Identification of environmental stressors and validation of light preference as a measure of anxiety in larval zebrafish.

Yiming Bai,Bo Huang,Harrison Liu,Mahendra Wagle,Su Guo

doi:10.1186/s12868-016-0298-z

Yiming Bai, Bo Huang + Show 3 more

Open Access

https://doi.org/10.1186/s12868-016-0298-z

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Abstract

BackgroundLarval zebrafish, with a simple and transparent vertebrate brain composed of ~100 K neurons, is well suited for deciphering entire neural circuit activity underlying behavior. Moreover, their small body size (~4–5 mm in length) is compatible with 96-well plates, making larval zebrafish amenable to high content screening. Despite these attractive features, there is a scarcity of behavioral characterizations in larval zebrafish compared to other model organisms as well as adult zebrafish.ResultsIn this study, we have characterized the physiological and behavioral responses of larval zebrafish to several easily amenable stimuli, including heat, cold, UV, mechanical disturbance (MD), and social isolation (SI). These stimuli are selected based on their perceived aversive nature to larval zebrafish. Using a light/dark choice paradigm, in which larval zebrafish display an innate dark avoidance behavior (i.e. scotophobia), we find that heat, cold and UV stimuli significantly enhance their dark avoidance with heat having the most striking effect, whereas MD and SI have little influence on the behavior. Surprisingly, using the cortisol assay, a physiological measure of stress, we uncover that all stimuli but heat and SI significantly increase the whole body cortisol levels.ConclusionThese results identify a series of stressors that can be easily administered to larval zebrafish. Those stimuli that elicit differential responses at behavioral and physiological levels warrant further studies at circuit levels to understand the underlying mechanisms. The findings that various stressors enhance while anxiolytics attenuate dark avoidance further reinforce that the light/dark preference behavior in larval zebrafish is fear/anxiety-associated.

Highlights

Larval zebrafish, with a simple and transparent vertebrate brain composed of ~100 K neurons, is well suited for deciphering entire neural circuit activity underlying behavior
The dark avoidance can be significantly alleviated by anxiolytic compounds [21, 22], suggesting that the behavior is anxiety-related
If the behavior was anxiety-related, one would expect that stressors would have a modifying effect on the behavior that would be opposite to that of anxiolytics

Summary

Introduction

With a simple and transparent vertebrate brain composed of ~100 K neurons, is well suited for deciphering entire neural circuit activity underlying behavior. Studies of the effect of stress on behavior and physiology during the last century, conducted at cellular, molecular, physiological, and systems levels, have led to important knowledge on the brain and neuroendocrine structures involved (e.g. hypothalamus, amygdala, hippocampus, prefrontal cortex, locus coeruleus, raphe nucleus, pituitary gland, and adrenal gland) and associated neurochemical substrates (e.g. corticotropin-releasing factor-CRF, adrenocorticotropic hormone-ACTH, cortisol, noradrenaline serotonin, and neuropeptide Y) [14] These studies have led to the realization of a strong connection between stress and illness, including depression and anxiety disorders, addiction, cardiovascular abnormalities and cancer: chronic and uncontrollable stressors turn the acute adaptive response to maladaptive in the long run. Several challenges remain: What are the cell types that respond to various stressors and activate the stress axis? Once the stress axis is activated, how does it help coping with acute stressors, and how can it become maladaptive in the presence of chronic and uncontrollable stressors? What accounts for individual differences in stress susceptibility versus resilience?

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