Zebrafish as a Tool in the Study of Sleep and Memory-related Disorders

Abstract

: Sleep is an evolutionarily conserved phenomenon, being an essential biological necessity for the learning process and memory consolidation. The brain displays two types of electrical activity during sleep: slow-wave activity or non-rapid eye movement (NREM) sleep and desynchronized brain wave activity or rapid eye movement (REM) sleep. There are many theories about “Why we need to sleep?” among them the synaptic homeostasis. This theory proposes that the role of sleep is the restoration of synaptic homeostasis, which is destabilized by synaptic strengthening triggered by learning during waking and by synaptogenesis during development. Sleep diminishes the plasticity load on neurons and other cells to normalize synaptic strength. In contrast, it re-establishes neuronal selectivity and the ability to learn, leading to the consolidation and integration of memories. The use of zebrafish as a tool to assess sleep and its disorders is growing, although sleep in this animal is not yet divided, for example, into REM and NREM states. However, zebrafish are known to have a regulated daytime circadian rhythm. Their sleep state is characterized by periods of inactivity accompanied by an increase in arousal threshold, preference for resting place, and the “rebound sleep effect” phenomenon, which causes an increased slow-wave activity after a forced waking period. In addition, drugs known to modulate sleep, such as melatonin, nootropics, and nicotine, have been tested in zebrafish. In this review, we discuss the use of zebrafish as a model to investigate sleep mechanisms and their regulation, demonstrating this species as a promising model for sleep research.

The interplay between sleep and ecophysiology, behaviour and responses to environmental change in fish

“…This suggests that lacking sleep results in the accumulation of physiological debt that, if not repaid/compensated for (by rebound sleep, for instance), may result in direct and indirect fitness effects. Zebrafish deprived of sleep by light exposure perform worse cognitively (Pinheiro-da-Silva et al, 2017a, supporting the hypothesised function of sleep to reduce neural load and replenish learning skills (Altenhofen and Bonan, 2022). Sleepdeprived zebrafish also show differences in their activity: they travel shorter distances and reach slower maximum speeds when partially or fully sleep deprived, compared with their counterparts with a full night of sleep (Pinheiro-da-Silva et al, 2018), and they show anxious behaviours (Singh et al, 2013).…”

Structural neuroplasticity after sleep loss modifies behavior and requires neurexin and neuroligin

“… 11 , 13 , 25 , 26 , 27 , 28 Analysis in Caenorhabditis elegans, Drosophila , zebrafish, and rodents demonstrates that sleep regulates synapse strength, number, composition, and morphology, as well as learning, memory, mood, and social behaviors. 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 However, the functional role of the synaptic changes on behaviors, and the mechanisms that bridge them remain elusive. Neuronal activity during wakefulness correlates with sleep behavior itself, 46 uncovering a reciprocal relationship between sleep and plasticity.…”

Alternative Models in Neuropharmacology: The Zebrafish (Danio rerio)

“…The review by Altenhofen and Bonan [ 7 ] discussed the use of zebrafish as a model to investigate sleep mechanisms and memory-related disorders. In addition, drugs are known to modulate sleep, such as melatonin, nootropics, and nicotine, demonstrating this species as a promising model for sleep research.…”