model for sleep research (Zhdanova, 2006; Zhdanova et al, 2006; Yokogawa et al, 2007; Rihel et al, 2010a,b; Sigurgeirsson et al, 2011)

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