Zebrafish sleep: from geneZZZ to neuronZZZ

doi:10.1016/j.conb.2017.02.009

Current Opinion in Neurobiology

Volume 44, June 2017, Pages 65-71

https://doi.org/10.1016/j.conb.2017.02.009 Get rights and content

Highlights

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Zebrafish have advanced genetic and functional imaging toolkits to study sleep.
•
Zebrafish have conserved sleep genes and neurons.
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Recent zebrafish studies have identified novel regulators of sleep and arousal.
•
Behavioral drug screens can identify links between disease and sleep disruption.

All animals have a fundamental and unavoidable requirement for rest, yet we still do not fully understand the processes that initiate, maintain, and regulate sleep. The larval zebrafish is an optically translucent, genetically tractable model organism that exhibits sleep states regulated by conserved sleep circuits, thereby offering a unique system for investigating the genetic and neural control of sleep. Recent studies using high throughput monitoring of larval sleep/wake behaviour have unearthed novel modulators involved in regulating arousal and have provided new mechanistic insights into the role of established sleep/wake modulators. In addition, the application of computational tools to large behavioural datasets has allowed for the identification of neuroactive compounds that alleviate sleep symptoms associated with genetic neurological disorders.

Introduction

Work over the past 15 years has demonstrated that sleep is evolutionarily conserved across the animal kingdom, indicating that sleep serves an essential, possibly universal, function [1^•]. Moreover, the negative impact that sleep disruption has on immune, metabolic, cardiac and cognitive health demonstrates sleep’s critical role in optimising daily behaviour and general physiological well-being. Many molecular and neuronal control systems are in place to regulate sleep’s timing and duration; however, we are still discovering these systems and their rules. Two major discoveries have spearheaded advances in the field. First, the discovery that the human sleep disease, narcolepsy, is a dysfunction in hypocretin/orexin signalling demonstrated that small populations of peptidergic neurons can have profound consequences on human and animal sleep [2]. Second, the recognition that genetically tractable non-mammalian species exhibit sleep states has expanded the models available to sleep researchers and have facilitated screens for sleep mutants [3].

The study of sleep regulation in zebrafish larvae has taken up a unique model system niche, as they offer a sophisticated genetic toolkit coupled with the ability to monitor and manipulate the activity of conserved sleep/wake neurons in vivo (see Box 1). In this review, we discuss recent insights into sleep in this diurnal vertebrate and highlight novel methods that use the special properties of the zebrafish model.

Section snippets

Monitoring sleep and arousal in larval zebrafish

To enable relatively high-throughput monitoring of sleep/wake states in zebrafish larvae, the animals are tracked by videography in a 96-well plate format for several days on either a 24-hour light–dark cycle or on constant illumination (Figure 1a). Larval and adult zebrafish are diurnal and at night exhibit an increased number and duration of inactive bouts (Figure 1b), which have a typical duration around three minutes but can last for hours [4]. Quiescent bouts lasting at least one minute

Neurocircuitry of sleep in zebrafish

Classical and modern lesion studies in mammals highlighted numerous brain areas, including the basal forebrain, posterior hypothalamus, reticular formation, and hindbrain as critical for the regulation of arousal and sleep [16, 17, 18]. More recently, systematic searches for sleep/wake regulatory neurons using chemogenetic and optogenetic modulation of putative sleep/wake-inducing neurons are more precisely defining many key subpopulations as well as unravelling the complex dynamics at play

Sleep, disease, and predictive pharmacology

Many neuropsychiatric and neurodevelopmental disorders, including depression, schizophrenia, Alzheimer’s disease, and autism, are associated with sleep disturbances [44, 45], but it remains unclear in most cases to what extent sleep disruption contributes to disease severity and progression. Several studies have now identified sleep and arousal endophenotypes in zebrafish genetic models of disease. For example, a zebrafish model of the most common cause of mental retardation, Fragile-X

Concluding remarks

Studies into the genetic and neural components involved in regulating evolutionarily conserved behaviours such as sleep have profited from advances in zebrafish genetic and imaging tools. Validation of conserved network modules involved in regulating sleep and wake in zebrafish has paved the way for genetic and neuropeptide screens that have identified novel modulators of vertebrate sleep that are likely to be relevant in mammals. Moving forward, studies that combine in vivo neuronal imaging

References and recommended reading

Papers of particular interest, published within the period of review, have been highlighted as:

• of special interest
•• of outstanding interest

Conflict of interest

None.

Acknowledgements

We thank all the members of the Rihel lab for helpful comments on the manuscript. This work is supported by an ERC Starting Grant, a UCL Excellence Fellowship, and a Grand Challenges Grant awarded to JR.

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A vertebrate family without a functional Hypocretin/Orexin arousal system
2024, Current Biology
The Hypocretin/Orexin signaling pathway suppresses sleep and promotes arousal, whereas the loss of Hypocretin/Orexin results in narcolepsy, including the involuntary loss of muscle tone (cataplexy).¹ Here, we show that the South Asian fish species Chromobotia macracanthus exhibits a sleep-like state during which individuals stop swimming and rest on their side. Strikingly, we discovered that the Hypocretin/Orexin system is pseudogenized in C. macracanthus, but in contrast to Hypocretin-deficient mammals, C. macracanthus does not suffer from sudden behavioral arrests. Similarly, zebrafish mutations in hypocretin/orexin show no evident signs of cataplectic-like episodes. Notably, four additional species in the Botiidae family also lack a functional Hypocretin/Orexin system. These findings identify the first vertebrate family that does not rely on a functional Hypocretin/Orexin system for the regulation of sleep and arousal.
Genetic and chemical disruption of amyloid precursor protein processing impairs zebrafish sleep maintenance
2024, iScience
Amyloid precursor protein (APP) is a brain-rich, single pass transmembrane protein that is proteolytically processed into multiple products, including amyloid-beta (Aβ), a major driver of Alzheimer disease (AD). Although both overexpression of APP and exogenously delivered Aβ lead to changes in sleep, whether APP processing plays an endogenous role in regulating sleep is unknown. Here, we demonstrate that APP processing into Aβ40 and Aβ42 is conserved in zebrafish and then describe sleep/wake phenotypes in loss-of-function appa and appb mutants. Larvae with mutations in appa had reduced waking activity, whereas larvae that lacked appb had shortened sleep bout durations at night. Treatment with the γ-secretase inhibitor DAPT also shortened night sleep bouts, whereas the BACE-1 inhibitor lanabecestat lengthened sleep bouts. Intraventricular injection of P3 also shortened night sleep bouts, suggesting that the proper balance of Appb proteolytic processing is required for normal sleep maintenance in zebrafish.
Sleep circuits and physiology in non-mammalian systems
2020, Current Opinion in Physiology
Citation Excerpt :
At least three sleep-homeostasis regulating neuronal populations have been recently discovered in the zebrafish: Galanin-expressing neurons [26••], neurons that produce the RF-amide Neuropeptide VF (NPVF) [47], and the serotonergic neurons of the raphe [48••]. The full extent to which these populations interact with zebrafish wake-promoting circuits of Hypocretin (Hcrt) [49], norepinephrine neurons of the locus coeruleus [50], the arousing neuropeptide Neuromedin U (Nmu) [51], and Insulin-like Growth Factor [52], or with other sleep-promoting signals, such as the circadian sleep-output signal melatonin [53], the locus coeruleus-inhibiting Neuropeptide Y [54], or even each other is not yet clear and has been reviewed elsewhere [55]. Additionally, the discovery of sleep regulatory circuits in mammals continues in tandem with elucidation of their conservation in zebrafish.
Research over the last 20 years has firmly established the existence of sleep states across the animal kingdom. Work in non-mammalian animal models such as nematodes, fruit flies, and zebrafish has now uncovered many evolutionarily conserved aspects of sleep physiology and regulation, including shared circuit architecture, homeostatic and circadian control elements, and principles linking sleep physiology to function. Non-mammalian sleep research is now shedding light on fundamental aspects of the genetic and neuronal circuit regulation of sleep, with direct implications for the understanding of how sleep is regulated in mammals.
Modeling autism spectrum disorders in zebrafish
2020, Behavioral and Neural Genetics of Zebrafish
The explosion of genome-wide association studies and whole genome sequencing of tens of thousands of individual humans have led to the rapid discovery of many genetic alterations implicated in neurodevelopmental and neuropsychiatric disorders, including schizophrenia, intellectual disability, and autism spectrum disorder (ASD). This wealth of genetic information brings new challenges to uncover how these genes work, alone and in concert, to sculpt the development and function of neuronal circuits that impact behavior. The zebrafish is an excellent system in which to tackle this challenge, as the zebrafish model combines the facility to quickly and in parallel generate mutations in dozens or hundreds of genes with a reasonable fidelity to human biology, including a highly conserved genome and a vertebrate brain plan. Moreover, their rapid development and complex behavioral repertoire at young ages grant experimental access to both early and late stages of nervous system form and function. Although no animal model can completely capture all aspects of human neurodevelopmental disorders, which can impact unique human traits such as language, the zebrafish does have many clinically important behaviors, including sleep, learning and memory, and complex social interactions, and these behaviors are governed by conserved genetic and neuronal processes.
This chapter will examine the use of zebrafish to investigate the neurodevelopmental disorder, ASD. In particular, we will discuss the genetics of ASD, the zebrafish models of ASD that have been generated to date, and the scope for examining critical aspects of ASD biology, especially social interactions, in the zebrafish model.
NREM Sleep Regulation From Neuronal Assembly to Ion
2019, Handbook of Behavioral Neuroscience
Citation Excerpt :
In both cases, EEG recordings show that one hemisphere is desynchronized, while the other displays a synchronized state indicative of SWS (Lyamin, Pryaslova, Lance, & Siegel, 2005; Mascetti, 2016; Rattenborg et al., 2016). Finally, as developed in several chapters of this volume, flies, fish, and worms are also very powerful models to study the genetics of sleep (Artiushin & Sehgal, 2017; Barlow & Rihel, 2017; Trojanowski & Raizen, 2016). A conceptual model for the timing of sleep onset was proposed in the 1980s (Borbely, 1982; Daan, Beersma, & Borbely, 1984) and has largely been confirmed as the most prevalent model today (Borbely, Daan, Wirz-Justice, & Deboer, 2016).
Compared with the two other vigilance stages, wakefulness and rapid eye movement (REM) sleep, non-REM (NREM) neuronal circuitry is less well understood, even though its role in neurophysiological functions and its involvement in diseases appear to be critical. In this chapter, we review NREM sleep features, the history of NREM sleep studies, and challenges and recent advances in understanding NREM sleep control.
Pitpnc1a Regulates Zebrafish Sleep and Wake Behavior through Modulation of Insulin-like Growth Factor Signaling
2018, Cell Reports
Citation Excerpt :
Expression analysis of dorsal forebrain (egr3, tbr1a, and eomesa) and hypothalamic (npvf) markers found no changes in pitpnc1a−/− larvae, suggesting that Pitpnc1a is not required for the specification or differentiation of these areas that strongly express pitpnc1a (Figures S3D and S3E). Because Pitpnc1a is exclusively detected in the zebrafish brain, including areas that have been implicated in larval sleep and arousal (Barlow and Rihel, 2017), we asked whether behavior might be affected in pitpnc1a−/− larvae by video-tracking them for several days (Rihel et al., 2010). Mutants showed a consistent increase in waking activity across a 14:10 hr light:dark cycle relative to pitpnc1a+/+ and pitpnc1a+/− (Figures 2C–2E).
The lipid transporters of the phosphatidylinositol transfer protein (PITP) family dictate phosphoinositide compartmentalization, and specific phosphoinositides play crucial roles in signaling cascades, membrane traffic, ion channel regulation, and actin dynamics. Although PITPs are enriched in the brain, their physiological functions in neuronal signaling pathways in vivo remain ill defined. We describe a CRISPR/Cas9-generated zebrafish mutant in a brain-specific, conserved class II PITP member, pitpnc1a. Zebrafish pitpnc1a mutants are healthy but display widespread aberrant neuronal activity and increased wakefulness across the day-night cycle. The loss of Pitpnc1a increases insulin-like growth factor (IGF) signaling in the brain, and inhibition of IGF pathways is sufficient to rescue both neuronal and behavioral hyperactivity in pitpnc1a mutants. We propose that Pitpnc1a-expressing neurons alter behavior via modification of neuro-modulatory IGF that acts on downstream wake-promoting circuits.

View all citing articles on Scopus

View full text

Zebrafish sleep: from geneZZZ to neuronZZZ

Highlights

Introduction

Section snippets

Monitoring sleep and arousal in larval zebrafish

Neurocircuitry of sleep in zebrafish

Sleep, disease, and predictive pharmacology

Concluding remarks

References and recommended reading

Conflict of interest

Acknowledgements

Curr. Biol.

Nat. Rev. Neurosci.

Brain Res.

J. Neurosci.

Nat. Neurosci.

Neuron

Nat. Methods

J. Neurosci.

Nature

Brain Res.

PLoS Genet.

J. Neurosci.

Mol. Cell. Biol.

Curr. Opin. Neurobiol.

The sleep disorder canine narcolepsy is caused by a mutation in the hypocretin (orexin) receptor 2 gene

Cell

Monitoring sleep and arousal in zebrafish

Methods Cell Biol.

Norepinephrine is required to promote wakefulness and for hypocretin-induced arousal in zebrafish

Elife

Slow waves, sharp waves, ripples, and REM in sleeping dragons

Science

A dynamic deep sleep stage in Drosophila

J. Neurosci.

Neural control and modulation of swimming speed in the larval zebrafish

Neuron

Neuropeptidergic signaling partitions arousal behaviors in zebrafish

J. Neurosci.

Brain-wide mapping of neural activity controlling zebrafish exploratory locomotion

Elife

Brain-wide neuronal dynamics during motor adaptation in zebrafish

Nature

From whole-brain data to functional circuit models: the zebrafish optomotor response

Cell

Sleep as a problem of localization

J. Nerv. Ment. Dis.

Brain stem reticular formation and activation of the EEG

Electroencephalogr. Clin. Neurophysiol.