Abstract
The startle reflex in larval zebrafish describes a C-bend of the body occurring in response to sudden, unexpected, stimuli of different sensory modalities. Alterations in the startle reflex habituation (SRH) have been reported in various human and animal models of neurological and psychiatric conditions and are hence considered an important behavioural marker of neurophysiological function. The amplitude, offset and decay constant of the auditory SRH in larval zebrafish have recently been characterised, revealing that the measures are affected by variation in vibratory frequency, intensity, and interstimulus-interval. Currently, no study provides a model-based analysis of the effect of physical properties of light stimuli on the visual SRH. This study assessed the effect of incremental light-stimulus intensity on the SRH of larval zebrafish through a repeated-measures design. Their total locomotor responses were normalised for the time factor, based on the behaviour of a (non-stimulated) control group. A linear regression indicated that light intensity positively predicts locomotor responses due to larger SRH decay constants and offsets. The conclusions of this study provide important insights as to the effect of light properties on the SRH in larval zebrafish. Our methodology and findings constitute a relevant reference framework for further investigation in translational neurophysiological research.
Highlights
A simple visual startle reflex habituation (SRH) task was applied repeatedly over 10 runs during which the larvae were stimulated at incrementing lux levels from 0.5 to 16 kLux (1 run = 20 stimuli)
The T DT20 of the stimulated group was normalised for the effect of time, subtracting the free locomotor distance travelled by a control group, which was tested concomitantly to the experimental group at all the runs in the absence of additional light stimulation
The TDT20 distribution of both groups at all test-times approximately met the assumptions for single linear regression analysis, which was performed to predict the change in TDT20 as an effect of light intensity
Summary
The study was performed in accordance with the animal welfare guidelines of the Swiss. Federal Veterinary Office, and all animal experiments were approved by the ethics committee of the Veterinary Office of the Canton of Zurich (ZH190/2020, 32971). The study and methods were conducted in compliance with the ARRIVE guidelines of animal research. Wild Indian Karyotype (WIK) Danio rerio adult zebrafish were bred and maintained in accordance with standard protocols[48]. Their eggs were raised in transparent breeding tanks of 1.7 L water, incubated at 28 °C, under a 14:10 light–dark cycle. MO, USA) and kept in the same location until the test day
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