New technique illuminates sleep similarities between humans and zebrafish, with implications for better understanding human sleep

Researchers recently identified several neural activity signatures in the zebrafish brain that suggest certain sleep states in these fish are similar to human sleep and that they could thus be used for studying the role of sleep in health and disease. In humans, appropriate sleep patterns support emotional and physical well-being and quality of life, and chronic sleep deficiency has been linked to obesity, diabetes, kidney disease, and other health problems. How exactly sleep contributes to good health, however, is still unclear, and more research in this area could yield important insights. Zebrafish share neural and biochemical similarities with other vertebrates, including humans, that make them a potentially good model for studying sleep and sleep-related disorders. Zebrafish are also uniquely useful in biological research, partially because their larvae are transparent, allowing use of advanced visualization techniques to answer scientific questions in living animals. However, measuring the neural signatures of sleep in zebrafish has been technically challenging, and it was unknown whether or not they organize their sleep cycle similar to humans and other vertebrate animals.

To explore this question, researchers sought to determine whether the zebrafish brain undergoes sleep states found in people and other vertebrates, such as the slow-wave and rapid eye movement (REM) states. To do this, the scientists developed a technique they called fluorescence polysomnography to visualize the brain and muscle activity, eye movement, and heart rate of living fish during sleep. This technique allowed the researchers to analyze not just the behavioral characteristics of sleep such as muscle relaxation and decrease in heart rate, but also the neural signatures of sleep in the zebrafish brain. One state they observed, which they named “slow bursting sleep,” shared features with slow-wave sleep, while another state, named “propagating wave sleep,” was similar to REM sleep. This new visualization technique also enabled the researchers to study and identify cellular and molecular regulators of zebrafish sleep, such as a hormone that controls the onset of propagating wave sleep.

Given the zebrafish’s place in the vertebrate family tree, these results suggest that common mechanisms of sleep are shared among animals as disparate as zebrafish and humans. These findings suggest that zebrafish, and the novel imaging techniques possible in this model organism, could be powerful new tools for research to increase understanding of human sleep and its impacts on health and disease.