Chapter 11 - Monitoring Sleep and Arousal in Zebrafish

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Abstract

Zebrafish has emerged in the past 5 years as a model for the study of sleep and wake behaviors. Experimental evidence has shown that periods of behavioral quiescence in zebrafish larvae and adults are sleep-like states, as these rest bouts are regulated by the circadian cycle, are associated with decreases in arousal, and are increased following rest deprivation. Furthermore, zebrafish share with mammals a hypocretin/orexin system that promotes wakefulness, and drugs that alter mammalian sleep have similar effects on zebrafish rest. In this chapter, we review the zebrafish sleep literature and describe a long-term, high-throughput monitoring system for observing sleep and wake behaviors in larval zebrafish.

Introduction

Sleep is essential, time consuming, and conserved across the animal kingdom, yet it remains one of the major mysteries of biology. What is the function of sleep, and how is it regulated by genes and neurons? Since the discovery of characteristic electroencephalographic (EEG) signatures for states of sleep and waking in the late 1930s (Davis et al., 1937), mammalian model systems have dominated sleep research. However, behavioral observations over the past decade have demonstrated that non-mammalian systems, including Drosophila (Hendricks et al., 2000, Shaw et al., 2000), Caenorhabditis elegans (Raizen et al., 2008, Van Buskirk and Sternberg, 2007), and zebrafish (Prober et al., 2006, Yokogawa et al., 2007, Zhdanova et al., 2001), have sleep-like states. These “simple” model systems allow researchers to bring large-scale genetics and in vivo imaging to bear on fundamental questions of sleep biology. Zebrafish is an attractive model because it combines the facile genetics of invertebrates with brains that are morphologically and molecularly analogous to mammals. In this chapter, we review the progress of sleep studies in zebrafish and discuss the high-throughput methods (Fig. 1) we have developed to study larval zebrafish sleep/wake behaviors.

Section snippets

Behavior

Sleep is a period of reversible, inattentive behavioral quiescence that can be distinguished from quiet wakefulness using several behavioral criteria (Borbely and Tobler, 1996, Campbell and Tobler, 1984, Cirelli, 2009). Sleep-like rest periods are typically associated with a species-specific posture and location, and are regulated in a circadian (about 24 h) manner (Borbely and Tobler, 1996). Importantly, sleep is associated with an increased arousal threshold in response to stimuli, although

Methodological Considerations—from Drosophila to Danio

Two major methods have been used to track locomotor behavior of animals, either by counting the number of times an animal breaks an infrared beam or by direct analysis of movements captured by video. Pioneering work on circadian rhythms (Konopka and Benzer, 1971) and sleep (Hendricks et al., 2000, Shaw et al., 2000) in Drosophila predominantly used the infrared beam break method, which measures when the fly crosses an infrared beam in the center of a tube. Some work on zebrafish (Hurd et al.,

Conclusion

Only a decade old, the study of sleep in non-mammalian systems is still in its infancy. While early zebrafish sleep studies have focused on establishing the existence of behavioral sleep regulated by conserved mechanisms, the challenge ahead is to use the zebrafish sleep model to uncover heretofore unsuspected aspects of the neuronal and genetic control of sleep/wake regulation. Recent studies that potentially link Hcrt signaling to pineal gland regulation (Appelbaum et al., 2009) and that

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