Alterations in locomotor activity of feeding zebrafish larvae as a consequence of exposure to different environmental factors

Abstract

Behavioral studies are important tools for understanding the development and pathology of neurological diseases. Zebrafish are an emerging alternative model in behavioral and neurological studies as the behavioral repertoire of zebrafish (Danio rerio) is similar to humans, and nervous system structures and functions are highly conserved. In this study, we investigated alterations in day/night locomotor activity of free swimming, feeding wild-type zebrafish larvae (8-15dpf) due to changes in the rhythm of light/dark cycles or caloric content of food. We furthermore exposed zebrafish larvae to continuous stress by applying alternated minor vibrations. Under altered rhythms of light/dark cycle's zebrafish larvae still expressed a distinct light/dark activity pattern but the total activity was reduced compared to control animals. When the larvae were exposed to continuous light, they still had coordinated resting cycles but maximal activity and excitation rates after feeding were increased, indicating that food became the new zeitgeber. Feeding food of high caloric content induced continuously high activity levels during light cycles and significantly elevated activity levels during the dark. Exposure to continuous vibrations lowered total activity levels. We showed previously that changes in environmental factors like light/dark cycles or changes in caloric content of food can affect adipogenesis, lipid composition, and circadian rhythm of free swimming, feeding larvae but this is the first time showing how theses factor alter behavior.

Keywords: Diet; Environmental stimuli; Light; Locomotor activity; Sound/vibrations; Zebrafish.

Fig. 1

Overview of the experimental design. Zebrafish were raised with constant light/dark cycles till day 9. From 6dpf on larvae were feed twice a day, one time during the light period, and one time during the dark period. Differences in light condition or vibration started at day 9, and locomotion was monitored till 15dpf

Fig. 2

Sound waves of the vibration experiment

Fig. 3

Activity patterns (relative activity in %) throughout different experimental conditions. Light-on is marked with gray shading. Feeding time is marked with *. The scale of the y- and x-axis differs between graphs

Fig. 4

Total activity calculated as area under the activity curve covering the whole experimental period and subdivided into lights-on and lights-off periods. For the LL group, lights-off periods were calculated for the corresponding time window of the control group

Fig. 5

a Detailed view of the response to lights off for jet lag (long and short light phase) and control. Activity patterns (relative activity in %) throughout different experimental conditions. Light-on is marked with gray shading. The difference between data points is 10 min. The short light phase jet lag larvae do not decrease their activity level directly when the lights go off. b Bar-graph representing the average activity at the last data point before the light went off (black) and the first two following data points after (gray). Significant differences of data points to the corresponding data point before are marked with *

Fig. 6

Excitation rate induced at lights-on or feeding during light or dark periods as mean over all events of an experimental period and over all individual experimental groups