Zebrafish: High throughput approach to sleep research

I. Zhdanova

Boston University School of Medicine, Boston, MA, USA

The physiological function of sleep remains a scientific enigma. If sleep process in mammals evolved from the ubiquitous basic rest behavior, many conserved sleep mechanisms and functions could and should be studied in lower vertebrates. Currently, sleep is defined using behavioral and electrophysiological criteria. Although patterns of brain electrical activity characteristic of human sleep have been documented only in other mammals and in birds, the specific behavioral patterns of sleep are similar among different species. Furthermore, ‘limbic brain’ of the lower vertebrates possesses most of the brain structures, neurotransmitters and neuromodulators that were found to regulate the sleep process in mammals.

We have chosen to investigate sleep-related processes in a genetically and developmentally well-characterized species, zebrafish (Danio rerio), a diurnal vertebrate with a robust circadian pattern of daytime activity and nighttime rest. The results show that rest state in this fish has important similarities with sleep in mammals and can be considered a sleeplike state.

Small size and high reproductive rate of adult zebrafish, and fast (within 48 hours post fertilization) development of zebrafish larvae, which are, in many ways, miniature versions of the adult fish, provides an abundant resource for behavioral and genetic analysis. Highthroughput image-analysis techniques allow continuous recording of locomotor activity patterns in hundreds of zebrafish larvae individually housed in the wells of 96-well plates. Sleep-related compounds are often small size molecules. They easily penetrate larval skin and can be administered directly into the water, providing an effective non-invasive drug delivery. Relative ease of developing transgenic fish lines and a possibility of continuous monitoring of reporter-linked gene expression in transparent transgenic zebrafish makes it possible to study the role of individual genes in sleep process. Large-scale forward genetic screens carried out in zebrafish offer numerous mutant phenotypes to select for behavioral and sleep-related traits and identify genes that may be involved in normal sleep regulation or sleep disorders. Overall, zebrafish represent an excellent animal model for high throughput sleep research and drug discovery.

Paper presented at Measuring Behavior 2005 , 5^th International Conference on Methods and Techniques in Behavioral Research, 30 August - 2 September 2005, Wageningen, The Netherlands.

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